Article

Blood flow dynamics in the limb conduit artery during dynamic knee extensor exercise assessed by continuous Doppler ultrasound measurements

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Abstract

Exercising muscle blood flow (BF) may be an indicator of oxygen supply change allowing increased muscle energy metabolism through the circulatory response between central and peripheral hemodynamics. During exercise an increase in cardiac output may represent the interplay of alterations in both blood pressure and vascular conductance. Dynamic muscle contractions lead to an increase in cardiac output and promote venous return at the onset of exercise, and concurrently lead to enhanced muscle vasodilatation (and thus increased muscle BF) due to metabolites, neurological responses and/or other mechanisms, causing exercise hyperaemia. Doppler ultrasound can non-invasively detect with high resolution the temporal pulsatile blood velocity profiles in the conduit artery at rest as well as during muscle contractions. Based on this technique, it has been shown that alterations in the physiological blood velocity profile related to cardiac systole-diastole and fluctuations in the beat-by-beat blood velocity profile are due to rapid changes in the blood velocity profile concurrent with muscle contraction and/or relaxation during exercise (dynamic/static) or respiratory cycle, in different states (muscle contraction time/frequency or workload), or of any other type of vasodilatation/vasoconstriction. Muscle contraction-induced alterations in the blood velocity profile may be due in general to the magnitude of intramuscular pressure variation (mechanical factors) and the superimposed influence of perfusion pressure variation (pulsatile hemodynamic factors). This review therefore focuses on methodological considerations for muscle contraction-induced blood velocity/flow variability in the leg conduit artery, which in turn influences the magnitude of exercising BF during dynamic knee extensor exercise.

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... Ultrasound images of the dominant forearm flexors were obtained using brightness mode (B-mode) and blood flow was assessed from the brachial artery proximal to the antecubital fossa 28 using Pulsed Wave Doppler at a repetition frequency of 10MHz obtained using an ultrasound-imaging device (GE Logiq e, USA) and a multi-frequency linear-array probe (12L-Rs; 5-13MHz; 38.4 mm field-of-view). All blood flow measurements were assessed at an insonation angle of 60° to the brachial artery collected over a period of 3 cardiac cycles 29,30 and derived from arterial cross-sectional area (arterial diameter 2 × 0.785) and time averaged flow velocity based on previous recommendations 31 . All measurements were taken while the subjects were lying in the supine position on the isokinetic dynamometer with both their arms and legs supported. ...
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Objectives The purpose of this study was to examine the effects of exercise intensity and strength on sex-related differences in eccentric peak torque (PT), muscle blood flow, and neuromuscular responses following fatiguing, submaximal forearm flexion eccentric protocols. Methods Thirty-six subjects were stratified by sex and strength into 4 equal groups and randomly performed fatiguing eccentric, isokinetic (180°·s⁻¹), forearm flexion protocols at 40% or 80% of eccentric PT. Eccentric PT, muscle blood flow, and neuromuscular responses were measured prior to (pretest), immediately (posttest), and 5-min after (5-min recovery) performing the fatiguing protocols. Results There was no sex-, intensity-, or strength-related difference in the magnitude of decrease in eccentric PT at posttest (80.0% of pretest) or the magnitude of recovery at 5-min (87.8% of pretest). Muscle blood flow increased similarly for men (139.8% of pretest) and women (178.7% of pretest) at posttest, but the magnitude of recovery was greater for the women (62.9%) than the men (41.4%). The neuromuscular responses were not affected by sex-, intensity-, or strength-related differences. Conclusions These findings indicated that there were few sex-related differences in eccentric PT, muscle blood flow, and neuromuscular responses as a result of the fatiguing eccentric protocols performed at a high or low intensity of exercise.
... Blood flow was assessed from the brachial artery proximal to the antecubital fossa [7] using Pulsed Wave Doppler at a repetition frequency of 10 MHz and once identified, the location was marked with a permanent marker. All blood flow measurements were assessed at an insonation angle of 60 ° to the brachial artery collected over a period of three cardiac cycles [37,38] and derived based on previous recommendations [8]. All measurements were taken while the subjects were lying in the supine position on the isokinetic dynamometer with both their arms and legs supported. ...
Article
The primary purpose of the present investigation was to examine sex-related differences as a result of fatiguing eccentric muscle actions on torque, muscle blood flow, electromyography, and mechanomyography. Eighteen men and 18 women performed peak torque trials prior to (pretest), immediately after (posttest), and 5-min after (recovery) completing 50 submaximal (60% of eccentric peak torque), eccentric, isokinetic (180°·s −1) muscle actions of the elbow flexors. Electromyographic and mechanomyographic responses were simultaneously recorded from the biceps brachii muscle, and muscle blood flow was measured at pretest, posttest and recovery. There were sex- and mode-specific responses for torque, but there were no sex-specific muscle blood flow or neuromuscular responses. From pretest to posttest, torque decreased (80.0–88.2% of pretest) for both the men and women. At recovery concentric peak torque recovered to a greater extent in women (95.0% of pretest) than men (88.0% of pretest), while eccentric peak torque recovered to a greater extent in men (88.9% of pretest) than women (86.9% of pretest). The sex-specific torque responses were not associated with different motor control strategies or differences in the occlusion of muscle blood flow between the men and women. For both men and women, eccentric fatiguing exercise is manifested similarly during isometric muscle actions, but not during eccentric and concentric muscle actions.
... All ultrasound measurements were performed at an insonation angle of 60° to the brachial artery, and time-averaged flow velocity was determined over a period of three cardiac cycles [ Figure 1]. [10,11] Brachial artery blood flow was derived using Equation 1. [6] All measurements were taken while the subjects were lying in the supine position on the isokinetic dynamometer with both their arms and legs supported. Great care was taken to ensure that consistent, minimal pressure was applied with the probe to limit compression of the artery. ...
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Background Ultrasound has been used for noninvasive assessments of endothelial function in both clinical and athletic settings and to identify changes in muscle blood flow in response to exercise, nutritional supplementation, and occlusion. The purposes of the present study were to examine the reliability and relative contributions of arterial cross-sectional area and time-averaged flow velocity to predict muscle blood flow as a result of fatiguing exercise in men and women. Methods Eighteen healthy men and 18 healthy women performed 50 consecutive eccentric repetitions of the elbow flexors at 60% of their pretest eccentric peak torque at a velocity of 180° s⁻¹. Test-retest reliability and stepwise linear regression analyses were performed to determine the ability of arterial cross-sectional area and time-averaged flow velocity to predict brachial artery muscle blood flow for the men, women, and combined sample. Results There was no systematic test versus retest mean differences (P > 0.05) for any of the ultrasound determined variables. The two-variable regression models significantly improved the ability to predict muscle blood flow and were associated with smaller standard error of the estimates (3.7%–10.1% vs. 16.8%–37.0% of the mean baseline muscle blood flow values) compared to the one-variable models. Conclusions The findings of the present study supported the use of ultrasound for reliable assessments of arterial diameter, arterial cross-sectional area, time-averaged flow velocity, and muscle blood flow from the brachial artery in men and women. Furthermore, time-averaged flow velocity was a more powerful predictor of muscle blood flow than arterial cross-sectional area.
... In the knee extensor exercise model utilizing a relatively small thigh muscle mass, the local factors regulating BF are thought to be of most importance including the voluntary repeated muscle contractions. It has previously been discussed that muscle contraction-induced rapid alterations in the conduit arterial blood velocity profile may be closely related to the magnitude of intramuscular pressure variation (muscle mechanical factors) and superimposed influence of perfusion pressure variation (pulsatile hemodynamic factors) [10,11,[13][14][15][20][21][22]. During steady-state, high intramuscular pressure during muscle contractions Figure 5a adapted from Osada and Rådegran [12], reproduced with permission from Edizioni Minerva Medica. ...
... Blood velocity, vessel diameter, and calculation of leg blood flow Measurements in the femoral artery (dominant leg) were performed using an ultrasound system (Model CFM 800; Vingmed Sound, Horten, Norway), which had previously been validated with accurate absolute values at rest and during knee extensor exercise [19][20][21][22][23][24][25][26][27][28]. The probe position was stable (<60°), and the sample volume was precisely positioned in the centre of the vessel and adjusted to cover the diameter width of the vessel. ...
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Article
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Hill, EC, Housh, TJ, Smith, CM, Keller, JL, Schmidt, RJ, and Johnson, GO. High- vs. low-intensity fatiguing eccentric exercise on muscle thickness, strength, and blood flow. J Strength Cond Res 35(1): 33-40, 2021-The purpose of this investigation was to examine the acute effects of equal volumes of fatiguing high- vs. low-intensity eccentric muscle actions on changes in muscle thickness, echo intensity, muscle blood flow, and adipose thickness. Eighteen men (mean ± SD = 23.2 ± 3.0 years) performed eccentric peak torque (PT) and maximal voluntary isometric contraction (MVIC) trials before (pretest), immediately after (posttest), and 5 minutes after (recovery) performing randomly ordered fatiguing eccentric, isokinetic (180°·s-1) muscle actions of the elbow flexors at 40% (72 repetitions) or 80% (36 repetitions) of eccentric PT. Muscle thickness, exercise-induced edema, muscle blood flow, and adipose thickness were also assessed via ultrasound at pretest, posttest, and recovery. There were no intensity-specific effects on the patterns of responses for eccentric PT, MVIC, muscle thickness, echo intensity, muscle blood flow, or adipose thickness. There were, however, effects across time that decreased from pretest to posttest and from pretest to recovery for eccentric PT (21.5 and 13.0%), MVIC (14.6 and 5.8%), and adipose thickness (10.0 and 6.0%), but increased for muscle thickness (7.6 and 5.9%), echo intensity (13.7 and 9.9%), and muscle blood flow (129.6 and 90.1%) (collapsed across 40 and 80%). These findings indicated that when matched for exercise volume, there were no intensity-related effects on the increases in muscle thickness, echo intensity, muscle blood flow, or the decreases in eccentric PT, MVIC, and adipose thickness after fatiguing eccentric muscle actions. Therefore, exercise volume, independent of exercise intensity and number of repetitions, may be a mediating factor of muscle fatigue and performance during eccentric muscle actions.
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Endothelial dysfunction is an early event in experimental studies of atherogenesis, preceding formation of plaques. We have devised a non-invasive method for testing endothelial function, to find out whether abnormalities are present in symptom-free children and young adults at high risk of atherosclerosis. With high-resolution ultrasound, we measured the diameter of the superficial femoral and brachial arteries at rest, during reactive hyperaemia (with increased flow causing endothelium-dependent dilatation), and after sublingual glyceryl trinitrate (GTN; causing endothelium-independent dilatation) in 100 subjects--50 controls without vascular risk factors (aged 8-57 years), 20 cigarette smokers (aged 17-62 years), 10 children with familial hypercholesterolaemia (FH; aged 8-16 years), and 20 patients with established coronary artery disease (CAD). Adequate scans were obtained in all but 6 cases. Flow-mediated dilatation was observed in arteries from all control subjects. Dilatation was inversely related to baseline vessel diameter (r = -0.81, p < 0.0001); in arteries of 6.0 mm or less, mean dilatation was 10 (SE 2)%. In smokers, FH children, and adults with CAD, flow-mediated dilatation was much reduced or absent (p < 0.001 for comparison with each relevant control group). Dilatation in response to GTN was present in all groups. Endothelial dysfunction is present in children and adults with risk factors for atherosclerosis, such as smoking and hypercholesterolaemia, before anatomical evidence of plaque formation in the arteries studied. This may be an important early event in atherogenesis.
Article
Ten healthy male subjects performed single (< 1 s), sustained and intermittent plantarflexions (up to 40 s) of one foot in sitting exercise position. Two different absolute forces were applied, which, in terms of maximal voluntary contraction, ranged between 5%-10% and 25%-30%. Blood velocity was continuously recorded in the proximal arteria femoralis by means of the Doppler technique. Heart rate (HR) and mean blood pressure (BP) were simultaneously determined using standard ECG and the FINAPRES method. Despite the distance between the proximal arteria femoralis and the exercising muscle the Doppler data showed: effects of single contractions on the individual Doppler data, the influence of consecutive contractions, variation with exercise intensity and differences between sustained and intermittent contractions. In all exercise tests there was an immediate significant increase in blood velocity at the onset of exercise. The major part (range 52%-73%) of the response to the 40 s tests was seen during the first 6 s. It was followed by a second phase of adjustment which depended on the type of exercise and exercise intensity. The single plantarflexion provoked increases in blood velocity for about 20 s. A comparison of HR and BP tracings with the Doppler data demonstrated the importance of local mechanical factors for the perfusion of the exercising muscle. The early adjustment of muscle perfusion were not correlated to the systemic blood pressure and, therefore, appeared to be related to muscle pump effects. The subsequent flow values were influenced by passive vessel compression and changes in local vasomotor tone.(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of muscle contraction frequency on blood flow to the calf muscle (Q calf) were studied in six female subjects, who performed dynamic plantar flexions at frequencies of 20, 40, 60, 80 and 100 contractions · min−1, in a supine position. TheQ calf measured by a mercury-in-rubber strain gauge plethysmograph, increased as contraction frequency increased and reached a peak at 60–80 contractions · min−1. After 100 plantar flexions at 60 contractions · min−1, the meanQ calf was 30.95 (SEM 4.52) ml · 100 ml−1 · min−1. At 100 contractions · min−1, however, it decreased significantly compared with that at 60 contractions · min−1 at a specified time (2 min or exhaustion) or after a fixed amount of work (100 contractions). The contraction frequency at whichQ calf reached a peak depended on the duration of exercise. The heart rate showed its highest mean value at 60 contractions · min−1 and decreased significantly at 100 contractions · min−1. The mean blood pressure was lower at 100 contractions · min−1 than at 60 contractions · min−1. The relaxation period between contractions, measured by recording the electromyogram from the gastrocnemius muscles, shortened markedly as the frequency increased; the mean value at 100 contractions · min−1 was 0.14 (SEM 0.02) s, which corresponded to 35.7% of the contraction time. This shortened relaxation period between contractions should have led to the inhibition of exercise hyperaemia at the higher contraction frequencies.
The aim of the present paper was to study the development of fatigue during isometric intermittent handgrip exercise. Using a handgrip dynamometer, four combinations of contraction-relaxation periods were studied (10 + 10, 10 + 5, 10 + 2 s and continuous contraction) at three contraction intensities (10, 25 and 40% maximum voluntary contraction, MVC). Local blood flow (BF) in the forearm (venous occlusion plethysmography) was followed before, during and after the exercise period. Electromyography (EMG) (frequency analysis) and the perceived effort and pain were recorded during the exercise period. Forearm BF is insufficient even at isometric contractions of low intensity (10% MVC). The results indicate that vasodilating metabolites play an active role for BF in low-intensity isometric contractions. It is shown that maximal BF in the forearm during relaxation periods (25-30 ml.min-1.100 ml-1) is already reached at 25% MVC. Only intermittent exercise at 10% MVC and (10 + 5 s) and (10 + 10 s) at 25% MVC was considered acceptable with regard to local fatigue, which was defined as a switch of local BF to the post-exercise period, a decrease in the number of zero-crossings (EMG) and marked increases in subjective ratings.
Article
A duplex ultrasound system was used to measure volumetric flow in the human common femoral artery. The accuracy of the technique was validated using a flow rig. The average resting common femoral artery flow rate in a population of subjects clinically unaffected by peripheral vascular disease was 350 +/- 141 mls min-1. Although mean common femoral artery diameter was greater in males (10 +/- 0.9 mm) than in females (7.8 +/- 0.7 mm) (p less than 0.01), there was no significant difference in resting blood flow. Repeated measurements in individual subjects showed a high variability, largely due to physiological fluctuations (75 percent of total variability). There was a close correlation between volume flow and the reciprocal of pulsatility index (100/PI). In normal subjects 100/PI represents a simpler method of determining individual changes in blood flow. The temporal variations in volume flow during periods of reactive hyperaemia had a characteristic profile, which was dependent on the duration of circulatory arrest. The data derived from the resting hyperaemia flow profile provides normal ranges for future comparison with patients suffering from peripheral vascular disease.
Article
Blood velocities in the human femoral artery were measured using pulsed bidirectional Doppler-ultrasound equipment before, during and after single isometric contractions of the quadriceps muscle group. After contraction periods lasting more than 20 s (long) and of tensions from 10% up to 75% of maximal voluntary contraction (m.v.c.), an increase in blood velocities of seven to eight times the resting level was observed. Estimated maximal volume flow to the whole leg during the post-contraction hyperaemic phase calculated from these blood velocity measurements and vessel diameter (measured with echo-ultrasound equipment) was in two of the subjects 2.4 l/min (female) and 4.4 l/min (male), respectively. In the latter, this estimate fitted very well with results obtained using a venous thermo-dilution method. When using computer tomography to estimate the volume of the quadriceps muscle group, the calculated maximum flow to this muscle group in the post-contraction hyperaemic phase was approximately 175 (female) and 185 (male) ml/min. 100 ml muscle, respectively. This was about forty times the estimated resting volume flow to this muscle of 4.7 (female) and 4.5 (male) ml/min. 100 ml muscle. The length of the post-contraction hyperaemia after short (less than 10 s) contraction periods was 12-13 s, by which time velocities had reached 25% above the precontraction level. After long contractions, the corresponding values were 23-25 s. By contrast, previous plethysmographic observations by others indicate that postcontraction hyperaemias following long contractions last 10-15 min. There was a marked difference between the times taken to reach maximal velocity in the hyperaemic phase when comparing short and long contractions. Maximal velocity was reached four to six cardiac cycles following short periods of contraction but during the very first heart beat after long periods of contractions. The present observations are compatible with the hypothesis that locally released metabolites or hormones play a dominant role in the regulation of the post-contraction hyperaemia. Since during the short contraction periods maximal velocity was reached only after some seconds, whereas with the longer contraction periods it was reached during the first heart beat, it is suggested that these metabolites are released at some distance from the resistance vessels and that some time is needed for diffusion.
Article
Five subjects exercised with the knee extensor of one limb at work loads ranging from 10 to 60 W. Measurements of pulmonary oxygen uptake, heart rate, leg blood flow, blood pressure and femoral arterial-venous differences for oxygen and lactate were made between 5 and 10 min of the exercise. Flow in the femoral vein was measured using constant infusion of saline near 0 degrees C. Since a cuff was inflated just below the knee during the measurements and because the hamstrings were inactive, the measured flow represented primarily the perfusion of the knee extensors. Blood flow increased linearly with work load right up to an average value of 5.7 l min-1. Mean arterial pressure was unchanged up to a work load of 30 W, but increased thereafter from 100 to 130 mmHg. The femoral arterial-venous oxygen difference at maximum work averaged 14.6% (v/v), resulting in an oxygen uptake of 0.80 l min-1. With a mean estimated weight of the knee extensors of 2.30 kg the perfusion of maximally exercising skeletal muscle of man is thus in the order of 2.5 l kg-1 min-1, and the oxygen uptake 0.35 l kg-1 min-1. Limitations in the methods used previously to determine flow and/or the characteristics of the exercise model used may explain why earlier studies in man have failed to demonstrate the high perfusion of muscle reported here. It is concluded that muscle blood flow is closely related to the oxygen demand of the exercising muscles. The hyperaemia at low work intensities is due to vasodilatation, and an elevated mean arterial blood pressure only contributes to the linear increase in flow at high work rates. The magnitude of perfusion observed during intense exercise indicates that the vascular bed of skeletal muscle is not a limiting factor for oxygen transport.
Article
In an attempt to approach a system of isolated exercising muscle in humans, a model has been developed that enables the study of muscle activity and metabolism over the quadriceps femoris (QF) muscles while the rest of the body remains relaxed. The simplest version includes the subject sitting on a table with a rod connecting the ankle and the pedal arm of a bicycle ergometer placed behind the subject. Exercise is performed by knee extension from a knee angle of 90 to approximately 170 degrees while flywheel momentum repositions the relaxed leg during flexion. Experiments where electromyographic recordings have been taken from biceps femoris, gastrocnemius, tibialis anterior, and other muscles in addition to QF indicate that only the QF is active and that there is an equal activation of the lateral, medial, and rectus femoris heads relative to maximum. Furthermore, virtually identical pulmonary O2 uptake (Vo2) during and without application of a pressure cuff below the knee emphasizes the inactivity of the lower leg muscles. The advantages of the model are that all external work can be localized to a single muscle group suitable for taking biopsies and that the blood flow in and sampling from the femoral vein are representative of the active muscles. Thus all measurements can be closely related to changes in the working muscle. Using this model we find that a linear relationship exists between external work and pulmonary Vo2 over the submaximal range and the maximal Vo2 per kilogram of muscle may be as much as twice as high as previously estimated.
Common iliac arterial blood flow was measured with implanted electromagnetic flow probes in 6 patients after reconstruction of the aorto-iliac-femoral region. On the 3rd, 4th or 5th day after operation heart rate, oxygen uptake and local leg blood flow were studied at rest and during exercise on a bicycle ergometer in supine and sitting position. Heart rate at rest was 10 beats/min higher in sitting than in supine position. During exercise there was no significant difference in heart rate between the two postures. Oxygen uptake was 8% higher in sitting than in supine position at rest. During exercise oxygen uptake did not differ significantly between the two postures. Local leg blood flow was significantly lower in sitting position both at rest and during exercise.
Article
Twenty male college students served as subjects for lhe study which investigated the relationship between maximum isometric strength and the isometric tension necessary to produce total occlusion of intramuscular circulation. Subjects performed a scries of progressively increasing static contractions by squeezing a hand dynamometer and the subsequent blood flow responses were measured. Blood flow was occluded at a mean of 63-5% maximum handgrip strength for the total group tested. To determine whether individuals of different maximum strength occlude at different percentages of their MVC, subjects were divided into high and low strength groups. The high strength group was found to occlude at 51-5% of MVC while the low strength group occluded at 75-5% of MVC. A significant negative correlation (r= -0.58) was found between maximum isometric strength and the per cent of maximum strength necessary to produce intra-muscular occlusion. There was no significant difference between the absolute tension producing occlusion in the high strength group (34-8 kg) and that of the low strength group (34 3 kg).
Article
The kinetics of femoral artery mean blood velocity (MBV; measured by pulsed Doppler) and whole body oxygen uptake (VO2; measured breath by breath) were assessed from the time constant during the on (tau on) and off (tau off) transients to step changes in work rate between complete rest and dynamic knee extension (KE) exercise. Six healthy men performed 5 min of seated KE exercise, with each leg alternately raising and lowering a weight (10% maximum voluntary contraction) over a 2-s duty cycle. Because kinetic analysis of VO2 kinetics during KE exercise is a new approach, the VO2 responses were also evaluated during the on and off transitions to the more familiar upright cycling exercise in which the magnitude of increase in VO2 and cardiac output was similar to that during KE exercise. During KE exercise, VO2 tau on [mean 72.2 +/- 11.2 (SE) s] was slower than VO2 tau off (33.3 +/- 1.8 s; P < 0.01). Cardiac output, measured with impedance cardiography, was not different for tau on (67.1 +/- 20.0 s) compared with that for tau off (52.9 +/- 7.6 s). Likewise, MBV tau on (34.5 +/- 3.9 s) was not different from tau off (35.3 +/- 3.2 s). During cycling, the VO2 tau on (18.0 +/- 2.4 s) and tau off (30.7 +/- 1.2 s) were both faster than KE VO2 tau on (P < 0.01). Even though the MBV kinetics indicated a rapid adaptation of blood flow during KE exercise, there was a slow adaptation of VO2. A transient hyperemia immediately on cessation of KE exercise, indicated by both MBV and calculated systemic vascular conductance responses, suggested that blood flow might have been inadequate and could have contributed to the delayed adaptation of VO2 at the onset of exercise, although other explanations are possible.
Article
During sustained isometric exercise, central command has very little effect on muscle sympathetic nerve activity (MSNA). To determine if central command has a greater effect on MSNA during intermittent than during sustained contractions, MSNA was recorded with microelectrodes (peroneal nerve) during intermittent isometric handgrip at 25%, 50%, and 75% maximum voluntary contraction (MVC) in 9 human subjects with paced breathing. Similar experiments were performed in 11 additional subjects before and after partial neuromuscular blockade (intravenous curare) to isolate the influence of central command while minimizing force output and thus muscle afferent feedback. Before curare, handgrip at 25% and 50% MVC had no effect on MSNA, whereas handgrip at 75% MVC synchronized the MSNA to the handgrip such that MSNA was 5.7 +/- 1.3 times higher (mean +/- SEM, P < .001) during the contraction periods than during the relaxation periods. After curare, this synchronization of MSNA persisted without attenuation, even though force output fell to < 25% of the initial MVC. From these observations, we conclude that central command causes synchronization of motor activity and muscle sympathetic activity during intense intermittent isometric exercise.
Article
The purpose of this study was to determine forearm blood flow changes during static handgrip exercise at different intensities in relation to heart rate and blood pressure. Seven active women performed static handgrip exercise at intensities of 10, 30, 50 and 70% maximum voluntary contraction (MVC) in a supine position for 1 min. During exercise at different intensities, the brachial arterial blood flow (Doppler ultrasound method), calculated from vessel diameter, flow velocity and heart rate (measured by ECG), increased to a similar level (137.3 +/- 20.2-160.9 +/- 26.1 mL min-1) from pre-exercise control value (87.5 +/- 14.1 mL min-1). These increases at the lower intensities were attributable to increased in-flow during one cardiac cycle, whereas at the higher intensities, they were due to increased heart rate. Both systolic and diastolic blood pressure (Finapres) changes increased from 10% MVC (16.1 +/- 3.4, 9.0 +/- 1.7 mmHg) up to 50% MVC (33.8 +/- 6.7, 25.0 +/- 4.9 mmHg), but were disproportionately more elevated at 70% MVC (46.1 +/- 7.9, 42.9 +/- 8.9 mmHg), suggesting neural vasoconstriction had occurred. Immediate post-exercise hyperaemia, used as an indicator of poor blood supply, became greater as the exercise intensity increased. These results suggest that the brachial arterial blood flow was maintained at a similar level during 60-s static handgrip exercise at different intensities by elevating the blood pressure and heart rate, which probably counteracted the increased intramuscular pressure and neural vasoconstriction occurring at the higher exercise intensity. The magnitude of the post-exercise hyperemic response increased as exercise level increased despite increased blood-flow to the arm during-exercise. This suggests a worsening imbalance in oxygen delivery in forearm muscles at higher levels of exercise.
Article
To evaluate the temporal relationship between blood flow, blood pressure, and muscle contractions, we continuously measured femoral arterial inflow with ultrasound Doppler at onset of passive exercise and voluntary, one-legged, dynamic knee-extensor exercise in humans. Blood velocity and inflow increased (P < 0.006) with the first relaxation of passive and voluntary exercise, whereas the arterial-venous pressure difference was unaltered [P = not significant (NS)]. During steady-state exercise, and with arterial pressure as a superimposed influence, blood velocity was affected by the muscle pump, peaking (P < 0.001) at approximately 2.5 +/- 0.3 m/s as the relaxation coincided with peak systolic arterial blood pressure; blood velocity decreased (P < 0.001) to 44.2 +/- 8.6 and 28.5 +/- 5.5% of peak velocity at the second dicrotic and diastolic blood pressure notches, respectively. Mechanical hindrance occurred (P < 0.001) during the contraction phase at blood pressures less than or equal to that at the second dicrotic notch. The increase in blood flow (Q) was characterized by a one-component (approximately 15% of peak power output), two-component (approximately 40-70% of peak power output), or three-component exponential model (> or = 75% of peak power output), where Q(t) = Qpassive + delta Q1.[1 - e-(t - TD1/tau 1)]+ delta Q2.[1 - e-(t - TD2/tau 2)]+ delta Q3.[1 - e-(t - TD3/tau 3)]; Qpassive, the blood flow during passive leg movement, equals 1.17 +/- 0.11 l/min; TD is the onset latency; tau is the time constant; delta Q is the magnitude of blood flow rise; and subscripts 1-3 refer to the first, second, and third components of the exponential model, respectively. The time to reach 50% of the difference between passive and voluntary asymptotic blood flow was approximately 2.2-8.9 s. The blood flow leveled off after approximately 10-150 s, related to the power outputs. It is concluded that the elevation in blood flow with the first duty cycle(s) is due to muscle mechanical factors, but vasodilators initiate a more potent amplification within the second to fourth contraction.
Article
Endothelial function is thought to be an important factor in the pathogenesis of atherosclerosis, hypertension and heart failure. In the 1990s, high-frequency ultrasonographic imaging of the brachial artery to assess endothelium-dependent flow-mediated vasodilation (FMD) was developed. The technique provokes the release of nitric oxide, resulting in vasodilation that can be quantitated as an index of vasomotor function. The noninvasive nature of the technique allows repeated measurements over time to study the effectiveness of various interventions that may affect vascular health. However, despite its widespread use, there are technical and interpretive limitations of this technique. State-of-the-art information is presented and insights are provided into the strengths and limitations of high-resolution ultrasonography of the brachial artery to evaluate vasomotor function, with guidelines for its research application in the study of endothelial physiology.
Article
Whether limb blood flow is directly regulated to match the work rate, independent of the rate of contraction, remains elusive. This study therefore investigated the relationship between femoral arterial blood flow (FABF; Doppler ultrasound) and "external" (applied load) as well as "total" [external + "internal" (potential and kinetic energy changes of the moving lower leg)] work rate, during steady-state one-legged, dynamic, knee extensor exercise (1L-KEE) in the sitting position at different contraction rates. Ten subjects performed 1L-KEE at 30, 60, and 90 contractions/min (cpm) 1) at constant resistive loads of 0.2 and 0.5 kg inducing incremental external work rates (study I) and 2) at different relative resistive loads inducing constant external work rates of 9 and 18 W (study II). Moreover, 3) six subjects performed 1L-KEE at 60 and 100 cpm at incremental total work rates of 40, 50, 60, and 70 W (study III). In study I, FABF increased (P < 0.001) with increasing contraction frequency and external work rate, for each resistive load. In study II, FABF increased (P < 0.001) with increasing contraction frequency for each constant external work rate. Of major importance in study III, however, was that FABF, although increasing linearly with the total work rate, was not different (P = not significant) between contraction rates, at the total work rates of 40, 50, 60, and 70 W, respectively. Furthermore, FABF correlated linearly and positively with both the external and total work rate for each contraction frequency. In conclusion, the findings support the concept that leg blood flow during 1L-KEE in a normal knee extensor ergometer is matched directly in relation to the total work rate and metabolic activity, irrespective of the contraction frequency. The rate of contraction seems erroneously to influence the results only when it is related to the external work rate without taking into account the internal work component.
Article
Post-exercise related time course of muscle oxygenation during recovery provides valuable information on peripheral vascular disease. The purpose of the present study was to examine post-exercise hyperemia (forearm blood flow; FBF, Doppler ultrasound) assessed by peak FBF, excess FBF and the time constant for FBF (FBF(Tc)) following isometric handgrip exercise (IHE). Post-exercise hyperemia was assessed in an ischemic and non-ischemic state at different exercise intensities and durations. Peak FBF and excess FBF were defined as the maximum FBF during recovery, and the total amount of FBF volume, respectively. FBF(Tc) represents the time to reach approximately 37% of the change in FBF between peak FBF and resting FBF (delta peak FBF). Ten subjects performed IHE at "10% and 30% maximum voluntary contraction (MVC)" for 2 min with or without arterial occlusion (AO), followed by 2 min of AO alone (Study I). In Study II, six subjects performed 30%MVC-IHE with AO for "100%, 66%, 33% and 10% of the exhausted exercise duration" (time to exhaustion). In Study I, although peak FBF and excess FBF were significantly higher in ischemic than non-ischemic IHE for both 10% and 30%MVC (p<0.05), FBF(Tc) was similar in the ischemic and non-ischemic conditions. The peak FBF, excess FBF and FBF(Tc) were all significantly higher at 30% than at 10%MVC (p<0.05). In Study II, the peak FBF and excess FBF increased linearly compared to the absolute and relative exercise durations for ischemic IHE. FBF(Tc) increased exponentially when compared to the absolute and relative exercise durations. These data suggest the ischemic exercise has a larger hyperemic response compared to the non-ischemic exercise. In conclusion, the peak FBF, excess FBF and FBF(Tc) seen during post-exercise hyperemia are closely correlated with exercise intensity and duration, not only in non-ischemic, but also in the ischemic exercise. In combination with the ischemic exercise, these parameters could potentially prove to be valuable indicators of peripheral vascular disease.
Article
Studies in selected samples have linked impaired endothelial function with cardiovascular disease and its risk factors. The clinical correlates and heritability of endothelial function in the community have not been described. We examined a measure of endothelial function, brachial artery flow-mediated dilation (FMD), expressed as both percent (FMD%) and actual dilation by ultrasound with the occlusion cuff below the elbow in 2883 Framingham Study participants (52.9% women; mean age, 61 years). A subset of 1096 participants performed a 6-minute walk test before FMD determination. Mean FMD% was 3.3+/-3.0% in women and 2.4+/-2.4% in men. In stepwise multivariable linear regression models, FMD% was inversely related to age, systolic blood pressure, body mass index (BMI), lipid-lowering medication, and smoking, whereas it was positively related to female gender, heart rate, and prior walk test. The estimated heritability of FMD% was 0.14. FMD actual dilation findings were similar, except that female sex and BMI were not significantly associated. Increasing age, systolic blood pressure, BMI, and smoking were associated with lower FMD% in our community-based sample, whereas prior exercise and increasing heart rate were associated with higher FMD%. The estimated heritability of FMD was modest. Future research will permit more complete characterization of the genetic and environmental determinants of endothelial function and its prognostic value in the community.
Article
To evaluate whether muscle contraction-induced variability of limb femoral arterial blood flow (FABF) can be reduced with longer sampling durations. This was assessed in relation to muscle contraction-relaxation cycles (CRcycles) during steady-state, one-legged, dynamic knee-extensor exercise (KEE) at varying "exercise intensities" and "contraction frequencies." Eleven male subjects performed steady-state KEE at 10-40 W at 30 and 60 contractions per minute (cpm). FABF (Doppler ultrasound) and contraction-relaxation-induced variability in FABF was determined for 1-, 2-, 5-, 10-, 15-, 20-, and 30-CRcycles during approximately 4-min steady-state KEE. Variability was determined as coefficients of variation (CV). During KEE at 30 and 60 cpm CVFABF was significantly higher for 1-CRcycles (12.3% and 15.5%) and 2-CRcycles (9.6% and 11.8%) than for 30-CRcycles (4.0% and 5.2%), but similar for 10-CRcycles to 30-CRcycles at all work rates and contraction frequencies. The CVFABF between work rates at 30 and 60 cpm did not statistically differ (P = NS) for any of the CRcycle measurements. However, the single CRcycles-induced CVFABF at 60 cpm was significantly higher (P < 0.05) than that at 30 cpm at the lower exercise intensities of 10 and 20 W, but with no significant difference at 30 and 40W. Limb blood flow variability was markedly reduced with a longer sampling measurement of at least 10-CRcycles, which had a CVFABF of approximately 5%. Furthermore, the 1-CRcycle-induced FABF variability was similar at each exercise intensity, but significant variations were seen between contraction frequencies at lower exercise intensities. It is speculated the difference between the contraction frequencies at lower exercise intensities may be due to the muscle contraction-relaxation-induced variations in muscle force (intramuscular pressure), along with the superimposed blood pressure waves.
Article
The present study examined the rheological blood velocity profile in the conduit femoral artery during rhythmic muscle contractions at different muscle forces. Eight healthy volunteers performed one-legged, dynamic knee-extensor exercise at work rates of 5, 10, 20, 30, and 40 W at 60 contractions per minute. The time and space-averaged, amplitude-weighted mean (V(mean)) and maximum (V(max)) blood flow velocities in the common femoral artery were measured during the cardiosystolic phase (CSP) and cardiodiastolic phase (CDP) by the Doppler ultrasound technique. The V(max)/V(mean) ratio was used as a flow profile index, in which a ratio of approximately 1 indicates a "flat velocity flow profile" and a ratio significantly >1 indicates a "parabolic velocity flow profile." At rest, the V(max)/V(mean) ratio was approximately 1.3 and approximately 1.8 during the CSP and CDP, respectively. The V(max)/V(mean) ratio was higher (p < 0.01) during the CDP than during the CSP, both at rest and at all work rates. The V(max)/V(mean) ratio during the CSP was higher (p < 0.01) at 30 and 40 W compared to at rest. The V(max)/V(mean) ratio during the CDP was lower (p < 0.05) at 5 and 10 W compared to at rest. There was a positive linear correlation between blood flow and incremental work rates during both the CSP and CDP, respectively. Thus under resting conditions, the findings indicate a "steeper" parabolic velocity profile during the CDP than during the CSP. The velocity profile during the CDP furthermore shifts to being less "steep" during rhythmic muscle contractions at lower intensities, but to being reelevated and normalized as at rest during higher intensities. The "steepness" of the parabolic velocity profile observed during the CSP at rest increased during muscle contraction at higher intensities. In conclusion, the blood velocity in the common femoral artery is parabolic both at rest and during exercise for both the CSP and CDP, indicating the persistence of laminar flow. The occurrence of any temporary slight disturbance or turbulence in the flow at the sight of measurement in the common femoral artery does consequently not induce a persisting "disturbed" and fully flat "plug-like" velocity profile. Instead, the "steepness" of the parabolic velocity profile is only slightly modified, whereby blood flow is not impaired. Thus the blood velocity profile, besides being influenced by the muscle contraction-relaxation induced mechanical "impedance," seems also to be modulated by the cardiac- and blood pressure-phases, consequently influencing the exercise blood flow response.
Article
The interaction between skeletal muscle contraction and sympathetic nerve activation (SNA) on blood flow during exercise has remained ambiguous due to indirect estimates of vasomotor control. In the hamster retractor muscle (n=54), interactions between three levels of SNA (approximately 3, 6 and 12 Hz) and of contractile activity (2.5, 10 and 20 % duty cycle) were studied in feed arteries (FA) and first- (1A), second- (2A), and third-order (3A) arterioles using intravital microscopy. During functional dilatation with rhythmic muscle contractions, sympathetic vasoconstriction was sustained in FA and 1A but impaired in 2A and 3A (P<0.05), where vessels 'escaped' from responding to SNA. To account for changes in baseline diameter and blood flow during contractions, vasodilatation was induced passively (2-3 levels) in resting muscles with papaverine or sodium nitroprusside. Compared to functional dilatation, the range of passive dilatation was similar in 3A and progressively greater in 2A, 1A and FA. With passive dilatation, SNA responses were sustained in 2A and increased with baseline diameter in 3A. Blood flow through FA (rest, approximately 20 nl s(-1)) increased approximately 5-fold during contractile activity and approximately 10-fold during passive dilatation. Absolute flow reductions (nl s(-1)) with SNA increased during contractile activity and during passive dilatation; relative flow reductions were impaired during functional dilatation (P<0.05) and remained constant during passive dilatation. Thus, SNA can restrict blood flow to exercising muscle by constricting FA and 1A while dilatation prevails in 2A and 3A. Such concerted interaction will promote oxygen extraction when blood flow is restricted to maintain arterial pressure.
Article
The present study examined the influences of the muscle contraction (MCP) and relaxation (MRP) phases, as well as systole and diastole, on the blood velocity profile and flow in the conduit artery at different dynamic muscle contraction forces. Eight healthy volunteers performed one-legged dynamic knee-extensor exercise at work rates of 5, 10, 20, 30, and 40 W at 60 contractions per minute. The time- and space-averaged, amplitude-weighted, mean (V(mean)) and maximum (V(max)) blood flow velocities were continuously measured in the common femoral artery during the cardiosystolic (CSP) and cardiodiastolic (CDP) phases during MCP and MRP, respectively. The V(max)/V(mean) ratio was used as a flow profile index where a ratio of approximately (~) 1 indicates a "flat" velocity profile, and a ratio significantly greater than (>) 1 indicates a "parabolic" velocity profile. At rest, a "steeper" parabolic velocity profile was found during the CDP (ratio: 1.75 +/- 0.06) than during the CSP (ratio: 1.31 +/- 0.02). During the MRP of exercise, the V(max)/V(mean) ratio shifted to be less steep (p < 0.05) than at rest during the CDP (ratio: 1.41-1.54) at 5, 10, 20, 30, and 40 W; whereas it was slightly higher (p < 0.05) at 30 and 40 W than at rest during the CSP (ratio: 1.43-1.46). During the MCP, the parabolic blood velocity profile was enhanced (p < 0.05) at higher contraction forces, 20 W during the CDP (ratio: 2.15-2.52) and 30 W during the CSP (ratio: 1.49-1.77), potentially because of a greater retrograde flow component. A higher blood flow furthermore appeared during the MRP compared to during the MCP, coinciding with a greater uniformity of the red blood cells moving at higher blood velocities during the MRP. Thus part of the difference in the magnitude of blood flow during the MRP vs. MCP may be due to the alterations of the blood velocity flow profile.
Article
Blood flow in peripheral conduit arteries during steady-state, dynamic exercise, can be estimated noninvasively with Doppler ultrasound, by measuring the conduit arterial diameter and the mean blood velocity averaged over consecutive cardiac beat-by-beat cycles (BB(cycle)) or muscle contraction-relaxation cycles (CR(cycle)). The precise impact fluctuations in the 1-BB(cycle)- or 1-CR(cycle)-rate may impose on the average blood flow measurements has previously not been clearly defined. The hypothesis investigated in the present study was that the blood flow measurements obtained, and its variability, during exercise, may differ between the 1-BB(cycle) and 1-CR(cycle) at incremental exercise intensities; as the BB(cycle)-measurements may be influenced by transient alterations in heart rate; whereas the CR(cycle)-measurements are dependent on the muscle contraction-relaxation frequencies independent of the exercise intensities per se. The main purpose was therefore to determine if fluctuations in blood flow for 1-BB(cycle) and 1-CR(cycle)varies at incremental exercise intensities (work rates) using the one-legged dynamic knee-extensor exercise (DKE) model. Limb femoral artery blood flow (LBF) was determined, for 1-BB(cycle) and 1-CR(cycle), in 8 healthy male subjects during 4-min of steady-state DKE at 60 contractions per minute at 10, 20, 30 and 40 W. The variability of LBF was determined from the coefficients of variation (CVLBF). The CV(LBF) for the CR(cycle)-measurements at each work rate were similar (P=NS). The CV(LBF) for the BB(cycle)-measurements were higher (P<0.05) at 40 W compared to at 10 W. Furthermore, the CV(LBF) for the 1-BB(cycle) was higher (P<0.05) than for the 1-CR(cycle) at 30 and 40 W, despite almost identical mean LBF values for the BB(cycle)- and the CR(cycle)-measurements at each exercise intensity. The present data suggests that estimates of LBF at slightly higher exercise intensities such as above 30 W, for a few number of consecutive BB(cycle), renders a higher variability than for CR(cycle)-measurements. This may consequently result in slight over- and under-estimations of LBF compared to the CR(cycle)-measurement.