Stamatis Agiovlasitis

Mississippi State University, Mississippi, United States

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Publications (44)77.64 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The altered gait patterns of adults with Down syndrome (DS) may contribute to their higher net metabolic rate (net-MR) during walking than adults without DS, leading to mobility limitations. This study examined the extent to which gait characteristics explain differences in net-MR during walking between adults with and without DS. Fifteen adults with DS (27 ± 8 yrs) and 15 adults without DS (28 ± 6 yrs) completed two testing sessions in which expiratory gases and kinematic data were collected, respectively, during treadmill walking. Participants walked at six, randomly-presented dimensionless speeds, ranging from slow to fast. Hierarchical and stepwise regressions were used to determine the proportion of the variance in net-MR explained by gait variables that differed between groups, after controlling for variance due to walking speed. Positive work rate, the range of the body center of mass (COM) mediolateral position and its square, variability in the time-course of COM anteroposterior velocity, and the variability of step length, step width, and step time significantly predicted net-MR (p < 05). These variables collectively explained 73.9% of the variance in net-MR that was explained by DS but not by walking speed. After accounting for shared variance among predictors, step length variability made the greatest unique contribution (10.6%) to the higher net-MR in adults with DS, followed by the range of COM mediolateral motion (6.3%), step width variability (2.8%), and variability in COM anteroposterior velocity (0.7%). Therefore, the gait characteristics of adults with DS appear to largely explain their higher net-MR during walking.
    Gait & Posture. 10/2014;
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    ABSTRACT: Persons with Down syndrome (DS) have altered heart rate modulation and very low aerobic fitness. These attributes may impact the relationship between metabolic equivalent units (METs) and the heart rate index (HRindex-the ratio between heart rate during activity and resting heart rate), thereby altering the HRindex thresholds for moderate- and vigorous-intensity physical activity. This study examined whether the relationship between METs and HRindex differs between persons with and without DS and attempted to develop thresholds for activity intensity based on the HRindex for persons with DS. METs were measured with portable spirometry and heart rate with a monitor in 18 persons with DS (25±7 years; 10 women) and 18 persons without DS (26±5 years; 10 women) during 6 over-ground walking trials, each lasting 6min, at the preferred walking speed and at 0.5, 0.75, 1.0, 1.25, and 1.5m/s. The relationship between METs and HRindex in the two groups was analyzed with multi-level modeling with random intercepts and slopes. Group, HRindex, and the square of HRindex were significant predictors of METs (p<0.001; R(2)=0.65). Absolute percent error did not differ significantly between groups across speeds (DS: 19.6±14.4%; non-DS: 21.0±14.5%). Bland-Altman plots demonstrated somewhat greater variability in the difference between actual and predicted METs in participants with than without DS. The HRindex threshold for moderate-intensity activity was 1.32 and 1.20 for persons with and without DS, respectively. The HRindex threshold for vigorous-intensity activity was 1.80 and 1.65 for persons with and without DS, respectively. Persons with DS have an altered relationship between METs and HRindex and higher HRindex thresholds for moderate- and vigorous-intensity physical activity.
    Research in developmental disabilities. 06/2014; 35(10):2423-2429.
  • Brian M Sandroff, Barry J Riskin, Stamatis Agiovlasitis, Robert W Motl
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    ABSTRACT: There has been increased interest in objectively quantifying time spent in moderate-to-vigorous physical activity (MVPA) using accelerometry as an outcome among persons with multiple sclerosis (MS). This requires development of a cut-point for interpreting the rate of accelerometer output based on its association with energy expenditure during physical activity. The current study measured activity counts from a waist-worn accelerometer and energy expenditure based on indirect calorimetry during three speeds of over-ground walking for deriving cut-points for interpreting accelerometer output in persons with mild, moderate, and severe MS disability. 54 participants with MS initially completed a neurological examination for generation of an EDSS score. Participants were then fitted with an ActiGraph model GT3X+ accelerometer and a Cosmed portable metabolic system, and completed three, 6-minute walk (6 MW) tests that were interspersed with 10-15min of rest. The first 6 MW was undertaken at a comfortable walking speed (CWS), and the two remaining 6 MW tests were undertaken above (faster walking speed) or below (slower walking speed) the participant's CWS in a counterbalanced order. The linear association between activity counts per minute and energy expenditure did not differ between persons with mild and moderate MS disability, but it was significantly different among persons with severe disability. This resulted in disability-specific cut-points for MVPA of 1980 and 1185 counts per minute for groups with mild/moderate disability and severe disability, respectively. We believe that this research will facilitate a better understanding of time spent in MVPA across a broad range of MS disability.
    Journal of the neurological sciences 02/2014; · 2.32 Impact Factor
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    ABSTRACT: This study compared arterial stiffness and wave reflection at rest and following maximal exercise between individuals with and without Down syndrome (DS), and the influence of body mass index (BMI), peak oxygen uptake (VO2peak) on changes in arterial stiffness. Twelve people with DS (26.6±2.6yr) and 15 healthy controls (26.2±0.6yr) completed this study. Intima-media thickness (IMT) and stiffness of common carotid artery was examined. Hemodynamic and arterial variables were measured before and 3-min after exercise. Persons with DS had higher BMI and lower VO2peak than controls. IMT did not differ between groups. At rest, carotid β stiffness was significantly higher in persons with DS (P<0.05) but there was no difference in between groups for any of the other arterial stiffness measures. After exercise, persons with DS exhibited attenuated arterial stiffness responses in AIx-75, carotid β stiffness and Ep in contrast with controls (significant group-by-time interactions). When controlling for BMI and VO2peak, the interactions disappeared. In both groups combined, BMI was correlated significantly with carotid Ep and β at rest. VO2peak correlated significantly with AIx-75 and its pre-post change (r=-0.45, P=0.029; r=0.47, P=0.033, respectively). The arterial stiffness responses to maximal exercise in persons with DS were blunted, potentially reflecting diminished vascular reserve. Obesity and particularly VO2peak influenced these findings. These results suggest impaired vascular function in people with DS.
    Research in developmental disabilities 07/2013; 34(10):3139-3147. · 4.41 Impact Factor
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    Ken Pitetti, Tracy Baynard, Stamatis Agiovlasitis
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    ABSTRACT: Children (5–12 years) and adolescents (13–19 years) with Down syndrome (DS) possess a set of health, anatomical, physiological, cognitive, and psycho-social attributes predisposing them to limitations on their physical fitness and physical activity (PA) capacities. The paucity of studies and their conflicting findings prevent a clear understanding and/or substantiation of these limitations. The purpose of this article was to review the measurement, determinants and promotion of physical fitness and PA for youth (i.e., children and adolescents) with DS. The existing body of research indicates that youth with DS: 1) have low cardiovascular and muscular fitness/exercise capacity; 2) demonstrate a greater prevalence of overweight and obesity; 3) a large proportion do not meet the recommended amount of daily aerobic activity; and 4) their PA likely declines through childhood and into adolescence. Future research should focus on: 1) strength testing and training protocols; 2) methodologies to determine PA levels; and 3) practical interventions to increase PA.
    Journal of Sport and Health Science. 03/2013; 2(1):47–57.
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    ABSTRACT: The relationship between effective arterial elastance (E(A)) and left ventricular end-systolic elastance (E(LV)) is a determinant of cardiac performance, known as arterial-ventricular coupling (AVC). The purpose of this study was to examine the acute effects of high-intensity interval (HI) and low-intensity steady state (SS) exercise on AVC. Twenty-three (13 men, 10 women) young (26 years), endurance-trained individuals completed a VO(2) peak test followed by an acute SS and HI exercise bout on separate visits. Before (Pre) and 30- and 60-min after each bout, measures of aortic end-systolic pressure (ESP), left ventricular end-systolic volume and stroke volume were obtained. Across both conditions (HI and SS) and both sexes, at 30 and 60 min post exercise, ESP and E(LV) were reduced from Pre 30 and 60-min exercise (ESP: 86±7, 77±8 and 73±8 mm Hg; E(LV): 4.93±1.53, 4.19±1.38 and 4.10±1.53 mm Hg ml(-1) m(-2)). E(A) was only reduced at 60 min post exercise (1.90±0.36, 1.78±0.50 and 1.57±0.36). Both E(A) and E(LV) were reduced following acute SS and HI exercise. This is likely because of similar reductions in total peripheral resistance following both exercise bouts. These results suggest that endurance-trained individuals are able to match peripheral vascular changes with changes in left ventricular function following dynamic exercise of different intensities.Journal of Human Hypertension advance online publication, 21 February 2013; doi:10.1038/jhh.2013.7.
    Journal of human hypertension 02/2013; · 2.80 Impact Factor
  • Stamatis Agiovlasitis, Michael W Beets, Robert W Motl, Bo Fernhall
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    ABSTRACT: Monitoring physical activity intensity in persons with Down syndrome (DS) may be affected by an altered relationship between metabolic equivalent units (METs) and step-rate. This study examined whether the relationship between METs and step-rate is altered in persons with DS and developed step-rate thresholds for activity intensity for these persons. Cross-sectional. Eighteen persons with DS (25±7years; 8 women) and 22 persons without DS (26±5 years; 9 women) completed six over-ground walking trials each lasting 6 min at their preferred speed and at 0.5, 0.75, 1.0, 1.25, and 1.5 ms⁻¹. METs were measured with portable spirometry and step-rate with hand-tally. Random effects models were used to predict METs from step-rate, squared step-rate, height, presence of DS, sex, and body mass index (BMI). Step-rate, squared step-rate, height, and presence of DS contributed significantly to the model (SE=0.20 METs; R²=0.63); sex and BMI did not contribute. As height increased, step-rate thresholds for moderate and vigorous-intensity activity decreased. For a given height, participants with DS had lower step-rate at the moderate-intensity threshold than participants without DS. Across participant heights, the moderate-intensity cut-off ranged between 101 and 76 steps min⁻¹ in persons with DS and between 103 and 80 steps min⁻¹ in persons without DS. For persons with DS, step-rate at the vigorous-intensity threshold ranged between 136 and 126 steps min⁻¹. Persons with DS showed altered relationship between METs and step-rate and had lower step-rate thresholds for moderate-intensity activity than persons without DS.
    Journal of science and medicine in sport / Sports Medicine Australia. 04/2012; 15(5):425-30.
  • Stamatis Agiovlasitis, Robert W Motl, John T Foley, Bo Fernhall
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    ABSTRACT: This study examined the relationship between energy expenditure and wrist accelerometer output during walking in persons with and without Down syndrome (DS). Energy expenditure in metabolic equivalent units (METs) and activity-count rate were respectively measured with portable spirometry and a uniaxial wrist accelerometer in 17 persons with DS (age: 24.7±6.9 years; 9 women) and 21 persons without DS (age: 26.3±5.2 years; 12 women) during six over-ground walking trials. Combined groups regression showed that the relationship between METs and activity-count rate differed between groups (p<.001). Separate models for each group included activity-count rate and squared activity-count rate as significant predictors of METs (p≤.005). Prediction of METs appeared accurate based on Bland-Altman plots and the lack of between-group difference in mean absolute prediction error (DS: 17.07%; Non-DS: 18.74%). Although persons with DS show altered METs to activity-count rate relationship during walking, prediction of their energy expenditure from wrist accelerometry appears feasible.
    Adapted physical activity quarterly: APAQ 04/2012; 29(2):179-90. · 1.13 Impact Factor
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    ABSTRACT: Acute aerobic exercise decreases arterial stiffness based on the intensity of the exercise and the arterial segment studied. Arm exercise may differentially affect arterial stiffness compared to leg exercise but this has not been studied. We hypothesized that maximal aerobic exercise would reduce local peripheral pulse wave velocity i.e. femoral-dorsalis pedis (LPWV) following leg exercise and carotid-radial (APWV) following arm exercise without any crossover effect. The main purpose of the study is to compare the effects of maximal arm versus leg aerobic exercise on peripheral and central arterial stiffness. Fifteen healthy participants (9 males and 6 females, 25 ± 5 years) performed maximal arm-ergometer and leg-ergometer exercise in a randomized, crossover design. Peripheral and central pulse wave velocities (PWV) were obtained using applanation tonometry before and 10 min after each maximal exercise bout. 2 × 2 repeated measures analysis of variance was used to detect differences between conditions. There was a significant interaction in the APWV between the two exercise modes. However, there was no condition or interaction effect on LPWV following maximal arm versus leg exercise. There was no significant difference in central PWV between conditions or with time. There was no change in MAP (75 ± 6-77 ± 3) after maximal arm exercise as compared to the maximal leg exercise (73 ± 6-80 ± 2). Arm exercise produced a more generalized effect on arterial stiffness than leg exercise. The prescription of upper limb exercise may be considered for purposes of eliciting post-exercise systemic changes in arterial stiffness.
    Arbeitsphysiologie 11/2011; 112(7):2631-5. · 2.66 Impact Factor
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    ABSTRACT: Sudden cardiac events are the leading cause of line-of-duty firefighter deaths, but little information exists elucidating the physiologic responses. Wave intensity (WI) is a new hemodynamic index that provides information about the dynamic behavior of the heart and the vascular system and their interaction. The larger first peak wave (W1) occurs during early systole and is associated with cardiac contractility. The second smaller peak (W2) follows a period of relatively little net wave (NA) production and may be caused by reflected waves from the brain. This study aimed at determining arterial WI changes in response to live firefighting activities. We examined the WI of 39 firefighters (2 females) with a mean age of 28 ± 1 years and BMI of 26.6 ± 0.7 kg m(-2) at rest, and immediately after 3 h of live firefighting drills. WI was assessed on the right common carotid artery using an Aloka high-resolution ultrasound. The magnitude of the W1 decreased significantly from 15,925 ± 1,341 to 11,540 ± 886 mmHg m s(-3), p < 0.05. The magnitude of W2 remained unchanged (W2: from 2,080 ± 200 to 2,144 ± 358 mmHg m s(-3)). Net NA decreased from 53 ± 5 to 40 ± 4 mmHg m s(-2). In conclusions, our data suggest that left ventricular function and arterial-ventricular coupling decreased following live firefighting, and this may be related to the documented increase in risk of clinical events during and after firefighting activities.
    Arbeitsphysiologie 10/2011; 112(7):2385-91. · 2.66 Impact Factor
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    ABSTRACT: The reduced gait stability and aerobic fitness of people with Down syndrome (DS) may increase their rate of gross oxygen uptake (gross-VO(2)) during over-ground walking. If so, the ACSM equation predicting gross-VO(2) from speed may not be appropriate and an equation specifically for these individuals may be needed. This study therefore examined whether the relationship between gross-VO(2) and speed differs between individuals with and without DS during over-ground walking and attempted to develop a gross-VO(2) prediction equation for people with DS. Gross-VO(2) was measured in 18 persons with DS (24.7 ± 6.8 years; 8 men) and 22 persons without DS (25.9 ± 4.8 years; 9 men) at rest and during five over-ground walking trials, each lasting 6 min, at 0.5, 0.75, 1.0, 1.25, and 1.5 m/s. Multi-level modeling with random intercepts and slopes demonstrated significant effects of speed, group, group-by-speed interaction, and speed squared (P < 0.001). In each group, actual gross-VO(2) did not differ from gross-VO(2) predicted by the regression equation across speeds. Bland-Altman plots showed somewhat greater variability in the difference between actual and predicted gross-VO(2) for participants with DS. Mean absolute error of prediction was 10.75 and 10.67% for participants with and without DS, respectively. In participants with DS, the ACSM formula under-estimated gross-VO(2) across speeds, whereas, in participants without DS, only at 1.5 m/s (P < 0.001). Therefore, individuals with DS show altered curvilinear gross-VO(2) to speed relationship during over-ground walking. The present regression equation appears to offer accurate prediction in people with DS and could be used for prescribing over-ground walking intensities.
    Arbeitsphysiologie 08/2011; 111(8):1739-45. · 2.66 Impact Factor
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    Vascular Medicine 04/2011; · 1.62 Impact Factor
  • Stamatis Agiovlasitis, Kenneth H Pitetti, Myriam Guerra, Bo Fernhall
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    ABSTRACT: This study examined whether 20-m shuttle-run performance, sex, body mass index (BMI), age, height, and weight are associated with peak oxygen uptake (VO2peak) in youth with Down syndrome (DS; n = 53; 25 women, age 8-20 years) and whether these variables can be used to develop an equation to predict VO2peak. BMI, 20-m shuttle-run performance, and sex were significantly associated with VO2peak in youth with DS, whereas age, height, and weight were not. A regression model included only shuttle-run performance as a significant predictor of VO2peak; however, the developed prediction equation had low individual predictability. Therefore, 20-m shuttle-run performance alone does not provide valid prediction of VO2peak in youth with DS. Sex, BMI, age, height, and weight do not improve the prediction of VO2peak.
    Adapted physical activity quarterly: APAQ 04/2011; 28(2):146-56. · 1.13 Impact Factor
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    ABSTRACT: Walking impairment is a ubiquitous feature of multiple sclerosis (MS) and the O(2) cost of walking might quantify this dysfunction in mild MS. This paper examined the difference in O(2) cost of walking between persons with MS who have mild disability and healthy controls and the correlation between the O(2) cost of walking and disability. Study 1 included 18 persons with mild MS and 18 controls and indicated that the O(2) cost of walking was significantly higher in MS than controls and that disability was significantly associated with the O(2) cost of slow, moderate, and fast treadmill walking. Study 2 included 24 persons with mild MS and indicated that disability was significantly correlated with O(2) cost of comfortable, fast, and slow over-ground walking. We provide evidence that the O(2) cost of walking is an indicator of walking dysfunction in mildly disabled persons with MS and should be considered in clinical research and practice.
    Neurological Sciences 04/2011; 32(2):255-62. · 1.41 Impact Factor
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    ABSTRACT: Sudden cardiac events are responsible for 40-50% of line-of-duty firefighter fatalities, yet the exact cause of these events is unknown. Likely, combinations of thermal, physical, and mental factors impair cardiovascular function and trigger such events. Therefore, the purpose of this study was to examine the impact of firefighting activities on vascular function. Sixty-nine young (28 ± 1 years) male firefighters underwent 3 hours of firefighting activities. Carotid, aortic, and brachial blood pressures (BP), heart rate (HR), augmentation index (AIx), wave reflection timing (TR), aortic pulse wave velocity (PWV), forearm blood flow (FBF), and forearm reactive hyperemia (RH) were measured before and after firefighting activities. Paired samples t-tests revealed significant (p < 0.05) increases in aortic diastolic BP, HR, AIx, PWV, RH, and FBF, and significant decreases in brachial and aortic pulse pressure and TR following firefighting activities. In conclusion, these results suggest that 3 hours of firefighting activities increase both arterial stiffness and vasodilation.
    Vascular Medicine 04/2011; 16(2):113-8. · 1.62 Impact Factor
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    ABSTRACT: Individuals with Down syndrome (DS) show reduced gait stability that may increase the metabolic rate (MR) during over-ground walking and alter their energetic cost per unit distance (EC(transport)) to speed relationship. If so, the preferred walking speed (PWS) of people with DS may coincide with their speed at minimal EC(transport), reflecting energetic optimization. This study therefore examined whether MR and EC(transport) during over-ground walking differ between individuals with and without DS and whether PWS minimizes their EC(transport). Expired gases were collected from 18 individuals with DS and 18 without during six over-ground walking trials, each lasting 6 min, at PWS and at 0.51, 0.76, 1.01, 1.26, and 1.51 m/s. Gross- and net-MR, and gross- and net-EC(transport) were expressed in dimensionless form. Energetically optimal walking speeds and minimal gross- and net-EC(transport) were determined from the gross- and net-EC(transport) to speed curves for each participant. Individuals with DS showed higher gross-MR, net-MR, gross-EC(transport), and net-EC(transport). PWS minimized gross-EC(transport) in participants with DS, but not in those without. PWS did not minimize net-EC(transport) in either group. Therefore, gross-EC(transport) minimization during over-ground walking may determine PWS when impairments alter the gross-EC(transport) to speed relationship.
    Gait & posture 03/2011; 33(4):630-4. · 2.58 Impact Factor
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    Clinical Autonomic Research 03/2011; · 1.48 Impact Factor
  • Juhee Kim, Bala Mutyala, Stamatis Agiovlasitis, Bo Fernhall
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    ABSTRACT: We examined the levels of physical activity, sedentary behaviors, and obesity among children with attention deficit hyperactivity disorder (ADHD) by gender and medication use and estimated the associations between health behaviors and obesity. Cross-sectional analysis of children 6-17 years-old enrolled in the National Survey of Children's Health 2003 (n=66,707). Odds ratios were adjusted for multistage-sampling and survey-design effects. ADHD prevalence was 8.6%. In general, children with ADHD engaged in less physical activity, organized sports, and reading than their counterparts. Children with ADHD had increased risk of obesity for boys [24.9% vs. 21.6%, OR(95% CI): 1.42(1.13-1.77)] and girls [21.9% vs. 16%, 1.85(1.26-2.73)], if not medicated. Only girls with ADHD and not on medication were more likely to have higher media time (52.7% vs. 42%) and this was associated with higher odds for obesity [27.7% vs. 19.5%, 2.51 (1.24-5.08)]. Children with ADHD on medication had higher prevalence of depression than those not taking medication [boys: 29.5% vs. 26.3%; girls: 30.9% vs. 23.6%] and the odds of being depressed remained significant after controlling for obesity [boys: 1.45 (1.09-1.94); girls: 2.27 (1.48-3.49)]. Health promotion and obesity prevention programs targeting children with ADHD should take gender and medication use into consideration.
    Preventive Medicine 01/2011; 52(3-4):218-22. · 3.50 Impact Factor
  • Robert W Motl, Erin M Snook, Stamatis Agiovlasitis
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    ABSTRACT: Accurate measurement is required by researchers and clinicians who are interested in the physical activity behavior of individuals with multiple sclerosis (MS). Advances in technology have resulted in an increased number of motion sensors such as pedometers and accelerometers that are worn on the body and that measure bodily movement. Accelerometers are becoming less expensive and more user-friendly, but there is limited evidence regarding the accuracy of measurement in persons with MS. The present study examined the accuracy of an ActiGraph accelerometer for measuring steps taken during controlled conditions in persons with MS compared with a sample of individuals without MS. The participants were 24 adults with mild MS and 24 adults without MS who undertook three 6-minute periods of walking at 54, 80, and 107 m·min(-1) on a motor-driven treadmill. We measured steps taken through observation and an ActiGraph model 7164 accelerometer worn around the waist above the right hip. The accelerometer accurately measured steps during moderate (80 m·min(-1)) and fast (107 m·min(-1)) walking in both persons with MS and control subjects. There was a small degree of underestimation of step counts (≈4% error) for the accelerometer during slower walking (54 m·min(-1)) in both persons with MS and control subjects. Such findings support the accuracy of a waist worn ActiGraph accelerometer for the measurement of steps in persons with MS and control subjects.
    Disability and Health Journal 01/2011; 4(1):52-7. · 1.50 Impact Factor
  • Stamatis Agiovlasitis, Tracy Baynard, Kenneth H Pitetti, Bo Fernhall
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    ABSTRACT: People with Down syndrome (DS) show altered autonomic response to sympatho-excitation. Cardiac autonomic modulation may be examined with heart rate (HR) complexity which is associated uniquely with cardiovascular risk. This study examined whether the response of HR complexity to passive upright tilt differs between persons with and without DS and whether potential between-group differences in this response are accounted for by differences in body mass index (BMI). The electrocardiogram of 16 persons with DS (8 women, 8 men) and 16 persons without DS (8 women, 8 men) was recorded during 10 min of supine rest and 10 min of upright tilt. For each participant, 550 continuous, steady state, and ectopy-free R-R intervals under each condition were analyzed. Dependent variables were approximate entropy, correlation dimension, StatAv, and the mean R-R interval. In response to tilt, changes in approximate entropy and correlation dimension were reduced in participants with DS (p<0.05). These differences were explained by higher BMI in participants with DS. StatAv increased in persons with DS (p < 0.05) and stayed the same in those without DS even when controlling for BMI. The response of R-R interval did not differ between groups. None of the variables differed between groups at rest. Therefore, people with DS show smaller decrease in HR complexity in response to upright tilt than people without DS partially due to their higher BMI. Resting HR complexity does not differ between persons with and without DS. These results may have implications for cardiovascular risk in people with DS.
    Research in developmental disabilities 01/2011; 32(6):2102-7. · 4.41 Impact Factor

Publication Stats

241 Citations
77.64 Total Impact Points


  • 2009–2014
    • Mississippi State University
      • Department of Kinesiology
      Mississippi, United States
  • 2010
    • University of South Carolina
      • Department of Exercise Science
      Columbia, SC, United States
  • 2008–2010
    • University of Illinois, Urbana-Champaign
      • Department of Kinesiology and Community Health
      Urbana, IL, United States