Cardiovascular responses to water drinking: does osmolality play a role?
ABSTRACT Water drinking activates the autonomic nervous system and induces acute hemodynamic changes. The actual stimulus for these effects is undetermined but might be related to either gastric distension or to osmotic factors. In the present study, we tested whether the cardiovascular responses to water drinking are related to water's relative hypoosmolality. Therefore, we compared the cardiovascular effects of a water drink (7.5 ml/kg body wt) with an identical volume of a physiological (0.9%) saline solution in nine healthy subjects (6 male, 3 female, aged 26 +/- 2 years), while continuously monitoring beat-to-beat blood pressure (finger plethysmography), cardiac intervals (electrocardiography), and cardiac output (thoracic impedance). Total peripheral resistance was calculated as mean blood pressure/cardiac output. Cardiac interval variability (high-frequency power) was assessed by spectral analysis as an index of cardiac vagal tone. Baroreceptor sensitivity was evaluated using the sequence technique. Drinking water, but not saline, decreased heart rate (P = 0.01) and increased total peripheral resistance (P < 0.01), high-frequency cardiac interval variability (P = 0.03), and baroreceptor sensitivity (P = 0.01). Neither water nor saline substantially increased blood pressure. These responses suggest that water drinking simultaneously increases sympathetic vasoconstrictor activity and cardiac vagal tone. That these effects were absent after drinking physiological saline indicate that the cardiovascular responses to water drinking are influenced by its hypoosmotic properties.
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ABSTRACT: As with water ingestion, the activation of the muscle metaboreflex leads to heightened muscle sympathetic nerve activity. Thus, we hypothesized that water ingestion might enhance the pressor effect of the muscle metaboreflex activation. We examined the effect of water ingestion (50 vs. 500 mL) on the cardiovascular and autonomic responses to static handgrip followed by postexercise circulatory occlusion (PECO) in 19 healthy participants (29.2 ± 8.6 years). Beat-to-beat blood pressure, baroreflex sensitivity (BRS), and R-R intervals were recorded in both conditions (pre- and postingestion). Changes in stroke volume and cardiac output were assessed using Modelflow. Cardiac autonomic regulation was investigated by spectral heart rate variability (HRV); baroreflex control of heart rate was assessed by the sequence method. Water ingestion did not increase the pressor effect induced by PECO. Even though 500 mL of water elicited an overall bradycardia, paired by an increase in the high-frequency HRV, there were no differences between conditions for the decrease in BRS or the resetting of the baroreflex to operate at higher blood pressure. Nevertheless, after the ingestion of 500 mL of water, there were no significant correlations between the percent change in cardiac output and that of BRS, from rest to PECO. This contrasts with that seen in the 50 mL condition (r = -0.68, p < 0.05). Contrasting with our hypothesis, 500 mL of water did not increase the pressor effect induced by PECO. Nevertheless, we found that water ingestion may influence the mechanisms by which the muscle metaboreflex elicits an increased cardiac output during PECO.Applied Physiology Nutrition and Metabolism 10/2012; · 2.01 Impact Factor
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ABSTRACT: In prolonged exercise, the state of hypohydration due to sweating raises physiological stress and induces a drop in sports performance. However, the impact of water intake in cardiorespiratory parameters when administered during and after physical activity has not been well studied. This study aimed to analyze the effects of water intake in heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), partial oxygen saturation (SpO2) and respiratory rate during and after prolonged exercise. Thirty-one young males (21.55 +/- 1.89 yr) performed three different protocols (48 h interval between each stage): I) maximal exercise test to determine the load for the protocols; II) Control protocol (CP) and; III) Experimental protocol (EP). The protocols consisted of 10 min at rest with the subject in the supine position, 90 min of treadmill exercise (60% of VO2 peak) and 60 min of rest placed in the dorsal decubitus position. No rehydration beverage consumption was allowed during CP. During EP, however, the subjects were given water (Vittalev, Spaipa, Brazil). The parameters HR, SBP, DBP, SpO2 and respiratory rate were measured at the end of the rest, in 30, 60 and 90 minutes of the activity, except the respiratory rate parameter, and at 1, 3, 5, 7, 10, 20, 30, 40, 50 and 60 minute post- exercise. The hydration protocol provided minimal changes in SBP and DBP and a smaller increase in HR and did not significantly affect SpO2 during exercise and better HR recovery, faster return of SBP and DBP and a better performance for SpO2 and respiratory rate post-exercise. Hydration with water influenced the behavior of cardiorespiratory parameters in healthy young subjects.International Archives of Medicine 09/2013; 6(1):35.
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ABSTRACT: Hydration plays a key role in the physiological maintenance required by exercise. To evaluate the behavior of heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure, pulse oxygen saturation (SpO2) and respiratory rate (RR) of young people during and after prolonged physical exercise, with and without the intake of water or isotonic solution. 31 young individuals (21.63 +/- 1.86 years) were subjected to a four-step protocol with a 48-hour interval between each step, namely: i) a test to determine the incremental load used in subsequent steps, ii) a control protocol without hydration (CP), iii) an experimental protocol with water intake (PE1), iv) an experimental protocol with ingestion of isotonic (PE2). The protocols consisted of 10 min rest, 90 min of exercise on a treadmill at 60% of VO2 peak and 60 min of recovery. The parameters HR, SBP, DBP, RR and SPO2 were measured at rest, at 30, 60 and 90 min of exercise, with the exception of RR; and at 1, 3, 5, 7, 10, 20, 30, 40, 50 and 60 min of recovery. The two-factor analysis of variance for repeated measures model was used for analysis (p<0.05). There was a moment effect for all variables in exercise (p<0.001), however, no effect was observed between the protocols (SBP, p=0.998; DBP, p=0.897; SpO2, p=0.077, HR=0.281) and in the interaction moment and protocol (SBP, p=0.058; DBP, p=0.191 and SpO2, p=0.510, HR=0.496). In recovery there was also a moment effect for all variables analyzed (p<0.001). There was no effect among protocols for SBP (p=0.986), DBP (p=0.536) and RR (p=0.539), however in the SpO2 (p=0.001) and HR (p=0.033) variables, effects were observed between the protocols. Regarding the moment and protocol interaction, an effect was observed for HR (SBP, p=0.431; DBP, p=0.086; SpO2, p=0.445, RR, p=0.147, HR, p=0.022). For the type of exercise performed, both the water and the isotonic solution influenced the behavior of cardiorespiratory parameters, and independent of the type of hydration given the behavior of the parameters studied was similar.International Archives of Medicine 08/2013; 6(1):33.