Influence Of Hydration Status Research Articles

Influence of Hydration Status and Plasma Copeptin on Ambulatory Blood Pressure in Healthy Young Adults

BACKGROUND: Adequate hydration is essential for regulating various physiological systems and may influence blood pressure (BP). Hypohydration is linked with elevated copeptin (surrogate of arginine vasopressin), which is associated with elevated cardiovascular disease risk. However, there is limited information on the influence of hydration and copeptin on ambulatory BP measures in young adults. Therefore, we sought to investigate associations between hydration, copeptin, and ambulatory BP. METHODS: We studied 41 participants (19 M/22 F, 24 White/17 Black, age 21±1 years, body mass index 26±5 kg/m 2 , screening BP 111± 10/67±8 mmHg; Mean ± SD) who provided a 24-hour urine sample. We measured urine specific gravity (USG), urine osmolality (OSM), and plasma copeptin as biomarkers of hydration. We used ambulatory BP monitoring (Suntech Oscar2) to assess BP during daytime (1000-2000) and nighttime (0000-0600). Our primary outcomes were plasma copeptin (pmol/L) and night-to-day BP dip ratio (nighttime/daytime BP) in dehydrated (USG >1.020 or OSM >800 mOsm/kg) vs euhydrated participants. Statistical procedures included Student’s t-tests and Mann-Whitney U tests. We also used Spearman’s rho correlation (controlling for BMI, sex, and race). We set α at ≤0.05. RESULTS: Copeptin concentration was elevated in dehydrated compared with euhydrated participants (USG: 6.6±2.9 vs 4.3±2.0 pmol/L, p<0.005; OSM: 6.6±2.7 vs 4.1±2.0 pmol/L, p<0.001). After controlling for BMI, sex, and race, copeptin was associated with USG (rho=0.44, p=0.005) and OSM (rho=0.51, p=0.001). Systolic and diastolic BP dip ratios did not differ by hydration status for either USG or OSM ( ps>0.179). Additionally, adjusted BP dip ratios were not correlated with OSM or USG ( ps>0.149). Plasma copeptin was not associated with BP dip ratios ( ps>0.155) but was associated with absolute nocturnal systolic (rho=-0.34, p=0.036) and diastolic BP dip (rho=-0.33, p=0.041). When we split participants by low and high copeptin concentration (median split), higher copeptin was associated with a lower (i.e., worse) systolic BP dip ratio (0.87±0.06 vs 0.90±0.06, p=0.048) and lower absolute nocturnal systolic and diastolic BP dip ( ps<0.01). CONCLUSIONS: Hydration biomarkers were correlated with plasma copeptin, but not ambulatory BP. The significance of our findings are that higher copeptin was associated with blunted nocturnal BP dipping in younger adults, which could predispose them to increased future cardiovascular disease risk. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The influence of hydration status on ion transport in the rabbit (Oryctolagus cuniculus) skin-An in vitro study.

The preservation of physiological transport of ions and water content is particularly important for maintaining the skin barrier, touch and pain stimuli, as well as the initiation of skin regeneration processes, especially after treatments associated with breaking skin continuity and wound healing difficulties. The aim of the study was to assess changes in ion transport, measured as values of transepithelial electric resistance and potential difference in stationary conditions and during mechanical-chemical stimulations, depending on the hydration status of isolated rabbit skin specimens. The specimens were divided into five groups: control (n = 22), dehydrated in 10% NaCl (n = 30), rehydrated after dehydration (n = 26), dried at 37°C (n = 26), and rehydrated after drying (n = 25). Dehydrated tissue samples showed altered resistance compared to the control; this change was maintained regardless of rehydration. In the dehydrated samples, changes in the measured electric potential were also noted, which returned to values comparable with the control after rehydration. Dehydrated skin, regardless of the cause of dehydration, responds with changes in the transport of sodium and chloride ions and the altered cellular microenvironment. It could influence the perception of stimuli, particularly pain, and slow down the regeneration processes.

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies.

A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.

Heat Acclimation with Controlled Heart Rate: Influence of Hydration Status.

This study aimed to characterize the adaptive responses to heat acclimation (HA) with controlled heart rate (HR) and determine whether hydration strategy alters adaptations. The influence of HA on maximal oxygen uptake (V˙O2max) in cool conditions and self-paced exercise in the heat was also determined. Eight men (V˙O2max, 55 ± 7 mL·kg·min) completed two 10-d interventions in a counterbalanced crossover design. Fluid intakes differed between interventions to either maintain euhydration (HA-EUH) or elicit similar daily body mass deficits (2.85% ± 0.26%; HA-DEH). HA consisted of 90 min of cycling in 40°C and 40% relative humidity. Initial workload (172 ± 22 W) was adjusted over the last 75 min to maintain exercising HR equivalent to 65% V˙O2max. A V˙O2max test in cool conditions and 30-min time trial in hot-humid conditions were completed before and after HA. HR at the end of the initial 15 min workload was 10 ± 5 bpm lower on day 10 in both interventions (P < 0.001). The workload necessary to maintain exercising HR (145 ± 7 bpm) increased throughout HA-EUH (25 ± 10 W, P = 0.001) and HA-DEH (16 ± 18 W, P = 0.02). There was a main effect of HA on sweat rate (P = 0.014), which tended to increase with HA-EUH (0.19 ± 0.18 L·h, P = 0.06), but not HA-DEH (P = 0.12). Skin temperature decreased during HA-EUH (0.6°C ± 0.5°C, P = 0.03), but not HA-DEH (P = 0.30). There was a main effect of HA on V˙O2max (~3 mL·kg·min, P = 0.02); however, neither intervention independently increased V˙O2max (both, P = 0.08). Time-trial performance increased after HA-EUH (19 ± 16 W, P = 0.02), but not HA-DEH (P = 0.21). Controlled HR exercise in the heat induces several HA adaptations, which may be optimized by maintaining euhydration. HA-EUH also improves self-paced exercise performance in the heat. However, HA does not seem to significantly increase V˙O2max in cool conditions.

Influence of hydration status on cardiovascular magnetic resonance myocardial T1 and T2 relaxation time assessment: an intraindividual study in healthy subjects

BackgroundMyocardial native T1 and T2 relaxation time mapping are sensitive to pathological increase of myocardial water content (e.g. myocardial edema). However, the influence of physiological hydration changes as a possible confounder of relaxation time assessment has not been studied. The purpose of this study was to evaluate, whether changes in myocardial water content due to dehydration and hydration might alter myocardial relaxation times in healthy subjects.MethodsA total of 36 cardiovascular magnetic resonance (CMR) scans were performed in 12 healthy subjects (5 men, 25.8 ± 3.2 years). Subjects underwent three successive CMR scans: (1) baseline scan, (2) dehydration scan after 12 h of fasting (no food or water), (3) hydration scan after hydration. CMR scans were performed for the assessment of myocardial native T1 and T2 relaxation times and cardiac function. For multiple comparisons, repeated measures ANOVA or the Friedman test was used.ResultsThere was no change in systolic blood pressure or left ventricular ejection fraction between CMR scans (P > 0.05, respectively). T1 relaxation times were significantly reduced with dehydration (987 ± 27 ms [baseline] vs. 968 ± 29 ms [dehydration] vs. 986 ± 28 ms [hydration]; P = 0.006). Similar results were observed for T2 relaxation times (52.9 ± 1.8 ms [baseline] vs. 51.5 ± 2.0 ms [dehydration] vs. 52.2 ± 1.9 ms [hydration]; P = 0.020).ConclusionsDehydration may lead to significant alterations in relaxation times and thereby may influence precise, repeatable and comparable assessment of native T1 and T2 relaxation times. Hydration status should be recognized as new potential confounder of native T1 and T2 relaxation time assessment in clinical routine.

Influence of Hydration Status on Cognitive Function and Skill Performance in Division III Collegiate Female Basketball Players.

Proper hydration has been documented as an important component in optimum athletic performance. The current body of research lacks sports specific analysis of effects of hydration on athletic performance, and rather generalizes to a classification of exercise, whether anaerobic or aerobic. PURPOSE: To compare two hydration interventions (Gatorade vs. placebo) on various skills needed to successfully perform in a collegiate basketball game in order to gain an accurate understanding of fluid requirements for the sport. METHODS: Participants were 8 females (Age: 20 ± 2 yrs, Ht: 166.68 ± 4.06 cm, Wt: 76.91 ±10.74 kg) current members of the women’s basketball team. Participation consisted of two testing days completing a NCAA regulation first half of basketball followed by a series of skills tests including maximal vertical jump, T-test, lay-up shooting, jump shooting, and a 300-yard shuttle run. Participants also completed a computerized test of memory and reaction time pre-game and post-skills. Fingerstick blood samples were taken pre-game, post-game and post-skills tests to assess hydration status and to calculated plasma volume change. Intake of fluid throughout testing was continuously monitored and measured. RESULTS: Plasma volume was decreased by 1.3 ± 4.0% vs. 3.2 ± 5.0% in Gatorade vs. placebo despite similar volumes of fluid consumed (402 ± 344 ml vs. 313 ±214 ml in Gatorade vs. placebo) and the same distance covered during the game (2.9 km). There was a negative correlation between reaction time and total fluid consumed (r = -0.71, p = .048). Similarly, lower plasma volume change resulted in higher scores on the memory test when consuming Gatorade (r = -0.90, p = 0.005), suggesting fluid intake is important to cognitive performance. Increased Gatorade ingestion resulted in lower blood lactate concentrations (r = -0.90, p=.003), potentially due to glycogen sparing from carbohydrate intake. There were no further statistically significant differences in outcome variables. CONCLUSION: The current study suggests fluid intake is important to cognitive performance. This may play a role during team sports games when decision making under pressure is likely to occur.

The influence of hydration status during prolonged endurance exercise on salivary antimicrobial proteins.

Antimicrobial proteins (AMPs) in saliva including secretory immunoglobulin A (SIgA), lactoferrin (SLac) and lysozyme (SLys) are important in host defence against oral and respiratory infections. This study investigated the effects of hydration status on saliva AMP responses to endurance exercise. Using a randomized design, 10 healthy male participants (age 23 ± 4 years, [Formula: see text] 56.8 ± 6.5 ml/kg/min) completed 2 h cycling at 60 % [Formula: see text] in states of euhydration (EH) or dehydration (DH) induced by 24 h fluid restriction. Unstimulated saliva samples were collected before, during, immediately post-exercise and each hour for 3 h recovery. Fluid restriction resulted in a 1.5 ± 0.5 % loss of body mass from baseline and a 4.3 ± 0.7 % loss immediately post-exercise. Pre-exercise urine osmolality was higher in DH than EH and overall, saliva flow rate was reduced in DH compared with EH (p < 0.05). Baseline SIgA secretion rates were not different between conditions; however, exercise induced a significant increase in SIgA concentration in DH (161 ± 134 to 309 ± 271 mg/L) which remained elevated throughout 3 h recovery. SLac secretion rates increased from pre- to post-exercise in both conditions which remained elevated in DH only. Overall, SLac concentrations were higher in DH than EH. Pre-exercise SLys concentrations were lower in DH compared with EH (1.6 ± 2.0 vs. 5.5 ± 6.7 mg/L). Post-exercise SLys concentrations remained elevated in DH but returned to pre-exercise levels by 1 h post-exercise in EH. Exercise in DH caused a reduction in saliva flow rate yet induced greater secretion rates of SLac and higher concentrations of SIgA and SLys. Thus, DH does not impair saliva AMP responses to endurance exercise.

Influence of Hydration Status on Changes in Plasma Cortisol, Leukocytes, and Antigen-Stimulated Cytokine Production by Whole Blood Culture following Prolonged Exercise.

Elevated antigen-stimulated anti-inflammatory cytokine production appears to be a risk factor for upper respiratory tract illness in athletes. The purpose of this study was to determine the effects of prolonged exercise and hydration on antigen-stimulated cytokine production. Twelve healthy males cycled for 120 min at 60% on two occasions, either euhydrated or moderately hypohydrated (induced by fluid restriction for 24 h). Blood samples were collected before and after exercise and following 2 h recovery for determination of cell counts, plasma cortisol, and in vitro antigen-stimulated cytokine production by whole blood culture. Fluid restriction resulted in mean body mass loss of 1.3% and 3.9% before and after exercise, respectively. Exercise elicited a significant leukocytosis and elevated plasma cortisol, with no differences between trials. IL-6 production was significantly reduced 2 h postexercise (P < 0.05), while IL-10 production was elevated postexercise (P < 0.05). IFN-γ and IL-2 production tended to decrease postexercise. No significant effect of hydration status was observed for the measured variables. Prolonged exercise appears to result in augmented anti-inflammatory cytokine release in response to antigen challenge, possibly coupled with acute suppression of proinflammatory cytokine production, corresponding with studies using mitogen or endotoxin as stimulant. Moderate hypohydration does not appear to influence these changes.

Influence of Hydration Status on Thermoregulation and Cycling Hill Climbing

Although dehydration can impair endurance performance, a reduced body mass may benefit uphill cycling by increasing the power-to-mass ratio. This study examined the effects of a reduction in body mass attributable to unreplaced sweat losses on simulated cycling hill-climbing performance in the heat. Eight well-trained male cyclists (mean +/- SD: 28.4 +/- 5.7 yr; 71.0 +/- 5.9 kg; 176.7 +/- 4.7 cm; VO2peak: 66.2 +/- 5.8 mL x kg(-1) x min(-1)) completed a maximal graded cycling test on a stationary ergometer to determine maximal aerobic power (MAP). In a randomized crossover design, cyclists performed a 2-h ride at 53% MAP on a stationary ergometer, immediately followed by a cycling hill-climb time-to-exhaustion trial (88% MAP) on their own bicycle on an inclined treadmill (8%) at approximately 30 degrees C. During the 2-h ride, they consumed either 2.4 L of a 7% carbohydrate (CHO) drink (HIGH) or 0.4 L of water (LOW) with sport gels to match for CHO content. After the 2-h ride and before the hill climb, drinking strategies influenced body mass (LOW -2.5 +/- 0.5% vs HIGH 0.3 +/- 0.4%; P < 0.001), HR (LOW 158 +/- 15 vs HIGH 146 +/- 15 bpm; P = 0.03), and rectal temperature (T(re): LOW 38.9 +/- 0.2 vs HIGH 38.3 +/- 0.2 degrees C; P = 0.001). Despite being approximately 1.9 kg lighter, time to exhaustion was significantly reduced by 28.6 +/- 13.8% in the LOW treatment (LOW 13.9 +/- 5.5 vs HIGH 19.5 +/- 6.0 min, P = 0.002), as was the power output for a fixed speed (LOW 308 +/- 28 vs HIGH 313 +/- 28 W, P = 0.003). At exhaustion, T(re) was higher in the LOW treatment (39.5 vs HIGH 39.1 degrees C; P < 0.001), yet peak HR, blood lactate, and glucose were similar. Exercise-induced dehydration in a warm environment is detrimental to laboratory cycling hill-climbing performance despite reducing the power output required for a given speed.

The influence of hydration status on heart rate variability after exercise heat stress

While exercise heat stress and hydration status are known to independently influence heart rate variability (HRV), the combined effect of these physiological stressors is unknown. Thus, heat-acclimated subjects ( n=5) performed exercise heat trials (40 °C, 20% relative humidity) in the euhydrated and hypohydrated state (3.9±0.7% body weight loss). During each trial, cardiac cycle R–R interval data were collected for 45 min at rest (pre-) and after (post-) completing 90 min of cycle ergometer exercise. Pre- and post-exercise RRI data were analyzed by Fast Fourier Power Spectral analysis to determine the high-frequency (HF), low-frequency (LF), very low-frequency (VLF), and total power (TP) components of HRV. Overall HRV was decreased by both hypohydration and exercise heat stress. Hypohydration reduced TP, LF, VLF, and LF:HF ratio ( P < 0.05 ) while HF was significantly higher. The change in both LF and HF power (pre- vs. post-exercise) were blunted during hypohydration compared to euhydration. These data suggest that dehydration alone positively influences the parasympathetic (HF) control of HRV, but the reduction in overall HRV and the blunted oscillations in LF and HF power following exercise heat stress support an overall deleterious effect of dehydration on autonomic cardiac stability.

The influence of hydration status on stress‐induced hemoconcentration

This study examined the effects of hydration status on rheological and hemodynamic activity during rest, mental stress, postural stress, and combined mental/postural stress in 24 men when euhydrated and hyperhydrated. The stress tasks elicited hemoconcentration, although the effects were less pronounced during mental stress. Hyperhydration was associated with higher plasma volume throughout. All stress tasks also perturbed hemodynamic activity, irrespective of hydration status, with the exception of heart rate reactivity, which was attenuated when hyperhydrated. As expected the combined stress during euhydration was associated with an unfavorable rheological and cardiovascular profile, which may help explain the increased incidence of cardiovascular events in the morning.

Influence of hydration status and fluid replacement on heat tolerance while wearing NBC protective clothing.

The purpose of the present study was to investigate the influence of hypohydration and fluid replacement on tolerance to an uncompensable heat stress. Eight healthy young males completed a matrix of six trials in an environmental chamber, set at 40 degrees C and 30% relative humidity, while wearing nuclear, biological, and chemical protective clothing. Subjects performed either light (3.5 km x h(-1), 0% grade, no wind) or heavy (4.8 km x h(-1), 4% grade, no wind) treadmill exercise combined with three hydration states [euhydration with fluid replacement (EU/F), euhydration without fluid replacement (EU/NF), and hypohydration with fluid replacement (H/F)]. Hypohydration of 2.2% body mass was achieved by exercise and fluid restriction on the day preceding the trials. No differences in the endpoint mean skin temperature (Tsk), sweat rate, or rectal temperature (Tre) were observed among the hydration conditions for either work rate. During light exercise, the change in Tre (deltaTre) was significantly higher with H/F than EU/F after 40 min, and heart rate was greater after 25 min. The heart rate was greater during EU/NF than during EU/F after 60 min. Tolerance times were significantly greater for EU/F than for either EU/NF or H/F. With heavy exercise, no differences in deltaTre were observed across hydration conditions. Compared to EU/F, heart rates were higher after 10 and 30 min for H/F and EU/NF, respectively. Tolerance times were significantly less during H/F than with either of the EU conditions. Stroke volume was significantly decreased in H/F trials compared to EU/F trials for both light and heavy work rates, but no differences in cardiac output were observed. It was concluded that even minor levels of hypohydration significantly impaired exercise tolerance in a severely uncompensable heat stress environment at both light and heavy exercise intensities.