Hypohydration affects forearm vascular conductance independent of heart rate during exercise

Abstract

Elevated body core temperature stimulates cutaneous vasodilation, which can be modified by nonthermal factors. To test whether hypohydration affects forearm vascular conductance discretely from relative alterations in heart rate (HR), eight trained cyclists exercised progressively for 20 min each at 60, 120, and 180 W [approximately 22, 37, and 55% of maximal cycling O2 consumption (VO2peak), respectively] in a warm humid environment (dry bulb temperature 30 degrees C; wet bulb temperature 24 degrees C). Esophageal temperature and forearm blood flow were measured every 30 s, and mean arterial pressure and HR were measured at rest and during each exercise intensity (minutes 15, 35, and 55). In the hypovolemic (HP) compared with the euvolemic (EU) state, blood volume was contracted by 24-h fluid restriction an average of 510 ml, and this difference was sustained throughout exercise. The esophageal temperature and HR responses were similar between EU and HP states at 60 and 120 W but were significantly (P < 0.05) higher in HP by the end of 180 W. In contrast, the forearm blood flow response was significantly (P < 0.05) depressed during exercise at 120 and 180 W in HP, whereas mean arterial pressure remained similar between conditions. When body core temperature is elevated in a hypohydrated state, forearm vascular conductance is reduced at exercise intensities of approximately 37% VO2peak, which is independent of relative changes in HR. These findings are consistent with the notion that during exercise an attenuated cutaneous vasodilation is elicited by alterations in regionalized sympathetic outflow, which is unaccompanied by activation of cardiac pacemaker cells.

Impaired High-Intensity Cycling Performance Time at Low Levels of Dehydration

“…Although it has been suggested that fluid ingestion during exercise can prevent the adverse effects of dehydration on endurance performance (39,44), there are no adequately controlled studies which have directly addressed this hypothesis. Furthermore, most such studies have been performed at low (<50% ofTO2max; 11, 12,23,36,41) or moderately low (<60% VO2max) exercise intensities (3,7,42) over prolonged periods leading to large fluid losses. Conclusions from these studies may not apply to more intense (>70% VO2max), prolonged (>90 mm) exercise.…”

Short‐term water deprivation attenuates the exercise pressor reflex in older female adults

“…Other work has reported moderate hypohydration (4 % body mass loss) to blunt mean BP responses during exercise with an ambient temperature of 40 °C, but not in ambient temperatures between 10 and 30 °C in young male adults (Kenefick, Sollanek, Charkoudian, & Sawka, 2014). Another study in young male adults reported similar BP responses during cycling exercise in mild heat (30 °C) following 24‐hr fluid restriction (Tankersley, Zappe, Meister, & Kenney, 1985). A more recent study in young male adults reported lower absolute mean BP during exercise following mild and moderate hypohydration (2 and 3.5 % body mass loss, respectively), but this study elicited hypohydration via exercise in the heat (37 °C) (Pearson et al., 2013).…”

Free-living, continuous hypo-hydration, and cardiovascular response to exercise in a heated environment

“…Previous studies demonstrate sweat rate varies widely depending on exercise intensity, environment and clothing worn (Tankersley et al. ; Gill et al. ).…”

“…However, the environment and work rate may not have produced enough stress on the CV system to significantly alter SBF or sweat response. Previous studies demonstrate sweat rate varies widely depending on exercise intensity, environment and clothing worn (Tankersley et al 1992;Gill et al 2000). In addition, the participants' baseline fitness level may have impacted their sweat rate.…”