Mild hypohydration did not affect tolerance time to presyncope (p=0.48), but females exhibited lower tolerance to lower-body negative pressure than males (12.8 vs 16.7 min; p=0.037).
RCT (n=28)
Counterbalanced order
Does mild hypohydration and sex influence cardiovascular responses and tolerance to progressive lower-body negative pressure in healthy young adults?
Mild hypohydration does not significantly impair tolerance to central hypovolemia induced by LBNP, though females exhibit lower tolerance and distinct cardiac responses compared to males.
p-value: p=0.48
The arterial baroreflex maintains blood pressure during mild-to-moderate orthostatic stress, but the roles of hydration status and sex in this response are unclear. This study used progressive lower-body negative pressure (LBNP) to examine how both fluid restriction and sex influence blood pressure regulation during central hypovolemia. Twenty-eight healthy young adults (15 females) completed two visits, in a counterbalanced order: 24-hr fluid restriction (hypohydrated) or 24-hr ad libitum fluid intake (euhydrated). Hydration status was assessed by changes in body mass and urine specific gravity. Beat-by-beat blood pressure, heart rate, stroke volume, and cardiac output were measured during progressive LBNP to presyncope, defined as systolic blood pressure 0.39), stroke volume (p = 0.87), or cardiac output (p = 0.21), but heart rate was borderline elevated during LBNP when hypohydrated (p = 0.051). Females exhibited lower tolerance to LBNP than males (12.8 ± 4.2 min vs. 16.7 ± 5.7 min; p = 0.037), and a distinct cardiac response, characterized by a higher heart rate (~ 4.3 bpm) and a greater reduction in stroke volume (~ 2.6 mL) during LBNP (both p 0.05). These data indicate that sex and hydration status influence cardiac function in response to LBNP.
Hunt et al. (Mon,) conducted a rct in Healthy young adults (n=28). 24-hr fluid restriction (hypohydration) vs. 24-hr ad libitum fluid intake (euhydration) was evaluated on Tolerance time to presyncope during progressive lower-body negative pressure (p=0.48). Mild hypohydration did not affect tolerance time to presyncope (p=0.48), but females exhibited lower tolerance to lower-body negative pressure than males (12.8 vs 16.7 min; p=0.037).