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<p>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&#xa0;&lt; 90 mmHg for three consecutive cardiac cycles. 24-hr fluid restriction reduced body mass (Δ − 1.27 ± 0.70&#xa0;kg; <i>p</i> &lt; 0.01) and elevated urine specific gravity (Δ + 0.013; <i>p</i> &lt; 0.01), confirming that participants were mildly hypohydrated after 24-hr of fluid restriction. Mild hypohydration did not affect tolerance time to presyncope (<i>p</i> = 0.48), blood pressure (all <i>p</i> &gt; 0.39), stroke volume (<i>p</i> = 0.87), or cardiac output (<i>p</i> = 0.21), but heart rate was borderline elevated during LBNP when hypohydrated (<i>p</i> = 0.051). Females exhibited lower tolerance to LBNP than males (12.8 ± 4.2&#xa0;min vs. 16.7 ± 5.7&#xa0;min; <i>p</i> = 0.037), and a distinct cardiac response, characterized by a higher heart rate (~ 4.3&#xa0;bpm) and a greater reduction in stroke volume (~ 2.6 mL) during LBNP (both <i>p</i> &lt; 0.01). However, no significant interactions were observed between sex and hydration status for any cardiovascular responses to LBNP (all <i>p</i> &gt; 0.05). These data indicate that sex and hydration status influence cardiac function in response to LBNP.</p>

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The impact of mild hypohydration and sex on the cardiovascular responses to progressive lower-body negative pressure

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Megan Hunt,
  • Jenna C. McCrone,
  • Christopher Pignanelli,
  • Monica M. Grigore,
  • Katrin Turetskiy,
  • Gavin C. Lydiate,
  • Alexa A. Robertson,
  • Regan E. J. Parris,
  • Ella M. Bisset-Cavallin,
  • Connor Wideman,
  • Philip J. Millar,
  • Jamie F. Burr,
  • Michael M. Tymko

摘要

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 < 90 mmHg for three consecutive cardiac cycles. 24-hr fluid restriction reduced body mass (Δ − 1.27 ± 0.70 kg; p < 0.01) and elevated urine specific gravity (Δ + 0.013; p < 0.01), confirming that participants were mildly hypohydrated after 24-hr of fluid restriction. Mild hypohydration did not affect tolerance time to presyncope (p = 0.48), blood pressure (all p > 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 < 0.01). However, no significant interactions were observed between sex and hydration status for any cardiovascular responses to LBNP (all p > 0.05). These data indicate that sex and hydration status influence cardiac function in response to LBNP.