Sex Differences in Sympathetic Responses to Lower Body Negative Pressure

Caitlin P Jarrard; Joseph C Watso; Whitley C Atkins; Zachary J McKenna; Josh Foster; Mu Huang; Luke N Belval; Craig G Crandall

doi:10.1249/MSS.0000000000003392

Sex Differences in Sympathetic Responses to Lower Body Negative Pressure

Caitlin P Jarrard, Joseph C Watso, Whitley C Atkins, Zachary J McKenna, Josh Foster, Mu Huang, Luke N Belval, Craig G Crandall

Centre for Human & Applied Physiological Sciences

Deakin University

Research output: Contribution to journal › Article › peer-review

Abstract

Introduction Trauma-induced hemorrhage is a leading cause of death in prehospital settings. Experimental data demonstrate that females have a lower tolerance to simulated hemorrhage (i.e., central hypovolemia). However, the mechanism(s) underpinning these responses are unknown. Therefore, this study aimed to compare autonomic cardiovascular responses during central hypovolemia between the sexes. We hypothesized that females would have a lower tolerance and smaller increase in muscle sympathetic nerve activity (MSNA) to simulated hemorrhage. Methods Data from 17 females and 19 males, aged 19-45 yr, were retrospectively analyzed. Participants completed a progressive lower-body negative pressure (LBNP) protocol to presyncope to simulate hemorrhagic tolerance with continuous measures of MSNA and beat-to-beat hemodynamic variables. We compared responses at baseline, at two LBNP stages (-40 and -50 mmHg), and at immediately before presyncope. In addition, we compared responses at relative percentages (33%, 66%, and 100%) of hemorrhagic tolerance, calculated via the cumulative stress index (i.e., the sum of the product of time and pressure at each LBNP stage). Results Females had lower tolerance to central hypovolemia (female: 561 ± 309 vs male: 894 ± 304 min·mmHg [time·LBNP]; P = 0.003). At LBNP -40 and -50 mmHg, females had lower diastolic blood pressures (main effect of sex: P = 0.010). For the relative LBNP analysis, females exhibited lower MSNA burst frequency (main effect of sex: P = 0.016) accompanied by a lower total vascular conductance (sex: P = 0.028; main effect of sex). Conclusions Females have a lower tolerance to central hypovolemia, which was accompanied by lower diastolic blood pressure at -40 and -50 mmHg LBNP. Notably, females had attenuated MSNA responses when assessed as relative LBNP tolerance time.

Original language	English
Pages (from-to)	1056-1065
Number of pages	10
Journal	Medicine and Science in Sports and Exercise
Volume	56
Issue number	6
Early online date	18 Jan 2024
DOIs	https://doi.org/10.1249/MSS.0000000000003392
Publication status	Published - 1 Jun 2024

Keywords

BLOOD PRESSURE
HEMORRHAGE
MUSCLE SYMPATHETIC NERVE ACTIVITY

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10.1249/MSS.0000000000003392

Cite this

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title = "Sex Differences in Sympathetic Responses to Lower Body Negative Pressure",

abstract = "Introduction Trauma-induced hemorrhage is a leading cause of death in prehospital settings. Experimental data demonstrate that females have a lower tolerance to simulated hemorrhage (i.e., central hypovolemia). However, the mechanism(s) underpinning these responses are unknown. Therefore, this study aimed to compare autonomic cardiovascular responses during central hypovolemia between the sexes. We hypothesized that females would have a lower tolerance and smaller increase in muscle sympathetic nerve activity (MSNA) to simulated hemorrhage. Methods Data from 17 females and 19 males, aged 19-45 yr, were retrospectively analyzed. Participants completed a progressive lower-body negative pressure (LBNP) protocol to presyncope to simulate hemorrhagic tolerance with continuous measures of MSNA and beat-to-beat hemodynamic variables. We compared responses at baseline, at two LBNP stages (-40 and -50 mmHg), and at immediately before presyncope. In addition, we compared responses at relative percentages (33%, 66%, and 100%) of hemorrhagic tolerance, calculated via the cumulative stress index (i.e., the sum of the product of time and pressure at each LBNP stage). Results Females had lower tolerance to central hypovolemia (female: 561 ± 309 vs male: 894 ± 304 min·mmHg [time·LBNP]; P = 0.003). At LBNP -40 and -50 mmHg, females had lower diastolic blood pressures (main effect of sex: P = 0.010). For the relative LBNP analysis, females exhibited lower MSNA burst frequency (main effect of sex: P = 0.016) accompanied by a lower total vascular conductance (sex: P = 0.028; main effect of sex). Conclusions Females have a lower tolerance to central hypovolemia, which was accompanied by lower diastolic blood pressure at -40 and -50 mmHg LBNP. Notably, females had attenuated MSNA responses when assessed as relative LBNP tolerance time.",

keywords = "BLOOD PRESSURE, HEMORRHAGE, MUSCLE SYMPATHETIC NERVE ACTIVITY",

author = "Jarrard, {Caitlin P} and Watso, {Joseph C} and Atkins, {Whitley C} and McKenna, {Zachary J} and Josh Foster and Mu Huang and Belval, {Luke N} and Crandall, {Craig G}",

note = "Publisher Copyright: Copyright {\textcopyright} 2024 by the American College of Sports Medicine.",

year = "2024",

month = jun,

day = "1",

doi = "10.1249/MSS.0000000000003392",

language = "English",

volume = "56",

pages = "1056--1065",

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TY - JOUR

T1 - Sex Differences in Sympathetic Responses to Lower Body Negative Pressure

AU - Jarrard, Caitlin P

AU - Watso, Joseph C

AU - Atkins, Whitley C

AU - McKenna, Zachary J

AU - Foster, Josh

AU - Huang, Mu

AU - Belval, Luke N

AU - Crandall, Craig G

PY - 2024/6/1

Y1 - 2024/6/1

N2 - Introduction Trauma-induced hemorrhage is a leading cause of death in prehospital settings. Experimental data demonstrate that females have a lower tolerance to simulated hemorrhage (i.e., central hypovolemia). However, the mechanism(s) underpinning these responses are unknown. Therefore, this study aimed to compare autonomic cardiovascular responses during central hypovolemia between the sexes. We hypothesized that females would have a lower tolerance and smaller increase in muscle sympathetic nerve activity (MSNA) to simulated hemorrhage. Methods Data from 17 females and 19 males, aged 19-45 yr, were retrospectively analyzed. Participants completed a progressive lower-body negative pressure (LBNP) protocol to presyncope to simulate hemorrhagic tolerance with continuous measures of MSNA and beat-to-beat hemodynamic variables. We compared responses at baseline, at two LBNP stages (-40 and -50 mmHg), and at immediately before presyncope. In addition, we compared responses at relative percentages (33%, 66%, and 100%) of hemorrhagic tolerance, calculated via the cumulative stress index (i.e., the sum of the product of time and pressure at each LBNP stage). Results Females had lower tolerance to central hypovolemia (female: 561 ± 309 vs male: 894 ± 304 min·mmHg [time·LBNP]; P = 0.003). At LBNP -40 and -50 mmHg, females had lower diastolic blood pressures (main effect of sex: P = 0.010). For the relative LBNP analysis, females exhibited lower MSNA burst frequency (main effect of sex: P = 0.016) accompanied by a lower total vascular conductance (sex: P = 0.028; main effect of sex). Conclusions Females have a lower tolerance to central hypovolemia, which was accompanied by lower diastolic blood pressure at -40 and -50 mmHg LBNP. Notably, females had attenuated MSNA responses when assessed as relative LBNP tolerance time.

AB - Introduction Trauma-induced hemorrhage is a leading cause of death in prehospital settings. Experimental data demonstrate that females have a lower tolerance to simulated hemorrhage (i.e., central hypovolemia). However, the mechanism(s) underpinning these responses are unknown. Therefore, this study aimed to compare autonomic cardiovascular responses during central hypovolemia between the sexes. We hypothesized that females would have a lower tolerance and smaller increase in muscle sympathetic nerve activity (MSNA) to simulated hemorrhage. Methods Data from 17 females and 19 males, aged 19-45 yr, were retrospectively analyzed. Participants completed a progressive lower-body negative pressure (LBNP) protocol to presyncope to simulate hemorrhagic tolerance with continuous measures of MSNA and beat-to-beat hemodynamic variables. We compared responses at baseline, at two LBNP stages (-40 and -50 mmHg), and at immediately before presyncope. In addition, we compared responses at relative percentages (33%, 66%, and 100%) of hemorrhagic tolerance, calculated via the cumulative stress index (i.e., the sum of the product of time and pressure at each LBNP stage). Results Females had lower tolerance to central hypovolemia (female: 561 ± 309 vs male: 894 ± 304 min·mmHg [time·LBNP]; P = 0.003). At LBNP -40 and -50 mmHg, females had lower diastolic blood pressures (main effect of sex: P = 0.010). For the relative LBNP analysis, females exhibited lower MSNA burst frequency (main effect of sex: P = 0.016) accompanied by a lower total vascular conductance (sex: P = 0.028; main effect of sex). Conclusions Females have a lower tolerance to central hypovolemia, which was accompanied by lower diastolic blood pressure at -40 and -50 mmHg LBNP. Notably, females had attenuated MSNA responses when assessed as relative LBNP tolerance time.

KW - BLOOD PRESSURE

KW - HEMORRHAGE

KW - MUSCLE SYMPATHETIC NERVE ACTIVITY

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U2 - 10.1249/MSS.0000000000003392

DO - 10.1249/MSS.0000000000003392

M3 - Article

C2 - 38233995

SN - 0195-9131

VL - 56

SP - 1056

EP - 1065

JO - Medicine and Science in Sports and Exercise

JF - Medicine and Science in Sports and Exercise

IS - 6

ER -

Sex Differences in Sympathetic Responses to Lower Body Negative Pressure

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