Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion

Research output: Contribution to journalArticlepeer-review

Standard

Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion. / Lucas, Rebekah; Wilson, Luke; Ainslie, P. N.; Fan, Jui-Lin; Thomas, Kate N; Cotter, James D.

In: AJP Regulatory Integrative and Comparative Physiology, Vol. 314, No. 3, 01.03.2018, p. R415-R426.

Research output: Contribution to journalArticlepeer-review

Harvard

APA

Vancouver

Author

Lucas, Rebekah ; Wilson, Luke ; Ainslie, P. N. ; Fan, Jui-Lin ; Thomas, Kate N ; Cotter, James D. / Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion. In: AJP Regulatory Integrative and Comparative Physiology. 2018 ; Vol. 314, No. 3. pp. R415-R426.

Bibtex

@article{f327c1766deb4ac4a1bf178c156d1a5d,
title = "Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion",
abstract = "The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (Tc; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5–2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAvmean; transcranial Doppler), partial pressure of end-tidal carbon dioxide (PETCO2), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, −15, −30, and −45 mmHg). Four subjects became intolerant before +2.0°C Tc, unrelated to hydration status. Without LBNP, decreases in PETCO2 accounted fully for reductions in MCAvmean across all Tc. With LBNP at heat tolerance (+1.5 or +2.0°C), PETCO2 accounted for 69 ± 25% of the change in MCAvmean. The HYPO condition did not affect MCAvmean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAvmean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in Tc are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.",
keywords = "Dehydration, heat stress, lower body negative pressure, middle cerebral artery blood velocity",
author = "Rebekah Lucas and Luke Wilson and Ainslie, {P. N.} and Jui-Lin Fan and Thomas, {Kate N} and Cotter, {James D}",
year = "2018",
month = mar,
day = "1",
doi = "10.1152/ajpregu.00109.2017",
language = "English",
volume = "314",
pages = "R415--R426",
journal = "AJP Regulatory Integrative and Comparative Physiology",
issn = "0363-6119",
publisher = "American Physiological Society",
number = "3",

}

RIS

TY - JOUR

T1 - Independent and interactive effects of incremental heat strain, orthostatic stress, and mild hypohydration on cerebral perfusion

AU - Lucas, Rebekah

AU - Wilson, Luke

AU - Ainslie, P. N.

AU - Fan, Jui-Lin

AU - Thomas, Kate N

AU - Cotter, James D

PY - 2018/3/1

Y1 - 2018/3/1

N2 - The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (Tc; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5–2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAvmean; transcranial Doppler), partial pressure of end-tidal carbon dioxide (PETCO2), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, −15, −30, and −45 mmHg). Four subjects became intolerant before +2.0°C Tc, unrelated to hydration status. Without LBNP, decreases in PETCO2 accounted fully for reductions in MCAvmean across all Tc. With LBNP at heat tolerance (+1.5 or +2.0°C), PETCO2 accounted for 69 ± 25% of the change in MCAvmean. The HYPO condition did not affect MCAvmean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAvmean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in Tc are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.

AB - The purpose of this study was to identify the dose-dependent effects of heat strain and orthostasis [via lower body negative pressure (LBNP)], with and without mild hypohydration, on systemic function and cerebral perfusion. Eleven men (means ± SD: 27 ± 7 y; body mass 77 ± 6 kg), resting supine in a water-perfused suit, underwent progressive passive heating [0.5°C increments in core temperature (Tc; esophageal to +2.0°C)] while euhydrated (EUH) or hypohydrated (HYPO; 1.5–2% body mass deficit). At each thermal state, mean cerebral artery blood velocity (MCAvmean; transcranial Doppler), partial pressure of end-tidal carbon dioxide (PETCO2), heart rate (HR) and mean arterial blood pressure (MAP; photoplethysmography) were measured continuously during LBNP (0, −15, −30, and −45 mmHg). Four subjects became intolerant before +2.0°C Tc, unrelated to hydration status. Without LBNP, decreases in PETCO2 accounted fully for reductions in MCAvmean across all Tc. With LBNP at heat tolerance (+1.5 or +2.0°C), PETCO2 accounted for 69 ± 25% of the change in MCAvmean. The HYPO condition did not affect MCAvmean or any cardiovascular variables during combined LBNP and passive heat stress (all P > 0.13). These findings indicate that hypocapnia accounted fully for the reduction in MCAvmean when passively heat stressed in the absence of LBNP and for two- thirds of the reduction when at heat tolerance combined with LBNP. Furthermore, when elevations in Tc are matched, mild hypohydration does not influence cerebrovascular or cardiovascular responses to LBNP, even when stressed by a combination of hyperthermia and LBNP.

KW - Dehydration

KW - heat stress

KW - lower body negative pressure

KW - middle cerebral artery blood velocity

U2 - 10.1152/ajpregu.00109.2017

DO - 10.1152/ajpregu.00109.2017

M3 - Article

VL - 314

SP - R415-R426

JO - AJP Regulatory Integrative and Comparative Physiology

JF - AJP Regulatory Integrative and Comparative Physiology

SN - 0363-6119

IS - 3

ER -