TY - JOUR
T1 - Normothermic central hypovolemia tolerance reflects hyperthermic tolerance
AU - Schlader, Zachary J.
AU - Crandall, Craig G.
N1 - Funding Information:
Acknowledgments We would like to thank the subjects for participating in our study. We would also like to thank the following individuals who assisted in data collection over a number of years that resulted in the acquisition of the presented data: Drs. Thad Wilson, Jian Cui, Sylvain Durand, Manabu Shibasaki, Scott Davis, Jonathan Wingo, David Low, David Keller, Matt Brothers, James Pearson, Rebekah Lucas, Matt Ganio. This study was supported by Award Numbers R01HL061388, T32HL007360, and F32AG04328 from the National Institutes of Health, and W81XWH-12-1-0152 from the Department of Defense.
PY - 2014/6
Y1 - 2014/6
N2 - Purpose: To test the hypothesis that those who are highly tolerant to lower body negative pressure (LBNP) while normothermic are also highly tolerant to this challenge while hyperthermic. Methods: Sixty pairs of normothermic and hyperthermic LBNP tests to pre-syncope were evaluated. LBNP tolerance was quantified via the cumulative stress index (CSI), which is calculated as the sum of the product of the LBNP level and the duration of each level until test termination (i.e., 20 mmHg x 3 min + 30 mmHg x 3 min, etc.). CSI was compared between normothermic and hyperthermic trials. Internal and skin temperatures, heart rate, and arterial pressure were measured throughout. Results: Hyperthermia reduced (P < 0.001) CSI from 997 ± 437 to 303 ± 213 mmHg min. There was a positive correlation between normothermic and hyperthermic LBNP tolerance (R2 = 0.38; P < 0.001). As a secondary analysis, the 20 trials with the highest LBNP tolerance while normothermic were identified (indicated as the HIGH group; CSI 1,467 ± 356 mmHg min), as were the 20 trials with the lowest normothermic tolerance (indicated as the LOW group; CSI 565 ± 166 mmHg min; P < 0.001 between groups). While hyperthermia unanimously reduced CSI in both HIGH and LOW groups, in this hyperthermic condition CSI was ∼threefold higher in the HIGH group (474 ± 226 mmHg min) relative to the LOW group (160 ± 115 mmHg min; P < 0.001). Conclusions: LBNP tolerance while hyperthermic is related to normothermic tolerance and, associated with this finding, those who have a high LBNP tolerance while normothermic remain relatively tolerant when hyperthermic.
AB - Purpose: To test the hypothesis that those who are highly tolerant to lower body negative pressure (LBNP) while normothermic are also highly tolerant to this challenge while hyperthermic. Methods: Sixty pairs of normothermic and hyperthermic LBNP tests to pre-syncope were evaluated. LBNP tolerance was quantified via the cumulative stress index (CSI), which is calculated as the sum of the product of the LBNP level and the duration of each level until test termination (i.e., 20 mmHg x 3 min + 30 mmHg x 3 min, etc.). CSI was compared between normothermic and hyperthermic trials. Internal and skin temperatures, heart rate, and arterial pressure were measured throughout. Results: Hyperthermia reduced (P < 0.001) CSI from 997 ± 437 to 303 ± 213 mmHg min. There was a positive correlation between normothermic and hyperthermic LBNP tolerance (R2 = 0.38; P < 0.001). As a secondary analysis, the 20 trials with the highest LBNP tolerance while normothermic were identified (indicated as the HIGH group; CSI 1,467 ± 356 mmHg min), as were the 20 trials with the lowest normothermic tolerance (indicated as the LOW group; CSI 565 ± 166 mmHg min; P < 0.001 between groups). While hyperthermia unanimously reduced CSI in both HIGH and LOW groups, in this hyperthermic condition CSI was ∼threefold higher in the HIGH group (474 ± 226 mmHg min) relative to the LOW group (160 ± 115 mmHg min; P < 0.001). Conclusions: LBNP tolerance while hyperthermic is related to normothermic tolerance and, associated with this finding, those who have a high LBNP tolerance while normothermic remain relatively tolerant when hyperthermic.
KW - Heat stress
KW - Lower body negative pressure
KW - Simulated hemorrhage
KW - Syncope
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U2 - 10.1007/s10286-014-0237-y
DO - 10.1007/s10286-014-0237-y
M3 - Article
C2 - 24700256
AN - SCOPUS:84902240737
SN - 0959-9851
VL - 24
SP - 119
EP - 126
JO - Clinical Autonomic Research
JF - Clinical Autonomic Research
IS - 3
ER -