Clinical Autonomic Research

, Volume 24, Issue 3, pp 119–126

Normothermic central hypovolemia tolerance reflects hyperthermic tolerance

Research Article

DOI: 10.1007/s10286-014-0237-y

Cite this article as:
Schlader, Z.J. & Crandall, C.G. Clin Auton Res (2014) 24: 119. doi:10.1007/s10286-014-0237-y

Abstract

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 × 3 min + 30 mmHg × 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.

Keywords

Lower body negative pressure Heat stress Simulated hemorrhage Syncope 

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Institute for Exercise and Environmental MedicineTexas Health Presbyterian Hospital of DallasDallasUSA
  2. 2.Department of Internal MedicineUniversity of Texas Southwestern Medical CenterDallasUSA