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The Role of Plasma Angiotensin II in Orthostatic Intolerance during Heat Stress Conditions
Author(s) -
Harrison Michelle L.,
Lee Josh F.,
Brown Skyler,
Brothers R. Matthew
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.1080.10
Subject(s) - orthostatic vital signs , medicine , angiotensin ii , heat stress , blood pressure , endocrinology , chemistry , cardiology , anesthesia , zoology , biology
An increase in internal temperature renders individuals more susceptible to syncope during a simulated hemorrhage challenge relative to during normothermia but the extent of this susceptibility varies amongst individuals. The objective of this study was to investigate the role of plasma angiotensin II (AngII) in this interindividual variability. This study tested the hypothesis that individuals with the greatest reduction in orthostatic tolerance between normothermic and heat stress conditions would have the smallest heat‐stress induced increase in plasma AngII. On separate days, 10 individuals were subjected to a maximal simulated hemorrhage challenge via a lower body negative pressure (LBNP) protocol. One trial was conducted under normothermic conditions and the other under hyperthermic conditions, following a 1.5 °C increase in internal temperature. Tolerance was quantified as cumulative stress index (CSI); calculated by summing the product of the LBNP and the time at each level until the test was terminated (i.e., 10 mmHg × 3 min + 20 mmHg × 3 min + 30 mmHg × 3 min, etc.). There was no correlation between the difference in CSI and the increase in plasma AngII from normothermic to heat‐stress conditions (r=0.05, p>.05). These results indicate that plasma AngII does not play a role in the interindividual variability in the tolerance to a simulated hemorrhage challenge during heat stress.