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Acute volume expansion preserves orthostatic tolerance during whole‐body heat stress
Author(s) -
Keller David M,
Low David A.,
Wingo Jonathan E.,
Brothers R. Matthew,
Davis Scott L.,
Crandall Craig G.
Publication year - 2008
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.22.1_supplement.737.3
Subject(s) - orthostatic vital signs , medicine , anesthesia , heat stress , blood pressure , zoology , biology
Whole‐body heat stress reduces orthostatic tolerance. The mechanisms responsible remain incompletely understood. The purpose of this study was to test the hypothesis that acute volume expansion improves orthostatic tolerance during passive heat stress (Δ core temperature ∼1.5 °C). Seven subjects participated in the following experimental protocol. Orthostatic tolerance was determined on 3 successive days using graded lower‐body negative pressure during normothermia (NT), whole‐body heating (WBH) and whole‐body heating with infusion of a volume expander (Dextran; WBH‐DEX) to restore central venous pressure (measured via a central venous catheter) to pre‐heat stress values. NT and WBH were randomized between Days 1 and 2, while WBH‐DEX was always performed on Day 3. As expected, orthostatic tolerance, expressed as cumulative stress index (CSI, mm Hg • min), was markedly reduced during WBH (182 ± 57 CSI) compared to NT (938 ± 152 CSI, P < 0.0001). Interestingly, WBH‐DEX (1109 ± 152 CSI) not only improved orthostatic tolerance relative to WBH (P < 0.0001), it also preserved tolerance compared to NT (P = 0.47). Therefore, despite marked reductions in orthostatic tolerance due to heat stress alone, acute volume expansion restored orthostatic tolerance similar to that observed during normothermic conditions. Supported by NIH Grant NIH‐HL61388 & HL84072