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Hysteresis in the heart rate‐core temperature relationship during acute heat stress in rats: implications for systemic hemodynamics
Author(s) -
Charkoudian Nisha,
Leon Lisa,
Helwig Bryan
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.lb742
Subject(s) - heart rate , hyperthermia , hemodynamics , baroreflex , core temperature , medicine , cardiac output , vasodilation , heat stress , cardiology , anesthesia , core (optical fiber) , thermoregulation , blood pressure , materials science , zoology , biology , composite material
Heart rate (HR) increases during hyperthermia, even in the absence of exercise and contributes to increased cardiac output necessary for dissipation of excess heat. It is unknown whether the onset and recovery from heat stress have different cardiovascular profiles. We hypothesized that hyperthermia‐induced tachycardia would exhibit hysteresis. Core temperature (Tc), HR and MAP were measured via radiotelemetry in conscious male Fischer 344 rats (n=8; 262±8 gms) during exposure to 37°C until a Tc of 41.8°C was reached and during recovery at 20°C. Tc, HR and MAP significantly increased during heat exposure (ascending phase; P<0.01 vs. control) and HR was significantly lower for a given Tc compared to recovery (descending phase; p<0.001). For example, at Tc = 39.5°C, HR was 365±27 bpm during the ascending phase and 527±50 bpm during the descending phase (P<0.001). Hysteresis during heat stress recovery may be a compensatory, baroreflex‐mediated response to maintain MAP during thermoregulatory vasodilation and decreased peripheral vascular resistance. These findings may have implications for understanding cardiovascular stress during recovery from heat exposure. Research supported by MRMC. Author views not official US Army or DoD policy.