• Nathan T Mowery, John A Morris, Judith M Jenkins, Asli Ozdas, and Patrick R Norris.
• Department of Surgery, Wake Forest University, Winston-Salem, NC 27157, USA. nmowery@wfubmc.edu
• J Crit Care. 2011 Oct 1;26(5):534.e9-534.e17.

PurposeThe purpose of this study is to determine if temperature extremes are associated with reduced heart rate variability (HRV) and "cardiac uncoupling."Materials And MethodsThis was a retrospective, observational cohort study performed on 278 trauma intensive care unit admissions that had continuous HR, cardiac index (CI), and core temperature data from "thermodilution" Swan-Ganz catheter. Dense (captured second-by-second) physiologic data were divided into 5-minute intervals (N = 136 133; 11 344 hours of data). Mean CI, mean temperature, and integer HR SD were computed for each interval. Critically low HRV was defined as HR SD from 0.3 to 0.6 beats per minute. Temperature extremes were defined as less than 36°C or greater than 39°C.ResultsLow HRV and CI vary with temperature. Temperature extremes are associated with increased risk for critically low HRV (odds ratio, >1.8). Cardiac index increases with temperature until hyperthermia (>40°C). At temperature extremes, changes in CI were not explained solely by changes in HR.ConclusionsThe conclusions of this study are (1) temperature extremes are associated with low HRV, potentially reflecting cardiac autonomic dysfunction; (2) CI increases with temperature; and (3) HRV provides additional physiologic information unobtainable via current invasive cardiac monitoring and current vital signs.Copyright © 2011 Elsevier Inc. All rights reserved.

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