title: Heart rate variability and electrocardiogram waveform as predictors of morbidity during hypothermia and rewarming in rats.
abstract: This study examined electrocardiogram (ECG) waveform, heart rate (HR), mean blood pressure (BP), and HR variability as potential autonomic signatures of hypothermia and rewarming. Adult male Sprague-Dawley rats had telemetry transmitters surgically implanted, and 2 weeks were allowed for recovery prior to induction of hypothermia. Rats were lightly anesthetized (sodium pentobarbital, 35 mg/kg i.p.) and placed in a coil of copper tubing through which temperature-controlled water was circulated. Animals were cooled to a core temperature (Tc) of 20 degrees C, maintained there for 30 min, and then rewarmed. Data (Tc, BP, HR from ECG, and 10-s strips of ECG waveforms) were collected every 5 min throughout hypothermia and rewarming. Both HR and BP declined after initial increases with the drop in HR starting at a higher Tc than the drop in BP (29.6 +/- 2.4 degrees C vs. 27.1 +/- 3.3 degrees C, p < 0.05). Animals that were not successfully rewarmed exhibited a significant (p < 0.05) increase in the normalized standard deviation of interbeat intervals (IBI) throughout cooling compared with animals that were successfully rewarmed. The T wave of the ECG increased in amplitude and area with decreasing Tc. T-wave amplitude and IBI variability show potential as predictors of survival in hypothermic victims.
authors.affiliation: U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760-5007, USA. candace.matthew@na.amedd.army.mil
authors.forename: C B
authors.initials: CB
authors.lastname: Matthew
authors.forename: A M
authors.initials: AM
authors.lastname: Bastille
authors.forename: R R
authors.initials: RR
authors.lastname: Gonzalez
authors.forename: I V
authors.initials: IV
authors.lastname: Sils
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D004562:Electrocardiography / Q000706:statistics & numerical data; D006339:Heart Rate / Q000502:physiology*; D007035:Hypothermia / Q000401:mortality / Q000503:physiopathology*; D008297:Male; D011237:Predictive Value of Tests; D051381:Rats; D017207:Rats, Sprague-Dawley; D017694:Rewarming / Q000379:methods* / Q000706:statistics & numerical data