Author/Editor		Lun, V; Sun, JC; Giesbrecht, GG; Mekjavić, IB
Title		Shivering thermogenesis during acute hypercapnia
Type		članek
Source		Can J Physiol Pharmacol
Vol. and No.		Letnik 72, št. 3
Publication year		1994
Volume		str. 238-42
Language		eng
Abstract		The effects of acute hypercapnia on human thermoregulation during cold exposure were investigated by immersion of eight male subjects to the neck in a 15 degrees C water bath until their core temperatures dropped to 35 degrees C or until 1 h of immersion had elapsed. Air was inspired throughout each experiment, with the exception of a 15-min period commencing with the attainment of an esophageal temperature (Tes) of 36.5 degrees C, during which subjects inspired a gas mixture containing 4 percent CO2, 20 percent O2, and 76 percent N2. Oxygen uptake (VO2, L.min-1), inspired minute ventilation (Vi, L.min-1), esophageal temperature (Tes, degrees C), rectal temperature (Tre, degrees C), mean unweighted skin temperature (Tsk, degrees C), mean heat flux (Q, W.m-2), and electromyographic activity (EMG, mV) of the trapezius and masseter muscles were recorded continuously. VO2 and integrated EMG activity (IEMG) were used as the primary indicators of shivering thermogenesis. Shivering EMG was attenuated immediately following the switch of the inhaled gas mixture from air to 4 percent CO2. For both the masseter and trapezius muscles the IEMG was significantly suppressed (p less th. 0.05) during the hypercapnic period. The IEMG values preceding the switch to the hypercapnic mixture were 15 percent greater than those during the CO2 period. Similarly, IEMG values in the post-CO2 period were 55 percent greater than during the CO2 period. It is concluded that acute periods of hypercapnia during cold exposure may result in transient suppression of shivering tremor, but this does not appear to affect thermal balance, as reflected in the absence of any significant effect on Tes.
Descriptors		BODY TEMPERATURE REGULATION HYPERCAPNIA SHIVERING ACUTE DISEASE ADMINISTRATION, INHALATION CARBON DIOXIDE COLD ELECTROMYOGRAPHY ESOPHAGUS HYPERCAPNIA OXYGEN OXYGEN CONSUMPTION RESPIRATION SKIN TEMPERATURE