Control of Cardiorespiration During Shivering Thermogenesis in Pigeons

Abstract

Shivering thermogenesis is the most important source of extra heat production in resting birds for the maintenance of deep body temperature at a nearly constant level under cold conditions. The cold tremor in birds is obviously due to contractions of white, fast-twitch glycolytic muscle fiber types (George 1984; Hissa 1988). The main source of heat by shivering is the large breast muscle of bird, whose mass amounts to 15–25% body weight (Rautenberg 1983). The frequency of electrical activity recorded in the pectoral muscle is about 200 Hz and seems to be independent of the intensity of tremor or avian body size (Hohtola 1982, own unpublished observation). Hohtola (1982) has previously demonstrated a close correlation between the intensity of shivering and oxygen consumption in pigeons. In contrast to severe physical work no oxygen debt nor increase of blood lactate level have been observed during shivering. The correlation between oxygen consumption and shivering intensity requires a precise control function of the cardiorespiratory system. How this interaction of the three autonomic feedback systems, circulation, respiration and thermoregulation, may function, will be described in this chapter.