Adaptive cardiovascular modifications in the western chipmunks genusEutamias
- Additional Document Info
- View All
Metabolic and cardiovascular parameters were studied in four western chipmunks, genus Eutamias, to elucidate the mechanisms underlying the maintenance of normal aerobic metabolism while the heart rate were profoundly depressed (Jones and Wang, 1976). It was postulated that cardiovascular adaptations involving either an increase of stroke volume and/or an increase of arterial-venous oxygen difference (A-V O2) must have evolved to account for such alterations (Jones and Wang, 1976). Simultaneous measurements of O2 consumption, heart rate and A-V O2 were made in anesthetized animals at thermal neutral temperature of 25°C. The mean cardiac output ranged between 16.2-23.5 ml/min, and the calculated stroke volume was between 0.032-0.057 ml/beat, not atypical for similar sized mammals (Table 1). Measurements of heart weight as an indirect indicator for stroke volume also indicated normal stroke volume in the chipmunks (Table 2). The mean A-V O2, on the other hand, was between 5.6-10.4 vol % (Table 1), comparatively greater than the 4-6 vol % typical of resting mammals. The measured hematocrit, hemoglobin concentration, red blood cell counts, and blood volume, were within the range of values for similar sized mammals (Table 3), suggesting normal O2 capacity as well as O2 content carried in blood. Taken together, it was concluded that the major cardiovascular modification in the chipmunks while accomplishing normal aerobic metabolism under profoundly depressed heart rates is by the increased ability to extract O2 across the capillary beds. Possible mechanisms relating to this adaptation are discussed. © 1976 Springer-Verlag.
author list (cited authors)
complete list of authors