Aspects of cardiovascular oxygen transport in vertebrates

Abstract

The hematological and rheological characteristics of blood from a number of vertebrates was compared to assess possible species differences in blood viscosity that may influence cardiovascular oxygen The predicted in vitro optimal hematocrit (Bo) for oxygen transport was determined for each species and compared to the observed ill.1i!2. hematocrit (Bet). There was a very close correspondence between the predicted Bo and the observed normal Bet for the blood tested, with the exception of elephant seal (Mirounga angustirostris) blood.Resting and maxim.al rates of blood flow at lOoc, 2ooc and 3oocwere measured in Bufo marinus with magnetic blood flow probes to assess the relative contributions of heart rate, systemic arch pulse volume and arteriovenous (A-V) oxygen difference to increased oxygen consumption (V02). A-V 02 difference accounted for 100%, 84% and 88% of the increase in V02 during maximal exercise at iooc, 2ooc and 3ooc, respectively.Systemic arch pulse volume remained nearly constant over a wide range of heart~rates (15-115 beats min-l)thus contributing little to increased cardiac output during increased V02.Changes in blood flow rates through the systemic arches of resting toads were predicted by in vitro changes in blood viscosity over a 1ooc to 30oc interval. Resting animals did not appear to actively compensate for the passive alterations in viscosity that seemed to influence blood flow rates in viyo.

The effect of body temperature on arteriovenous oxygen difference during rest and activity in the toad, Bufo marinus

“…Similar results were obtained by Hedrick (1985) in his investigation of the effects of body temperature and activity on heart rate and pulse volume. In that study, Carey, 1979;Hedrick, 1985;Withers~ _gl., 1987).…”

“…Considering the high heart rates in active toads at 30°C (Hedrick, 1985), It is interesting to note that open chest point microsampling techniques reveal reduced venous % saturation in B. paracnemis (Johansen and Ditadi, 1966) Resting A-V 02 difference was the same in toads at all three temperatures (Figure 3). Therefore, thermally-induced • changes in resting V02 could be accounted for by changes in blood flow as reported by Weathers (1976).…”

“…Thus, the increase in V02 associated with activity results primarily from an increase in oxygen extraction, verifying hypotheses formulated by other authors (Becker~ _gl., 1970; Carey, 1979;Hedrick, 1985;Withers~~., 1987).…”

“…However, the value of such predictions is questionable. First, the blood flow rates reported by Hedrick (1985) are only for the systemic arches; the measurement of stroke volume by blood flow is presently not possible.…”

“…In that study, Carey, 1979;Hedrick, 1985;Withers~ _gl., 1987). This contribution of A-V 02 difference is estimated to be 100%, 84%, and 88% for increases in V02 during maximal exercise at 10°, 20°, and 30°c, respectively (Hedrick, 1985). Withers ~ .aJ.. (1987) reported a contribution of 85% to V02 during maximal activity in~.…”