Energy metabolism and circulation in dogs exercising in hypoxia.

Role of Central and Peripheral Circulatory Adjustments in Oxygen Transport at the Onset of Exercise

“…This effect of training is supported by data of other investigators (48) where t 1/2 V02on was slower in legs than arms for arm trained and leg untrained individuals and can be changed by specific muscle training (11,15,48). In the most fit subjects, the t 1/2 V02on approaches the minimal t 1/2 set biochemically (31,43) and observed in running dogs and isolated muscle preparations (8,41,46,47,53). The Q exercise time relationship for one subject is shown in Fig.…”

“…This can be related to the rate constant, t 1/2 = 0.69 'kl,or time constant, t 1/2 = 0.69r, assuming that V02on is a single exponential function. The t 1/2 V02on has been shown to be 15 to 17 s for dog gastrocnemius (46,47,53) in an isolated perfused preparation as well This investigation was supported in part by National Heart, Lung, and Blood Institute, Grant HL 14414-06 as in an intact anesthetized preparation (8). The observed time course of the drop in mixed venous 02 in light of a constant arterial oxygen saturation during the transition from rest to exercise (49) would suggest that measurements of V02 at the mouth would reflect events in the muscle.…”

“…It appears that the primary adjustment of Q is related to changes of HR. The kinetics of MBF adjustment at the onset of exercise has been studied in isolated perfused muscle preparations (46,47,53) and in running dogs (10). The adjustment in MBF is very fast reaching a new steady state within 3 to 30 s. This rapid response is a product of vasodilatation of vessels in active tissue while simultaneous vasoconstriction occurs in nonexercising muscles (3,5,54).…”

Effects of high altitude and season on fasting heat production in the yak <I>Bos grunniens</I> or <I>Poephagus grunniens</I>

“…However, the present results are in good agreement with observation in sheep by Blaxter (1978), who evaluated the effect of simulated altitude on energy metabolism, and could not detect any effect of a reduction in the O 2 concentration in the air from 200 to 150 ml/l on heat production in both fasted or fed conditions, energy retention or heat increment. Our results also agree well with studies with goats (Forster et al 1981), ponies (Forster et al 1976), dogs (Hemingway & Nahas, 1952;Piiper et al 1966;Bouverot et al 1981) and human subjects (Dempsey & Forster, 1982;Armellini et al 1997;Mawson et al 2000), which demonstrated that at or slightly below the thermoneutral range, O 2 consumption was not significantly affected during hypoxia. In the 1960s, Hannon et al (1969Hannon et al ( , 1976 Hannon & Sudman (1973) Hannon (1978) performed the most thorough study of the question to date in women, and their subjects demonstrated only a transient elevation in BMR in the first week when taken to 4300 m and provided with a diet ad libitum.…”

“…Subsequently, both maximal and basal O 2 consumption are reduced, as observed in newborn mammals and small-to medium-sized adult species exposed to high altitude (Mortola & Rezzonico, 1988;Mortola et al 1989;Frappell et al 1992), although the colder thermal environment at high altitude may result in thermal acclimation that increases the maximal aerobic metabolic rate. In relatively large species, however, O 2 consumption is not found to decrease constantly during hypoxia (Piiper et al 1966;Forster et al 1976Forster et al , 1981Blaxter, 1978). In human subjects studied at thermoneutrality, a drop in O 2 consumption is usually absent during hypoxia, and more often the BMR is significantly but transiently elevated (Kellogg et al 1957;Hannon et al 1969, Hannon & Sudman, 1973, Hannon, 1978Moore et al 1987;Armellini et al 1997;Mawson et al 2000).…”