ISSN:
1439-6327
Keywords:
Cardiac output
;
Time constant
;
Exercise
;
Denervation of the heart
;
Adrenergic beta-receptor blockade
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Normal and cardiac denervated dogs, with an electromagnetic aortic flowprobe implanted at least 14 days before the experiments, ran at different speeds on a 25% graded treadmill. The experiments were carried out before and after blockade of betareceptors in the heart by PO administration of 125 mg·kg−1 practolol per day. Changes in stroke volume, heart rate, and cardiac output were measured. After beta-adrenergic blockade, only two of the seven dogs with denervated hearts were prepared to run at a limited number of speeds. Time constants of the cardiac output changes at the onset of exercise were significantly different (P〈0.001) for the normal (11.5±0.7 s, mean ± SEM) and the denervated dogs (29.5±1.1 s), but in normal dogs did not change with practolol (11.8±0.8 s). The steady state relationship between cardiac output (CO) and work per unit time performed on the treadmill (P) was for normal dogs: CO=156+1.55P, for normal dogs after practolol treatment: CO=156+0.43P (slope significantly different, P〈0.05), and for dogs with denervated hearts: CO=121+2.06P (not significantly different from normal dogs). It was concluded that changes in the venous or arterial system alone are not sufficient to increase cardiac output appreciably during exercise. The magnitude of the cardiac output increase depends more on the presence of intact beta-receptors than on the presence of intact cardiac nerves. However, the rapid adaptation of cardiac output to a new exercise level is due to nervous control of the heart, most likely transmitted by the vagus.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00429027
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