A STUDY OF ALLEGED QUANTITATIVE CRITERIA OF VASOMOTOR ACTION

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Abstract
By use of simultaneous cardiometric records of the ventricles and mean arterial pressure in mildly ventilated, vagotomized dogs, data were obtained for calculating peripheral resistance changes according to the formula[image] in [image], and comparing such values with the absolute and percentile changes in mean pressure. Pressor effects on mean arterial pressure were induced in normal and "shock" dogs by reflex stimulation of the central vagus and phrenic nerves, by bilateral carotid compression, by use of epinephrine and pitressin. The results, supported by previous tests on artificial circulation machines, strongly suggest that the quantitative estimation of changes in vasomotor tone of smaller vessels either by absolute or percentile changes in mean arterial pressures or by mathematical calculation of peripheral resistance is highly restricted even in expt. in which cardiac output is also measured. Mathematical calculations fail because mean arterial pressure, which enters into the formula, is affected by the relationship between systolic discharge and aortic capacity[long dash]but not by aortic elasticity. The formula does not take into account the aortic capacity in relation to systolic discharge either in the same animal or in animals of different sizes.

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