Cardiovascular Dynamics of Vasovagal Reactions in Man

Abstract

The dynamics of vasovagal reactions which occurred in 2 patients during right heart catheterization were studied. Both subjects initially had systemic hypertension with corresponding increases in peripheral resistances. Subject B had considerably decreased blood flow, moderately elevated pulmonary artery and right ventricular end-diastolic pressures, and elevated central blood volume. These parameters were normal in subject A. The characteristic features of the reactions were appreciable declines in cardiac outputs coincident with decreased systemic arterial systolic, diastolic, and pulse pressures, decreased heart rates, and slight increases in calculated peripheral resistances. Stroke volumes were moderately reduced. A slight decrease in pulmonary artery systolic pressure occurred in subject A. In subject B, pulmonary artery and right ventricular enddiastolic pressures declined to normal and central blood volume decreased moderately. The return of heart rate to control values had no significant effects on the other physiologic parameters. The data demonstrate that reductions in cardiac output, due primarily to decreased stroke outputs, were predominantly responsible for the arterial hypotensions during the vasovagal reactions in these 2 subjects. The ineffectiveness of atropine in restoring hemodynamics in one subject suggested the importance of inhibition of efferent sympathetic activity in the etiology of this reaction. The failure of peripheral resistance to compensate for decreased blood flow suggested inhibition of arteriolar tone.