Systemic circulatory response to stress of simulated flight and to physical exercise before and after propranolol blockade.

Abstract

Heart rate, systemic arterial blood pressure, and cardiac output, when measured in 15 pilots throughout a Link trainer simulated flight, all increased. This resulted in only a slight decrease in the peripheral vascular resistance. A 2nd Link trainer simulated flight after saline administration was performed by 4 of the pilots. Similar hemodynamic changes were recorded as initially. Eleven of the pilots went through a 2nd Link trainer simulated flight after the intravenous administration of 5 mg propranolol, a beta adrenergic blocking agent. While the responses in heart rate and diastolic blood pressure to injected iso-prenaline were marked before the receptor blockade, only slight responses were observed after the blockade. During the preflight period after propranolol had been given, the heart rate and the cardiac output were significantly reduced while the arterial pressure was unchanged. Consequently, the peripheral vascular resistance had increased. During flight the increase in heart rate and cardiac output was significantly less as compared with the initial flight period. The augmented response in arterial blood pressure was not influenced by the beta adrenergic receptor blockade, and thus the peripheral vascular resistance remained increased. In 5 of the 11 pilots to whom propranolol was given, physical exercise with the pilots sitting on a bicycle ergometer was also performed before and after the beta-receptor blockade. Increases in cardiac output and arterial blood pressure associated with conspicuous falls in peripheral vascular resistance occurred in both periods and to similar levels of each parameter. Effects of beta adrenergic blockade in this situation were seen as a lower level of heart rate was achieved. The mean arterial plasma concentration of norepinephrine, measured in the majority of pilots, increased slightly during flight and during exercise. In contrast, the arterial plasma concentration of epinephrine was not measurable except in a few pilots. Beta adrenergic receptor activity is extensively involved in the circulatory reaction to emotional stress. In contrast, this activity appears to be involved but less essential in the achievement of the circulatory adjustments during moderate physical exercise.