United States Department of Transportation
i
Tolerance of Beta Blocked Hypertensives during Orthostatic and Altitude Stress
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1992-04-01
[PDF-2.29 MB]
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Abstract:To evaluate the effects of orthostatic, altitude, and pharmacologic stresses upon civil aviation-specific performance, a double-blind, randomized, crossover trial of atenolol, 100mg, was designed and executed. Hypertensive males are females qualifying for the FAA class 3 certificate with mean age of 34 were studied during simulated altitude exposure to 12,500 ft, orthostatic stress, and moderate exercise. Seated lower body negative pressure to -4C mmHg supplied orthostatic stress simulating +2G vertical acceleration. A total of 160 lower body negative pressure tests were performed, 80 at ground and 80 at altitude. Beta-blockade caused a modest impairment in orthostatic tolerance.
Five of the 80 lower body negative pressure runs at ground level were marked by intolerance, and all of those responses were in beta-blocked subjects. Of the 80 altitude runs, 30 were terminated for intolerance, of which, ch 18 included beta-blockade. These findings had a Chi-square significance value of P < .05. The effect of altitude was significant at P < .01. In a modest exercise protocol (100 watts for 3 minutes) meant to be no more stressful. than the exertional requirements of piloting an aircraft during adverse conditions, neither beta-blockade or altitude appeared to limit performance.Quantitative performance on a computerized cognitive battery clearly demonstrated impaired performance during lower body negative pressure stress at altitude. The degree of impairment was significant compared to a learning curve response at the P < .001 level. The degree of impairment was similar for placebo treated and betablocked subjects.
Monitoring of mean arterial pressure, heart rate, and stroke volume was necessary for quantitative analysis of hemodynamic responses to these stressors. These parameters demonstrated progressive decrements in systemic vascular resistance in intolerant subjects, implicating a defective peripheral autonomic nervous system response. Moreover, monitoring of systemic vascular resistance, blood pressure, and transcranial Doppler middle cerebral artery flow velocities allowed prediction of impending cognitive and hemodynamic collapse. These data implicate the synergistic deleterious effects of beta-blockade and altitude in the potentiation of intolerance to orthostatic stress. These findings may have most revelance to the personnel of unpressurized aircraft who are being treated with beta-blocking drugs for hypertension. No common clinical parameter predicts subsequent intolerance. It appears that only formal stress testing will uncover orthostatic-prone individuals.
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