Propranolol and the Compensatory Circulatory Responses to Orthostasis at High Altitude,
Abstract
Tachycardia has been shown to be an important response involved in the defense of cardiac output during orthostasis at high altitude. This study was undertaken to determine if tachycardia, mediated by beta-adrenergic sympathetic stimulation, actually represents an essential response. Twelve young, healthy male subjects received either 80 mg propranolol (n=6) or placebo (n=6) treatment, t.i.d. at sea level and for 3 days prior to and during the first 15 days of a 19-day altitude sojourn. Individuals were randomly assigned to each group. Upright tilt tests were performed at sea level on and off treatment, at high altitude during days 2,7, and 15 on treatment, and on day 19 off treatment. Heart rate, stroke volume, calf blood flow, and blood pressure were obtained during supine rest and after 12 minutes of 60 deg tilt. There were no differences between groups in any of the circulatory measurements at sea level and altitude while off treatment. While on treatment at sea level and altitude, propranolol caused reductions in heart rate and blood pressure values in each position (p<0.05). Supine and upright cardiac output, however, were found not altered due to compensatory increases in stroke volume (p<0.05). It was concluded that tachycardia, both at rest and during upright tilt at high altitude is important, but not essential to defend cardiac output. Keywords: Beta-blocker, Sympathetic nervous system.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 14, 1988
- Accession Number
- ADA192675
Entities
People
- Allen Cymerman
- Charles S. Fulco
- John T. Reeves
- Laurie A. Trad
- Paul B. Rock
Organizations
- United States Army Research Institute of Environmental Medicine