Stroke volume during submaximal exercise in endurance-trained normotensive subjects and in untrained hypertensive subjects with beta blockade (propranolol and pindolol).
The effect of beta-adrenergic blockade on stroke volume (SV) at increasing submaximal exercise intensities was studied in 12 endurance-trained normotensive and 12 untrained hypertensive (diastolic blood pressure greater than 95 mm Hg) men, aged 18 to 34 years. Subjects were assigned to each of 3 treatments in a double-blind, randomized order: placebo, propranolol (80 mg twice daily) and pindolol (10 mg twice daily) for 10 days, with a period of 48 to 60 hours from the initial dose to the first treadmill test and a 4-day washout period between drugs. Cardiac output was measured using the carbon dioxide rebreathing method and SV was calculated from cardiac output and heart rate as follows: SV = cardiac output/heart rate. Cardiac outputs were estimated at rest and while walking on a treadmill at 25, 45, 60 and 75% of the subject's previously determined maximal oxygen uptake (VO2max). No significant differences were found in cardiac output between either of the drugs and placebo at rest, or at any of the 4 rates of work. Propranolol significantly increased SV above placebo values (p less than 0.05) for both trained and untrained groups at the intensities of 45, 60 and 75%. Significant differences in SV were found between pindolol and placebo only at the intensities of 60 and 75% in the trained group. Contrary to expectations, SV showed no indication of a plateau with propranolol in the trained subjects throughout the 4 different exercise intensities, whereas a plateau was established under placebo conditions by 45% of VO2max in both trained and untrained subjects. These results suggest that both trained and untrained hypertensive persons can exercise with beta-adrenergic blockade at submaximal levels without compromised cardiac function.
Scruggs
K D
KD
Department of Kinesiology and Health Education, University of Texas, Austin 78712.
Martin
N B
NB
Broeder
C E
CE
Hofman
Z
Z
Thomas
E L
EL
Wambsgans
K C
KC
Wilmore
J H
JH
D000328:Adult; D002302:Cardiac Output / Q000187:drug effects; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006973:Hypertension / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D010807:Physical Endurance / Q000502:physiology; D010869:Pindolol / Q000627:therapeutic use*; D011433:Propranolol / Q000627:therapeutic use*; D013318:Stroke Volume / Q000187:drug effects*
D011433:Propranolol; D010869:Pindolol