Abstract
Cardiovascular reactions to isoproterenol stimulation (2 and 4 µg min for 12 min each)
were evaluated in seven endurance-trained athletes (marathon runners, V̇O2 max 66.0±3.7 ml/kg) and seven untrained subjects (V̇O2 max 54.4±3.6 ml/kg). At rest and during stimulation, the heart rate, blood pressure
as well as one-dimensional (end-diastolic and end-systolic dimensions, shortening
fraction) and two-dimensional (end-diastolic and end-systolic volumes, ejection fraction,
stroke volume, cardiac output) echocardiographic parameters were determined.
The increase in the heart rate of the endurance-trained athletes (28%; 2 µg/min) (58%;
4 µg/min) was less than in the untrained controls (34%/76%). The blood pressure behaved
similarly in both groups. The stroke volume of the endurance-trained subjects rose
during stimulation (14%, 4µg/min); the end-diastolic volume remained nearly constant
as the end-systolic emptying increased. The stroke volume of the untrained subjects
tended to decrease as the end-diastolic and end-systolic volumes were reduced. In
absolute terms, the shortening fraction and ejection fraction were identical. Referring
to the heart rate, however, they were elevated in the endurance-trained subjects.
Hence, under isoproterenol the rise in heart rate was weaker and the increase in ventricular
performance seemed to be stronger in the trained subjects compared to the untrained
controls. The causes appear to be different regulative effects of the autonomic nervous
system on the sinus node and the ventricular myocardium; intrinsic cardiac mechanisms
remain to be discussed.
Key words
trained- - untrained subjects - isoproterenol stimulation - cardiovascular reaction
- echocardiography
