Effect of isometric exercise and autonomic blockade on the haemodynamics: a noninvasive study in healthy volunteers.

Sixteen healthy young volunteers were studied with echocardiography and systolic time intervals at rest and after three minutes' isometric exercise before and during autonomic blockade with atropine and propranolol. Isometric exercise increased cardiac output by raising the heart rate from 64 +/- 3 to 72 +/- 4 bpm (SEM) (p less than 0.01). Mean blood pressure increased from 86 +/- 2 to 104 +/- 3 mmHg (p less than 0.001) without any changes in the calculated total peripheral vascular resistance. Afterload (left ventricular systolic wall stress) rose but preload (left ventricular end-diastolic diameter, LVEDD) did not change. There was no variation in fractional shortening, maximal velocity of circumfertial fibre shortening (VCFmax) or pre-ejection period (PEP) despite increased afterload. This indicates stimulated intropy during isometric exercise. Autonomic blockade enhanced cardiac output by increasing heart rate from 64 +/- 3 to 97 +/- 2 bpm (p less than 0.001). Mean blood pressure rose from 86 +/- 2 to 93 +/- 2 mmHg (p less than 0.01) while vascular resistance fell. Afterload did not change but LVEDD shortened form 45.5 +/- 0.9 to 43.5 +/- 0.9 mm (p less than 0.001). Preload-independent VCFmax did not increase despite raised heart rate. PEP rose from 99 +/- 4 to 107 +/- 3 ms (p less than 0.01) and fractional shortening fell from 29 +/- 1 to 25 +/- 1% (p less than 0.001); these changes were greater than expected from the reduced preload. Consequently autonomic blockade seems to impair myocardial contractility despite vagal dominance at rest. Heart rate and cardiac output were not influenced by isometric exercise during autonomic blockade.(ABSTRACT TRUNCATED AT 250 WORDS)