Sympathetic hyperreflexia in tetraplegics. The value of systolic time intervals in assessing drug effects.

The arterial blood pressure, heart rate and systolic time intervals were measured in 10 male tetraplegic subjects before and during the filling of the bladder with sterile normal saline. This procedure was repeated on separate occasions after pretreatment of the patients with blocking dosages of propranolol, labetalol, phenoxybenzamine and guanethidine respectively. During hyperreflexia the pre-ejection period/left ventricular ejection time (PEP/LVET) ratio and the PEP and electromechanical systole (QS2) reduced, suggesting positive inotropic effects. Propranolol practically eliminated these effects and labetalol also opposed them. The effects of phenoxybenzamine and guanethidine were unpredictable.