Aminophylline has little positive inotropic effect and a slightly negative diastolic effect on the left ventricle during hypoxic conditions in dogs.

We examined the effect of aminophylline on left ventricular (LV) mechanics and central hemodynamics under normoxic and hypoxic conditions in respective groups of dogs. In an open-chest preparation, LV end-systolic and diastolic dimensions were measured with ultrasonic crystal transducers seated subendocardially along the anterior to posterior and apex to base axes. In the group studied during hypoxia, measurements were obtained during 3 conditions: normoxia; hypoxia to a PO2 of 30 mm Hg; and during hypoxia when aminophylline was infused to a blood level of about 15 mg/L. In the group studied under normoxic conditions, measurements were initially obtained during normoxia after which aminophylline was also infused to a blood level of 15 mg/L. Intravascular volume was given or removed to maintain LV filling pressures at about 10 mm Hg during all conditions. In the normoxic group, aminophylline caused an increase in stroke volume (SV) and had a positive inotropic effect on the LV. End-systolic dimensions were reduced, while end-diastolic dimensions did not change with aminophylline. On the other hand, under hypoxic conditions, aminophylline did not have a positive inotropic effect: SV did not increase and end-systolic dimensions remained unchanged. Under hypoxic conditions, moreover, aminophylline caused a slight decrease in end-diastolic dimensions by augmenting hypoxia-induced increases in myocardial resting tension. Our results indicate that unlike normoxic conditions, aminophylline may have little beneficial effect on LV performance during hypoxic conditions.