New index of cardiac contractility during stress testing with treadmill.

Experimental demonstration that the external phonocardiogram is similar to the third derivative (rate of acceleration) of LV pressure, and that catecholamines cause a similar increase of the early systolic wave of the first derivative of LV pressure and of S1 prompted a study of the first sound during stress testing. Following a previous study with different types of ergometers, the present investigation was based on records of 10 normal, young volunteers, taken during treadmill exercise while a phonocardiogram was recorded at the apex. The first heart sound increased in all of them averaging an eightfold increase during maximal stress. Comparison of the changes in amplitude of S1 with changes of heart rate, blood pressure, and cardiac output revealed that the first showed the most constant proportional increase while sometimes one or the other parameter showed only a moderate change. The possible causes of this apparent lack of reaction is discussed. The importance of the first sound as an index of contractility is stressed, and the suggestion of a routine study of this index in cardiac patients submitted to stress tests is advanced.