Noninvasive stress testing. Methodology for elimination of the phonocardiogram

Measurement by systolic time intervals (STI) of cardiac responses requires extremely careful recording during actual stress test performance. Previous work indicated no significant changes in the pulse transmission time (PTT) during exercise and other challenges. Since external STI depend on the carotid pulse offset by the PTT as an aortic curve equivalent, stable PTT implies that timing of the carotid upstroke (CARu) and the carotid incisura (CARIN) would respectively track the pre-ejection period (i.e., the externally calculated onset of the aortic upstroke) and the aortic incisura which is externally timed by the aortic component of SII (IIA). In ten subjects, STIs were recorded at supine rest, sitting, standing, during prompt and sustained squatting and during isometric and dynamic exercise. The results demonstrated the tracking of both points: regression slopes and correlation coefficients were close to 1.00 for each series and for each subset. Coefficients of correlation (r) and of determination (r2) were uniformly high for all challenges except isometric handgrip (IHG). Since left ventricular ejection time is obtained directly from the pulse curve, with the exception of IHG, STI responses during stress testing can be measured without a phonocardiogram.