Introduction: We investigated non-invasive quantification of the systolic interaction between left ventricle and central arterial system by carotid artery distension waveform analysis.

Methods: ECG, finger-cuff pressure, and common carotid artery distension waveforms (M-mode ultrasound) were obtained in 14 young healthy volunteers in supine and sitting position.

Results: Distension waveform analysis enabled determination of isovolumic contraction period (ICP), ejection period (EP), aorta-carotid (TTa-c) and aorta-femoral (TTa-f) transit times with a precision of 3.2, 4.5, 3.1, and 7.9ms, respectively. From supine to sitting position, diastolic arterial pressure (DAP) increased by 7±4 mmHg (p < 0.001, paired t-test) and the R-R interval decreased by 70±87 ms (p < 0.05) due to the baroreflex response. The decrease in carotid transmural pressure in sitting position was reflected by an increase in TTa-c of 15±9ms (p < 0.001). ICP increased from 42±7 to 49±5ms (p < 0.001) while DAP/ICP, a load-independent measure of left ventricular contractility, decreased by 7% (p = 0.058). This implies that the cardiac response to the postural intervention is predominantly based on an increase in heart rate. EP decreased from 303±18 to 267±19 ms (p < 0.001) as a result of the earlier arrival of the lower body reflection wave (TTa-f decreased by 57±25 ms, p < 0.001). The ejection period and the peripheral transit time exhibited a clear correlation (R² = 0.66).

Conclusions: Modest postural changes affect systolic cardiovascular interaction through changes in arterial transmural pressure and the baroreflex but leave left ventricular contractility unaltered. Carotid artery ultrasonography enables precise quantitative evaluation of systolic cardiovascular interaction. The application of this non-invasive method in patients appears promising.