Carotid artery pulse wave time characteristics to quantify ventriculoarterial responses to orthostatic challenge

Central blood pressure waveforms contain specific features related to cardiac and arterial function. We investigated posture-related changes in ventriculoarterial hemodynamics by means of carotid artery (CA) pulse wave analysis. ECG, brachial cuff pressure, and common CA diameter waveforms (by M-mode ultrasound) were obtained in 21 healthy volunteers (19-30 yr of age, 10 men and 11 women) in supine and sitting positions. Pulse wave analysis was based on a timing extraction algorithm that automatically detects acceleration maxima in the second derivative of the CA pulse waveform. The algorithm enabled determination of isovolumic contraction period (1CP) and ejection period (EP): ICP = 43 +/- 8 (SD) ms (4-ms precision), and EP = 302 +/- 16 (SD) ms (5-ms precision). Compared with the supine position, in the sitting position diastolic blood pressure (DBP) increased by 7 +/- 4 mmHg (P < 0.001) and R-R interval decreased by 49 +/- 82 ms (P = 0.013), reflecting normal baroreflex response, whereas EP decreased to 267 +/- 19 ins (P < 0.001). Shortening of EP was significantly correlated to earlier arrival of the lower body peripheral reflection wave (r(2) = 0.46, P < 0.001). 1CP increased by 7 +/- 7 ms (P < 0.001), the ICP-to-EP ratio increased from 14 +/- 3% (supine) to 19 3% (P < 0.001) and the DBP-to-ICP ratio decreased by 7% (P = 0.023). These results suggest that orthostasis decreases left ventricular output as a result of arterial wave reflections and, presumably, reduced cardiac preload. We conclude that CA ultrasound and pulse wave analysis enable noninvasive quantification of ventriculoarterial responses to changes in posture.