A noninvasive method of measuring wave intensity, a new hemodynamic index:application to the carotid artery in patients with mitral regurgitation before and after surgery

Wave intensity (WI) is a new hemodynamic index, which is defined as (dP/dt) (dU/dt) at any site of the circulation, where dP/dt and dU/dt are the time derivatives of blood pressure and velocity, respectively. Arterial WI in no rmal subjects has two positive sharp peaks. The first peak occurs during ea rly systole when a forward-traveling compression wave is generated by the l eft ventricle. The magnitude of this peak increases markedly with an increa se in cardiac contractility. The second peak, which occurs towards the end of systole, is caused by generation of a forward-traveling expansion wave b y the ability of the left ventricle to actively stop aortic blood flow. The interval between the R wave of tho ECG and the first peak of WI (R-1st pea k interval) and the interval between the first and second peaks (1st-2nd in terval) are approximately equal to the preejection period and left ventricu lar ejection time, respectively. Using a combined Doppler and echo-tracking system, we obtained carotid arterial WI noninvasively. We examined the cha racteristics of WI in 11 patients with mitral regurgitation (MR) before and after surgery, and 24 normal volunteers. In the MR group before surgery, t he second peak was decreased and the (1st-2nd interval)/(R-R interval) rati o was reduced, compared with the normal group (140 +/- 130 vs 750 +/- 290 m m Hg m/s(3), P < 0.0083; 20.7% +/- 3.4% vs 26.7% +/- 2.8%, P < 0.0083). The re were no significant differences in the first peak between the normal gro up acid the MR group before and after surgery. The second peak in the MR gr oup was increased significantly (P < 0.016 vs before surgery) to 1150 +/- 8 30 mm Hg m/s(3) in the early period after surgery (stage I), and to 1090 +/ - 580 mm Hg m/s(3) in the late period after surgery (stage II). These value s did not differ significantly from that of the normal group. At stage I, t he (R-1st peak interval)/(R-R interval) ratio was increased from 13.4% +/- 2.7% to 20.6% +/- 5.6% (P < 0.016 vs before surgery). At stage II, this rat io decreased to 16.2% +/- 2.8% (P < 0.016 vs stage I), but was still signif icantly higher than that before surgery. The (1st-2nd interval)/(R-R interv al) ratio increased significantly after surgery (P < 0.016 vs before surger y) to values (27.0% +/- 4.5% at stage I and 28.9% +/- 2.6% at stage II) whi ch did not differ significantly from that of the normal group. The recovery of the second peak after surgery suggests that the left ventricle had reco vered the ability to actively stop aortic blood flow. Wave intensity is use ful for analyzing changes in the working condition of the heart.