Analysis of wave reflections in the arterial system using wave intensity: A novel method for predicting the timing and amplitude of reflected waves

Abstract

The timing and amplitude of reflected arterial waves in the ascending aorta were studied by analysis of the aortic pressure waveform and were compared with those derived using wave intensity analysis. Wave intensity analysis considers aortic pressure changes to be the result of forward and backward wavelets carrying energy. Wave intensity (dI = dPdU) is calculated from changes in pressure (dP) and flow velocity (dU), and its sign indicates the direction of travel of propagating wavelets (positive for forward-traveling waves and vice versa). We measured aortic pressure and flow velocity in 14 patients, mean age 60+/-9 years, with three-vessel coronary artery disease at the time of surgical revascularization. The travel time of the reflected wave derived from analysis of the aortic pressure waveform (tp) was measured from the foot of the aortic pressure waveform to the inflection point of the aortic pressure (derived objectively from the zero of second derivative of aortic pressure). From wave intensity analysis, the travel time of the reflected wave was measured to the onset of the wave intensity of the backward-traveling wave dI_ (t(i)), and to the onset of the separated backward pressure wave (t(b)). All patients showed an aortic pressure waveform characterized by an inflection point on the rising limb of the aortic pressure, followed by a secondary rise in pressure, representing the return of reflected waves. Wave intensity analysis consistently showed a negative peak in mid systole, the timing of its onset corresponding closely to the inflection point of the aortic pressure. The travel time of the reflected wave derived from the analysis of the aortic pressure waveform (t(p)) was 121+/-21ms and showed close agreement with ti (118+/-28 ms) and t(b) (115+/-29ms), with mean differences of 4 and 6ms, and 95% confidence intervals of difference (-2 to 7 ms) and (1 to 12ms), respectively. The augmentation index, a measure of the secondary increase in aortic pressure due to reflected waves, was significantly correlated with the magnitude of dI_ (r = 0.63, P < 0.001). Wave intensity is a quantity that indicates the rate of energy flux due to wave travel and since its value is positive for forward-traveling waves and negative for backward-traveling waves, its calculation allows the timing of reflected waves to be accurately predicted. Furthermore, the magnitude of wave intensity in backward-traveling waves (dI_) is related to the augmentation index and may provide a measure of the amplitude of the reflected wave. This analysis of the arterial system is done in the time domain and therefore can be easily applied to assess temporal changes in arterial characteristics.

Dynamic characterization and hemodynamic effects of pulmonary waves in fetal lambs using cardiac extrasystoles and beat-by-beat wave intensity analysis

“…In the aorta and other major systemic arteries (17,18,22,30), or the adult PT in hypoxia (14), BCW ms is considered to be due to reflection of the preceding FCW is from "closed-end" reflection sites. The extent of reflection is quantified with a "reflection coefficient," which has been calculated as the BCW ms /FCW is ratio of CI, ⌬P, or ⌬U (14,19,27,31), and which typically has a value of Ͻ0.2.…”

“…For WI analysis, the rates of change of PT and left PA blood pressure (dP/dt) and velocity (dU/dt), and the product of these differentials (i.e., net WI), were calculated. Note that WI is a "time-corrected" variable that is independent of the digitizing sample rate (8,15,31,34,43), which contrasts with wave intensity defined by absolute changes in P and U between samples (i.e., dP ⅐ dU) used in a number of previous reports (12,14,18,22,30,46). However, the latter can be obtained from the time-corrected WI via division by the square of the sampling frequency (22).…”

Clinical usefulness of wave intensity analysis

“…Using a multi-sensor catheter which contained a pressure sensor and a velocity probe energized by an electromagnetic flowmeter, Koh et al [18] measured wave intensity in the ascending aorta in patients undergoing coronary artery surgery. Using applanation tonometry and pulsed Doppler, Zambanini et al [42] measured wave intensity in the carotid, brachial, and radial arteries in healthy nonsmokers.…”

Rats with adenine-induced chronic renal failure develop low-renin, salt-sensitive hypertension and increased aortic stiffness

“…From the data recorded, heart rate, systolic BP, mean arterial pressure (MAP), diastolic BP, and pulse pressure (PP) were extracted in real-time using the built-in routines. Aortic PWV (m/s) was calculated using the foot-to-foot method, the foot being objectively defined by the peak of the second derivative of the pressure curve during each pressure waveform (13,19). Augmented aortic pressure was calculated as the difference between systolic BP and the pressure at the inflection point in the pressure waveform representing the arrival of the reflected pulse wave (13).…”

“…Aortic PWV (m/s) was calculated using the foot-to-foot method, the foot being objectively defined by the peak of the second derivative of the pressure curve during each pressure waveform (13,19). Augmented aortic pressure was calculated as the difference between systolic BP and the pressure at the inflection point in the pressure waveform representing the arrival of the reflected pulse wave (13). Aortic augmentation index (AI, %) was calculated as augmented pressure divided by PP ϫ 100.…”