EVOLUTION OF TRANSIT TIME BETWEEN THE SYSTOLIC AND DIASTOLIC PRESSURE PEAKS OF THE RADIAL PULSE WAVEFORM AFTER KIDNEY TRANSPLANTATION

Abstract

Objective: The transit time between peak systolic and peak diastolic digital volume pulse had been proposed as a measure of arterial stiffness. Indeed, the height of an individual divided by such transit time can be used to estimate a pulse wave velocity. In a cohort of patients with end-stage kidney disease, we aim to examine whether the reduction of aortic stiffness that occurs after kidney transplantation (KTx), translates into improvement of radial artery systolic-diastolic pulse transit time. Design and method: Before and three months after KTx, we recorded radial pressure waveforms using applanation tonometry in 62 patients. We used a two gaussian method to break down the radial pressure waveforms to extract transit time. Radial waveforms were recorded over a 10 seconds period and ensemble-averaged (using in house-MATLAB program) to obtain a single waveform and then modelled using two Gaussian functions. Transit time (dT) was determined as the difference between the first systolic peak (T1) and the early diastolic peak (T2). Generalized transfer function was used to estimate central blood pressures. Carotid-radial and carotid-femoral pulse wave velocities (cr-PWV, cf-PWV) were also measured. Results: 62 patients (66% male, mean age: 48 ± 14 years, mean eGFR: 66 ± 17 ml/min/1.73m2) were assessed. After KTx, there was a significant reduction in cr-PWV (9.49 ± 1.50 to 8.94 ± 1.34, p = 0.001) and cf-PWV (11.56 ± 2.65 to 10.19 ± 1.72, p < 0.001), as well as in central and peripheral blood pressure (p < 0.001). While T1 significantly declined (0.184 [0.172–0.199] to 0.179 [0.164–0.194]s, p = 0.008), there were no significant changes in transit time (0.139 [0.119–0.165] to 0.134 [0.118–0.178]s, p = 0.390) nor in T2 (0.325 [0.293–0.361] to 0.319 [0.283–0.357]s, p = 0.119). Conclusions: Contrary to our expectation, three months after KTx, we did not observe a significant change in transit time. Our results suggest that transit time between the systolic and diastolic pressure peaks of the radial pulse waveform may not be used as a marker of arterial stiffness. We propose that the radial artery pressure wave integrates information from both upstream and downstream vascular beds and so the transit time cannot be used as a reliable surrogate for arterial stiffness.