Analysis of the effect of hemodialysis on peripheral and central arterial pressure waveforms

Abstract

Arterial stiffening is very pronounced in renal patients. Carotid artery stiffening is a powerful predictor of future cardiovascular mortality, and measures of arterial compliance correlate much better with left ventricular mass (LVM) in dialysis patients than does brachial artery blood pressure (BP). The aim of our study was to describe the influence of a hemodialysis (HD) session on arterial cushioning function and to correlate the potential different types of behavior with echocardiographic derived parameters. Radial artery pressure waveforms were measured and recorded noninvasively by applanation tonometry in 51 healthy patients on regular three times weekly HD. The data were then converted into aortic pressure waveforms using a regression equation (SphymoCortrade mark apparatus). Measurements were done pre- and post-HD in order to ascertain the effect of a single HD session on arterial hemodynamics. The augmentation index (AGI; the difference between early and late pressure peaks divided by the pulse pressure amplitude) was used as an index for vascular compliance. Reproducibility was assessed in 20 young healthy subjects by determining the aortic pulse wave augmentation index twice from radial artery BP measurements one minute apart. Intraobserver error was 2.4%. For 10 dialysis patients similarly studied, the intraobserver error was 1.6%. AGI was correlated with subjects' height (r = -0.37, P = 0.009), weight (r = -0.41, P = 0.002), and BP levels: radial systolic BP (r = 0.33, P = 0.018), radial diastolic BP (r = 0.29, P = 0.036), and central systolic BP (r = 0.51, P < 0.001). Comparing the pre- with the post-HD AGI values, four patterns of evolution became apparent: (1) The AGI was negative before the HD session and became even more negative afterward (N = 3 out of 51). (2) The AGI was positive before the HD session but became negative after dialysis (N = 19 out of 51). (3) The AGI was positive before the HD session and, although diminished afterward, remained positive (N = 23 out of 51). (4) The AGI was positive before the HD session and increased afterward (N = 6 out of 51). We also found that in some patients, AGI remained at lower than predialysis levels for at least 24 hours. Significant relationships between echocardiographic parameters and pulse wave contour (PWC) variables included pre-HD AGI and LVM (r = 0.47, P < 0. 001). There was better correlation between LVM and derived predialysis aortic systolic BP (r = 0.56, P < 0.001) than measured brachial (peripheral) systolic BP (r = 0.35, P = 0.04). Patients whose waveform remained abnormal (AGI remained positive) after HD had a more dilated LV (LV-EDD = 52.07 +/- 3.48 mm) than did those patients for whom HD restored "normal" arterial hemodynamics (LV-EDD 46.86 +/- 4.06 mm, P < 0.05). A standard HD session profoundly affected aortic BP waveform characteristics, with a reduction in wave reflection in 88% of patients. However, restoration by HD of a normal aortic waveform was unusual. Patients whose waveform remained abnormal after HD had larger more dilated LV chambers than did those patients for whom HD restored "normal" arterial hemodynamics.