Ultrafiltration improves aortic compliance in haemodialysis patients

Abstract

An elevated pulse pressure leads to an increased pulsatile cardiac load, and results from arterial stiffening. The aim of our study was to test whether a reduction in volume overload by ultrafiltration (UF) during haemodialysis (HD) leads to an improvement of aortic compliance. In 18 patients, aortic compliance was estimated noninvasively before and after HD with UF using a pulse pressure method based on the Windkessel model. This technique has not been applied before in a dialysis population, and combines carotid pulse contour analysis by applanation tonometry with aortic outflow measurements by Doppler echocardiography. The median UF volume was 2450 ml (range 1000-4000 ml). The aortic outflow volume after HD (39 ml; 32-53 ml) was lower (P ¼ 0.01) than before (46 ml; 29-60 ml). Carotid pulse pressure after HD (42 mmHg; 25-85 mmHg) was lower (P ¼ 0.01) than before (46 mmHg; 35-93 mmHg).Carotid augmentation index after HD (22%; 3-30%) was lower (P ¼ 0.001) than before (31%; 7-53%). Carotidfemoral pulse wave velocity was not different after HD (8.7 m/s; 5.6-28.9 m/s vs 7.7 m/s; 4.7-36.8 m/s). Aortic compliance after HD (1.10 ml/mmHg; 0.60-2.43 ml/ mmHg) was higher (P ¼ 0.02) than before (1.05 ml/mmHg; 0.45-1.69 ml/mmHg). The increase in aortic stiffness in HD patients is partly caused by a reversible reduction of aortic compliance due to volume expansion. Volume withdrawal by HD moves the arterial wall characteristics back to a more favourable position on the nonlinear pressure-volume curve, reflected in a concomitant decrease in arterial pressure and improved aortic compliance.

Acute vs chronic volume overload on arterial stiffness in haemodialysis patients

“…17 Although volume withdrawal in the study had an acute, albeit small, impact on arterial wall characteristics, high aPWV values and marked augmentation continued to be present afterhaemodialysis. 8 This indicates that the acute large swing in volume status before and after haemodialysis affects arterial stiffness on top of a more permanent alteration in arterial structure and function, which is likely to be caused by chronic volume overload. 8 The deranged body fluid distribution in haemodialysis patients has been demonstrated to be significantly related to structural and functional alterations of the large arteries related to chronic volume overload and/or body fluid distribution.…”

“…8 This indicates that the acute large swing in volume status before and after haemodialysis affects arterial stiffness on top of a more permanent alteration in arterial structure and function, which is likely to be caused by chronic volume overload. 8 The deranged body fluid distribution in haemodialysis patients has been demonstrated to be significantly related to structural and functional alterations of the large arteries related to chronic volume overload and/or body fluid distribution. 18 With the intermittent and brief nature of routine 4-h thrice-weekly dialysis schedule, high ultrafiltration rate is often required for adequate chronic volume removal.…”

“…As a result of this square root relationship, aPWV may not be a sensitive measure of a change in physical arterial properties. 8 On the other hand, aortic compliance describes arterial stiffness as an absolute volume expansion over a given pressure increment, and may therefore be more straightforward to reveal the effect of absolute volume reduction from ultrafiltration. 8 (2) Timing of measurements: Large swing of volume status could affect vascular parameters.…”

“…8 On the other hand, aortic compliance describes arterial stiffness as an absolute volume expansion over a given pressure increment, and may therefore be more straightforward to reveal the effect of absolute volume reduction from ultrafiltration. 8 (2) Timing of measurements: Large swing of volume status could affect vascular parameters. Taken the thrice-weekly haemodialysis schedule, for example, the impacts of volume removal on vascular functions are expected to be more conspicuous at the first dialysis session of the week due to larger volume accumulation over the weekend.…”

“…While aPWV was not different after haemodialysis in the study, the results suggested that the increase in aortic stiffness in haemodialysis patients is partly caused by a reversible reduction of aortic compliance due to volume expansion. 8 Why has it been difficult to demonstrate an acute beneficial effect of volume removal by haemodialysis on arterial stiffness? Possible reasons are as follow:…”