Inter- and intradialytic fluid volume changes and vascular stiffness parameters in patients on hemodialysis

Abstract

Background: Whether fluid overload is associated with vascular stiffness parameters in hemodialysis (HD) patients has not been fully elucidated. We hypothesized that interdialytic fluid accumulation increases vascular stiffness parameters, which improves with intradialytic ultrafiltration.

Methods: Fluid overload and vascular stiffness parameters were assessed in 39 HD patients (20 with and 19 without fluid overload) and compared to 26 healthy controls. Fluid status was assessed 15 minutes before the mid-week HD session by bio-impedance spectroscopy. Following this, ambulatory pulse wave velocity (PWV) and augmentation index (AIx) were measured for 24 hours before another mid-week HD session and then for 5 hours starting 30 minutes before and ending 30 minutes after the session.

Results: HD patients had significant fluid overload compared to healthy controls (2.0±2.4 vs. -0.2±0.6 L; P<0.001) and baseline PWV was higher (10.3±1.7 vs. 8.8±1.4 m/s; P<0.001). There was no significant difference between PWV and AIx in fluid overloaded and non-fluid overloaded HD patients prior to, or during the HD session. AIx of non-fluid overloaded HD patients improved after the HD session (P = 0.04). Average 24-hour AIx was higher in fluid overloaded HD patients (P<0.001).

Conclusions: Inter- and intradialytic changes in fluid volume were only weakly related to vascular stiffness parameters in HD patients. Although there was a modest reduction in AIx in non-fluid overloaded HD patients after the dialysis session, fluid removal did not improve vascular stiffness parameters during the HD session. We speculate that the effect of fluid overload correction on vascular stiffness parameters requires long-term adjustments in the vasculature.

Fig 1. Results of blood pressure and vascular stiffness parameters at the baseline and over 5-hours in HD patients and healthy controls.

Significant differences in baseline systolic blood pressure (SBP), mean arterial pressure (MAP), and diastolic blood pressure (DBP), were observed in HD patients (black bar) compared to healthy controls (white bar) (A). Baseline pulse wave velocity (PWV) was significantly higher in HD patients than in healthy controls (B). Augmentation index (AIx) was not different between the two groups (C). No significant changes in PWV (D) and AIx (E) were observed during the 5-hours measurements in fluid overloaded HD (closed symbol; dash dotted-line) and non-fluid overloaded HD patients (opened symbol; solid line). That was matching with the results of healthy controls (inverted triangle; dash-solid lines).

Fig 2. Correlation analysis between fluid overload and interdialytic ambulatory measurements of blood pressure and vascular stiffness parameters in HD patients.

Fluid overload was positively correlated with the 24-hour mean systolic blood pressure (SBP; A), mean arterial pressure (MAP; B), and augmentation index (AIx; D), but it was not correlated with the 24-hour mean pulse wave velocity (PWV; C).

Fig 3. Results of the ambulatory interdialytic assessments of blood pressure and vascular stiffness metrics in fluid overloaded and non-fluid overloaded HD patients.

The 24-hour mean systolic blood pressure (SBP) and mean arterial pressure (MAP), but not diastolic blood pressure (DBP), were higher in fluid overloaded HD (black bar) versus non-fluid overloaded HD patients (grey bar) (A). No significant difference in the 24-hour mean pulse wave velocity (PWV) was shown between fluid overloaded HD and non-fluid overloaded HD patients (B). The 24-hour mean augmentation index (AIx) was higher in fluid overloaded HD than non-fluid overloaded HD patients (C). There were no clear changes in the 24-hour PWV (D) and AIx (E) in the two HD groups.