Abnormal Cardiovascular Functional Responses after the Long Interdialytic Interval

Key Points Body fluid volumes are significantly higher at the end of the 3-day interdialytic interval compared with the 2-day interdialytic interval. V E /VCO 2 slope, a noninvasive index of exercise pulmonary vascular resistance, is elevated after the 3-day interdialytic interval. VO 2 Peak is similar across interdialytic intervals but was limited following dialysis by postdialysis fatigue. Background The long interdialytic interval in thrice-weekly hemodialysis is associated with volume accumulation and excess cardiovascular risk. Few studies have evaluated cardiovascular functional changes after interdialytic intervals. This study sought to evaluate cardiovascular functional response patterns, as assessed by cardiopulmonary exercise testing, after the short and long interdialytic intervals. Methods We conducted an exploratory single-center, quasi-experimental 2-arm study involving crossover of treatment sequences in patients on conventional thrice-weekly maintenance hemodialysis. All patients underwent cardiopulmonary exercise testing, bioelectrical impedance spectroscopy, and physical function testing on three study visits: posthemodialysis and prehemodialysis at the end of a 2-day and the 3-day interdialytic intervals. Results Thirty-one patients ( n =19 men, mean [SD] age 55 [12] years, median [interquartile range] dialysis vintage 56 [24–96] months) completed all study visits. Interdialytic weight gain and total body fluid were greater after the 3-day compared with the 2-day interval ( P < 0.001). Ventilation/carbon dioxide production (V E /VCO 2 ) slope, a noninvasive index of exercise pulmonary vascular resistance and right ventricular (RV) dysfunction, was significantly elevated at the 3-day (31.2 [4.8] L V E /L VCO 2 ; P = 0.002) compared with the 2-day interval (29.5 [3.9] L V E /L VCO 2 ). No significant differences between interdialytic intervals were observed for peak oxygen uptake (VO 2 Peak) or VO 2 at the anaerobic threshold. Change (Δ) in V E /VCO 2 slope (ΔV E /VCO 2 ) the 2-day to the 3-day interval was correlated with Δbody weight ( r =0.36, P = 0.04) and left ventricular mass index ( r= 0.44, P = 0.02). Conclusions The long interdialytic interval is associated with abnormal exercise-derived ventilatory and hemodynamic responses, including ventilation-perfusion mismatch and potentially RV dysfunction and RV-pulmonary artery uncoupling during exercise as suggested by elevated V E /VCO 2 slope.