BACKGROUND: Hemodialysis is associated with numerous symptoms and side effects which, in part, maybe due to sub-clinical hypoxia. However, acute cardio-pulmonary and metabolic physiology during hemodialysis is not well defined. Intra-dialytic and inter-dialytic exercise appear to be beneficial and may alleviate these side effects. To better understand these potential benefits, the acute physiological response to exercise should be evaluated. The aim of this study was to compare and characterise the acute physiological response during hemodialysis, intra-dialytic and inter-dialytic exercise.
METHODS: Cardiopulmonary physiology was evaluated during three conditions; 1) hemodialysis without exercise (HD), 2) intra-dialytic exercise (IDEx), and 3) inter-dialytic exercise (Ex). Exercise consisted of 30 minutes constant load cycle ergometry at 90% VO2AT. Central hemodynamics (via non-invasive bio-reactance) and ventilatory gas exchange were recorded during each experimental condition.
RESULTS: Twenty participants (59 ± 12 yrs, 16/20 male) completed the protocol. Cardiac output (Δ = -0.7 L/min), O2 uptake (Δ = -1.4 ml.kg-1.min-1) and arterial-venous O2 difference (Δ = -2.0 ml/O2/100ml) decreased significantly during HD. Respiratory exchange ratio exceeded 1.0 throughout HD and IDEx. Minute ventilation was lower (p = 0.001) during IDEx (16.5 ± 1.1 L/min) compared to Ex (19.8 ± 1.0 L/min). Arterial-venous O2 difference was partially restored further to IDEx (4.6 ± 1.9 ml/O2/100ml) compared to HD (3.5 ± 1.2 ml/O2/100ml).
CONCLUSION: Hemodialysis altered cardiopulmonary and metabolic physiology, suggestive of hypoxia. This dysregulated physiology contributed to a greater physiological demand during intra-dialytic compared to inter-dialytic exercise. Despite this, intra-dialytic exercise partly normalised physiology during treatment.
- NICOM, non-invasive cardiac output monitor
- VE, minute ventilation
- (a-v) O2 difference, arterial-venous O2 difference
- CPEX, cardiopulmonary exercise test
- • IDEx, constant load exercise during hemodialysis