Muscle Oxygenation and Microvascular Reactivity Across Different Stages of CKD: A Near-Infrared Spectroscopy Study

Cardiac dysfunction in dialysing adults with end-stage kidney disease is associated with exercise intolerance: A pilot observational study

People with end-stage kidney disease (ESKD) often exhibit impaired cardiac structure and function, which may contribute to poor exercise capacity. This study used multimodal exercise testing to investigate the central and peripheral mechanisms of exercise limitation in adults with ESKD, also comparing in-centre hemodialysis (ICHD) to home hemodialysis (HHD). Seventeen adults (55.5 ± 14.5 years; n = 14 male; n = 12 HHD) participated. Resting cardiac examinations, followed by submaximal cycling cardiopulmonary exercise testing (CPET) and functional exercise testing, revealed cardiac structural abnormalities (increased left ventricular mass) and cardiac injury. Aerobic fitness in adults with ESKD was low, with pulmonary oxygen uptake (V̇O2) at the gas exchange threshold (GET) occuring at 39 ± 8% predicted V̇O2peak. O2 pulse, an estimate of stroke volume (SV), was higher in HHD at rest (p = 0.05, ES = 0.58) and during unloaded cycling (p = 0.05, ES = 0.58) compared to ICHD. However, thoracic bioreactance derived SV at the GET was significantly higher in adults receiving ICHD versus HHD (p = 0.01, ES = 0.74). In adults with ESKD, cardiac output was positively associated with V̇O2 at the GET (r = 0.61, p = 0.04). This study highlights prevalent exercise dysfunction in adults with ESKD undergoing dialysis, with potential distinct differences between in-centre and home hemodialysis, mechanistically linked to underlying cardiac abnormalities.

Blunted cerebral hemodynamic responses to incremental exercise in patients with end-stage renal disease

PURPOSE

The aims of this study were to compare cerebral hemodynamics and maximal oxygen uptake (VO2peak) in patients with end-stage renal disease (ESRD) vs. age-matched healthy controls during maximal exercise.

METHODS

Twelve patients with ESRD and twelve healthy adults (CTR group) performed exhaustive incremental exercise test. Throughout the exercise test, near-infrared spectroscopy allowed the investigation of changes in oxyhemoglobin (∆O2Hb), deoxyhemoglobin (∆HHb), and total hemoglobin (∆THb) in the prefrontal cortex.

RESULTS

Compared to CTR, VO2peak was significantly lower in ESRD group (P < 0.05). Increase in ∆THb (i.e., cerebral blood volume) was significantly blunted in ESRD (P < 0.05). ESRD patients also had impaired changes in cerebral ∆HHb and ∆O2Hb during high intensity of exercise (P < 0.05). Finally, no significant correlation was observed between VO2peak and changes in cerebral hemodynamics parameters in both groups (All P > 0.05).

CONCLUSION

Maximal exercise highlights subtle disorders of both hemodynamics and neuronal oxygenation in the prefrontal cortex in patients with ESRD. This may contribute to both impaired cognitive function and reduced exercise tolerance throughout the progression of the disease.

Muscle oxygen supply impairment during maximal exercise in patients undergoing dialysis therapy

This study aimed to investigate whether Chronic Kidney Disease (CKD) influences O2 supply including O2 delivery and release to the active muscles during maximal physical exercise. Twelve CKD patients undergoing dialysis therapy (HD group) and twelve healthy adults (CTR group) performed an incremental exercise test to determine maximal oxygen uptake (VO2peak). Throughout the exercise, near-infrared spectroscopy allowed the investigation of changes in oxyhemoglobin (∆O2Hb), deoxyhemoglobin (∆HHb), and total hemoglobin (∆THb) in the vastus lateralis muscle. VO2peak was significantly lower in HD group. In addition, HD patients had impaired changes in muscular oxygenation (∆HHb and ∆O2Hb) and blood volume (∆THb) during the exercise (p < 0.05). Moreover, a positive correlation was observed between VO2peak and muscle blood volume (∆THb) in both groups (p < 0.05). This study provides the first evidence that HD patients displayed lower VO2peak and blunted muscular deoxyhemoglobin increase during exercise. This result supports the hypothesis of an increase in oxygen affinity and/or mitochondrial dysfunction in this population.

Cerebral oxygenation during exercise deteriorates with advancing chronic kidney disease

BACKGROUND

Cognitive impairment and exercise intolerance are common in chronic kidney disease (CKD). Cerebral perfusion and oxygenation play a major role in both cognitive function and exercise execution. This study aimed to examine cerebral oxygenation during a mild physical stress in patients at different CKD stages and controls without CKD.

METHODS

Ninety participants (18 per CKD stage 2, 3a, 3b and 4 and 18 controls) underwent a 3-min intermittent handgrip exercise at 35% of their maximal voluntary contraction. During exercise, cerebral oxygenation [oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb) and total haemoglobin (tHb)] was assessed by near-infrared spectroscopy. Indices of microvascular (muscle hyperaemic response) and macrovascular function (carotid intima-media thickness and pulse wave velocity (PWV)) and cognitive and physical activity status were also evaluated.

RESULTS

No differences in age, sex and body mass index were detected among groups. The mini-mental state examination score was significantly reduced with advancing CKD stages (controls: 29.2 ± 1.2, stage 2: 28.7 ± 1.0, stage 3a: 27.8 ± 1.9, stage 3b: 28.0 ± 1.8, stage 4: 27.6 ± 1.5; P = .019). Similar trends were observed for physical activity levels and handgrip strength. The average response in cerebral oxygenation (O2Hb) during exercise was lower with advancing CKD stages (controls: 2.50 ± 1.54, stage 2: 1.30 ± 1.05, stage 3a: 1.24 ± 0.93, stage 3b: 1.11 ± 0.89, stage 4: 0.97 ± 0.80 μmol/l; P < .001). The average tHb response (index of regional blood volume) showed a similar decreasing trend (P = .003); no differences in HHb among groups were detected. In univariate linear analysis, older age, lower estimated glomerular filtration rate (eGFR), Hb, microvascular hyperaemic response and increased PWV were associated with poor O2Hb response during exercise. In the multiple model, eGFR was the only parameter independently associated with the O2Hb response.

CONCLUSIONS

Brain activation during a mild physical task appears to decrease with advancing CKD as suggested by the smaller increase in cerebral oxygenation. This may contribute to impaired cognitive function and reduced exercise tolerance with advancing CKD.