Effects of cardiac rehabilitation on the renal function in patients aged 75 years and older with moderate to severe renal dysfunction

Background As a conservative treatment is an option for end-stage renal failure patients aged 75 years and older in some countries around the world, an effective treatment for the renal function in patients of that age with moderate to severe renal dysfunction might be essential. Our previous study reported that cardiac rehabilitation (CR) improved the renal function in chronic kidney disease (CKD) patients using serum cystatin C (Scys). However, it is unknown whether CR has a favorable effect on the renal function in patients aged 75 years and older with moderate to severe renal dysfunction. Methods We conducted a retrospective cohort study of patients admitted to our hospital for evaluating and treating cardiovascular disease from April 2014 to June 2022. The subjects were patients who participated in our 3-month CR program with moderate to severe CKD (estimated glomerular filtration rate based on an Scys [eGFRcys]<45 ml/min/1.73m²) at the beginning of the program. The controls were patients referred to the program but that did not participate. For both groups, patients with the Scys measured upon program referral and approximately 3 months after referral were selected. Dialysis patients were excluded. First, we compared whether there was a significant change in eGFRcys in each group, and then examined whether there was an interaction between the changes in the two groups. Second, to determine the association of any changes in the renal function due to the effects of the CR, we fitted a linear regression model using the percent change in the eGFRcys (%ΔeGFRcys) as an outcome. Results Out of 182 patients, there were 136 in the subject group and 46 in the control group. In the subject group, the eGFRcys improved (33.3±8.9 to 35.0±10.5 ml/min/1.73m², p=0.007), but it worsened in the control group (63.4±21.5 to 60.4±22.9 ml/min/1.73m², p=0.014) (Figure 1). There was a significant interaction between the two groups regarding the change in the eGFRcys (p<0.001). The %ΔeGFRcys was larger among the patients that participated in CR (6.69% greater improvement in the %ΔeGFRcys/CR participation; 95% CI, 2.73-10.64%). This association remained significant after adjusting for potential confounders (6.75% greater improvement in the %ΔeGFRcys/CR participation; 95% CI, 1.62-11.88%). Conclusion CR might improve the renal function in patients aged 75 years and older with moderate to severe renal dysfunction.