Exercise intolerance in Kearns-Sayre syndrome

Exercise intolerance is a common finding in mitochondrial diseases, including Kearns-Sayre syndrome (KSS), characterised by progressive external ophthalmoplegia, cardiac conduction defects and atypical pigmentary degeneration of the retina. Exercise studies were performed in a 32 year old woman with KSS who had received an atrio-ventricular sequential pacemaker because of continuing breathlessness, having presented with complete heart block requiring a fixed rate demand pacemaker 6 years earlier. Minute ventilation, oxygen consumption, and carbon dioxide production were measured at different workloads on 3 consecutive days by collecting expired air. Compared to controls, after exercise at a subanaerobic workload, heart rate and ventilation were exaggerated relative to both oxygen consumption and carbon dioxide production. The findings are consistent with the hypothesis that, in mitochondrial disorders, impaired oxidative phosphorylation leads to uncoupling of cardiac ouput and ventilation relative to muscle metabolic rate. © Pearson Professional 1996.