Nephrol Dial Transplant (2001) 16: 70-77
© 2001 European Renal Association-European Dialysis and Transplant Association
Autonomic neuropathy is linked to nocturnal hypoxaemia and to concentric hypertrophy and remodelling in dialysis patients
1 CNR, Centre of Clinical Physiology and Division of Nephrology, Ospedali Riuniti, and 2 Cardiology Unit, Ospedale Morelli, Reggio Calabria, Italy
Background. Autonomic dysfunction and sleep apnoea are frequent complications of chronic renal failure. Since nocturnal hypoxaemia in sleep apnoea dampens autonomic reflexes, we postulated that altered autonomic control is in part linked to nocturnal hypoxaemia in uraemic patients.
Methods. To test the hypothesis we performed continuous monitoring of O2 saturation during night by pulse oximetry (Ohmeda-Biox) as well as echocardiography, 24-h ambulatory blood pressure monitoring, and standard tests of autonomic function in 50 patients on chronic dialysis (40 on haemodialysis and 10 on CAPD). For haemodialysis patients all studies were performed during a mid-week non-dialysis day.
Results. Twenty-five patients had at least one episode of nocturnal hypoxaemia (median 13, interquartile range 4–31) while the other 25 patients had no episodes at all. Minimal and average SaO2 were strongly interrelated (r=0.64, P=0.0001). In a multiple regression model, besides age, average nocturnal SaO2 was the only independent predictor of the parasympathetic function. Similarly, average nocturnal SaO2 was the only independent predictor of the autonomic response to standing. Sex, 24-h mean arterial pressure, body mass index, haematocrit, serum albumin, serum parathyroid hormone and duration of dialysis treatment had no independent effect on the autonomic tests.
Interestingly, the average nocturnal SaO2 and the interaction between the responses to the autonomic tests were independently related to posterior-wall thickness. This interaction term represented also the stronger independent predictor of the relative wall thickness of the left ventricle. In a multiple logistic regression model the interaction parasympathetic–sympathetic function was the only independent predictor of concentric remodelling or hypertrophy, while average nocturnal SaO2 entered into this model (P=0.03) only after exclusion of the autonomic function interaction term.
Conclusions. Thus, altered cardiovascular autonomic control appears to be linked to nocturnal hypoxaemia and to concentric hypertrophy or remodelling in dialysis patients. Since nocturnal hypoxaemia is an established cardiovascular risk factor, altered autonomic control is a potential mechanism whereby hypoxaemia may trigger cardiovascular events in dialysis patients. It remains to be seen whether the link between nocturnal hypoxaemia and autonomic dysfunction is a causal one.
Keywords: cardiovascular risk; chronic renal failure; dysautonomia; parasympathetic system; sympathetic system
Correspondence and offprint requests to: Professor Carmine Zoccali, CNR Centro Fisiologia Clinica & Divisione di Nefrologia, Via Sbarre Inferiori 39, I-89100 Reggio Calabria, Italy.
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