Cardiovascular autonomic nerve function in patients with hypoxaemic chronic obstructive pulmonary disease

Intraneural hypoxaemia is recognized as a pathogenic mechanism in diabetic neuropathy. A similar pathophysiological process may occur in chronic obstructive pulmonary disease (COPD). Autonomic neuropathy is not recognized in COPD. We compared 96 patients with hypoxaemic COPD to 22 age-matched control subjects to see whether autonomic dysfunction occurs in COPD and whether there was any correlation with the severity of hypoxaemia. The cardiovascular autonomic tests consisted of heart rate responses (mainly parasympathetic function) to a Valsalva manoeuvre, deep breathing and postural change and blood pressure responses (mainly of sympathetic origin) to postural change and sustained handgrip. Early autonomic neuropathy is defined as one abnormal test and definite autonomic neuropathy as two abnormal tests according to the normal range. These autonomic tests were reproducible in our study population. Although the symptoms and signs of autonomic neuropathy were rare, definite autonomic dysfunction was found in 35%, and early autonomic neuropathy in a further 47%, of patients whose arterial oxygen tension (PaO2) was less than 8 kPa (60 mmHg). Only 18% of the control group had evidence of an age-related early autonomic dysfunction. Parasympathetic autonomic dysfunction was significantly correlated with PaO2 whilst the sympathetic tests were relatively normal. Correction of hypoxaemia for one hour or administration of ipratropium bromide or terbutaline had no effect on autonomic function. Subclinical autonomic neuropathy is a feature of hypoxaemic COPD. Its importance in the disease process and its role in prognosis needs evaluation.