Autonomic nerve dysfunction in COPD as assessed by the acetylcholine sweat-spot test

Patients with hypoxic chronic obstructive pulmonary disease (COPD) have evidence of a subclinical parasympathetic autonomic neuropathy, with apparent preservation of sympathetic function. However, these cardiovascular-respiratory tests might have been biased by concomitant chest disease, the acetylcholine sweat-spot test avoids this bias. This sweat-spot test assesses sympathetic nerve function, it relies upon the fact that denervated sweat glands do not produce sweat. 35 patients with hypoxaemic COPD and seven age matched normal subjects were studied. Following intradermal injection of 0.1 of 1% acetylcholine into the dorsum of the feet, the number of sweatglands able to respond in a given surface area was recorded. Cardiovascular autonomic nerve function, arterial oxygen and carbon dioxide tensions, lung function and cigarette consumption were also recorded. The acetylcholine sweat-spot test was highly repeatable in eight COPD patients, no person with normal or frankly abnormal function being wrongly assigned. The age matched control subjects had normal acetylcholine sweat-spot scores and cardiovascular autonomic tests. The acetylcholine sweat-spot test was abnormal in 24 patients, borderline in 8 and normal in 3 patients. The abnormal sweat-spot test group had significant worse FEV1, arterial blood gases and autonomic function. The acetylcholine sweat-spot score correlated with the severity of arterial hypoxaemia (r = 0.78, p < 0.001) and with the parasympathetic cardiovascular tests (r = 0.80, p < 0.001). In conclusion, patients with hypoxaemic COPD have a parasympathetic cardiovascular and a peripheral sympathetic autonomic neuropathy. The acetylcholine sweat-spot test is repeatable, easy to perform and a sensitive indicator for autonomic dysfunction in breathless individuals with COPD.