Cough Test to Assess Cardiovascular Autonomic Reflexes in Diabetes

Coughing induces cardioacceleratory responses under cholinergic control. The Cough Test (CT), a standardized test that uses a series of coughs with electrocardiographic monitoring, was used to assess the functional integrity of cardiovascular autonomic nerves. In 224 control subjects and 235 diabetic patients, heart-rate (HR) responses were compared with four established tests: lying to standing (LS), standing to lying (SL), deep breathing (DB), and Valsalva maneuver (VM). In control subjects, HR responses declined significantly with age in a curvilinear pattern. Logtransformed indices were used to estimate percentiles. The CT-HR responses were reproducible and significantly associated with other HR-response tests. Sixty-nine (29%) diabetic patients had an abnormal value ≤1st percentile, whereas only 2 control subjects had such an abnormality. Among diabetic patients, age and duration of diabetes exerted a significant negative influence. With the use of the criteria of two abnormal or one abnormal and two borderline tests (among CT, LS, SL, DB, or VM) as a minimal criteria for cardiovascular autonomic neuropathy, CT and LS had the least overlap between the control and diabetic populations and were significantly better than SL or VM (P < 0.005 for CT, P < 0.01 for LS). They were not different from DB. We found the CT to be simple to perform, reproducible, and useful for the assessment of cardiovascular autonomic reflexes.