HEART-RATE RESPONSE TO SUSTAINED HAND GRIP - COMPARISON OF THE EFFECTS OF CARDIAC AUTONOMIC BLOCKADE AND DIABETIC AUTONOMIC NEUROPATHY

The heart-rate response during sustained hand grip was studied in four normal subjects before and after intravenous atropine, propranolol and combined cardiac autonomic blockade with both drugs. The results suggest that the increase in heart rate during the first 20 s is due to para-sympathetic withdrawal, whereas the further increase between 30 s and 180 s is proably mediated by a combination of parasympathetic withdrawal and sympathetic stimulation. The increases in heart rate during each minute of sustained hand grip were compared in 26 normal subjects, 37 diabetic subjects without and 24 diabetic subjects with proven autonomic neuropathy. In the diabetic subjects with autonomic neuropathy the increase in heart rate during the first minute was impaired, whereas the increases during the second and third minutes were similar in all three groups. The initial increase in heart rate over the first 30 s of hand grip and the later increase between 30 s and 180 s were compared in nine normal subjects, ten diabetic subjects without and six diabetic subjects with autonomic neuropathy. The increase during the first 30 s was impaired in the diabetic subjects with autonomic neuropathy, whereas the later phase of the response was similar in all three groups. It is concluded that impairment of the heart-rate response to sustained hand grip in diabetic autonomic neuropathy is mainly due to impairment of the early parasympathetic phase, but that the presence of cardiac sympathetic damage can also be detected.