Testing for autonomic neuropathy: heart rate changes after orthostatic manoeuvres and static muscle contractions

1. The initial heart rate (HR) response evoked by standing, 70 degrees head-up tilt, handgrip and contraction of abdominal and leg muscles was analysed in diabetic patients with autonomic neuropathy and in matched controls. 2. In healthy subjects standing induced an immediate, large, HR increase lasting 20s that far exceeded the small HR rise induced by tilt. The HR response with handgrip and to contraction of abdominal and leg muscles was strikingly similar for the first 5 s to the HR increase after standing. 3. In diabetic patients handgrip and standing induced a small HR increase starting after 2-3 s. Contraction of abdominal and leg muscles evoked little or no HR changes. The HR rise after tilt up was delayed by 10 s compared with healthy controls. 4. It is concluded that the circulatory response to active and passive changes of posture differs fundamentally. Standing and handgrip are superior to head-up tilt as a test for vagal HR control. An abrupt and large HR increase after standing excludes cardiac parasympathetic neuropathy. A modified response, however, may be due to afferent as well as to efferent lesions, e.g. in muscle afferents or in vagal afferents from cardiopulmonary receptors.