Autonomic function in amyotrophic lateral sclerosis: a study of cardiovascular responses.

Autonomically mediated cardiovascular responses were evaluated in 15 ALS patients and compared with 15 healthy subjects. The respiratory sinus arrhythmia, the heart rate response to a Valsalva manoeuvre, to isometric handgrip and to a dive reflex test was normal, indicating a normal function of vagal nerves. The heart rate and blood pressure responses during an orthostatic test were normal, indicating a normal function of sympathetic nerves. The increase in blood pressure and blood flow in the contralateral forearm which occurs on handgrip in healthy subjects was reduced in the ALS patients. The cause of this is unclear, but could be related to decreased function of "ergoreceptors" or altered vascular reactivity in atrophic muscle.