Testing for Autonomic Neuropathy: Heart Rate Changes after Orthostatic Manoeuvres and Static Muscle Contractions

Abstract

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.

Estresse ortostático ativo e arritmia sinusal respiratória em chagásicos com função sistólica global do ventrículo esquerdo preservada

“…Such variability in the response to autonomic tests depends not only on neural control, but also on different hemodynamic and methodological aspects. Although predominantly related to the vagus, the immediate cardioaccelerating response that follows the beginning of the standing maneuver is also linked to hemodynamic modifications subject to reflex adjustments, and also influenced by sympathetic stimulation [9][10][11] . The initial increase in heart rate (3 seconds after beginning the maneuver) is related to the removal of vagal influence by voluntary abdominal muscle contraction; a second peak of increase in heart rate (around 12 seconds) is mediated by both vagal inhibition and sympathetic stimulation, elicited by the decrease in the arterial baroreflex activation, caused by the drop in blood pressure associated with the decrease in venous return 11 .…”

“…Although predominantly related to the vagus, the immediate cardioaccelerating response that follows the beginning of the standing maneuver is also linked to hemodynamic modifications subject to reflex adjustments, and also influenced by sympathetic stimulation [9][10][11] . The initial increase in heart rate (3 seconds after beginning the maneuver) is related to the removal of vagal influence by voluntary abdominal muscle contraction; a second peak of increase in heart rate (around 12 seconds) is mediated by both vagal inhibition and sympathetic stimulation, elicited by the decrease in the arterial baroreflex activation, caused by the drop in blood pressure associated with the decrease in venous return 11 . The hemodynamic and autonomic response is influenced by the resting time that precedes the examination, as well as by the velocity and effort made in the act of standing 32 , factors that may vary from patient to patient, being difficult to standardize.…”

“…The 10 RR intervals immediately preceding maneuver onset were computed to obtain the mean cardiac interval and mean heart rate at baseline immediately before starting the maneuver. The longest and shortest RR intervals were recorded right after the maneuver, and the max:min RR index was calculated 4,[8][9][10][11][12][13][14][15][16] .…”

“…Because the highest heart rate usually occurs around the 15th beat after assuming the standing position, followed by maximum bradycardia around the 30th beat, Ewing et al 12 standardized an autonomic test of the parasympathetic division based on the 30:15 ratio (the longest RR interval around the 30th beat divided by the shortest RR around the 15th beat). Wieling et al 11,13 , considering that the 30:15 ratio underestimates the maximal variability in heart rate occurring after orthostatism, have proposed the use of a ratio between the maximum RR interval and the minimum RR interval (max:min RR index).…”

“…When the individual stands up, from a horizontal position, approximately 300 to 800 mL of blood are rapidly transferred from the thorax to the lower limbs. A few seconds after assuming a standing position, tachycardia is observed, caused mainly by suppression of the vagal influence, related to voluntary muscle contraction and the transient reduction in blood pressure [9][10][11] . The baroreflex activation that follows leads to recovery of blood pressure and a vagus-mediated reduction in heart rate, which is completed at 30 seconds of orthostatism.…”