Cold face test: adrenergic phase

The cold face test (CFT) evokes reflex bradycardia and pressor responses. Bradycardia has been used to assess vagal function. This study evaluated two aspects of physiology and clinical applicability of the pressor response. During constant monitoring of blood pressure (Finapres) and heart rate (EKG), CFT was induced by the application of three cold packs (0.5°C) to the face for 1 min. Group 1: Latencies of systolic blood pressure (SBP) and heart rate (HR) response to the CFT were recorded in 10 normal subjects. Group 2: CFT was performed in eight normal subjects after cholinergic blockade with atropine (0.03 mg/kg body weight intravenously). Group 3: Four patients with baroreflex failure and five patients with pure autonomic failure were subjected to CFT. In Group 1, mean latency of CFT-induced SBP rise (mean ± SD) (13.8 ± 16.6 s) was longer than that of bradycardia (5.6 ± 4.6 s). In Group 2, bradycardia was abolished in all subjects and SBP was unaffected after atropine administration. In Group 3, patients with baroreflex failure demonstrated normal HR and SBP responses to CFT. In the pure autonomic failure patients, bradycardia was absent and SBP response was either absent or subnormal. The adrenergic phase of the CFT is independent of the cholinergic phase (bradycardia) and baroreceptors. Rise in SBP is useful in evaluating the integrity of the efferent sympathetic pathway with baroreflex failure. Absence of SBP rise in response to the CFT may be of diagnostic value in detecting the sympathetic component of pure autonomic failure.