THE COLD FACE TEST (DIVING REFLEX) IN CLINICAL AUTONOMIC ASSESSMENT - METHODOLOGICAL CONSIDERATIONS AND REPEATABILITY OF RESPONSES

1. Cold stimulus applied to the face causes bradycardia and peripheral vasoconstriction (i.e. the diving reflex), and has been suggested as a test of the autonomic pathways involved. The purpose of this study was to define standard procedures for conducting the test and analysing the responses to the cold face test, to evaluate variability in responses between subjects and within subjects when the same test is repeated, and to examine its usefulness in clinical autonomic assessment. 2. Sixteen (nine female, seven male) healthy adult (21-35 years old) subjects were used. Cold stimulus was applied with gel-filled compresses. Forehead temperature under the compress as an indication of stimulus magnitude, heart rate, blood flow in the finger, toe and calf by venous occlusion plethysmography, and systolic and diastolic blood pressure were monitored. Three protocols were carried out in which the temperature (0, 5, 10, 15°C), placement (whole face, unilateral, forehead) and duration (20, 40, 60, 120 s) of the cold compress application were varied. 3. The data indicate that 0°C compresses applied bilaterally for 40 s produced the maximum bradycardia and peripheral vasoconstriction. No subject found this test to be obnoxious, but a 120 s application was objectionable to some subjects. This cold face test resulted in 22%, 72%, 59% and 44% reductions in heart rate and blood flow to the finger, toe and calf, respectively. There was significant between-subject variability, but good consistency in responses to tests repeated in the same subject on different days, at different times of day and in different seasons. 4. Two advantages of the cold face testt are: (a) it can assess sympathetic-vascular smoothe muscle pathways as well as the cardiac-vagal pathway; and (b) because its afferents are independent of the stretch and pressure receptors that are stimulated in other vagal-cardiac tests (Valsalva manoeuvre and respiratory sinus arrhythmia), it can help differentiate between abnormal vagal-cardiac and abnormal transducer-afferent pathway function.