The Absence of Vasoconstrictor Reflexes in the Fore- Head Circulation. Effects of Cold1

Plethysmographic data were presented in earlier publications (1, 2, 3) to illustrate the selective character of vasomotor activity in the skin. These plethysmograms indicated the absence of vasoconstrictor reflexes in head skin (with the exception of the ear). It has been suggested that these results “may be due rather to relative vasomotor inactivity of certain vessels than to an independence of rhythmic activity” (4). It is possible that vasoconstrictor fibers do not reach the forehead skin. There are many observations which so suggest: the constancy of the forehead temperature and its failure to fall during prolonged constriction of the fingers and toes; the throbbing of the temporal artery during excitement; the frequent increase in forehead volume pulses during vasoconstrictor discharges (1) ; the relative constancy of the blood supply of head skin during massive disturbances of the circulation by drugs (5) ; the failure of unilateral cervical sympathectomy to increase the temperature of the forehead skin on that side (6)-the effects are also very small on the cheek, upper lip, nose and chin. The present communication reports data which extend this list and further deny the existence of vasoconstrictor reflexes in the forehead skin. The reactions of the minute arteries in the forehead skin were studied bv recording their volume pulses with the photoelectric technique which has been described elsewhere (7). RESULTS. Spontaneous arterial constrictions which are seen so commonly in plethysmograms of the extremities and which are generally considered as due to vasomotor activity, have not been observed in the forehead skin. A striking illustration is provided in figure 1 obtained from a normal male while he rested, slept, and awakened. The frequent vasomotor discharges to the finger are wholly absent, in the forehead. Reduction in finger flow (third record), probably due to increased vasomotor tone, occurred without evident change in the forehead circulation. Startle due to loud unexpected noises, immersion of the hand in ice water, or a deep breath, are known to elicit vasoconstrictor reflexes which not only affect both the upper and lower extremity, but also are often sufficiently extensive to increase the arterial blood pressure. If these stimuli are effective, the finger’s