A comparison of cardiovascular and autonomic adjustments to three types of cold stimulation tasks.

Two types of 'cold pressor' tasks are used frequently in research settings: immersing the hand or foot in ice water, and applying an icebag to the forehead. Both tasks have commonly been selected as 'alpha-adrenergic' tasks due to expected increases in blood pressure and peripheral resistance. However, the forehead cooling task has been used by others to produce increased vagal tone due to the elicitation of the 'diving reflex' and subsequent bradycardia. This differs from the prototypical increase in heart rate during hand immersion. The present study directly compared the cardiovascular adjustments of hand immersion and forehead stimulation. As stimulation of the trigeminal nerve is thought to increase vagal activity during forehead cooling, a third condition in which most of the face was covered with an icebag was included to ostensibly stimulate more of the trigeminal. 18 males had counterbalanced exposures to hand immersion, forehead cooling, and facial cooling for 90 s each. Cardiovascular variables derived from impedance cardiography and the ECG were measured. Respiration was paced at 14 breaths/min to facilitate comparisons of respiratory sinus arrhythmia across conditions. No differences among baseline or tasks were found for respiratory rate or cardiac output. The pattern of results for hand immersion was that of increased heart rate with moderate blood pressure increases. In contrast, the forehead and facial cooling tasks elicited small heart rate decreases with little change in blood pressure. Facial cooling elicited significantly more vagal activation than hand cooling as indexed by respiratory sinus arrhythmia. The patterns of response for facial and forehead cooling were almost identical. Probable reasons for the lack of significant blood pressure responses during the facial and forehead cooling are discussed.