Simulated diving in man: comparison of facial stimuli and response in arrhythmia.

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Abstract
The effect of breath holding and 4 facial stimuli - application of a wet cloth at 25 degrees C and 0 degrees C, facial immersion in 25 degrees C and 0 degrees C water - on heart rate and rhythm were compared in 20 physically untrained subjects. During all 5 maneuvers heart rate was significantly slower than resting control. Of the 10 comparisons among the different stimuli only breath holding compared to a wet cloth at 25 degrees C and face immersion at 25 degrees C compared to a wet cloth at 0 degrees C were not significantly different. The colder stimuli caused greater slowing and pacemaker depression. Bradycardia developed from a decrease in the sinus rate, nodal escape, and subsequent slowing of the atrioventricular nodal rate. Prolonged PR time and atrioventricular block were uncommon. Results in 10 physically trained athletes were similar although heart rates recorded at rest and during the experimental maneuvers were lower and the incidence of nodal rhythm was higher than in the untrained subjects. Cardiac slowing occurred during nonapneic facial immersion, but the effect was less marked than during apneic immersion. A variety of responses were observed in patients with arrhythmia. In one patient, facial immersion abolished apparent ventricular premature beats. to another, ventricular tachycardia developed. Heart rate and rhythm response to the diving reflex may be elicited in man without facial immersion. Colder stimuli have a greater effect. Facial stimuli may be a significant factor in the evocation of arrhythmia in patients with heart disease.