Effects of apnea and facial submersion on heart rate and peripheral blood flow in humans

Abstract

It is well accepted that humans show a submersion reflex under specific conditions. This reflex is initiated by facial receptors, integrated in the brainstem, and alters both central and peripheral cardiovascular functions. Apnea is also known to elicit cardiovascular effects. It was the purpose of this study to examine the effects of apnea and apneic facial submersion on heart rate (HR) and blood flow (BF) to the skin of the hand. HR was determined by ECG leads or heart rate pulsations on the blood flow tracings. BF was evaluated by a dual-channel laser Doppler flowmeter at two locations on the dominant hand (thumb base and middle finger). Seven female subjects were studied during apnea in air at 22 C and facial submersion in water at 22 C. Five additional female subjects were studied in a similar fashion except that the water temp was 10 C. Apnea in air resulted in a reduction in HR of 12% (P=0.03). Facial submersion in 22 C water reduced HR by 19% (P=0.02), and in 10 C water by 28% (P=0.02). Mean BF to the hand declined by 34% during apnea in air (P=0.01), by 41% during facial submersion in 22 C water (P=0.01), and by 57% during facial submersion in 10 C water (P=0.01). Conclusion: facial submersion causes a greater degree of bradycardia and vasoconstriction than does apnea alone; and the cooler the water, the greater the submersion reflex.