Letter: Water temperature and the "diving reflex"

Effects of water and ambient air temperatures on human diving bradycardia

Upon apnoeic face immersion, humans develop a diving response resembling that found in diving mammals. There have been contradictory reports regarding the influence of water temperature on the magnitude of the resulting bradycardia. This study examined the influence of both water and ambient air temperatures on human diving bradycardia. A group of 23 volunteers performed three series of apnoeic episodes after 60 min exposure to air at temperatures of 10, 20 or 30 degrees C. Oral and skin temperatures were measured during this exposure and during the subsequent test on 5 subjects. At 20 degrees C air temperature oral and skin temperatures were measured on 10 subjects. Heart rate (HR) was recorded for the 23 subjects during apnoea in air and apnoea with the face immersed in water of 10, 20 or 30 degrees C, at each air temperature. We found that both air and water temperatures had significant effects on immersion bradycardia, but in opposite directions. Face immersion in cold water after exposure to a high ambient air temperature induced the most pronounced bradycardia. We further observed that exposure to different ambient air temperatures resulted in different patterns of HR response to water temperature. The range in which the response was positively correlated to water temperature differed at 30 degrees C ambient air from that at 10 and 20 degrees C ambient air. We concluded from these studies that human bradycardia resulting from apnoeic face immersion is inversely proportional to water temperature within a range which is determined by the ambient air temperature. Thus, the interval in which the response to cold stimulation varies with temperature, would appear to be determined by the ambient temperature before stimulation.

Supraventricular tachycardia in infants: use of the "diving reflex"

The effectiveness of the "diving reflex" in treating paroxysmal supraventricular tachycardia (PSVT) in 10 infants aged under 6 months is demonstrated. No rhythm disturbances were encountered during the maneuver, even in patients receiving digitalis. The recommended water temperature is 5 degrees C and the total time of facial immersion, between 6 and 7 seconds. The diving reflex might be considered the first therapeutic approach in infants under 6 months old with PSVT.

The use of the diving reflex to terminate supraventricular tachycardia in a 2-week-old infant

The use of the diving reflex to terminate a case of paroxysmal supraventricular tachycardia (PST) is described in a 2-week-old infant who presented in severe congestive heart failure with supraventricular tachycardia at a rate of 300. The infant's face was placed in a basin of ice water at 5 degrees C. for 5 seconds with manual occlusion of the infant's nostrils to prevent aspiration. The PST converted to a sinus rhythm of 120 within 3 seconds of facial immersion. The physiology of the diving reflex is reviewed and the uses and hazards of this reflex in terminating attacks of PST in infants is discussed.