CARDIOVASCULAR CHANGES DURING DEEP BREATH-HOLD DIVES IN A PRESSURE CHAMBER

Electrocardiogram, cardiac output, and blood lactate accumulation were recorded in three elite breath-hold divers diving to 40-55 m in a pre ssure chamber in thermoneutral (35 degrees C) or cool (25 degrees C) w ater. In two of the divers, invasive recordings of arterial blood pres sure were also obtained during dives to 50 m in cool water. Bradycardi a during the dives was more pronounced and developed more rapidly in t he cool water, with heart rates dropping to 20-30 beats/min. Arrhythmi as occurred, particularly during the dives in cool water, when they we re often more frequent than sinus beats. Because of bradycardia, cardi ac output decreased during the dives, especially in cool water (to <3 l/min in 2 of the divers). Arterial blood pressure increased dramatica lly, reaching values as high as 280/200 and 290/150 mmHg in the two di vers, respectively. This hypertension was secondary to peripheral vaso constriction, which also led to anaerobic metabolism, reflected in inc reased blood lactate concentration. The diving response of these diver s resembles the one described for diving animals, although the presenc e of arrhythmias and large increases in blood pressure indicate a less perfect adaptation in humans.