He opened by talking about the growth of "extreme sports". Well 25 years ago there was a lot of interest in extreme depth breath-hold diving but it more or less died out although lately there has been an extensive revival. He showed a graph of breath-hold dive depth records from 1945 through 1995. It showed that unassisted divers have reached depths of the order of 100 metres but assisted divers who use a weight to descend and a buoyance device to resurface have reached depths of the order of 140 metres. The Italian Majorca and his daughters have been in this range. From the photo you can see this is quite the spectator sport. How deep can a diver go and how long can he stay are the questions we wanted answered.

If you start at total lung capacity (TLC), you can compress the lung to residual volume (RV). The predictor for maximum depth is the equation TLC/RV, e.g. a person with a TLC of 6 litres and RV of 1 litre can dive to a predicted maximum of 6 atmospheres. However, expert divers these days go much deeper. Yet, the Cuban, Pipin has a TLC of 9.6 litres and RV of 2.2 litres giving a factor of 4.4 which equals 34 metres but his record in 133 metres. By reverse calculation, his residual volume at depth is 0.67 litres. Obviously blood flows into the chest to make up for the difference of 1.5 litres and in an average person simple immersion alone will move as much as 1 litre from the periphery into the chest.

In Buffalo they measured the lung volume in the chest with special instrumentation. The shift of blood into the chest offsets chest compression and in cold water the shift is even greater. Dr. Lundgren illustrated this with a series of slides and diagrams. As the chest gets compressed to RV, bood shifts into the RV space and displaced air. There is a point beyond which a breath-hold diver cannot go because once the ambient pressure is greater than the pressure in the RV, blood vessels will rupture and leak blood into the air spaces. However, at great depths the amount of blood that has to shift becomes increasingly small because the volume changes with very high pressures is very small.

How long can one breath-hold? It depends on the total store of oxygen in the blood and lungs. On average this is 1.5 litres and at rest should last about 4.5 to 5 minutes. Breath-hold endurance was measured it in the lab and the breath-hold divers seem to be able to decrease the oxygen consumption as they breath-hold. Non breath-hold divers do not show this effect. The drive to breathe is driven by carbon dioxide. We can reduce the drive by hyperventilating and blowing off carbon dioxide. In this way the diver may loose consciousness from hypoxia before the carbon dioxide levels have been increased enough to make the drive to breathe return.

Another aspect is the treachery of the hypoxia of ascent. Hyperventilating allows staying down longer but the stimulus to breathe comes later and by then more oxygen is depleted and on ascent it drops more due to pressure drop in the water and therefore in the lung air and hypoxic unconsciousness ensues.

Heart rate slows a lot more than normal in these super breath-hold divers. In one of the Majorca daughters it dropped to 8 beats per minute in a submersed dive to 50 meters in the pressure chamber.Also, blood pressure rises phenomenally at first and then drops dramatically.