He expresses disappointment that such techniques are not mentioned in the manuals. A diver who becomes accustomed to a raised level of CO2 with repeated exposure to higher levels can become more hypercapnoeic in the future. Hypercapnia can result in disorientation, dizziness, unsteadiness, sweaty forehead and palms, flushing, muscular twitching, inco-ordination and confusion. Headaches can occur during the dive and remain for several hours after. These symptoms might be noticeable on dry land but not necessarily during a dive in the cooling environment of the water, with the diver working hard and concentrating on other things.
Unconsciousness can occur suddenly and without warning.
Hypercapnia also enhances nitrogen narcosis and makes one more susceptible to oxygen toxicity. By increasing tissue perfusion and red cell agglutination, it increases the possibility of decompression sickness. It is important that divers do not try to reduce their breathing to save gas. Breathing rate can be improved by becoming slimmer if overweight, exercising if unfit and with practice becoming more comfortable in the water. Just as importantly, buy a bigger bottle and don't worry about your gas consumption.