All living tissue consumes O2 and exerts CO2. For every pint of oxygen that it consumed, the human body produces almost a pint of carbon dioxide. The exact amount depends upon the individual and varies according to diet, fitness and other factors. Obviously this changes dramatically when a diver is subjected to increased workloads and exercise. The more the system is exerted the greater the amount of CO2 production. Rather than thinking about where the CO2 is produced i.e. legs, arms, brain, etc. keep it simple. If you want to limit CO2 excess just breath or take the mosquito test.
