The breathing pattern and ventilatory response to carbon dioxide of 10 experienced divers was compared with that of 10 nondivers of similar age and build. Breathing pattern was described by the equation VE = M (VT - K) and the response to carbon dioxide by VE = S(PCO2 - B). The divers exhibited a value form 27% lower than the nondivers; S was 33% lower. The difference was significant (P less than 0.05) in both cases. B was significantly higher (P less than 0.05) in the divers than nondivers. These differences are not attributable to age, build, or vital capacity. S was well correlated with M when all subjects were considered a single group. Within the diving group no correlation of S and M with diving experience was found.
Respiratory heat loss was measured during cold water (5-6 degrees C) excursions to depths of 300 m. Losses were computed with and without respiratory gas heating when wearing a diving helmet in current commercial and Service use. A magnitude of heat loss, sufficient to cause undue stress to the respiratory tract, was observed even with gas heating provided, particularly at maximum depth. If the hyperbaric gas is both heated and humidified to a maximum comfort level then respiratory gains in the order of 40 W are possible at 250 m. This technique of utilizing warm wet gas introduced into the respiratory tract was tested as a rewarming technique following immersion in cold water (4-5 degrees C) to the limit of peripheral endurance.
A method of measuring both oxygen uptake (~~,) and ventilation (~') when breathing from a double counterlung semi-closed circuit underwater breathing apparatus is presented. The analysis requires a knowledge of the gas concentrations of oxygen and carbon dioxide in the inspired and expired counterlungs of the breathing set as well as the mass flow rate of gas injected into the apparatus. Values for~Ol and (' were obtained at pressures between 100 kPa and 1·1 MPa in moderate temperature (22-25"C) and very cold (about 4"C) water. The reliability and accuracy of the devised techniques were validated at 100 kPa by comparison to an open circuit measurement of VOl and Jiunder the same conditions of rest and work. Further confirmation of the accuracy or the method was established at depth by measuring the ventilation equivalent for oxygen (~)~01) during intermittent rest and work.
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