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Effects of Carbon Dioxide and UBA-Like Breathing Resistance on Exercise Endurance

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Technical rept. Jun 2008-Dec 2009

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Effects of inspired CO2 and of resistance on exercise endurance were tested dry at sea level. Resistance R was designed to mimic that of the MK 16 underwater breathing apparatus UBA at 50 feet of seawater. The MK 16 UBA has turbulent inspiratory and laminar expiratory pressure drops. At the design flow, expiratory pressure was twice inspiratory pressure. Endurance was assessed as duration of exercise on a bicycle ergometer at 85 peak oxygen consumption. Ventilatory parameters and end tidal CO2 also were measured. Three groups of twelve subjects participated one breathing air with 0, 2, or 3 CO2 without R one breathing air against moderate, high, or no R without CO2 and against moderate R with 1 or 2 CO2 and one breathing O2 with or without 2 CO2, once with moderate and once with no R. Endurance in air was reduced by 20 or more relative to that with neither R nor CO2 in 2 of 10 subjects breathing against moderate R, 3 of 10 subjects breathing against high R, 4 of 9 subjects with 2 CO2, 6 of 9 subjects with 3 CO2, 3 of 10 subjects breathing against moderate R with 1 CO2, and 5 of 10 subjects breathing against moderate R with 2 CO2. Among 10 subjects breathing O2, endurance was reduced similarly in 2 subjects breathing against moderate R, 3 with 2 CO2, and 2 breathing against moderate R with 2 CO2. When CO2 was added without R, minute ventilation increased relative to that with air alone without R, but when R was present, minute ventilation decreased with or without inspired CO2. Average end tidal CO2 remained normal during air breathing without CO2 but increased in all other cases. A few subjects reached alarmingly high end tidal CO2 with combinations of R and CO2 or with 3 CO2 in air. We conclude that to allow inspired CO2 in the MK 16 or other UBAs with similar pressure-flow characteristics would be hazardous.

Subject Categories:

  • Stress Physiology
  • Life Support Systems

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