Posthyperventilation hypoxia

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Abstract
Body CO2 stores are larger and require a longer period of adjustment when altered, compared to body O2 stores. The hyperventilation with air which depletes body CO2 stores does not significantly increase the body O2 stores. Recovery from this CO2 depletion can be produced only by hypoventilation. During air breathing, this hypoventillation must produce a decrease in alveolar and arterial oxygen tension. Dogs were hyperventilated for 1 hr. with air to examine this disturbance. In 11 studies the average value for arterial CO2 pressure [PaCO2] at the enc'' of 1 hr of hyperventilation was 16 mm Hg. When mechanical hyperventilation was discontinued apnea lasted 1 1/4 min. At the end of 2 min arterial O2 pressure [PaQ2] had fallen from 110 to 35 mm Hg. Although PacO2 reached a stable level of 35 mm Hg at the end of 15 min of spontaneous ventilation, minute volume increased progressively as did Pap2reaced a stable level of 35 mm Hg at the end of 15 min of spontaneous ventilation, minute volume increased proresively as did PaCO2, throughout the remainder of the hour. It was concluded that the obligatory hypoventilation necessary to restore depleted body CO2 stores must result in hypoxia during air breathing which lasted up to one hr. in these studies.

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