Single-breath oxygen tests for individual lungs in awake man

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Abstract
Single-breath oxygen (SBO2) tests for individual lungs were performed in 5 healthy awake volunteers. In the supine position, all subjects consistently showed a closing volume (CV) for both lungs. In the lateral position, CV was demonstrated in all analyzable SBO2 tests for the dependent and in 20 of 28 for the nondependent lung. CV consistently occurred in the dependent before it occurred in the nondependent lung (asynchronous onset of CV). After CV had been reached in the nondependent lung, a mean of 77 ml of gas was still expired from the dependent lung. No changes in CV for individual lungs were demonstrated with changes in body position. Expiratory flow limitation consistently occured 1st in the dependent lung (asynchronous onset of flow limitation). In the lateral position, at high lung volumes, the dependent lung achieved higher flow rates; later in expiration, the nondependent lung contributed progressively more gas to the total expirate (asynchronous emptying). Findings were consistent with both the asychronous flow limitation and the airway closure interpretations of CV. Some results were not consistent with either theory.