Respiratory elastances in relaxed and paralyzed states in normal and abnormal men.

Abstract

Lung, thoracic, and total respiratory elastances were measured in both the voluntarily relaxed and anesthetized paralyzed states in 26 normal men and in 30 abnormal men with obstructive lung disease, ankylosing spondylitis, or severe obesity. Thoracic and total respiratory elastances were consistently greater (i.e., compliance was lower) in the conscious, voluntarily relaxed state than in the anesthetized, paralyzed state, and elastances in the 2 states correlated poorly. Assuming thoracic and total respiratory elastances measured in the paralyzed state to be the true values, close reproducibility of elastance measurements made in the conscious relaxed state was not found to be a reliable criterion for their validity. The most reasonable explanation for higher thoracic and total respiratory elastances in the relaxed state is the presence of expiratory muscle activity at the resting midposition. This muscle activity is probably not under voluntary control and may be activated by muscle spindle reflexes. Thoracic and total respiratory elastances measured in the conscious relaxed state are of questionable validity, particularly in lightly trained subjects.