Respiratory Mechanics by the Passive Relaxation Technique in Conscious Healthy Adults and Patients With Restrictive Respiratory Disorders

Abstract

The passive relaxation single-breath technique has been used primarily in anesthetized human subjects to measure total respiratory system elastance and resistance. This method was used to assess the pressure-flow characteristics in 32 relaxed, conscious patients with restrictive respiratory disorders (20 with neuromuscular disease, 12 with sarcoidosis) and 27 similarly aged control subjects free of cardiothoracic disease. Using Rohrer's pressure-flow relationship during passive expiration, P/V = K1 + K2V, considerable curvilinear pressure-flow characteristics were found in both groups. These can be attributed to a combination of the upper airway and viscoelastic and elastoplastic behavior of the respiratory system. Despite the greater elastic recoil pressure (and respiratory elastance) of the restrictive patients, their pressure-flow characteristics were similar to those of the control subjects. These findings imply structural similarities in at least the lower airways, or in the effects of retractile forces along airways compensating for reduced lung volumes.