Influence of posture on lung volumes and impedance of respiratory system in healthy smokers and nonsmokers

In 105 adults we investigated the influence of the body positions, sitting with respect to supine, on lung volumes and on the input resistance, (Rrs) and reactance (Xrs) of the respiratory system. Rrs and Xrs were measured between 2 and 26 Hz by means of a forced oscillation technique. Vital capacity (VC) and expiratory reserve volume (ERV) are smaller in the supine position; this reduction decreases with age and is less for ERV in male smokers than in nonsmokers. The Rrs values are larger in the supine position, and the slope of the Rrs-frequency curves tends to become less positive or negative, depending on sex, age, and smoking habits. Xrs decreases at lower frequencies. The changes in Rrs due to posture are larger in young smokers than in young nonsmokers. This is not explained by changes in ERV and may reflect changes in the intrinsic properties of the airways induced by smoking.