Chapter 4. Principles of Lung Ventilation and Spirometry
A 31-year-old woman with no previous history of pulmonary disease obtains routine spirometry before beginning work in a textile plant. The PFT lab utilizes a whole-body plethysmograph and an esophageal balloon catheter to estimate lung volumes, PIT, PA, and PIP during various ventilatory maneuvers. At what lung volume would her PIP be most positive?
a. Approaching her total lung capacity (TLC)
b. Resting quietly at her functional residual capacity (FRC)
c. As her expiratory reserve volume (ERV) is achieved
d. At the lung volume equal to FRC − RV
e. Approaching her residual volume (RV)
The most correct answer is e.
Subjects attempting to empty their lungs completely toward RV exert considerable inwardly directed force by the chest wall and diaphragm. This is perceived as a strongly positive pressure in both the intrapleural space and in the esophagus being monitored in this subject as a surrogate for her PIP.