Pulmonary Physiologic Testing

Key Points

• Spirometry is the most commonly performed and standardized measurement of pulmonary function; it measures the volume and flow rate of air that leaves the lungs (how much and how fast).
• Two separate methodologies are used to quantitate RV, FRC, and TLC: body plethysmography and gas dilution.
• Other pulmonary function tests include maximal voluntary ventilation, maximal respiratory pressures, and lung compliance.
• Cardiopulmonary exercise testing not only delineates the reserve of each of the contributing subcomponents of the process of respiration but also allows us to integrate the effects of a myriad of measurable and unmeasurable system subcomponents to assess functional status through measurements of maximal power output and oxygen consumption.

The physiologic role of the lung is to maintain homeostasis of the arterial pH, Pco₂, and Po₂ under varying conditions of oxygen consumption and carbon dioxide production, a goal that is dependent on the lung’s properties both as a mechanical structure and as a gas-exchanging surface. Clinical pulmonary function tests (PFTs) provide practical assessment of the integrity of the components of the respiratory system. Such testing provides a key ingredient in the diagnosis and assessment of severity of lung disease and is critical in the determination of perioperative risk. Cardiopulmonary exercise testing (CPET) may offer further diagnostic and prognostic advantages over resting assessment of the respiratory system because it measures physiologic reserve and integrated functional capacity that can only be inferred from resting measurements. It is imperative that the thoracic surgeon be competent not only in the application of lung function indices but also in the assessment of the techniques and quality of the data provided. In this chapter we offer a practical approach to the assessment of lung function and exercise physiology.