The assessment of human pulmonary function dates back to the seventeenth century, when the earliest measurements of tidal volume were noted. In 1800, Humphry Davy employed a hydrogen dilution technique to measure his own residual volume (RV).1 Subsequently, John Hutchinson, in his treatise, On the Capacity of the Lungs and on Respiratory Functions, defined the functional subdivisions of lung volume and reported the results of vital capacity measurements performed in more than 1800 subjects. He related these measurements to the subjects' height, age, and weight, thereby establishing a basis for determining normal values.2,3
Progress in development of techniques for pulmonary function testing progressed slowly over the next century. However, in the 1950s, pulmonary physiologists made use of the tools provided by the evolving fields of electronics and computer science. Currently, many techniques exist for assessing both the integrated performance of the cardiovascular and respiratory systems and their individual components. This chapter focuses on commonly used tests of pulmonary function.4 Detailed assessment of integrated pulmonary and cardiovascular function is described in Chapter 34. Additional tests that have not yet been validated or are not routinely available for clinical purposes5 are not included in the discussion.
Lung Volumes and Subdivisions
Important quantitative aspects of respiratory function are the changes in lung volume with inspiration and expiration and the absolute volume of air that the lungs hold at various times during the respiratory cycle. These volumes and changes in volume are described in subsequent sections.
Definitions and Assessment
For purposes of quantification and comparison, the total volume of gas in the lungs is conventionally subdivided into compartments (volumes) and combinations of two or more volumes (capacities). For many of these subdivisions, the end-expiratory volume – the volume of gas remaining in the lungs at the end of normal expiration – is the point of reference. Lung volumes and capacities are defined in Table 33-1 and are depicted schematically in the tracing shown in Figure 33-1, which was obtained using a device called a spirometer. The relationships between the volumes recorded directly by the spirometer and the other lung volumes and capacities – including total lung capacity (TLC), functional residual capacity (FRC), RV, and inspiratory capacity (IC) – are highlighted in the figure.
Table 33-1Glossary for Static Lung Volumes and Capacities ||Download (.pdf) Table 33-1Glossary for Static Lung Volumes and Capacities
|Term ||Symbol ||Definition |
|Volumes || || |
|Residual volume ||RV ||Volume of air remaining in the lungs after maximal expiration |
|Expiratory reserve volume ||ERV ||Maximal volume of air expired from the resting end-expiratory level |
|Tidal volume ||TVa ||Volume of air inspired or expired with each breath during quiet breathing |
|Inspiratory reserve volume ||IRV ||Maximal volume of air inspired from the resting end-inspiratory level |
|Capacities || || |
|Inspiratory capacity ||IC...|