MODULE SUPPLEMENT: PULMONARY SYSTEM
Changes that Occur with Age in
Pulmonary Volumes and Capacities

There are four volumes that we speak of when we describe pulmonary capacity.

1. Tidal Volume (TV): the amount of air we breath in and out during a normal breath, which is approximately 500ml.
2. Inspiratory Reserve Volume (IRV): the amount we can breath in over and above tidal volume, or about 3000ml.
3. Expiratory Reserve Volume (ERV): This is the amount we can breathe out beyond normal exhalation (that is, the end of a normal tidal volume breath), which is about 1100 ml. This is somewhat decreased with age.
4. Residual Volume (RV): the amount of air that is left in the lung even after we try our best to get everything out, approximately 1200ml. Residual volume is important to respiratory function because it provides a supply of oxygen between breaths (Guyton, 2000). In this way, residual volume provides for stability of our gas exchange and prevents rapid fluctuations in blood gases. Residual volume increases with age.

There are also four capacities that represent combinations of volumes.

1. Inspiratory Capacity (IC): Tidal volume plus IRV
2. Vital Capacity (VC): IRV plus TV plus ERV (or IRC + ERV): This is the maximum amount of air that can be expelled from the lungs after first taking in as much air as you can. Vital capacity is a very important component of pulmonary function testing (PFT). Because of changes in the properties of the lungs and altered muscle strength, older adults can not get air out as fast so there is a decrease in VC and in FEV₁.

To learn more about PFTs and their interpretation see: Interpretation of Pulmonary Function Tests: Spirometry (Note: This link will open in a new browser window, which you can close to return here.)

3. Total Lung Capacity: VC plus RV: The total volume that the lung can contain after a maximum inspiration. This doesn't change much with age, although there may be some decrease related to decreased inspiratory muscle strength and decreased skeletal height (Rossi et al, 96).
4. Functional Residual Capacity (FRC): ERV plus RV: The amount left in the lungs after normal expiration. This is about 2300ml, but increases slightly as we get older.

These changes in lung volumes and capacities are demonstrated very schematically below.

Caveats:

Several caveats need to be considered about pulmonary changes and PFTs in older people. First, ethnicity can make a difference. People of African descent have a lower trunk/leg ratio than those of European descent, so their normal pulmonary function values are 12-15% lower than those predicted (Culver and Butler, 1985). Most of the standards for spirometric testing were established on Caucasians. Second, Culver and Butler (1985) note that lung function doesn't necessarily decline in the linear fashion we once thought from age 18 or 20. Rather it may reach a maximum in the late 20s and then decline, but there is variability in older adulthood depending on lung capacity at the time of lung maturation, as discussed earlier. Finally, it's very important to understand that current spirometry values have NOT been normed on older adults--the values in later life are extrapolated from predicted declines. Each of these points need to be kept in mind when evaluating results of pulmonary testing.