A decreased change in volume for each unit change in pressure (decreased compliance, or decreased dV/dP) is the hallmark of pulmonary fibrosis.
Idiopathic pulmonary fibrosis is diagnosed if there is a pattern of usual interstitial pneumonia (honeycombing) on high-resolution CT. Biopsy results may confirm diagnosis if CT is not definitive. Connective tissue diseases, drug toxicity, exposure to asbestos and causes of hypersensitivity pneumonitis must be ruled out through history and laboratory testing. Pulmonary function testing reveals restricted volume, normal flow (or above normal), with evidence of decreased gas exchange.
Barreiro and Perillo provide an overview of spirometry interpretation. Provided patient effort is good, the first step is to determine whether the pattern is obstructive (FEV/FVC<0.7) or restrictive (FEV/FVC>0.7, FVC decreased). They provide an algorithm in Figure 3 for further interpretation of spirometry results.
Papandrinopoulou et al. review the effects of chronic obstructive pulmonary disease on lung compliance. They provide examples of low compliance states besides IPF, including infant respiratory distress syndrome, tuberculosis, asbestos exposure, or cardiovascular causes such as mitral stenosis and left ventriuclar failure. Higher than normal compliance may be due to emphysema, bronchodilator therapy, or pulmonary stenosis.
Illustration A compares flow-volume loops in restrictive (A) vs. normal (B) vs. obstructive (C) lung diseases.
Illustration B shows a gross pathology specimen of lungs with the changes indicative of pulmonary fibrosis.
Answer 1: ALS affects respiratory muscles, causing decreased total pressure, but not changes in lung compliance until late-stage disease when the chest wall stiffens.
Answer 2: Asthma causes small increases in pulmonary compliance.
Answer 3: Centriacinar emphysema causes lung parenchyma to have an increased lung compliance.
Answer 5: Alpha-1-antitrypsin deficiency is a cause of emphysema and increases lung compliance.
Barreiro TJ, Perillo I. An approach to interpreting spirometry. Am Fam Physician. 2004 Mar 1;69(5):1107-14. Review. PubMed PMID: 15023009
PMID:15023009 (Link to Abstract)
Papandrinopoulou D, Tzouda V, Tsoukalas G. Lung compliance and chronic obstructive pulmonary disease. Pulm Med. 2012;2012:542769. doi: 10.1155/2012/542769. Epub 2012 Oct 22. PubMed PMID: 23150821; PubMed Central PMCID: PMC3486437
PMID:23150821 (Link to Abstract)
USMLE World Step 1 QBank Question #1650. Copyright © USMLEWorld, LLC 2012.