Patient perception of the severity of asthma is important to the management of asthma, but a pulmonary function test provides an objective, reproducible, reliable means of assessing severity.
The fatality rate for asthma has risen, despite increased recognition of asthma and better therapies for asthma maintenance. This troublesome fact has led to studies that have demonstrated that individuals who have had episodes of near-fatal asthma seem to have a decreased perception of dyspnea and airway obstruction.1 Recent evidence suggests an accentuation of this perception in the presence of hypoxia.2 A review in RT (January 2005) by Carter et al suggests a practical approach to determining which patients might be at increased risk for poorly controlled asthma due to decreased symptom perception. The author cites a recent publication by Klein et al3 that attempts to assess risk based on perception of peak flow versus actual peak flow. This paper and the review in RT are a nice first step in the direction of attempting to determine an at-risk group of asthmatics that may have a diminished perception of increased resistive load.
Ongoing management of asthmatics by specialists in respiratory disease involves use of pulmonary function testing. The specialist with the resources of an excellent pulmonary function laboratory has a distinct advantage over the primary care physician relying solely on history and examination (and peak expiratory flow measurements) in assessing perception of symptoms versus disease severity. The advantage of using pulmonary function tests (PFTs) in the ongoing management of asthma is that the test is objective, reproducible, and reliable. The issue of perceptive hypersensitivity (eg, the patient who is convinced that his or her asthma has flared when it has not) is easily put to rest by PFTs. In my own practice, I use PFTs to determine when symptoms of airway obstruction might be better explained by anxiety. Conversely, obtaining regular spirometry on asthmatics allows me to determine the degree of perception of airway obstruction relative to the PFT and select those patients who may be at risk for poor perception of worsening airway obstruction.
The pulmonary function test is one of the most underutilized tests available to the primary care physician. My own laboratory does not require referral to pulmonology for testing; a prescription for the test is all that is necessary. The overreliance on peak flow monitoring in asthmatics may lead to a false sense of security on the part of the primary care physicians since peak flow is generally well preserved until there is a fairly high degree of peripheral airway obstruction. The peak flow is not an early warning device as commonly believed. I suspect that the PFT is not ordered routinely on asthmatics (ages 6 and older) for two reasons: the physicians are uncomfortable with interpretation of results, and they do not wish to refer the patient for consultation in order to have the test performed. Nearly every hospital runs a pulmonary function laboratory, and these laboratories are as a rule extremely responsive to referring physicians. Pre- and post-bronchodilator spirometry can determine baseline airway responsiveness.
I support Carter et als view that patients perception of severity of asthma is incredibly important to the ongoing management of asthma. Where I diverge from this author is in the use of applied physiology in sorting out asthma. My starting point in managing asthma is the PFT. All decisions and recommendations follow from the PFT. If the patient feels great, but the PFT is poor, I will treat the patient aggressively and follow closely. If the patient feels limited and dyspneic, despite normal pulmonary function, I am obliged to investigate other causes of dyspnea (cardiac, pulmonary vascular, anxiety, etc).
Jonathan D. Finder, MD, is associate professor of pediatrics, division of pulmonology, Childrens Hospital of Pittsburgh.
1. Kikuchi Y, Okabe S, Tamura G, et al. Chemosensitivity and perception of dyspnea in patients with a history of near-fatal asthma. New Engl J Med. 1994;330:1329-34 [see comment].
2. Eckert DJ, Catcheside PG, Smith JH, Frith PA, McEvoy RD. Hypoxia suppresses symptom perception in asthma. Am J Respir Crit Care Med. 2004;169:1224-30. Epub 2004 Mar 12.
3. Klein RB, Walders N, McQuaid E, Adams S, Yaros D, Fritz GK. The asthma risk grid: clinical interpretation of symptom perception. Asthma Allergy Proc. 2004;25(1):1-6.