Resp Care
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Review Case Reports
What is the best pulmonary diagnostic approach for wheezing patients with normal spirometry?
Asthma is characterized by airway inflammation, airway hyper-responsiveness (AHR) and variable air flow obstruction. The diagnosis of asthma, however, is often based upon nonspecific clinical symptoms of cough, wheeze, and shortness of breath. Furthermore, the physical examination and measurements of pulmonary function are often unremarkable in patients with asthma, thereby complicating the diagnosis of the disease. The following discussion will review approaches to the diagnosis of asthma when lung functions are normal, and will largely focus on the use of bronchial provocation tests to detect underlying AHR.
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Measurement of various aspects of pulmonary function is a relatively easy, noninvasive, and inexpensive way to gauge the status of the respiratory system. Interest in using these tests to determine risk from medical and surgical interventions stems from their presumed ability to be more sensitive than history or physical examination in detecting underlying lung disease. ⋯ This paper attempts to review the literature addressing several of the more difficult of these areas. It is clear that more research, involving more rigorously designed studies, will be necessary, before definitive answers are available.
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Lung function parameters vary considerably with age and body size, so that, unlike many laboratory tests, the normal range of expected values must be individualized. For spirometry, only low values are considered to be abnormal, so the lower limit of normal (LLN) is taken to be equal to the 5th percentile of a healthy, non-smoking population. Simple and commonly used "rules of thumb," such as an FEV(1)/FVC < 0.70 to indicate air-flow obstruction, or assuming values < 80% of predicted to be abnormal, are inaccurate and will cause misclassification, specifically under-diagnosis of abnormalities in younger, taller individuals and over-diagnosis in those older or shorter. ⋯ A future goal for the pulmonary community would be the development of risk stratified outcome data that would allow an estimation of the probability of disease with progressive decrements in lung function. While interpreting spirometry results near the LLN will continue to be problematic, a more important task for the pulmonary community is to focus on finding the pool of individuals with clear-cut, but undiagnosed, COPD. And for this, good quality spirometry remains the best tool and must be widely available.
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With the introduction of the stair climb test of surgical patients in the 1950s, the role of exercise-based testing as a useful diagnostic tool and an adjunct to conventional cardiopulmonary testing was established. Since then, we have witnessed a rapid development of numerous tests, varying in their protocols and clinical applications. The relatively simple "field tests" (shuttle walks, stair climb, 6-minute walk test) require minimal equipment and technical support, and so are generally available to physicians and patients. ⋯ Is it sufficiently robust and informative to replace the more demanding and less available CPET? In many instances, the clinical applications are overlapping, with the 6MWT functioning as an adequate surrogate. However, in the initial evaluation of unexplained dyspnea, in formal evaluation of impairment and disability, in detailed evaluation of congestive heart failure, and in the selected lung cancer patient prior to resection, CPET remains superior. Investigations of portable metabolic and cardiovascular monitoring devices aiming to enhance the diagnostic capabilities of 6MWT may further narrow or close the remaining gap between these two exercise studies.
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Professional societies have encouraged primary care providers to conduct spirometry testing for the detection of chronic obstructive pulmonary disease (COPD). In spite of this effort, the success rate is unacceptably low. Simple flow-sensing spirometers have technical flaws that can cause misreadings, and they are rarely checked for accuracy. ⋯ Use of spirometry in primary care will continue to be problematic unless high quality testing is tied to reimbursement. Using FEV(1) or peak flow measurements to rule out airway abnormality in the majority of patients, followed by referral for more sophisticated studies in those remaining, may be the best approach. Respiratory therapists should engage in this effort.