Resp Care
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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.
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The pulmonary function lab of today is heavily focused on describing pathophysiology and quantifying the extent of disease. As we move forward, it is important that the results of pulmonary function tests go beyond this and be linked to important outcomes that truly affect clinical decision making. To get there, improvements in device performance are required, high quality technicians are critical, and properly trained interpreting clinicians with good reference standards are mandatory. ⋯ These range from modification of current technologies to brand new technologies that are still in early development. Examples include exhaled breath analysis, sophisticated analyses of lung mechanics and gas exchange, cardiac and tissue oxygenation assessments, and imaging technologies. Adoption of any new technology will require, even more than today, clear evidence that the new technology is a real adjunct to clinical decision making.