Switch to the new peak flow reference equations for adults in India
University of Arizona, USA
Dr. P Enright
University of Arizona
|How to cite this article:|
Enright P. Switch to the new peak flow reference equations for adults in India.J Postgrad Med 2014;60:156-157
|How to cite this URL:|
Enright P. Switch to the new peak flow reference equations for adults in India. J Postgrad Med [serial online] 2014 [cited 2022 Jun 28 ];60:156-157
Available from: https://www.jpgmonline.com/text.asp?2014/60/2/156/132324
Kodgule and coworkers, in a paper in this issue of the journal, have reported the results of a study that has developed new peak flow reference equations for adults of wide age range and living in India.  While diagnostic-quality spirometry is widely available in urban areas and tertiary referral centers, it is often not available to general practitioners in the community. However, peak expiratory flow (PEF) meters and pocket spirometers are inexpensive, widely available in primary care settings, and quick and easy to use. The major clinical value of PEF is to help to grade the degree of control in patients with asthma exacerbations and to rule out clinically important chronic obstructive pulmonary disease (COPD) in adult smokers.  Reasonably accurate PEF-predicted values are necessary for both of these indications.
It has long been known that lung volumes, FEV1, PEF, and DLCO are lower for healthy Indians when compared to Caucasians in North America and Europe, but the degree has varied from study to study. Earlier studies were either under-powered or poorly representative of patients from the various regions of India. The PEF reference equations from the study by Kodgule et al.  are fairly robust and with adequate quality control. While there were statistically significant differences between mean PEF values from healthy adults in the five regions, the differences were not clinically significant, and thus, a single set of reference equations may be used to evaluate patients throughout India.
To expedite the widespread clinical use of these new reference equations, laminated nomograms and apps for smartphones should be quickly developed and verified by the investigators. The distributors of peak flow meters in India should then make these available without charge to every physician who buys a peak flow meter or pocket spirometer. The nomograms and apps should not only calculate the predicted and percent predicted PEF values, but also indicate when the PEF is below the fifth percentile lower limit of the normal range, when the diagnostic-quality pre- and post-bronchodilator spirometry is indicated for adult smokers, and the degree of asthma control for patients with asthma. The optimal cut-off point for referring a smoker for diagnostic-quality spirometry needs to be determined by a separate study (since the results from the BOLD and PLATINO studies used the National Health and Nutrition Examination Survey (NHANES) III reference equations for Caucasians or Mexican-Americans which do not apply to people in India).  The manufacturers of COPD inhalers will probably then give peak flow meters at no cost to primary care providers to prompt screening for COPD and enhanced utilization of their products.
The recently published PURE study  obtained good-quality spirometry tests from about 6000 healthy adults from South Asia (including 150 sites in India, Bangladesh, and Pakistan) and found that mean forced vital capacity (FVC) from these sites (after correction for height, age, and sex) was about 35% lower than from high-income countries in Europe and North America. They did not measure PEF, but a lower FVC (maximal inhalation) causes a proportionally lower PEF (and lower FEV1). Peter Burney and colleagues have recently suggested that spirometry reference values developed from healthy Caucasians can be used worldwide for all racial and ethnic groups.  They argue that poor nutrition and excessive environmental toxins are responsible for the lower lung function in developing/resource-poor countries, implying that improvement in these conditions will not follow if the reference equations developed from healthy local people are used. It seems alright for epidemiologists to choose to analyze and report their data in this way to promote their goal of increasing awareness of disparities (and funding to reduce them from one generation to the next). However, when this approach is used clinically, it affects many patients who are falsely labeled as having a pulmonary function abnormality, followed by treatment attempts. The lower lung function of economically disadvantaged people occurs during the growth phase of the lungs (childhood and adolescence), which cannot be reversed by interventions attempted during adulthood. Thus, the American Thoracic Society (ATS)/European Respiratory Society (ERS) pulmonary function guidelines recommend using locally developed reference equations (such as the new PEF equations for adults in India) for testing patients, whenever possible. 
As a practical suggestion, most PEF meters were designed for use by a single patient to monitor their asthma control. When PEF meters are used in health care settings, they test several patients and these patients are often tested during an exacerbation of their respiratory disease, usually caused by a virus. I would recommend the following to reduce the risk of cross-contamination: 1) disposable cardboard mouthpieces with a one-way valve (which prevents inhalation from the device); 2) hand washing by the patient and the technologist, nurse, or doctor before and after the test; and 3) wiping the exterior of the meter with alcohol after each use.
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