Medical Barriers: Reduced Pulmonary Function

Today’s post is another excerpt from “Best Weight: A Practical Guide to Office-Based Weight Management“, recently published by the Canadian Obesity Network.

This guide is meant for health professionals dealing with obese clients and is NOT a self-management tool or weight-loss program. However, I assume that even general readers may find some of this material of interest.

REDUCED PULMONARY FUNCTION

There is a clear association between dyspnea and obesity in both adults and children. Although cardiopulmonary fitness as assessed by maximal oxygen consumption is generally preserved in obese patients, exercise capacity is reduced because of the higher metabolic cost of carrying extra body weight. Obesity also increases the work involved in breathing because it reduces both chest wall compliance and respiratory muscle strength, which further contribute to the perception of increased breathing effort.

High BMI is typically associated with a reduction in forced expiratory volume in one second (FEV1), forced vital capacity (FVC), total lung capacity, functional residual capacity, and expiratory reserve volume. Thoracic restriction associated with obesity is usually mild and is attributed to the mechanical effects of fat on the diaphragm and the chest wall: diaphragm excursion is impeded and thoracic compliance reduced. A clinically significant restrictive pattern (total lung capacity <85% predicted) is usually seen only in super-morbid obese patients (BMI >50) and hypercapnic respiratory failure and cor pulmonale are frequently observed in super-super-morbid obesity (BMI >60). Respiratory muscle strength may be compromised in obesity, and reduced maximal inspiratory pressure is often noted in obese patients.

When obesity is less than super-morbid, a restrictive defect should not be attributed to fat accumulation until other causes of restrictive impairment, such as interstitial lung disease or neuromuscular disease, have been excluded.

Patients with obesity frequently report dyspnea and wheezing and are often treated for asthma without objective diagnostic confirmation through pulmonary function testing. An accurate diagnosis is important because dyspnea related to other mechanisms or diseases may require a different therapeutic strategy. The diagnosis of asthma or COPD in obese individuals requires confirmation with spirometry and should not be based solely on symptoms.

Interventions aimed at improving pulmonary function may enable patients to be more physically active.

© Copyright 2010 by Dr. Arya M. Sharma and Dr. Yoni Freedhoff. All rights reserved.

The opinions in this book are those of the authors and do not represent those of the Canadian Obesity Network.

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