A 38-year-old man comes to the office with reports of dyspnea on exertion and decreased exercise tolerance. His medical history is unremarkable, and he has no history of childhood asthma or cough. He has never smoked and has no known occupational exposures. The patient has gained almost 100 lb over the past 4 years since leaving the military due to a sedentary lifestyle. He currently weighs 135 kg (297.6 lb) and has a BMI of 41 kg/m². His respiratory rate is 22/min and pulse oximetry is 93% on room air at rest. Physical examination is notable for central obesity. Lungs are clear on auscultation bilaterally. Which of the following changes (forced expiratory volume in 1 second [FEV₁], forced vital capacity [FVC], expiratory reserve volume [ERV], residual volume [RV], and total lung capacity [TLC]) are most likely to be seen on pulmonary function testing in this patient?

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Quizplus · Accepted Answer

11ec160b_3b3e_df6c_9249_8d2887fea19e_MD0001_00 This young patient presenting with respiratory symptoms and central obesity without a history of pulmonary disease likely has obesity-related restrictive lung disease. Obesity alters respiratory compliance, which is the ability of the lung and chest wall to stretch in response to increased lung pressures. Respiratory compliance is diminished both by a reduction in chest wall compliance from increased weight and by a reduction in lung compliance due to microatelectasis. To compensate for the reduced compliance, obese patients typically have increased respiratory rates with reduced tidal volumes (rapid-shallow breathing). The most common indicator of obesity-related disease is a reduction in expiratory reserve volume (ERV), which is the maximum volume of air that can be expired after a normal tidal expiration. Obesity has minimal effect on residual volume (RV), but functional residual capacity, which is the sum of RV and ERV, is reduced due to the marked reduction in ERV. Obesity can also cause reductions of forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), and total lung capacity (TLC), depending on the severity of obesity and body fat distribution (abdominal obesity causes greater impairment). However, these reductions are generally modest, especially relative to decrements in ERV. (Choices B and C) These are patterns that may be seen in a patient with chronic obstructive pulmonary disease, with FEV₁ reduced and FVC normal or only mildly diminished in comparison to FEV₁. TLC and RV are increased with emphysema. (Choices D and E) FEV₁, FVC, and TLC may be increased in trained athletes. Educational objective: Obesity, particularly morbid, central obesity, can cause a pattern of extrinsic restrictive pulmonary function tests. The most common indicator of obesity-related disease is a reduction in expiratory reserve volume and functional residual capacity, but forced expiratory volume in 1 second, forced vital capacity, and total lung capacity are also typically decreased. __________ References: Altered resting and exercise respiratory physiology in obesity. (http://www.ncbi.nlm.nih.gov/pubmed/19700043)

A 38-Year-Old Man Comes to the Office with Reports of Dyspnea