The effects of obesity on lung volumes and oxygenation

Abstract Introduction Obesity can cause hypoxemia by decreasing lung volumes so that there is closure of lung units during normal breathing. Studies describing this phenomenon are difficult to translate into clinical practice. We wanted to determine the lung volume measurements that are associated with hypoxemia in obese patients, and how we could use these measurements to identify them. Methods We collected pulmonary function test results and arterial blood gas data on 118 patients without obstruction on pulmonary function testing. We included only patients with normal chest imaging and cardiac testing within one year of the pulmonary function test, to exclude extraneous causes of hypoxemia. Results We found that as BMI increases, the mean paO2, ERV % predicted, and ERV/TLC decrease (BMI 20-30: paO2=90±8, ERV% predicted 112±50, ERV/TLC % 19.7±6.5; BMI 30-40: pO2=84±10, ERV 84±40 ERV/TLC% 13.6±7.6; BMI>40: pO2 78 ±12, ERV 64±27 ERV/TLC% 11.4±5.8, ANOVA p