Alteration in respiratory physiology in obesity for anesthesia-critical care physician

摘要

For several decades, the global prevalence of obesity has been rising dramatically [1, 2]. The greatest increase has been noted in the United States. Compared with some European countries, the prevalence of obesity in the United States is three times higher than in France, and one and a half times higher than in the United Kingdom [3]. Between 1980 and 2004, the prevalence of obesity in the US more than doubled in adults and more than tripled in children. The greatest relative increase has been in the proportion of individuals with a body mass index (BMI) greater than 50 kg/m2. This review describes the mechanisms whereby obesity brings about the functional abnormalities on resting and exercise related respiratory physiology.Lung mechanicsObesity decreases total respiratory compliance by as much as two-thirds of the normal value measured in non-obese individuals [4]. The decrease in compliance was thought to result primarily from a reduced chest wall compliance associated with the deposition of fat in and around the ribs, the diaphragm and the abdomen. Subsequent investigations in healthy obese subjects revealed higher total respiratory system and chest wall elastance during voluntary muscle relaxation than during paralysis [5], suggestingthat incomplete relaxation may have contributed to lower chest wall compliance reported in earlier studies. Actually, the chest wall compliance is usually normal in obese subjects and the decrease in total respiratory compliance is that of the lung. The reduction in lung compliance in obese individuals is exponentially related to BMI [6]. This decrement is the result of increased pulmonary blood volume, closure of dependent airways [10], and increased alveolar surface tension due to the reduction in functional residual capacity (FRC) [7,8,9].Lung volumes and spirometryThe most common and consistent characteristic of obesity on lung function is a reduction in FRC (Figure 1).