Obesity and Pulmonary Function Tests.

Abstract

Obesity in children and adolescents is rapidly increasing all over the world. Approximately one-fourth of children and adolescents are overweight or obese in the United States [1]. Though the studies from India are limited, the prevalence of overweight and obesity in children is reported to be between 5.6 and 24 % [2]. Obesity may adversely affect many systems of the body and the respiratory system is no exception. Obesity may affect respiratory mechanics and pulmonary function tests (PFTs) parameters in many ways. Dysfunctions of respiratory muscles, both inspiratory and expiratory, have been reported in obese subjects [3]. Obesity may limit chest expansion mechanically during forced maneuvers of PFTs. Diaphragm descent during breathing may be impaired by the abdominal obesity with a resulting increase in the intrathoracic pressure. Finally, visceral fatty tissue may affect serum concentrations of tumor necrosis factor-alpha, interleukin-6, leptin, adiponectin, and many other cytokines that may act through an inflammatory cascade to affect the respiratory efforts and gas exchange [4]. There is a growing literature correlating PFT parameters with obesity indices. This issue of the journal has published a study from Thailand where authors included 45 children and adolescents of 8 to 18 y of age with obesity and correlated anthropometric and body composition indices with pulmonary function parameters [5]. In the study, obesity was defined as per criteria of International Obesity Task Force (IOTF); body composition and fat distribution indices were measured by bioelectrical impedance analysis (BIA); and PFTs were measured by spirometry and body plethysmography [5]. Authors reported abnormal PFT in 33 (73 %) cases with decreased functional residual capacity (FRC) being most common (29 cases; 64.4 %). The obstructive and restrictive abnormalities were found in three (7 %) and one (2 %) case respectively only. Five obesity indices namely waist-to-height ratio, body mass index (BMI) z-score, body fat percentage, fat mass index (FMI), and truncal fat percentage were negatively correlated with FRC. The FRC was not correlated with weight, height, and BMI [5]. The strengths of the study include use of BIA to assess the body fat composition and use of plethysmography for measuring lung volumes. There are some limitations of the study. The study included 84 % boys. It is difficult to presume that results will be applicable to girls also. Ideally, non-obese controls should also have been included in the study to make the results more robust. The previous studies have also reported correlation between obesity indices and PFT parameters but results were somewhat different from the present study. Lazarus et al. reported positive correlation between weight and forced vital capacity (FVC) and forced expiratory volume in first second (FEV1), irrespective of age, sex, and height in 2464 Australian children [6]. Authors also found that increasing total body fat, as a percentage of weight, as estimated from skin fold thickness measurements was significantly associated with decrease in height-adjusted FVC and FEV1 values. Ulger et al. included 38 obese (based on relative weight and BMI) and 30 healthy children of 9 to 15 y of age and found negative correlation between relative weight, BMI, skin fold thickness, waist/hip circumference ratio and FVC, FEV1, and PEF values [7]. They also reported significantly higher positive exercise test and positive provocation test with hypertonic saline in obese children compared to healthy children. Chow et al. enrolled 55 Chinese subjects of 6–18 y of age in four * Sushil K. Kabra skkabra@hotmail.com