It is well recognized that obesity affects the mechanics and physiology of the respiratory system. However, the specifics of that relationship have not been clearly established. This study examines the impact of body mass index (BMI) on Pulmonary Function Tests (PFT).
4610 complete pulmonary function tests were included. The study subjects were divided into three groups- BMI>30 (N=1345), BMI 25-30 (N=1572) and BMI<25 (N=1693). The mean forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), peak expiratory flow (PEF), total lung capacity (TLC), expiratory reserve volume (ERV), inspiratory capacity (IC), residual volume (RV), diffusing capacity (DLCO) values were entered for each of the 3 groups along with the percentage of predicted values for FEV1, TLC, DLCO and RV. Analysis of variance (ANOVA) was performed for each variable with subsequent pair-wise comparisons.
FEV1 was not affected and had no relationship to BMI. However, the impact of BMI on TLC, RV, DLCO and ERV was substantial (Figure 1, 2). DLCO showed a direct proportional relationship to BMI- the higher BMI, the higher DLCO- a fact suggested by other studies but not universally accepted. Pearson correlation performed on TLC and BMI showed the highest coefficient in the group with BMI>30 (correlation coefficient -0.13). Linear regression demonstrated that for each increase of BMI by 1, TLC% decreases by 0.42 points.
Increased BMI impacts on TLC, RV and ERV, but not on FEV1. DLCO increases as BMI rises.
Awareness of the effects of BMI on lung function testing will result in better interpretation of the results and hopefully avert unnecessary pulmonary work up.
Boris Medarov, None.