Hypoxemia in obesity is attributed to gas exchange abnormality secondary to physical effect of obesity on the FRC and other lung volumes. However it seems that factors other than the physical effects of obesity are contributing to hypoxemia in obesity. We studied the relationship between fat content of mild-moderately obese subjects with their lung function changes and arterial oxygen pressure and saturation.
We selected 22 ( 2 men and 20 women) otherwise healthy obese subjects (BMI = 35.68 ± 3.2 and ages 17 to 60 years) from Obesity Clinic of the Tabriz University of Medical Sciences. All subjects completed a structured questionnaire indicating full medical and sleep disorder history and underwent complete physical examination. All subjects had spirometry and lung volume studies (using Jaeger Bodyplethysmograph, Germany), arterial blood gases(using AVL 995, Austria), pulse oxymetry, capnography, body mass composition analysis (using Tanita TBF215 Analyzer, Japan), and echocardiography with estimation of pulmonary artery pressure. Matrix Pearson correlation was performed to obtain correlation between parameters.
None of the subjects had CO2 retention. We found a significant negative correlation between both arterial oxygen pressure(PaO2) and saturation (O2Sat)and body fat mass, BMI and body fat % (r= -0.56; p=0.007, r= -0.57; p= 0.008, r = -0.533; p= 0.013 respectively) while there was no relationship between PaO2 and PaCO2, FRC%predicted, TLC%predicted, FVC%predicted or BMI. There was no meaningful relationship between lung function parameters and body fat mass or fat % which may be related to a less than severe degree of obesity in subjects studied.
PaO2 and SaO2 in obese subjects are negatively but significantly related to fat mass and fat percent of the body which it seems to be at least partly independent of the effect of the obesity on the physical changes of respiratory system and lung function.
Arterial oxygen tension in obesity may be related to factors other than physical effect of the obesity on the respiratory system and may be addressed accordingly for therapeutic purposes.
Khalil Ansarin, University grant monies From Tabriz University of Medical Sciences