Abstract 835: Small Airway Closure Causes Hypoxemia in Inferior Pulmonary Veins in Obese Subjects Under Physiological Breathing
Background: Although arterial oxygen concentration decreases in obese subjects, its mechanism remains to be elucidated. We recently reported that the oxygen concentration is significantly lower in the inferior pulmonary veins (PVs) than the superior PVs (Am J Respir Crit Care Med 2008).
Objectives: We attempted to elucidate the mechanism of impaired oxygenation in the inferior PVs
Methods: 30 subjects with normal cardiopulmonary function who underwent a catheter ablation for atrial fibrillation were included. Before radiofrequency application, blood samples were obtained from each of the four PVs during physiological breathing in a supine position to measure the PaO2. Spirometry and lung scintigraphy were also performed.
Results: The PO2 value was significantly higher in superior PVs than inferior PVs (88.6±14.4, 92.0±16.8, 67.1±16.8 and 78.5±14.7 mmHg, in the left superior, right superior, left inferior and right inferior PVs, respectively). Neither the basic results of spirometry (FEV1.0 and %VC) nor the lung scintigraphy could detect any remarkable findings explaining the low PO2 value in the inferior PVs. Among the various clinical characteristics, only the BMI value was significantly associated with the decreased PO2 value in the inferior PVs (p<0.01). In the evaluation of small airway ventilation, closing capacity (CC) exceeded the functional residual capacity (FRC) in 18 cases. The difference value between the FRC and CC (FRC-CC) positively and negatively correlated with the BMI (r=0.42, p<0.01) and PO2 value in the inferior PVs (r=−0.32, p<0.01), respectively. It suggests that more small-airway closure occurs according to the increase of BMI value in the lower ling field within the range of tidal breathing.
Conclusions: Obesity-related respiratory insufficiency occurs not only during sleeping but also under the physiological breathing during daytime.