Abstract
Obesity produces an increment in total blood volume and cardiac output and a decrease in lung compliance as a result of increased pulmonary blood volume and alveolar collapse in the lung bases.
Aim: To evaluate gas exchange parameters under incremental exercise in “healthy” obese patients (pts).
Methods: Analysis of symptom limited incremental cardiopulmonary exercise tests in supine position of 115 pts (36M, 79F) with FEV1,VC and TLCO ≥ 80% predicted (ECCS) and without history of cardiovascular disease. Punctions of arteria radialis were made to evaluate arterial oxygen and carbon dioxide pressure (PaO2, PaCO2) at peak exercise (PE) and to calculate dead-space to tidal volume ratio at PE (VD/VT) and alveolar-arterial oxygen pressure difference (PA-aO2). Slope of heart rate to oxygen uptake (DHR/DVO2 beat. l/min) was determined. Pts were divided into 2 groups: Ob (n=58): Body mass index (BMI) ≥ 30kg/m2, N (n=57): BMI < 30kg/m2.
Results: Significant differences were found between group Ob and N at PE in PaO2 (83.3 vs 89.1mmHg, p<0.01) and in PA-aO2 (26.4 vs 22.0mmHg, p< 0.05), but no in minute ventilation (mean 51.6 vs 52.0 l/min), VD/VT (mean 0.22 vs 0.22) and PaCO2 (mean 37.5 vs 36.7mmHg). Significant differences were found in DHR/DVO2 between groups in both sexes (M: mean 42.5 vs 31.4, p<0.01; F: mean 58.1 vs 48.7, p<0.05). These data indicate an increased extent of lung units with low ventilation/perfusion ratio (V'/Q'), but no differences in parameters of alveolar ventilation. Lowering of V'/Q' ratio seems to be produced mainly by increase in lung perfusion.
Conclusion: Hypervolemia and pulmonary over-perfusion may be an important factor of gas exchange impairment under exercise in obese patients.
- © 2011 ERS