Blood capillary volume as a determinant of high DLCO in subjects living at moderate altitude

Introduction: Pulmonary diffusion capacity of carbon monoxide (DLCO) performed in conjunction with the nitric oxide pulmonary diffusion test (DLNO), dissects the vascular and membrane component. It is well know that the inspired oxygen pressure is an important factor that determines DLCO, (higher altitude-lower PiO2-higher DLCO); however, other mechanisms - such as the blood capillary volume (Vc) - can be involved. Aim: 1) to inform the main determinants of DLCO and DLNO in children; 2) to compare the values of Vc, DLCO, DLNO and membrane diffusion capacity in both altitudes. Methods: Children between 5 and 20 years old of age, residents from Mexico City (2,240-m, moderate altitude) and Veracruz, Mex (4-m, sea level), were invited to participate. If they met the selection criteria (by health questionnaire), anthropometric, DLCO, DLNO and hemoglobin measurements where done. Results: 156 children (54% women) were recruited; 95 (61%) living at 2240-m. DLCO at moderate altitude was 27.9 (±7.43) ml/min/mmHg (U) vs. 18.55 (± 5.44) U at sea level, DLNO = 85.63 (± 24.99) U vs. 70.60 (± 24.23) U respectively and Vc = 101 (± 30.12) mL at 2240-m vs 60 (± 18.56) mL at 4-m (p