Determination of Pulmonary Gases (O2& CO2) Metabolic-Rates and Lung Diffusion Coefficients Based on the Inspired and Expired Air Compositions and Venous Blood and Gas Concentration

The primary function of the lung is to (i) oxygenate the blood and thereby provide oxygen to the cells for metabolization purposes, and (ii) to remove the CO
2
produced by the tissues from the pulmonary blood. Herein, we provide a noninvasive methodology to asses the capacity of the lung to oxygenate the pulmonary capillary blood and to reduce its CO
2
concentration. For this purpose, we analyze the compositions of the inspired and expired air per breath, and therefrom compute the metabolic O
2
consumption rate (V̊O
2
) and CO
2
production rate (V̊CO
2
). Next we compute the cardiac out (CO) as CO = V̊
O
2
(C
^AB
O
2
- C
^VB
O
2
). We have derived the expressions for diffusion coefficients (i) D
O
2
in terms of V̊
O
2
and the alveolar and venous partial pressures, P
^al
O
2
and P
^VB
O
2
and (ii) D
CO
2
in terms of V̊
CO
2
, P
^al
CO
2
and P
^VB
CO
2
. The coefficients D
O
2
and D
CO
2
represent the gas transfer capacity of the lung. The paper provides a case study for the determination of Q,D
O
2
and D
CO
2
. The derived information of D
O
2
and D
CO
2
as well as of O
2
and CO
2
metabolic rates can be of considerable clinical use including for SARS assessment.