Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension
The diffusing capacity of the lung for carbon monoxide (Dlco) estimates the amount of gas uptake by the lungs and is a valuable tool in the assessment of pulmonary diseases. According to the model of Roughton and Forster, Dlco is determined by the following several factors: the passage of carbon monoxide (CO) through the alveolocapillary membrane; the transfer of CO into the plasma and the intraerythrocytic compartments; and the reaction rate for the binding of CO on hemoglobin (Hb). Equation 1 enables the estimation of the two components of the Dlco (ie, the diffusing capacity of the alveolocapillary membrane for CO [Dmco] and the pulmonary capillary blood volume [Vcap]) using duplicate measurements of the Dlco with high and low oxygen concentrations.
Although numerous articles have been published concerning the clinical value of the Dmco and Vcap, this test has not become a standard tool in the pulmonary function laboratory for the following reasons: first, the measurement of the Dmco is complicated and time-consuming; and, second, measurements of Dmco and Vcap are not entirely accurate. The reason for this is that the co value in the Roughton and Forster1 equation is an estimate, and the Dmco value is determined by two separate breathholding periods, with high and low oxygen concentrations, in which several factors can influence the measurement. canadian neighbor pharmacy viagra
Nitric oxide (NO) offers a solution to these problems and can be used as a gas in testing the diffusing capacity of the lung. NO binds 400 times stronger than CO to Hb; therefore, the diffusing capacity of lung for NO (Dlno) is much less influenced by changes in the Vcap and reflects the properties of the alveolocapillary membrane better than the Dlco. Borland and Higenbottam4 measured Dlno and Dlco in one single-breath maneuver, and calculated the Dmco and Vcap using differences in the co and the ©no values.5 Several interesting studies have been conducted in this field. Phansalkar et al showed that the Dlno (using the rebreathing technique) closely relates to the Dmco measured by the high/low oxygen method. Tamhane et al3 measured the combined Dlno-Dlco values with a rebreathing technique and found that the Dlno directly correlates to the diffusing capacity of the pulmonary membrane. Thus the Dlno/Dlco ratio should be able to locate the position of the diffusion impairment.