Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension: Discussion
In this prospective study, we found a difference in the Dlno/Dlco ratio between patients with DPLD and patients with PAH. Although this difference did reach statistical significance, the large overlap between the groups makes the Dlno/Dlco ratio inapplicable as a clinical tool in discriminating between PAH and DPLD.
Although we used a lower inspiratory NO concentration compared to others, we had no reason to expect that this would influence our data as it has been shown that the Dlno is independent of inspiratory NO in rabbits. It has been taken into account that the NO concentration in the alveolar sample is well above the natural alveolar output, which is approximately 2 to 3 ppb in healthy sub-jects, 4.7 ppb in subjects with scleroderma-associated interstitial lung disease with or without pulmonary hypertension, and 4.1 ppb in subjects with hypersensitivity pneumonitis and IPF. In our study the NO concentration in the sample volume was well > 200 ppb; therefore, the neglect of natural alveolar NO output can only lead to a very slight underestimation of the Dlno. The NO production by the conducting airways can be neglected because of the very high exhalation flows used. We found Dlno/ Dlco ratios of 4.36 in healthy subjects, which are comparable to the ratio of 4.3 in 13 healthy subjects assessed by Borland and Higenbottam by the singlebreath method and of 4.52 in 8 healthy men (singlebreath technique) measured by Zavorsky et al. In addition, the Dlno strongly correlated with the Dmco. canadian family pharmacy
We observed a relation of 2.48, which is similar to the value found by Tamhane et al (2.49) using a rebreathing technique and that found by Phansalkar et al6 (2.42). Dlco is often, but not always, decreased in patients with PAH.- Consequently, Dlco cannot be used as a screening test to exclude pulmonary hypertension in cases in which the pretest probability is high. Borland et al found the Dlno/Dlco ratio (combined singlebreath technique) to be 5.02 in 12 patients with severe PPH vs 4.51 in 10 matched healthy volunteers. This is in accordance with our results. Steen-huis et al observed decreased Dlco in subjects with PPH and CTEPH, mainly due to a decreased Dmco (high/low oxygen method). There were no differences in the mean values of Dlco, Dmco, and Vcap between the two groups. Bernstein et al measured the Dmco and Vcap (high/low oxygen method) before and 3 weeks after pulmonary throm-boendarterectomy in 29 subjects with CTEPH. Dmco and Vcap were decreased prior to the operation, and Dmco decreased further after the operation. However, the short interval after the pulmonary thromboendarterectomy, the fall in VA postoperatively, and the known dependency of Dlco and Dmco on VA make it difficult to draw conclusions from this study.