Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension: Results
The Dlco and Dlno were corrected to BTPS conditions, and a minimum of two measurements was performed, in which a variability of < 10% for the VA and Dlco was acceptable. All Dlco measurements were corrected to the standard Hb value according to American Thoracic Society recommendations. The obtained Dlno/ Dlco ratios were compared by means of analysis of variance using a statistical software package (SPSS for Windows, version 11.0; SPSS; Chicago, IL). The relation between the Dlno/Dlco ratio and Dmco was performed with the Pearson correlation coefficient. In a period of 1 year (April 2003 to April 2004), 71 patients were screened for study inclusion, and 67 patients were included in the study based on eligibility. Four DPLD subjects were excluded due to the presence of secondary pulmonary hypertension. In one patient, this was probably due to left ventricular failure with mitral valve regurgitation, and in the other three patients the cause of the secondary hypertension was associated with the DPLD. In the control group, 71 healthy volunteers were included (36 female volunteers and 35 male volunteers).
In the DPLD category (total, subjects; female subjects; male subjects, 18), sarcoidosis was diagnosed in 27 patients, 4 with nonspecific interstitial pneumonia, 5 with idiopathic pulmonary fibrosis (IPF), 2 with pulmonary alveolar proteinosis, 1 with lymphangioleiomyomatosis, 1 with respiratory bronchiolitis-associated interstitial lung disease, and 1 with cryptogenic organizing pneumonia. In the PAH category (total, 26 patients; female patients, 16; male patients, 10), primary pulmonary hypertension (PPH) was diagnosed in 4 patients, chronic thromboembolic pulmonary hypertension (CTEPH) was diagnosed in 20 patients, and pulmonary hypertension associated with scleroderma (without signs of interstitial lung disease) was diagnosed in 2 patients. more
The demographics of the study population are shown in Table 1; the mean age of the control group is lower than that in subjects with DPLD and PAH. The mean Dlno/Dlco ratios in patients with DPLD and PAH were 4.56 and 4.98, respectively; this difference was statistically significant (p = 0.01). The mean Dlno/Dlco ratio in healthy subjects was 4.36, which is significantly different from the Dlno/ Dlco ratio of subjects with PAH (p < 0.001) [Table 1] but is not significantly different from that in the DPLD group (p = 0.127). As shown in Figure 1, the three groups had a high degree of overlap. The Dlno and the Dmco are highly correlated (r2 = 0.81), and the slope of the regression line (dlno/Dmco) was 2.48 (Fig 2).
Table 1—Demographics and Main Results of the Study Population
Variables | Normal (n = 71) | DPLD (n = 41) | PAH (n = 26) |
Age, yr | 38.1 (10.1) | 48.1 (13.0) | 56.8 (11.8) |
Height, m | 1.75 (0.09) | 1.71 (0.08) | 1.69 (0.07) |
VC, % predicted | 115% (16) | 92% (22) | 97% (16) |
TLC, % predicted | 108% (13) | 87% (20) | 89% (16) |
Dlco, mL/min/mm Hg | 32.8 (7.3) | 17.9 (5.6) | 16.7 (5.2) |
Dlco, % predicted | 105% (16) | 65% (20) | 65% (17) |
Kco, mL/min/mm Hg/L | 5.1 (0.8) | 4.0 (0.9) | 3.4 (0.8) |
Kco, % predicted | 104% (15) | 85% (20) | 76% (17) |
Dlno, mL/min/mm Hg | 142.4 (32.8) | 82.1 (30.0) | 82.2 (30.4) |
Kno, mL/min/mm Hg/L | 30.0 (2.4) | 18.0 (4.1) | 16.5 (3.2) |
Dlno/Dlco ratio | 4.36 (0.6) | 4.56 (0.6) | 4.98 (0.9) |
Dmco, mL/min/mm Hg | 31.4(11.5) | 28.1 (10.7) | |
Dmco, % predicted | 53% (20) | 54% (24) | |
Vcap, mL | 48.6 (13.9) | 50.3 (14.4) | |
Vcap, % predicted | 63% (19) | 67% (17) |
Figure 1. Dlno/Dlco ratios in all three categories. Depicted is the mean ± 2 SEs.
Figure 2. Dlno vs Dmco in all subjects with disease. The line of reference for total population is displayed (r2 = 0.81).