Diffusing capacity for nitric oxide and carbon monoxide in patients with diffuse parenchymal lung disease and pulmonary arterial hypertension.
BACKGROUND
The passage of carbon monoxide (CO) through the alveolocapillary membrane and into the plasma and intraerythrocytic compartments determines the diffusing capacity of the lung for CO (DLCO) as defined by the Roughton and Forster equation. On the other hand, the single-breath diffusing capacity of the lung for nitric oxide (DLNO) is thought to represent the true membrane diffusing capacity because of its very high affinity for hemoglobin (Hb) and its independence from pulmonary capillary blood volume. Therefore, the DLNO/DLCO ratio can be used to differentiate between thickened alveolocapillary membranes (both DLNO and DLCO are decreased, and the DLNO/DLCO ratio is normal) and decreased perfusion of ventilated alveoli (the DLNO less decreased than the DLCO; therefore, the DLNO/DLCO ratio is high) in patients with pulmonary disease.


METHODS
We measured the combined values of DLCO and DLNO in 41 patients with diffuse parenchymal lung disease (DPLD), 26 patients with pulmonary arterial hypertension (PAH), and 71 healthy subjects.


RESULTS
The DLCO (corrected to the standard Hb value) was lowered in the DPLD group (64% of predicted) and in the PAH group (64% of predicted), and was normal in the control group (105% of predicted). The DLNO/DLCO ratio in patients with PAH (4.98) was significantly higher than that in patients with DPLD (4.56) and in healthy subjects (4.36).


CONCLUSIONS
The DLNO/DLCO ratio is significantly higher in patients with PAH than in healthy subjects, although this ratio cannot be applied as a screening test to discriminate between patients with DPLD and PAH as the overlap between these groups is too large.
van der Lee
Ivo
I
Heart Lung Centre Utrecht, Department of Pulmonary Diseases, St. Antonius Hospital, Nieuwegein, Netherlands. Electronic address: vdlee@tiscali.nl.
Zanen
Pieter
P
Heart Lung Centre Utrecht, Department of Pulmonary Diseases, St. Antonius Hospital, Nieuwegein, Netherlands.
Grutters
Jan C
JC
Heart Lung Centre Utrecht, Department of Pulmonary Diseases, St. Antonius Hospital, Nieuwegein, Netherlands.
Snijder
Repke J
RJ
Heart Lung Centre Utrecht, Department of Pulmonary Diseases, St. Antonius Hospital, Nieuwegein, Netherlands.
van den Bosch
Jules M M
JMM
Heart Lung Centre Utrecht, Department of Pulmonary Diseases, St. Antonius Hospital, Nieuwegein, Netherlands.
D000328:Adult; D002248:Carbon Monoxide / Q000378:metabolism*; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000503:physiopathology*; D017563:Lung Diseases, Interstitial / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000378:metabolism*; D011653:Pulmonary Diffusing Capacity; D012129:Respiratory Function Tests
D009569:Nitric Oxide; D002248:Carbon Monoxide