Pulmonary artery occlusion increases the ratio of diffusing capacity for nitric oxide to carbon monoxide in prone sheep.
OBJECTIVE
To test the hypothesis that the ratio of diffusing capacity of the lung for nitric oxide (DLno) to diffusing capacity of the lung for carbon monoxide (DLco) would be affected by occlusion of a fraction of the pulmonary vascular bed.


METHODS
Interventional physiologic study.


METHODS
Animal laboratory of a university hospital.


METHODS
Thirteen sheep.


METHODS
We simultaneously measured single-breath DLno and DLco in anesthetized and mechanically ventilated sheep (fraction of inspired oxygen [Fio(2)] of 1.0) before and after pulmonary artery occlusion by inflation of a balloon (n = 6), and by autologous clot embolism (n = 4). To see if the effect also occurred on Fio(2) of 0.21, four animals were studied during ventilation with room air, one of which was also in the Fio(2) of 1.0 group (14 total experiments with 13 sheep).


RESULTS
On Fio(2) of 1.0, the mean DLno/Dlco ratio rose by 35% from 4.76 +/- 0.41 in control to 6.42 +/- 0.82 after balloon occlusion (p = 0.002), and by 54% from 7.55 +/- 2.09 to 11.6 +/- 2.61 (p = 0.005) after autologous clot embolism (+/- SD). An equivalent relative increase of 27% took place during ventilation with room air, but the DLno/DLco ratio was lower (3.14 +/- 0.22 in control and 3.98 +/- 0.38 after balloon occlusion). Independent of the method of obstruction or Fio(2), the increase in DLno/DLco ratio was mostly due to a drop in DLco. The DLno/Dlco ratio reduced much of the intersubject variability of either DLno or DLco alone.


CONCLUSIONS
The DLno/DLco ratio increased after pulmonary artery occlusion regardless of the method of occlusion or Fio(2). This increase may be a result of a greater sensitivity of DLco than DLno to a regional reduction in capillary blood flow.
Pulmonary and Critical Care Unit, Massachusetts General Hospital and Harvard Medical School, Boston 02114, USAL. rharris@partners.org
R Scott
RS
Harris
Mehrnaz
M
Hadian
Dean R
DR
Hess
Yuchiao
Y
Chang
José G
JG
Venegas
D000818:Animals; D002196:Capillaries / Q000502:physiology; D002248:Carbon Monoxide / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D016684:Prone Position; D011651:Pulmonary Artery / Q000502:physiology*; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D012756:Sheep
D009569:Nitric Oxide; D002248:Carbon Monoxide