Re. Carlin et al., DETERMINANTS OF NITRIC-OXIDE IN EXHALED GAS IN THE ISOLATED RABBIT LUNG, American journal of respiratory and critical care medicine, 155(3), 1997, pp. 922-927
Citations number
30
Categorie Soggetti
Emergency Medicine & Critical Care","Respiratory System
Nitric oxide concentrations in the exhaled gas (NOe) increases during
various inflammatory conditions in humans and animals. Little is known
about the sources and factors that influence NOe. NOe at end expirati
on was measured by chemiluminescence in an isolated, blood-perfused ra
bbit lung. The average end-expiratory concentration over 10 breaths wa
s used. The effect of positive end-expiratory pressure (PEEP), flow ra
te, pH, hypoxia, venous pressure, and flow pulsatility on NOe were det
ermined. At constant blood flow, increasing PEEP from 1 to 5 cm H2O el
icited a reproducible increase in NOe from 49 +/- 7 to 53 +/- 8 parts
per billion (ppb) (p < 0.05). When blood pH was increased from 7.40 to
7.74 by breathing low CO2 gas, NOe rose from 45 +/- 7 to 55 +/- 7 ppb
(p < 0.001). Hypoxia caused a dose-dependent decrease in NOe from 37
+/- 3 during baseline to 23 +/- 2 during ventilation with 0%, O-2 (p <
0.01). Venous pressure elevation from 0 to 5 and 10 mm Hg decreased N
Oe from 32 +/- 5, to 26 +/- 5 and 24 +/- 5 ppb, respectively (p < 0.05
). Switching from steady to pulsatile flow (same mean flow) resulted i
n a small, albeit significant reduction in NOe; 30 +/- 4 to 28 +/- 4 p
pb (p < 0.05). Changes in flow rate between 200 and 20 ml/min were ass
ociated with small changes in NOe; however, when flow was stopped, NOe
rose substantially to 56 +/- 6 ppb (p < 0.05). The changes in NOe wer
e rapid (1 to 2 min) and reversible. The results suggest that NOe is i
nfluenced by ventilatory and hemodynamic variables, pH, and hypoxia. W
e suggest that caution must be taken when interpreting changes in exha
led NO in humans or experimental animals. Changes in total and regiona
l blood how capillary blood volume, ventilation, hypoxia, and pH shoul
d not be overlooked.