Effects of ventilatory pattern on exhaled nitric oxide in mechanically ventilated rabbits.
BACKGROUND
Nitric oxide [NOexp] is present in exhaled air in many species. During experiments on pressure-controlled inverse ratio ventilation (PCIRV) in rabbits, increased [NOexp] was observed during PCIRV. The present study was undertaken to clarify which component of PCIRV increased [NOexp].


METHODS
Three groups of six New Zealand White rabbits were anaesthetised and mechanically ventilated. Exhaled nitric oxide, lung mechanics and gas exchange were measured using an experimental protocol designed to assess the effects of variations in 1) flow profile, 2) inspiratory time and 3) time-weighted tidal volume. Ventilator settings used were volume and pressure control ventilation at I:E ratios of 1:2 and 4:1.


RESULTS
Constant and decelerating flow gave comparable [NOexp] levels (20.0 +/- 6.4 vs. 21.9 +/- 7.7 ppb, n.s.) when time-weighted tidal volume was kept constant. Using conventional (I:E 1:2) or inverted (I:E 4:1) I:E ratios in combination with decelerating flow and constant time-weighted tidal volumes did not alter [NOexp] (26.0 +/- 3.6 vs. 24.0 +/- 5.8 ppb, n.s.). An increased time-weighted tidal volume produced by pressure control with an I:E ratio of 4:1 increased [NOexp] (29.6 +/- 7.4) in comparison to constant (19.3 +/- 4.1, P < 0.05) and decelerating flow ventilation (19.6 +/- 3.6, P < 0.05) with I:E ratios of 1:2.


CONCLUSIONS
The exhaled NO concentration was affected by ventilator setting. Increased levels of [NOexp] were observed with increases in time-weighted tidal volume, whereas changes in flow pattern and inspiratory time did not seem to influence airway NO production or release.
Forsberg
S
S
Department of Medicine, Södersjukhuset, Stockholm, Uppsala University Hospital, Sweden.
Ludwigs
U
U
Hedenstierna
G
G
D000818:Animals; D005260:Female; D016166:Free Radical Scavengers / Q000378:metabolism*; D001239:Inhalation / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D011312:Pressure; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology; D011817:Rabbits; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology; D013997:Time Factors
D016166:Free Radical Scavengers; D009569:Nitric Oxide