Exhaled Nitric Oxide Increases During High Frequency Oscillatory Ventilation in Rabbits

Abstract

summaryThis study compared the effects of high frequency oscillatory ventilation (HFOV) and intermittent mandatory ventilation (IMV) on the homeostasis of nitric oxide (NO) in the lower respiratory tract of healthy rabbits. The mechanisms underlying a putative stretch response of NO formation in the airways were further elucidated. Male New Zealand White rabbits were anaesthetized, tracheotomized and ventilated with IMV or HFOV in random order. Total NO excretion increased from 9·6 ± 0·8 nl min¢ (mean ± s.e.m.) during IMV to 22·6 ± 2·7 nl min¢ during HFOV (P < 0·001). This increase was not explained by changes of functional residual capacity (ÄFRC). A similar increase in NO excretion during HFOV was seen in isolated buffer-perfused lungs under constant circulatory conditions (P < 0·05, n = 4). Intratracheal mean COµ and NO concentrations, measured at 2·5, 5, 7·5 and 10 cm below tracheostomy, increased significantly with increasing distance into the lung during both IMV and HFOV (P < 0·001 for each comparison). At every intratracheal location of the sampling catheter, particularly low in the airways, both COµ and NO concentrations were significantly higher during HFOV than during IMV (P < 0·01 for each comparison). We conclude that HFOV increases pulmonary NO production in healthy rabbits. Increased stretch activation of the respiratory system during HFOV is suggested as a possible underlying mechanism. The increase in mean airway NO concentrations may have biological effects in the respiratory tract. Whether it can account for some of the benefits of HFOV treatment needs to be considered. introduction NO, which is continuously produced within the lower respiratory tract (Gustafsson et al. 1991;Persson et al. 1993), can be detected in the exhaled gas of most mammalian species, offering a unique possibility to study features of NO metabolism non-invasively (Gustafsson, 1997). However, the anatomic site and main cell type producing those NO molecules detected in exhaled gas is still a matter of debate (Gustafsson, 1997). Thus the extent to which the various biological functions of NO are reflected in the concentration of NO in exhaled gas merits further study. Moreover, factors influencing the amount of NO detected in exhaled gas are only beginning to evolve. We have recently shown in rabbits and guinea-pigs that lower airway NO formation is suppressed by high airway concentrations of COµ Str omberg et al. 1997;Adding et al. 1999). This rapid effect is also present in isolated buffer-perfused rabbit lungs and cannot be explained by either altered sympathetic outflow or changes of extracellular pH (Adding et al. 1999). Another mechanism to increase lower airway NO formation is revealed during increases of positive end-expiratory pressure (PEEP)

Microgravity decreases and hypergravity increases exhaled nitric oxide

“…the increase of FE NO (at 50 ml/s) from 1 to 2 G. There are a number of factors, which theoretically can influence JЈ awNO in hypergravity. Tissue stretch may induce increased NO synthesis (4,5), and during hypergravity lung tissue is certainly both stretched in some parts and compressed in others (22). Both stretch and compression may cause reductions of peripheral airway caliber.…”

“…Tissue relaxation may lead to peripheral airway lumen increase improving peripheral molecular diffusion and decreasing the net NO production as measured at the mouth. In addition, decreased mechanical stress of lung tissue might have resulted in less induction of NO formation in the lung tissue (4). Also, FE NO in microgravity might represent a much better estimate of the NO concentrations in the lungs because a more representative sample for all lung units is obtained during exhalation.…”

Exhaled Breath Condensate Nitrite and Its Relation to Tidal Volume in Acute Lung Injury

“…7 High-frequency oscillatory ventilation for example leads to an increase in exhaled nitric oxide in rabbits. 8 Preliminary data from our laboratory suggest that nitrite (NO 2 Ϫ ) concentration in BAL fluid (BALF) of rabbit lungs are influenced strongly by Vt. 9 We therefore investigated the applicability of this parameter that is also easy to determine. Increased production of nitric oxide has often been related to inflammatory processes, such as asthma and cystic fibrosis.…”

Η Επίδραση Της Τάσης Ηρεμίας Στη Σύσπαση Των Λείων Μυϊκών Ινών Τραχείας Κουνελιού. Ο Ρόλος Του Ενδογενώς Παραγόμενου Οξειδίου Του Αζώτου

“…Διάγραμμα 10. Καμπύλη δόσης-απάντησης ακετυλοχολίνης σε αυξανόμενες συγκεντρώσεις από 10"9 Μ έως 10'3 Μ σε λείες μυϊκές ίνες τραχείας ενήλικου κουνελιού σε τάση ηρεμίας Πίνακας 17 4…”