Spontaneous breathing affects the spatial ventilation and perfusion distribution during mechanical ventilatory support.
OBJECTIVE
In acute respiratory failure, gas exchange improves with spontaneous breathing during airway pressure release ventilation (APRV). The mechanisms for this improvement are not fully clear. We have shown that APRV with spontaneous breathing reopens nonaerated lung tissue in dorsal juxtadiaphragmatic regions. We hypothesized that spontaneous breathing during APRV may redistribute ventilation and perfusion toward these reopened regions.


METHODS
Prospective, randomized, controlled study.


METHODS
Animal research laboratory


METHODS
Twenty controlled mechanically ventilated pigs.


METHODS
Lung injury was induced by injection of oleic acid into the central circulation; thereafter, pigs were randomized to APRV with or without spontaneous breathing. To induce spontaneous breathing during APRV with spontaneous breathing, the mechanical respiratory rate was decreased by 50% in this group.


RESULTS
We measured respiratory mechanics, hemodynamics, gas exchange including the multiple inert gas elimination technique, and the spatial ventilation and perfusion distribution using single photon emission tomography. At similar minute ventilation and airway pressures, shunt remained stable during APRV with spontaneous breathing, whereas it increased during APRV without spontaneous breathing during the 2-hr study period (p = .006). Single photon emission tomography showed more ventilation (p < .001) and pulmonary blood (p < .025) flow in dorsal, juxtadiaphragmatic lung regions when spontaneous breathing was present.


CONCLUSIONS
The beneficial effects of spontaneous breathing on intrapulmonary shunt and oxygenation are explained both by increased ventilation of aerated dependent lung tissue and by opening up nonaerated tissue so that ventilation is distributed to a larger share of the lung. Redistribution of perfusion is possibly secondary to the altered ventilation. The overall effect is a more efficient use of available lung tissue for gas exchange.
Neumann
Peter
P
Department of Clinical Physiology, Universities of Göttingen and Bonn, Germany.
Wrigge
Hermann
H
Zinserling
Jörg
J
Hinz
Jose
J
Maripuu
Enn
E
Andersson
Lars G
LG
Putensen
Christian
C
Hedenstierna
Göran
G
D000818:Animals; D001794:Blood Pressure; D045422:Continuous Positive Airway Pressure; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange; D011877:Radionuclide Imaging; D012119:Respiration; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013552:Swine; D014692:Ventilation-Perfusion Ratio