Pulmonary morphofunctional effects of mechanical ventilation with high inspiratory air flow.
OBJECTIVE
Uncertainties about the numerous degrees of freedom in ventilator settings leave many unanswered questions about the biophysical determinants of lung injury. We investigated whether mechanical ventilation with high air flow could yield lung mechanical stress even in normal animals.


METHODS
Prospective, randomized, controlled experimental study.


METHODS
University research laboratory.


METHODS
Thirty normal male Wistar rats (180-230 g).


METHODS
Rats were ventilated for 2 hrs with tidal volume of 10 mL/kg and either with normal inspiratory air flow (V') of 10 mL/s (F10) or high V' of 30 mL/s (F30). In the control group, animals did not undergo mechanical ventilation. Because high flow led to elevated respiratory rate (200 breaths/min) and airway peak inspiratory pressure (PIP,aw = 17 cm H2O), two additional groups were established to rule out the potential contribution of these variables: a) normal respiratory rate = 100 breaths/min and V' = 30 mL/sec; and b) PIP,aw = 17 cm H2O and V' = 10 mL/sec.


RESULTS
Lung mechanics and histology (light and electron microscopy), arterial blood gas analysis, and type III procollagen messenger RNA expression in lung tissue were analyzed. Ultrastructural microscopy was similar in control and F10 groups. High air flow led to increased lung plateau and peak pressures, hypoxemia, alveolar hyperinflation and collapse, pulmonary neutrophilic infiltration, and augmented type III procollagen messenger RNA expression compared with control rats. The reduction of respiratory rate did not modify the morphofunctional behavior observed in the presence of increased air flow. Even though the increase in peak pressure yielded mechanical and histologic changes, type III procollagen messenger RNA expression remained unaltered.


CONCLUSIONS
Ventilation with high inspiratory air flow may lead to high tensile and shear stresses resulting in lung functional and morphologic compromise and elevation of type III procollagen messenger RNA expression.
Garcia
Cristiane Sousa Nascimento Baez
CS
Laboratory of Pulmonary Investigation, Carlos Chagas Filho Institute of Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Abreu
Soraia Carvalho
SC
Soares
Roberta Marques Lassance
RM
Prota
Luiz Felipe Mancilha
LF
Figueira
Rogério Cruz
RC
Morales
Marcelo Marcos
MM
Capelozzi
Vera Luiza
VL
Zin
Walter Araújo
WA
Rocco
Patricia Rieken Macedo
PR
D000818:Animals; D001784:Blood Gas Analysis; D024061:Collagen Type III / Q000378:metabolism; D004195:Disease Models, Animal; D006612:High-Frequency Ventilation / Q000009:adverse effects*; D008297:Male; D011446:Prospective Studies; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D012128:Respiratory Distress Syndrome / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D015656:Respiratory Mechanics
D024061:Collagen Type III; D012333:RNA, Messenger