James C. Parker

Mechanisms of ventilator-induced lung injury.

ObjectivesTo describe the physiologic mechanisms of ventilator-induced lung injury and to define the major ventilator and host-dependent risk factors that contribute to such injury. Data SourcesBasic science and clinical studies related to ventilator-induced barotrauma and lung pathophysiology. Study SelectionEmphasis on controlled, experimental studies and clinical studies related to specific mechanisms. Data ExtractionPreference given to studies with quantitative end-points to assess damage and causal relationships. Data SynthesisRelated studies are integrated to obtain basic mechanisms of damage where possible. ConclusionsVentilation with high tidal volumes can increase vascular filtration pressures; produce stress fractures of capillary endothelium, epithelium, and basement membrane; and cause lung rupture. Mechanical damage leads to leakage of fluid, protein, and blood into tissue and air spaces or leakage of air into tissue spaces. This process is followed by an inflammatory response and possibly a reduced defense against infection. Predisposing factors for lung injury are high peak inspiratory volumes and pressures, a high mean airway pressure, structural immaturity of lung and chest wall, surfactant insufficiency or inactivation, and preexisting ing disease. Damage can be minimized by preventing overdistention of functional lung units during therapeutic ventilation. (Crit Care Med 1993; 21:131–143)

TRPV4 channels augment macrophage activation and ventilator-induced lung injury

We have previously implicated transient receptor potential vanilloid 4 (TRPV4) channels and alveolar macrophages in initiating the permeability increase in response to high peak inflation pressure (PIP) ventilation. Alveolar macrophages were harvested from TRPV4(-/-) and TRPV4(+/+) mice and instilled in the lungs of mice of the opposite genotype. Filtration coefficients (K(f)) measured in isolated perfused lungs after ventilation with successive 30-min periods of 9, 25, and 35 cmH(2)O PIP did not significantly increase in lungs from TRPV4(-/-) mice but increased >2.2-fold in TRPV4(+/+) lungs, TRPV4(+/+) lungs instilled with TRPV4(-/-) macrophages, and TRPV4(-/-) lungs instilled with TRPV4(+/+) macrophages after ventilation with 35 cmH(2)O PIP. Activation of TRPV4 with 4-alpha-phorbol didecanoate (4alphaPDD) significantly increased intracellular calcium, superoxide, and nitric oxide production in TRPV4(+/+) macrophages but not TRPV4(-/-) macrophages. Cross-sectional areas increased nearly 3-fold in TRPV4(+/+) macrophages compared with TRPV4(-/-) macrophages after 4alphaPDD. Immunohistochemistry staining of lung tissue for nitrotyrosine revealed increased amounts in high PIP ventilated TRPV4(+/+) lungs compared with low PIP ventilated TRPV4(+/+) or high PIP ventilated TRPV4(-/-) lungs. Thus TRPV4(+/+) macrophages restored susceptibility of TRPV4(-/-) lungs to mechanical injury. A TRPV4 agonist increased intracellular calcium and reactive oxygen and nitrogen species in harvested TRPV4(+/+) macrophages but not TRPV4(-/-) macrophages. K(f) increases correlated with tissue nitrotyrosine, a marker of peroxynitrite production.

Barotrauma and microvascular injury in lungs of nonadult rabbits: effect of ventilation pattern.

To study the pulmonary microvascular injury produced by ventilation barotrauma, the isolated perfused lungs of 4 to 6-wk-old New Zealand white rabbits were ventilated by one of the following methods: peak inspiratory pressure (PIP) 23 cm H2O, gas flow rate 1.1 L/min (group 1); PIP 27 cm H2O, gas flow rate 6.9 L/min (group 2); PIP 50 cm H2O, gas flow rate 1.9 L/min (group 3); or PIP 53 cm H2O, gas flow rate 8.3 L/min (group 4). Microvascular permeability was assessed using the capillary filtration coefficient (Kfc) before and 5, 30, and 60 min after a 15-min period of ventilation. Baseline Kfc was not significantly different between groups. A significant increase over the baseline Kfc was noted at 60 min in group 2 and in all postventilation Kfc values in groups 3 and 4 (p less than .05). Group 1 Kfc values did not change significantly after ventilation. At all post-ventilation times, values for Kfc were significantly greater in groups 3 and 4 than in group 1 (p less than .05). Group 4 Kfc values were significantly greater than those in group 2 at 5 and 30 min postventilation. These data indicate that high PIP, and to a lesser extent, high gas flow rates cause microvascular injury in the compliant nonadult lung and suggest that the combination of high PIP and high gas flow rates are the most threatening to microvascular integrity.

Analysis of altered capillary pressure and permeability after thermal injury

In order to investigate the effects of thermal injury on microvascular hemodynamics and permeability, hindpaw arterial (PA), venous (PV), and capillary (PC) pressures, blood (QB) and lymph (QL) flows, and lymph (CL) and plasma (CP) total protein concentrations were measured before and for 3 hr after a 10-sec 100 degrees C scald burn in 11 dogs. Prior to injury in eight experiments (Group I--permeability analysis) venous pressure was elevated by outflow restriction until the minimal CL/CP was obtained. In three experiments (Group II--hemodynamic analysis) outflow was not restricted. Lymph and plasma protein fractions ranging in size from 37 to 120 A were measured using gradient gel electrophoresis and capillary equivalent pore sizes were calculated. In the early postburn period, PC increased from 24 +/- 2 (mean +/- SE) to 47 +/- 5 mm Hg (P less than 0.05) and precapillary resistance (RA) decreased from 6.6 +/- 0.2 to 2.5 +/- 0.2 mm Hg/ml/min/100 g (P less than 0.05) while postcapillary resistance (RV) remained unchanged. Pre- to postcapillary resistance (RA/RV) fell by 74%. The reflection coefficient for total proteins (calculated as sigma = 1 - CL/CP) decreased from 0.87 +/- 0.01 to 0.45 +/- 0.02 (P less than 0.01). Permeability of the postburn capillary endothelium was described by using two populations of equivalent pores. Preburn pore radii were 50 and 300 A with 13% of the capillary filtrate passing through the large pores. Pore radii increased after injury to 70 and 400 A with 49% of the filtrate passing through the large pores. The postburn total tissue filtration coefficient (Kf) increased to 2.4 times the control. Over the first 3 hr postburn, 53% of the increase in capillary filtration was attributable to increased capillary pressure and 47% to increased permeability. We conclude that the early rapid edema formation following thermal injury is the result of marked increases in both capillary filtration pressure and filtration through large nonsieving pores.

Increased sensitivity to mechanical ventilation after surfactant inactivation in young rabbit lungs.

ObjectivesTo study the individual and combined effects of surfactant inactivation and mechanical ventilation on pulmonary microvascular permeability and lung compliance. DesignProspective, controlled trial. An isolated, perfused, lung model of surfactant inactivation and mechanical ventilation at 15,30, and 45 cm H2O peak inspiratory pressure was developed in young (4 to 6 wks) New Zealand white rabbits. SettingLaboratory of a university-affiliated medical school. Measurements and Main ResultsIsolated, perfused lungs were prepared for measurement of the capillary filtration coefficient before and after one of four interventions: instillation of dioctyl succinate, a surfactant inactivator, without ventilation (group 1); ventilation without dioctyl succinate at 15, 30, or 45 cm H2O peak inspiratory pressure (group 2); ventilation after dioctyl succinate pretreatment at 15,30, or 45 cm H2O peak inspiratory pressure (group 3); and control lungs without dioctyl succinate or ventilation (group 4). A significant increase in the capillary filtration coefficient was noted after dioctyl succinate treatment alone, after ventilation alone at 45 cm H2O peak inspiratory pressure, and after dioctyl succinate plus ventilation at 15,30, and 45 cm H2O peak inspiratory pressure. Dioctyl succinate plus ventilation produced a significantly greater increase in the capillary filtration coefficient than ventilation alone at 15 and 45 cm H2O peak inspiratory pressure. ConclusionsThese data suggest that ventilation after surfactant inactivation is more injurious to the pulmonary microvasculature than ventilation alone, and that generalized lung over-distention is not the primary mechanism for microvascular injury in the diseased, noncompliant lung. The increases seen in the capillary filtration coefficient in postventilated surfactant inactivated lungs, even at low-ventilation pressures, suggest that low peak inspiratory pressures do not overdistend the dioctyl succinate-treated lung. (Crit Care Med 1992; 20:635–640)

Reduction in alveolar macrophages attenuates acute ventilator induced lung injury in rats

ObjectiveAlveolar macrophages are the sentinel cell for activation of the inflammatory cascade when the lung is exposed to noxious stimuli. We investigated the role of macrophages in mechanical lung injury by comparing the effect of high-volume mechanical ventilation with or without prior depletion of macrophages.Design and settingRandomized sham-controlled animal study in anesthetized rats.MethodsLung injury was induced by 15 min of mechanical ventilation (intermittent positive pressure ventilation) using high peak pressures and zero end-expiratory pressure. The mean tidal volume was 40 ± 0.7 ml/kg. One group of animals was killed immediately after this period of volutrauma (HV), while in a second group normoventilation was continued for 2 h at a tidal volume less than 10 ml/kg (HV-LV). One-half of the animals were depleted of alveolar macrophages by pretreatment with intratracheal liposomal clodronate (CL2MDP).MeasurementsArterial blood gas, blood pressure. After kill: lung static pressure volume curves, bronchoalveolar fluid concentration for protein, macrophage inflammatory protein 2, tumor necrosis factor α, and wet/dry lung weight ratio (W/D).ResultsDuring HV and HV+LV oxygenation, lung compliance, and alveolar stability were better preserved in animals pretreated with CL2MDP. In both groups W/D ratio was significantly greater in ventilated than in nonventilated animals (4.5 ± 0.6), but the increase in W/D was significantly less in CL2MDP treated HV and HV-LV groups (6.1 ± 0.4, 6.6 ± 0.6) than in the similarly ventilated nontreated groups (8.7 ± 0.2 and 9.2 ± 0.5).ConclusionsAlveolar macrophages participate in the early phase of ventilator-induced lung injury.

Age affects susceptibility to pulmonary barotrauma in rabbits

Objective.We studied the effect of age on the development of pulmonary barotrauma after mechanical ventilation with high peak inspiratory pressures (PIP). Design.Young (4 to 6 wk old) and adult rabbits were ventilated for 1 hr at PIPs of 15, 30, and either 45 cm H2O (young group) or 55 cm H2O (adult group). Measurements and Main Results.The pulmonary capillary filtration coefficient (Kf, c) was measured in an isolated lung perfusion system after the animals were killed. In young rabbits, Kf, c increased significantly from the 15 cm H2O PIP value in both the 30 cm H2O (55%) and 45 cm H2O (507%) PIP groups, whereas Kf, c was increased in adult rabbits only in the 55 cm H2O (113%) PIP group. Kf, c was significantly (p < .01) higher in young rabbits than in adult rabbits after ventilation, with every level of PIP being 91% higher at 15 cm H2O PIP and 440% higher at 45 to 55 cm H2O PIP. Also, a greater incidence of pneumothorax and airleaks was observed in the young rabbits. Pressure-volume loops demonstrated that the young rabbits had more compliant lungs and chest wall than adult rabbits. Conclusions.These data indicate that the lungs of young rabbits had a higher baseline microvascular permeability and were more susceptible to the development of ventilator-induced increased microvascular permeability. More compliant lungs and chest wall and the larger distending volumes attained at each peak airway pressure appear to be the mechanisms. (Crit Care Med 1991; 19:390)

Automated region of interest analysis of dynamic Ca2+ signals in image sequences

Ca(2+) signals are commonly measured using fluorescent Ca(2+) indicators and microscopy techniques, but manual analysis of Ca(2+) measurements is time consuming and subject to bias. Automated region of interest (ROI) detection algorithms have been employed for identification of Ca(2+) signals in one-dimensional line scan images, but currently there is no process to integrate acquisition and analysis of ROIs within two-dimensional time lapse image sequences. Therefore we devised a novel algorithm for rapid ROI identification and measurement based on the analysis of best-fit ellipses assigned to signals within noise-filtered image sequences. This algorithm was implemented as a plugin for ImageJ software (National Institutes of Health, Bethesda, MD). We evaluated the ability of our algorithm to detect synthetic Gaussian signal pulses embedded in background noise. The algorithm placed ROIs very near to the center of a range of signal pulses, resulting in mean signal amplitude measurements of 99.06 ± 4.11% of true amplitude values. As a practical application, we evaluated both agonist-induced Ca(2+) responses in cultured endothelial cell monolayers, and subtle basal endothelial Ca(2+) dynamics in opened artery preparations. Our algorithm enabled comprehensive measurement of individual and localized cellular responses within cultured cell monolayers. It also accurately identified characteristic Ca(2+) transients, or Ca(2+) pulsars, within the endothelium of intact mouse mesenteric arteries and revealed the distribution of this basal Ca(2+) signal modality to be non-Gaussian with respect to amplitude, duration, and spatial spread. We propose that large-scale statistical evaluations made possible by our algorithm will lead to a more efficient and complete characterization of physiologic Ca(2+)-dependent signaling.

Mitochondrial-targeted DNA repair enzyme 8-oxoguanine DNA glycosylase 1 protects against ventilator-induced lung injury in intact mice

This study tested the hypothesis that oxidative mitochondrial-targeted DNA (mtDNA) damage triggered ventilator-induced lung injury (VILI). Control mice and mice infused with a fusion protein targeting the DNA repair enzyme, 8-oxoguanine-DNA glycosylase 1 (OGG1) to mitochondria were mechanically ventilated with a range of peak inflation pressures (PIP) for specified durations. In minimal VILI (1 h at 40 cmH(2)O PIP), lung total extravascular albumin space increased 2.8-fold even though neither lung wet/dry (W/D) weight ratios nor bronchoalveolar lavage (BAL) macrophage inflammatory protein (MIP)-2 or IL-6 failed to differ from nonventilated or low PIP controls. This increase in albumin space was attenuated by OGG1. Moderately severe VILI (2 h at 40 cmH(2)O PIP) produced a 25-fold increase in total extravascular albumin space, a 60% increase in W/D weight ratio and marked increases in BAL MIP-2 and IL-6, accompanied by oxidative mitochondrial DNA damage, as well as decreases in the total tissue glutathione (GSH) and GSH/GSSH ratio compared with nonventilated lungs. All of these injury indices were attenuated in OGG1-treated mice. At the highest level of VILI (2 h at 50 cmH(2)O PIP), OGG1 failed to protect against massive lung edema and BAL cytokines or against depletion of the tissue GSH pool. Interestingly, whereas untreated mice died before completing the 2-h protocol, OGG1-treated mice lived for the duration of observation. Thus mitochondrially targeted OGG1 prevented VILI over a range of ventilation times and pressures and enhanced survival in the most severely injured group. These findings support the concept that oxidative mtDNA damage caused by high PIP triggers induction of acute lung inflammation and injury.

Analysis of lymphatic protein data: IV. Comparison of the different methods used to estimate reflection coefficients and permeability-surface area products

The reflection coefficients (σ) and permeability surface area products ( PS ) were estimated for total plasma proteins in dog-paw lymph. σ and PS values were estimated using several existing mathematical formulations. σ and PS were functions of lymph flow at levels below 10 μl/min. As lymph flow increased to high values, σ approached 0.90 and PSΔC approached 0 for all analyses. At low-lymph-flow states convection provides for 70% of the protein transport and diffusion only 30%. At high lymph flows, protein transport is predominantly convective and diffusion appears to approach zero. The same results were obtained using lymph collected from flexed and unflexed paws.