Protective effect of lung inflation in reperfusion-induced lung microvascular injury

We used the isolated-perfused rat lung model to study the influence of pulmonary ventilation and surfactant instillation on the development of postreperfusion lung microvascular injury. We hypothesized that the state of lung inflation during ischemia contributes to the development of the injury during reperfusion. Pulmonary microvascular injury was assessed by continuously monitoring the wet lung weight and measuring the vessel wall (125)I-labeled albumin ((125)I-albumin) permeability-surface area product (PS). Sprague-Dawley rats (n = 24) were divided into one control group and five experimental groups (n = 4 rats per group). Control lungs were continuously ventilated with 20% O(2) and perfused for 120 min. All lung preparations were ventilated with 20% O(2) before the ischemia period and during the reperfusion period. The various groups differed only in the ventilatory gas mixtures used during the flow cessation: group I, ventilated with 20% O(2); group II, ventilated with 100% N(2); group III, lungs remained collapsed and unventilated; group IV, same as group III but pretreated with surfactant (4 ml/kg) instilled into the airway; and group V, same as group III but saline (4 ml/kg) was instilled into the airway. Control lungs remained isogravimetric with baseline (125)I-albumin PS value of 4.9 +/- 0.3 x 10(-3) ml x min(-1) x g wet lung wt(-1). Lung wet weight in group III increased by 1.45 +/- 0.35 g and albumin PS increased to 17.7 +/- 2.3 x 10(-3), indicating development of vascular injury during the reperfusion period. Lung wet weight and albumin PS did not increase in groups I and II, indicating that ventilation by either 20% O(2) or 100% N(2) prevented vascular injury. Pretreatment of collapsed lungs with surfactant before cessation of flow also prevented the vascular injury, whereas pretreatment with saline vehicle had no effect. These results indicate that the state of lung inflation during ischemia (irrespective of gas mixture used) and supplementation of surfactant prevent reperfusion-induced lung microvascular injury.     

Contribution of tree structures in the lung to lung elastic recoil

The direct contribution of forces in tree structures in the lung to lung recoil pressure and changes in recoil pressure induced by alterations of the forces are analyzed. The analysis distinguishes the contributions of axial and circumferential tensions in the trees and indicates that only axial tensions directly contribute to static recoil. This contribution is derived from analysis of the axial forces transmitted across a random plane transecting the lung. The change in recoil pressure induced by changes in axial tension is similarly derived. Alterations of circumferential tensions in the trees indirectly change recoil by causing nonuniform deformations of the surrounding lung parenchyma, and a continuum elasticity solution for the stress induced by the deformations is derived. Sample calculations are presented for the airway tree based on available data on airway morphometric and mechanical properties. The increase in recoil pressure accompanying increases in axial and circumferential tensions with contraction of airway smooth muscle is also analyzed. The calculations indicate that axial stresses in the airway tree out to bronchioles directly contribute only a small fraction of the static recoil pressure. However, it is found that contraction of smooth muscle in these airways can increase recoil pressure appreciably (10-20%), mainly by the deformation of the parenchyma with increases in circumferential tension in smaller airways. The results indicate that the geometric and mechanical properties of the airway tree are such that only peripheral elements of the tree can substantially affect the elastic properties of the lung. The possible contributions of vascular trees for which data on mechanical and morphometric properties are more limited are also discussed.     

Identification of bronchioalveolar stem cells in normal lung and lung cancer

Injury models have suggested that the lung contains anatomically and functionally distinct epithelial stem cell populations. We have isolated such a regional pulmonary stem cell population, termed bronchioalveolar stem cells (BASCs). Identified at the bronchioalveolar duct junction, BASCs were resistant to bronchiolar and alveolar damage and proliferated during epithelial cell renewal in vivo. BASCs exhibited self-renewal and were multipotent in clonal assays, highlighting their stem cell properties. Furthermore, BASCs expanded in response to oncogenic K-ras in culture and in precursors of lung tumors in vivo. These data support the hypothesis that BASCs are a stem cell population that maintains the bronchiolar Clara cells and alveolar cells of the distal lung and that their transformed counterparts give rise to adenocarcinoma. Although bronchiolar cells and alveolar cells are proposed to be the precursor cells of adenocarcinoma, this work points to BASCs as the putative cells of origin for this subtype of lung cancer.     

Sound transmission in the lung as a function of lung volume.

We were interested in how the transmission of sound through the lung was affected by varying air content in intact humans as a method of monitoring tissue properties noninvasively. To study this, we developed a method of measuring transthoracic sound transit time accurately. We introduced a "coded" sound at the mouth and measured the transit time at multiple microphones placed over the chest wall by using a 16-channel lung sound analyzer (Stethographics). We used a microphone placed over the neck near the trachea as our reference and utilized cross-correlation analysis to calculate the transit times. The use of the coded sound, composed of a mix of frequencies from 130 to 150 Hz, greatly reduced the ambiguity of the cross-correlation function. The measured transit time varied from 1 ms at the central locations to 5 ms at the lung bases. Our results also indicated that transit time at all locations decreased with increasing lung volume. We found that these results can be described in terms of a model in which sound transmission through the lung is treated as a combination of free-space propagation through the trachea and a propagation through a two-phase system in the parenchyma.     

Altered fatty acid composition of lung surfactant phospholipids in interstitial lung disease

Deterioration of pulmonary surfactant function has been reported in interstitial lung disease; however, the molecular basis is presently unclear. We analyzed fatty acid (FA) profiles of several surfactant phospholipid classes isolated from large-surfactant aggregates of patients with idiopathic pulmonary fibrosis (IPF; n = 12), hypersensitivity pneumonitis (n = 5), and sarcoidosis (n = 12). Eight healthy individuals served as controls. The relative content of palmitic acid in phosphatidylcholine was significantly reduced in IPF (66.8 +/- 2.5%; means +/- SE; P < 0.01) but not in hypersensitivity pneumonitis (78.5 +/- 1.8%) and sarcoidosis (78.2 +/- 3.1%; control 80.1 +/- 0.7%). In addition, the phosphatidylglycerol FA profile was significantly altered in the IPF patients, with a lower relative content of its major FA, oleic acid, at the expense of saturated FA. In the phosphatidylcholine class, a significant correlation between the impairment of biophysical surfactant function and decreased percentages of palmitic acid was noted. We conclude that significant alterations in the FA profile of pulmonary surfactant phospholipids occur predominantly in IPF and may contribute to the disturbances of alveolar surface activity in this disease.     

GST polymorphism and cytogenetic changes in lung tissues of lung cancer patients

Carriers of GSTT1 gene deletion were found to be more subject to a risk of emerging non-small-cell lung cancer (NSLC) than those of normal GSTT1(+) genotype. A study of the relation between GST gene polymorphism and cytogenetic indices in lung cancer patients has shown a significant excess of the group average level in cells with micronuclei in NSLC patients with GSTT1(?). The frequency of cells with micronuclei was higher in smoking patients with a mutant genotype than in smoking carriers of the GSTT1(+) genotype.     

Effects of lung volume on lung and chest wall mechanics in rats

To investigate the effect of lung volume onchest wall and lung mechanics in the rats, we measured theimpedance (Z) under closed- and open-chest conditions at variouspositive end-expiratory pressures (0-0.9 kPa) by using acomputer-controlled small-animal ventilator (T. F. Schuessler andJ. H. T. Bates. IEEE Trans. Biomed. Eng. 42: 860-866, 1995) that we have developed fordetermining accurately the respiratory Z in small animals. The Z oftotal respiratory system and lungs was measured with small-volumeoscillations between 0.25 and 9.125 Hz. The measured Z was fitted to amodel that featured a constant-phase tissue compartment (withdissipation and elastance characterized by constantsG andH, respectively) and a constant airwayresistance (Z. Hantos, B. Daroczy, B. Suki, S. Nagy, and J. J. Fredberg. J. Appl.Physiol. 72: 168-178, 1992). We matched the lungvolume between the closed- and open-chest conditions by using thequasi-static pressure-volume relationship of the lungs to calculate Zas a function of lung volume. Resistance decreased with lung volume andwas not significantly different between total respiratory system andlungs. However, G andH of the respiratory system weresignificantly higher than those of the lungs. We conclude that chestwall in rats has a significant influence on tissue mechanics of thetotal respiratory system.

     

Effect of lung resection on blood lactate threshold in lung cancer patients

We studied the effect of a decrease in vital capacity (VC) on the blood lactate threshold detected during exercise in 16 preoperative (PRE) and 10 postoperative (POST) lung cancer patients who had undergone lobectomy or pneumonectomy. The PRE patients were selected on the basis of having normal preoperative pulmonary function. The POST patients were selected on the basis of having normal preoperative pulmonary function and a postoperative VC of less than 80%. The oxygen consumption/body surface area at a 2.2 m.mol.l-1 arterial lactate concentration (VO2/BSA at La-2.2) was adopted as the blood lactate threshold. VC/BSA in the POST group significantly correlated with VO2/BSA at La-2.2 (r = 0.85, P less than 0.01), but not in the PRE group. SaO2 at La-2.2 was 95.4 +/- 1.5% in the PRE group and 95.2 +/- 1.3% in the POST group. SaO2 at La-2.2 did not correlated with VC/BSA in either group. The hemoglobin concentration (Hb) in the arterial blood correlated significantly with VC/BSA in the POST group (r = 0.65, P less than 0.05) but not in the PRE group. These results indicate that VO2/BSA at La-2.2 was restricted by VC in patients with restrictive pulmonary function disorder. Of the three elements of oxygen delivery, Hb was a limiting factor for VO2/BSA at La-2.2 but SaO2 was not. Cardiac output, which was not measured in our study, was speculated to be another limiting factor for VO2/BSA at La-2.2.     

Activation of calpains mediates early lung neutrophilic inflammation in ventilator-induced lung injury

Lung inflammatory responses in the absence of infection are considered to be one of primary mechanisms of ventilator-induced lung injury. Here, we determined the role of calpain in the pathogenesis of lung inflammation attributable to mechanical ventilation. Male C57BL/6J mice were subjected to high (28 ml/kg) tidal volume ventilation for 2 h in the absence and presence of calpain inhibitor I (10 mg/kg). To address the isoform-specific functions of calpain 1 and calpain 2 during mechanical ventilation, we utilized a liposome-based delivery system to introduce small interfering RNAs targeting each isoform in pulmonary vasculature in vivo. Mechanical ventilation with high tidal volume induced rapid (within minutes) and persistent calpain activation and lung inflammation as evidenced by neutrophil recruitment, production of TNF-α and IL-6, pulmonary vascular hyperpermeability, and lung edema formation. Pharmaceutical calpain inhibition significantly attenuated these inflammatory responses caused by lung hyperinflation. Depletion of calpain 1 or calpain 2 had a protective effect against ventilator-induced lung inflammatory responses. Inhibition of calpain activity by means of siRNA silencing or pharmacological inhibition also reduced endothelial nitric oxide (NO) synthase (NOS-3)-mediated NO production and subsequent ICAM-1 phosphorylation following high tidal volume ventilation. These results suggest that calpain activation mediates early lung inflammation during ventilator-induced lung injury via NOS-3/NO-dependent ICAM-1 phosphorylation and neutrophil recruitment. Inhibition of calpain activation may therefore provide a novel and promising strategy for the prevention and treatment of ventilator-induced lung injury.