High alveolar surface tension increases clearance of technetium 99m diethylenetriamine-pentaacetic acid

Keratinocyte growth factor-2 intratracheal instillation significantly attenuates ventilator-induced lung injury in rats

Preservation or restoration of normal alveolar epithelial barrier function is crucial for pulmonary oedema resolution. Keratinocyte growth factor-2 (KGF-2), a potent epithelial cell mitogen, may have a role in preventing ventilator-induced lung injury (VILI), which occurs frequently in mechanically ventilated patients. The aim of the study was to test the role of KGF-2 in VILI in rats. Forty healthy adult male Sprague-Dawley rats were randomly allocated into four groups, where rats in Groups HVZP (high-volume zero positive end-expiratory pressure) and HVZP+KGF-2 were given intratracheally equal PBS and 5 mg/kg KGF-2 72 hrs before 4 hrs HVZP ventilation (20 ml/kg), respectively, while PBS and KGF-2 were administered in the same manner in Groups Control and KGF-2, which underwent tracheotomy only with spontaneous breathing. Inflammatory cytokines (tumour necrosis factor-α, macrophage inflammatory protein 2), neutrophil and total protein levels in bronchoalveolar lavage fluid and surfactant protein mRNA expression in lung tissue were detected; the number of alveolar type II cells, lung water content and lung morphology were also evaluated. The results indicate that pre-treatment with KGF-2 showed dramatic improvement in lung oedema and inflammation compared with HVZP alone, together with increased surfactant protein mRNA and alveolar type II cells. Our results suggest that KGF-2 might be considered a promising prevention for human VILI or other acute lung injury diseases.

Toxicity Profile of Solvents by Aspiration Approach for Topical Agent Delivery to Respiratory Tract Epithelium

Agent solubility is a problem for aspiration of agents into lungs for chemopreventive efficacy evaluation, since many agents have to be dissolved in solvents. These solvents may be toxic to the lung epithelium. A study was conducted in female A/J mice to determine toxicity of different solvent concentrations by using saline, dimethyl sulfoxide (DMSO), ethanol, polyethylene glycol 400 (PEG-400), and labrasol for 1, 5, and 28 days via aspiration route. Toxicity was determined by measuring changes in body weight and bronchoalveolar lavage fluid (BALF). No significant difference was observed in body weight, differential cell counts, lactate dehydrogenase (LDH) and total protein in all solvent groups compared to saline by 28 days except 50% ethanol. However, myeloperoxidase (MPO) and macrophage inflammatory protein-2 (MIP-2) showed significant increase in 2% and 10% DMSO, 10% ethanol, 0.1% and 2% PEG-400, and 1% labrasol by longer dosing. All solvents except for 10% ethanol and 2% PEG-400 are suitable for agent aspiration.

Dependence of lung injury on surface tension during low-volume ventilation in normal open-chest rabbits

To evaluate the role of pulmonary surfactant in the prevention of lung injury caused by mechanical ventilation (MV) at low end-expiratory volumes, lung mechanics and morphometry were assessed in three groups of eight normal, open-chest rabbits ventilated for 3-4 h at zero end-expiratory pressure (ZEEP) with physiological tidal volumes (Vt = 10 ml/kg). One group was left untreated (group A); the other two received surfactant intratracheally (group B) or aerosolized dioctylsodiumsulfosuccinate (group C) before MV on ZEEP. Relative to initial MV on positive end-expiratory pressure (PEEP; 2.3 cmH(2)O), quasi-static elastance (Est) and airway (Rint) and viscoelastic resistance (Rvisc) increased on ZEEP in all groups. After restoration of PEEP, only Rint (124%) remained elevated in group A, only Est (36%) was significantly increased in group B, whereas in group C, Est, Rint, and Rvisc were all markedly augmented (274, 253, and 343%). In contrast, prolonged MV on PEEP had no effect on lung mechanics of eight open-chest rabbits (group D). Lung edema developed in group C (wet-to-dry ratio = 7.1), but not in the other groups. Relative to group D, both groups A and C, but not B, showed histological indexes of bronchiolar injury, whereas all groups exhibited an increased number of polymorphonuclear leukocytes in alveolar septa, which was significantly greater in group C. In conclusion, administration of exogenous surfactant largely prevents the histological and functional damage of prolonged MV at low lung volumes, whereas surfactant dysfunction worsens the functional alterations, also because of edema formation and, possibly, increased inflammatory response.

Visual validation of the mechanical stabilizing effects of positive end-expiratory pressure at the alveolar level

BACKGROUND

Positive end-expiratory pressure (PEEP) reduces ventilator-induced lung injury (VILI), presumably by mechanically stabilizing alveoli and decreasing intrapulmonary shear. Although there is indirect support for this concept in the literature, direct evidence is lacking. In a surfactant depletion model of acute lung injury we observed unstable alveolar mechanics referred to as repeated alveolar collapse and expansion (RACE) as measured by changes in alveolar area from inspiration to expiration (I - E(Delta)). We tested the hypothesis that over a range of tidal volumes PEEP would prevent RACE by mechanically stabilizing alveoli.

MATERIALS AND METHODS

Yorkshire pigs were randomized to three groups: control (n = 4), Tween (surfactant-deactivating detergent) (n = 4), and Tween + PEEP (7 cm H(2)O) (n = 4). Using in vivo video microscopy individual alveolar areas were measured with computer image analysis at end inspiration and expiration over consecutive increases in tidal volume (7, 10, 15, 20, and 30 cc/kg.) I - E(Delta) was calculated for each alveolus.

RESULTS

Surfactant deactivation significantly increased I - E(Delta) at every tidal volume compared to controls (P < 0.05). PEEP prevented this change, returning I - E(Delta) to control levels over a spectrum of tidal volumes.

CONCLUSIONS

RACE occurs in our surfactant deactivation model of acute lung injury. PEEP mechanically stabilizes alveoli and prevents RACE over a range of tidal volumes. This is the first study to visually document the existence of RACE and the mechanical stabilizing effects of PEEP at the alveolar level. The ability of PEEP to stabilize alveoli and reduce shear during mechanical ventilation has important implications for therapeutic strategies directed at VILI and acute respiratory distress syndrome.

Pulmonary clearance of 99mTc-DTPA in experimental surfactant dysfunction treated with surfactant instillation

BACKGROUND

Breakdown of the alveolo-capillary barrier is a characteristic feature of respiratory distress syndrome. Restoration of alveolo-capillary barrier function may be an important aspect of surfactant replacement therapy. We examined the effect of surfactant instillation on alveolo-capillary barrier function in an experimental model of surfactant dysfunction by measuring pulmonary clearance of 99mTc-DTPA.

METHODS

Nineteen rabbits were tracheotomized and mechanically ventilated. Surfactant dysfunction was induced by administration of a synthetic detergent in aerosol form. Detergent was given to 13 rabbits; seven rabbits were then treated with instillation of natural surfactant, whereas six rabbits received saline. Six rabbits were used as untreated controls. An aerosol of 99mTc-DTPA was administered to all animals and the pulmonary clearance was measured with a gamma camera.

RESULTS

99mTc-DTPA cleared from the lungs with a half-life of 71 +/- 22 min in the control animals, 21.4 +/- 7.4 min in the surfactant-treated animals and 5.8 +/- 1.5 min in the saline-treated animals. The difference in half-life between groups was highly significant (P < 0.001). There was no change in arterial oxygenation or compliance in controls or in animals treated with saline. In animals treated with surfactant, a small transient reduction in arterial oxygen tension and a more long-standing reduction in compliance were observed.

CONCLUSION

Surfactant treatment thus significantly attenuated the effect of detergent treatment but did not restore alveolo-capillary transfer of 99mTc-DTPA to normal.

Pulmonary 99mTc-human serum albumin clearance and effects of surfactant replacement after lung lavage in rabbits

OBJECTIVE

Pulmonary clearance of technetium-labeled human serum albumin was measured in order to investigate whether the surfactant layer is a rate-limiting factor for the permeability of the alveolar-capillary membrane for 99mTc-labeled albumin.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Research laboratory.

SUBJECTS

Nineteen white New Zealand adult rabbits.

INTERVENTIONS

Three groups of rabbits were studied: group 1 animals received natural surfactant after lung lavage; group 2 animals underwent lung lavage only; and group 3 animals were not lavaged and served as an untreated, healthy control group. All animals were ventilated with high pressures.

MEASUREMENTS AND MAIN RESULTS

99mTc-labeled albumin was nebulized into the inspiratory line of the breathing circuit with an air jet nebulizer. The clearance measurements were then immediately started. Gamma camera images were obtained in 1-min frames for 120 mins and stored in a 64 x 64 image matrix in a computer. In group 1 animals, surfactant restored blood gases to near normal, and all animals except one had bi-exponential clearance curves. The half-life of the fast compartment was 35.9 +/- 6.4 mins, and the half-life of the slow compartment was 847.5 +/- 143.5 mins. All group 2 animals also had bi-exponential clearance curves of the tracer (the half-lives of the fast and slow compartments were 14.6 +/- 6.7 and 459.8 +/- 167 mins, respectively). The half-lives of both the fast (p < .01) and slow (p < .01) components were significantly different between groups 1 and 2. Group 3 had a mono-exponential half-life of 580 +/- 225 mins.

CONCLUSIONS

The use of 99mTc-human serum albumin as a tracer molecule is possible and feasible. The clearance of this tracer is, in part, determined by the integrity of the pulmonary surfactant system, as it is with 99mTc-diethylenetriamine pentaacetate.

Lung clearance of aerosolized 99mTc erythromycin lactobionate in rabbits

In order to assess the lung clearance of aerosolized 99mTc Erythromycin Lactobionate (EL), 99mTc EL was administered to 9 New Zealand rabbits by inhalation. 5 rabbits inhaled cigarette smoke before 99mTc EL. Clearance half times were 3.0 +/- 0.9 hours in normals, 5.5 +/- 1.0 hours after smoke exposure. Clearance was not affected after destroying the surfactant layer. Slower clearance after smoke exposure may be due to the inhibition of mucociliary clearance. 99mTc EL can be considered as an alternative radioaerosol for ventilation imaging.

Effect of detergent combined with large tidal volume ventilation on alveolocapillary permeability

The combined effect of large tidal volume ventilation (LTVV) and detergent-induced surfactant dysfunction on the clearance kinetics of technetium-99m-labelled diethylene triamine pentaacetate was investigated. Four groups of rabbits (n = 6 in each) were studied: (1) controls, (2) detergent, (3) LTVV, and (4) detergent + LTVV. Clearance was measured for 3 h and the kinetics was analysed by fitting mono- and biexponential equations to the clearance curve and was expressed as a half-life (T 1/2). Pulmonary clearance of 99mTc-DTPA was monoexponential in control animals (T 1/2 = 194 min) and in animals ventilated with LTVV (T 1/2 = 43 min, P < 0.01 compared with controls). In contrast, clearance was biexponential after detergent administration with or without LTVV. T 1/2 values of the fast and slow compartments were 5.4 and 80 min, respectively, with the fast fraction comprising 81% of the radioactivity after detergent alone. When detergent was combined with LTVV, clearance was bicompartmental as with detergent alone, with the same size of the fast fraction. However, clearance from each of the slow (P < 0.01) and fast compartments (P < 0.05) increased significantly. Clearance from the slow compartment was thus similar to T 1/2 during LTVV alone. Large tidal volume ventilation induced a faster than normal clearance of a single compartment, whereas detergent induced kinetics that was distinctly bicompartmental. The mechanisms increasing permeability of the alveolocapillary barrier after detergent and during LTVV seem different and may be additive.

Evaluation of lung function after intratracheal perfluorocarbon administration in healthy animals

OBJECTIVES

To investigate the effects of partial liquid ventilation (i.e., mechanical ventilation in combination with intratracheal administration of perfluorocarbon) on lung function, with particular attention to the integrity of the alveolocapillary membrane in healthy adult animals.

DESIGN

Prospective, randomized, controlled study.

SETTING

Laboratory at the Department of Experimental Anesthesiology, Erasmus University Rotterdam.

SUBJECTS

Ten adult male New Zealand rabbits.

INTERVENTIONS

Five rabbits were intratracheally treated with 12 mL/kg of perfluorocarbon while conventional mechanical ventilation (volume-controlled, tidal volume of 12 mL/kg, respiratory rate of 30 breaths/min, inspiration/expiration ratio of 1:2, positive end-expiratory pressure of 2 cm H2O, and an FIO2 of 1.0) was applied for 3 hrs. To assess the permeability of the alveolocapillary membrane, pulmonary clearance of inhaled technetium-99m-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) measurements were performed at 3 hrs and compared with data from the control group (n = 5) treated with mechanical ventilation only, using the same ventilatory parameters.

MEASUREMENTS AND MAIN RESULTS

Pulmonary gas exchange and lung mechanical parameters were measured in both groups at 30-min intervals. Mean values for PaO2 in the perfluorocarbon group, although at adequate levels, were less than those values of the control group during the 3-hr study period (370 +/- 44 vs. 503 +/- 44 torr at 3 hrs [49.3 +/- 5.9 vs. 67.1 +/- 5.9 kPa]). Peak and mean airway pressures were higher in the perfluorocarbon group (ranging from 1.9 to 3.4 cm H2O and 0.7 to 1.3 cm H2O, respectively) compared with the control group, while end-inspiratory airway pressure was similar in both groups. The half-life of 99mTc-DTPA was 83.7 +/- 24.5 mins in the control group, which was significantly longer (p < .01) than in the perfluorocarbon group (49.8 +/- 6.1 mins).

CONCLUSIONS

These findings suggest that partial liquid ventilation with perfluorocarbons lowers pulmonary gas exchange in healthy animals, and the increased pulmonary clearance of 99mTc-DTPA after 3 hrs of this type of ventilatory support may reflect minimal reversible changes in the lung surfactant system.

Exercise increases the rate of pulmonary absorption of inhaled terbutaline

The purpose of the study was to investigate whether a constant submaximal exercise challenge affected the plasma pharmacokinetics of an inhaled beta 2-adrenoceptor agonist, terbutaline sulfate. Eight healthy nonsmokers participated in a study comprising measurements of plasma concentrations of terbutaline on two separate study days. Plasma samples were frequently collected at rest during study day 1, and on the second study day, during and after a 30-min exercise challenge, which was performed immediately after inhalation of the drug. The rate of increase of plasma concentrations and the maximal plasma concentrations were higher during exercise than during rest (p less than 0.01 and p less than 0.05, respectively). The plasma concentration fell rapidly after cessation of the exercise and approached those obtained at rest. We suggest that increased pulmonary and/or bronchial blood flow and altered surface tension of the liquid lining of the air space may contribute to the enhancement of absorption of this hydrophilic compound during exercise. Based on the levels of the maximal plasma concentrations reached during exercise in this study, the results would be to increase the frequency of administration of the drug, rather than to increase the administered doses, if the aim is to prevent or ameliorate exercise-induced asthma and potential systemic side effects.