Short-term administration of a high oxygen concentration is not injurious in an ex-vivo rabbit model of ventilator-induced lung injury

BACKGROUND

Mechanical ventilation and administration of a high oxygen concentration are simultaneously used in the management of respiratory failure. We conducted this study to evaluate the effect of a high inspired oxygen concentration on ventilator-induced lung injury.

METHODS

Forty sets of isolated/perfused rabbit lungs were randomized for 60 min of pressure-control ventilation at a plateau inspiratory pressure of 25 or 15 cm H(2)O and positive end-expiratory pressure of 3 cm H(2)O while receiving 100% or 21% O(2). The temperature, pH, and partial pressure of CO(2) in the perfusate were maintained the same in all groups (n = 10 for each group). The outcome measures used to assess lung injury included: the change in weight gain and ultrafiltration coefficient, the frequency of vascular failure, the histological lesions and the concentration of tumor necrosis factor-alpha and malondialdehyde in the bronchoalveolar lavage fluid.

RESULTS

The two groups ventilated at the higher inspiratory pressure/tidal volume experienced greater weight gain and increases in the ultrafiltration coefficient, more frequently suffered vascular failure, and presented higher composite scores of histological damage than the two groups ventilated at the lower inspiratory pressure/tidal volume. Hyperoxia was not found to further increase any of the monitored markers of lung injury. No difference was noticed among the four experimental groups in the alveolar lavage fluid levels of tumor necrosis factor-alpha or malondialdehyde.

CONCLUSIONS

These findings suggest that short-term administration of a high oxygen concentration is not a major determinant of ventilator-induced lung injury in this experimental model.

Vasopressin, epinephrine, and corticosteroids for in-hospital cardiac arrest

BACKGROUND

Animal data on cardiac arrest showed improved long-term survival with combined vasopressin-epinephrine. In cardiac arrest, cortisol levels are relatively low during and after cardiopulmonary resuscitation. We hypothesized that combined vasopressin-epinephrine and corticosteroid supplementation during and after resuscitation may improve survival in refractory in-hospital cardiac arrest.

METHODS

We conducted a single-center, prospective, randomized, double-blind, placebo-controlled, parallel-group trial. We enrolled 100 consecutive patients with cardiac arrest requiring epinephrine according to current resuscitation guidelines. Patients received either vasopressin (20 IU per cardiopulmonary resuscitation cycle) plus epinephrine (1 mg per resuscitation cycle) (study group; n = 48) or isotonic sodium chloride solution placebo plus epinephrine (1 mg per resuscitation cycle) (control group; n = 52) for the first 5 resuscitation cycles after randomization, followed by additional epinephrine if needed. On the first resuscitation cycle, study group patients received methylprednisolone sodium succinate (40 mg) and controls received saline placebo. Postresuscitation shock was treated with stress-dose hydrocortisone sodium succinate (300 mg daily for 7 days maximum, with gradual taper) (27 patients in the study group) or saline placebo (15 patients in the control group). Primary end points were return of spontaneous circulation for 15 minutes or longer and survival to hospital discharge.

RESULTS

Study group patients vs controls had more frequent return of spontaneous circulation (39 of 48 patients [81%] vs 27 of 52 [52%]; P = .003) and improved survival to hospital discharge (9 [19%] vs 2 [4%]; P = .02). Study group patients with postresuscitation shock vs corresponding controls had improved survival to hospital discharge (8 of 27 patients [30%] vs 0 of 15 [0%]; P = .02), improved hemodynamics and central venous oxygen saturation, and more organ failure-free days. Adverse events were similar in the 2 groups.

CONCLUSION

In this single-center trial, combined vasopressin-epinephrine and methylprednisolone during resuscitation and stress-dose hydrocortisone in postresuscitation shock improved survival in refractory in-hospital cardiac arrest.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00411879.

Effect of median sternotomy on respiratory system compliance in humans: evaluation without sophisticated instrumentation

To evaluate the effect of median sternotomy on the static compliance of the respiratory system (C(RS)) in humans, we used a new technique for pressure-volume (PV) curve tracing without sophisticated instrumentation. The accuracy and the reproducibility of the new technique were tested in a lung simulator, while its agreement with multiple-occlusion (MO) technique (the technique most often used in the ICU for C(RS) measurement) was evaluated in 12 mechanically ventilated patients. Finally, the NCI technique was used in 13 cardiosurgical patients to measure C(RS) before and after median sternotomy. Measurements provided by the NCI technique were at least as accurate as standard measurements in the bench study. In ICU patients, we observed a good agreement of C(RS) measurements provided by the two techniques (bias 0.8, 95% limits of agreement -5.6 to 7.2 ml/cm H(2)O) and a similar reproducibility. In cardiosurgical patients we observed a significant (P=0.037) increase in C(RS) with an upward and leftward shift of the PV-curve after median sternotomy. No adverse effect was observed during PV-curve tracing maneuvers. The simplicity of NCI technique allowed for the first time, to our knowledge, PV-curve tracing in humans during cardiosurgery and revealed 5% increase in C(RS) immediately after median sternotomy.

A central role for tumor-derived monocyte chemoattractant protein-1 in malignant pleural effusion

BACKGROUND

Tumor cells in malignant pleural effusions (MPEs) are an important source of monocyte chemoattractant protein (MCP)-1. However, the role of tumor-derived MCP-1 in the pathogenesis and progression of MPE has not been determined.

METHODS

B16 mouse skin melanoma cells, which are deficient in MCP-1 expression, and mouse Lewis lung cancer (LLC) cells, which express high levels of MCP-1, were engineered to stably express MCP-1 and short hairpin RNAs (shRNAs) targeting the MCP-1 transcript, respectively. Cells were injected into the pleural cavities of syngeneic immunocompetent mice, and MPE volume and pleural tumors were quantified at necropsy (day 14). MCP-1 and other mediators were determined by cytometric bead array and enzyme-linked immunosorbent assay, and mononuclear and endothelial cells were identified by immunolabeling of F4/80 and factor VIII-related antigen respectively. Mouse survival was assessed using Kaplan-Meier analysis. Vascular permeability in mice with MPE was assessed using albumin-binding Evans blue. Statistical tests were two-sided.

RESULTS

LLC cells expressing shRNA against MCP-1 elaborated less than 5% of the MCP-1 level in cells expressing nonspecific shRNA (control cells), and intrapleural delivery of these cells resulted in less MPE (mean MPE volume = 86 and 585 muL, respectively; difference = 499 muL; 95% confidence interval [CI] = 331 to 669 muL; P < .001), reduced MCP-1 levels in the pleural fluid, and lower mortality than when control cells were delivered. Overexpression of MCP-1 in intrapleurally injected B16 melanoma cells led to increased MPE and reduced survival. In mice with MPE, MCP-1 was a potent inducer of vascular permeability, mononuclear recruitment, and, in pleural tumors, of angiogenesis.

CONCLUSION

MCP-1 produced by tumor cells is an important determinant of their capacity to induce the formation of MPE and may be a useful target for the treatment of malignant pleural disease.

Contribution of respiratory muscle blood flow to exercise-induced diaphragmatic fatigue in trained cyclists

We investigated whether the greater degree of exercise-induced diaphragmatic fatigue previously reported in highly trained athletes in hypoxia (compared with normoxia) could have a contribution from limited respiratory muscle blood flow. Seven trained cyclists completed three constant load 5 min exercise tests at inspired O(2) fractions (FIO2) of 0.13, 0.21 and 1.00 in balanced order. Work rates were selected to produce the same tidal volume, breathing frequency and respiratory muscle load at each FIO2 (63 +/- 1, 78 +/- 1 and 87 +/- 1% of normoxic maximal work rate, respectively). Intercostals and quadriceps muscle blood flow (IMBF and QMBF, respectively) were measured by near-infrared spectroscopy over the left 7th intercostal space and the left vastus lateralis muscle, respectively, using indocyanine green dye. The mean pressure time product of the diaphragm and the work of breathing did not differ across the three exercise tests. After hypoxic exercise, twitch transdiaphragmatic pressure fell by 33.3 +/- 4.8%, significantly (P < 0.05) more than after both normoxic (25.6 +/- 3.5% reduction) and hyperoxic (26.6 +/- 3.3% reduction) exercise, confirming greater fatigue in hypoxia. Despite lower leg power output in hypoxia, neither cardiac output nor QMBF (27.6 +/- 1.2 l min(-1) and 100.4 +/- 8.7 ml (100 ml)(-1) min(-1), respectively) were significantly different compared with normoxia (28.4 +/- 1.9 l min(-1) and 94.4 +/- 5.2 ml (100 ml)(-1) min(-1), respectively) and hyperoxia (27.8 +/- 1.6 l min(-1) and 95.1 +/- 7.8 ml (100 ml)(-1) min(-1), respectively). Neither IMBF was different across hypoxia, normoxia and hyperoxia (53.6 +/- 8.5, 49.9 +/- 5.9 and 52.9 +/- 5.9 ml (100 ml)(-1) min(-1), respectively). We conclude that when respiratory muscle energy requirement is not different between normoxia and hypoxia, diaphragmatic fatigue is greater in hypoxia as intercostal muscle blood flow is not increased (compared with normoxia) to compensate for the reduction in PaO2, thus further compromising O(2) supply to the respiratory muscles.

Predisposing factors for critical illness polyneuromyopathy in a multidisciplinary intensive care unit

OBJECTIVE

To investigate risk factors of critical illness polyneuromyopathy (CIPM) in a general multidisciplinary intensive care unit (ICU).

PATIENTS AND METHODS

Prospective observational study in a 28-bed university multidisciplinary ICU. Four hundred and seventy-four (323 M/151 F, age 55 +/- 19) consecutive patients were prospectively evaluated. All patients were assigned admission Acute Physiology and Chronic Health Evaluation (APACHE II; 15 +/- 7) and Sequential Organ Failure Assessment (SOFA; 6 +/- 3) scores and were subsequently evaluated for newly developed neuromuscular weakness. Other potential causes of new-onset weakness after ICU admission were excluded before CIPM was diagnosed.

RESULTS

Forty-four (23.8%) of 185 patients developed generalized weakness that met the criteria for CIPM. Patients with CIPM had higher APACHE II (18.9 +/- 6.6 vs 15.6 +/- 6.4, P = 0.004) and SOFA scores (8.4 +/- 2.9 vs 7.1 +/- 2.9, P = 0.013). According to multivariate logistic regression analysis, the following risk factors were independently associated with the development of CIPM: severity of illness at the time of ICU admission, administration of aminoglycoside antibiotics and high blood glucose levels. Analysis according to severity of illness stratification revealed the emergence of Gram (-) bacteremia as the most important independent predisposing factor for CIPM development in less severely ill patients.

CONCLUSIONS

CIPM has a high incidence in the ICU setting. Our study revealed the association of aminoglycosides, hyperglycemia and illness severity with CIPM development, as well as the association between Gram (-) bacteremia and development of CIPM in less severely ill patient population.

Soluble guanylyl cyclase activation by HMR-1766 (ataciguat) in cells exposed to oxidative stress

Many vascular diseases are characterized by increased levels of ROS that destroy the biological activity of nitric oxide and limit cGMP formation. In the present study, we investigated the cGMP-forming ability of HMR-1766 in cells exposed to oxidative stress. Pretreatment of smooth muscle cells with H(2)O(2) reduced cGMP production stimulated by sodium nitroprusside (SNP) or BAY 41-2272. However, pretreatment with H(2)O(2) significantly increased HMR-1766 responses. Similar results were obtained with SIN-1, menadione, and rotenone. In addition, HMR-1766 was more effective in stimulating heme-free sGC compared with the wild-type enzyme. Interestingly, in cells expressing heme-free sGC, H(2)O(2) inhibited instead of potentiated HMR-1766 responses, suggesting that the ROS-induced enhancement of cGMP formation was heme dependent. Moreover, using truncated forms of sGC, we observed that the NH(2)-terminus of the beta(1)-subunit is required for the action of HMR-1766. Finally, to study tolerance development to HMR-1766, cells were pretreated with this sGC activator and reexposed to HMR-1766 or SNP. Results from these experiments demonstrated lack of tolerance development to HMR-1766 as well as lack of cross-tolerance with SNP. We conclude that HMR-1766 is an improved sGC activator as it has the ability to activate oxidized/heme-free sGC and is resistant to the development of tolerance; these observations make HMR-1766 a promising agent for treating diseases associated with increased vascular tone combined with enhanced ROS production.

Determinants of subjective sleepiness in suspected obstructive sleep apnoea

Although daytime sleepiness is commonly associated with obstructive sleep apnoea (OSA), the relationship between OSA severity and subjective sleepiness has been documented elusive. This study aimed to identify clinical and polysomnographic determinants of subjective sleepiness among patients suspected of having OSA. A sleep clinic-based sample of 915 patients was interviewed with a structured questionnaire and underwent diagnostic overnight polysomnography. Subjective sleepiness was quantified by Epworth Sleepiness Scale (ESS). Excessive daytime sleepiness (defined as ESS score > 10) was present in 38.8% of patients. In multiple linear regression analysis, respiratory disturbance index [RDI; used to define (whenever RDI was >5) and quantify OSA], depression and diabetes were the most important determinants of ESS score accounting for 17%, 11% and 6% of its variability respectively. Chronic obstructive pulmonary disease (COPD), stroke, heart disease, alcohol use and body mass index were less important determinants of ESS score explaining 1-3% of its variability. In conclusion, OSA should not be considered the sole potential cause of increased subjective sleepiness in patients suspected of having OSA. Primarily depression and diabetes, but also COPD, stroke, heart disease, alcohol use and increased body mass index may contribute to increased subjective sleepiness.

cGMP-independent anti-tumour actions of the inhibitor of soluble guanylyl cyclase, ODQ, in prostate cancer cell lines

BACKGROUND AND PURPOSE

Soluble guanylyl cyclase (sGC) is a receptor for nitric oxide that generates cGMP. This second messenger molecule has established roles in cellular physiology; however, less is known about its effects in tumour cells.

EXPERIMENTAL APPROACH

The effects of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS2028), both selective sGC inhibitors on proliferation, death and migration were determined in prostate cancer cell lines.

KEY RESULTS

Western blot analysis confirmed the presence of alpha1 and beta1 subunits of sGC in LNCaP and PC-3 cells. Sodium nitroprusside (SNP) increased cGMP accumulation in LNCaP and PC-3, but not DU-145 cells. SNP-stimulated cGMP production in LNCaP cells was dose-dependently reduced by ODQ, with more than 90% inhibition being observed at 0.1 microM. ODQ activated caspase-3 in all three cell lines, but not in normal prostate epithelial cells, at concentrations over 10 muM. High concentrations of ODQ also promoted DNA fragmentation and nucleosome accumulation in the cytosol of LNCaP cells. Interestingly, the chemically related inhibitor, NS2028 was without effect on caspase-3. In addition, ODQ inhibited LNCaP, Du145 and PC-3 cell growth. Finally, although fibroblast growth factor-2 did not enhance cGMP levels in LNCaP cells, its ability to stimulate LNCaP motility was abolished by ODQ.

CONCLUSIONS AND IMPLICATIONS

These observations taken together suggest that the action of ODQ in LNCaP cells did not reflect sGC inhibition. We conclude that ODQ promotes cell death and inhibits growth and migration of prostate cancer cells and that these actions are independent of its effects on GMP levels.

Effect of clarithromycin in patients with sepsis and ventilator-associated pneumonia

BACKGROUND

Because clarithromycin provided beneficiary nonantibiotic effects in experimental studies, its efficacy was tested in patients with sepsis and ventilator-associated pneumonia (VAP).

METHODS

Two hundred patients with sepsis and VAP were enrolled in a double-blind, randomized, multicenter trial from June 2004 until November 2005. Clarithromycin (1 g) was administered intravenously once daily for 3 consecutive days in 100 patients; another 100 patients were treated with placebo. Main outcomes were resolution of VAP, duration of mechanical ventilation, and sepsis-related mortality within 28 days.

RESULTS

The groups were well matched with regard to demographic characteristics, disease severity, pathogens, and adequacy of the administered antimicrobials. Analysis comprising 141 patients who survived revealed that the median time for resolution of VAP was 15.5 days and 10.0 days among placebo- and clarithromycin-treated patients, respectively (P = .011); median times for weaning from mechanical ventilation were 22.5 days and 16.0 days, respectively (p = .049). Analysis comprising all enrolled patients showed a more rapid decrease of the clinical pulmonary infection score and a delay for advent of multiple organ dysfunction in clarithromycin-treated patients, compared with those of placebo-treated patients (p = .047). Among the 45 patients who died of sepsis, time to death was significantly prolonged in clarithromycin-treated compared with placebo-treated patients (p = .004). Serious adverse events were observed in 0% and 3% of placebo- and clarithromycin-treated patients, respectively (P = .25).

CONCLUSIONS

Clarithromycin accelerated the resolution of VAP and weaning from mechanical ventilation in surviving patients and delayed death in those who died of sepsis. The mortality rate at day 28 was not altered. Results are encouraging and render new perspectives on the management of sepsis and VAP.

Protein kinase G phosphorylates soluble guanylyl cyclase on serine 64 and inhibits its activity

OBJECTIVE

Binding of nitric oxide (NO) to soluble guanylyl cyclase (sGC) leads to increased cGMP synthesis that activates cGMP-dependent protein kinase (PKG). Herein, we tested whether sGC activity is regulated by PKG.

METHODS AND RESULTS

Overexpression of a constitutively active form of PKG (DeltaPKG) stimulated (32)P incorporation into the alpha1 subunit. Serine to alanine mutation of putative sites revealed that Ser64 is the main phosphorylation site for PKG. Using a phospho-specific antibody we observed that endogenous sGC phosphorylation on Ser 64 increases in cells and tissues exposed to NO, in a PKG-inhibitable manner. Wild-type (wt) sGC coexpressed with DeltaPKG exhibited lower basal and NO-stimulated cGMP accumulation, whereas the S64A alpha1/beta1 sGC was resistant to the PKG-induced reduction in activity. Using purified sGC we observed that the S64D alpha1 phosphomimetic /beta1 dimer exhibited lower Vmax; moreover, the decrease in Km after NO stimulation was less pronounced in S64D alpha1/beta1 compared to wild-type sGC. Expression of a phosphorylation-deficient sGC showed enhanced responsiveness to endothelium-derived NO, reduced desensitization to acute NO exposure, and allowed for greater VASP phosphorylation.

CONCLUSIONS

We conclude that PKG phosphorylates sGC on Ser64 of the alpha1 subunit and that phosphorylation inhibits sGC activity, establishing a negative feedback loop.

Airway inflammation in obstructive sleep apnea: is leptin the missing link?

BACKGROUND

Local and systemic inflammation is implicated in the pathophysiology of Obstructive Sleep Apnea (OSA). Exhaled breath condensate (EBC) is a non-invasive sampling method for the lower airways. However, it is important to consider the potential effect of the systemic origin whereas systemic inflammation is significantly elevated. This prospective study was designed to investigate whether airway inflammation is significantly related to plasma leptin levels in OSA patients. Simultaneously, it was designed to investigate whether inflammatory variables predict parameters expressing disease severity and finally whether smoking habit affect the above measurements.

PATIENTS & METHODS

About 45 OSA patients (mean AHI 40+/-25, 28 smokers) and 25 healthy controls (AHI<5, 15 smokers) were studied and underwent overnight diagnostic polysomnography. We measured pH, 8-isoprostane, TNF-alpha and IL-6 in EBC and leptin in plasma. Plausible associations between leptin and inflammatory parameters were analyzed after adjustment for proper variables. Similar associations between inflammatory variables and parameters of disease severity were also performed.

RESULTS

An increased level of leptin and respective increase of inflammatory variables was found. No significant association was observed between parameters of EBC and plasma leptin levels. A part of the parameters of disease severity is significantly associated with pH and 8-isoprostane. Smoking did not seem to be a critical confounding factor for evaluation of the above measurements.

CONCLUSIONS

Increased levels of leptin were not associated with the observed airway inflammation in OSA. The observed airway inflammation seemed to be independent of smoking habit with limited association with disease severity.

Inotropic agents improve the peripheral microcirculation of patients with end-stage chronic heart failure

BACKGROUND

Skeletal muscle microcirculation impairment in patients with chronic heart failure (CHF) seems to correlate with disease severity. We evaluated the microcirculation by near-infrared spectroscopy (NIRS) occlusion technique before and after inotropic infusion.

METHODS

We evaluated 25 patients with stable CHF, 30 patients with end-stage CHF (ESCHF) receiving treatment with intermittent infusion of inotropic agents, and 12 healthy subjects. Thenar muscle tissue oxygen saturation (StO(2)%) was measured noninvasively by NIRS before, during, and after 3-minute occlusion of the brachial artery (occlusion technique) in all subjects and in patients with ESCHF before and after 6 hours of inotropic infusion (dobutamine and/or levosimendan) or placebo (N = 5).

RESULTS

Patients with ESCHF or CHF presented significantly lower StO(2)% than healthy subjects (74.5% +/- 7%, 78.6% +/- 6%, and 85% +/- 5%, respectively; P = .0001), lower oxygen consumption rate during occlusion (24.6% +/- 8%/min, 28.6% +/- 10%/min, and 38.1% +/- 11.1%/min, respectively; P = .001), and lower reperfusion rate (327% +/- 141%/min, 410% +/- 106%/min, and 480% +/- 133%/min, respectively; P = .002). After 6 hours of inotropic infusion, patients with ESCHF showed significantly increased StO(2)% (74.5% +/- 7% to 82% +/- 9%, P = .001), oxygen consumption rate (24.6% +/- 8%/min to 29.3% +/- 8%/min, P = .009), and reperfusion rate (327% +/- 141%/min to 467% +/- 151%/min, P = .001). No statistical difference was noted in the placebo group.

CONCLUSION

Peripheral muscle microcirculation as assessed by NIRS is impaired in patients with CHF. This impairment is partially reversed by infusion of inotropic agents in patients with ESCHF.

The pathophysiology of inspiratory muscle fatigue

The critical value of the rate of energy consumption of the inspiratory muscles above which fatigue occurs appears in some instances to be predictable from the relationship between energy demands and energy supplies rather than from the percentage of fatigue-resistant fibres in the inspiratory muscles. When this is the case the critical value of the external power produced by the inspiratory muscles is given by the product of muscular efficiency and the rate at which energy is supplied. Efficiency is reduced by hyperinflation and recruitment of the intercostal and accessory muscles of inspiration. The rate at which energy is supplied is decreased in states characterized by low cardiac output. The condition of low cardiac output, combined with the high oxygen cost of breathing against fatiguing loads, may be lethal in cardiogenic shock. Although the immediate cause of fatigue may not be related to reduced energy supplies, clinically useful predictions of conditions predisposing to fatigue result from an understanding of factors determining the balance between the energy demands and supplies of the inspiratory muscles. These predictions aid in the diagnosis of inspiratory muscle fatigue and have important therapeutic implications.

Neural drive and electromechanical alterations in the fatiguing diaphragm

It is suggested that respiratory failure in the compromised circulation might occur as a result of respiratory muscle fatigue in the presence of adequate neural drive and muscle excitation. As the cardiac output decreases acidosis develops and ventilation increases, resulting in an increase in the work of breathing, which requires the delivery of large supplies of energy. As these demands cannot be met by the energy supply, because of low cardiac output, the diaphragm fails as a force generator and respiratory failure ensues. Diaphragmatic fatigue may occur in normal subjects if the pressure developed with each breath is greater than 40% of the maximum transdiaphragmatic pressure and hypoxia predisposes the diaphragm to fatigue. Diaphragmatic fatigue, as in other skeletal muscles, might be located either at the neuromuscular junction or distal to it and can be detected either by phrenic stimulation or by frequency analysis of the myoelectric signal. Phrenic stimulation shows that after fatigue the diaphragm develops less force at any frequency of stimulation, but the loss of force at low frequencies persists for a longer period than at high frequencies. Frequency analysis of the electromyogram reveals that the power spectrum shifts to lower frequencies. This shift occurs long before the diaphragm fails as a force generator.

Pneumothorax-associated pleural eosinophilia is tumour necrosis factor-alpha-dependent and attenuated by steroids

BACKGROUND AND OBJECTIVES

The pathogenesis and the optimal treatment of eosinophilic pleural effusions are unknown. We aimed to examine whether pneumothorax-associated pleural eosinophilia in mice is dependent on tumour necrosis factor (TNF)-alpha, and whether it is affected by systemic administration of corticosteroids.

METHODS

Mice were injected intrapleurally with 0.4 mL air to create pneumothoraces. Animals were sacrificed 24 or 48 h later, and pleural lavage (PL) was performed. In the first experiment, comparisons were made between wild-type and TNF-alpha knockout mice with pneumothorax. In the second experiment, wild-type mice were injected intraperitoneally with different doses of dexamethasone (0, 0.25, 0.5 and 1 mg/kg), 5 min before and 24 h after the induction of pneumothorax.

RESULTS

After induction of a pneumothorax, TNF-alpha knockout mice had significantly fewer total number of cells (P = 0.004), mononuclear cells (P = 0.01), neutrophils (P = 0.017) and eosinophils (P = 0.002) in their PL compared with wild-type animals. TNF-alpha was detected in the PL of most of the control mice but not in TNF-alpha knockouts. Dexamethasone induced a significant, dose-dependent reduction of PL total cells (P < 0.001), eosinophils (P < 0.001), mononuclear cells (P = 0.007) and lymphocytes (P = 0.04) at 48 h, and significantly reduced the number of PL total cells (P = 0.045) and eosinophils (P = 0.005) at 24 h. Furthermore, dexamethasone prevented eosinophil infiltration of lung and pleural tissue.

CONCLUSION

Pneumothorax-associated pleural eosinophilia in mice is TNF-alpha-dependent and is significantly attenuated by corticosteroid treatment. In addition, both TNF-alpha deficiency and dexamethasone treatment were associated with a significant reduction of other types of inflammatory cells in PL.

Zoledronic acid is effective against experimental malignant pleural effusion

RATIONALE

Aminobiphosphonates, such as zoledronic acid (ZA), exert potent indirect antitumor effects and are currently being tested against human solid tumors. The antitumor actions of aminobiphosphonates, including angiostasis, are relevant to the pathogenesis of malignant pleural effusion (MPE), but no study has addressed the efficacy of these compounds against malignant pleural disease.

OBJECTIVES

Here we hypothesized that treatment of immunocompetent mice with ZA would halt tumor progression in a mouse model of adenocarcinoma-induced MPE.

METHODS

To induce MPE in mice, Lewis lung carcinoma cells were delivered directly into the pleural space. Subsequently, animals were treated with ZA in both a prevention and a regression protocol.

MEASUREMENTS AND MAIN RESULTS

ZA treatment resulted in significant reductions in pleural fluid accumulation and tumor dissemination, while it significantly prolonged survival. These effects of ZA were linked to enhanced apoptosis of pleural tumor cells, decreased formation of new vessels in pleural tumors, and reduced pleural vascular permeability. In addition, ZA was able to inhibit the recruitment of mononuclear cells to pleural tumors, with concomitant reductions in matrix metalloproteinase-9 release into the pleural space. Finally, ZA limited the expression of proinflammatory and angiogenic mediators, as well as the activity of small GTP proteins Ras and RhoA, in tumor cells in vivo and in vitro.

CONCLUSIONS

ZA is effective against experimental MPE, suggesting that this intervention should be considered for testing in clinical trials.

Human respiratory muscle blood flow measured by near-infrared spectroscopy and indocyanine green

Measurement of respiratory muscle blood flow (RMBF) in humans has important implications for understanding patterns of blood flow distribution during exercise in healthy individuals and those with chronic disease. Previous studies examining RMBF in humans have required invasive methods on anesthetized subjects. To assess RMBF in awake subjects, we applied an indicator-dilution method using near-infrared spectroscopy (NIRS) and the light-absorbing tracer indocyanine green dye (ICG). NIRS optodes were placed on the left seventh intercostal space at the apposition of the costal diaphragm and on an inactive control muscle (vastus lateralis). The primary respiratory muscles within view of the NIRS optodes include the internal and external intercostals. Intravenous bolus injection of ICG allowed for cardiac output (by the conventional dye-dilution method with arterial sampling), RMBF, and vastus lateralis blood flow to be quantified simultaneously. Esophageal and gastric pressures were also measured to calculate the work of breathing and transdiaphragmatic pressure. Measurements were obtained in five conscious humans during both resting breathing and three separate 5-min bouts of constant isocapnic hyperpnea at 27.1 ± 3.2, 56.0 ± 6.1, and 75.9 ± 5.7% of maximum minute ventilation as determined on a previous maximal exercise test. RMBF progressively increased (9.9 ± 0.6, 14.8 ± 2.7, 29.9 ± 5.8, and 50.1 ± 12.5 ml·100 ml−1·min−1, respectively) with increasing levels of ventilation while blood flow to the inactive control muscle remained constant (10.4 ± 1.4, 8.7 ± 0.7, 12.9 ± 1.7, and 12.2 ± 1.8 ml·100 ml−1·min−1, respectively). As ventilation rose, RMBF was closely and significantly correlated with 1) cardiac output ( r = 0.994, P = 0.006), 2) the work of breathing ( r = 0.995, P = 0.005), and 3) transdiaphragmatic pressure ( r = 0.998, P = 0.002). These data suggest that the NIRS-ICG technique provides a feasible and sensitive index of RMBF at different levels of ventilation in humans.

Angiopoietin-1 protects against airway inflammation and hyperreactivity in asthma

RATIONALE

The angiopoietins (Ang) comprise a family of growth factors mainly known for their role in blood vessel formation and remodeling. The best-studied member, Ang-1, exhibits antiapoptotic and antiinflammatory effects. Although the involvement of Ang-1 in angiogenesis is well recognized, little information exists about its role in respiratory physiology and disease. On the basis of its ability to inhibit vascular permeability, adhesion molecule expression, and cytokine production, we hypothesized that Ang-1 administration might exert a protective role in asthma.

OBJECTIVES

To determine changes in the expression of Ang and to assess the ability of Ang-1 to prevent the histologic, biochemical, and functional changes observed in an animal model of asthma.

METHODS

To test our hypothesis, a model of allergic airway disease that develops after ovalbumin (OVA) sensitization and challenge was used.

MEASUREMENTS AND MAIN RESULTS

Ang-1 expression was reduced at the mRNA and protein levels in lung tissue of mice sensitized and challenged with OVA, leading to reduced Tie2 phosphorylation. Intranasal Ang-1 treatment prevented the OVA-induced eosinophilic lung infiltration, attenuated the increase in IL-5 and IL-13, and reduced eotaxin and vascular cell adhesion molecule 1 expression. These antiinflammatory actions of Ang-1 coincided with higher levels of IkappaB and decreased nuclear factor-kappaB binding activity. More importantly, Ang-1 reversed the OVA-induced increase in tissue resistance and elastance, improving lung function.

CONCLUSIONS

We conclude that Ang-1 levels are decreased in asthma and that administration of Ang-1 might be of therapeutic value because it prevents the increased responsiveness of the airways to constrictors and ameliorates inflammation.

The contribution of intrapulmonary shunts to the alveolar-to-arterial oxygen difference during exercise is very small

Exercise is well known to cause arterial PO2 to fall and the alveolar-arterial PO2 difference(Aa PO2 ) to increase. Until recently, the physiological basis for this was considered to be mostly ventilation/perfusion ((.)VA/(.)Q) inequality and alveolar-capillary diffusion limitation. Recently, arterio-venous shunting through dilated pulmonary blood vessels has been proposed to explain a significant part of the Aa PO2 during exercise. To test this hypothesis we determined venous admixture during 5 min of near-maximal, constant-load, exercise in hypoxia (in inspired O2 fraction, FIO2 , 0.13), normoxia (FIO2 , 0.21) and hyperoxia (FIO2 , 1.0) undertaken in balanced order on the same day in seven fit cyclists ((.)VO2max, 61.3 +/- 2.4 ml kg(-1) min(-1); mean +/- S.E.M.). Venous admixture reflects three causes of hypoxaemia combined: true shunt, diffusion limitation and ((.)VA/(.)Q) inequality. In hypoxia, venous admixture was 22.8 +/- 2.5% of the cardiac output; in normoxia it was 3.5 +/- 0.5%; in hyperoxia it was 0.5 +/- 0.2%. Since only true shunt accounts for venous admixture while breathing 100% O2, the present study suggests that shunt accounts for only a very small portion of the observed venous admixture, Aa PO2 and hypoxaemia during heavy exercise.

Chest wall volume regulation during exercise in COPD patients with GOLD stages II to IV

The present study investigated how end-expiratory ribcage and abdominal volume regulation during exercise is related to the degree of dynamic chest wall hyperinflation in patients with different spirometric severity of chronic obstructive pulmonary disease (COPD) based on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification. In total, 42 COPD patients and 11 age-matched healthy subjects were studied during a ramp-incremental cycling test to the limit of tolerance (W(peak)). Volume variations of the chest wall (at end expiration (EEV(cw)) and end inspiration) and its compartments (ribcage (V(rc)) and abdominal (V(ab))) were computed by optoelectronic plethysmography. At W(peak), only patients in GOLD stages III and IV exhibited a significant increase in EEV(cw) (increase of 454+/-509 and 562+/-363 mL, respectively). These patients did not significantly reduce end-expiratory V(ab), whereas patients in GOLD stage II resembled healthy subjects with significantly reduced end-expiratory V(ab) (decrease of 287+/-350 mL). In patients, the greater the increase in EEV(cw) at W(peak), the smaller the reductions in end-expiratory V(ab) and the greater the increase in end-expiratory V(rc). In chronic obstructive pulmonary disease patients with different spirometric disease severity, greater degrees of exercise-induced dynamic chest wall hyperinflation were accompanied by lower degrees of end-expiratory abdominal volume displacement and larger increases in end-expiratory ribcage volume.

Propofol-induced hyperamylasaemia in a general intensive care unit

This study examined the incidence of hyperamylasaemia, in the absence of other plausible causes of pancreatic dysfunction, in intensive care unit (ICU) patients who received propofol. One-hundred-and-seventy-two consecutive patients of a general ICU who stayed for more than 24 hours were studied. Patients with a diagnosis consistent with elevated serum amylase levels at admission were excluded from the study, as were patients who had received medications known to raise serum amylase levels. Forty-four patients 53 +/- 20 years of age and median duration of ICU stay of five days (range two to 55) were eligible. Thirty of those, aged 54 +/- 21 years and median duration of ICU stay of five days (range two to 27) received continuous infusion of propofol for sedation (maximum dose 45 microg/kg/min). Of the 30 patients who received propofol, 16 (53%) developed hyperamylasaemia (125 to 466 IU/l) after two to nine days of continuous infusion. Liver and kidney function remained normal throughout the observation period. Of the 14 patients who did not receive propofol (aged 51 +/- 18 years), only two (14%) developed hyperamylasaemia, a significantly lower incidence (P = 0.021). Propofol infusion is associated with biochemical evidence of pancreatic injury. Amylase levels monitoring of propofol-sedated patients is warranted.