The role of Mac-1 (CD11b/CD18) in antigen-induced airway eosinophilia in mice.

Mac-1 (CD11b/CD18) is an important adhesion molecule involved in the migration of leukocytes, cell signaling, and subsequent secretory responses. Its precise role in eosinophil recruitment and activation in vivo is not entirely clear. We wished to directly examine the role of Mac-1 in eosinophil migration in a murine model of allergic pulmonary inflammation. Briefly, wild-type (C57Bl/6) and Mac-1-deficient/knockout (Mac-1 KO) mice were intraperitoneally sensitized with ovalbumin (OVA) and alum (AlOH) on Days 0 and 14, and intranasally challenged with OVA either once on Day 14 or five times on Days 14 and 25 through 28. Control animals were challenged with saline. Bronchial hyperresponsiveness was measured, bronchoalveolar lavage (BAL) fluid was collected, and lungs were harvested for histology 24 h after the last challenge. The data demonstrate that wild-type (WT) mice do not respond to one OVA challenge but do develop bronchial hyperreactivity and airway and tissue eosinophilia after five OVA challenges. Conversely, Mac-1 KO mice develop significant airway eosinophilia after one OVA challenge, and the degree of airway inflammation is comparable to that observed in allergic WT mice after five challenges. In Mac-1 KO mice, after five challenges, bronchial hyperreactivity and airway inflammation was significantly enhanced compared with their wild-type counterparts. Administration of an anti-Mac-1 antibody to WT mice, before each of five intranasal OVA challenges, significantly reduces the airway eosinophilia but has no effect on tissue eosinophilia or bronchial hyperresponsiveness. Intravenous injection of interleukin-5 induced a significant blood eosinophilia in both WT and Mac-1 KO mice. Intranasal eotaxin administration induced similar levels of eosinophil migration into the lung tissues and airways of both WT and Mac-1 KO mice. In conclusion, Mac-1-deficient mice develop enhanced eosinophilic inflammation in the lung in response to allergic antigen challenge.

Respiratory mechanics and lung development in the rat from early age to adulthood.

The purpose of the present study was to establish how the dependence of respiratory mechanics on lung inflation changes during development. We studied seven groups of rats from 10 days to 3 mo of age at five levels of positive end-expiratory pressure (PEEP) from 0 to 7 hPa (1 hPa = 0.1 kPa approximately 1 cmH(2)O). At each PEEP level, we measured respiratory system resistance and elastance at both 0.9 and 4.8 Hz to partition the mechanical properties into its airway and tissue components. Elastance increased more rapidly with PEEP in the younger animals, which we interpret as reflecting a more pronounced strain stiffening of the younger parenchyma. However, the decrease in airway resistance with PEEP was more pronounced in the older animals. Morphometric analysis showed that mean tissue density decreased and total alveolar surface area increased with age. Our data suggest that the mechanical interdependence between airways and parenchyma is weaker in very young animals compared with mature animals. This may play a role in the hyperresponsiveness of immaturity.

Effects of smooth muscle activation on axial mechanical properties of excised canine bronchi.

This study tested the hypothesis that airway smooth muscle (ASM) activation produces an airway active axial force (AAAF). Bronchi (n = 10) immersed in a tissue bath containing 95% O2-5% CO2-equilibrated Krebs solution were subjected to passive axial lengthening and shortening at 0-20 cmH2O of transmural pressure. ASM was relaxed with isoproterenol and activated with methacholine. Axial tensile (epsilonx), transverse compressive (epsilony), and shear strains (epsilonxy) were computed from the displacements of four markers placed onto the specimen's surface. The AAAF was estimated by subtracting the control axial force (AF) values at a given epsilonx from those obtained after methacholine. epsilonx-AF relationships were curvilinear, with maximum epsilonx being approached at approximately 15 g of AF. The epsilony decreased during bronchial lengthening. Cholinergic stimulation produced 1) a decrease of both epsilonx and epsilony at a given AF relative to control, indicating ASM shortening, and 2) an AAAF that increased with increasing epsilonx and transmural pressure. A portion of the work of expanding the lungs is required to lengthen the airways; therefore, an AAAF would increase lung elastance and recoil.

Recurrent milk aspiration produces changes in airway mechanics, lung eosinophilia, and goblet cell hyperplasia in a murine model.

Recurrent aspiration of milk into the respiratory tract has been implicated in the pathogenesis of a variety of inflammatory lung disorders including asthma. However, the lack of animal models of aspiration-induced lung injury has limited our knowledge of the pathophysiological characteristics of this disorder. This study was designed to evaluate the effects of recurrent milk aspiration on airway mechanics and lung cells in a murine model. Under light anesthesia, BALB/c mice received daily intranasal instillations of whole cow's milk (n = 7) or sterile physiologic saline (n = 9) for 10 d. Respiratory system resistance (Rrs) and dynamic elastance (Edyn,rs) were measured in anesthetized, tracheotomized, paralyzed and mechanically ventilated mice 24 h after the last aspiration of milk. Rrs and Edyn,rs were derived from transrespiratory and plethysmographic pressure signals. In addition, airway responses to increasing concentrations of i.v. methacholine (Mch) were determined. Airway responses were measured in terms of PD(100) (dose of Mch causing 100% increase from baseline Rrs) and Rrs,max (% increase from baseline at the maximal plateau response) and expressed as % control (mean +/- SE). We found recurrent milk aspiration did not affect Edyn and baseline Rrs values. However, airway responses to Mch were increased after milk aspiration when compared with control mice. These changes in airway mechanics were associated with an increased percentage of lymphocytes and eosinophils in the bronchoalveolar lavage, mucus production, and lung inflammation. Our findings suggest that recurrent milk aspiration leads to alterations in airway function, lung eosinophilia, and goblet cell hyperplasia in a murine model.

Therapeutic efficacy of an anti-IL-5 monoclonal antibody delivered into the respiratory tract in a murine model of asthma.

BACKGROUND: IL-5 is central to the pathogenesis of airway eosinophilic inflammation and hyperresponsiveness associated with both atopic and nonatopic asthma. The therapeutic potential of IL-5 antagonists in asthma is supported by the inhibition of airway eosinophilia and hyperresponsiveness in animal models receiving neutralizing anti-IL-5 mAbs intravenously or intraperitoneally. OBJECTIVE: The purpose of this study was to test the hypothesis that mAbs against IL-5 delivered by way of the respiratory tract are as effective as those delivered intraperitoneally in diminishing the pulmonary eosinophilic inflammation and airway hyperresponsiveness in a murine model of ovalbumin-induced asthma. METHODS: Ovalbumin-sensitized Balb/c mice were given an anti-IL-5 mAb delivered intranasally or an isotype-matched control mAb delivered intranasally before respiratory challenge with ovalbumin. Outcome variables included respiratory system resistance responses to methacholine, bronchoalveolar lavage fluid cellularity, and lung histopathology. RESULTS: Anti-IL-5 mAbs administered intranasally to ovalbumin-sensitized and challenged mice significantly decreased eosinophil counts in bronchoalveolar lavage fluid and lung tissue and significantly reduced airway hyperresponsiveness relative to ovalbumin-sensitized and challenged mice that received either no mAb treatment or an isotype-matched control mAb. Similar results were obtained when an anti-IL-5 mAb was given intraperitoneally. CONCLUSION: This is the first study to demonstrate that delivery of anti-IL-5 mAbs into the respiratory tract is efficacious in attenuating the asthma phenotype in a murine model. These results provide impetus for the development of inhaled IL-5 antagonists for the treatment of human asthma.

Frequency dependence of pulmonary and chest wall mechanics in young and adult cats.

The frequency (f) dependence of pulmonary and chest wall mechanics was assessed in nine kittens and four cats. Kittens and cats were anesthetized, paralyzed, and mechanically ventilated at various f between 0.13 and 1.6 Hz and 0.09 and 0.79 Hz, respectively. Resistance and dynamic compliance pertaining to the respiratory system (Rrs and Cdyn,rs), lungs (RL and Cdyn,L), and chest wall (RW and Cdyn,W) were estimated by fitting a single-compartment model to data obtained from regular ventilation. Static lung and chest wall compliances (Cst,L and Cst,W) were computed from quasi-static pressure-volume data. Lung tissue resistance (Rti) was estimated with alveolar capsules in open-chest animals. The f dependence of the two-compartment viscoelastic model of the respiratory system was assessed by computing the effective resistance [Rmod,rs(omega)] and compliance [Cmod,rs(omega)] from data obtained at the lowest experimental f. Both Cdyn,L and Cdyn,W decreased with increasing f in all animals. Cdyn,L/Cst,L and Cdyn,W/Cst,W were lower in kittens than in cats. RL and RW decreased markedly with f in all animals. Rti/RL showed a marked f dependence, its values being similar in both young and adult cats at their respective resting f. CstW/Cst,L ratio was higher in kittens than in cats. A better agreement was found between Cmod,rs(omega) and Cdyn,rs than between Rmod,rs(omega) and Rrs.

Effects of positive end-expiratory pressure on lung tissue mechanics in rabbits.

The effects of positive end-expiratory pressure (PEEP) on lung tissue resistance (Rti) and dynamic elastance (Edyn,L) were examined separately during histamine-induced lung constriction and after saline lung lavage in anesthetized paralyzed New Zealand White rabbits. During mechanical ventilation in the open-chest state, Rti and Edyn,L were estimated by fitting the appropriate signals to the equation of motion of the single-compartment linear model of the lung. Data were analyzed in relation to the structural damping hypothesis, which assumes that energy dissipation (Rti) and energy storage (Edyn,L) within the lung tissues are coupled at a fundamental level; the coupling parameter, termed hysteresivity (eta), = Rti.omega/Edyn,L, where omega is angular frequency. Under baseline conditions, elevation in PEEP resulted in significant increases in both Rti and Edyn,L, with eta remaining unchanged. During induced constriction and after lung lavage, Rti and Edyn,L significantly increased relative to their baseline values. During histamine-induced constriction, increasing PEEP was associated with increases in Edyn,L, whereas Rti and eta were reduced. After lung lavage, elevation in PEEP from 5 to 7 cmH2O was associated with proportional increases in Rti and Edyn,L, resulting in a relative constancy of eta. By contrast, when PEEP was decreased from 5 to 3 cmH2O, the values of Rti increased, whereas Edyn,L remained unchanged, resulting in significant increases in eta. Collectively, these findings suggest that the effects of PEEP on Rti during agonist-induced constriction and after perturbations of the gas-liquid interface are dependent on the state of alveolar/airway stability.

Effect of body posture on concentration-response curves to inhaled methacholine.

Lung volume has been shown to be a major determinant of the bronchoconstrictor response to inhaled methacholine (MCh). Because a change in body posture from sitting to supine is associated with a reduction in lung volume, we hypothesized that airway responsiveness to inhaled MCh should be affected by body posture. Responsiveness to MCh was assessed in both sitting and supine postures on separate days in 10 subjects aged 24 to 42 yr. Subjects inhaled aerosols of saline and MCh in progressively doubling concentration (0.125 to 256 mg/ml). Responses were assessed by measuring partial and complete forced expiratory flow-volume curves (PEFV and MEFV, respectively). As indices of airway responsiveness, we took the MCh concentration ([MCh]) at which the FEV1 fell by 10% relative to postsaline (PC10), the maximal percentage fall in FEV1 (MR), the [MCh] at which FEV1 reached 50% of MR (EC50), and the [MCh] at which the flow at 20% vital capacity on PEFV curves fell by 20% relative to postsaline (FP20). Responsiveness to MCh was increased in the supine compared with the sitting posture. In the sitting posture, the geometric mean values of MR, PC10, and FP20 were 16.3%, 16.3 mg/ml, and 2.0 mg/ml; supine they were 29.9% (p less than 0.009), 3.0 mg/ml (p less than 0.02), and 0.6 mg/ml (NS), respectively. EC50 did not change with posture. These results are consistent with the notion that airway responsiveness is influenced by airway-parenchymal interdependence and indicate that the results of bronchial provocation testing in the supine posture cannot be directly compared with those in the upright posture.

Effects of volume history and vagotomy on pulmonary and chest wall mechanics in cats.

Using the technique of rapid airway occlusion during constant-flow inflation, we studied the effects of inflation volume, different baseline tidal volumes (10, 20, and 30 ml/kg), and vagotomy on the resistive and elastic properties of the lungs and chest wall in six anesthetized tracheotomized paralyzed mechanically ventilated cats. Before vagotomy, airway resistance decreased significantly with increasing inflation volume at all baseline tidal volumes. At any given inflation volume, airway resistance decreased with increasing baseline tidal volume. After vagotomy, airway resistance decreased markedly and was no longer affected by baseline tidal volume. Prevagotomy, pulmonary tissue resistance increased progressively with increasing lung volume and was not affected by baseline tidal volume. Pulmonary tissue resistance decreased postvagotomy. Chest wall tissue resistance increased during lung inflation but was not affected by either baseline tidal volume or vagotomy. The static volume-pressure relationships of the lungs and chest wall were not affected by either baseline tidal volume or vagotomy. The data were interpreted in terms of a linear viscoelastic model of the respiratory system (J. Appl. Physiol. 67: 2276-2285, 1989).

Low-frequency respiratory system resistance in the normal dog during mechanical ventilation.

The low-frequency resistances of the respiratory system, lung, and chest wall were investigated in four anesthetized paralyzed dogs mechanically ventilated at various frequencies between 0.08 and 0.83 Hz. The resistances were calculated by three different methods: 1) as the real part of the complex impedance obtained from regular ventilation data, 2) as the effective resistance of a two-compartment model fitted to the same data, and 3) as the resistance of a single-compartment model fitted to data obtained during sinusoidal ventilation at various frequencies. Alveolar pressures were measured by a closed-chest alveolar capsule technique and afforded a direct measure of airways resistance. All three resistance estimates were very similar and decreased markedly with frequency between 0 and 1 Hz. The real part of lung impedance at the higher frequencies investigated (around 5 Hz) closely approximated airways resistance, as predicted by the eight-parameter viscoelastic model of respiratory mechanics proposed by Bates et al. (J. Appl. Physiol. 67:2276-2285, 1989).

Airway pressures during crying: an index of respiratory muscle strength in infants with neuromuscular disease.

The purpose of this study was to assess the strength of the respiratory muscles in 12 infants with neuromuscular disease (age range: 0.17-2.08 years) by measuring the maximal inspiratory and expiratory airway pressures (Pimax and PEmax) during crying efforts. Infants were divided into two groups according to their respiratory history. Group A included six infants in stable condition without clinical evidence of respiratory abnormalities, and Group B included six infants with severe generalized muscle weakness and previous respiratory failure. The infants in Group B had been weaned from mechanical ventilation 6 to 14 days before being studied. For infants of Group A, Pimax and PEmax values were 77 +/- 28 cmH2O and 62 +/- 18 cmH2O, respectively; for infants of Group B, they were 38 +/- 8 cmH2O and 34 +/- 8 cmH2O, respectively. A positive correlation was found between PEmax and body mass percentile. No infant had hypercapnia at the time of the study, and Pao2 values in infants of Group B were significantly lower than those of Group A. These results suggest that measurements of airway pressures during crying may provide an index of respiratory muscle strength in infants with generalized muscle weakness.

High-frequency characteristics of respiratory mechanics determined by flow interruption.

When flow at the airway opening is suddenly interrupted, the pressure measured just behind the point of interruption generally exhibits certain characteristic features, including some rapid and highly damped oscillations immediately after the interruption. It has previously been assumed that these oscillations reflect ringing of central airways gas. In the present study we investigated this hypothesis by performing flow interruptions during relaxed expiration in normal, tracheostomized, anesthetized, paralyzed dogs while the lungs were filled with four different gas mixtures having widely varying physical properties. We found that the power spectrum of the oscillations exhibited two peaks. The larger peak was centered about a frequency that varied approximately linearly with the inverse of the square root of the gas density. The other peak was smaller and was located at approximately 70 Hz with all gas mixtures. The area under the power spectrum of the ringing varied approximately linearly with the density of the gas mixture. These results indicate that the larger peak in the power spectrum reflects the quarter-wave resonance of the gas in the airways, whereas the smaller peak reflects a tissue resonance.

Effect of serotonin on expiratory pulmonary resistance in cats.

In five anesthetized paralyzed cats, mechanically ventilated with tidal volumes of 36-48 ml, the isovolume pressure-flow (IVPF) relationships of the lung were studied under control conditions and during serotonin-induced bronchoconstriction. At the end of a tidal inspiration, airway opening pressure was set between +3 and -15 cmH2O for single tidal expirations. After control measurements, animals were treated with progressively increasing doses of intravenous serotonin (10, 20, 50, and 100 micrograms.kg-1.min-1) and all measurements were repeated at each dose. No animal became flow limited during passive expiration against atmospheric pressure. Disregarding flow-limited segments, IVPF plots for three lung volumes showed that the resistive pressure-flow relationships were curvilinear under all conditions, thus fitting Rohrer's equation. Under control conditions and during the lowest dose of serotonin, the volume dependence of pulmonary resistance (RL) tended to balance its flow dependence so that during lung deflation against atmospheric pressure RL remained nearly constant. However, as bronchoconstriction became more pronounced, RL often increased disproportionately at the lower lung volumes. Changes in expiratory RL with serotonin relative to control values varied according to the flow rates used to make comparisons. The technique used to determine RL will partly determine the results obtained.

Quasi-static pressure-volume hysteresis in the canine respiratory system in vivo.

We investigated the quasi-static pressure-volume (P-V) hysteresis of the normal canine lung in vivo by performing 15-s flow interruptions at various points throughout the breathing cycle in mechanically ventilated anesthetized paralyzed dogs. By measuring the transpulmonary pressure (Ptp) at 5 s after each interruption, we built up a quasi-static P-V loop of the lungs. We found, however, that the area of the loop was significantly smaller (by a factor of 4-6) than has been reported by others for the isolated canine lung. We also found the hysteresis loop area of the chest wall to be of similar magnitude. If we measured Ptp 10-15 s after interruption, we found it always decreased at a rate expected to result from continuing gas exchange in the lungs. We conclude that 1) the areas of the quasi-static P-V loop in vivo for the total respiratory system, as well as the lungs and chest wall separately, are significantly smaller than has been reported previously for isolated lungs and 2) continuing gas exchange in the lungs places a lower limit on the frequencies (equivalent to flow interruptions of greater than 5- to 7-s duration) at which the P-flow-V behavior of the lungs in vivo can be considered in purely mechanical terms.

The low-frequency dependence of respiratory system resistance and elastance in normal dogs.

The resistance (R) and elastance (E) of the respiratory system were determined by fitting the equation: pressure = R x flow + E x volume to data obtained from normal anesthetized/paralyzed dogs during mechanical ventilation at different frequencies (5 to 50 breaths per min) and tidal volumes. R exhibited a 50% decrease with increasing frequency while E showed a less marked but still distinct increase with frequency. Volume-time profiles were also recorded in the same animals during passive expiration, and the frequency dependence of resistance and elastance from 0 to 1 Hz predicted from the bi-exponential curves fitted to the profiles. The way in which resistance and elastance were predicted to vary with frequency was similar to the variations determined from regular ventilation data. There were, however, some systematic differences between the actual values of resistance and elastance obtained by the two methods which may reflect certain nonlinear characteristics of the respiratory system such as static hysteresis. Nonlinearities were also evident in that both the resistances and the elastances at all frequencies showed a slight decrease with increasing tidal volume. We conclude that a large part of the mechanical behaviour of the normal canine respiratory system at low frequencies can be accounted for in terms of a two-compartment model describing a homogeneous alveolar region surrounded by viscoelastic tissue.

Flow and volume dependence of expiratory resistance in anesthetized cats.

In five anesthetized paralyzed cats, mechanically ventilated with tidal volumes of 36-48 ml, the isovolume pressure-flow relationships of the lung and respiratory system were studied. The expiratory pressure was altered between 3 and -12 cmH2O for single tidal expirations. Isovolume pressure-flow plots for three lung volumes showed that the resistive pressure-flow relationships were curvilinear in all cases, fitting Rohrer's equation: P = K1V + K2V2, where P is the resistive pressure loss, K1 and K2 are Rohrer's coefficients, and V is flow. Values of K1 and K2 declined with lung inflation, consistent with the volume dependence of pulmonary (RL) and respiratory system resistances (Rrs). During lung deflation against atmospheric pressure, RL and Rrs tended to remain constant through most of expiration, resulting in a nearly linear volume-flow relationship. In the presence of a fixed respiratory system elastance, the shape of the volume-flow profile depended on the balance between the volume and the flow dependence of RL and Rrs. However, the flow dependence of RL and Rrs indicates that their measured values will be affected by all factors that modify expiratory flow, e.g., respiratory system elastance, equipment resistance, and the presence of respiratory muscle activity.

[Severe asthmatic crisis in children]. / Crisis asmática grave en niños.

The aim of the present study was to evaluate clinical and laboratory features of acute severe asthma (ASA) in children and their outcome of mechanical ventilation (MV). Twenty ASA episodes admitted to the hospital with hypercapnia (HC) and/or lost of consciousness (LC) and/or severe non reversible bronchial obstruction (NRBO) were retrospectively studied. Long lasting asthma and frequent admissions were registered in the majority of cases. In HC group (14 cases) the PaCO2 was 70 +/- 26 mmHg (X +/- SD). Hypercapnia was associated with intravenous administration of sodium bicarbonate in three cases. In NRBO group (4 cases) the acute response to salbutamol brought out during the first week of treatment and it was associated with increased basal forced expiratory volume in one second (FEV1). Ten cases were treated with MV because of hypercapnia and/or lost of consciousness, seizures (one case), and cardiac arrest (one case). The later patient died in 24 hours. Pneumothorax and atelectasis (one case), and pneumonia (one case) were the complications of mechanical ventilation. Three cases with PaO2 less than 60 mmHg and four cases with FEV1 less than 60% were sent home. After 27 days one patient from the later group had a new episode of ASA. Arterial gases and expiratory flow measurements are paramount tools for close monitoring of children with ASA. It is suggested that normalization of those parameters are an essential criteria for discharging those patients.

Airway pressures during crying in healthy infants.

Maximal inspiratory and expiratory airway pressures (PI max and PE max) were measured in 100 healthy infants (51 males, 49 females; age range, 0.06-3.76 years) by occluding the airway with a suitable face mask during a crying effort. Mean values +/- SD for PI max and PE max were 118 +/- 21 cm H2O and 125 +/- 35 cm H2O, respectively. Maximal inspiratory pressure was independent of age, sex, and anthropometrics, while maximal expiratory pressure showed a low but statistically significant positive correlation with body weight (P less than 0.001).