Lung tissue behavior in the mouse during constriction induced by methacholine and endothelin-1

Nagase, Takahide, Hirotoshi Matsui, Tomoko Aoki, YasuyoshiOuchi, and Yoshinosuke Fukuchi. Lung tissue behavior in the mouseduring constriction induced by methacholine and endothelin-1. J. Appl. Physiol. 81(6):2373-2378, 1996.Recently, mice have been extensively used toinvestigate the pathogenesis of pulmonary disease because appropriatemurine models, including transgenic mice, are being increasinglydeveloped. However, little information about the lung mechanics of miceis currently available. We questioned whether lung tissue behavior andthe coupling between dissipative and elastic processes, hysteresivity(), in mice would be different from those in the other species. Toaddress this question, we investigated whether tissue resistance (Rti)and  in mice would be affected by varying lung volume, constrictioninduced by methacholine (MCh) and endothelin-1 (ET-1), andhigh-lung-volume challenge during induced constriction. From measuredtracheal flow and tracheal and alveolar pressures in open-chest ICRmice during mechanical ventilation [tidal volume = 8 ml/kg,frequency (f) = 2.5 Hz], we calculated lung resistance(RL), Rti, airway resistance(Raw), lung elastance (EL),and  (=2fRti/EL). Underbaseline conditions, increasing levels of end-expiratory transpulmonarypressure decreased Raw and increased Rti. The administration ofaerosolized MCh and intravenous ET-1 increasedRL, Rti, Raw, andEL in a dose-dependent manner.Rti increased from 0.207 ± 0.010 to 0.570 ± 0.058 cmH₂O ^· ml^{1 ·} safter 10⁷ mol/kg ET-1(P < 0.01). After inducedconstriction, increasing end-expiratory transpulmonary pressuredecreased Raw. However,  was not affected by changing lung volume,constriction induced by MCh and ET-1, or high-lung-volume challengeduring induced constriction. These observations suggest that1)  is stable in mice regardlessof various conditions, 2) Rti is animportant fraction of RL andincreases after induced constriction, and3) mechanical interdependence mayaffect airway smooth muscle shortening in this species. In mammalianspecies, including mice, analysis of  may indicate that both Rti andEL essentially respond to asimilar degree.

     

Greater airway narrowing in immature than in mature rabbits during methacholine challenge

Shen, X., V. Bhargava, G. R. Wodicka, C. M. Doerschuk, S. J. Gunst, and R. S. Tepper. Greater airway narrowing in immature thanin mature rabbits during methacholine challenge. J. Appl. Physiol. 81(6): 2637-2643, 1996.It hasbeen demonstrated that methacholine (MCh) challenge produces a greaterincrease in lung resistance in immature than in mature rabbits (R. S. Tepper, X. Shen, E. Bakan, and S. J. Gunst.J. Appl. Physiol. 79: 1190-1198, 1995). To determine whether this maturational difference in the response to MCh was primarily related to changes in airway resistance (Raw) or changes in tissue resistance, we assessed airway narrowing in1-, 2-, and 6-mo-old rabbits during intravenous MCh challenge (0.01-5.0 mg/kg). Airway narrowing was determined frommeasurements of Raw in vivo and from morphometric measurements on lungsections obtained after rapidly freezing the lung after the MChchallenge. The fold increase in Raw was significantly greater for 1- and 2-mo-old animals than for 6-mo-old animals. Similarly, the degree of airway narrowing assessed morphometrically was significantly greaterfor 1- and 2-mo-old animals than for 6-mo-old animals. The foldincrease in Raw was highly correlated with the degree of airwaynarrowing assessed morphometrically(r² = 0.82, P < 0.001). We conclude that thematurational difference in the effect of MCh on lung resistance isprimarily caused by greater airway narrowing in the immature rabbits.

     

Measurement of interrupter resistance in rabbits exposed to methacholine aerosols.

We studied the effect of increasing airway resistance on equilibration of airway and alveolar pressure during passive expiratory airflow interruption. In 10 anesthetized and paralyzed rabbits, airway and alveolar pressures were compared before and after airway resistance was increased with methacholine. In all studies, airway pressure rose to equilibrate with alveolar pressure immediately after the interruption (delta Pinit) regardless of increases in airway resistance. The pressures then remained equal during the interruption while gradually increasing to plateau (delta Pdiff). Before methacholine exposure, delta Pdiff was small (0.6 +/- 0.3 cmH2O). Steady-state resistance calculated from the sum of delta Pinit and delta Pdiff was similar to airway resistance calculated from delta Pinit alone. After methacholine, increased airway resistance was accompanied by increased delta Pdiff (2.0 +/- 0.5 cmH2O), causing disproportionate increase in steady-state resistance. delta Pdiff increases were equal in the airway and alveoli, implying resistive changes distal to the sampled alveoli. Thus increasing airway resistance did not delay pressure equilibration across airways. However, increases in airway resistance were accompanied by tissue resistive changes that were greater than the increases in airway resistance.     

Low-frequency pulmonary impedance in rabbits and its response to inhaled methacholine.

We assessed pulmonary mechanics in six open-chest rabbits (3 young and 3 adult) by the forced oscillation technique between 0.16 and 10.64 Hz. Under control conditions, pulmonary resistance (RL) decreased markedly between 0.16 and 4 Hz, after which it became reasonably constant. Measurements of alveolar pressure from two alveolar capsules in each rabbit showed that the large decrease of RL with increasing frequency below 4 Hz was due to lung tissue rheology and that tissue resistance was close to zero above 4 Hz. Estimates of resistance and elastance, also obtained by fitting tidal ventilation data at 1 Hz to the equation of the linear single-compartment model, gave values for RL motion that were slightly higher than those obtained by forced oscillations at the same frequency, presumably because of the flow dependence of airways resistance. After treatment with increasing doses of aerosolized methacholine, RL and pulmonary elastance between 0.16 and 1.34 Hz progressively increased, as did the point at which the pulmonary reactance crossed zero (the resonant frequency). The alveolar pressure measurements showed the lung to become increasingly inhomogeneously ventilated in all six animals, whereas in the three younger rabbits lobar atelectasis developed at high methacholine concentrations and the alveolar capsules ceased to communicate with the central airways. We conclude that the low-frequency pulmonary impedance of rabbits exhibits the same qualitative features observed in other species and that it is a sensitive indicator of the changes in pulmonary mechanics occurring during bronchoconstriction.     

Upper airway extraluminal tissue pressure fluctuations during breathing in rabbits.

Transmural pressure at any level in the upper airway is dependent on the difference between intraluminal airway and extraluminal tissue pressure (ETP). We hypothesized that ETP would be influenced by topography, head and neck position, resistive loading, and stimulated breathing. Twenty-eight male, New Zealand White, anesthetized, spontaneously breathing rabbits breathed via a face mask with attached pneumotachograph to measure airflow and pressure transducer to monitor mask pressure. Tidal volume was measured via integration of the airflow signal. ETP was measured with a pressure transducer-tipped catheter inserted in the tissues of the lateral (ETPlat, n = 28) and anterior (ETPant, n = 21) pharyngeal wall. Head position was controlled at 30, 50, or 70 degrees, and the effect of addition of an external resistor, brief occlusion, or stimulated breathing was examined. Mean ETPlat was approximately 0.7 cmH2O greater than mean ETPant when adjusted for degree of head and neck flexion (P < 0.05). Mean, maximum, and minimum ETP values increased significantly by 0.7-0.8 cmH2O/20 degrees of head and neck flexion when adjusted for site of measurement (P < 0.0001). The main effect of resistive loading and occlusion was an increase in the change in ETPlat (maximum - minimum ETPlat) and change in ETPant at all head and neck positions (P < 0.05). Mean ETPlat and ETPant increased with increasing tidal volume at head and neck position of 30 degrees (all P < 0.05). In conclusion, ETP was nonhomogeneously distributed around the upper airway and increased with both increasing head and neck flexion and increasing tidal volume. Brief airway occlusion increased the size of respiratory-related ETP fluctuations in upper airway ETP.     

Lung tissue resistance during contractile stimulation: structural damping decomposition.

Research in the mechanics of soft tissue, and lung tissue in particular, has emphasized that dissipative processes depend predominantly on the viscous stress. A corollary is that dissipative losses may be expressed as a tissue viscous resistance, (Rti). An alternative approach is offered by the structural damping hypothesis, which holds that dissipative processes within soft tissue depend directly more on the elastic stress than on the viscous stress. This implies that dissipative and elastic processes within lung tissues are coupled at a fundamental level. We induced alterations of Rti by exposing canines to aerosols of the constrictors prostaglandin F2 alpha, histamine, and methacholine and by changing volume history. Using the structural damping paradigm, we could separate those alterations in Rti into the product of two distinct contributions: change in the coefficient of coupling of dissipation to elastance (eta) and change in the elastance itself (Edyn). Response of Edyn accounted for most of the response of resistance associated with contractile stimulation; it accounted for almost all the response associated with differences in volume history. The eta changed appreciably with constriction but accounted for little of the response of Rti with volume history. According to the structural damping hypothesis, induced changes in eta with constriction must reflect changes in the kinetics of the stress-bearing process, i.e., differences in cross-bridge kinetics within the target contractile cell and/or differences in the influence of the target cell on other stress-bearing systems. We conclude that, regardless of underlying processes, the structural damping analysis demonstrates a fundamental phenomenological simplification: when Edyn responds, Rti is obligated to respond to a similar degree.     

Lung and chest wall mechanics in rabbits during high-frequency body-surface oscillation

In eight anesthetized and tracheotomized rabbits, we studied the transfer impedances of the respiratory system during normocapnic ventilation by high-frequency body-surface oscillation from 3 to 15 Hz. The total respiratory impedance was partitioned into pulmonary and chest wall impedances to characterize the oscillatory mechanical properties of each component. The pulmonary and chest wall resistances were not frequency dependent in the 3- to 15-Hz range. The mean pulmonary resistance was 13.8 +/- 3.2 (SD) cmH2O.l-1.s, although the mean chest wall resistance was 8.6 +/- 2.0 cmH2O.l-1.s. The pulmonary elastance and inertance were 0.247 +/- 0.095 cmH2O/ml and 0.103 +/- 0.033 cmH2O.l-1.s2, respectively. The chest wall elastance and inertance were 0.533 +/- 0.136 cmH2O/ml and 0.041 +/- 0.063 cmH2O.l-1.s2, respectively. With a linear mechanical behavior, the transpulmonary pressure oscillations required to ventilate these tracheotomized animals were at their minimal value at 3 Hz. As the ventilatory frequency was increased beyond 6-9 Hz, both the minute ventilation necessary to maintain normocapnia and the pulmonary impedance increased. These data suggest that ventilation by body-surface oscillation is better suited for relatively moderate frequencies in rabbits with normal lungs.     

Lung mechanics in papain-treated rabbits

To further investigate the effects of airway cartilage softening on static and dynamic lung mechanics, 11 rabbits were treated with 100 mg/kg iv papain, whereas 9 control animals received no pretreatment. Lung mechanics were studied 24 h after papain injection. There was no significant difference in lung volumes, lung pressure-volume curves, or chest wall compliance. Papain-treated rabbits showed increased lung resistance: 91 +/- 63 vs. 39 +/- 22 cmH2O X l-1 X s (mean +/- SD; P less than 0.05), decreased maximal expiratory flows at all lung volumes, and preserved density dependence of maximal expiratory flows. We conclude that increased airway wall compliance is probably the mechanism that limited maximal expiratory flow in this animal model. In addition the increased lung resistance suggests that airway cartilage plays a role in the regulation of airway caliber during quiet tidal breathing.     

Inability of dimethylthiourea to limit tissue necrosis during acute myocardial infarction in rabbits.

This study examined the effect of treatment with dimethylthiourea (DMTU), a highly cell-permeable scavenger of hydroxyl radicals, on tissue necrosis in rabbit hearts during myocardial ischemia and reperfusion. Sixty-two rabbits underwent 45 minutes of coronary occlusion with, or without, coronary reperfusion for 3 hours. A saline vehicle, or DMTU (500 mg/kg intravenously [iv]) was administered over 45 minutes starting either 10 minutes before or 10 minutes after coronary occlusion, or 10 minutes before coronary reperfusion. Anatomic risk zone size was assessed using microsphere autoradiography, and the area of necrosis was determined using tetrazolium staining. Cardiac hemodynamics and risk zone size were similar for all treatment groups. No differences were observed in the extent of tissue necrosis (normalized to risk zone size) for saline- and DMTU-treated rabbits subjected to 45 minutes (61.2 +/- 23.1% vs. 70.6 +/- 16.5%) or 225 minutes (82.8 +/- 5.4% vs. 78.3 +/- 5.9%) of permanent coronary occlusion without reperfusion. Similarly, tissue necrosis in rabbits with 45 minutes coronary occlusion followed by 3 hours reperfusion was not significantly reduced when DMTU was administered either 10 minutes before coronary occlusion, 10 minutes after coronary occlusion, or 10 minutes before coronary reperfusion (67.0 +/- 9.9%; 57.6 +/- 10.6%; 68.3 +/- 13.3%) compared to saline-treated controls (76.6 +/- 10.5%). These results demonstrate that the hydroxyl radical scavenger DMTU does not appear to influence the progression of myocyte injury in this experimental model of acute myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lung and alveolar wall elastic and hysteretic behavior in rats: effects of in vivo elastase treatment.

We investigated the relationship between the microscopic elastic and hysteretic behavior of the alveolar walls and the macroscopic mechanical properties of the whole lung in an in vivo elastase-treated rat model of emphysema. We measured the input impedance of isolated lungs at three levels of transpulmonary pressure (Ptp) and used a linear model to estimate the dynamic elastance and hysteresivity of the lungs. The elastance of the normal lungs increased steeply with Ptp, whereas this dependence diminished in the treated lungs. Hysteresivity decreased significantly with Ptp in the normal lungs, but this dependence disappeared in the treated lungs. To investigate the microscopic origins of these changes, the alveolar walls were immunofluorescently labeled in small tissue strips. By using a fluorescent microscope, the lengths and angular orientations of individual alveolar walls were followed during cyclic uniaxial stretching of the tissue strips. The microstrains (relative change in segment length) and changes in angle of the alveolar walls showed considerable heterogeneity, which was interpreted in terms of a network model. In the normal strips, the alveolar walls showed larger angular changes compared with the treated tissue, whereas the alveolar walls of the treated tissue tended to be more extensible. Hysteresis in the average angle change was also larger in the treated tissue than in the normal tissue. We conclude that the decreased Ptp dependence of elastance and the constant hysteresivity in the treated lungs are related to microstructural remodeling and network phenomena at the level of the alveolar walls.     

The pattern of methacholine responsiveness in mice is dependent on antigen challenge dose

Background

The relative contributions of the cytotoxic phenotype of P. aeruginosa expressing type III secretory toxins and an immunocompromised condition lacking normal Toll-like receptor 4 (TLR4) signaling in the pathogenesis of acute lung injury and sepsis were evaluated in a mouse model for Pseudomonas aeruginosa pneumonia. By using lipopolysaccharide-resistant C3H/HeJ mice missing normal TLR4 signaling due to a mutation on the tlr4 gene, we evaluated how TLR4 signaling modulates the pneumonia caused by cytotoxic P. aeruginosa expressing type III secretory toxins.

Methods

We infected C3H/HeJ or C3H/FeJ mice with three different doses of either a cytotoxic P. aeruginosa strain (wild type PA103) or its non-cytotoxic isogenic mutant missing the type III secretory toxins (PA103ΔUT). Survival of the infected mice was evaluated, and the severity of acute lung injury quantified by measuring alveolar epithelial permeability as an index of acute epithelial injury and the water to dry weight ratios of lung homogenates as an index of lung edema. Bacteriological analysis and cytokine assays were performed in the infected mice.

Results

Development of acute lung injury and sepsis was observed in all mouse strains when the cytotoxic P. aeruginosa strain but not the non-cytotoxic strain was instilled in the airspaces of the mice. Only C3H/HeJ mice had severe bacteremia and high mortality when a low dose of the cytotoxic P. aeruginosa strain was instilled in their lungs.

Conclusion

The cytotoxic phenotype of P. aeruginosa is the critical factor causing acute lung injury and sepsis in infected hosts. When the P. aeruginosa is a cytotoxic strain, the TLR4 signaling system is essential to clear the batcteria to prevent lethal lung injury and bacteremia.     

Effects of microbial challenge on sleep in rabbits

Rabbits challenged with viable Staphylococcus aureus exhibit marked time-dependent changes in sleep patterns. To examine the generality of this observation, we monitored sleep patterns for 24 h before and for 48 h after intravenous inoculation of rabbits with Streptococcus pyogenes, Escherichia coli, or Candida albicans. All three agents produced complex time-dependent changes in sleep. Inoculation with S. pyogenes or C. albicans increased the time spent in slow-wave sleep (SWS) during h 4-20 after challenge. Electroencephalographic delta wave amplitudes (DWA) increased during h 4-8 after injection, but decreased during h 24-38 after inoculation. Altered sleep patterns were not observed when similar doses of heat-killed organisms were administered. In contrast, inoculation with E. coli produced a large increase in both SWS time and DWA for the first 2-4 h after inoculation. DWA then decreased from 6 to 32 h after inoculation. Similar effects occurred when heat-killed E. coli were administered. Rapid eye movement sleep was reduced by all three agents. These data demonstrate that altered sleep patterns occur in response to infectious challenge in rabbits, and that these changes are related to the type of infectious organism involved.     

Lung function and ventilation inhomogeneity in rat lungs after allergen challenge.

We studied the early response to ovalbumin challenge in sensitized Brown-Norway rats through its effect on N(2), He, and SF(6) phase III slopes of the single-breath washout and on indexes of lung function. Sensitized rats showed varying degrees of response in terms of pulmonary pressure (PL), with increases ranging between 125 and 225% of baseline. The sensitized rats presented decreased quasistatic compliance, forced vital capacity, and end-expiratory flow, with all three lung function indexes showing a significant negative correlation with corresponding PL values. They also showed significant positive correlations of PL with the N(2), He, and SF(6) phase III slopes, reflecting diffusion-convection-dependent inhomogeneities generated by conformation changes throughout the entire rat lung. In addition, the rats showing the most marked PL increases (>150% baseline PL) also revealed a reversal of the SF(6)-He slope difference because of a more marked SF(6) than He slope increase. This latter finding suggests that the degree of structural heterogeneity during early response is even more marked in the most peripheral rat lung generations.