Substance P-inducing massive postmortem bronchoconstriction in guinea pig lungs

To further examine the role that substance P plays in initiating the observed massive postmortem bronchoconstriction in guinea pig lungs and to explore the role of neural reflex in this airway spasm, six groups of animals were employed: control (n = 6), morphine (n = 6), substance P (n = 5), chronic capsaicin pretreatment + substance P (n = 5), tetrodotoxin (TTX) + acute capsaicin (n = 4), and chlorisondamine + acute capsaicin (n = 5). Pressure-volume curves were performed prior to and following the initiation of artificial pulmonary perfusion with 1% bovine serum albumin and 5% dextran in Tyrode's solution. A decrease in inflation volume (the lung volume between transpulmonary pressure of 0 and 30 cmH2O during inflation) was used as an index of bronchoconstriction. In control animals, inflation volume decreased to 20-30% of the base-line value at 15-30 min of perfusion, indicating massive bronchial constriction during this time period. Morphine (an agent inhibiting substance P release) significantly attenuated the spasm, whereas the presence of substance P in the perfusate markedly enhanced the constriction. Depletion of endogenous substance P by chronic capsaicin pretreatment did not affect exogenous substance P-induced spasm. Acute capsaicin-induced bronchoconstriction was significantly attenuated by TTX but was not affected by the ganglionic blocking agent, chlorisondamine. These data suggest that substance P initiates the massive postmortem bronchoconstriction in guinea pig lungs and that substance P is released by local stimulation of sensory nerve endings via axonal reflex.     

Prevention of abnormal pulmonary mechanics in the postmortem guinea pig lung

Severe postmortem bronchoconstriction has been shown previously in guinea pig lungs and linked to pulmonary blood loss during exsanguination (Lai et al., J. Appl. Physiol. 56: 308-314, 1984). To reexamine this phenomenon we measured postmortem airway function in anesthetized open-chest guinea pigs after sudden circulatory arrest. Animals were divided into 4 groups of 10 and ventilated for 15 min postmortem with different gases: 1) room air, 2) conditioned air, 3) dry 5% CO2-21% O2-74% N2, and 4) conditioned 5% CO2-21% O2-74% N2. In room air-ventilated lungs there was a 50% decrease in dynamic compliance (Cdyn) by 15 min and marked gas trapping compared with control lungs. Conditioning the room air did not attenuate these changes, but when 5% CO2 was added to the conditioned postmortem inspirate, gas trapping was eliminated and the fall in Cdyn was almost abolished. Ventilation with a dry 5% CO2 gas mixture at room temperature resulted in a 31% fall in Cdyn at 15 min but no gas trapping. We conclude that marked abnormalities of airway function occur postmortem in room air-ventilated guinea pig lungs in the absence of pulmonary blood loss. The changes are mainly due to airway hypocarbia, a known cause of bronchoconstriction, but a reduction in Cdyn can also occur if there is marked airway cooling and drying. Acute postmortem airway dysfunction can be prevented in the guinea pig by maintaining normal airway gas composition.     

Factors affecting massive postmortem bronchoconstriction in guinea pig lungs

To examine endogenous factors affecting the development of the massive bronchoconstriction in the postmortem guinea pig lung, 58 anesthetized open-chest animals were divided into three groups: 1) exsanguination only (n = 13), 2) pulmonary perfusion with 5% dextran and 1% bovine serum albumin (BSA) in Tyrode's solution (Ca2+ perfusate) (n = 21), and 3) pulmonary perfusion with 5% dextran and 1% BSA in saline (Ca2+-free perfusate) (n = 24). These groups were further divided into several subgroups according to treatments: 1) substance P depletion by chronic administration of capsaicin, 2) acute capsaicin treatment to release substance P, 3) dazoxiben treatment to block endogenous synthesis of thromboxane A2, 4) diethylcarbamazine treatment to eliminate leukotriene (LT) synthesis, and 5) FPL 55712 treatment to antagonize actions of LT. Vital capacity from the deflation pressure-volume (PV) curve of the lung was used as the indicator of bronchoconstriction. Most PV curves were performed for 30 min following exsanguination or artificial perfusion. Ca2+-free perfusate enhanced the airway spasm at 5-10 min, but the spasm disappeared gradually after 10 min. Substance P depletion significantly decreased (P less than 0.01) the bronchial constriction at 20-30 min, whereas substance P release induced severe airway spasm (P less than 0.01) during the entire study. In addition, FPL 55712 reduced the bronchospasm (P less than 0.05) in Ca2+ perfusate at 30 min. Thus Ca2+ and several endogenous mediators may be involved with the airway spasm of the postmortem guinea pig lung.     

Clapping or percussion causes atelectasis in dogs and influences gas exchange

We examined the effects of 10 min of lower lateral chest wall percussion with a mechanical percussor or hand clapping in groups of anesthetized, paralyzed, and ventilated supine dogs. Mechanical percussion was applied at 10-16 Hz and caused an esophageal pressure swing (delta Pes) of 10-17 cmH2O. Hand clapping was applied at 4-7 Hz and caused a delta Pes of 6-17 cmH2O. At necropsy there were large reddened areas on the lateral surface of the underlying lung as well as smaller reddened areas on the hilar surfaces of both lungs and on the lateral surface of the opposite lung. These reddened regions were demonstrated to be atelectatic by postmortem lung inflation (which caused the reddened areas to disappear) and by microscopic examination. Despite the atelectasis, gas exchange improved toward the end of the percussion or clapping period. In four dogs that were ventilated for an additional 20 min after percussion, there was a tendency for gas exchange initially to worsen and then to gradually improve.     

Tachykinins mediate hypocapnia-induced bronchoconstriction in guinea pigs

The aim of this study was to determine whether hypocapnia causes bronchoconstriction by releasing tachykinins (TKs) from C-afferent nerves in airways. Hypocapnia-induced bronchoconstriction (HIBC) was induced in anesthetized vagotomized guina pigs by ventilating lungs with a heated humidified hypocapnic gas mixture for 15 min after sudden circulatory arrest. The intensity of bronchoconstriction was assessed by calculating changes in dynamic compliance and by measuring the relaxation lung volume at the completion of experiments. Visualization of the airways by tantalum bronchography showed constriction of segmental bronchi with relative sparing of more proximal airways. Hypocapnia-induced bronchoconstriction was prevented by prior administration of salbutamol aerosol. Three experimental interventions were used to investigate the role of TKs in HIBC: 1) repeated capsaicin injections to deplete airway sensory nerves of TKs, 2) treatment with phosphoramidon, an inhibitor of enkephalinase, the main enzyme responsible for TK inactivation, and 3) topical airway anesthesia. Capsaicin pretreatment markedly attenuated the hypocapnia-induced changes in dynamic compliance (P less than 0.0005) and relaxation lung volume (P less than 0.0002), whereas phosphoramidon augmented these changes (P less than 0.02, P less than 0.03, respectively). Topical anesthesia of airways with lignocaine postponed the onset of bronchoconstriction, whereas the longer-acting, more lipid-soluble local anesthetic, bupivacaine, almost completely prevented HIBC. We conclude that, in the guinea pig lung, HIBC is mediated by TKs that are released after the activation of bronchial axonal reflexes.     

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

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

Chronological relationships between mediator release and changes in airway dynamics during an ascaris response in sensitive cynomolgus monkeys

Recently identified Ascaris suum sensitive cynomolgus monkeys were further characterized to determine if a chronologic relationship existed between mediator release and onset of bronchoconstriction. In these anesthetized Ascaris-sensitive monkeys, aerosol antigen challenge of each animal produced rapid and severe bronchoconstriction, as determined by decreases in dynamic lung compliance (-80.2 +/- 4.1%) and airway conductance (-64.5 +/- 13.8%). Maximum changes were achieved within 5 min following exposure and remained substantially altered throughout the 30 min observation period. However, changes in pulmonary function related to duration of onset and maximum change seemed to have some correlation with each animals' sensitivity to the antigen. Comparison of pre- and post-challenge blood gas profiles, showed a progressive formation of respiratory acidosis through decreases in arterial blood pH, partial pressure of O2 (pO2), O2 saturation (sO2) and an increase in partial pressure of CO2 (pCO2). When arterial blood plasma was assayed by RIA for mediators of anaphylaxis, large increases in 5-hydroxyeicostetraenoi acid (5-HETE), leukotriene B4 (LTB4) and histamine were observed. No amount of prostaglandin F2-alpha (PGF2 alpha) or thromboxane A2 were detected. Two of the three monkeys also produced detectable amounts of leukotriene C4 (LTC4). Therefore, in Ascaris-sensitive monkeys, histamine is the predominate mediator released and is probably responsible for at least the early part (5-10 min) of the observed bronchoconstriction. However, mediators from the lipoxygenase pathway may also be playing a role in the antigen-induced bronchoconstriction, especially beyond the 10 min period following anaphylaxis.     

Comparison of three tracers for detecting lung epithelial injury in anesthetized sheep

We compared the ability of three aerosolized tracers to discriminate among control, lung inflation with a positive end expired pressure of 10 cmH2O, lung vascular hypertension and edema without lung injury, and lung edema with lung injury due to intravenous oleic acid. The tracers were 99mTc-diethylenetriaminepentaacetate (99mTc-DTPA, mol wt 492), 99mTc-human serum albumin (99mTc-ALB, mol wt 69,000), and 99mTc-aggregated albumin (99mTc-AGG ALB, mol wt 383,000). 99mTc-DTPA clearance measurements were not able to discriminate lung injury from lung inflation. The 99mTc-AGG ALB clearance rate was unchanged by lung inflation and increased slightly with lung injury. The 99mTc-ALB clearance rate (0.06 +/- 0.02%/min) was unchanged by lung inflation (0.09 +/- 0.02%/min, P greater than 0.05) or 4 h of hypertension without injury (0.09 +/- 0.04%/min, P greater than 0.05). Deposition of 99mTc-ALB within 15 min of the administration of the oleic acid increased the clearance rate to 0.19 +/- 0.06%/min, which correlated well with the postmortem lung water volume (r = 0.92, P less than 0.01). This did not occur when there was a 60-min delay in the deposition of 99mTc-ALB. We conclude that 99mTc-ALB is the best indicator for studying the effects of lung epithelial injury on protein and fluid transport into and out of the air spaces of the lungs in a minimally invasive manner.     

Morphological evidence for alveolar recruitment during inflation at high transpulmonary pressure

The effect of continuous inflation of lungs at 30 cmH2O transpulmonary pressure (Ptp) on air-space size was assessed by chord length-frequency distribution analysis. Lungs from gerbils were excised, allowed to collapse freely, and inflated to 30 cmH2O Ptp in a humidified chamber kept at 37 degrees C. When the lungs appeared fully inflated with no observable pleural surface atelectasis, the left lung was occluded while the right was maintained at 30 cmH2O for 10 min longer and then occluded. During this time, the right lung increased its volume from 70 to 100%. Then both lungs were quick frozen, freeze dried, and embedded in glycol methacrylate, and 1- to 2-microns-thick histological sections cut. Lungs from a control group of gerbils were similarly inflated to 30 cmH2O, both left and right were occluded, the left was quick frozen immediately, and the right was frozen 10 min later. Chord lengths of air spaces from cranial and caudal lobes of lungs were acquired using a Dapple Systems image analyzer, and a two-population frequency distribution was generated for analysis with an IBM PC. The results indicate that the volume increase during continuous inflation at 30 cmH2O Ptp was associated with a shift in the chord length distribution toward the smaller chord lengths. A two-population statistical analysis indicated that the inflation resulted in an increase in the relative proportion of smaller chord lengths, with no increase in the mean of this smaller population. We conclude that continuous inflation at 30 cmH2O Ptp results in alveolar recruitment.     

Cyclooxygenase-2-dependent bronchoconstriction in perfused rat lungs exposed to endotoxin.

BACKGROUND: Lipopolysaccharides (LPS), widely used to study the mechanisms of gram-negative sepsis, increase airway resistance by constriction of terminal bronchioles. The role of the cyclooxygenase (COX) isoenzymes and their prostanoid metabolites in this process was studied. MATERIALS AND METHODS: Pulmonary resistance, the release of thromboxane (TX) and the expression of COX-2 mRNA were measured in isolated blood-free perfused rat lungs exposed to LPS. RESULTS: LPS induced the release of TX and caused increased airway resistance after about 30 min. Both TX formation and LPS-induced bronchoconstriction were prevented by treatment with the unspecific COX inhibitor acetyl salicylic acid, the specific COX-2 inhibitor CGP-28238, dexamethasone, actinomycin D, or cycloheximide. LPS-induced bronchoconstriction was also inhibited by the TX receptor antagonist BM-13177. The TX-mimetic compound, U-46619, increased airway resistance predominantly by constricting terminal bronchioles. COX-2-specific mRNA in lung tissue was elevated after LPS exposure, and this increase was attenuated by addition of dexamethasone or of actinomycin D. In contrast to LPS, platelet-activating factor (PAF) induced immediate TX release and bronchoconstriction that was prevented by acetyl salicylic acid, but not by CGP-28238. CONCLUSIONS: LPS elicits the following biochemical and functional changes in rat lungs: (i) induction of COX-2; (ii) formation of prostaglandins and TX; (iii) activation of the TX receptor on airway smooth muscle cells; (iv) constriction of terminal bronchioles; and (v) increased airway resistance. In contrast to LPS, the PAF-induced TX release is likely to depend on COX-1.     

On defining total lung capacity in the mouse.

Maximal lung volume or total lung capacity in experimental animals is dependent on the pressure to which the lungs are inflated. Although 25-30 cm H2O are nominally used for such inflations, mouse pressure-volume (P-V) curves show little flattening on inflation to those pressures. In the present study, we examined P-V relations and mean alveolar chord length in three strains (C3H/HeJ, A/J, and C57BL/6J) at multiple inflation pressures. Mice were anesthetized, and their lungs were degassed in vivo by absorption of 100% O2. P-V curves were then recorded in situ with increasing peak inflation pressure in 10-cm H2O increments up to 90 cm H2O. Lungs were quickly frozen at specific pressures for morphometric analysis. The inflation limbs never showed the appearance of a plateau, with lung volume increasing 40-60% as inflation pressure was increased from 30 to 60 cm H2O. In contrast, parallel flat deflation limbs were always observed, regardless of the inflation pressure, indicating that the presence of a flat deflation curve cannot be used to justify measurement of total lung capacity in mice. Alveolar size increased monotonically with increasing pressure in all strains, and there was no evidence of irreversible lung damage from these inflations to high pressures. These results suggest that the mouse lung never reaches a maximal volume, even up to nonphysiological pressures >80 cm H2O.     

Effect of ventilation and perfusion imbalance on inert gas rebreathing variables

The effects of ventilation-to-perfusion (VA/Qc) maldistribution within the lungs on measured multiple gas rebreathing variables were studied in 14 dogs. The rebreathing method (using He, C18O, and C2H2) allows for measurements of pulmonary capillary blood flow (Qc), diffusing capacity (DLco), lung gas volume, and the combined pulmonary tissue and capillary blood volume (VTPC). VA/Qc imbalance was created by reversibly occluding the right main pulmonary artery or by reversibly obstructing the left main bronchus in eight dogs. Six additional dogs were ventilated with 10 cmH2O positive end-expiratory pressure (PEEP) to create a bimodal distribution of VA/Qc within the lungs. No significant alterations in computed rebreathing variables, except for a small (14%) decrease in DLco, occurred during right main pulmonary artery occlusion, whereas obstruction of the left main bronchus caused parallel decreases (mean of 46%) in all rebreathing variables. Ventilation with 10 cmH2O PEEP for 3 h caused no alterations in VTPC when compared with postmortem determinations of total lung water. Thus marked alterations in distribution of Qc or creation of VA/Qc maldistributions with PEEP caused no significant changes in rebreathing parameters, whereas obstruction of the left main bronchus resulted in decreases in all rebreathing values consistent with the presumed size of the ventilation defect. Thus it appears that rebreathing estimates of VTPC and other rebreathing parameters are accurate in states of moderate VA/Qc maldistribution within the lung.     

Oxygen radical scavengers protect against eosinophil-induced injury in isolated perfused rat lungs.

The protective effect of oxygen radical scavengers on lung injury induced by activated eosinophils was examined in isolated perfused rat lungs. Eosinophils were obtained by bronchoalveolar lavage from rats infected with Toxocara canis and activated with phorbol myristate acetate (PMA). There were no changes in pulmonary vascular (RT) and airway (Raw) resistances and only minimal changes in vascular permeability assessed using the capillary filtration coefficient (Kf,c) in PMA control lungs and nonactivated eosinophil-treated lungs. In lungs receiving 3 x 10(6) PMA-activated eosinophils, there were significant increases from baseline of 7.3-fold in RT at 30 min, primarily due to the constriction of small arteries and veins; 3.6-fold in Kf,c at 90 and 130 min; and 2.5-fold in Raw. The lungs also became markedly edematous. Both superoxide dismutase and catalase pretreatment prevented the significant increase in Kf,c and lung wet-to-dry weight ratios and partially attenuated the increase in Raw, but did not significantly inhibit the increase in RT induced by activated eosinophils. Heat-inactivated catalase did not attenuate the eosinophil-induced increases in Kf,c, Raw, or RT. Thus, activated eosinophils acutely increased microvascular permeability primarily through production of oxygen free radicals. The free radical scavengers superoxide dismutase and catalase partially attenuated the bronchoconstriction but had no significant effect on the vasoconstriction induced by activated eosinophils.     

Evaluation of two-way protein fluxes across the alveolo-capillary membrane by scintigraphy in rats: effect of lung inflation.

Pulmonary microvascular and alveolar epithelial permeability were evaluated in vivo by scintigraphic imaging during lung distension. A zone of alveolar flooding was made by instilling a solution containing 99mTc-albumin in a bronchus. Alveolar epithelial permeability was estimated from the rate at which this tracer left the lungs. Microvascular permeability was simultaneously estimated measuring the accumulation of (111)In-transferrin in lungs. Four levels of lung distension (corresponding to 15, 20, 25, and 30 cmH2O end-inspiratory airway pressure) were studied during mechanical ventilation. Computed tomography scans showed that the zone of alveolar flooding underwent the same distension as the contralateral lung during inflation with gas. Increasing lung tissue stretch by ventilation at high airway pressure immediately increased microvascular, but also alveolar epithelial, permeability to proteins. The same end-inspiratory pressure threshold (between 20 and 25 cmH2O) was observed for epithelial and endothelial permeability changes, which corresponded to a tidal volume between 13.7 +/- 4.69 and 22.2 +/- 2.12 ml/kg body wt. Whereas protein flux from plasma to alveolar space ((111)In-transferrin lung-to-heart ratio slope) was constant over 120 min, the rate at which 99mTc-albumin left air spaces decreased with time. This pattern can be explained by changes in alveolar permeability with time or by a compartment model including an intermediate interstitial space.     

Tachykinin recovery during postmortem bronchoconstriction in guinea pig lungs.

We examined the role of substance P (SP) and neurokinin A (NKA) in the postmortem bronchoconstriction in guinea pig lungs using isolated lungs superfused via the trachea. Airway opening pressure (Pao) during superfusion was monitored and the superfusate collected for analysis of SP- and NKA-like immunoreactivities (SP-LI and NKA-LI, respectively). Peak Pao (39.0 +/- 3.9 cmH2O) was reached 10 min after starting superfusion; Pao decreased slowly thereafter, reaching only 9.9 +/- 2.2% of the peak value 2 h after starting superfusion (P less than 0.005); 12.6 +/- 2.6 and 34.0 +/- 9.7 fmol of SP-LI and NKA-LI, respectively, were found in the fraction corresponding to 10-20 min of superfusion. Recovered immunoreactivities decreased to 5.2 +/- 0.3 and 9.3 +/- 1.8 fmol of SP-LI and NKA-LI, respectively, in the fraction corresponding to 110-120 min of superfusion (P less than 0.05). Inhibition of neutral endopeptidase with thiorphan resulted in significantly greater increases in Pao (P less than 0.005) and augmentation of the recovery of SP-LI and NKA-LI (P less than 0.05 and P less than 0.001, respectively). Capsaicin treatment of animals 7-10 days before the removal of their lungs abolished the increase in Pao during superfusion and resulted in a significant decrease in the amount of SP-LI and NKA-LI recovered. Our data confirm that tachykinin release occurs during postmortem bronchoconstriction in guinea pig lungs and, furthermore, that tachykinin degradation by NEP modulates the intensity of this response.     

Phosphoinositide 3-kinase, Src, and Akt modulate acute ventilation-induced vascular permeability increases in mouse lungs

To determine the role of phosphoinositide 3-OH kinase (PI3K) pathways in the acute vascular permeability increase associated with ventilator-induced lung injury, we ventilated isolated perfused lungs and intact C57BL/6 mice with low and high peak inflation pressures (PIP). In isolated lungs, filtration coefficients (K(f)) increased significantly after ventilation at 30 cmH(2)O (high PIP) for successive periods of 15, 30 (4.1-fold), and 50 (5.4-fold) min. Pretreatment with 50 microM of the PI3K inhibitor, LY-294002, or 20 microM PP2, a Src kinase inhibitor, significantly attenuated the increase in K(f), whereas 10 microM Akt inhibitor IV significantly augmented the increased K(f). There were no significant differences in K(f) or lung wet-to-dry weight (W/D) ratios between groups ventilated with 9 cmH(2)O PIP (low PIP), with or without inhibitor treatment. Total lung beta-catenin was unchanged in any low PIP isolated lung group, but Akt inhibition during high PIP ventilation significantly decreased total beta-catenin by 86%. Ventilation of intact mice with 55 cmH(2)O PIP for up to 60 min also increased lung vascular permeability, indicated by increases in lung lavage albumin concentration and lung W/D ratios. In these lungs, tyrosine phosphorylation of beta-catenin and serine/threonine phosphorylation of Akt, glycogen synthase kinase 3beta (GSK3beta), and ERK1/2 increased significantly with peak effects at 60 min. Thus mechanical stress activation of PI3K and Src may increase lung vascular permeability through tyrosine phosphorylation, but simultaneous activation of the PI3K-Akt-GSK3beta pathway tends to limit this permeability response, possibly by preserving cellular beta-catenin.     

Bronchoconstriction elicited by isocapnic hyperpnea in guinea pigs

We demonstrated spontaneous self-limited bronchoconstriction after eucapnic dry gas hyperpnea in 22 anesthetized, mechanically ventilated guinea pigs pretreated with propranolol (1 mg/kg iv). Eucapnic hyperpnea "challenges" of room temperature dry or humidified gas (5% CO2-95% O2) were performed by mechanically ventilating animals (150 breaths/min, 3-6 ml tidal volume) for 5 min. During a "recovery" period after hyperpnea, animals were returned to standard ventilation conditions (6 ml/kg, 60 breaths/min, 50% O2 in air, fully saturated at room temperature). After dry gas hyperpnea (5 ml, 150 breaths/min), respiratory system resistance (Rrs) increased in the recovery period by 7.7-fold and dynamic compliance (Cdyn) decreased by 79.7%; changes were maximal at approximately 3 min posthyperpnea and spontaneously returned to base line in 10-40 min. This response was markedly attenuated by humidification of inspired air. Four consecutive identical dry air challenges resulted in similar posthyperpnea responses in four animals. Increasing the minute ventilation during hyperpnea (by varying tidal volume from 3 to 6 ml) caused increased bronchoconstriction in a dose-dependent fashion in six animals. Neither vagotomy nor atropine altered the airway response to dry gas hyperpnea. We conclude that dry gas hyperpnea in anesthetized guinea pigs results in a bronchoconstrictor response that shares five similar features with hyperpnea-induced bronchoconstriction in human asthma: 1) time course of onset and spontaneous resolution, 2) diminution with humidification of inspired gas, 3) reproducibility on consecutive identical challenges, 4) stimulus-response relationship with minute ventilation during hyperpnea, and 5) independence of parasympathetic neurotransmission.     

Effects of lung volume, bronchoconstriction, and cigarette smoke on morphometric airway dimensions

To examine the role of airway wall thickening in the bronchial hyperresponsiveness observed after exposure to cigarette smoke, we compared the airway dimensions of guinea pigs exposed to smoke (n = 7) or air (n = 7). After exposure the animals were anesthetized with urethan, pulmonary resistance was measured, and the lungs were removed, distended with Formalin, and fixed near functional residual capacity. The effects of lung inflation and bronchoconstriction on airway dimensions were studied separately by distending and fixing lungs with Formalin at total lung capacity (TLC) (n = 3), 50% TLC (n = 3), and 25% TLC (n = 3) or near residual volume after bronchoconstriction (n = 3). On transverse sections of extraparenchymal and intraparenchymal airways the following dimensions were measured: the internal area (Ai) and internal perimeter (Pi), defined by the epithelium, and the external area (Ae) and external perimeter (Pe), defined by the outer border of smooth muscle. Airway wall area (WA) was then calculated, WA = Ae - Ai. Ai, Pe, and Ae decreased with decreasing lung volume and after bronchoconstriction. However, WA and Pi did not change significantly with lung volume or after bronchoconstriction. After cigarette smoke exposure airway resistance was increased (P less than 0.05); however, there was no difference in WA between the smoke- and air-exposed groups when the airways were matched by Pi. We conclude that Pi and WA are constant despite changes in lung volume and smooth muscle tone and that airway hyperresponsiveness induced by cigarette smoke is not mediated by increased airway wall thickness.     

Density dependence of maximal flow is lung volume dependent during bronchoconstriction

We examined the changes in maximum expiratory flow (Vmax) and the density dependence of maximum expiratory flow (delta Vmax) during histamine-induced bronchoconstriction in dogs. Histamine acid phosphate solution was nebulized into the airways of six dogs to produce predominantly peripheral airway obstruction. Vmax air, Vmax with the dogs breathing 80% He-20% O2 (delta Vmax), and airway sites of flow limitation (choke points) were examined at four lung volumes (VL), which ranged from 51 to 23% of the control vital capacity (VC). The findings were interpreted in terms of the wave-speed theory of flow limitation. At all VL, Vmax air decreased during bronchoconstriction by approximately 30% compared with the control value. Resistances peripheral to a 0.3-cm-diam airway were increased about threefold with histamine, whereas resistances between 0.6-cm-diam bronchi and main-stem bronchi increased just slightly. Airway diameters were measured in the air-dried lung at 20 cmH2O transpulmonary pressure. Our results showed that only at 44% VC did delta Vmax decrease in all experiments after histamine to indicate peripheral obstruction (mean: 68.5 to 45%). At 23% VC, delta Vmax increased slightly, from 22 to 28%. At 23 and 36% VC, substantial differences in the wave-speed variables between air and HeO2 were present before bronchoconstriction, so that delta Vmax was low in some dogs, although peripheral airway obstruction was not evident. When bronchoconstriction was produced, delta Vmax at 23% VC could not be decreased further and even increased in four of six dogs. Thus changes in delta Vmax at given lung volume may not reflect the predominant site of airflow obstruction during bronchoconstriction.     

Effect of acute lymphatic obstruction on fluid accumulation in the chest in dogs.

The effect of acute obstruction to lymphatic drainage on fluid accumulation in the lungs, pleura, and pericardium was assessed in the intact dog. Catheters were positioned in the venae cavase, right atrium (RA), left atrium (LA), age on fluid accumulation in the lungs, pleura, and pericardium was assessed in the intact dog. Catheters were positioned in the venae cavae, right atrium (RA), left atrium (LA), and aorta (Ao) of nine anesthetized, spontaneouly breathing dogs, and hydrostic and colloid osmotic pressures were continuously monitored. Lymphatic obstruction was achieved by raising systemic venous pressure to either 10 mmHg or 25 mmHg by a combination of fluid infusion and inflation of balloon catheters in the venae cavae for 2 h. The same constant net intravascular filtration pressure was maintained in both groups by appropriate use of saline or colloid-containing fluids. Pleural and pericardial fluids were measured postmortem and lung water content was determined by weighing before and after drying. Failure to detect greater fluid accumulation at the higher obstructing pressure (25 mmHg) than at the lower obstructing pressure (10 mmHg) suggests that over the range of obstructing pressures used there is no acute change in the magnitude of lymphatic drainage in the chest.