Bronchial challenge, assessed with forced expiratory manoeuvres and airway impedance.

OBJECTIVE: The Methacholine concentration at which a 20% decrease of the forced expiratory volume in 1s (PC20_FEV1) or a 40% increase in airway resistance (PC40_Rrs6) occur are accepted indicators for airway hyperresponsiveness. We hypothesised that the level of detection of bronchial hyperresponsiveness will differ between the two methods. METHODS: The response to Methacholine was assessed by forced oscillation technique (FOT) and spirometry in 20 stable hyperresponsive asthmatics. The effects of repeated lung function measurements on respiratory muscle fatigue were measured from maximal inspiratory mouth pressure (MIP). After each dose, patients scored their perception of dyspnoea on a BORG scale. Differences in patient's burden were measured by comparing the BORG-score at PC40_Rrs6 (BORG-PC40_Rrs6) and at PC20_FEV1 (BORG-PC20_FEV1). Reproducibility was also evaluated. RESULTS: The PC20_FEV1-values were 2.2 (0.4) doubling dose higher as compared to the PC40_Rrs6 (P<0.001). The mean BORG-score at PC40_Rrs6 was 1.7 points lower as compared to the BORG-score at PC20_FEV1 (P<0.001). The difference (mean(sd)) between the PC20_FEV1 of measurement 1 and 2 was -0.1 (1.4) doubling dose, and -0.3 (2.7) doubling dose for PC40_Rrs6. The MIP after Methacholine provocation was 1.0(0.2) kPa lower as compared to the MIP before the challenge test (P<0.001), suggesting respiratory muscle fatigue. CONCLUSION: Measuring PC40_Rrs6 shortens the challenge test and lowers the concentrations of bronchoconstrictor agents as compared to measurements of PC20_FEV1. The FOT-method was less strenuous for patients. In spite of the fact that the reproducibility is two-fold worse than measuring PC20_FEV1, it still remains quite acceptable at a mean of 0.3 doubling dose. The respiratory muscle strength was deteriorated after the challenge test.

Hiperreactividad bronquial en pacientes con bronquiolitis / Bronchial hyperreactivity secondary to bronchiolitis

La hiperreactividad bronquial (HRB) se caracteriza por un incremento de la respuesta de la vía aérea a diversos estímulos químicos, físicos y/o biológicos. De estos últimos las infecciones virales que ocasionan bronquiolitis (Br) pueden dejar como secuela una HRB tardía. En este estudio nuestro objetivo fue la detección de HRB en niños que tuvieron Br. Se eligieron pacientes de 7 a 13 años asintomáticos (clínicamente y espirométricamente) sin asma. Se formaron dos grupos, uno de los cuales cursó con Br. siendo lactante y el otro de control, de las mismas características sin este antecedente. Todos fueron sometidos a la inhalación de concentraciones crecientes de metacolina. Las respuestas fueron evaluadas clínicamente y espirométricamente. En el grupo de estudio los restos con metacolina fueron positivos en 40 por ciento, con manifestaciones clínicas (tos, opresión torácica) y/o disminución de los parámetros ventilatorios. En contraste en los controles sólo en dos fue positivo con las concentraciones máximas permisibles. Concluimos que los médicos y los padres deben estar alerta de la posibilidad de HRB tardía en los niños que padecieron

Effects of increased bronchial blood flow on airway morphometry, resistance, and reactivity.

It has been suggested that airway obstruction may be mediated in part by airway vascular engorgement or airway wall edema. However, there are few data that support this conjecture. In this study we examined the effects of increased bronchial blood flow (Qba) on airway wall dimensions, conducting airway resistance, peripheral airway resistance, and airway reactivity assessed by methacholine aerosol challenge. The bronchial artery was perfused with autologous blood (control Qba = 0.6 ml.min-1.kg-1) in anesthetized ventilated sheep. The artery was perfused at either control (C) Qba or at high (H) Qba (300% of C Qba) for 3 h. Morphometry showed a doubling of the vascular area in airways exposed to H Qba (n = 4) compared with C Qba (n = 4). However, the significant increase in wall area could be accounted for only partially by the vascular changes, with edema fluid accumulation accounting for the major increase. Despite these changes, baseline airway resistance (n = 16) and peripheral airway resistance were both unaltered. Airway reactivity to methacholine before and after H Qba was also examined (n = 12). The 3 h of H Qba had no effect on airway reactivity regardless of whether challenge occurred with C or H Qba. The lack of effect of vascular engorgement on airway resistance or reactivity does not support a primary role for these factors in mediating airway obstruction.

Differential inhibition by NG-monomethyl-L-arginine of vasodilator effects of acetylcholine and methacholine in human forearm vasculature.

1. We compared the effects of NG-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor, on vasodilatation produced by acetylcholine and methacholine in human forearm vasculature. 2. Acetylcholine (83 nmol min-1) infused into the brachial artery of 8 healthy volunteers caused a submaximal increase in forearm blood flow, measured by venous occlusion plethysmography, from 3.3 +/- 0.5 (mean +/- s.e. mean) to 13.3 +/- 1.7 ml min-1 100 ml-1. 3. Co-infusion of L-NMMA (4 mumol min-1) with acetylcholine (83 nmol min-1) over 6 min resulted in a 58% +/- 12% fall in the response to acetylcholine whereas during co-infusion of saline over the same time period in the same subjects (n = 8) on a different day the response to acetylcholine fell by only 9% +/- 17% (P < 0.01). 4. Methacholine (1.5 and 15 nmol min-1) increased forearm blood flow from 2.5 +/- 0.4 to 5.9 +/- 0.9 and from 3.2 +/- 0.4 to 17.0 +/- 1.9 ml min-1 100 ml-1 respectively. 5. Co-infusion of L-NMMA (4 mumol min-1) had no significant effect on the response to methacholine (1.5 or 15 nmol min-1) when compared with saline control (n = 8). Co-infusion of a higher dose of L-NMMA (8 mumol min-1) with methacholine (1.5 nmol min-1) did not significantly inhibit the vasodilator response (n = 7). 6. These results suggest that, in human forearm vasculature, methacholine acts predominantly through mechanisms other than the L-arginine/nitric oxide pathway.

Methacholine inhalation challenge. Practical consequences of using duplicate spirograms after each concentration.

Several studies have shown that during bronchial provocation tests with pharmacologic agents, a prior deep inspiration causes transient bronchodilatation in normal subjects and patients with allergic rhinitis. We investigated the influence of using two consecutive spirograms after each methacholine concentration on the results of methacholine inhalation challenge. Methacholine inhalation challenge was performed in 70 nonsmoking subjects (26 with current asthma, 23 asymptomatic asthmatic patients and 21 patients with allergic rhinitis). The aerosols (PBS, followed by twofold increasing concentrations of methacholine from 0.095 to 50 mg/mL) were inhaled by tidal breathing for two minutes; after two minutes of aerosol inhalation, the subject performed two forced vital capacity maneuvers, 30 to 40 seconds apart. Separate dose-response curves were constructed from FEV1 values of the first and second spirogram. The PC20FEV1 (provocative concentration of methacholine required to produce a 20% fall in FEV1) was calculated from the log dose-response curves (first and second spirogram). The PC20 values obtained from the first (PC20-1) and second (PC20-2) spirogram were not significantly different in patients with current asthma, but the PC20-2 values were higher than the PC20-1 values in asymptomatic asthmatic patients (P < .01) as well as in patients with allergic rhinitis (P < .01). On the other hand, the PC20-2 values were one doubling concentration of PC20-1 values in one current asthmatic patient, one asymptomatic asthmatic patient and five patients with allergic rhinitis. We conclude that the choice of the first or second FEV1 obtained after each methacholine concentration significantly modifies the PC20 in asymptomatic asthmatic patients and patients with allergic rhinitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Inherent coupling of elastic and dissipative behavior of the lung through a viscoelastic time constant.

The simple model best able to describe the viscoelastic behavior of lung tissues contains a Kelvin body. Some facets of the viscoelastic behavior of the model can be characterized by a time constant. We have performed a series of experiments to demonstrate this viscoelastic time constant in open-chest mechanically ventilated puppies by recording the stress recovery after midexpiratory flow interruption. In 19 8- to 10-wk-old puppies, the mean time constant was 0.64 +/- 0.01 (SE) s. This time constant remained unchanged after inhalation challenge with histamine, methacholine, or hypertonic saline, despite marked changes in tissue mechanics (resistance and elastance) and in hysteresivity. The constancy of the viscoelastic time constant demonstrates a tight coupling of the parameters of the Kelvin body model, effectively reducing the viscoelastic parameters to a single degree of freedom, and may explain the coupling between the dynamic elastic and resistive properties of the lung tissues previously demonstrated.

Airway-parenchymal interdependence and bronchial responsiveness in two highly inbred rat strains.

To investigate if airway-parenchymal interdependence may account for differing bronchial responsiveness between inbred rat strains, Fisher and Lewis 12-wk-old male rats were anesthetized, tracheostomized, and placed in a pressure plethysmograph. Functional residual capacity, total lung capacity [lung volume at transpulmonary pressure (PL) of 30 cmH2O], and specific compliance were determined and were found to be similar. Rats were paralyzed and mechanically ventilated. Concentration-response curves were constructed by calculating lung resistance (RL) and lung elastance (EL) after nebulization of saline and then doubling doses of methacholine (0.0625-512 mg/ml). In Fisher (n = 8) and Lewis (n = 7) rats RL and EL were again determined at a lung volume corresponding to 2 cmH2O PL above FRC. The doubling, maximal, and half-maximal effective concentrations were determined for RL and EL. The doubling of effective concentrations of RL and EL were significantly less for Fisher rats. Other groups of Fisher (n = 5) and Lewis (n = 5) rats were similarly exposed to three concentrations of methacholine (64, 128, and 256 mg/ml), and determinations of RL and EL were made at lung volume corresponding to PL of 0, 2, 4, and 8 cmH2O. In both groups, Lewis rats exhibited a significant effect of volume on maximal RL and EL, whereas Fisher rats did not. The absence of volume effect on bronchoconstriction in the hyperresponsive Fisher strain is consistent with the hypothesis that altered airway-parenchymal interdependence contributes to bronchial hyperresponsiveness.

Multiple antigen challenge produces pulmonary eosinophilia but not pulmonary hyperresponsiveness in actively sensitized guinea pigs.

Exposure of actively sensitized boosted guinea pigs to aerosolized antigen, 3 times on alternate days, produced pulmonary eosinophilia but not pulmonary hyperresponsiveness to methacholine Cl measured 3 days after the last antigen challenge. These data suggest that the presence of large numbers of eosinophils in the airways and tissues of the lungs is not sufficient to produce nonspecific pulmonary hyperresponsiveness. These data also suggest that actively sensitized and boosted guinea pigs respond differently to repeated antigen exposure than do asthmatics or wild caught allergic cynomolgus monkeys.

Oxatomide modifies methacholine- and exercise-induced bronchoconstriction in asthmatic children.

Oxatomide is a potent inhibitor of both the release and effects of allergic mediators and is similar to calcium antagonists in chemical structure. It prevents histamine release by inhibiting not only the increase in calcium intake, but also intracellular calcium release. We investigated its effect on methacholine-induced and exercise-induced bronchoconstriction in asthmatic children. Methacholine challenges were performed after oral administration of 0.88 mg/kg oxatomide or placebo in nine asthmatic children in a double-blind placebo-controlled study. Respiratory thresholds were improved in seven patients and log PC20 in the oxatomide group (6.65 +/- 1.34 micrograms/mL) was significantly higher than that in the placebo group (5.74 +/- 1.04 micrograms/mL) (P < .05). Exercise challenges were performed after oral administration of 1.5 mg/kg oxatomide or placebo in eight asthmatic children in a double-blind placebo-controlled study. Oxatomide produced acute bronchodilatation with 6.1% improvement on an average in FEV1. The mean maximal % fall obtained by oxatomide was 13.5%, while that by placebo was 22% (P < .05). These results indicate that oxatomide reduces nonspecific bronchial hyperresponsiveness.

In vivo evaluation of airway and pulmonary tissue response to inhaled methacholine in the rat.

The current study was designed to assess the methacholine dose-response behaviour of the airways and pulmonary parenchyma with the aid of alveolar capsules. The experiments were performed in eight adult female Wistar rats (155-250 g). The animals were anaesthetized with sodium pentobarbital (30 mg kg-1 i.p.) and mechanically ventilated. Measurements of tracheal (ptr) and alveolar (pA) pressures and the pressure change across the airway (p(aw)) were performed prior to and after exposing rats to aerosols generated from sequentially increasing concentrations of methacholine chloride solution (2, 4, 8, 16, 32, 64 and 128 mg ml-1) through the breathing circuit. Baseline p(aw) and pA mean (+/- SD) values (6.44 +/- 2.06 and 8.25 +/- 3.44 cmH2O, respectively) were not statistically different (P = 0.220). The increases in ptr and pA were significant during the dose-response study (P = 0.001), whereas p(aw) was not increased. The increase in pA was significantly higher than that of p(aw) (P less than 0.001). The relationship between the mean (+/- SE) values of ptr and pA could be well described by a straight line (r = 0.990, P less than 0.001). There were also significant correlations based on regression equations between ptr and p(aw) (r = 0.947, P less than 0.001) and pA and p(aw) (r = 0.913, P = 0.004). These findings suggest that the pulmonary tissue of rats is a major component responsible for the increase in lung impedance observed after methacholine challenge. In addition, airway and pulmonary parenchyma pressure changes were correlated, suggesting that both lung regions have a similar sensitivity to the agonist. Our results indicate that the response of peripheral tissues should be considered during bronchial challenge protocols in rats.

Lung tissue behavior during methacholine challenge in rabbits in vivo.

Previous studies have shown that lung challenge with smooth muscle agonists increases tissue viscance (Vti), which is the pressure drop between the alveolus and the pleura divided by the flow. Passive inflation also increases Vti. The purpose of the present study was to measure the changes in Vti during positive end-expiratory pressure- (PEEP) induced changes in lung volume and with a concentration-response curve to methacholine (MCh) in rabbits and to compare the effects of induced constriction vs. passive lung inflation on tissue mechanics. Measurements were made in 10 anesthetized open-chest mechanically ventilated New Zealand male rabbits exposed first to increasing levels of PEEP (3-12 cmH2O) and then to increasing concentrations of MCh aerosol (0.5-128 mg/ml). Lung elastance (EL), lung resistance (RL), and Vti were determined by adjusting the equation of motion to tracheal and alveolar pressures during tidal ventilation. Our results show that under baseline conditions, Vti accounted for a major proportion of RL; during both passive lung inflation and MCh challenge this proportion increased progressively. For the same level of change in EL, however, the increase in Vti was larger during MCh challenge than during passive inflation; i.e., the relationship between energy storage and energy dissipation or hysteresivity was dramatically altered. These results are consistent with a MCh-induced change in the intrinsic rheological properties of lung tissues unrelated to lung volume change per se. Lung tissue constriction is one possible explanation.

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.

Partitioning of pulmonary responses to inhaled methacholine in puppies.

Twelve open-chest mongrel puppies, 8-10 wk old, were studied to localize the site of action of inhaled methacholine within the lungs. Six puppies were challenged with methacholine aerosols and six were challenged with an equal number of nebulizations of normal saline (control group). Pulmonary mechanics were measured during mechanical ventilation and after midexpiratory flow interruptions. Alveolar pressure was measured to allow the partitioning of pulmonary mechanics into airway and tissue components. Good matching between airway opening and alveolar pressures was seen throughout the study. After methacholine challenge, lung resistance increased fivefold. Increases in airway resistance and in the parameters reflecting tissue viscoelastic properties contributed to this increase in lung resistance. Dynamic lung elastance also increased threefold. The response of the methacholine group was statistically different from that of the control group. These data indicate that both the airways and pulmonary parenchyma contribute to the response to inhaled methacholine in 8- to 10-wk-old puppies.

[Data on methods in methacholine inhalation provocation tests (dose-response relationship)]. / Methodische Daten zum inhalativen Methacholin-Provokationstest (Dosis-Wirkungsbeziehung).

The cholinergic agonist Methacholine is widely used in unspecific inhalation provocation tests. The maximum changes in lung function take place within two minutes after inhalation. The following spontaneous regression of bronchoconstriction to baseline is prolonged. Therefore, cumulative dose response curves are possible to do. The results of those tests are very dependent on the methods used. Strict standardization of the individual method is necessary. One possible inhalation provocation technique is described.

Local cholinergic sweat stimulation in atopic dermatitis. An evaporimetric study.

In atopic dermatitis the nature of potential sweating disturbances is still obscure. Using an evaporimeter, local sweating response to a supra-threshold concentration of methacholine and baseline water loss were measured from non-eczematous back skin of 167 young males in five main groups (pure atopic dermatitis, atopic dermatitis with rhinitis/asthma, rhinitis/asthma, non-atopic dermatosis, and non-atopic healthy). Subjects with atopic dermatitis were further divided into two subgroups: dry-looking and normal-looking back skin. Compared with non-atopic healthy individuals, the sweat loss was significantly depressed (p less than 0.01) and the baseline water loss significantly increased (p less than 0.001) in the main groups with atopic dermatitis. Both these trends were most distinct in atopic dry-looking skin, whereas in normal-looking atopic skin only the sweat loss was depressed (p less than 0.05). Respiratory atopy had no effect on the sweating response. No significant correlation was found between the individual baseline water loss and the sweating response.

Normal responsiveness of superficial hand veins to alpha- and beta-adrenergic stimuli in allergic asthma: effects of terbutaline and prednisolone on beta-adrenergic responsiveness.

Impaired function of the adrenergic-receptor system has been postulated to contribute to the pathogenesis of bronchial asthma. Using the dorsal hand-vein compliance technique, we compared the changes in diameter of superficial hand veins in response to phenylephrine, an alpha-adrenoceptor agonist, and to isoproterenol, a beta-adrenoceptor agonist, in 14 untreated patients with allergic asthma and in 16 nonatopic control subjects. There were no significant differences in the median effective dose of phenylephrine that produced 50% of maximal venoconstriction (ED50) or in the maximal response (Emax) between the two groups. Bronchial hyperreactivity (assessed by methacholine-challenge tests) in the patients with asthma was uncorrelated with the ED50 or Emax of isoproterenol. These results demonstrate no evidence for a generalized change in alpha- or beta-adrenergic responsiveness on smooth muscle cells in asthma. Hand-vein responsiveness to isoproterenol was unchanged after treatment for 7 days with oral terbutaline (5 mg three times per day). Thus, unlike leukocytes, smooth muscle appears not readily susceptible to beta-adrenoceptor desensitization in vivo. Local infusions of prednisolone or dexamethasone during 2 hours and systemic administration of dexamethasone (24 hours) caused a significant fall in the Emax for isoproterenol. The mechanism of attenuation of beta-adrenoceptor responsiveness by corticosteroids remains to be determined.

Airflow obstruction after substance P aerosol: contribution of airway and pulmonary edema.

We have studied the effects of aerosolized substance P (SP) in guinea pigs with reference to lung resistance and dynamic compliance changes and their recovery after hyperinflation. In addition, we have examined the concomitant formation of airway microvascular leakage and lung edema. Increasing breaths of SP (1.5 mg/ml, 1.1 mM), methacholine (0.15 mg/ml, 0.76 mM), or 0.9% saline were administered to tracheostomized and mechanically ventilated guinea pigs. Lung resistance (RL) increased dose dependently with a maximum effect of 963 +/- 85% of baseline values (mean +/- SE) after SP (60 breaths) and 1,388 +/- 357% after methacholine (60 breaths). After repeated hyperinflations, methacholine-treated animals returned to baseline, but after SP, mean RL was still raised (292 +/- 37%; P less than 0.005). Airway microvascular leakage, measured by extravasation of Evans Blue dye, occurred in the brain bronchi and intrapulmonary airways after SP but not after methacholine. There was a significant correlation between RL after hyperinflation and Evans Blue dye extravasation in intrapulmonary airways (distal: r = 0.89, P less than 0.005; proximal: r = 0.85, P less than 0.01). Examination of frozen sections for peribronchial and perivascular cuffs of edema and for alveolar flooding showed significant degrees of pulmonary edema for animals treated with SP compared with those treated with methacholine or saline. We conclude that the inability of hyperinflation to fully reverse changes in RL after SP may be due to the formation of both airway and pulmonary edema, which may also contribute to the deterioration in RL.

Effect of inhaled furosemide on metabisulfite- and methacholine-induced bronchoconstriction and nasal potential difference in asthmatic subjects.

To evaluate the hypothesis that furosemide inhibits indirect bronchoconstrictor challenges by altering airway epithelial ion transport, we studied its effects on indirect bronchoconstriction induced by inhaled metabisulfite (MBS) and nasal potential difference (PD) in seven subjects with mild asthma. Its effect on direct bronchoconstriction by the inhaled muscarinic agonist methacholine (MC) was studied in six of these subjects. Each subject inhaled furosemide, 30 mg, in a randomized, double-blind, placebo-controlled fashion immediately before challenge with MBS (0.3 to 160 mg/ml in increasing doubling concentrations) and, in another study, MC (0.125 to 32 mg/ml) aerosols from a nebulizer attached to a dosimeter. PC20MBS and PC20MC, the concentration of each agent needed to lower FEV1 by 20%, were calculated by linear interpolation of the log dose-response curves. Furosemide had no effect on resting lung function, but it caused a significant threefold reduction in sensitivity to MBS (PC20MBS: GM +/- GSEM, 15.1 +/- 1.6 mg/ml after placebo and 40.7 +/- 1.7 mg/ml after furosemide; p less than 0.001) with a protective index of 64.8 +/- 10.7%. Furosemide caused no change in sensitivity to MC (PC20 MC:GM +/- GSEM, 2.37 +/- 1.61 mg/ml after placebo and 2.19 +/- 1.751 mg/ml after furosemide; NS). In a third study, furosemide, 30 mg, and placebo were inhaled through the nose in a randomized double-blind fashion immediately prior to inhalation of a PC20 concentration of MBS through the nose. Nasal PD was measured before and after placebo or furosemide, and again after MBS inhalation.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-response relationship of ozone-induced airway hyperresponsiveness in unanesthetized guinea pigs.

The effect of ozone dose (the product of ozone concentration and exposure time) on airway responsiveness was examined in unanesthetized, spontaneously breathing guinea pigs. Airway responsiveness was assessed by measuring specific airway resistance (sRaw) as a function of increasing concentration of inhaled methacholine (Mch) aerosol (the concentration of Mch required in order to double the baseline sRaw: PC200Mch). The airway responsiveness was measured before and at 5 min, 5 h, and 24 h after exposure. A 30-min exposure to 1 ppm ozone (dose 30 ppm.min) did not change PC200Mch at any time after exposure. Both a 90-min exposure to 1 ppm ozone and a 30-min exposure to 3 ppm ozone, which are identical in terms of ozone dose (90 ppm.min), decreased PC200Mch to a similar degree. A 120-min exposure to 3 ppm ozone (360 ppm.min) produced a much greater decrease of PC200Mch at 5 min and 5 h after exposure, compared with low-dose exposure. There was a significant correlation between ozone dose and the change in airway responsiveness. In all groups, the baseline sRaw was increased by approximately 50% at 5 min after exposure, but there was no correlation between the changes in PC200Mch and the baseline sRaw. This study suggests that ozone-induced airway hyperresponsiveness in guinea pigs is closely related to ozone dose.