A study on tracheobronchial deposition and 2-hour retention in rabbits.

Deposition of well-defined test aerosols of polystyrene particles was studied in rabbits. The deposition was estimated in a standardized part of the tracheobronchial tree following free dissection of the bronchial parts. Ten rabbits were exposed to a mixture of two test aerosols of about the same size(6-7 mum) tagged with 51-Cr and 46-Sc, respectively. There were interindividual differences in tracheobronchial deposition but a correlation (r equals 0.98) between 51-Cr and 46-Sc tagged particles. Eleven rabbits were first exposed to the 46-Sc tagged aerosol and 2 hours later to the 51-Cr tagged aerosol. In this experiment there was also a correlation (r equals 0.74) between the tracheobronchial deposition of 51-Cr tagged particles and the 2-hour retention of 46-Sc tagged particles. This result together with results from an earlier study indicate that the large interindividual differences in deposition are real and are not caused by differences in exposure technique, or in the aerosols.     

Airway deposition of hygroscopic heterodispersed aerosols: results of a computer calculation

A new computer model is developed and used to calculate the deposition of inhaled heterodispersed hygroscopic aerosols for mouth breathing in a Weibel symmetric bronchial tree. The model was first validated by obtaining good agreement with recent experimental and theoretical data on regional and total airway deposition of monodispersed and heterodispersed nonhygroscopic aerosols. The model was then used to obtain predictions of regional and total deposition of heterodispersed hygroscopic aerosol particles (droplets of NaCl solutions). Parameters that were varied in the hygroscopic calculations include initial droplet NaCl concentration, time of inspiration and expiration, volume of aerosol inspired, period of breath holding, and initial inhaled lognormal aerosol mass median diameter and geometric standard deviation. Results of the computer calculations show that increasing heterodispersity tends to flatten and broaden regional deposition curves when fraction of inhaled mass deposited is plotted vs. inhaled mass median aerodynamic particle diameter. Hygroscopicity is shown to increase tracheobronchial and pulmonary airway deposition with hypertonic NaCl solution aerosols showing increases over isotonic and nonhygroscopic aerosols of up to 200%.     

Systemic pilocarpine increases deposition of and decreases responsiveness to inhaled carbachol in sheep.

The purpose of this study was to determine whether excessive airway secretions could serve as a barrier function against inhaled particulate matter. To increase airway secretions, six conscious sheep were treated with pilocarpine (0.8 mg/kg i.v.). Pilocarpine increased pulmonary resistance (RL) and total aerosol deposition within five breaths (AD5) as determined by the rebreathing of an inert monodisperse aerosol. When RL had returned to baseline, AD5 remained elevated [21 +/- 2% (SE), P < 0.05] and tracheal secretions were increased (237 +/- 77%, P < 0.05) above the values before pilocarpine administration. A carbachol aerosol dose-response curve was carried out at this time and compared with a control carbachol dose-response curve by calculating the dose of carbachol required to increase RL by 400% (PD400). Mean PD400 was increased postpilocarpine by 53 +/- 18 (P < 0.05) and 85 +/- 25% (P < 0.05) when normalized for increased aerosol deposition. Thus, pilocarpine decreased airway responsiveness to inhaled carbachol despite increasing aerosol deposition. The pilocarpine-induced airway hyporesponsiveness to inhaled carbachol is consistent with the hypothesis that excessive secretions have a protective role in the airways.     

Analytical model of hygroscopic particle behavior in human airways

A model is developed to calculate the deposition of hygroscopic aerosols in the human tracheobronchial (TB) tree. The TB airflow pattern assumed is consistent with experimental observations and accounts for anatomical features such as the larynx and cartilaginous rings in large airways. Some original deposition efficiency formulae are presented for laminar and turbulent airstreams. Stepwise growth is simulated by changes in particle size and density at each TB generation. The dose distribution of NaCl aerosols is studied as a function of inhaled particle size and flow rate. Two NaCl growth rate curves are used which differ in the mode of aerosol-air mixing in the trachea. The initial rate of aerosol mixing in the human due to the laryngeal jet is shown to be an important factor affecting the deposition of hygroscopic aerosols. Total TB deposition of NaCl exceeds that for nonhygroscopic particles of the same inhaled aerodynamic size. Hygroscopic growth can also influence the regional TB distribution of dose when submicron NaCl particles grow rapidly enough to deposit by impaction and sedimentation.     

Differences in airway responsiveness to leukotriene D4 in allergic sheep with and without late bronchial responses

Allergic sheep respond to inhaled Ascaris suum antigen with either acute and late bronchial obstructions (dual responders) or only acute bronchoconstriction (acute responders). In this study we tested the hypothesis that one factor which may distinguish between these two populations is the difference in sensitivity to a specific mediator of airway anaphylaxis, leukotriene (LT) D4 (a major component of slow reacting substance of anaphylaxis). We postulated that if the hypothesis was correct then dual responders should demonstrate increased airway responses to inhaled LTD4 and that this increased responsiveness should also be reflected by a more severe response to inhaled antigen. To test this we used animals from both groups with the same degree of non-specific airway responsiveness to carbachol and determined their airway responses to controlled inhalation challenges with synthetic LTD4 and Ascaris suum antigen. Airway responsiveness to carbachol was determined by measuring the change in specific lung resistance (SRL) to increasing concentrations of carbachol aerosol, and then identifying, by linear interpolation, the provocative carbachol concentration which produced a 150% increase (PC150) in SRL. Airway responses to LTD4, and antigen were determined by measuring the percentage change in SRL after a controlled inhalation challenge with either aerosol. Airway responsiveness to carbachol was not different between the two groups. There was, however, a difference (p less than 0.05) in the airway response to the same dose of LTD4 in the two groups. Dual responders showed a 297 +/- 72% increase in SRL as compared to a 90 +/- 13% increase in SRL in the acute responders. Dual responders also showed a greater immediate and more prolonged response to antigen than did acute responders. These results suggest that increased responsiveness to LTD4 may be one factor which may distinguish dual responders from acute responders.     

Determining the basic characteristics of aerosols suitable for studies of deposition in the respiratory tract

Studies of aerosol particle deposition in the respiratory tract requires experimental inhalation of artificial model aerosols. The paper formulates some of the most important requirements for the properties of such aerosols. Several suitable fractions were prepared as part of a research project dealing with the use of microporous polymers for diagnostic purposes. 5 fractions of the polymer designated G-gel 60 with the particle size as stated by the manufacturer, ranging from 3 to 7 micron were evaluated using a 16-channel particle dispersity analyzer HIAC/ROYCO MT 3210 with the sensor 1200 and operated by a microprocessor, the equipment being coupled to an APPLE IIe computer. G-gel 60 particles introduced into the aerosol were characterized by the parameters CMAD, MMAD and sg both numerically and graphically. The measurement procedure was found to be very sensitive with respect to all fractions in evaluating the subtile differences between different lot numbers of the aerosol. G-gel 60 fractions characterized both numerically and graphically were compared with the known aerosols from paraffin oil and atmospheric air. The equipment MT 3210 enables prompt determination of the percentages of aerosol particles distribution by size class. The authors conclude that the procedure, both in its numerical and graphical versions, is particularly suitable for the diagnosis of aerosol particles deposition in the respiratory tract, offering a new application for HIAC/ROYCO in the field of medicine. In evaluating atmospheric aerosol in exhaled air, the number of particles was found to be below that in inhaled air, the difference being dependent on the choice of investigation methods. Percentual distribution of deposited particles following one minute ventilation proved to be at its maximum, as regards atmospheric aerosol, in the 0.30-0.50 micron range. The deposition curve was similar to already published curves, being characterized by an S-shaped pattern with maximum deposition in the greater size classes. An analysis of inhaled, exhaled and deposited aerosol suggested that deposited aerosol is more polydisperse and has particles of greater sizes than inhaled aerosol. Investigation of the effect of apnoe on deposition indicated that deposition increased as a function of apnoeic pause.     

Effects of aerosol histamine and carbachol on central and peripheral airflow resistance in sheep

Sixteen anesthetized artificially ventilated open-chest sheep were prepared with retrograde catheters to allow for measurement of dynamic compliance of the lungs (Cdyn), total airflow resistance of the lungs (RL), and central (Rc) and peripheral (Rp) airflow resistance. Twelve sheep received aerosol histamine and 12 sheep received aerosol carbachol. Eight sheep received and responded to both aerosol histamine and aerosol carbachol. Three sheep received both aerosol histamine and aerosol carbachol but failed to respond to both agents. Under base-line conditions, for the 16 sheep, 69% of total RL was located in the peripheral component, Rp, and 31% in the central component, Rc. Aerosol histamine caused only peripheral small airway changes while aerosol carbachol predominantly effected the central large airways. When aerosol histamine responsiveness, defined using Cdyn or Rp, was compared to aerosol carbachol responsiveness using Rc, a correlation was demonstrable (r = 0.84, n = 8, P less than 0.05). It is possible in sheep to cause relatively pure peripheral small airway and relatively pure central large airway changes by using different bronchoconstrictor agents. Aerosol histamine and aerosol carbachol responsiveness correlated with each other in these artificially ventilated anesthetized sheep.     

Quantitative deposition of ultrafine stable particles in the human respiratory tract

Theoretical models of particle deposition in the respiratory tract predict high fractional deposition for particles of less than 0.1 micron, but there are few confirming experimental data for those predictions. We have measured the deposition fraction of a nonhygroscopic aerosol in the human respiratory tract. The aerosol had a count mean diameter of 0.044 micron SD of 1.93, as measured with an electrical aerosol analyzer, and was produced from a 0.01% solution of bis(2-ethylhexyl) sebacate using a condensation generator. Subjects inhaled the aerosol using a controlled respiratory pattern of 1 liter tidal volume, 12/min. Deposition was calculated as the difference in concentration between inhaled and exhaled aerosol of five size fractions corrected for system deposition and dead-space constants. Three deposition studies were done on each of five normal male volunteers. Means (+/- SE) for the five size fractions were 0.024 micron, 0.71 +/- 0.06; 0.043 micron, 0.62 +/- 0.06; 0.075 micron, 0.53 +/- 0.05; 0.13 micron, 0.44 +/- 0.04; and 0.24 micron, 0.37 +/- 0.06. These data demonstrate that deposition of inhaled particles in the 0.024- to 0.24-micron size range is high and increases with decreasing size. These observations agree with and validate predictions of mathematical models.     

Intravenous versus inhaled atropine for inhibiting bronchoconstrictor responses in dogs

We studied whether the muscarinic antagonist, atropine, given intravenously or by inhalation, inhibits the bronchoconstrictor responses to inhaled acetylcholine and to acetylcholine released by electrical stimulation of the vagus nerves to the same degree. We assessed bronchoconstrictor responses in anesthetized dogs by determining the increase in total pulmonary resistance before and after increasing doses of atropine and then constructing inhibition dose-response curves. Before atropine the responses to the two stimuli were equal in magnitude. After intravenous atropine (initial dose 0.12 micrograms/kg, total dose 16 micrograms/kg) both responses were progressively inhibited to a similar degree. By contrast, after inhaled atropine (initial dose 0.02 micrograms/kg, total dose 2.4 micrograms/kg) the response to acetylcholine inhalation was inhibited to a much greater degree than the response to vagal stimulation. Thus, in studies designed to inhibit bronchoconstriction due to an inhaled muscarinic agonist to the same degree as bronchoconstriction due to a vagal reflex, atropine might better be given intravenously than by inhalation.     

Differences in airway responsiveness to leukotriene D4 in allergic sheep with and without late bronchial responses

Allergic sheep respond to inhaled antigen with either acute and late bronchial obstructions (dual responders) or only acute bronchoconstriction (acute responders). In this study we tested the hypothesis that one factor which may distinguish between these two populations is the difference in sensitivity to a specific mediator of airway anaphylaxis, leukotriene (LT) D₄ (a major component of slow reacting substance of anaphylaxis). We postulated that if the hypothesis was correct than dual responders should demonstrate increased airway responses to inhaled LTD₄ and that this increased responsiveness should also be reflected by a more severe response to inhaled antigen. To test this we used animals from both groups with the same degree of non-specific airway responsiveness to carbachol and determined their airway responses to controlled inhlation challenges with synthetic LTD₄ and antigen. Airway responsiveness to carbachol was determined by measuring the change in specific lung resistance (SR_L) to increasing concentrations of carbachol aerosol, and then identifying, by linear interpolation, the provocative carbachol concentration which produced a 150% increase (PC₁₅₀) in SR_L. Airway responses to LTD₄, and antigen were determined by measuring the percentage change in SR_L after a controlled inhlation challenge with either aerosol. Airway responsiveness to carbachol was not different between the two groups. There was, however, a difference (p<0.05) in the airway response to the same dose of LTD₄ in the two groups. Dual responders showed a 297±72% increase in SR_L as compared to a 90±13% increase in SR_L in the acute responders. Dual responders also showed a greater immediate and more prolonged response to antigen than did acute responders. These results suggest that increased responsiveness to LTD₄ may be one factor which may distinguish dual responders from acute responders.     

Inhibition of allergic late airway responses by inhaled heparin-derived oligosaccharides.

Inhaled heparin has been shown to inhibit allergic bronchoconstriction in sheep that develop only acute responses to antigen (acute responders) but was ineffective in sheep that develop both acute and late airway responses (LAR) (dual responders). Because the antiallergic activity of heparin is molecular-weight dependent, we hypothesized that heparin-derived oligosaccharides (<2, 500) with potential anti-inflammatory activity may attenuate the LAR in the dual-responder sheep. Specific lung resistance was measured in 24 dual-responder sheep before and serially for 8 h after challenge with Ascaris suum antigen for demonstration of early airway response (EAR) and LAR, without and after treatment with inhaled medium-, low-, and ultralow-molecular-weight (ULMW) heparins and "non-anticoagulant" fractions (NAF) of heparin. Airway responsiveness was estimated before and 24 h postantigen as the cumulative provocating dose of carbachol that increased specific lung resistance by 400%. Only ULMW heparins caused a dose-dependent inhibition of antigen-induced EAR and LAR and postantigen airway hyperresponsiveness (AHR), whereas low- and medium-molecular-weight heparins were ineffective. The effects of ULMW heparin and ULMW NAF-heparin were comparable and inhibited the LAR and AHR even when administered "after" the antigen challenge. The ULMW NAF-heparin failed to inhibit the bronchoconstrictor response to histamine, carbachol, and leukotriene D(4), excluding a direct effect on airway smooth muscle. In six sheep, segmental antigen challenge caused a marked increase in bronchoalveolar lavage histamine, which was not prevented by inhaled ULMW NAF-heparin. The results of this study in the dual-responder sheep demonstrate that 1) the antiallergic activity of inhaled "fractionated" heparins is molecular-weight dependent, 2) only ULMW heparins inhibit the antigen-induced EAR and LAR and postantigen AHR, and 3) the antiallergic activity is mediated by nonanticoagulant fractions and resides in the ULMW chains of <2,500.     

Refractoriness for ultrasonically nebulized distilled water and histamine after histamine challenge

Refractoriness for bronchial provocation frequently occurs after different challenge tests used to assess bronchial hyperresponsiveness in asthmatic patients. We investigated whether histamine inhalation could cause refractoriness for bronchoconstriction induced by ultrasonically nebulized distilled water (UNDW) and whether histamine causes tachyphylaxis for a subsequent histamine challenge in nine stable asthmatic patients. Preinhalation of histamine induced a significant diminished bronchoconstrictor response to UNDW cumulative dose of inhaled UNDW causing a 20% fall in forced expired volume in 1 s. The mean increased from 3.5 +/- 0.8 to 11.8 +/- 2.6 (SE) ml after histamine challenge (P less than 0.01). However, repeated inhalation of histamine did not change the bronchoconstrictor response to histamine within 1 h after rechallenge (P greater than 0.5). The magnitude of refractoriness for UNDW inhalation after preinhalation of histamine was correlated to the bronchoconstrictor response to histamine (r = 0.73, P less than 0.05). We conclude that inhaled histamine can induce refractoriness for UNDW, which seems to be related to the degree of bronchial hyperresponsiveness.     

Desensitization to PAF-induced bronchoconstriction and to activation of alveolar macrophages by repeated inhalations of PAF in the guinea pig

Guinea-pig alveolar macrophages are activated in the presence of PAF-acether (PAF), as shown by O2.- production, suggesting that these cells, abundant in the lungs, are involved in PAF-induced bronchoconstriction. Alveolar macrophages collected after in vivo desensitization to the bronchoconstrictor effect of PAF became refractory to it in vitro, whereas the O2.- production in response to f-met-leu-phe persisted, although it was diminished suggesting a partial cross-desensitization. A similar desensitization to PAF was also observed in alveolar macrophages in vitro, demonstrating a stimulus-specific process. This study suggests that alveolar macrophages may be involved in bronchoconstriction induced by aerosol of PAF.     

Aerosol particle deposition in human lungs

The pneumoconiosis developing after inhalation of air-borne dusts in the work place depends on the relation between the value of particle deposition in the respiratory tract and the rate of particle clearance from sites of their deposition. For testing the deposition in humans an aerosol of paraffin oil was given to a cohort of healthy persons. The characteristic parameters of the aerosol had been defined. The concentration of particles in 5 channels were measured in both the inhaled and exhaled air samples using the particle counter ROYCO 225. The deposition fraction was calculated from the relation of particle amount in expired air to the amount in inhaled air in each distribution class. In this preliminary report the results comparable with the prediction mathematical curve are discussed.     

Effect of exercise on deposition and subsequent retention of inhaled particles

To investigate the effect of exercise and its associated increase in ventilation on the deposition and subsequent retention of inhaled particles, we measured the fractional and regional lung deposition of a radioactively tagged (99mTc) monodisperse aerosol (2.6 microns mass median aerodynamic diam) in normal human subjects at rest and while exercising on a bicycle ergometer. Breath-by-breath deposition fraction (DF) was measured throughout the aerosol exposures by Tyndallometry. Following each exposure gamma camera analysis was used to 1) determine the regional distribution of deposited particles and 2) monitor lung retention for 2.5 h and again at 24 h. We found that DF was unchanged between ventilation at rest (6-10 l/min) and exercise (32-46 l/min). Even though mouth deposition was enhanced with exercise, it was not large enough to produce a significant difference in the deposition fraction of the lung (DFL) between resting and exercise exposures. The central-to-peripheral distribution of deposited aerosol was larger for the exercise vs. resting exposure, reflecting a shift of particle deposition to more central bronchial airways. Apical-to-basal distribution was not different for the two exposures. Retention at 2.5 h and 24 h (R24) was reduced following the exercise vs. the resting exposure, consistent with greater bronchial deposition during exercise. The product of DFL and R24 gave a measure of fractional burden at 24 h (B24), i.e., the fraction of inhaled aerosol residing in the lungs 24 h after exposure. B24 was not significantly different between rest and exercise exposures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in the time course of proximal and distal airway response to inhaled histamine studied by synchrotron radiation CT.

We studied the kinetics of proximal and distal bronchial response to histamine aerosol in healthy anesthetized and mechanically ventilated rabbits up to 60 min after histamine administration using a novel xenon-enhanced synchrotron radiation computed tomography imaging technique. Individual proximal airway constriction was assessed by measuring the luminal cross-sectional area. Distal airway obstruction was estimated by measuring the ventilated alveolar area after inhaled xenon administration. Respiratory system conductance was assessed continuously. Proximal airway cross-sectional area decreased by 57% of the baseline value by 20 min and recovered gradually but incompletely within 60 min. The ventilated alveolar area decreased immediately after histamine inhalation by 55% of baseline value and recovered rapidly thereafter. The results indicate that the airway reaction to inhaled histamine and the subsequent recovery are significantly slower in proximal than in distal bronchi in healthy rabbit. The findings suggest that physiological reaction mechanisms to inhaled histamine in the airway walls of large and small bronchi are not similar.     

Tracheobronchial irritancy of inhaled prostaglandins in the conscious cat

A novel test was developed to measure the tracheobronchial irritant activity of inhaled prostaglandins. Conscious restrained cats were challenged with separate aerosols of PGE1, PGF2alpha, acetylcholine or isoprenaline. All of the aerosols except isoprenaline caused coughing in a concentration related manner. Tolerance developed very quickly to the tracheobronchial irritation and lasted 1-2 days for PGE1 and less than 1 day for PGF2alpha and acetylcholine. When a 3 day interval between each aerosol challenge was used, PGF2alpha was approximately 700 times more potent than acetylcholine as a tracheobronchial irritant. The highest PGE1 aerosol concentration (500microgram/ml) also caused sedation, diarrhoea and salivation. This test probably provides a useful method for evaluating the tracheobronchial irritant activity of potential prostaglandin bronchodilator analogues and for investigating the mechanism of action of prostaglandin induced tracheobronchial irritancy.     

Modified Spinning Top Homogeneous Spray Apparatus for Use in Experimental Respiratory Disease Studies

The May spinning top generator was adapted to a modified Henderson tube for producing large aerosol particles (>4 mum) to obtain almost exclusive upper respiratory tract deposition of infectious aerosols in exposed mice. The system was installed in a biological safety cabinet to permit experimentation with pathogens. A novel mechanism utilizing parts from a machinists micrometer and the mechanical stage from a light microscope was developed for the spinning top generator as a means for precisely positioning the liquid feed needle. Aerosol light-scatter properties were continuously analyzed to provide relative measures of particle size distribution and aerosol concentration. When mice were exposed to influenza virus aerosols in which none of the virus was contained in particles with aerodynamic diameters <4 mum, essentially all of the virus was deposited in the upper respiratory tract tissues.     

Pulmonary defense mechanisms in Boa constrictor

We studied aerosol deposition and the response to inhaled particles and irritants in lungs of Boa constrictor. Snakes which breathed submicrometric particles radiolabeled with 99mTc retained 41.4 +/- 9.9% of the aerosol in the trachea, 42.5 +/- 8.8% in the anterior faveolar regions, and 8.7 +/- 4.1% in the posterior saccular regions of the lungs. Low activity recovered in the gastrointestinal tract over a 5-h period following aerosol exposure indicated slow clearance of inhaled particles. In contrast to mammalian lungs, there are no macrophages resident on the surface of boa lungs, and uningested particles persist for up to 4 days without being phagocytized. Particles and irritant stimuli (Fe2O3, endotoxin, and N-formylmethionylphenylalanine) elicited only eosinophilic granulocytes that were not phagocytic. The numbers of these cells peaked at 24 h following exposure and declined gradually over the next 7 days. Lavage fluid from stimulated snake lungs contained many large lamellar figures continuous with tubular myelin, a form of surfactant. Very little of this material was recovered from control lungs. Response to inhaled particles and lung injury in boas increased surfactant release, elicited eosinophilic granulocytes, but did not recruit phagocytic mononuclear cells.