The mechanism of exercise-induced asthma is

Exercise-induced asthma (EIA) refers to the transient narrowing of the airways that follows vigorous exercise. The mechanism whereby EIA occurs is thought to relate to the consequences of heating and humidifying large volumes of air during exercise. In 1978 airway cooling was identified as an important stimulus for EIA; however, severe EIA also occurred when hot dry air was inspired, and there was no abnormal cooling of the airways. In 1986 the thermal hypothesis proposed that cooling of the airways needed to be followed by rapid rewarming and that these two events caused a vasoconstriction and a reactive hyperemia of the bronchial microcirculation, together with edema of the airway wall, causing the airways to narrow after exercise. The osmotic, or airway-drying, hypothesis developed from 1982-1992 because neither airway cooling nor rewarming appeared to be necessary for EIA to occur. As water is evaporated from the airway surface liquid, it becomes hyperosmolar and provides an osmotic stimulus for water to move from any cell nearby, resulting in cell volume loss. It is proposed that the regulatory volume increase, after cell shrinkage, is the key event resulting in release of inflammatory mediators that cause airway smooth muscle to contract and the airways of asthmatic subjects to narrow. This event may or may not be associated with airway edema. The osmotic and thermal theories come together by considering that inspiration of cold air not only cools the airways but also increases the numbers of airway generations becoming dehydrated in the humidifying process.

The effect of inhaled mannitol on bronchial mucus clearance in cystic fibrosis patients: a pilot study

It has been postulated that hypertonic saline (HS) might impair the antimicrobial effects of defensins within the airways. Alternative non-ionic osmotic agents such as mannitol may thus be preferable to HS in promoting bronchial mucus clearance (BMC) in patients with cystic fibrosis (CF). This study reports the effect of inhalation of another osmotic agent, dry powder Mannitol (300 mg), compared with its control (empty capsules plus matched voluntary cough) and a 6% solution of HS on BMC in 12 patients with cystic fibrosis (CF). Mucus clearance was measured using a radioaerosol/gamma camera technique. Post-intervention clearance was measured for 60 min, followed by cough clearance for 30 min. Neither mannitol nor HS improved BMC during the actual intervention period compared with their respective controls. However during the post-intervention measurement there was a significant improvement in BMC for both the mannitol (8.7+/-3.3% versus 2.8+/-0.7%) and HS (10.0+/-2.3% versus 3.5+/-0.8%). There was also a significant improvement in cough clearance with the Mannitol (9.7+/-2.4%) compared with its control (2.5+/-0.8%). Despite premedication with a bronchodilator, a small fall in forced expiratory volume in one second (FEV1) was seen immediately after administration of both the mannitol (7.3+/-2.5%) and HS (5.8+/-1.2%). Values of FEV1 returned to baseline by the end of the study. Inhaled mannitol is a potential mucoactive agent in cystic fibrosis patients. Further studies are required to establish the optimal dose and the long-term effectiveness of mannitol.

Inhalation of hypertonic saline aerosol enhances mucociliary clearance in asthmatic and healthy subjects

Hyperosmolarity of the airway surface liquid (ASL) has been proposed as the stimulus for hyperpnoea-induced asthma. We found previously that mucociliary clearance (MCC) was increased after isocapnic hyperventilation (ISH) with dry air, and we proposed that the increase related to transient hyperosmolarity of the ASL. We investigated the effect of increasing the osmolarity of the ASL on MCC, by administering an aerosol of concentrated salt solution. MCC was measured using 99mTc-sulphur colloid, gamma camera and computer analysis in 12 asthmatic and 10 healthy subjects on three separate days, involving administration of each of the following: 1) ultrasonically nebulized 14.4% saline; 2) ultrasonically nebulized 0.9% saline; and 3) no aerosol intervention (control). The (mean +/- SD) volume of nebulized 14.4% saline was 2.2 +/- 1.2 mL for asthmatics and 3.2 +/- 0.7 mL for healthy subjects. This volume was delivered over a period of 5.4 +/- 1.3 and 6.4 +/- 0.7 min for asthmatic and healthy subjects, respectively. The airway response to 14.4% saline was assessed on a separate visit and the fall in forced expiratory volume in one second (FEV1) was 22 +/- 4% in the asthmatic and 3 +/- 2% in the healthy subjects. Compared to the MCC with the 0.9% saline and control, the hypertonic aerosol increased MCC in both groups. In asthmatic subjects, MCC of the whole right lung in 1 h was 68 +/- 10% with 14.4% saline vs 44 +/- 14% with 0.9% saline and 39 +/- 13% with control. In healthy subjects, MCC of the whole right lung in 1 h was 53 +/- 12% with 14.4% saline vs 41 +/- 15% with 0.9% saline and 36 +/- 13% with control. We conclude that an increase in osmolarity of the airway surface liquid increases mucociliary clearance both in asthmatic and healthy subjects. These findings are in keeping with our previous suggestion that the increase in mucociliary clearance after isotonic hyperventilation with dry air is due to a transient hyperosmolarity of the airway surface liquid.

Inhalation of dry powder mannitol improves clearance of mucus in patients with bronchiectasis

Bronchiectasis is a disease characterized by hypersecretion and retention of mucus requiring physical and pharmacologic treatment. Recently we reported that inhalation of dry powder mannitol markedly increases mucociliary clearance (MCC) in asthmatic and in healthy subjects (Daviskas, E., S. D. Anderson, J. D. Brannan, H. K. Chan, S. Eberl, and G. Bautovich. 1997. Inhalation of dry-powder mannitol increases mucociliary clearance. Eur. Respir. J. 10:2449-2454). In this study we investigated the effect of mannitol on MCC in patients with bronchiectasis. Eleven patients 40 to 62 yr of age inhaled mannitol (approximately 300 mg) from a Dinkihaler. MCC was measured over 90 min, in the supine position, on three occasions involving: mannitol or control or baseline, using a radioaerosol technique. On the control day patients reproduced the breathing maneuvers and the number of coughs induced by the mannitol. Mannitol significantly increased MCC over the 75 min from the start of the intervention compared with control and baseline in the whole right lung, central, and intermediate region. Mean (+/- SEM) clearance with mannitol was 34.0 +/- 5.0% versus 17.4 +/- 3.8% with control and 11.7 +/- 4.4% with baseline in the whole right lung (p < 0.0001). The mean number of coughs induced by mannitol was 49 +/- 11. In conclusion, inhalation of dry powder mannitol increased clearance of mucus and thus has the potential to benefit patients with bronchiectasis.

Effect of low dose nebulised morphine on exercise endurance in patients with chronic lung disease

Low dose nebulised morphine may relieve dyspnoea through a direct effect on lung afferent nerves. To study this further 11 adult patients with advanced chronic lung disease (FEV1 range 0.4-1.41), whose exercise endurance was limited by dyspnoea, were entered into a double blind, randomised, crossover study in which low dose morphine or a placebo was inhaled. The effects were assessed by an endurance exercise test at 80% of maximum work load. One hour after a control endurance test patients inhaled 5 ml of morphine 1 mg/ml or isotonic saline for 12 minutes from a jet nebuliser. An endurance exercise test was repeated 15 minutes later and change in endurance time recorded. The two endurance tests were repeated on a separate day, before and after inhalation of the alternative solution. In all tests 100% oxygen was inhaled from a demand valve. The mean (SD) increase in endurance time was significantly greater after the subjects had inhaled morphine (64.6 (115) s, 35%) than after placebo (8.9 (55) s, 0.8%; p less than 0.01). The mean dose of morphine nebulised was 1.7 (0.66) mg, giving a mean inhaled dose of about 0.6 mg, on the assumption of 30% retention of the nebulised dose by each patient. No side effects were reported. Possibly small amounts of morphine delivered to the lungs act directly on lung afferent nerves to reduce dyspnoea.

Inhalation of dry-powder mannitol increases mucociliary clearance

Inhalation of hypertonic saline stimulates mucociliary clearance (MCC) in healthy subjects and those with obstructive lung disease. We investigated the effect of inhaling the osmotic agent mannitol on MCC. We used a dry-powder preparation of mannitol British Pharmacopea (BP) which was encapsulated and delivered using a Dinkihaler. MCC was measured for 75 min in six asthmatic and six healthy subjects on two occasions before and after the mannitol inhalation or its control, using 99mTc-sulphur colloid and a gamma camera. The inhaled dose of mannitol was 267+/-171 mg (mean+/-SD) and 400 mg and the percentage fall in forced expiratory volume in one second (FEV1) was 22+/-3 and 4+/-2% in the asthmatic and healthy subjects, respectively. The total clearance in the whole right lung for the 60 min from the start of inhalation of mannitol was greater by 263+/-11.9% in the asthmatic and 18.1+/-4.9% in the healthy subjects compared to the control. The total clearance over 75 min was 54.7+/-9.6% and 33.6+/-9.4% on the mannitol and control day (p<0.002), respectively, in the asthmatic subjects and 40.5+/-7.1% and 24.8+/-7.8% (p<0.002) in the healthy subjects. In conclusion, inhalation of dry-powder mannitol increases mucociliary clearance in asthmatic and healthy subjects and may benefit patients with abnormal mucociliary clearance.

Mathematical modeling of heat and water transport in human respiratory tract

Excessive heat and water losses from the airways are stimuli to asthma. To study heat and water vapor transport in the human respiratory tract, a time-dependent model, based on a single differential equation with an analytical solution, was developed that could predict the intra-airway temperatures and water vapor contents. The key feature is the dependence of the temperature and water vapor along the respiratory tract as a function of the air residence time at each location. The model assumes disturbed laminar flow leading to enhanced transport mechanisms and wall temperature profiles modeled according to experimental data (E. R. McFadden, Jr., B. M. Pichurko, H. F. Bowman, E. Ingenito, S. Burns, N. Dowling, and J. Soloway. J. Appl. Physiol. 58: 564-570, 1985). It predicts that 1) the air equilibrates with the wall before it reaches body conditions (37 degrees C, 99.5% relative humidity); 2) conditioning of the inspired air involves several generations, with the number depending on the respiratory conditions; and 3) the walls of the upper airways are unsaturated, although it is difficult to judge at this state the depth of the respiratory tract affected.

The 24-h effect of mannitol on the clearance of mucus in patients with bronchiectasis

STUDY OBJECTIVE

To investigate the acute effect of mannitol on the clearance of mucus, and (1) the 24-h mucus retention, and (2) the mucus clearance rate and lung function 24 h after inhalation of a single dose of mannitol.

DESIGN

Clearance of mucus was measured on 3 consecutive days using (99m)Tc-sulfur colloid radioaerosol and a gamma camera.

INTERVENTIONS

Mannitol, 330 +/- 68 mg (mean+/- SD), was inhaled using a dry powder inhaler only on day 2.

PATIENTS

Eight patients with bronchiectasis (age range, 29 to 70 years).

MEASUREMENTS AND RESULTS

On each day, lung images were collected over 2 h and at 24 h. Key findings of the study are as follows: (1) the 24-h retention of mucus was reduced the day after mannitol had been inhaled, compared to the day without mannitol (day 1) in the whole right lung (57.6 +/- 6.2% vs 68.1 +/- 5.9%), central (47.5 +/- 6.7% vs 56.9 +/- 6.5%), intermediate (61.7 +/- 5.6% vs 73.8 +/- 5.5%), and peripheral regions (70.9 +/- 4.3% vs 86.6 +/- 4.6%)(p < 0.02); and (2) mannitol helped patients clear mucus within 2 h that might otherwise take up to 24 h, from the whole right lung and defined regions. However, clearance over 60 min measured 24 h after mannitol inhalation was not significantly different to baseline clearance without mannitol (8.7 +/- 1.9% on day 1 vs 9.7 +/- 3.7% 24 h after mannitol; p > 0.8). The patients maintained the same lung function the day before and after mannitol had been inhaled: FEV(1) (percent predicted), 79 +/- 5 on day 1 vs 80 +/- 5 on day 3; and forced expiratory flow, midexpiratory phase (percent predicted), 50 +/- 6 on day 1 vs 51 +/- 6 on day 3; p > 0.6).

CONCLUSIONS

Mannitol inhalation acutely increases clearance of mucus, and this effect extends beyond the acute study period, resulting in decreased mucus retention at 24 h.

The airway microvasculature and exercise induced asthma

It has been proposed that exercise induced asthma is a result of "rapid expansion of the blood volume of peribronchial plexi" (McFadden ER, Lancet 1990;335:880-3). This hypothesis proposes that the development of exercise induced asthma depends on the thermal gradient in the airways at the end of hyperpnoea. The events that result in exercise induced asthma are vasoconstriction and airway cooling followed by reactive hyperaemia. We agree that the airway microcirculation has the potential for contributing to the pathophysiology of exercise induced asthma. We do, however, question whether reactive hyperaemia, in response to airway cooling, is the mechanism whereby hyperpnoea provokes airways obstruction in asthmatic patients. Further, we question whether vasoconstriction accompanies dry air breathing and whether an abnormal temperature gradient and rapid rewarming of the airways are prerequisites for exercise induced asthma. From published experiments we conclude that dry air breathing is associated with vasodilation and increase in airway blood flow rather than vasoconstriction and a decrease in blood flow to the airways. We propose that the stimulus for the increase in airway blood flow is an increase in osmolarity of the airway submucosa. This osmotic change is caused by the movement of water to the airway lumen in response to evaporative water loss during hyperpnoea. The increase in airway blood flow may occur directly or indirectly by the osmotic release of mediators. Exercise induced asthma is most likely to be due to the contraction of bronchial smooth muscle caused by the same mediators. Whether it is enhanced or inhibited by alterations in airway blood flow is not yet established in man.

Local airway heat and water vapour losses

A previously developed time-dependent mathematical model of the heat and water vapour transport in the human respiratory tract for mouth breathing (Daviskas et al., J. Appl. Physiol. 69:362-372, 1990) was applied to calculate the local quantities of heat and water transfer. The results of the heat and water losses agreed with experimental data. The contribution of each airway to the conditioning of inspired air was found to depend on the inspired air conditions and the pattern of breathing as expected. The greater proportion of the total heat and water loss was calculated to occur within the upper airways. However, below the pharynx, the rate of water loss during hyperpnea was calculated at a much faster rate than in the resting state. The rate at which water is returned to the airways may not be adequate to keep the periciliary fluid isotonic. These findings support the proposal that the intrathoracic airways could become significantly dehydrated during hyperpnea. The use of calculated local heat and water transfer rates may help to predict the site of stimuli to exercise-induced asthma.

Exercise-induced asthma: a difference in opinion regarding the stimulus

There has been some controversy regarding the mechanism whereby exercise can provoke an attack of asthma. It is generally agreed that heat and water are lost from the respiratory tract in bringing the air inspired to body conditions. During strenuous exercise, there is a marked increase in ventilation rate and some of the burden to heat and humidify the inspired air is transferred to the intrathoracic airways. The net effect of the air conditioning process is to cool and dehydrate these airways. There have been two hypotheses put forward to account for the mechanism whereby these events lead to exercise-induced asthma (EIA). One hypothesis proposes that cooling of the airways followed by rapid rewarming, at the end of exercise, leads to a reactive hyperemia and edema of the bronchial vascular bed "which if sufficiently severe results in the airway obstruction of EIA." The other hypothesis proposes that the rate of loss of water from the periciliary fluid during exercise exceeds the rate of return and, as a result, there is an increase in ion concentration and subsequent hyperosmolarity of the periciliary fluid. Thus the events related to drying rather than cooling are the stimulus to EIA. This paper presents the case against rapid rewarming of the bronchial vasculature as the stimulus to EIA and puts forward an argument and data in support of the case for airway drying and an increase in osmolarity being the critical event which determines the presence and severity of EIA.

Regional mucociliary clearance in patients with cystic fibrosis

This paper reports on a large retrospective analysis of mucociliary clearance (MCC) studies in a group of 59 patients with cystic fibrosis (CF) and 17 age-matched healthy subjects. As many of the CF patients were studied on multiple occasions, a total of 184 patient studies are presented. MCC was measured using a radioaerosol and gamma camera technique. In addition to whole lung clearance, MCC was measured from the central, intermediate, peripheral, basal, mid and apical regions of the lung. MCC was markedly decreased in the CF patient group. Not only was whole lung clearance (14.2 +/- 1.4% vs. 28.0 +/- 3.7%) impaired, but also clearance from the central (19.1 +/- 1.9% vs. 35.6 +/- 4.3%), intermediate (10.7 +/- 1.6% vs. 25.5 +/- 3.7%), apical (12.4 +/- 2.6% vs. 31.6 +/- 4.6%) and mid (14.0 +/- 1.9% vs. 30.4 +/- 4.0%) regions. Attempts were made to identify factors that may have influenced MCC in both the normal subjects and CF patients. Age, gender, body mass index, patient genotype, penetration index, spontaneous cough, and various lung function parameters were entered into a stepwise multiple regression model, but none of the factors proved to be statistically important in determining MCC. Both intrasubject repeatability and intersubject variability estimates are presented for the patients and normal subjects that had multiple studies. The values were found to be remarkably similar for both CF patients and normal subjects and for both intra- and intersubject repeatability. With marked deviation from normal ranges and good repeatability, the measurement of MCC in CF patients would seem to be a valuable outcome measure for clinical trials involving new pharmaceuticals and physical therapy designed to improve removal of secretions from the airways.

Aerosol deposition and clearance measurement: a novel technique using dynamic SPET

Planar gamma camera scintigraphy is a well-established technique for characterising the deposition and clearance of radiolabelled aerosols. While single-photon emission tomography (SPET) can offer superior assessment of radioaerosol deposition and better differentiation between peripheral and central deposition, the long acquisition times of single-headed SPET have largely prevented its use for measuring clearance or deposition of fast-clearing radioaerosols. This study investigated the feasibility of fast dynamic SPET imaging (1 min/frame) using a three-headed gamma camera to assess the regional and total deposition and clearance of different radioaerosols over a period of 26 min. Six subjects inhaled nebulised technetium-99m diethylene triamine penta-acetic acid radiolabelled aerosols with small and large droplet sizes [mass median aerodynamic diameter (MMAD) 3.2 +/- 0.2 and 6.5 +/- 0.2 microm, span 1.8 and 1.7, respectively] and in normal (0.9%) or hypertonic (7%) saline with controlled breathing on four separate occasions. The penetration indices (PIs) calculated from the SPET data for normal saline were 0.50 +/- 0.04 and 0.36 +/- 0.02 for the small and large droplet sizes, respectively. Consistent with the hygroscopic growth of the hypertonic aerosols, the PIs for hypertonic saline were lower, at 0.43 +/- 0.02 and 0.34 +/- 0.02 for the small and large droplet sizes, respectively. PIs calculated from the planar data showed similar trends, but failed to detect the significant difference seen with SPET between small normal and small hypertonic saline radioaerosols. In conclusion, the feasibility of using fast dynamic SPET for imaging radioaerosol deposition and associated radiolabel clearance in the lung has been successfully demonstrated. The fast SPET was able to reveal important differences in aerosol deposition that were not detected by planar imaging.

Deposition of aqueous aerosol of technetium-99m diethylene triamine penta-acetic acid generated and delivered by a novel system (AERx) in healthy subjects

Deposition of technetium-99m diethylene triamine penta-acetic acid aqueous radioaerosols generated by a novel aerosol delivery system (AERx) was studied in six healthy subjects using both planar and single-photon emission tomography (SPET) imaging. AERx is a microprocessor-controlled, bolus inhalation device that is actuated at pre-programmed values of inspiratory flow rate and volume. The aims of the study were to determine the effects of posture and inhaled volume upon deposition of the aerosol in the lungs. Each subject inhaled the radioaerosol in two positions (supine vs sitting) and with two inspiratory manoeuvres [vital capacity (VC) vs "fixed volume" of 1 l above functional residual capacity]. Simultaneous transmission-emission planar and tomographic images were acquired. The results showed diffuse deposition of the aerosol in the lung. Neither the breathing manoeuvre nor the posture was found to affect the distribution of the aerosol as measured by the ratio of the activity (counts per pixel) in the peripheral:central (penetration index, PI) or in the apex:base regions of the planar lung images (P>0.1). A small, albeit statistically significant, difference in PI (P<0.03) was found between VC and fixed volume sitting manoeuvres with SPET only. The PI values themselves indicate that the radioaerosol was well distributed in the lung, with the periphery having 45%-64% of the activity of the central region. Superposition of transmission SPET lung outline on emission SPET visually confirmed the excellent peripheral deposition of the aerosol. The AERx system showed high efficiency of delivery, with approximately 50% of the extruded dose in the device depositing in the lung. The uniformity of radioactivity distributed throughout the lung is attributed to the fine particle size (mass median aerodynamic diameter of 2 microm) of the aerosol and the electronic control of aerosol inhalation by the device. In conclusion, the AERx system can be ideal for diffuse aerosol deposition of therapeutic or diagnostic agents and is largely unaffected by inhaled volume and posture. The efficiency of the device device can limit the total radiation exposure of patients and staff administering the radioaerosols, and can make it suitable for delivery of expensive drugs.

Effects of terbutaline in combination with mannitol on mucociliary clearance

Beta2-agonists and osmotic agents stimulate mucociliary clearance (MCC) via different mechanisms which could potentially interact. The effects of inhaling terbutaline in combination with mannitol on MCC were investigated in nine healthy (aged 19+/-1 yrs) and 11 mild (aged 21+/-4 yrs) asthmatic subjects. Using 99mTc-sulphur colloid radioaerosol and a gamma camera, MCC was studied on four separate days with each of the following interventions: 1) terbutaline or its placebo inhaled 10 min before mannitol (in random, double blind); 2) terbutaline inhaled 5 min after mannitol; and 3) terbutaline inhaled 10 min before the control for mannitol. Lung images were collected over a period of 120 min postintervention and over 150 min in total. The mannitol-induced increase in clearance was transiently inhibited by terbutaline pretreatment and transiently enhanced when terbutaline was administered after mannitol both in asthmatic and healthy subjects. The order of administration of mannitol and terbutaline did not affect the total clearance of radioactive mucus over 140 min from the start of intervention in both groups. The pathways through which terbutaline and mannitol increase mucociliary clearance may transiently interact in an inhibitory or synergistic way, depending on the order of administration. However, this did not affect the overall increase in mucociliary clearance over 140 min.

Mucociliary clearance during and after isocapnic hyperventilation with dry air in the presence of frusemide

We have previously shown that mucociliary clearance (MCC) decreased during and increased after isocapnic hyperventilation (ISH) with dry air, both in asthmatic and healthy subjects. Inhaled frusemide, an inhibitor of the Na+/K+/2Cl- and NaCl co-transporters on the basolateral membrane of the epithelial cell, prevents the airway narrowing provoked by ISH with dry air. The co-transport system controls epithelial cell volume and chloride secretion and, thus, frusemide has the potential to modify the rate of recovery of periciliary fluid volume during and after ISH with dry air, and hence affect MCC. Frusemide also blocks mediator release from mast cells, which may also modify the increase in MCC after ISH. Eleven asthmatic and 11 healthy subjects inhaled frusemide (35.7 +/- 0.44 mg) or its vehicle, from a Fisoneb ultrasonic nebulizer 30 min before ISH with dry air, on two separate occasions. MCC was measured using 99mTc-sulphur colloid and a gamma camera. Frusemide, compared to its vehicle, did not affect MCC during or 45 min after ISH. However, in the presence of frusemide, the onset of the increase of MCC after ISH was significantly delayed for approximately 10 min in the whole right lung (p < 0.002) and central region (p < 0.01) in the asthmatic but not in the healthy subjects. These findings could be explained by frusemide delaying the recovery of the periciliary fluid volume after ISH with dry air and/or interfering with the stimulus that causes the increase in MCC in the asthmatic subjects after ISH.

The protective effect of nedocromil sodium and other drugs on airway narrowing provoked by hyperosmolar stimuli: a role for the airway epithelium?

The airways of persons with asthma are sensitive to acute changes in airway osmolarity and to dehydration. In reviewing the literature it is clear that airway narrowing provoked by these stimuli is blocked acutely by inhaling aerosols of nedocromil sodium, cromolyn sodium, frusemide, bumetanide, and antihistamines and by chronic use of aerosol corticosteroids. The responses are unaffected by inhalation of amiloride and verapamil. We have previously proposed that increases in the osmolarity of airway surface liquid (ASL) occur as a result of the water lost by evaporation during hyperpnea with dry air. An increase or decrease in osmolarity of the ASL will also occur with deposition of hyperosmolar and hypoosmolar droplets. Changes in osmolarity of the ASL result in the movement of water out of (shrinkage) and into (swelling) the epithelial cell, and this necessitates regulatory volume increase or decrease by the cell. We propose that nedocromil sodium and cromolyn sodium can affect water transport into and out of the epithelial cell by an action on chloride ion channels. A unifying hypothesis to explain the protective effect of these drugs may be their capacity to affect regulatory volume increase or decrease in a variety of cell types.

Changes in mucociliary clearance during and after isocapnic hyperventilation in asthmatic and healthy subjects

Hyperpnoea with dry air could lead to a reduction in depth and hyperosmolarity of the periciliary fluid layer (PFL) as a consequence of evaporative water loss. We investigated whether mucociliary clearance (MCC) is likely to be affected by dry air hyperpnoea, which also results in airway narrowing in asthmatics. MCC was measured by radioaerosol technique, for about 1 h, in 10 asthmatic and 8 healthy subjects on 3 separate days: 1) nasal resting breathing with ambient air; 2) isocapnic hyperventilation (ISH) with dry air; and 3) ISH with warm humid air. Analysis of the initial and post-intervention lung radioactivity for the whole right lung and for defined regions of interest showed that, compared to ISH with warm humid air and nasal resting breathing, MCC was reduced during and increased post-ISH with dry air in the whole right lung of both groups. The mean reduction in clearance (+/- 95% confidence interval (95% CI)) was -9.3% (-3.1 to -15.6%) and -3.6% (-2.0 to -9.1%), and the mean increase (+/- 95% CI) was 19.2% (11.8 to 26.6%) and 14.8% (7.1 to 22.5%), compared to warm humid air, in asthmatic and healthy subjects, respectively. However, regional analysis showed that the changes were present in all lung regions of the asthmatics, whilst only in the central region of the healthy subjects. The duration of the increased clearance rates post-ISH was also different in both groups. The changes in mucociliary clearance during and after isocapnic hyperventilation with dry air was probably related to the water content of the inspired air, causing transient changes in the periciliary fluid layer.

Changes in mucociliary clearance during and after isocapnic hyperventilation in asthmatic and healthy subjects

Hyperpnoea with dry air could lead to a reduction in depth and hyperosmolarity of the periciliary fluid layer (PFL) as a consequence of evaporative water loss. We investigated whether mucociliary clearance (MCC) is likely to be affected by dry air hyperpnoea, which also results in airway narrowing in asthmatics. MCC was measured by radioaerosol technique, for about 1 h, in 10 asthmatic and 8 healthy subjects on 3 separate days: 1) nasal resting breathing with ambient air; 2) isocapnic hyperventilation (ISH) with dry air; and 3) ISH with warm humid air. Analysis of the initial and post-intervention lung radioactivity for the whole right lung and for defined regions of interest showed that, compared to ISH with warm humid air and nasal resting breathing, MCC was reduced during and increased post-ISH with dry air in the whole right lung of both groups. The mean reduction in clearance (+/- 95% confidence interval (95% CI)) was -9.3% (-3.1 to -15.6%) and -3.6% (-2.0 to -9.1%), and the mean increase (+/- 95% CI) was 19.2% (11.8 to 26.6%) and 14.8% (7.1 to 22.5%), compared to warm humid air, in asthmatic and healthy subjects, respectively. However, regional analysis showed that the changes were present in all lung regions of the asthmatics, whilst only in the central region of the healthy subjects. The duration of the increased clearance rates post-ISH was also different in both groups. The changes in mucociliary clearance during and after isocapnic hyperventilation with dry air was probably related to the water content of the inspired air, causing transient changes in the periciliary fluid layer.

Airway cooling as the stimulus to exercise-induced asthma--a re-evaluation

Exercise-induced asthma (EIA) was recorded in 20 of 22 asthmatic children who cycled for 8 min while inspiring hot (32-40 degrees C) dry (3-10 mg H2O L-1) air. The mean +/- 1SD reduction in forced expiratory volume in one second was 39.8% +/- 22.3 of the pre-exercise value. To determine the relationship between respiratory heat loss (RHL) and retrotracheal temperature (RTT) under these inspired air conditions we studied 11 non-asthmatic adults who performed steady-state and incremental bicycle exercise. Exercise tests were also carried out while inspiring cold dry air. At the equivalent RHL, RTT was reduced by only 0.1 +/- 0.35 degrees C breathing hot air compared with 1.0 +/- 0.81 degrees C when cold air was inhaled. These data suggest that abnormal cooling of the airways is not occurring during the inhalation of hot dry air. Thus an additional stimulus to airway cooling must have been acting to induce asthma in the children. We propose that water loss and not heat loss is the stimulus to EIA under these inspired air conditions.