Tryptase and IgE concentrations in the respiratory tract of infants with acute bronchiolitis

It has been proposed that a specific IgE response contributes to the immunopathology of acute respiratory syncytial virus (RSV) bronchiolitis but previous work has been difficult to replicate. Indirect evidence that might support this contention was sought by measuring total IgE concentrations in bronchoalveolar lavage (BAL) samples obtained from intubated infants and by attempting to detect mRNA for IgE in cells obtained from both the upper and lower respiratory tract. Evidence of significant mast cell activation was sought by measuring tryptase concentrations in BAL fluid and serum. Detectable concentrations of IgE were found in two of seven BAL samples obtained more than five days after intubation and mRNA for IgE was demonstrated in three of six BAL samples and three of six samples obtained from the upper respiratory tract. Tryptase was detectable in 11 of 12 BAL samples with the two highest values detected on day 1. These values were raised compared with control samples but were not such to suggest that mast cell degranulation is the major contributor to the inflammatory process. These results suggest that IgE may be produced in the airways of infants in response to RSV infection. The relationships between IgE production, RSV infection, and symptoms of acute bronchiolitis remain obscure.

Analysis of cells obtained by bronchial lavage of infants with respiratory syncytial virus infection

To study the cellular infiltrate that occurs within the airways of infants with respiratory syncytial virus bronchiolitis, samples of airways secretions were obtained by bronchial lavage from the lower respiratory tract of infants ventilated for this condition and from the upper airway of non-intubated infants with this disorder using nasopharyngeal aspirates. Cytospin samples were prepared so that differential cell counts could be performed on the cells obtained and alkaline phosphatase-antialkaline phosphatase immunocytochemical analysis of lymphocyte subsets was carried out using a panel of monoclonal antibodies, which included anti-CD3, anti-CD4, anti-CD8, anti-CD19, and anti-TcR gamma delta. Results from the lower and upper airways were similar. Large numbers of inflammatory cells were obtained, of which neutrophils accounted for a median of 93% in the upper airway and 76% in the lower airway. The numbers of CD8 positive cells detected were small and consistently less than CD4 positive cells, median CD4:CD8 ratios being 22.5:1 and 15:1 for the lower and upper airways. CD19 positive cells were rarely observed and no gamma delta positive lymphocytes were detected. These results indicate that neutrophils probably play a major part in causing symptoms in these infants. They do not support the concept that excessive lymphocyte mediated cytotoxic activity is principally responsible for the pathology in respiratory syncytial virus bronchiolitis.

Is tapping jet nebulisers worthwhile?

An in vitro system was used to study the effect of tapping a jet nebuliser on the dose delivered to patients. Using a 2 ml fill, effective drug delivery had ceased by 3 minutes but a further 38% was delivered to the filter by 5 minutes if the chamber was tapped.

Improvement in sodium cromoglycate delivery from a spacer device

Images

Comparison of nebulised aerosol deposition in the lungs of healthy adults following oral and nasal inhalation

A standard jet nebuliser was used to generate a radiolabelled aerosol and the pattern of deposition within the airways of eight healthy adults was studied with a gamma camera. Penetration of aerosol to the lung was greatly reduced when breathing through the nose compared with mouth breathing.

New aerosol delivery system for neonatal ventilator circuits

There is mounting evidence that a variety of drugs delivered as aerosols are likely to be of benefit in neonatal units. To avoid many of the problems associated with the use of jet nebulisers in ventilator circuits, a chamber was designed to be used in conjunction with a metered dose inhaler (MDI). The dimensions (4 cm x 11 cm) were chosen in an attempt to maximise drug delivery. In vitro studies were subsequently performed in order to determine the optimum operating conditions. Sodium cromoglycate delivered via this system was collected on a filter placed between the tip of an endotracheal tube and a model lung. The dose delivered was determined by means of an ultraviolet spectrophotometric assay. Using a Draeger Babylog 8000 ventilator it was found that drug delivery as maximised by actuating the device just before the inspiratory cycle when the chamber was placed adjacent to the endotracheal tube and by using a long (one second) inspiratory time. Under these conditions 1.5-2% of the original dose was deposited upon the filter at tidal volumes of 11-22 ml. When considered in terms of body weight this is many times the equivalent dose delivered to adults from an MDI. Effective drug delivery to the filter was confirmed using a radiolabelled aerosol. Radiolabelled studies delivering aerosol to the lungs of intubated rabbits demonstrated that deposition aerosol was distributed uniformly between lobes when corrected for the weight of each lobe. In conclusion, the device appears likely to deliver significant, reproducible quantities of drug to the lower respiratory tract while being simple to use.

Drug delivery from holding chambers with attached facemask

There is much interest in the use of holding chambers with an attached facemask to deliver aerosols from metered dose inhalers to infants. In order to study the influence of various design factors on the dose inhaled at different tidal volumes, a model was constructed in which a Starling ventilator was used to generate an inspiratory/expiratory cycle across a filter. Sodium cromoglycate was administered via a Nebuhaler and mask, Aerochamber and mask, and a coffee cup using tidal volumes of 25, 50, and 150 ml and the dose deposited upon the filter after six breaths was assayed using an ultraviolet spectrophotometric method. At the lowest tidal volume the high aerosol concentration in the smaller chamber enhanced drug delivery while at the highest tidal volume delivery was greatest from the larger chamber reflecting the larger dose available. Multiple breaths ensured that the dose inhaled per kilogram from each chamber was relatively large and also permitted significant drug delivery despite the introduction of a relatively large dead space between valve and filter. The dose delivered was increased by increasing the dose introduced into the chamber though not proportionately. These devices appear likely to deliver significant quantities of aerosol to infants, though drug delivery may be enhanced by the use of an appropriate valve.

Drug delivery from jet nebulisers

Maximising the rate of drug delivered in particles small enough to reach the lower respiratory tract from jet nebulisers may allow treatment times to be reduced and thus improve the acceptability of this form of treatment, particularly in very young patients. The role of various technical factors such as driving gas flow (DGF) in determining the rate of drug delivery was studied by constructing a model to simulate the respiratory pattern of individuals with different tidal volumes using a Starling ventilator and filter. Sodium cromoglycate was nebulised under a variety of operating conditions and the dose deposited on the filter was assayed. Tidal volumes of 50 and 400 ml were used at a frequency of 32 breaths per minute. Increasing the DGF from 4 to 8 l/minute produced a 264% increase in the rate of drug output but only a 32% increase in aerosol concentration. The mass of drug contained within droplets less than 5 microns increased from 26.8% to 70.8% of the total. The resultant increase in rate of drug delivery to the filter was 34% for a tidal volume of 50 ml and 79% for a tidal volume of 400 ml though the dose contained within droplets less than 5 microns increased by 4-fold at 50 ml tidal volume and by more than 5-fold at the higher tidal volume. Halving the solution concentration halved the rate of drug delivery. Increasing the tidal volume 8-fold from 50 to 400 ml resulted in an increase in the rate of drug deposition upon the filter of only 2.2 to 3-fold depending upon the DGF so that substantially more drug per ml inhaled was delivered at the lower tidal volume. These results are explained by considering factors that influence the rate of drug delivery. At low tidal volumes the rate of drug delivery at a given respiratory rate is dependent on the tidal volume and aerosol concentration. At high tidal volumes it is dependent upon aerosol concentration and volume of available aerosol and is essentially independent of tidal volume.

Inhaled budesonide for chronic wheezing under 18 months of age

The role of budesonide in controlling chest symptoms in infants was assessed. It was administered from a metered dose inhaler into a large volume spacer (Nebuhaler) with attached Laerdal mask. Twenty nine infants were recruited into a double blind crossover trial. Five defaulted. The remaining 24 (mean age 11 months) were assessed for the tolerance of the device, adverse effects, treatment failures, parental opinion, and daily symptom and treatment records. Twenty tolerated the modified Nebuhaler. One developed meningitis on placebo. Two experienced exacerbations on placebo. Eleven of 18 parents whose children completed the maximum treatment preferred budesonide to placebo and one preferred placebo. Mean symptom scores on budesonide were better than on placebo for the 15 children with complete symptom records. Fewer bronchodilator doses were used while taking budesonide. Our findings indicate that budesonide given in this way is an effective treatment for infants who may need prophylaxis for their wheezing.

Unexpected side-effects of inhaled steroids: a case report

An asthmatic child is presented who developed a cushingoid appearance with evidence of adrenal suppression and growth impairment while on low dose inhaled topical steroids. When the inhaled steroids were replaced by inhaled sodium cromoglycate his adrenal function recovered while his appearance and growth returned to normal. This report indicates that there are some children who are at risk of developing side-effects on doses of inhaled topical steroids normally considered to be entirely safe.