Can thoracic gas volume be measured in infants with airways obstruction?

Monitoring early inflammation in CF. Infant pulmonary function testing

Infant pulmonary function tests (iPFTs) have primarily been used as research tools to further define physiologic pulmonary abnormalities in infants and young children with cystic fibrosis (CF). Methodologies used to measure pulmonary function in infants are described, with particular relevance to CF. A comprehensive review of studies and findings in CF infants using iPFTs is presented. Further goals in improving methodologies and in defining pulmonary disease in CF are presented.

Estimation of lung volume in infants by echo planar imaging and total body plethysmography

Echo planar imaging (an extremely fast method of magnetic resonance imaging) was used to measure lung volume in a group of nine infants, all of whom had had respiratory problems. The mean echo planar imaging estimate of total lung volume was 44 +/- 9 ml/kg. In each case the right lung was larger than the left (ratio 52.8:47.2%). The mean thoracic gas volume was 36 +/- 8 ml/kg. The entire sequence of images of the thorax (about 400) takes five minutes to complete, infants require no sedation, and there are no side effects.

Disturbance in respiratory mechanics in infants with bronchiolitis

The passive flow-volume and partial forced expiratory flow-volume techniques were used to assess pulmonary function in 14 spontaneously breathing infants with acute respiratory syncytial virus bronchiolitis. Two additional infants were studied while paralysed and ventilated. During the acute stage of the illness there was a significant reduction in forced expiratory flow rates and an increase in respiratory resistance. Although the mean thoracic gas volume for the group was increased, five infants did not compensate for their airways obstruction by hyperinflation. Curvilinear passive flow-volume curves were seen in three of the 14 non-ventilated infants and in both ventilated infants. At follow up three to four months later all passive flow-volume curves were linear. There was a significant reduction in hyperinflation and an increase in forced expiratory flow rates, but values still differed significantly from those in normal infants.

Dose-response relationships and time course of the response to systemic beta adrenoreceptor agonists in infants with bronchopulmonary disease

The lung function response to three doses of salbutamol 0.075 mg/kg given at 10 minute intervals by gastric tube was studied in 31 infants aged 2-22 months with bronchopulmonary disease (eight after the respiratory distress syndrome, 15 with wheezy bronchitis, and eight with cystic fibrosis). Lung function was measured by whole body plethysmography. Seven of 31 infants had normal lung function and 10 of the remaining 24 had an increase in thoracic gas volume (TGV), 10 an increase in airway resistance (Raw), and four an increase in both the TGV and Raw. The response of TGV and Raw to salbutamol was analysed by circular statistics, enabling analysis of coupled, directional data. Thirty minutes after administration of the first dose of salbutamol there was a reduction in TGV or Raw in 21 of the 24 infants, 11 showing a decrease in TGV ("volume responder") and 10 a fall in Raw ("flow responder"). These results indicate that in most infants with bronchopulmonary disease an improvement in lung function can be documented after systemic administration of beta agonists if both TGV and Raw are measured.

Nebulised salbutamol does have a protective effect on airways in children under 1 year old

Ten infants under the age of 1 year each of whom gave a history of recurrent wheezing attacks were studied with a total body plethysmograph. All the infants were free of wheeze when studied and were sedated with chloral hydrate. All 10 showed a significant deterioration in lung function when given nebulised water for two minutes with an increase in airways resistance and a decrease in specific conductance at one and five minutes after nebulisation compared with baseline readings. Measurements returned to baseline values within 15 minutes. When the same amount of nebulised water was given 20 minutes after nebulised salbutamol, however, there was no significant deterioration in lung function at one and five minutes after administration of nebulised water. We conclude that the airways were protected against the bronchoconstricting effect of nebulised water by the beta 2 adrenoreceptor stimulant salbutamol.

Evaluation of infants by echo planar imaging after repair of diaphragmatic hernia

Three infants were studied by echo planar imaging after repair of congenital diaphragmatic hernias. Total lung volume and individual lung volumes were estimated using echo planar imaging. In the two patients with left sided hernias, the right lung was more than twice as large as the left. The patient with a right sided hernia had developed emphysema on the right side, and the right lung was twice as large as the left when estimated by echo planar imaging. Echo planar imaging studies took less than five minutes to perform and no sedation was required.

Ipratropium bromide and airways function in wheezy infants

The airway response to nebulised ipratropium bromide was studied in 17 chronically or recurrently wheezy infants aged 4-15 months. The peripheral airway response was assessed by the change in maximum flow at functional residual capacity (Vmax FRC) and the upper and central airway response by the change in specific airways resistance. The significant reduction in specific airways resistance after treatment with ipratropium bromide signified an improvement in central and upper airway function. No change was found, however, in Vmax FRC and hence in peripheral airway function. It seems that, as in older subjects, inhaled antimuscarinic, anticholinergic drugs have their maximum effect on the large airways, and this may explain their lack of effect in the management of acute bronchiolitis.

Paradoxical response to nebulised salbutamol in wheezy infants, assessed by partial expiratory flow-volume curves

Lower airway responses to nebulised bronchodilators were studied in 18 chronically or recurrently wheezy infants, aged 3-15 months, by means of partial forced expiratory flow-volume manoeuvres performed with an inflatable jacket. Maximum flow at functional residual capacity (FRC) (VmaxFRC) was used as the index of intrathoracic airways function. Peak expiratory flow rate was also measured. Baseline airways resistance and lung volume were determined during quiet breathing in an infant whole body plethysmograph. Measurements were made on separate days before and after nebulised salbutamol 2.5 mg with nebulised saline as control. The results were paradoxical: there was no change in VmaxFRC after saline, but a significant decline in VmaxFRC was found after salbutamol. Peak expiratory flow remained unchanged. These observations suggest that under conditions of forced expiration intrathoracic airways function may be further impaired by nebulised bronchodilator treatment in wheezy infants. When nebulised bronchodilator drugs are used to treat severe airways obstruction in infancy, careful monitoring is essential.

Bronchial responsiveness to histamine in wheezy infants

Little is known about airway responsiveness in infancy. The bronchial response to incremental doses of nebulised histamine (to a maximum dose of 8 g/l) was measured in 11 wheezy infants with a mean age of 8.7 months. The study was repeated after a 30-40 minute recovery period in seven infants and again on a separate day in 10. The index of response was the provoking concentration of histamine that produced a 30% fall in the maximum expiratory flow at functional residual capacity (PC30), taken from partial forced expiratory flow-volume curves produced in a pressure jacket. Nine of 11 infants had a PC30 of less than 8 g/l. The response was consistent between tests in both the nine responders and the two who failed to respond at 8 g/l. The PC30 was lower in infants with more severe baseline airway obstruction. Spontaneous recovery after challenge was complete in 30 minutes in seven of eight infants studied. The highest doses of histamine caused changes in the configuration of the flow-volume curves and symptomatic cough and wheeze in addition to a change in forced flow rates. This study provides clear evidence of intrathoracic airway responsiveness to histamine in infancy.