Related Experiment Videos
Can thoracic gas volume be measured in infants with airways obstruction?
Insights
Infants with recurrent wheezing after bronchiolitis often show low thoracic gas volume (Vtg) measurements. This suggests potential issues with plethysmography validity in young children with airway obstruction.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
Background:
- Recurrent wheezing post-bronchiolitis and cystic fibrosis are common in infants.
- Accurate measurement of lung volumes is crucial for diagnosing and managing pediatric respiratory conditions.
Purpose of the Study:
- To investigate thoracic gas volume (Vtg) in infants with recurrent wheezing after bronchiolitis compared to cystic fibrosis and healthy infants.
- To assess the validity of plethysmographic Vtg measurements in wheezy infants.
Main Methods:
- Whole-body plethysmography was used to measure Vtg in 46 infants post-bronchiolitis, 25 with cystic fibrosis, and 6 controls.
- Vtg was correlated with body weight/length and functional residual capacity (FRC) via helium dilution in a subset of infants.
Main Results:
- 56.5% of infants with recurrent wheezing had Vtg values more than 2 SD below predicted normal.
- Bronchiolitic infants with normal Vtg ranges exhibited more severe airway obstruction.
- Albuterol or steroid treatments did not significantly alter Vtg in the bronchiolitic group.
Conclusions:
- Physiological factors, like uneven alveolar pressure changes or low compliance units, may cause Vtg underestimation in wheezy infants post-bronchiolitis.
- The findings question the accuracy of plethysmographic Vtg measurements in these infants.
- Specific airway conductance may remain reliable if Vtg underestimation stems from uneven alveolar pressure changes.
Abstract:
Thoracic gas volume (Vtg) was measured in a whole-body, infant plethysmograph in 46 infants with recurrent wheezing after bronchiolitis, 25 infants with cystic fibrosis, and 6 infants without overt lung disease during the first 13 months of life. When related to weight or length, 56.5% of the bronchiolitic infants had low Vtg values, which were more than 2 SD below their predicted normal. The Vtg of the other groups was normal or above. The bronchiolitic infants with Vtg values in the normal range had more severe airways obstruction and it is probable that their Vtg values were also underestimated. Investigation of possible sources of technical or experimental error failed to reveal any explanation for the low Vtg in the bronchiolitic infants. In 5 infants, Vtg determined plethysmographically was correlated linearly to functional residual capacity determined by helium dilution, although Vtg values were greater in all. The administration of albuterol or treatment with steroids failed to make significant changes in Vtg in the bronchiolitic infants. It is suggested that there is a physiologic basis for the presumed underestimation of Vtg in wheezy infants after bronchiolitis, either because of uneven alveolar pressure changes within the chest leading to the effective exclusion of a portion of the lung volume or because there are some alveolar units with very low compliance that change little in volume during respiratory efforts against an occlusion. These results call into question the validity of the plethysmographic measurement of Vtg or airway resistance in these infants. If the error in Vtg is due to uneven alveolar pressure changes, it is suggested that the calculated specific airway conductance is probably correct.