Should TGV be measured from end-inspiratory occlusions rather than end-expiratory occlusions in wheezy infants?
It has been suggested that thoracic gas volume (TGV) measured in infants in a plethysmograph most accurately represents true lung volume when calculated from end-inspiratory airway occlusions. The rationale proposed is that pressure measured at the mouth underestimates alveolar pressure more at end-expiration than at end-inspiration, presumably due to small airway closure, and this results in greater overestimation of TGV. To investigate this possibility we calculated TGV in 40 wheezy infants from occlusions at both end-inspiration (TGVei) and end-expiration (TGVee) using a 60 L whole body plethysmograph. TGV was corrected for equipment dead space and tidal volume. When a significant change in TGV was defined as lying outside the 95% confidence interval of the TGVee measurements, 8 of the 40 infants tested had significantly higher TGV values measured from occlusions made at end-expiration, while two infants had significantly lower TGV values measured from occlusions made at end-expiration. This trend was not more common in infants with "concave" flow-volume curves. Although it is technically easier to make occlusions at end-expiration, occluding at end-inspiration may minimize errors of TGV measures in a few individuals due to small airway closure at low lung volumes.
Lanteri
C J
CJ
Department of Thoracic Medicine, Royal Children's Hospital, Melbourne, Australia.
Raven
J M
JM
Sly
P D
PD
D001990:Bronchiolitis, Viral / Q000150:complications; D005652:Functional Residual Capacity; D006801:Humans; D007223:Infant; D008176:Lung Volume Measurements; D010993:Plethysmography, Whole Body; D012123:Pulmonary Ventilation; D012129:Respiratory Function Tests / Q000379:methods*; D012135:Respiratory Sounds / Q000209:etiology / Q000503:physiopathology*; D013909:Thorax / Q000503:physiopathology*