Comparison of plethysmographic and helium dilution lung volumes: which is best for COPD?
BACKGROUND
Theoretical considerations and limited scientific evidence suggest that whole-body plethysmography overestimates lung volume in patients with severe airflow obstruction. We sought to compare plethysmography (Pleth)-, helium dilution (He)- and CT scan-derived lung volume measurements in a sample containing many patients with severe airflow obstruction.


METHODS
We measured total lung capacity (TLC) in 132 patients at three hospitals, with monitored application of recommended techniques for Pleth and He measurements of lung volume and by thoracic CT scans obtained during breath hold at full inspiration.


RESULTS
Average TLC among 132 subjects was 6.18 L (+/- 1.69 L) by Pleth-derived TLC, 5.55 L (+/- 1.39 L) by He-derived TLC, and 5.31 L (+/- 1.47) by CT scan-derived TLC. Pleth-derived TLC was significantly greater than either He-derived TLC or CT scan-derived TLC (P < or = .001), whereas there was no significant difference between He-derived and CT scan-derived values. When examined separately, there were significant within-subject differences in TLC by measurement technique among subjects with airflow obstruction, but not among those without airflow obstruction. Plethysmographic overestimation of TLC was greatest among subjects with FEV(1) < 30% of predicted.


CONCLUSIONS
In the setting of airflow obstruction, Pleth systematically overestimates lung volume relative to He or thoracic imaging despite adherence to current recommendations for proper measurement technique.
O'Donnell
Carl R
CR
ScD, Beth Israel Deaconess Medical Center, Dana 717, 330 Brookline Ave, Boston, MA 02215, USA. codonne1@bidmc.harvard.edu
Bankier
Alexander A
AA
Stiebellehner
Leopold
L
Reilly
John J
JJ
Brown
Robert
R
Loring
Stephen H
SH
D000368:Aged; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006371:Helium; D006801:Humans; D007201:Indicator Dilution Techniques; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D008875:Middle Aged; D009929:Organ Size / Q000502:physiology; D010993:Plethysmography, Whole Body; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D015203:Reproducibility of Results; D012129:Respiratory Function Tests; D014057:Tomography, X-Ray Computed; D014109:Total Lung Capacity / Q000502:physiology
D006371:Helium