Maximal expiratory flow at FRC (V'maxFRC): Methods of selection and differences in reported values.
We compared three methods of reporting maximal expiratory flow (V'maxFRC) measured in partial expiratory flow-volume curves (PEFVCs) at the point of functional residual capacity (FRC). PEFVCs were obtained with the rapid thoracoabdominal compression technique (RTC) on a total of 446 occasions in 281 HIV-negative, asymptomatic infants (4.8-28.1 months old). Three different expressions of V'maxFRC were recorded: 1) the highest measured flow (maxV'FRC), 2) the mean of the three highest flows (mean3V'FRC), and 3) the flow at FRC in a composite curve (compV'FRC) consisting of PEFVCs, obtained at different jacket pressures and superimposed at their distal limb. The numerical value of maxV'FRC was 7.4% (+/-5.6%) higher than the mean3V'FRC, and 11.9% (+/-17.7%) higher than the compV'FRC; the mean3V'FRC was 5% (+/-18.3%) higher than the compV'FRC. Bland-Altman analysis was used to evaluate the agreement between the three indices. The mean difference and 95% limits of agreement were: maxV'FRC -mean3V'FRC, 14 +/- 18 ml/sec; maxV'FRC - compV'(FRC), 23 +/- 58 ml/sec; and mean3V'(FRC) - compV'(FRC), 10 +/- 52 ml/sec. The differences between the slopes of the three indices (regressed against height) were statistically significant, although clinically unimportant. We conclude that despite their high correlation, the mean3V'FRC and maxV'FRC should not be used interchangeably, and that the composite analysis, although useful, does not improve the reproducibility of V'maxFRC, and thus it cannot be recommended for routine use in its current form.
Koumbourlis
Anastassios C
AC
Pediatric Pulmonary Division, Columbia-Presbyterian Medical Center, New York, New York, USA. akoumbou@LIJ.edu
Chen
Xin C
XC
Rao
J Sunil
JS
Schluchter
Mark D
MD
Easley
Kirk
K
Colin
Andrew A
AA
Hiatt
Peter
P
Kattan
Meyer
M
McCarthy
Kevin
K
Mellins
Robert B
RB
Peavy
Hannah
H
Platzker
Arnold C G
AC
Steinbach
Suzanne
S
Ting
Andrew
A
Weisner
Michael D
MD
Wohl
Mary Ellen B
ME
D002675:Child, Preschool; D019992:Databases as Topic; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology; D006801:Humans; D007223:Infant; D008297:Male; D008448:Maximal Expiratory Flow Rate / Q000502:physiology*; D008449:Maximal Expiratory Flow-Volume Curves / Q000502:physiology*; D011446:Prospective Studies; D012016:Reference Values; D012044:Regression Analysis