Random variation of inspiratory lung function parameters in patients with COPD: a diagnostic accuracy study.
BACKGROUND
In chronic obstructive pulmonary disease (COPD), the response of the forced expiratory volume in 1 second (FEV1) after bronchodilator application is weak. Inspiratory parameters like the forced inspiratory volume in 1 second (FIV1) and inspiratory capacity (IC) can be responsive to bronchodilators. In an individual patient with COPD, a significant bronchodilator response must at least exceed the random variation for that parameter. Therefore, it is important that the type of scatter is homoscedastic, as the chance of underestimating or overestimating the random variation for low or high parameter values is minimized. The aim of this study is to investigate the random variation (type and quantity) of inspiratory parameters.


METHODS
In 79 stable COPD patients, spirometry was performed. The forced inspiratory volume in 1 second (FIV1), inspiratory capacity (IC), maximal inspiratory flow at 50% (MIF50) and peak inspiratory flow (PIF) were measured five times in one day and again within two weeks of the first measurement. The values of these parameters, taken within one hour, within one day and between two different days, were compared. The coefficient of repeatability (CR) was calculated, and, in addition, linear regression was performed to investigate the type of scatter (homo- or heteroscedastic) of the measured parameters.


RESULTS
The type of scatter was heteroscedastic for all of the parameters when the differences were expressed as absolute values; however, when the differences were expressed as the percent change from the initial values, we found a more homoscedastic scatter. The CR within one hour of each parameter expressed as the percent change from the initial value was: IC, 19%; FIV1, 14%; PIF, 18%; MEF50, 21%.


CONCLUSIONS
To obtain a more homoscedastic scatter, percentage changes in FIV1, IC and MIF50 are more appropriate than absolute changes. In an individual patient with COPD, a significant improvement for a particular parameter must at least exceed the above-mentioned CR.
Visser
Frank J
FJ
Department of Pulmonology, Canisius Wilhelmina Hospital, Nijmegen, 6532 SZ, the Netherlands. f.visser@cwz.nl
Ramlal
Sunil
S
Pelzer
Ben
B
Dekhuijzen
P N Richard
PN
Heijdra
Yvonne F
YF
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D007320:Inspiratory Capacity / Q000502:physiology; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000503:physiopathology*; D015203:Reproducibility of Results; D012129:Respiratory Function Tests; D013147:Spirometry / Q000592:standards*
Respir Med. 2003 May;97(5):568-77
12735677
Am J Respir Crit Care Med. 1999 Aug;160(2):542-9
10430726
Eur Respir J Suppl. 1993 Mar;16:5-40
8499054
Am Rev Respir Dis. 1983 Jul;128(1):153-7
6870056
Am Rev Respir Dis. 1980 Dec;122(6):859-66
7458059
Thorax. 2001 Sep;56(9):713-20
11514693
Am J Respir Crit Care Med. 1998 Nov;158(5 Pt 1):1557-65
9817708
Lancet. 1986 Feb 8;1(8476):307-10
2868172
Thorax. 2003 Oct;58(10):855-60
14514937
Eur Respir J. 2005 Nov;26(5):948-68
16264058
Eur Respir J. 2004 Jun;23(6):932-46
15219010
Eur Respir J. 2005 Aug;26(2):319-38
16055882
Eur Respir J. 1992 Sep;5(8):975-81
1426206
Am J Respir Crit Care Med. 2000 Jul;162(1):216-20
10903244
Am Rev Respir Dis. 1986 May;133(5):814-9
3706890
Chest. 2006 Mar;129(3):509-17
16537846
Respiration. 2008;76(1):46-52
18032882
Am J Respir Crit Care Med. 1995 Feb;151(2 Pt 1):406-11
7842199
Arch Intern Med. 1988 Sep;148(9):1949-52
3046537
Eur Respir J. 2003 Jul;22(1):1-2
12882441