Long-range correlations of serial FEV1 measurements in emphysematous patients and normal subjects.
J Appl Physiol (1985)
; 85(1): 259-65, 1998 Jul.
Article
em En
| MEDLINE
| ID: mdl-9655784
ABSTRACT
In obstructive lung disease the annual change in lung function is usually estimated from serial measurements of forced expiratory volume in 1 s (FEV1). Frequent measurements in each patient may not improve this estimate because data are not statistically independent; i.e., the measurements are autocorrelated. The purpose of this study was to describe the correlation structure in time series of FEV1 measurements. Nineteen patients with severe alpha1-antitrypsin deficiency (phenotype PiZ) and moderate to severe emphysema and two subjects with normal lungs were followed for several years with daily self-administered spirometry. FEV1 measurements fulfilling standard criteria were detrended, and the autocorrelation profile and the power spectrum were calculated. On average the subjects were followed for >3 yr and performed >1,000 acceptable spirometries. The autocorrelation of FEV1 measurements in the emphysematous patients was approximately 0.35 for short intervals and decreased almost exponentially with a half time of 38 days. Between 3 and 4 mo, the autocorrelation function became negative. It reached a minimum of -0.1 at approximately 8 mo and then increased toward zero over the following 12 mo. The autocorrelation function in the two normal subjects showed a similar pattern, but with a faster decay toward zero. In the patients, the power spectrum had a peak at 1 cycle/wk and showed a 1/f pattern, where f is frequency, with a slope of -0.88 at lower frequencies. We conclude that serial spirometric measurements show long-range correlations. The practical implication is that FEV1 need not be measured more often than once every 3 mo in studies of the long-term trends in lung function.
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Base de dados:
MEDLINE
Assunto principal:
Enfisema Pulmonar
/
Volume Expiratório Forçado
Limite:
Adult
/
Female
/
Humans
/
Male
/
Middle aged
Idioma:
En
Revista:
J Appl Physiol (1985)
Assunto da revista:
FISIOLOGIA
Ano de publicação:
1998
Tipo de documento:
Article