Dirksen A, Holstein-Rathlou N H, Madsen F, Skovgaard L T, Ulrik C S, Heckscher T, Kok-Jensen A
Department of Respiratory Medicine, The Rigshospital, DK-2200 Copenhagen N.
J Appl Physiol (1985). 1998 Jul;85(1):259-65. doi: 10.1152/jappl.1998.85.1.259.
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.
在阻塞性肺病中，肺功能的年度变化通常通过对一秒用力呼气量（FEV1）进行系列测量来估算。对每位患者进行频繁测量可能无法改善这种估算，因为数据并非统计独立；也就是说，测量值存在自相关性。本研究的目的是描述FEV1测量时间序列中的相关结构。对19名患有严重α1-抗胰蛋白酶缺乏症（PiZ表型）和中度至重度肺气肿的患者以及2名肺功能正常的受试者进行了数年的每日自我肺量计测量跟踪。符合标准标准的FEV1测量值进行了去趋势处理，并计算了自相关曲线和功率谱。受试者平均随访时间超过3年，进行了超过1000次可接受的肺量计测量。肺气肿患者FEV1测量值的自相关性在短时间间隔内约为0.35，并以38天的半衰期几乎呈指数下降。在3至4个月之间，自相关函数变为负值。在大约8个月时达到最小值-0.1，然后在接下来的12个月内朝着零增加。两名正常受试者的自相关函数显示出类似的模式，但向零衰减得更快。在患者中，功率谱在1周期/周处有一个峰值，并呈现出1/f模式，其中f是频率，在较低频率下斜率为-0.88。我们得出结论，系列肺量计测量显示出长期相关性。实际意义在于，在研究肺功能的长期趋势时，FEV1的测量频率不必超过每3个月一次。
