Alright so say normally your FVC is 5 L, and your FEV1 is 4 L, your FEV1 to FVC ratio would end up being 80%.

一般情况下FVC值是5L，FEV1值是4L，即FEV1比FVC是80%。

For that reason, the maximum amount of air people with COPD can breath out in a single breath, known as the FVC, or forced vital capacity, is lower.

因此，慢阻肺患者一口气可以呼出最大的气体量，称为FVC，即用力肺活量，会较低。

This reduction is especially noticeable in the first second of air breathed out in a single breath, called FEV1—forced expiratory volume (in one second), which typically is reduced even more than the FVC.

在患者用力呼气的第一秒，这种减少更为明显，此时的呼气量称为FEV1（第一秒用力呼气容积）；它的降低甚至比FVC更明显。

A useful metric therefore is the FEV1 to FVC ratio, which since the FEV1 goes down even more than FVC, causes the FEV1 to FVC ratio to go down as well.

因此FEV1与FVC的比值可以作为有效的度量标准，因为FEV1值下降较多，它们的比值将会同时降低。