Sometimes we hear that it's hard to exhale for a full six seconds.
As it turns out in 2019 the American Thoracic Society revised its guidance and no longer requires that a pulmonary function test of at least six seconds in duration for those age 7 and older.
So six seconds is not mandatory. We will record exhales as short as 1 second (so that FEV1 can be recorded) and as long as 15 seconds (again per the ATS).
Of course, the proper maneuver requires as complete as possible forceful exhale of all your lung volume. So if that takes 8 seconds, then it should be 8 seconds. If that's only 5 seconds, that's fine too.
We do, however, optionally record the inspiratory limb of the flow volume curve. Once we detect zero flow on the exhale the device will transition to its inhalation mode and the patient will receive a notification bell ring and a visual prompt asking for a deep, fast inhale.
And if you don't perform the final inhale we'll just show the exhale portion of the flow volume loop.