Dynamic volumes Forced vital capacity. Full inspiration, then rapid full expiration Forced expiratory volume in limited time. Volume of air moved per minute when breathing as deeply and rapidly as possible. Maximum slope of volume time curve during expiration. Asthma Campaign spirometers Water sealed spirometers.
Water seal minimises forces.
Counterweight cancels weight of bell. Valves minimise equipment dead space. Rotary potentiometer on wheels. Large, heavy, messy, poor frequency response. Volume shows a steady reduction during breathing.