Incentive spirometer (flow meter) contains floats, which raise according to how much air a patient pulls through the device during inhalation. It's used with patients at low risk for atelectasis (Complete or partial collapse of a lung or a section lobe of a lung). Incentive spirometry are used as a breathing device to help promote lung expansion after prolonged bedrest or surgery. Incentive spirometer requires that the patient take deep breath and hold if for several seconds. Performing incentive spirometry increases lung volume, boosts alveolar inflation, and promotes venour return. This lung exercise also establishes alveolar hyperinflation for a longer time than is possible with a normal deep breath, thus preventing and reversing the alveolar collapse that causes atelectasis and pneumonia.