Abstract: An improved system for making an accurate determination of the patient's compliance and airway resistance by ensuring that the flow to and/or from the patient at the end of a ventilator pause is, in fact, reduced to zero flow. The normal ventilator pause occurs at the end of an inspiratory cycle where the ventilator terminates the breathing air delivery to the patient and then enters a pause period. Values are taken for the airway flow and pressure at the beginning of the pause period, that is at peak pressure, and a second set of readings is taken at the end of the pause period, called the plateau pressure. This second set of readings greatly simplifies solving the equations for patient resistance and compliance if the flow at that time is assumed to be zero.

Abstract: An apnea detection system is disclosed for use with a medical ventilator and which detects the volume of gas delivered by the ventilator to a patient and also the volume of gas exhaled by the patient. The two flow measurements are compared, preferably in a microprocessor, to determine whether an apnea condition exists by comparing, against a known standard, the two detected volumes. The volume of the exhaled gas must be a predetermined percentage of the volume of gas delivered to the patient within a predetermined time period or an alarm is activated indicating an apnea condition.

Abstract: A control system where the clinician can have manual control of the state for various alarms, generally volume alarms and apnea alarms. The control is interactive, that is, while the clinician can manually set the state in a variety of settings, the control system automatically overrides the clinician's selection to activate both the volume and apnea alarms wherever the mechanical ventilator is turned on. In addition, there is another override where a breath is detected by the ventilator to turn all of the alarm systems from both being inactive to both alarms being active.

Abstract: An algorithm is disclosed that enables the display for a medical ventilator to automatically adjust its wave characteristics depending on the settings for that ventilator established by the clinician. As the respiratory rate, or rate at which the ventilator provides breaths to the patient, is changed by the user, the rate of sweep of the waveform generator displaying that data is also changed to insure that the data is displayed in the most relevant manner. As another parameter, as the pressure limit in the patient circuit is set by the clinician, the waveform vertical scale is adjusted to make sure the particular limit of pressure is displayed. As the pressure limit or the respiratory rate are changed in the ventilator by the clinician, the waveform of he data displayed also is automatically modified to make that data best presentable to the clinician.

Abstract: An improved system for the determining the collapse of a bellows within a canister as part of a ventilator system for delivering breaths to a patient via a patient circuit. The system measures the pressure in the bellows canister external of the bellows and measures the pressure within the interior of the bellow. A processor compares the pressures and determines when the pressure within the canister exceeds a predetermined offset in excess of the pressure within the interior of the bellows to conclude that the bellows is in a collapsed condition. In the preferred embodiment, the processor also uses, as input data, the flow delivered by the ventilator to the bellows canister to determine that offset value. When a bellows empty condition is determined, various actions can be taken, among them to signal an alarm and also to change various functions of the ventilator to prevent further difficulties in the overall system.