Abstract: A method and apparatus for performing self-tests on defibrillation and pacing circuits including a patient isolation switch is disclosed. Tests are provided for the defibrillation and pacing circuitry as well as the isolation switch. For testing the defibrillation circuitry, the impedance drive circuits and preamplifier may be utilized such that the energy storage capacitor is not required to be charged and discharged during the test, thus conserving energy. For testing the pacing circuitry and the isolation switch, the defibrillation circuitry is utilized. For certain of the tests, the test stimulus is the output voltage on the energy storage capacitor, while for other tests the test stimulus may be the pace current as indicated by the voltage across the input to the preamplifier. Alternative tests may be performed depending on whether the impedance at the output of the defibrillator is determined to be an open circuit or a short circuit.

Abstract: The power source in a portable defibrillator includes a replaceable first power pack and a rechargeable second power pack. The first power pack charges the second power pack. The second power pack supplies most of the energy needed to administer a defibrillation shock. The first power pack may include one or more lithium thionyl chloride batteries. The second power pack may include one or more lithium ion batteries and/or ultracapacitors.

Abstract: The present invention provides a system, method and apparatus for obtaining status information from a portable medical device and communicating said status information to a remote system or user. In one embodiment, the system comprises a sensing device that comprises an optical receiver for receiving status information from at least one status indicator of the portable medical device. The optical receiver is positioned in sufficient proximity to the status indicator to allow optical communication between the optical receiver and the status indicator. A circuit couplable to the optical receiver communicates the status information represented by the status indicator to the remote system or user. In another embodiment, the sensing device comprises a microphone to receive audible status signals from the portable medical device. In yet another embodiment, the sensing device is mounted to a housing, which allows sensing device to sense the status information of an enclosed portable medical device.

Abstract: A fluid infusion positive displacement pump includes a plunger driven by a stepping motor which is operated by a motor control system. The control system advances the plunger to expel liquid in a series of incremental steps at a user-set pumping rate and until a preset total dosage has been delivered with the pumping rate being determined by the waiting time between each step. In order to minimize shock to the patient, the pump is operated at a plurality of increasing fractional rates during the start of pumping and at a plurality of decreasing fractional rates at the termination of pumping with the user-set (maximum) pumping rate occurring between such fractional rate pumping periods.

Abstract: A controller for regulating current flow through a resistive heating element in order to adjust the temperature thereof is disclosed. The controller includes a means for periodically measuring the resistance of the heating element. During controller calibration, the rate of change of the measured heating element resistance is ascertained in order to determine whether the heating element is at ambient temperature. Computations are performed on the value of the measured heating element resistance associated with ambient temperature conditions, enabling the controller to predict the value of the heating element resistance at a desired temperature. Current is then conducted through the heating element to generate heat, while periodic measurements of the heating element resistance are performed.

Abstract: The controller of the present invention regulates the flow of current through a resistive heating element by computing the predicted resistance R.sub.hot of the heating element at the desired temperature and then adjusting the voltage drop across and current flow through the resistive heating element until the relationship V=IR.sub.hot is satisfied. In an analog embodiment of the present invention, measurement of the voltage drop is obtained from a voltage amplifying circuit connected across the resistive heating element, while a measure of the current flow through the resistive heating element is obtained from a current amplifying circuit connected across a current measuring resistor in series with the resistive heating element. The output of the current amplifying circuit is multiplied by first and second variable gain amplifier circuits to produce a signal output representing the product of the current flow and the predicted resistance at the desired temperature.

Abstract: A disposable gas sensor, such as for monitoring pO.sub.2 in blood or administered gases, includes a housing, a passageway therein for blood or gas, a membrane-anode-cathode polarographic assembly, and a temperature sensing element. The temperature sensing element penetrates the housing and includes a removable thermistor, which is matable with the housing for thermal contact with a metallic element, and which in turn is in direct contact with the fluid being monitored.