Abstract: An implantable atrial defibrillator includes a storage capacitor for storing electrical energy. A switch discharges at least a portion of the stored energy into a patient's heart as a discharge voltage and a charger charges the storage capacitor with the stored energy to a peak voltage. A voltage limiter precludes the discharge voltage from exceeding a voltage limit during capacitor discharge to permit a reduced applied cardioverting voltage with a lengthened discharge time. The voltage limit is a substantially constant fraction of the peak voltage.

Abstract: An implantable atrial defibrillator and method provides cardioverting electrical energy to the atria of a human heart in need of cardioversion. The atrial defibrillator includes a first detector for detecting R waves of the heart, a second detector for detecting T waves of the heart, and a third detector for detecting atrial activity of the heart. An atrial fibrillation detector is responsive to the third detector for determining when the atria of the heart are in need of cardioversion. A cardioverting stage applies the cardioverting electrical energy to the atria of the heart when the atria of the heart are in need of cardioversion, after the second detector detects a T wave, and in timed relation to an R wave detected by the first detector after the detected T wave is completed.

Abstract: Under the present invention, a method and apparatus are provided for compensating for the effect temperature variations have on the wavelength of light emitted by the oximeter sensor light source (40, 42). In pulse oximetry, LEDs (40, 42) are typically employed to expose tissue to light at two different wavelengths. The light illuminating the tissue is received by a detector (38) where signals proportional to the intensity of light are produced. These signals are then processed by the oximeter circuitry to produce an indication of oxygen saturation. Because current oximetry techniques are dependent upon the wavelengths of light emitted by the LEDs (40, 42), the wavelengths must be known. Even when predetermined combinations of LEDs (40, 42) having relatively precise wavelengths are employed, variations in the wavelength of light emitted may result. Because the sensor (12) may be exposed to a significant range of temperatures while in use, the effect of temperature on the wavelengths may be significant.

Abstract: A pulse generator for use in implantable atrial defibrillator provides cardiovertinq electrical energy to the atria of a heart through at least one lead having a pair of electrodes associated with the atria of the heart. The pulse generator includes a depletable, low voltage, power source such as a battery. A charging circuit coupled to the battery includes a flyback transformer for converting the battery voltage to low duty cycle pulsating high voltage electrical energy to store the high voltage electrical energy in a storage capacitor coupled to the charging circuit. A crosspoint switch selectively couples the storage capacitor to the electrodes for applying a portion of the stored electrical energy to the atria of the heart for cardioverting the atria of the heart.

Abstract: Under the present invention, a method and apparatus are provided for compensating for the effect temperature variations have on the wavelength of light emitted by the oximeter sensor light sources (40, 42). In pulse oximetry, LEDs are typically employed to expose tissue to light at two different wavelengths. The light illuminating the tissue is received by a detector (38) where signals proportional to the intensity of light are produced. These signals are then processed by the oximeter circuitry to produce an indication of oxygen saturation. Because current oximetry techniques are dependent upon the wavelengths of light emitted by the LEDs (40-42), the wavelengths must be known. Even when predetermined combinations of LEDs (40-42) having relatively precise wavelengths are employed, variations in the wavelength of light emitted may result. Because the sensor (12) may be exposed to a significant range of temperatures while in use, the effect of temperature on the wavelengths may be significant.

Abstract: A feedback control system is disclosed for use in processing signals employed in pulse transmittance oximetry. The signals are produced in response to light transmitted through, for example, a finger at two different wavelengths. Each signal includes a slowly varying baseline component representing the relatively fixed attenuation of light produced by bone, tissue, skin, and hair. The signals also include pulsatile components representing the attenuation produced by the changing blood volume and oxygen saturation within the finger. The signals are processed by the feedback control system before being converted by an analog-to-digital (A/D) converter (72) for subsequent analysis by a microcomputer (16). The feedback control system includes a controllable offset subtractor (66), a programmable gain amplifier (68), controllable drivers (44) for the light sources (40, 42), and the microcomputer (16).

Abstract: A feedback control system is disclosed for use in processing signals employed in pulse transmittance oximetry. The signals are produced in response to light transmitted through, for example, a finger at two different wavelengths. Each signal includes a slowly varying baseline component representing the relatively fixed attenuation of light produced by bone, tissue, skin, and hair. The signals also include pulsatile components representing the attenuation produced by the changing blood volume and oxygen saturation within the finger. The signals are processed by the feedback control system before being converted by an analog-to-digital (A/D) converter (72) for subsequent analysis by a microcomputer (16). The feedback control system includes a controllable offset subtractor (66), a programmable gain amplifier (68), controllable drivers (44) for the light sources (40,42), and the microcomputer (16).