Abstract: A method and apparatus for accurately determining a blood parameter that is calculated by measuring the transmittance of light through tissue having blood flowing therein is disclosed. A plurality of transmittance of light measurements are obtained for each transmittance of light parameter. The arithmetic mean of each transmittance of light parameter is calculated from the plurality of measurements. The arithmetic means are used to calculate the blood parameter from known formulations.

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 noise insensitive pulse transmittance oximeter (11) is disclosed. Two LEDs (21 and 23) are included in the pulse transmittance oximeter. The LEDs alternately emit a red light pulse and an infrared light pulse. A detector (13) detects corresponding red transmittance pulses and infrared transmittance pulses that are indicative of the amount of light transmitted through tissue having blood flowing therein. A microprocesser (29) determines the peak and valley values of the red transmittance pulses and infrared transmittance pulses over a cycle. The difference between the peak and valley values for the red transmittance pulses and infrared transmittance pulses are calculated by the microprocessor. The microprocessor generates control signals that vary the intensity of the LEDs until the differences between the peak and valley values of the red transmittance pulses and infrared transmittance pulses are substantially equal.

Abstract: A method of making a humidity sensor comprises providing a host device constituted by a semi-conductor substrate (10) and a gate insulator (13) of an insulated gate field effect transistor, forming a layer (14) of poly (vinyl) alcohol (PVA) on the exposed surface of the insulator, heat treating the layer to crystallize and stabilize the PVA, and forming a gate electrode (15) on the PVA layer, so that the gate electrode is porous allowing ambient water vapor to be absorbed by the PVA which, in response, undergoes a change of bulk dielectric constant, thereby causing a change in gate capacitance of the transistor resulting in a detectable change of electrical conductivity in the drain source channel.

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: The present invention discloses a method and apparatus for indicating perfusion and oxygen saturation trends in oximetry. In transmittance and reflectance oximetry, LEDs (40, 42) are typically employed to expose tissue to light at two different wavelengths. The light transmitted through, or reflected by, the tissue is received by a detector (38) where signals proportional to the intensity of light are produced. These signals are then processed by oximeter circuitry (14, 16) to determine oxygen saturation, pulse rate, and perfusion. Displays (20) are provided including a display (132, 134) of the change in the oxygen saturation during a specified interval. This display may include first (132) and second (134) trend indication displays that indicate when the oxygen saturation has either been increasing or decreasing at a rate in excess of some predetermined level. Preferably, these displays are triangular, upwardly and downwardly directed light-emitting diodes.

Abstract: The disclosed invention is for use in extracting more accurate information from signals employed in pulse oximetry. Basically, pulse oximetry involves the illumination of arterial blood flowing in tissue with light at two wavelengths. Upon emerging from the tissue the light is received by a detector (38) that produces signals that are proportional to the intensity of the light received at each of the wavelengths. Each signal includes a slowly varying baseline component representing the attenuation .beta.(t) of light produced by bone, tissue, skin, and hair. The signals also include pulsatile components representing the attenuation .alpha.(t) produced by the changing blood volume and oxygen saturation within the finger. The signals produced by the detector (38) are converted by an analog-to-digital (A/D) converter (72) for subsequent analysis by a microcomputer (16). The microcomputer (16) extracts the following information from the signal corresponding to each wavelength. V.sub.

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).