Abstract: A system is described for identifying a cable transmitting a signal from a sensor to an electronic instrument. The cable includes a reactance element such as a capacitor or an inductor. The system identifies the cable by applying a voltage to a combination of a resistance and the reactance element to measure the reactance of the reactance element either alone or in combination with the resistance.

Abstract: An oximeter sensor adapter which allows a sensor without a resistor in parallel with its LEDs to operate with an oximeter expecting such a resistor in parallel. The adapter has a switching circuit which has inputs connected to the LED drive outputs of the oximeter. The switching circuit has two pairs of outputs, one connected to the LED drive lines of the sensor, and the other connected to a resistor in the adapter itself. The switching circuit is controlled by a sensing circuit which senses when a signal on the input lines drops below a predetermined level, such as 0.5 volts. The sensing circuit, in response to a low voltage (corresponding to an attempt to read a resistor in parallel with the LEDs), will provide a signal to a switching circuit. The switching circuit will switch the resistor onto the input lines so that it can be read. When a higher voltage returns to the input lines, the switching circuit switches back to the LEDs themselves.

Abstract: A method for operating a spectrophotometric instrument of the type for measuring the oxygenation state of hemoglobin in tissue. The method includes the use of stored hemoglobin concentration relationship data characterizing the relationship between second derivative absorbance values at a hemoglobin-absorbing wavelength and hemoglobin concentration in a tissue as a function of hemoglobin oxygenation state. Data representative of a second derivative absorbance value of tissue being analyzed is received. The hemoglobin oxygenation state of the tissue is determined as a function of the second derivative absorbance value. The hemoglobin concentration in the tissue is then determined as a function of the hemoglobin concentration relationship data, the second derivative absorbance value and the hemoglobin oxygenation state. The accuracy of the hemoglobin oxygenation state can be determined as a function of the hemoglobin concentration value.

Abstract: A mechanism for storing and providing historical physiological data, such as blood oxygen saturation data, for a patient. In particular, the historical physiological data is stored in a storage medium that “travels” with the patient and is accessible wherever the patient is moved. This is achieved by storing the physiological data within a sensor assembly. At the destination site, a monitor or a device capable of interfacing with the sensor electronics can retrieve and display the data. The historical physiological data allows a clinician or medical personnel at the destination site to assess the condition of the patient for the entire time that the patient has been monitored. Various types of physiological data can be stored including, but not limited to, blood oxygen saturation, heart rate, and temperature data. Compression of the data can be performed to enhance the storage capability.

Abstract: A method and apparatus for non-invasively determining the blood oxygen saturation level within a subject's tissue is provided that utilizes a near infrared spectrophotometric (NIRS) sensor capable of transmitting a light signal into the tissue of a subject and sensing the light signal once it has passed through the tissue via transmittance or reflectance. The method includes the step of determining attenuation of the light signal as the sum of: (i) attenuation attributable to deoxyhemoglobin; (ii) attenuation attributable to oxyhemoglobin; and (iii) attenuation attributable to light scattering within the subject's tissue. The present method also makes it possible to account for attenuation attributable to fixed or constant light absorbing biological tissue components, and attenuation attributable to variable characteristics of the sensor.

Abstract: The invention relates to the calibration of a pulse oximeter intended for non-invasively determining the amount of at least two light absorbing substances in the blood of a subject. In order to take human variability into account, the calibration is based on an invariant which is a quotient of two pseudo-isobestic signals. Each pseudo-isobestic signal is a weighted sum of two signals, and the weighted sum is theoretically independent of the relative concentrations of said substances in the blood of the subject. By using theoretical values of the invariant on the one hand, and values based on in-vivo measurements on the other hand, the calibration curve of the pulse oximeter is adapted to the characteristics of each individual patient.

Abstract: A method for determining an arterial blood oxygen saturation level according to this invention includes measuring the light transmittance through tissue of light of a first wavelength and a second wavelength. A steady-state component of the measured light transmission is used to select an appropriate calibration curve. A pulsatile component of the measured light transmission is used to determine the arterial blood oxygen saturation level using the selected calibration curve. An oximetry system is also provided.

Abstract: An artificial blood flow simulator to be used to test or calibrate a pulse oximeter has a body which is at least partially transparent to red and infrared light waves. Within the body is a light valve which is responsive to an electronic signal for varying the amount of light passing through the body. Connected to the light valve is a signal generator for generating a pulsating electronic signal which corresponds to a given blood flow. The device has the permeability of a human appendage between pulses of blood in the arterial system when the signal generator is generating an electronic pulse and has the permeability of an appendage having arterial blood flowing therethrough when the signal generator is not generating an electronic pulse.

Abstract: The invention concerns a process for validation of devices for photometry of living tissue, which encompasses the following steps:

Abstract: A method for operating an oximeter sensor, and corresponding apparatus, which includes an encoded temperature characteristic of a light emitter in the sensor. The encoded temperature characteristic is read, and is used to modify a drive of the light emitter in the sensor. This enables a light emitter to be operated at its maximum allowable intensity to maximize a signal to noise ratio, without burning a patient, in accordance with the particular characteristics of that light emitter.

Abstract: An encoding element which is backward compatible and will provide a single coded value to older analyzers in response to first signal, but will also provide a second coded value to a new analyzer or monitor. In one embodiment, both coded values are provided over the same first and second leads which are compatible with existing sensors. In another embodiment, a first voltage level produces a first current from the encoding element, while a second voltage level will produce the second coded value. In another embodiment, a first coded value is provided in response to a DC current from older analyzers. A second coded value is provided in response to a AC signal from newer analyzers. Yet another embodiment provides the coded value in the form of a resonant circuit in the AC driven mode. In another embodiment, the first coded value is provided over the same two leads after a period of time, with the second value being provided prior to that period of time passing.

Abstract: An oximeter sensor with an encoding element connected to the photodetector. The encoding element is read by reverse-biasing the photodetector, rather than using a lower voltage.

Abstract: A problem in pulse oximetry is discriminating between arterial and non-arterial oxygen. Non-arterial oxygen can become detectable by an oximeter when a patient moves, obscuring the oximeter's measurement of arterial oxygen at critical times. Recent advances in pulse oximetry have made it possible to make the discrimination between arterial and non-arterial blood oxygen values. To allow manufacturers, hospitals, and medical researchers to evaluate the new oximetry technology, and evaluate oximeters which use it, new simulation technology is presented which can simulate simultaneous arterial and non-arterial blood oxygen on demand, with precision as to oxygen value, waveform amplitude, and waveform frequency. This invention provides the required simulation by double amplitude modulating the red and infra-red oximeter pulses.

Abstract: The invention concerns a process for validation of devices for photometry of living tissue, which encompasses the following steps:in vitro adjusting of a particular concentration of a substance to be detected in a bodily fluid;transporting the bodily fluid which has been adjusted to a pre-determined concentration to at least one measuring cell;transillumination of the bodily fluid; andsensing of the light intensity of at least one spectral window for determination of at least one suitable parameter in the bodily fluid, which is contained in the measuring cell, by means of at least one emitter and at least one receiver;thereby characterized,that one actively and in a defined manner dynamically changes the effective absorption length through the bodily fluid, without using the bodily fluid for transmission of the forces, wherein the bodily fluid is found in the optical space between the emitter and the receiver; andestablishment of at least one relationship between the concentration on the one hand and the suit

Abstract: The present invention utilizes differential measurement of radiation that migrated into two migration paths between two source-detector pairs placed on the head in a manner that each path is localized in a portion of one hemisphere of the brain. The present invention also provides various embodiments of spectrophotometer systems for in vivo examination of tissue of a human by measuring changes in electromagnetic radiation scattered and absorbed in a migration path in the tissue. Generally, the spectrophotometer systems comprise a light source for introducing the radiation into the tissue, a detector for detecting radiation that has migrated in the tissue, a processor for processing signals of the detected radiation to create processed data, and a system for determining physiological or pathophysiological changes in the tissue of interest. The present invention also provides for determining the metabolic condition of an aerobically stressed portion of tissue such as the muscle tissue of an exercising person.

Abstract: The present invention provides an encoding mechanism for a medical sensor which uses a modulated signal to provide the coded data to a remote analyzer. The modulated signal could be, for instance, a pulse width modulated signal or a frequency modulated signal. This signal is amplitude independent and thus provides a significant amount of noise immunity.