Method and circuit for storing and providing historical physiological data

ES 2 322 639 T3

DESCRIPTION

Procedure and circuit for storing and providing historical physiological data.

Background of the invention

The present invention relates to physiological test instruments and, in particular, to sensors that include a mechanism for storing and providing historical physiological data such as blood oxygen saturation data to a monitor.

Pulse oximetry is typically used to measure different characteristics of blood flow including, but not limited to, arterial blood hemoglobin blood oxygen saturation, the volume of individual blood pulsation delivered to a tissue, and the blood pulsation rate that corresponds to each heartbeat of a patient. Measurement of these characteristics has been achieved through the use of a non-invasive sensor that passes light through a portion of tissue perfused with blood from a patient and photoelectrically detects the absorption and scattering of light in said tissue. The amount of light absorbed is then used to estimate the amount of constituent blood in the tissue. The "pulse" in pulse oximetry comes from the varying amount of time the arterial blood is in the tissue during the cardiac cycle. The signal processed from the detected optical signal is the familiar plethysmographic waveform due to cyclical attenuation of light.

To estimate the oxygen saturation of a patient's blood, conventional two-wavelength pulse oximeters emit light from two light-emitting diodes (LEDs) on a pulsed tissue base and collect the emitted light with a photodiode (or photo detector) located on an opposite surface (for example, for pulse transmission oximetry) or an adjacent surface (for example, for pulse reflection oximetry). One of the two primary wavelengths of LEDs is selected at a point on the electromagnetic spectrum where the absorption of oxyhemoglobin (HbO2) differs from the absorption of reduced hemoglobin (Hb). The second of the two wavelengths of LEDs is selected at a different point in the spectrum, where the absorption of Hb and HbO2 also differ from each other, and also differ from those at the first wavelength. Commercial pulse oximeters typically use one wavelength in the near red part of the visible spectrum near 660 nanometers (nm) and one in the near infrared (IR) part of the spectrum in the 880-940 nm range.

Oxygen saturation can be estimated using various techniques. In a common technique, the photocurrent generated by the photodetector is conditioned and processed to determine the modulation ratio of the red to infrared signals. This modulation relationship has been found to correlate well with arterial oxygen saturation. Pulse oximeters and sensors are empirically calibrated by measuring the modulation ratio over a range of arterial oxygen saturations measured in vivo (SaO2) in a set of patients, healthy volunteers, or animals. The observed correlation is used in an inverse way to estimate blood oxygen saturation (SpO2) based on the measured value of a patient's modulation ratios. Estimation of oxygen saturation using the modulation ratio is described in US Patent 5,853,364, entitled "Method and Apparatus for Estimating Physiological Parameters Using Model-Based Adaptive Filtering", issued December 29, 1998, and US Patent 4,911,167, entitled "Procedure and apparatus for detecting optical pulses", issued on March 27, 1990. The relationship between oxygen saturation and modulation ratio is further described in US Patent 5,645,049, entitled "Medical Sensor with Modulated Coding Scheme," issued July 8, 1997. All three patents are assigned to the present assignee. invention.

The LEDs and the photodetector are typically housed in a reusable or disposable oximeter sensor that is coupled to the electronics of the pulse oximeter and the display unit (hereinafter referred to as the monitor). Sensors are often connected to patients for long periods of time. Conventionally, the historical physiological data of the patient is collected, where appropriate, by the monitor coupled to the sensor. Historical data can be valuable to a clinician or medical personnel for diagnostic and monitoring purposes.

Patients are often transferred to different locations during treatment. For example, a patient may be picked up in an ambulance, delivered to an emergency room, transferred to an operating room, transferred to a surgical recovery room, transferred to an intensive care unit, and then transferred to a nursing floor. or to other publications. Therefore, the patient can be transferred between different locations within the same hospital, or between different hospitals. In many cases, the sensor used to monitor a patient's conditions is adhesive in its attachment and therefore remains with the patient. The monitors, however, are typically local to the particular posts within the facility. The sensor is typically disconnected from the monitor at the exit site and reconnected to another monitor at the destination site. Consequently, any historical physiological data collected by the monitor at the exit site is normally not available to the clinician treating the patient at the destination site.

In the medical art, a combination of a catheter sensor and memory unit is described in US Patent 4,858,615, entitled "Catheter Sensor and Memory Unit", and issued August 22, 1989. In this patent , the sensor assembly (34) is located at a distal end of the catheter (32) and the memory unit (38) is connected via a multi-conductor cable (40) to the sensor (see figure 5). The catheter is an invasive instrument typically used in a particular location and is removed during transport. Neither the catheter nor the memory unit will travel

ES 2 322 639 T3 with the patient when he or she is transferred to different locations. Therefore, any data captured and stored in the memory unit (38) is also not available when the catheter is removed from the patient.

Accordingly, it is highly desirable to provide a mechanism for storing and providing historical physiological data moving with a patient.

Description of the invention

The invention provides a mechanism for storing and providing historical physiological data, such as blood oxygen saturation data, for a patient, as defined in claim 1. In particular, historical physiological data is stored on a storage medium. that "travels" with the patient and is accessible wherever the patient is moved. This is accomplished by storing the physiological data within the sensor assembly. At the destination site, a monitor or device capable of interacting with the sensor electronics can retrieve and display the data. Historical physiological data allows a clinician or medical staff at the destination site to assess the patient's condition for the entire time the patient has been monitored. The invention can be used to store and provide different types of physiological data including, but not limited to, blood oxygen saturation, heart rate, and temperature data.

A specific embodiment of the invention provides a physiological sensor that includes a plurality of light sources, at least one photodetector, and a memory circuit. The light sources are selected to operate at different wavelengths. The photodetector receives light emitted by the plurality of light sources. And the memory circuit stores physiological data and provides the data when requested. Physiological data is indicative of a physiological condition of a patient to be monitored by the sensor.

Another specific embodiment of the invention provides a physiological test instrument including a monitor and a sensor according to claim 20. The monitor includes a treatment circuitry and a processing circuitry. The processing circuitry receives the electrical signal and processes the electrical signal to provide sampled data. The processing circuitry processes the sampled data to provide physiological data, where the physiological data is indicative of a physiological condition of a patient. The sensor is coupled to the monitor and includes a plurality of light sources, at least one photodetector, and a memory circuit. The light sources are selected to operate at different wavelengths. The photodetector receives light emitted by the light sources. The memory circuit stores the physiological data and provides the data when required. An encoder can optionally be coupled to the processing circuitry to encode and compress the physiological data before storing it in the memory circuit. The test instrument can be an oximeter system for storing and providing historical saturation data for a patient.

Another specific embodiment of the invention provides a method for storing physiological data, as defined in claim 15. The method detects, through the sensor, at least one signal indicative of a physiological condition and conditions the detected signal to generate samples of data. The data samples are processed to generate the physiological data, where the physiological data describes the physiological condition. Physiological data is stored in a memory located within the sensor. Physiological data can be encoded and compressed before storage in memory.

The foregoing, along with other aspects of this invention, will become more apparent with reference to the following specification, claims, and accompanying drawings.

Brief description of the drawings

Figure 1 shows a simplified block diagram of one embodiment of a physiological measurement system;

Figure 2 shows a block diagram of an embodiment of a monitor and a sensor; Y

Figure 3 shows a block diagram of a compression scheme for oxygen saturation data.

Description of the specific realizations

Figure 1 shows a simplified block diagram of one embodiment of a physiological measurement system 100. The system 100 includes a monitor 110 that is coupled to a display unit 120 via an electrical cord 122. The monitor 110 is further coupled through a second electrical cable 128 to a sensor 130 that is applied to a patient 132. Sensor 130 includes light sources (eg, LEDs) and a photodetector along with components suitable for coupling the electro-optical components to electrical cable 128. Sensor 130 is shown in Figure 1 as a clamp sensor. However, the invention can be applied to many sensor implementations, including those attached to a patient by adhesive and other attachment means. In a specific embodiment, monitor 110 is a pulse oximeter.

To estimate blood oxygen saturation, light from light sources in two or more wavelengths (for example, red and infrared) is transmitted through perfused tissues by the patient's blood (for example, in a finger) and is detected by the photodetector. The selection of wavelengths is based on a

ES 2 322 639 T3 series of factors. Such factors include the absorption characteristics of the patient and the transmission medium. The light sources and the photodetector are typically housed within a sensor that is attached to the monitor (eg, the pulse oximeter). The detected optical signal is supplied to the monitor for processing.

Figure 2 shows a block diagram of an embodiment of monitor 110 and sensor 130. Within monitor 110, a time processing unit (TPU) 220 provides control signals 222 to an LED driver 224 which, through the Data line (s) 226, alternately drives LEDs 230 within sensor 130. Depending on the particular implementation, LEDs 230 include two or more LEDs and LED driver 224 provides the necessary conductive signal for the LEDs. When activated, the light from LEDs 230 passes through a medium (eg, air or a fiber optic cable, depending on the implementation) within the tissues of a patient 234. After being transmitted through or reflected from the tissues, light is received by a photodetector 240 through another medium (eg, air or other fiber optic cable). Photodetector 240 converts the received light into a photocurrent, which is then supplied to an amplifier 250 that amplifies the photocurrent.

As shown in Figure 2, the amplified signal from amplifier 250 is supplied to a circuitry for two different channels, one channel for each of the red and infrared wavelengths. For the three wavelength implementation, the circuitry is provided for three channels. Each channel circuitry includes an analog switch 252 coupled in series with a low-pass filter 254 that is further coupled in series with an analog-to-digital converter (ADC) 256. Control line 258 for the time processing unit 220 selects the data sampled from the channel corresponding to the LED that has been activated. Specifically, the data sampled from ADC 256a is selected when the red LED is activated and the data sampled from 256b is selected when the infrared LED is activated. The data sampled from the ADCs 256 is supplied to a buffer 260 which stores the data for further processing. In one implementation, as buffer 260 periodically completes, a processor 262 coupled to a bus 264 directs the transfer of data from buffer 260 to memory 266. The implementation of a monitor shown in Figure 2 is one of many implementations. Another implementation of the pulse oximeter is described in the aforementioned US patent 5,853,364. The present statement can be adapted for application in different monitor implementations.

The sensor of the invention further includes circuitry that stores historical physiological data and provides the data when required. As shown in Figure 2, sensor 130 includes memory 236 coupled to interface circuitry. The interface circuit 238 provides signal processing, and can also provide other functions such as address decoding, etc. Interface circuit 238 is coupled via bus 270 to data interface circuit 268 within monitor 110. Through interface circuitry 238 and 268, physiological data is transmitted between monitor 110 and sensor. 130.

In one embodiment, to improve the compatibility of the sensor of the invention with conventional sensors and conventional monitors, the bus 270 is implemented using new signal lines (that is, not using or sharing the existing signal lines of conventional sensors) . Bus 270 can be implemented with a serial bus, a parallel bus, or other bus architectures. With this implementation, when the sensor 130 of the invention is coupled to a monitor not capable of supporting the features of the invention, the signals on the interface circuit 238 are simply ignored by the monitor, or alternatively not required by the monitor.

In another embodiment, interface circuits 238 and 268 interact via existing signal line (s) or cable (s) in conventional sensors and monitors. For example, interface circuits 238 and 268 may be coupled via data line (s) 226 and time multiplexer with the LED drive signals from LED driver 224.

Time processing unit 220, buffer 260, processor 262, memory 266, and data interface circuit 268 can be implemented in different ways. For example, these elements can be implemented within a single integrated circuit, such as a Motorola DMC68HC16 microcontroller. These elements can also be implemented within an application specific integrated circuit (ASIC), a digital signal processor, a microcontroller, or other circuits.

Memory 236 can be implemented with a random access memory (RAM), a FLASH memory, a programmable read-only memory (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM) , a similar programmable and / or erasable memory, any kind of erasable memory, a one-write memory, or other memory technologies capable of write operations. Memory 236 and interface circuit 238 can be integrated within an integrated circuit to reduce size and cost.

In a specific embodiment, to preserve the historical data and avoid accidental erasure, the sensor memory can be written once. This memory feature also prevents erasure of data during sensor processing. A specific example of a memory device that can be written once is a 2-wire EPROM device available from Dallas Semiconductor Corp.

In another embodiment, the memory can be erased and overwritten multiple times. This memory feature can be advantageous, for example, for non-disposable sensors that may include a large amount of memory. Such "specialty" sensors may be more suitable for applications where there is a high propensity for

ES 2 322 639 T3 use reusable sensors, such as within an operating room or intensive care unit or during ambulance transport. Specific examples of memory devices that can be erased and overwritten are Flash, EEPOM, battery-backed RAM, and other technologies.

The invention is applicable for different implementations of the oximeter system. For example, in one embodiment, an adapter module and a fiber optic cable can be interposed between cable 128 and sensor 130 (see Figure 1). The adapter module may include suitable light sources, detector, and optics to couple the electro-optical components to the fiber optic cable that guides the light and receives light from the patient. Fiber optic cable can also be divided into a long extension cable and a relatively short “sensor” cable. Fiber optic cables can be either fiberglass or plastic. This embodiment allows the electro-optic components to be reused, and only the short sensor cable is replaced from patient to patient.

Figure 2 shows an oximeter implementation using light at two wavelengths. However, the light from more than one LEDs can be used (eg, for improved accuracy). Light from a single light source can also be used, typically in conjunction with an appropriate optical filter. On the other hand, light sources other than LEDs can be used. For example, laser or white light sources can be used with appropriate filters at both the transmitting and receiving end.

The sensor can include different series of elements, depending on the implementation of the sensor or the application for which the sensor is used. In one implementation, the sensor includes the LEDs and the photodetector. This implementation reduces transmission loss by placing the light source and detector close to the patient. In another implementation, the sensor includes only the transmission medium (eg, a short fiber optic cable), but no LEDs or photodetector. This implementation reduces the cost, because the LEDs and the photodetector are included within an adapter module and are reusable. In still another implementation, the sensor may include the LEDs or the photodetector, as a compromise to reduce cost and transmission loss. Because of these different variations, the sensor includes memory to store historical physiological data.

During normal operation, when the sensor is attached to the monitor, the monitor receives the signal from the photodetector within the sensor and processes this signal to obtain the desired physiological data. In some conventional monitors, physiological data is stored in memory within the monitor and retrieved at a later time when requested. However, when a patient moves to new locations and different monitors are used, the data stored on the monitor at the previous site is typically not available at the current site.

In accordance with the invention, physiological data is processed, displayed, and stored on the monitor in nominal form. In addition, the data is compressed and supplied by the sensor for storage in a memory 236 located within the sensor. When the sensor is attached to another monitor, the new monitor can retrieve the data stored in the sensor's memory, decompress the retrieved data, and display the tablet data. In one embodiment, when the sensor is first attached to a new monitor, the monitor retrieves and displays the historical physiological data for the most recent predetermined period (eg, the last 20 or 30 minutes). This predetermined period can be programmed with the clinician or can be pre-programmed into the sensor's memory.

Alternatively, the monitor can be configured to retrieve and display historical physiological data at any time upon request of a healthcare provider (or clinician), by the healthcare provider simply by activating a control button on the monitor. The control button can optionally be preset to automatically retrieve data when a predetermined event occurs, such as when the sensor is attached to the monitor, or it can be preset so that data is only retrieved under an explicit command. of the health caregiver.

As noted above, the invention can be used to store and provide various physiological data including, but not limited to, blood oxygen saturation and heart rate data. For the sake of clarity, the invention is described in the context of storing and retrieving blood oxygen saturation (SpO2) data. Based on the received signals representative of the intensity of light detected by photodetector 240, processor 262 estimates oxygen saturation using algorithms that are known in the art. These algorithms use calibration coefficients that can be determined empirically and correspond to, for example, the wavelengths of the lights used.

The saturation data for a particular patient is processed by the monitor attached to the sensor, and the processed data is supplied to the sensor for storage in sensor memory. Sensor memory selection is dependent on numerous factors including cost, the amount of data that needs to be stored for a particular application, the amount of data compression that can be achieved, the physical dimensions, and so on. For oxygen saturation, storing approximately seven days of historical data is adequate for many applications.

In one embodiment, to reduce the amount of data to be stored in the sensor memory, the physiological data is compressed prior to storage. In one embodiment, compression is done by facilities located within the monitor. Alternatively, the coding circuit can be on the sensor itself. The monitor further includes facilities for decompressing data retrieved from sensor memory. The compression per

ES 2 322 639 T3 allows the use of a smaller memory in the sensor. This is particularly advantageous because the sensor is critically discarded after use on a patient. Compression also allows more data to be stored in memory of a given size. The ability to store large amounts of data is important for many diagnostic applications that require data collected over hours or days.

The compression scheme can be designed to take advantage of known characteristics for the physiological data that is stored. For example, it is known that oxygen saturation generally does not change rapidly. This feature can be exploited to achieve meaningful compression, as described below.

Figure 3 shows a block diagram of a compression scheme for oxygen saturation data. The saturation data is fed to a filter 312 that filters the data. The filtered data is supplied to a differential pulse code encoder (DPCM) 314 that determines difference values ​​between successive samples of filtered data. The difference data is supplied to a quantizer 316 which "re-quantizes" the difference data. The quantized data is supplied to a differential coordinate encoder using an efficient code set. Each of these items is further described below.

In one relationship, since it is known that oxygen saturation does not change rapidly, the saturation data is averaged over a predetermined period of time (here referred to as a generation) and an averaged saturation sample is supplied as representative of the saturation during that generation. In a specific embodiment, a generation is a period of time that lasts from one to five minutes, although any different duration can be used. The generation can also be set based on the characteristics of the physiological data being stored (eg, a longer generation for slow-changing physiological data and a short generation for fast-changing data).

Filter 312 filters the saturation data. Filter 312 may be a digital filter designed in a manner known in the art. In one embodiment, filter 312 is a low-pass filter that has a bandwidth relative to generation (i.e., BW ~ a / t_GENERATION, where BW is the filter bandwidth, α is a constant of proportionality, and t_GENERACIor_N is the period of a generation). The characteristics of filter 312 can also be matched (ie spectrally shaped) to match the characteristics of the data being filtered.

To further equalize the data and increase the amount of compression, the saturation data can be filtered over a period of multiple generations. However, averaging the saturation data over a longer time interval masks rapid changes in saturation, which are flattened out and lost in the averaging process. To capture rapid change events, a scrollable average filter can be used.

In one embodiment, the scrollable average filter includes a filter that filters the saturation acts over one generation (i.e., a single-generation filter) and another filter that filters data over multiple generations (i.e., a multiple-generation filter). generations). The scrollable average filter monitors saturation data averaged from the single-generation filter and detects averaged saturation samples that are outside of a predetermined window. The default window that can be adjusted is plus or minus several saturation points around the current averaged saturation value. For example, if the current averaged saturation sample has a value of 90 saturation points, the default window can be adjusted by ± 2 saturation points centered around 90 (for example, 88 to 92). The scrollable average filter then triggers a signal if the next average saturation sample has a value below 88 or greater than 92. If the saturation sample averaged from the single-generation filter is in the window, the sample averaged from the multi-generation filter is used. Otherwise, a saturation sample averaged from the single-generation filter that is outside the window indicates a rapid change in saturation. This detected sample is used to reset the scrolling average and cause a change in the averaged saturation sample to the new value from the single generation filter. The scrolling averaging filter enables rapid change detection and capture of their magnitudes, while maintaining a stream of filtered data that improves understanding of nominal data.

The slowly variable nature of oxygen saturation suggests the use of differential coding, since fewer bits would be required to represent differences between samples than in actual sample values. With differential coding, the first saturation sample is stored using the actual sample value. A subsequent saturation sample is represented as a delta value from a preceding saturation sample. Periodically, the actual sample value is stored to avoid an accumulation of errors in differential coding and to limit the spread of the error. DPCM 314 determines the difference values ​​between successive saturation samples. The difference value is calculated by subtracting the current saturation sample from the previous saturation sample.

For many applications, it is not necessary to store saturation data with a great deal of precision. For example, for some applications, it is sufficient and acceptable to indicate a change of ± one saturation point as there is no change in saturation. Thus, the difference values ​​from DPCM 314 can be re-quantified by a quantizer 316.

In one embodiment, quantizer 316 is a window comparator having a quantization window of, for example, ± a saturation point. If the difference value is within the quantization window, the

ES 2 322 639 T3 quantizer 316 indicates a "no change" in saturation and sends a zero. If the value of the difference is outside the quantization window, the quantizer 316 passes this value without further processing. The quantizer 316 can also be implemented in other ways, for example, as a quantizer that has a stage size twice that of the saturation sample.

Further quantization by quantizer 316 introduces quantization errors in the reconstructed data. This error can accumulate over successive samples and exceed an acceptable limit. To avoid this phenomenon, an error accumulator 320 coupled to the quantizer 316 accumulates the error entered by the quantizer 316 and provides the accumulated error to the DPCM 314. The DPCM 314 takes the accumulated error into account when calculating the difference values.

Due to the slowly varying nature of oxygen saturation and the use of differential coding and additional quantification, many of the data values ​​from quantizer 316 are zero. In one embodiment, the differential coordinate encoder (RLC) 318 receives the quantized data from the quantizer 316, transmits the non-zero values, and sends a code representative of the number of zero values ​​among the non-zero values. For example, for a sequence of (3, 0, 0, 0, 0, 0, 0, 4, ..., the RLC 318 transmits the first "3", then a code indicating six consecutive zeros, then "4". In one embodiment, the code representative of the number of consecutive zeros is generated so that the most common sequences of consecutive zeros are assigned codes that have shorter code widths. Characteristic code is similar to that of a Huffman code, which is known in the art.

The elements shown in figure 3 can be implemented in various ways. For example, these elements can be implemented in a processor (ie, processor 262 in FIG. 2), a digital signal processor, an ASIC, or other circuitry. The functions of the elements in FIG. 3 can also be provided by program code executed in processor 262 with memory carrier 266.

Figure 3 shows an embodiment of compression. In another embodiment of compression, the non-zero difference values ​​are transmitted along with their generation numbers. For the sequence shown above, the transmitted values ​​can be (3, 1), (4, 8), and so on. The first number in the pair is the difference value and the second number is the generation number. For some applications, this organization can provide additional insight into the embodiment shown in Figure 3.

In another embodiment of compression, the saturation value and the number of generations over which the value is in a predetermined quantization window are recorded. In this embodiment, it is not necessary to compute the difference values. Again, this embodiment can significantly reduce the data storage requirement for some types of physiological data.

Various compression embodiments have been written for oxygen saturation data. Although the invention can be practiced without the use of compression, additional capabilities are provided through the judicious use of compression. As used herein, compression includes any processing that alters, even slightly, the original form of the physiological data as it is (nominally) generated by the monitor. Other compression schemes can also be used and are within the scope of the invention. Of course, optionally no compression could be used.

Additional data in addition to oxygen saturation can be stored in sensor memory (ie to aid in patient monitoring or diagnosis). For example, a timestamp of the data can be stored. In this case, the first data sample includes the specific time (for example, the date and time) when the data is recorded. Subsequent data samples can be indicated by the number of generations away from the first (or previous) data sample. Sensor memory can also store an indication of a sensor disconnection from the monitor. This data allows clinical or medical line personnel the events retrieved in the sensor memory.

The sensor memory can also include a field that indicates when the sensor memory is full. Information in this field can be provided to the monitor to direct the monitor to stop sending data to sensor memory. Information in this field can be prominently displayed by the monitor for notification to clinical or medical personnel. In addition, in response, the monitor may generate an alarm (ie, a flashing light or an audio alarm, or both) to draw the clinician's attention to the operational status of the sensor.

In a specific embodiment, the saturation data is stored in a data format that includes an N-bit data field and a field containing the number of generations over which the data value is maintained. However, many other data formats could be used and are within the scope of the invention.

As noted above, in a specific embodiment, the memory sensor is implemented as a one-write memory device. A field in the sensor's memory can be adjusted when the sensor is reprocessed, so that the monitor can determine that it is coupled to a sensor that has been reprocessed. The monitor can use the information in this field to disable the display of historical data (for example, if memory is written once and is relatively full). Alternatively, if the

ES 2 322 639 T3 memory can be erased, a field for storing historical physiological data could be erased during further sensor processing.

Disabling the data display may be preferable in some applications to ensure the integrity of the collected data. For a memory device that can be written once and has a fixed memory size, it may not be possible to determine where the “old” data came from or how much of the memory may still be available in a sensor that has become to process. Furthermore, it is highly desirable to avoid having data that is displayed from an old patient and that can potentially be mistaken for valid data for the patient to which the sensor is attached. Since it is not easy to control or determine the amount of unwritten memory available after one use, which can range from zero to the full amount, inconsistencies and potential customer dissatisfactions can result from the use of a sensor that has varying amounts lots of available memory. By not displaying sensor data that has been reprocessed, these potential problems are avoided.

The invention has been described for the storage of blood oxygen saturation data. However, the sensor memory can also store data on other physiological characteristics, such as, for example, heartbeat, temperature, and so on. For example, in either case, the sensor memory can be used to store NTBP, IBP, and ECG waveforms. Furthermore, as memory costs continue to fall and larger memories become available, more complex physiological parameters can be stored and measured.

In addition, the information about the monitor can be stored or integrated together with the physiological data. This additional information may include, for example, the serial number of the monitor to which the sensor is attached, sensor connect / disconnect times, monitor diagnostics, and others. This information will allow clinical access to historical information about the instrument, as well as physiological data, which could be useful, for example, in litigation or troubleshooting of the instrument.

The invention provides advantages not available in conventional monitors and sensors. For example, the invention allows monitoring of a patient in transit that can be connected to two or more monitors over a period of time. One of these situations is a patient who is transported by ambulance to an emergency center and then transferred to an intensive care unit. The invention is especially beneficial in this application, as this particular patient is more likely to need detailed monitoring.

The invention can also be used to document physiological characteristics. For example, for a patient in home care requiring oxygen, documentation of oxygen saturation is typically necessary. In this case, the intention sensor can be used to store saturation data for the patient over a predetermined period of time (ie, one week). At the end of this period, the caregiver can simply remove the sensor and submit it as documentation of the patient's saturation. The invention can also be used to collect data for other applications, such as, for example, sleep diagnostics, desaturation, etc.

The sensor of the invention has been described for use in combination with a monitor that performs signal processing of the detected signal and compression of the processed data. In another embodiment, the sensor of the invention includes a facility to process (and compress, if necessary or desirable) the detected signal. This embodiment advantageously allows independent operation of the sensor without supporting it from a monitor. The data stored in the sensor can be provided to a monitor for viewing. The amount of signal processing and compression that can be achieved by the circuitry in the sensor is only limited by the technology available, which inevitably improves over time. Next term, physiological data that does not require extensive compression and signal processing (e.g. temperature, peak amplitude in a waveform, heart rate, etc.) can be collected and stored by the sensor. .

For further understanding of the invention in its use for the storage of oxygen saturation data in blood, a description of the derivation of oxygen saturation from photodetected signals is included in US Patents 4,911,167, 5,645. 059, and 5,853,364 cited above.

The stored data can correspond to the value of a real physiological condition (that is, oxygen saturation) or it can be indicative of the value of the condition, with the value of the conditions being determined by the monitor with reference to a determination table, by the monitor that calculates the value of the condition from the stored data using a predetermined algorithm.

The preceding description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without the use of inventiveness. For example, the invention can be applied to the storage of other physiological data, such as data of a patient's heartbeat, temperature, the volume of the individual blood pulsation delivered to the tissue by the frequency of the blood pulsation , and so on. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is in accordance with the broader scope consistent with the principles and new features described herein.