The present invention generally relates to ways of characterizing health related disorders. More particularly, the invention provides a system and method for assessing quality of sleep in a mammal or other organism that sleeps. Merely by way of example, the invention is provides a numerical and/or graphical representation of certain aspects of an organism's sleep.
Many diseases and conditions are characterized by fatigue, tiredness, sleepiness, and/or related states. In some cases, inadequate sleep may contribute to such states. Thus, in trying to ascertain the cause of a patient's tiredness, sleepiness, fatigue, and/or related state, a physician or other health care provider will often want to have information about the adequacy of the patient's sleep.
Although there are distinctions between these states, many people, especially persons who are not health care professionals, use them in conversation without careful attention to the distinctions. Thus, in conversations with physicians or other health care providers,
Sleep may be inadequate in various ways. Merely by way of example, sleep may be inadequate in quantity or in quality.
In some cases the quantity of sleep may be ascertained by asking the patient how long he or she sleeps. Some patients cannot provide a reliable answer to this question. For this and other reasons, various techniques have been developed to provide information on how long a person sleeps. Merely by way of example, such techniques include polysomnography and actigraphy.
In some cases the quality of sleep may be ascertained by asking the patient how well he or she sleeps. Many people, however, find it more difficult to describe their sleep quality than their sleep quantity. Sleep quantity can, for example, be described in standard units of time such as hours, but sleep quality is often discussed in more vague terms such as “slept well,” “slept poorly,” and the like.
Various techniques have been tried in an effort to add rigor to assessments of sleep quality. Merely by way of example, these include questionnaires such as the Pittsburgh Sleep Quality Index. Questionnaires, however, are commonly regarded as less than fully objective because a subject may, consciously or unconsciously, alter responses in various ways, e.g. to minimize reported symptoms.
As an additional example, polysomnography has been used to measure sleep quality. Humans normally cycle through several “stages” of sleep during the night (e.g. stage 4 sleep, rapid eye movement sleep, etc.), and the duration of various stages of sleep can sometimes be related to sleep quality. However, polysomnography generally requires a skilled technician for successful use. Furthermore, due to the large number of sensors employed, polysomnography may disturb or otherwise affect the subject's sleep.
U.S. Pat. No. 6,468,234 (to van der Loos et al) teaches a method and apparatus for measuring sleep quality that utilizes sensors incorporated in a sheet that is laid on top of a conventional mattress on which the subject sleeps. Among the possible analyses of data from acquired by the aforementioned sensors is a count of body shift episodes during the night, from which an index of nightly restlessness (in units of events per hour) may be calculated.
U.S. Pat. No. 6,579,233 (to Hursh) teaches a relationship between sleep quality and sleep fragmentation. Chokroverty defines sleep fragmentation as ______ Awakenings from sleep are sometimes called “arousals.” Several types of environmental and physiological events may fragment (interrupt) sleep. Merely by way of example, sleep may be fragmented by arousals or awakenings. Arousals from sleep may occur abnormally frequently in some subjects. For example, sleep apnea and related conditions may be associated with frequent arousals from sleep.
U.S. Pat. Nos. 6,363,270 and 6,091,973 (to Colla and Brydon) teach a measurement of sleep quality based on correlating two or more physiological signals from a patient, then linearly or proportionally scaling the number of coincident changes in the correlated signals. The former disclosure further teaches that “a change in at least two sympathetic physiological variables . . . is indicative of an arousal.”
However, counting and linearly scaling the number of signal change events and/or arousals appears to have shortcomings. Under the so-called “sleep continuity” theory of restorative sleep, “the rate of periodic fragmentation of sleep and not simply [the] total number of arousals” is said to be a determinant of daytime performance and sleepiness (M. H. BONNET. Sleep. 1987; 10: 364-373).
Thus, U.S. Pat. Nos. 6,743,167 and 6,553,252 and 6,530,884 and 6,527,715 and 6,419,629 (to Balkin et al) teach that the effect of arousals is non-linearly dependent on inter-arousal duration. They say: “Available data suggest that five minutes is the approximate length of time required to return to recuperative sleep (stage 2 or deeper sleep) following an arousal to wake or stage 1 sleep. If many hours of sleep are obtained without interruption, then the delays make only a small difference in overall restoration of cognitive performance capacity. If sleep is interrupted with frequent awakenings, the delays in recuperation after each awakening will accumulate, and thus substantially reduce total cognitive performance capacity restored during the total sleep period.” Balkin et al teach how to estimate cognitive performance based upon a plurality of historical data be supplied to a model, but do not teach explicit assessment of sleep quality.
U.S. Pat. No. 6,045,514 (to Raviv and Weingarten) teaches a method of determining a breathing resistance index of a sleeping subject from a set of respiratory sounds.
From the above, it is desirable to have improved techniques for characterizing health related disorders, for example objective, practical, sleep quality assessments based on sleep fragmentation.
A method for improved visualization of information related to the physiology of a sleeping patient is disclosed. Physiological information from the patient is obtained by a device, converted to digital format, and processed to yield epochs of time based on whether the patient was in a physiologically desirable or undesirable state. The duration of epochs is plotted as a series of rectangles and a quality-of-sleep score is calculated based on the epoch lengths.
Various additional objects, features, and advantages of the present invention can be more fully appreciated with reference to the detailed description and accompanying drawings that follow.
According to the present invention, techniques for characterizing health related disorders are provided. More particularly, the present invention provides improved methods and systems for assessing sleep quality. Merely by way of example, the invention provides an index associated with sleep quality and/or a graphical representation associated with sleep quality for a patient that sleeps.
The digital data are transferred to data analysis device 735. In an embodiment of the invention, the transfer need not occur at a specified time. Interface unit 725 in data collection device 710 passes digital data from memory 720 across a connection 730 to an interface unit 740 in data analysis device 735. Merely by way of example, connection 730 may be an electrically conductive cable or a wireless coupling. It may be analog or digital. Connection 730 may consist of multiple sub-connections, e.g. a communications network. In an embodiment of the invention, interface units 725 and 740 implement a USB (universal serial bus) connection. In another embodiment of the invention, interface units 725 and 740 implement a Bluetooth connection.
Interface 740 in data analysis device 735 may send digital data to quality calculator module 750 or store digital data in memory 745 for later retrieval by quality calculator module 750 or other components.
Quality calculator module 750 produces one or more indices of sleep quality based on the digital data. Merely by way of example, quality calculator module 750 may be implemented as a set of software codes. The sleep quality indices may be sent from quality calculator module 750 to quality visualization module 755, or be stored in memory 745 for later retrieval by quality visualization module 755 or other components.
Quality visualization module 755 produces information based on the indices of sleep quality that, when rendered by a display device 760, communicates information about the sleep quality of subject 700 to a human viewer 765. Merely by way of example, quality visualization module 750 may be implemented as a set of software codes. Viewer 765 may or may not be the same mammal as subject 700. In some cases viewer 765 may be a health care professional, e.g. a physician, veterinarian, psychologist, and the like.
Those with ordinary skill in the art will recognize that components of data collection device 710 and data analysis device 735 can be distributed among these or other devices in a plurality of ways. Merely by way of example, display 760 need not be part of data analysis device 735. Software codes may execute on different computers, e.g. software codes for quality calculator module 750 may execute on a computer that is networked to a computer upon which software codes for quality visualization module 755 execute.
In an embodiment of the invention, data analysis device 735 is a personal computer with appropriate software codes, and subject 705 is the same as viewer 765. This embodiment can yield convenient, private in-home assessment of sleep quality.
U.S. patent application Ser. No. 11/094,911 teaches an embodiment of data collection device 710. U.S. patent application Ser. Nos. 10/721,115 and 11/094,911 teach embodiments of sensor(s) 705. In an embodiment of the invention, data collection device 710 and data analysis device 735 are a single device.
The calculation and visualization of information about the sleep of subject 700 produced by quality calculator module 750 and quality visualization module 755 are based, in whole or in part, on the duration of sleep-related “continuity periods.” Continuity periods may be defined according to a plurality of criteria. An actigraphic criterion is outlined below.
In an embodiment of the invention, sensor(s) 705 include an actigraph. An actigraph senses acceleration of the body part to which it is mechanically coupled. Some actigraphs, for example, are worn like a wristwatch. In many cases, actigraphically-detected body motion during a period of sleep (or attempted sleep) is associated with wakefulness at or near the time of the motion. Similarly, periods of time in which an actigraph detects no acceleration may be associated with sleep. Actigraphs do not perfectly identify sleep and wakefulness, but some sleep physicians have found them useful nevertheless.
Returning to
In an embodiment, continuity periods are characterized by a start, an end, and a duration of time.
Continuity processor 220 identifies zero or more continuity periods on the basis of data 200 and criteria parameters 230 for determining sleep interruption(s).
Each continuity period identified by continuity processor 220 has an associated duration in time, represented herein as duri for continuity period i. In an embodiment, continuity processor 220 is implemented as software codes in a digital computing device. In an embodiment, continuity processor 220 calculates each duri by subtracting the start-time of continuity period i from the end-time of continuity period i.
In an exemplary embodiment parameters 230 may include, but are not restricted to, the total duration of time represented by physiological data in data 200. Merely by way of example, parameters 230 may include, but are not restricted to, durtot, the sum of durations of all continuity periods, where:
In an embodiment, continuity processor 220 includes a restoration function (possibly passed as a parameter 230) that maps a duri to a dimensionless restoration value, restorei, ranging from 0 to 1 (inclusive) that represents the degree to which a period of uninterrupted sleep is restorative to the body and/or mind of a patient. A restoration value of 1, for example, indicates the continuity period was complete in its restorative effect while it occurred, whereas a restoration value of 0 would indicate the continuity period had no restorative effect. Higher restoration values normally contributoe to higher quality of sleep.
Merely by way of example,
Returning to
In an exemplary embodiment quality score 250 is calculated 240 to be the sum of the restorei values over all continuity periods i. This embodiment, however, has the disadvantage that there is no pre-determined upper bound on the quality score, because the number of continuity periods might vary from patient to patient, or from sleep period to sleep period.
In an alternative exemplary embodiment, quality score 250 is calculated 240 to be the mean of the restorei values for all continuity periods i. This embodiment, however, has the disadvantage that multiple very short continuity periods, e.g. 30 seconds, would have an influence on the final quality score 250 out of proportion to their clinical importance. For example, under this embodiment, a first person who had 10 continuity periods of 30 seconds each at the beginning of an 8-hour night of sleep could potentially have a significantly different quality score 250 from a second person who had only one or two such periods at night's start, but otherwise slept identically to the first person the remaining 8 hours of the night. This difference in scores would be suspect, since many persons would claim that a few minutes at the beginning of a night's sleep is unlikely to greatly influence the restorative nature of the full night's sleep.
In an alternative exemplary embodiment, quality score 250 is calculated 240 as a higher statistical moment of the restorei values for all continuity periods i, e.g. the second statistical moment that is sometimes known as variance (to which the standard deviation is closely related), the third statistical moment that is sometimes known as skew, or the fourth statistical moment that is sometimes known as kurtosis, and the like. This embodiment has the same disadvantage as the embodiment using the first moment (mean) of the restorei values.
In an exemplary embodiment, calculation 240 of quality score 250 includes use of restorei values as weightings for duri values over all continuity periods, e.g.:
where * is the symbol for multiplication. In this embodiment, the quality score may be likened to total restorative sleep time. This embodiment has the advantage that multiple short-continuity periods should not, in most cases, change the quality score appreciably when there are long continuity period(s) also present.
In an embodiment, restorei values are used as weightings for duri values and the sum over all continuity periods is normalized by durtot, e.g.:
In this embodiment, the quality score above, hereinafter referred to as the “quality index,” is dimensionless and ranges from 0 to 1. This embodiment, too, is relatively insensitive to the presence of multiple short-continuity periods.
Although steps 210, 220, 230, and 240 are shown as distinct in
Although providing a single number as a quality score for a patient's sleep episode(s) has advantages, there is a loss of information associated with reduction to a single number. Merely by way of example, clinicians may derive additional useful information from consideration of individual continuity periods. Such information may be provided with alphanumeric characters, possibly in tabular form. It may also be provided in graphical form by the quality visualizer 250.
The height and width of each rectangle in
In
The similarity between the rectangles 401-409 and the rectangles 501-509 is advantageous. The concept of continuity time is likely to be more readily grasped by clinicians who first encounter the present invention than is the concept of restoration. The similarity in rectangles is expected to help introduce clinicians to the concept of restoration. Thus, in some cases where time fraction and restoration are plotted (viz.
In
A feature of the present invention is that the sum of the areas of rectangles 501-509 (as measured according to the scales of vertical axis 510 and horizontal axis 520) is equal to the quality index described above. A further feature of the present invention is that the cross-hatched area of
Yet another feature of the present invention is that the limits on the axes 510 and 520 may be held constant regardless of patient or sleep episode. As a result,
Various numerical annotations may be made as well. For example, the quality index may be printed over the cross-hatched area within frame 540, and 1 minus the quality index may be printed in the non-cross-hatched area 550 within frame 540.
In some cases it may not be preferable to use restoration values to determine the horizontal extent of graphical representations of continuity periods, as was used for rectangles 501-509. Merely by way of example, there may be no restoration function of adequate reliability available for a certain subset of patients.
Frame 640 in
It is seen in
where threshold is a duration in minutes (
In some embodiments, it may be advantageous to define durtot as the subject's time-in-bed.
In an embodiment, different types of continuity periods may be defined and visualized according to the invention. For example, signal 100 may not be dichotomously valued, and a continuity period's type may vary according to the value of signal 100 ending the period. As a specific example, in a variant of signal 100, sleep may have value 0, an apnea event may have value 1, a hypopnea event may have value 2, an oxygen desaturation may have value 3, and so on. Types of continuity periods would correspond to periods ended by an apnea, hypopnea, oxygen desaturation, etc. Variations of shape, color, or other graphical features may be incorporated into visualization of such continuity periods, depending on their type.
In an embodiment, the duration of time between continuity events may also be figured into visualization or calculation of indices.
Other variations of quality calculator 240 and quality visualizer 260 are possible. In the boundary value case where there are zero continuity periods to be considered, a specific embodiment of quality calculator 240 would assign a reasonable value for quality score 240, e.g. zero.
The present invention has several potential advantages. Merely by way of example, perspicacious selection of restoration function and quality score definition can provide results in accord with the sleep continuity theory without undue influence from short periods of continuous sleep of lesser clinical importance. A further potential advantage of the present invention is the concise graphical representation of information about specific continuity periods that also communicates information about sleep continuity in aggregate.
Another potential advantage of the present invention is the ability to tailor sleep quality scores to various types of data 200. For example, a “sleep tranquility index” may be defined by using actigraphy data to determine when a patient moves during sleep. In a specific embodiment, periods without movement, i.e. tranquil periods, are defined as continuity periods. Thus, a higher value of the sleep tranquility index is associated with more tranquil sleep. In an alternative specific embodiment, any of several criteria may be used to determine when sleep has been interrupted. Merely by way of example, an interruption in sleep may be defined to occur when any of the following occur: an apnea, a hypopnea, a body movement, an oxygen desaturation, an electroencephalographic arousal, or a significant respiratory arrhythmia.
Another potential advantage of the present invention is its ability to facilitate comparisons between various criteria for interrupted and continuous sleep. Merely by way of example, different types of physiological events may predominantly occur in sleep apnea as compared to the upper airway resistance syndrome (UARS). Sleep apnea is generally characterized by repetitive apneas and hypopneas, whereas UARS is generally characterized by frequent respiratory effort-related arousals (RERAs). Continuity finder 210 could, in a first application of the present invention, be configured to include apneas and hypopneas as events indicating an interruption in sleep. Continuity finder 210 could then, in a second application of the present invention to data collected in association with the same sleep episode as the first application of the invention, be configured to additionally include RERAs as events indicating an interruption in sleep. The quality score 250 thereby produced and/or a representation thereby produced by quality visualizer 260 in each application of the invention could be compared to help understand the effect of different criteria in defining sleep interruption.
It should be noted that the above sequence of steps is merely illustrative. The steps can be performed using computer software or hardware or a combination of hardware and software. Any of the above steps can also be separated or be combined, depending upon the embodiment. In some cases, the steps can also be changed in order without limiting the scope of the invention claimed herein. One of ordinary skill in the art would recognize many other variations, modifications, and alternatives. It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
This application claims priority to U.S. Provisional Patent No. 60/610,888 filed Sep. 18, 2004, commonly assigned, and hereby incorporated by reference for all purposes. This application is a continuation-in-part of application Ser. No. 10/214,792 filed Aug. 7, 2002 and commonly assigned. This application is a continuation-in-part of application Ser. No. 10/721,115 filed Nov. 24, 2003 and commonly assigned. This application is a continuation-in-part of application Ser. No. 11/094,911 filed Mar. 30, 2005 and commonly assigned.
Number | Date | Country | |
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60610888 | Sep 2004 | US |
Number | Date | Country | |
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Parent | 10214792 | Aug 2002 | US |
Child | 11230942 | Sep 2005 | US |
Parent | 10721115 | Nov 2003 | US |
Child | 11230942 | Sep 2005 | US |
Parent | 11094911 | Mar 2005 | US |
Child | 11230942 | Sep 2005 | US |