Source: http://www.google.com/patents/US7613486?dq=5754119
Timestamp: 2017-01-16 13:49:39
Document Index: 664393475

Matched Legal Cases: ['Application No. 2003', 'art 72', 'art 75', 'art 72', 'art 75', 'art 78', 'art 78']

Patent US7613486 - Method and apparatus for evaluating human stress using photoplethysmography - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA method of evaluating human stress using photoplethysmography (PPG) includes defining at least one PPG parameter, radiating light having at least one wavelength, which reacts to a blood component to be measured, at a measuring target and measuring a PPG signal from the measuring target during a predetermined...http://www.google.com/patents/US7613486?utm_source=gb-gplus-sharePatent US7613486 - Method and apparatus for evaluating human stress using photoplethysmographyAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS7613486 B2Publication typeGrantApplication numberUS 10/760,544Publication dateNov 3, 2009Filing dateJan 21, 2004Priority dateJan 22, 2003Fee statusPaidAlso published asCN1297231C, CN1517070A, DE602004010939D1, DE602004010939T2, EP1440653A1, EP1440653B1, US20040220483Publication number10760544, 760544, US 7613486 B2, US 7613486B2, US-B2-7613486, US7613486 B2, US7613486B2InventorsHyung-Sok Yeo, Jeong-whan Lee, Gil-won Yoon, Hyun-tai HwangOriginal AssigneeSamsung Electronics Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (16), Non-Patent Citations (2), Classifications (15), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetMethod and apparatus for evaluating human stress using photoplethysmography
US 7613486 B2Abstract
The present invention provides a method and apparatus for evaluating a level of stress in a human subject, i.e., a degree of tranquility, using an amplitude of a pulse component of a photoplethysmography (PPG), a change in a baseline, and a variation in a peak-to-peak interval of the PPG generated in accordance with a heart rate.
The PPG measuring unit preferably has a block letter “C” shape so that the measuring target can be inserted into the PPG measuring unit, and has a transmissive or a reflective structure.
Korean Patent Application No. 2003-4256, filed on Jan. 22, 2003, and entitled: “Method and Apparatus for Evaluating Human Stress Using Photoplethysmography,” is incorporated by reference herein in its entirety.
Referring to FIG. 5, in step 51, PPG parameters are defined, as shown in FIG. 6. Referring to FIG. 6, a pulse component amplitude 61 is defined by a difference between a highest point and a lowest point of each pulse. In association with the pulse component amplitude 61, an AC mean and a total number of pulse components per a predetermined period of time are defined. In the total number of pulse components, the number of pulse components having an amplitude less than the AC mean is defined as a “small AC count”. A ratio of the small AC count to the total number of pulse components is defined as a “small AC count %”. A value obtained by subtracting the small AC count % from 100 is defined as a “large AC count %”.
PPI(i)=[i(n+k)−i(n)]×sampling rate (1)
In association with the PPI 63, an average PPI and a total number of PPIs per a predetermined period of time are defined. In the total number of PPIs, the number of PPIs less than the average PPI is defined as a “fast PPI count”. A ratio of the fast PPI count to the total number of PPIs is defined as a “fast PPI count %”. A value obtained by subtracting the fast PPI count % from 100 is defined as a “slow PPI count %”.
FIG. 7A shows a transmissive PPG measuring device including a light emitting part 72 with a light emitting element 71 radiating light and a light receiving part 75 with a light receiving element 74 detecting light transmitted by a measuring target 73. The housings of the light emitting part 72 and the light receiving part 75 are connected at one end to form a block letter “C” shape. FIG. 7B shows a reflective PPG measuring device including a light emitting/receiving part 78 with a light emitting element 76 for radiating light and a light receiving element 77 for detecting light reflected from a measuring target 73. A measuring target support 79 is connected to one end of the light emitting/receiving part 78 to form a block letter “C” shape. As shown in FIGS. 8A and 8B, a PPG measuring device 81, such as shown in FIG. 7A or 7B, may be used at any part of a human body, for example, an ear 83, a finger 85, or a toe.
Referring to FIG. 9, in step 91, a baseline spread range is compared with an AC mean to obtain a stress index SI. For example, stress indexes are classified into eight (8) classes according to conditional formulae shown in Table 3. If a data group to be compared satisfies a condition for a particular class among the eight (8) classes, subtraction or addition is performed on a stress index SI in accordance with the condition. The stress index obtained as the result of the above operation is referred to as SI—1 and is adjusted so as not to exceed 100.
In step 93, a fast PPI count % is calculated based on an average PPI, and it is determined whether the fast PPI count % is within a predetermined range to obtain a stress index SI. For example, stress indexes are classified into three (3) classes according to conditional formulae shown in Table 4. If a data group to be compared satisfies a condition for a particular class among the three (3) classes, subtraction or addition is performed on a stress index SI in accordance with the condition. The stress index obtained as the result of the above operation is referred to as SI—2 and is adjusted so as not to exceed 100.
In addition, if, in step 94, it is determined that a long period of time was required to collect PPG data, a statistical method can be used in order to increase the reliability of evaluation. For example, when it takes more than one minute to collect PPG data, it is determined whether a total number of PPIs in the collected PPG data is at least fifty (50). If it is determined that the total number of PPIs is at least fifty (50), a PPI time series data group from an initial PPI to a 25th PPI is defined as a first data group, dataset—1, a PPI time series data group corresponding to the next twenty-five (25) PPIs is defined as a second data group, dataset—2. An n-th data group, dataset_n is defined in the same manner. If there are two data groups to be compared, a two-sample paired t-test is performed to detect a p-value. If there are at least three data groups to be compared, one-way ANalysis Of VAriance (ANOVA) is performed to detect a p-value. If the detected p-value is greater than 0.05, a stable condition is determined. If the detected p-value is smaller than 0.05, an unstable condition is determined. In addition, determination of a degree of stress based on a p-value can be more precisely performed on the basis of 0.05. For example, stress indexes are classified into four (4) classes according to conditional formulae shown in Table 4. If a data group to be compared satisfies a condition for a particular class among the four (4) classes, subtraction or addition is performed on a stress index SI in accordance with the condition. The stress index obtained as the result of the above operation is referred to as SI—3 and is adjusted so as not to exceed 100.
Next, in step 95, a small AC count % is calculated based on an AC mean, and it is determined whether the small AC count % exists within a predetermined range in order to obtain a stress index SI. For example, stress indexes are classified into three (3) classes according to conditional formulae shown in Table 6. If a data group to be compared satisfies a condition for a particular class among the three (3) classes, subtraction or addition is performed on a stress index SI in accordance with the condition. The stress index obtained as the result of the above operation is referred to as SI—4 and is adjusted so as not to exceed 100.
In addition, if in step 96, it is determined that a long period of time was required to collect PPG data, a statistical method can be used in order to increase the reliability of evaluation. For example, when it takes more than one minute to collect PPG data, it is determined whether a total number of pulse components in the collected PPG data is at least fifty (50). If it is determined that the total number of pulse components is at least fifty (50), a pulse component amplitude time series data group from an initial pulse component to a 25th pulse component is defined as a first data group, dataset—1, a pulse component amplitude time series data group corresponding to the next twenty-five (25) pulse components is defined as a second data group, dataset—2. An n-th data group, dataset_n, is defined in the same manner. If there are two data groups to be compared, a two-sample paired t-test is performed to detect a p-value. If there are three or more data groups to be compared, one-way ANOVA is performed to detect a p-value. If the detected p-value is greater than 0.05, a stable condition is determined. If the detected p-value is smaller than 0.05, an unstable condition is determined. In addition, determination of a degree of stress based on a p-value can be more precisely performed on the basis of 0.05. For example, stress indexes are classified into four (4) classes according to conditional formulae shown in Table 7. If a data group to be compared satisfies a condition for a particular class among the four (4) classes, subtraction or addition is performed on a stress index SI in accordance with the condition. The stress index obtained as the result of the above operation is referred to as SI—5 and is adjusted so as not to exceed 100.
As described above, short-term stress indexes and long-term stress indexes can be obtained depending on time taken for collecting PPG data. A short-term stress index group 97 includes SI—1, SI—2, and SI—4, and a long-term stress index group 98 includes SI—1, SI—2, SI—3, SI—4, and SI—5. After setting maximum values for the respective stress indexes SI—1 through SI—5, a degree of stress can be evaluated based on the set values. For example, a maximum value of each of the stress indexes SI—1 through SI—5 can be set to an exemplary 100 to facilitate explanation, and a degree of stress, which is referred to as a stress index %, may be calculated as shown in Formulae (2) and (3).
Long-term stress index %=(sum of long-term stress indexes/300)*100 (2)
Short-term stress index %=(sum of short-term stress indexes/500)*100 (3)
Referring back to FIG. 5, in step 59, items of the stress indexes detected in step 57 and a final stress index % are displayed. The stress index items may be changed when necessary. When it is determined whether the stress index % exists within a predetermined reference range, the stress index % may be displayed along with the predetermined reference range. For example, the stress index % may be evaluated based on a distribution thereof, as shown in FIG. 10. More specifically, when the stress index % is within a range of ±10% centering around 43%, a normal condition is determined. When the stress index % exceeds the maximum limit of the normal range, a stressful condition is determined. When the stress index % is less than the minimum limit of the normal range, a relaxed condition is determined.
Referring to FIG. 11, the PPG measuring unit 101 has a block letter “C” shape, as shown in FIG. 7A or 7B, so that a measuring target may be inserted into the PPG measuring unit 101. The PPG measuring unit 101 measures a PPG signal generated from a part of a human body, such as a finger, toe, or earlobe, where peripheral blood vessels are concentrated. An on/off interval of the PPG measuring unit 101 is controlled by the signal processing unit 105. The amplifying and filtering unit 103 amplifies the PPG signal provided from the PPG measuring unit 101 to a predetermined level and performs filtering to remove noise components.
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