New pulse wave measurement method using different hold-down wrist pressures according to individual patient characteristics
© Yoo et al.; licensee Springer. 2013
Received: 23 May 2013
Accepted: 26 August 2013
Published: 27 August 2013
In traditional Chinese and Korean medicine, doctors first observe a patient’s pulse by gently and strongly pressing their fingers onto the wrist, and then make a diagnosis based on the observed pulse waves. The most common method to implement this diagnostic technique is to mechanically extract the pulse waves by applying a fixed range of pressures for all patients. However, this method does not consider the patients individual characteristics such as age, sex, and skin thickness. In the present study, we propose a new method of pulse wave extraction that incorporates the personal characteristics of the patients. This method measures the pulse wave signal at varying hold-down pressures, rather than applying a fixed hold-down pressure for all patients. To compare this new technique with existing methods, we extracted pulse waves from 20 subjects, and then determined the actual applied pressure at each step, the coefficient of floating and sinking pulse (CFS), and the distinction of floating/sinking pulse for each group. Consequently, each subject had a different pressure range in our proposed method, whereas all subjects had a similar pressure range in the existing method. Four of 20 subjects exhibited different floating/sinking pulse patterns due to the value of the first pressure step and the range of hold-down pressures. These four subjects were categorized as overweight based on BMI. In addition, the moving distance of the proposed method was longer than the existing method (p = 0.003, paired t-test), and the correlation coefficient between CFS values of two different methods was 0.321, indicating that there was no correlation.
In Traditional Chinese Medicine (TCM) and Korean Medicine (KM), four diagnostic methods of observation (listening, smelling, inquiring, and palpation) are used to diagnose diseases in patients. Pulse diagnosis is the representative diagnostic method belonging to the palpation diagnostic methods (Kim and Kang2008). The purpose of pulse diagnosis is to determine evolution of a disease, causes of a disease, position of a disease, and a cure for the disease. Pulse diagnosis is traditional and venerable. However, it is difficult to become proficient in measurement of pulse waves, and the measurement and analysis of pulse waves is subjective. Therefore, a pulse diagnosis can vary with different doctors. A number of studies have attempted to objectify and quantify pulse waves to overcome this problem (Ryu et al.2007; Kim et al.1999) by using pulse diagnosis sensors, pulse wave simulators, and pulse diagnosis instruments (or pulse taking devices) (Fu and Lai1989 Jeon et al.2008; Kim et al.2009a; Luo et al.2012; Shin et al.2010; Shin et al.2011; Yoo et al.2013). A pulse diagnosis sensor has been developed for pressure calibration, size, temperature and deployment, while a pulse wave simulator has been developed for an objective standard for pulse analysis. These advancements mainly focus on development of hardware to acquire objective and quantitative pulse waves. In the present study, we developed a software-based pulse wave measurement method.
The pulse diagnosis in KM has 28 representative pulse patterns determined by pulse parameters such as rate, rhythm, arterial width, depth, length, arterial tension, force, ease of occlusion, and pulse contour. Ten of 28 pulse patterns have particularly high clinical utility, and include floating/sinking pulse (defined by level of depth), slow/rapid pulse (defined by rate), long/short pulse (defined by length), vacuous/replete pulse (defined by force), and broad/fine pulse (defined by width). The floating/sinking pulse is associated with the hold-down pressure that can vary with individual patients. For example, a slim person’s radial artery may be more easily accessible because of the thinner layer of subcutaneous tissue, while someone with a higher proportion of body fat may have an artery that is more difficult to palpate because of the thicker subcutaneous tissue layer. As such, the level of hold-down pressure may differ from person to person. TCM and KM doctors distinguish between floating pulse and sinking pulse by the difference of pulse pressure felt at different levels of hold-down pressure. To implement applying weak and strong pressure on wrist by a mechanical system, existing pulse wave measurement methods apply a constant range of pressure for all subjects. Most pulse diagnosis instruments in common use have adopted this method. A 3D MAC (Daeyomedi, Korea) is a representative pulse diagnosis instrument. This instrument applies five different levels of hold-down pressure to the wrist, and measures pulse wave signals by using a piezoresistive pressure sensor and a control robot. A P-H curve is then generated by spline interpolation, and the pulse wave is analyzed from the measured pulse wave signals at five pressure steps. The concept of a P-H curve with hold-down pressure on the horizontal axis and pulse wave pressure on the vertical axis was introduced in KM. In addition, the distinction of pulse patterns such as floating/sinking pulse and rapid/slow pulse and diagnosis of chronic gastritis have been studied by using pulse waves measured by this method (Kim et al.2009b; Kim and Shin2010; Shin et al.2012). The existing method has the advantage of measuring pulse wave signals stably at each of five pressure steps. However, it does not consider that the hold-down pressure applied by an oriental doctor varies from person to person, as the sensitivity of the doctor’s finger varies with personal characteristics such as age, sex, and skin thickness. Therefore, the existing method of applying the same value of hold-down pressure can be problematic for acquisition and analysis of pulse wave signals (Barker1951; Lee et al.2008).
Therefore, in this study we propose a new method for measuring pulse wave signals that considers the personal characteristics of the patients. The proposed method measures pulse wave signal at varying values of hold-down pressure for each subject. To achieve this, the pulse diagnosis instrument constantly applies increasing pressure and measures the pulse waves until they reach the termination point. The start and last points are then detected, and are used to determine the specific pressure range in which the sensor detects the subjects pulse waves. The range is then equally divided into five steps, and at each step the subjects pulse waves are finally extracted and analyzed. We compared the measurements of floating/sinking pulse, pulse depth (motor moving distance), and actual applied pressure (AAP) at each of the five pressure steps between the two methods. The coefficient of floating and sinking pulse (CFS) is used to distinguish floating/sinking pulse (Lee et al.2005).
Existing measurement methods
The sensor then moves up at 0.125 m/s (slow). Once the hold-down pressure reaches the determined pressure for each step as listed above, the pulse diagnosis sensor stops and measures the pulse waves. This process is repeated until the hold-down pressure reaches the first pressure step. Note that motor down denotes increased hold-down pressure, while motor up denotes decreased hold-down pressure.
Comparison of the two methods
Results of the existing method and proposed method with respect to pulse depth
Step1 - Step 5 moving distance (mm)
Distinction of floating/sinking pulse pattern
In this study, we developed a new pulse wave measurement method that adjusts for the personal characteristics of the patients including age, sex, and skin thickness. We compared the pulse waves of 20 subjects between existing and our proposed methods. The APP at each of the five pressure steps and moving distance between the first pressure step and the last pressure step were calculated. In the existing method, the APP of 20 subjects at each of the five pressure steps were similar, as the range of the pressures applied onto each subjects’ wrist was the same. However, in the proposed method the APP of 20 subjects at each of the five pressure step was different because the proposed method measures the pulse wave signal at a hold-down pressure that varies according to individual subject characteristics. The result of the proposed method shows that pulse waves can be measured at pressures between 40 and 240 mmHg. In addition, the step-motor moving distance in the proposed method is longer than that in the existing method, suggesting that the proposed method perceives and measures pulse wave at deeper a level, while the existing method might miss pulse wave information at a deeper level and therefore provide inaccurate depth data. Although the range of hold-down pressures determined using the existing method in our study was also from 40 to 240 mmHg, the majority of existing pulse diagnosis instruments have a smaller range, and are more likely to provide inaccurate depth data. Therefore, the existing method is not suitable for subjects who have a pulse signal beyond the range of hold-down pressures. Conversely, the proposed method minimizes the overlooked pulse wave signal by varying the hold-down pressure from person to person.
In the present study, we calculated the value of CFS to distinguish between floating/sinking pulses. We found that four subjects who were categorized as overweight based on BMI exhibited different floating/sinking pulse patterns, while the remaining normal weight subjects exhibited the same pattern. Therefore, the thicker subcutaneous tissue layer of overweight subjects exerts an influence on pulse wave measurement. On closer examination, the existing method indicated that these four subjects had a sinking pulse, whereas the proposed method showed a floating pulse. This difference may have occurred when the hold-down pressure was strong enough to perceive pulse signal at a deep level. Although a new CFS value was calculated in the present study, it was not used to distinguish between floating/sinking pulses, as this distinction can only be defined when all pulse waves on Chon, Kwan, and Chuck position are measured (we measured the pulse wave only on Kwan). Nevertheless, we determined that the correlation coefficient between CFS values for the two different methods was 0.505, indicating that they were not significantly correlated.
Our proposed method could successfully measure pulse waves accounting for individual subjects characteristics. However, although the correlation analysis and pair t-test indicate a difference between the methods, we were unable to conclude which method is dominant. Therefore, further studies are required to compare CFS results of the two different methods with analysis of floating/sinking pulse by professional TCM and KM doctors, and by measuring hold-down pressure when a TCM/KM doctor palpates with a different level of hold-down pressure.
We would like to thank all participants who involve in this study and acknowledge the financial support of the Ministry of Knowledge Economy, Republic of Korea (Grant No. 10028436).
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