Resonance phenomenon during wrist pulse-taking: A stochastic simulation, model-based study of the ‘pressing with one finger’ technique

Abstract

This study analyzed the ‘pressing with one finger’ technique for wrist pulse-taking and explored the identification of internal organs according to the resonance theory in the circulatory system. A five-section discretized-transmission-line model of the distal upper limb was proposed considering the radial artery, the distal positions chi–guan–cun, and the hand vasculature. The transfer function of the model was parameterized in terms of its resonance frequency and respective amplification factor. Rheological and geometrical parameters of the modeled arterial system were used to simulate a sample of 1000 healthy volunteers subjected to wrist pulse-taking examination. The ‘pressing with one finger’ technique was simulated individually at each position by varying the vertical (minor) diameter of the elliptical cross-sectional radial artery from 0% to 99%. The pulse waveform harmonics were calculated in the frequency domain and had their internal organs assigned according to the resonance theory. Compressions in range 0–70% resulted in resonance frequencies around 3–6 Hz (related to the spleen) and amplification factors > 1. Compression in range 70–85% shifted up the resonance frequency of the majority of cases up to 6–8 Hz (related to the heart) and a minority of cases was shifted down to 0–2 Hz. A large decrease in the amplification factor occurred with module values <1. Compressions in range 85–99% increased the resonance frequency to 7–10 Hz (related to the gallbladder) with an even decent amplification factor. These effects were more pronounced in the proximal to distal sequence of positions. Therefore, pressing with one finger amplified specific pulse wave harmonics as a function of depth in all three positions, but it did not explore all harmonics described by the resonance theory.

Introduction

The use of traditional medicine among health providers and patients increased throughout the globe after the Alma-Ata Declaration [1]. It was estimated that between 70% and 95% of the population of developing countries use traditional medicine for management of health for disease prevention, treatment or rehabilitation [2]. Chinese medicine is among other traditional medical systems practiced by physicians, physical therapists, and other healthcare professionals as a coadjutant intervention or as the unique therapeutic intervention [3]. The scientific interest in Chinese medicine theory and physiologic mechanisms can be inferred from the large amount of experimental and clinical research conducted worldwide in the last decades. Despite this fact, the semiotics related to Chinese medicine diagnostic process remains poorly investigated.

The arterial pulse is the most fundamental sign in clinical medicine and it is probably the most antique one [4]. Chinese sphygmologists developed wrist pulse-taking methods long before the beginning of Hippocratic era of cardiology (460-c.375 BCE) [5]. Since no equipment was developed for this purpose, examiners developed several pulse-taking methods. In its early development, pulse-taking was performed in several superficial arteries near or underlying acupoints at the head and neck, the upper and lower limbs [6], [7], [8]. By the 2nd century, the wrist pulse-taking method at the radial artery was regarded the same importance as at the carotid and dorsalis pedis arteries with few diagnostic exceptions in which carotid and radial artery pulses should be compared [9]. According to the wrist pulse-taking method, three fingers are used for pattern differentiation [6], [7], [8]: a central position (guan) located above the styloid process of the radius, and a more proximal (chi) and distal position (cun) to guan. Each position is palpated at three subjective depths (deep, middle and superficial) according to the pressure applied by the examiner's fingers. The combination of depths and positions yields the concept of nine indicators. Using the ‘pressing with one finger’ technique [10], ancient Chinese medicine practitioners claimed to assess the health status of specific internal organs (representative correspondences are provided in Table 1) [6], [7], [8]. The relationship between the nine indicators and internal organs has being a subject of discrepancies among Chinese medicine practitioners [11], and of major controversy between them and scientific researchers.

Research using computational methods suggested that gathering information about the internal organs at a peripheral artery is plausible because of both wave reflection and resonance phenomenon. The arterial system favors anterograde pulse waveform transmission and wave reflections that originated at the trunk propagate to the upper limb arteries with minimal changes in amplitude [12]. Using both electric–hydraulic analog and hydraulic physical models, it was found that both position and physical properties of the internal organs are important factors in pulse waveform propagation [13]. The location of internal organs as side branches perpendicular to the aorta enhances the intensity of high-frequency harmonics of the pulse waveform. The circulatory system was compared to a musical instrument, where each internal organ has its own harmonic due to their unique shape, size, structure, and hemodynamic condition [14]. The heart provided the external force at the heart rate (HR) as a fundamental frequency and its harmonics are tuned to optimize cardiac output for a given pulse pressure and therefore highest flow transport. The steady-state component of the pressure waveform (i.e. mean arterial pressure) was not considered in this theory. Experimental data suggested that the heart, liver, kidney, spleen, lung, stomach, gallbladder, and urinary bladder corresponded to the 1st–8th harmonics of the pulse waveform, respectively [15], [16]. This bunch of evidence was named the ‘resonance theory’ in the circulatory system [13] or the ‘harmonic analysis of arterial pressure pulse waves’ [16]. However, it is not known if the pressing with one finger technique is consistent to the derived harmonics in the respective combination of depths and positions, for any ancient systematic correspondence.

Only one previous study [17] focused on system identification with applications to the Chinese medicine pulse-taking method. In the referred study, four pulse images at the radial artery (normal, smooth, wiry, and thready) obtained from 114 cases were analyzed using power cepstrum parameters. Accuracies in range 62.5–88.5% were obtained for classification of those four pulse images based on cepstrum formants. Those authors also stated that those four pulse images exhibited distinct frequency harmonics. In agreement with the resonance theory, those authors considered the study of transfer function (TF) of the arterial system as an important method for analyzing the pulse waveform transmission characteristics. However, two major limitations make difficult to link the observed results with the traditional systematic correspondences. Pulse waveform signals were recorded while holding the microphone with “proper force”, and therefore the depth for data collection was not provided for comparison to the TL5 model. Also, a “specified position” was used for data collection but was not properly described as the chi, guan or cun. Therefore, a model that allows the evaluation of a TF at each position and any depth would be valuable to study such a problem.

To perform scientific research on Chinese medicine, an interesting approach is to seek for the scientific evidence that corroborate or not data reported by Chinese medicine practitioners – ancient and contemporary ones included. Therefore, the aim of this study is to analyze the pressing with one finger technique for wrist pulse-taking and to explore the identification of internal organs based on the resonance theory using a five-section discretized-transmission-line model of the forearm-hand vascular system. It will be shown that the ‘pressing with one finger’ technique can indeed amplify specific pulse wave harmonics as a function of depth in all three positions, but it does not explore all harmonics – and consequently not all internal organs – described by the resonance theory.