Effect of auricular acupoint acupressure stimulation on the pulmonary function of healthy adults: A randomized, crossover, double-blinded study

doi:10.21203/rs.3.rs-1760412/v1

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Effect of auricular acupoint acupressure stimulation on the pulmonary function of healthy adults: A randomized, crossover, double-blinded study

https://doi.org/10.21203/rs.3.rs-1760412/v1

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Background

The study aimed to investigate the effect of auricular acupoint acupressure stimulation of the auricular vagus nerve on pulmonary function.

Methods

Fifteen healthy subjects were enrolled in this randomized, crossover, double-blinded study. All subjects received real and sham stimulation conditions at intervals of more than 24 h. On the real stimulation condition, auricular acupoint sticking with Vaccaria seeds and continuous stimulation of acupressure was delivered on the auricular vagus nerve area., but no Vaccaria seeds and no acupressure were used for the sham stimulation condition. Tidal volume (VT), vital capacity (VC), maximal inspiratory pressure (MIP), and diaphragmatic excursions (DE) of normal and forced breathing were assessed before and after each stimulation condition.

Results

Before stimulation, there were no significantly differences of VT, VC, MIP, and DE of normal breathing and forced breathing between real and sham conditions. After stimulation, the change rates of VT ( P = 0.005), VC(P = 0.021), MIP (P = 0.023), DE of normal breathing (P = 0.022) and DE of forced breathing (P < 0.001) was higher on the real condition.

Conclusions

Auricular acupoint acupressure stimulation of the auricular vagus nerve can significantly improve pulmonary function, and its use should be promoted in clinical settings.

Trial registration

This study has been registered in the Chinese Clinical Trial Registry (registration number: ChiCTR2200058836, Date of registration: 17/04/2022).

Auricular acupoint

Auricular vagus nerve

Diaphragm

Ultrasound

Pulmonary function

Breathing is the basic physiological activity to maintain human life. Normal breathing depends on the integrity and coordination of respiratory nerves, muscles, and lung. If these related tissues and organs become faulty or damaged, respiratory dysfunction could result. For example, chronic obstructive pulmonary disease (COPD) or brain injury could affect neurons that guide breathing function. Exercise of respiratory muscles is important on to respiratory rehabilitation.

The diaphragm is the main respiratory muscle, and its contraction accounts for 75–80% of inspiratory power in the resting state [1]. The disuse atrophy rate of the diaphragm is eight times higher than that of other skeletal muscles [2]. Hence, patients with severe COPD or neurological respiratory dysfunction have decreased exercise endurance, difficulty in discharging sputum, and dyspnea due to diaphragmatic dysfunction, resulting in an increased incidence of pulmonary infections. Therefore, the improvement of diaphragmatic function is conducive to the overall recovery of the disease and can accelerate the rehabilitation process.

Currently, diaphragmatic treatment mainly comprises techniques such as respiratory exercise, diaphragmatic pacemaker stimulation, and magnetic stimulation. However, respiratory exercise requires the patient's active cooperation, and its effectiveness is affected by the patient's compliance. Diaphragmatic pacemakers are divided into internal and external stimulation; the internal diaphragmatic pacemakers are invasive, while the external diaphragmatic pacemakers may cause diaphragmatic fatigue and poor patient tolerance [3]. Furthermore, there are few studies on improving diaphragmatic function by magnetic stimulation, which has not been widely used in clinical practice. Therefore, appropriate diaphragmatic treatment, which is economical, simple, easy to operate, and suitable for extensive promotion at the ground level, is urgently needed in clinical settings.

In recent years, pulmonary function regulation by the vagus nerve has attracted extensive attention because of its ability to regulate airway tension, blood supply, mucus secretion, and respiratory patterns [4]. The vagus nerve is a mixed nerve in which the peripheral branches of the cervical ganglion innervate parts of the sensory functions of the external auditory canal, tympanic membrane, and ear auricle. At the same time, the external ear nail area represents the internal organs of the auricular acupoint in traditional Chinese medicine, which is dominated by the auricular branch of the vagus nerve [5]. Currently, there are numerous studies on stimulating the auricular vagus nerve to interfere with the function of related muscles and organs [6]. However, limited studies related to the respiratory system are available. A study by Huan and Silberstein [7] has shown that the ear nail area is the only area with vagus nerve distribution on the body surface of mammals. Therefore, stimulation of the ear nail area can activate the auricular vagus nerve, and the incidence of vagus reflex is affected by auricular acupoint acupressure [8]. Hence, we hypothesize that pulmonary function can be improved through auricular acupoint acupressure stimulation.

In this study, we used auricular acupoint sticking to stimulate the auricular vagus nerve and then assessed pulmonary function changes. We aimed to investigate the effect of auricular acupoint acupressure stimulation of the auricular vagus nerve on pulmonary function.

Subjects

Fifteen healthy people were included in this study, comprising three men and 12 women, aged 25.8 ± 7.4 years (Table 1). Inclusion criteria were as follows: 1) healthy people aged 20–55 years; 2) availability of signed informed consent. Subjects with a history of lung diseases (e.g., pneumoconiosis, tuberculosis, COPD) were excluded from the study. This study was approved by the Ethics Committee of Yuedong Hospital of the Third Affiliated Hospital of Sun Yat-sen University (project number: project 9 in 2021) and was performed in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans. It has been registered in the Chinese Clinical Trial Registry (registration number: ChiCTR2200058836, Date of registration: 17/04/2022).

Table 1

Demographic information and stimulation sequence of fifteen subjects
Grouping		Age	Gender	Stimulation methods
Grouping		Age	Gender	First stimulus	Second stimulus
Group 1	1	26	W	T	F
	2	25	W	T	F
	3	20	M	T	F
	4	21	W	T	F
	5	23	W	T	F
	6	26	M	T	F
	7	45	W	T	F
	8	25	W	T	F
Group 2	1	24	W	F	T
	2	23	W	F	T
	3	20	M	F	T
	4	22	W	F	T
	5	21	W	F	T
	6	22	W	F	T
	7	43	W	F	T
Abbreviations: M, men; W, women; T, real stimulation; F, sham stimulation.

Experimental design

This study used a randomized, crossover, double-blinded controlled design. All subjects received real and sham stimulation conditions of the bilateral auricular vagus nerve and were randomly divided into groups 1 and 2. Real stimulation was performed before sham stimulation in group 1, while the reverse was done in group 2. The random order was generated using an Excel spreadsheet and saved by a person who was not involved in the intervention evaluation. All stimulations were performed by the same operator. The stimulation interval was > 24 h. Evaluation of pulmonary function was performed before and after stimulation by an operator who was blinded to the stimulation conditions. (Fig. 1)

Stimulation method

The subjects were placed in the supine position. The bilateral auricles were disinfected with 75% alcohol, and the area of the auricular vagus nerve, which is the cavity of the auricular concha and cymba of the auricular concha around the crus of the helix, was stimulated. The stimulation area is shown in Fig. 1. In the real stimulation condition, we used the auricular acupoint sticking with Vaccaria seeds in the area of the auricular vagus nerve for 20 min and then acupressed each sticking with an equal force thrice at intervals of 5 min. For the sham stimulation condition, we only used the ear acupuncture points with the Vaccaria seeds removed to adhere to the acupuncture points for 20 minutes without pressing.

Evaluation method

Regarding the pulmonary function test, subjects were seated, and a portable pulmonary function assessment instrument (Model X1, Sec (Xiamen) Medical Equipment Co., Ltd., China) was used to measure vital capacity (VC), tidal volume (VT), and maximal inspiratory pressure (MIP). We repeated the measurements three times and obtained the mean value. Nasal clips were used to prevent air nasal leakage.

Regarding diaphragmatic ultrasound, diaphragmatic excursions (DE) of subjects was measured via ultrasonography (Model EDGE03X48L, SonoSite, USA) with the subject in the supine position. The following steps were undertaken: 1) we used a convex array probe with a frequency of 3.5–5.0 MHz to scan the overall diaphragm and to evaluate the image quality; 2) the probe was placed in front of the subject’s right axillary line and pointed to the top of the diaphragm with the liver as the sound window when the angle was more than 70°; 3) the diaphragm was measured in 2D mode, and then switched to M mode to measure the displacement distance of subjects during normal and forced breathing in three breathing cycles. We then obtained the mean value of the displacement distance (Fig. 2).

Statistical method

SPSS software version 19.0 (IBM Corp., Armonk, NY, USA) was used for all statistical data analysis. The change rate was calculated as follows: change rate = (value after stimulation - value before stimulation)/value before stimulation. The Shapiro-Wilk method was used to test whether the data followed normal distribution before comparison. All measured data of VC, VT, MIP, and DE, as well as the change rate following the normal distribution in real and sham stimulation, was assessed. It was expressed as [mean ± standard deviation (SD)]. Paired t-test was used to compare the difference between the two conditions, and P < 0.05 was considered statistically significant.

Comparison of VT, VC, and MIP before stimulation in real and sham stimulation

Before stimulation, no significantly differences were found on VT (t = 0.717, P = 0.485), VC (t = 0.639 P = 0.533), and MIP (t = 1.524, P = 0.150) between real and sham conditions.

The change rates of VT on the real condition (61.0 ± 49.4%) was significantly higher than that of the sham condition (12.2 ± 35.6% t = 3.373, P = 0.005, Fig. 3a). The change rates of VC on the real condition (9.5 ± 14.3%) was significantly higher than that of the sham condition (-2.8 ± 9.5%, t = 2.611, P = 0.021, Fig. 3b). The change rates of MIP on the real condition (21.3 ± 26.4%) was significantly higher than that of the sham condition (2.6 ± 14.5%, t = 2.563, P = 0.023, Fig. 3c).

Comparison of the change rates of DE between real and sham stimulations

Before stimulation, no significantly differences were found on DE of normal breathing (t = 0.589 P = 0.565) and forced breathing (t = 0.423, P = 0.679) between real and sham conditions.

DE of normal breathing (16.1 ± 15.1%) in the real stimulation condition was higher than that of the sham condition (1.7 ± 14.9%, t = 2.585, P = 0.022, Fig. 4a). DE of forced breathing (19.9 ± 11.3%) in the real stimulation condition was higher than that of the sham condition (-3.4 ± 16.1%, t = 4.388, P < 0.001, Fig. 4b).

The diaphragm is an important respiratory muscle, and its functional improvement improves respiratory performance. In this study, we used the Chinese traditional therapy of auricular acupoint sticking to stimulate the auricular vagus nerve in healthy people and measured VT, VC, MIP, and DE of normal and forced breathing using pulmonary function tests and ultrasonography.

In the real stimulation, the DE of normal and forced breathing increased. We considered the ear nail area as a receptor of the auricular branch of the vagus nerve, which innervates sensory function, receives stimulation of auricular acupoint acupressure, and induces diaphragmatic contraction through the central nervous system. Dawson et al. [9] reported that vagus nerve stimulation could significantly improve upper limb function after stroke because it induces molecular and neuronal remodeling. This is consistent with the hypothesis that the vagus nerve afferent pathway induces skeletal muscle contraction, as observed in this study. In addition, some studies [10–12] have proven that the vagus nerve afferent fibers can project to other cortical areas through medullary reticular formation. Although the medulla oblongata and cerebral cortex are the control centers of respiratory function, the vagus nerve can regulate respiratory rhythm and depth. Rong et al. [13] verified that the auricular vagus nerve is a peripheral pathway that can reach the central nervous system using a nerve tracer technique.

We observed that VT, VC, and MIP significantly improved after real stimulation in this study, and that the diaphragm was the main agonist during inspiration. A recent study [14] reported that an increase in DE improves lung volume, which is consistent with the findings of this study. MIP and DE of forced breathing were the maximum inspiratory muscle strength indicators. Hence, with the excitatory activity of forced breathing, we believed that the auricular vagus nerve was a sensory input pathway, which further enhanced the transmission of central excitability after stimulation; this enabled the forced breathing of the subject to be more active.

There were significant differences in the change rate between the real and sham stimulations in this study. Some studies [15, 16] have pointed out that the pulmonary function test is related to the degree of subjects' cooperation. Therefore, we adopted the statistical analysis of change rate and analyzed changes above the baseline level to avoid the influence of individual subjectivity and to ignore individual differences. Although there were slight differences in the change rate of the sham stimulation before and after stimulation, there was no significant difference in the statistical results of change rate between both stimulation conditions. This observation was consistent with those reported by Boussuges et al. [17], who stated that there would be slight differences in pulmonary function test indicators and DE in healthy people at different times.

Pulmonary function tests and bedside diaphragmatic ultrasound, which are non-invasive, non-radiative tests, were used in this study [18, 19]. The measurement of DE by ultrasound has good repeatability and provides relatively stable data [19]. Moreover, auricular acupoint sticking is easy to promote at the grassroots level because of its universality and because it is a typical representation of the modernization of traditional Chinese medicine as a process that integrates the basic theory of traditional Chinese medicine and Western medicine. In addition, the cross-sequential blinded design of this study can eliminate the differential influence of various stimuli on different cases.

This study has some limitations. First, we only investigated the effect of auricular acupoint acupressure on healthy people. Therefore, further studies should be conducted on patients with pulmonary dysfunction. Second, this study only analyzed the effect of a single stimulation; however, the cumulative effect was not clear. Third, the effect of central conduction requires further verification by electrophysiological examination.

In conclusion, auricular acupoint acupressure stimulation of the auricular vagus nerve significantly improved pulmonary function, thereby providing preliminary evidence for the clinical promotion of this technique.

DE, diaphragmatic excursions

MIP, maximal inspiratory pressure

VC, vital capacity

VT, tidal volume

Ethics Approval and Consent to Participate

This study was approved by the Ethics Committee of Yuedong Hospital of the Third Affiliated Hospital of Sun Yat-sen University (project number: project 9 in 2021) and was performed in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans. The participants provided their written informed consent to participate in this study. It has been registered in the Chinese Clinical Trial Registry (registration number: ChiCTR2200058836, April 17,2022).

Consent for Publication

Not application.

Acknowledgments

We would like to thank all the participants.

Conflict of Interest Statement

The authors have no conflicts of interest to declare.

Funding Sources

This work was supported by the Medical Scientific Research Foundation of Guangdong Province (A2022240).

Data availability statement

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors' Contributions

All authors contributed to the study conception and design. Conceptualization: [Zhi-Ming Tang], [Man-Yun Bu]; Methodology: [Man-Yun Bu]. Assessment: [Shi-Liang Ke],[Yi Yu] ;Therapy in charge [Ying-Chan Quan],[Yi-Ting Li]. Formal analysis and investigation: [Hong Li], [Zhi-Ming Tang]; Writing - original draft preparation: [Man-Yun Bu]; Writing - review and editing: [Zhi-Ming Tang]; Funding acquisition: [Zhi-Ming Tang]; Supervision: [Zhi-Ming Tang]

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No competing interests reported.

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Version 1

posted

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Effect of auricular acupoint acupressure stimulation on the pulmonary function of healthy adults: A randomized, crossover, double-blinded study

Status:

Version 1

Abstract

Figures

Background

Methods

Subjects

Experimental design

Stimulation method

Evaluation method

Results

Comparison of VT, VC, and MIP before stimulation in real and sham stimulation

Comparison of the change rates of DE between real and sham stimulations

Discussion

Conclusions

Abbreviations

Declarations

References

Additional Declarations

Status:

Version 1