EFFECT OF ACUPUNCTURE IN HEART AURICULAR POINT IN TWO INDEXES OF DIGITAL VOLUME PULSE IN HEALTHY SUBJECTS

Objective: The aim of the study was to determine the changes in two indices derived from the digital volume pulse (DVP) elicited by acupuncture in auricular heart acupoint in healthy subjects. 
Methods: Eighteen healthy subjects aged 26.22±2.98 years (mean±standard deviation) were assigned to receive auricular acupuncture in auricular heart acupoint in the right ear. The DVP was recorded by photoplethysmography. RIDVP was determined by the relative amplitudes of systolic and diastolic components of the DVP and SIDVP, by the relative timing of these components. Auricular acupoint heart was stimulated by manual acupuncture. The RIDVP and SIDVP indices were calculated for basal and post-acupuncture conditions. 
Results: Both RIDVP (p=0.0375) and SIDVP (p=0.0063) were significantly decreased by acupuncture of the right auricular acupoint heart when comparing the pre- and post-acupuncture values. 
Conclusions: These results indicate that manual acupuncture of auricular acupoint heart produces acute effects on vascular physiology. RIDVP and SIDVP indices can be used to assess and demonstrate a vasodilatory activity of auricular acupoint heart.


INTRODUCTION
Photoplethysmography provides a photoplethysmogram (PPG) or digital volume pulse (DVP), and it is based on the estimation of light transmission through the finger pulp. Changes in the contour of the DVP associated with aging, vascular disease, and drugs have been described [1,2]. The shape of the DVP is influenced mainly by the systemic vasculature [3]. Two cardiovascular indices using the DVP, an index of pressure wave reflection (RI DVP ) and an index of large artery stiffness (SI DVP ), were derived [4,5]. Despite the well-recognized effects of auricular acupoints as coadjuvants in the treatment of some cardiovascular disorders, the mechanisms underlying their therapeutic effects remain poorly understood. Nogier described a pulse change when specific auricular acupoints were touched [6]. The detection of this socalled vascular autonomic signal enables the practitioner to precisely determine the location of an acupoint, whether there is a pathology in the region of the body that relates to specific points [7]. Ikezono et al. [8] have demonstrated the existence of an active auricular acupoint and that application of an electric stimulus at this point modifies the radial artery pulse wave. The aim is to examine the acute vascular effects of heart auricular acupuncture point evaluated through RI DVP and SI DVP .

Study design and setting
This study is designed as an experimental non-randomized singlecenter trial to check if manual acupuncture in heart auricular acupoint modifies de RI DVP and SI DVP in healthy subjects.

Population
The study population consisted of 18 healthy male or female (7/9) subjects recruited by advertisement from our medical school with a global mean age of 26.22±2.98 (23-32) years.

Ethical aspects
The Research Ethics Committee of the Biological and Health Sciences Division, Iztapalapa Campus, Universidad Autónoma Metropolitana, approved the study, and participants granted informed and written consent.

Acquisition of PPG
A transducer for photoplethysmograph (MP100, BIOPAC Systems, Goleta, CA, USA) that transmitted infrared light at 860±90 nm was placed on the right index finger to obtain the DVP. PPG was recorded through a 12-bit analog-to-digital converter, with a sampling frequency of 200 points/s, and the signal was analyzed with the platform AcqKnowledge v. 3.9 software (BIOPAC Systems, Goleta, CA, USA).

Signal processing and analysis
The DVP indices of each subject corresponding to basal (60-90 s) and post-acupuncture (300-330 s) periods were calculated using the average of five waves. The first derivative of the DVP was drawn through the Plot graphics analyzer v. 2.6.15 (apps.micw.org, M. Wesemann, Berlin, Germany) to specify inflection points (Fig. 1).
The height of the diastolic peak expressed as a percentage of the amplitude of the systolic peak let calculation of RI DVP . If no diastolic peak was present, an inflection point was used to extrapolate it. Therefore, diastolic peak was defined as the point at which the first derivative of the waveform was closest to zero, Fig. 1 [9]. SI DVP was calculated using subject height (h) divided for ΔT DVP , which is the time elapsed between the systolic peak and the diastolic peak/inflection point in the waveform [9], Fig. 2.

Serrano-Morales et al.
stainless steel needles (Hwato, Suzhou, China). The acupuncture needle was manually inserted into the auricular acupoint heart in the right auricle (Fig. 3) without additional electrical or laser stimulation, gently stimulated for 5 s, and needle remained in situ 1 min. Concerning the primary objective of the study, the clinical investigator calculating the DVP indices was blinded respect to if the data belonged to the basal of post-acupuncture period.

Study protocol
All subjects abstained from caffeine or smoking in the previous 12 h. Measurements were made with subjects in the supine position after a fast night to reach standard conditions and after at least 20 min rest in a quiet and temperature-controlled clinical room (24±1°C). In each subject, a 6 min long registration DVP was obtained. The acupuncture needle was inserted into the heart auricular acupoint in the right ear at 2 mm deep. The needle was maintained in place for 1 min (2-3 min) and removed after that contralateral to the side of the DVP recording.

Statistical analysis
Data are presented as means±standard deviation. Normally distributed continuous variables were compared using Student's t-test. p<0.05 was considered statistically significant. All testing were two sided. Statistical analyses were carried out using the SPSS software v. 21.0 (SPSS Inc., Chicago, IL, USA).  Table 1.
The effects of vasoactive drugs and nitrates in systemic hemodynamics are assessed through reflection and stiffness indices derived from DVP, such as changes in heart rate and blood pressure [10][11][12]. RI DVP and SI DVP have been used to study the mechanisms of acupoints, Rivas-Vilchis et al. [13] showed that manual stimulation of Shenmen and Knee auricular acupoints elicited acute changes in RI DVP and SI DVP .
DVP has a complex but predictable relationship to the aortic pulse pressure. DVP has a direct component arising from pressure waves propagating from the heart to the finger, as well as additional component derived from pressure waves generated in the peripheral arteries, mainly in the lower body, which reflects backward in the arterial system [4]. Therefore, the RI DVP index provides a measure of the amount of wave reflection in the systemic circulation [12]. RI DVP index is also related to vasodilator stimuli [14,15]. Otherwise, SI DVP is both associated with the time elapsed between the systolic and diastolic components of DVP and the pulse wave velocity in large arteries and, therefore, reflects large artery stiffness [4,5,9]. Hence, the present finding of a decrease in both RI DVP and SI DVP probably indicated that acupuncture in heart point evoked a vasoactive effect likely related to a vagal response.

CONCLUSIONS
Our results clearly showed the potential of auricular heart acupoint to modify RI DVP and SI DVP . These indices are valuable in assessing vascular tone and arterial stiffness. The present study has a potential limitation, that is, the unique analysis of the effect of acupuncture on the right ear. Therefore, contour analysis of the DVP can be used to assess the