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   Abstract
  Introduction
  Methods
  Results
  Discussion
  Conclusion
  Acknowledgment
   References
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  Table of Contents    
ARTICLE  
Year : 2014  |  Volume : 16  |  Issue : 68  |  Page : 57-62
Auditory stimulation with music influences the geometric indices of heart rate variability in response to the postural change maneuver

1 Centro de Estudos do Sistema Nervoso Autônomo, Departamento de Fonoaudiologia, Faculdade de Filosofia e Ciências, UNESP, Marília, Brasil
2 Departamento de Medicina, Disciplina de Cardiologia, UNIFESP, São Paulo, Brasil
3 Departamento de Morfologia e Fisiologia, Faculdade de Medicina do ABC, Santo André, SP, Brasil

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Date of Web Publication26-Feb-2014
 
  Abstract 

It is poor in the literature the behavior of the geometric indices of heart rate variability (HRV) during the musical auditory stimulation. The objective is to investigate the acute effects of classic musical auditory stimulation on the geometric indexes of HRV in women in response to the postural change maneuver (PCM). We evaluated 11 healthy women between 18 and 25 years old. We analyzed the following indices: Triangular index, Triangular interpolation of RR intervals and Poincarι plot (standard deviation of the instantaneous variability of the beat-to beat heart rate [SD1], standard deviation of long-term continuous RR interval variability and Ratio between the short - and long-term variations of RR intervals [SD1/SD2] ratio). HRV was recorded at seated rest for 10 min. The women quickly stood up from a seated position in up to 3 s and remained standing still for 15 min. HRV was recorded at the following periods: Rest, 0-5 min, 5-10 min and 10-15 min during standing. In the second protocol, the subject was exposed to auditory musical stimulation (Pachelbel-Canon in D) for 10 min at seated position before standing position. Shapiro-Wilk to verify normality of data and ANOVA for repeated measures followed by the Bonferroni test for parametric variables and Friedman's followed by the Dunn's posttest for non-parametric distributions. In the first protocol, all indices were reduced at 10-15 min after the volunteers stood up. In the protocol musical auditory stimulation, the SD1 index was reduced at 5-10 min after the volunteers stood up compared with the music period. The SD1/SD2 ratio was decreased at control and music period compared with 5-10 min after the volunteers stood up. Musical auditory stimulation attenuates the cardiac autonomic responses to the PCM.

Keywords: Auditory stimulation, autonomic nervous system, cardiovascular system, music

How to cite this article:
de Castro BC, Guida HL, Roque AL, de Abreu LC, Ferreira C, Marcomini RS, Monteiro CB, Adami F, Ribeiro VF, Fonseca FL, Santos VN, Valenti VE. Auditory stimulation with music influences the geometric indices of heart rate variability in response to the postural change maneuver. Noise Health 2014;16:57-62

How to cite this URL:
de Castro BC, Guida HL, Roque AL, de Abreu LC, Ferreira C, Marcomini RS, Monteiro CB, Adami F, Ribeiro VF, Fonseca FL, Santos VN, Valenti VE. Auditory stimulation with music influences the geometric indices of heart rate variability in response to the postural change maneuver. Noise Health [serial online] 2014 [cited 2020 May 27];16:57-62. Available from: http://www.noiseandhealth.org/text.asp?2014/16/68/57/127857

  Introduction Top


Auditory stimulation with music has been investigated as a therapy to prevent cardiovascular disorders and/or improve cardiac function. The relationship between the auditory and cardiovascular systems is based on common areas in the brain that regulate the both systems. [1],[2] A previous study investigated the responses of blood pressure, heart rate (HR), respiratory rate and flow of the middle cerebral artery during exposure to music with vocals, orchestra and progressive crescendos, the authors observed reduced sympathetic activity of the health subjects. [3]

The autonomic nervous system (ANS) has two branches that regulate the HR. The sympathetic nervous system activity increase HR and blood pressure, i.e., this system is activated during exercise. The parasympathetic nervous system is activated during relaxant activities, i.e. sleeping. [4] In this context, the heart rate variability (HRV) has been used to evaluate the cardiac autonomic regulation because it is a non-invasive and low cost that allows the analysis of the responses of cardiac autonomic modulation. This tool describes the oscillations of the intervals between consecutive cardiac ventricular depolarization and is directly related to the influences of the ANS on the sinusal node. [5]

Autonomic tests are applied to investigate the behavior of the ANS in response to certain stimulation. Among these tests, the postural change maneuver (PCM) was well-described by Ribeiro et al. [6] During this test, there is increased transfer of blood from the chest to the lower limbs due to the activation of these muscles, inducing, after a few moments, tachycardia, which is caused mainly by decreased of vagal activity. [6]

Although it has been reported the beneficial effects of musical auditory stimulation for a long period of time, [7] the short-term effects of classical musical auditory stimulation on cardiac autonomic regulation is not a consensus. [1],[2],[3],[8],[9] We hypothesized that auditory stimulation with classical baroque music influences the cardiac autonomic responses to the PCM. Therefore, we aimed to evaluate the acute effects of classical baroque music on the cardiac autonomic responses induced by the PCM in healthy women.


  Methods Top


Study population

We analyzed 11 female healthy subjects aged range between 18 and 25 years old, selected from our institution. All volunteers were informed about the procedures and objectives of the study and after agreeing, have signed a term of informed consent. All the study procedures were approved by the Ethics Committee in Research of the Faculty of Sciences of the UNESP-Marilia (Case No. CEP-2011-382) and followed the resolution 196/96 National Health 10/10/1996. No volunteer presented the following conditions: Body mass index (BMI) >35 kg/m 2 ; systolic blood pressure > 140 mmHg or diastolic blood pressure > 90 mmHg (at rest); cardiac arrhythmias reported (atrial flutter or fibrillation, multiple ventricular or atrial ectopy, second or third degree atrioventricular block), smoking, medication use, left ventricular dysfunction, neurological or respiratory disorders reported and serious postural deviation in the chest such as severe scoliosis, kyphosis or hyperlordosis that could influence the respiratory pattern. Cardiopulmonary disorders, neurological and other impairments that prevent the subject known to perform procedures. No individual presented previous experience with music instrument and classic ballet music, as well as volunteers, which like classical music styles since it affects cardiovascular responses.

Initial evaluation

Before the experimental procedure, volunteers were identified by collecting the following information: Age, gender, weight, height and BMI. Anthropometric measurements were obtained according to Lohman et al. [10] Weight was determined by using a digital scale (W 200/5, Welmy, Brazil) with a precision of 0.1 kg. Height was determined by using a stadiometer (ES 2020, Sanny, Brazil) with a precision of 0.1 cm and 2.20 m of extension. BMI was calculated using the following formula: Weight (kg)/height (m) 2 . Systolic arterial pressure (SAP) and diastolic arterial pressure (DAP) were collected with sphygmomanometer and stethoscope.

Measurement of the auditory stimulation

The measurements of the equivalent sound levels were conducted in a soundproof room, using a SV 102 audiodosimeter (Svantek, Poland). It was programmed the measurement in the "A" weighting circuit; slow response.

The measurement was made during a session, lasting a total of 4 min and 50 s for the classical baroque music and 5 min and 15 s for the excitatory heavy metal music. We used the insert type microphone (Microphone in real ear), which was placed inside the auditory canal of the subject, just below the microphone, connected to the personal stereo.

Before each measurement, the microphones were calibrated with the calibrator acoustic Cirrus Research: 514 model (CR plc.). The volunteers were exposed to an equivalent sound level between 70 and 80 dB(A). [9]

HRV analysis

The R-R intervals recorded by the portable HR monitor (with a sampling rate of 1000 Hz) were downloaded to the polar precision performance program (v. 3.0, Polar Electro, Finland). The software enabled the visualization of HR and the extraction of a cardiac period (R-R interval) file in "txt" format. Following digital filtering complemented with manual filtering for the elimination of premature ectopic beats and artifacts, at least 256 R-R intervals were used for the data analysis. Only series with more than 95% sinus rhythm was included in the study. HRV was analyzed at four moments: Seated rest with spontaneous breathing, 10 min of music exposure (in the protocol with music exposure), 0-5 min, 5-10 min and 10-15 min after the subjects stood up. We evaluated the linear (triangular interpolation of RR interval [TINN] histogram and triangular index [RRTri]) and non-linear (Standard deviation of the instantaneous variability of the beat-to beat heart rate [SD1], Standard deviation of long-term continuous RR interval variability [SD2] and Ratio between the short - and long-term variations of RR intervals [SD1/SD2] ratio) indices of HRV. For calculation of the indices, we used the HRV Analysis software (Kubios HRV v. 1.1 for Windows, Biomedical Signal Analysis Group, Department of Applied Physics, University of Kuopio, Finland). [11]

Geometric indices of HRV

The HRV behavior pattern was recorded beat-by-beat throughout the monitoring process at a sampling rate of 1000 Hz. Only series with more than 256 RR intervals were used to analysis, [12] following digital filtering complemented with manual filtering for the elimination of premature ectopic beats and artifacts. Only series with more than 95% sinus rhythm were included in the study. [13]

HRV analysis was performed by means of geometrical methods: RRtri, TINN and Poincaré plot (SD1, SD2 and SD1/SD2 ratio). [12]

The RRtri was calculated from the construction of a density histogram of RR intervals, which contains the horizontal axis of all possible values of RR intervals measured on a discrete scale with 78,125 ms boxes (1/128 s) and on the vertical axis, the frequency with which each occurred. The union of points of the histogram columns forms a shape like a triangle. The RRtri was obtained by dividing the total number of RR intervals used to construct the histogram by their modal frequency (RR interval value that most frequently appeared on RR).The TINN consists of the measure of the base of a triangle. The method of least squares is used to determine the triangle. The RRtri and the TINN express the overall variability of RR intervals.

The Poincaré plot is a map of points in Cartesian coordinates, constructed from the values of RR intervals obtained, where each point is represented on axis x (horizontal/abscissa) by the previous normal RR interval and on axis y (vertical/coordinate), by the following RR interval.

For quantitative analysis of the plot, an ellipse was fitted to the points of the chart, with the center determined by the average RR intervals and the SD1 indexes were calculated to measure the standard deviation of the distances of the points to the diagonal y = x and SD2 measures the standard deviation of the distances of points to the line y = ˗x + RRm, where RRm is the average of RR intervals. The SD1 is an index of instantaneous recording of the variability of beat-to-beat and represents parasympathetic activity, while the index SD2 represents HRV in long-term records and reflects the overall variability. Their ratio (SD1/SD2) shows the ratio between short and long variations of RR intervals. [12]

The qualitative analysis of the plot was made through the analysis of the figures formed by its attractor, which were described by Tulppo et al. [14]

Figure in which an increase in the dispersion of RR intervals is observed with increased intervals, characteristic of a normal plot.

Small figure with beat-to-beat global dispersion without increased dispersion of RR intervals in the long-term. We used the software HRV analysis.

Experimental protocol

Data were collected in our laboratory under controlled temperature (21-25°C) and humidity (50-60%) and volunteers were instructed to avoid consuming alcohol, caffeine and substances that influence the ANS for 24 h before evaluation. Data were collected between 8 a.m. and 12 a.m. All procedures necessary for the data collection were explained to individuals and the subjects were instructed to remain at rest and to not talking during the data collection.

After the initial evaluation, the heart monitor strap was placed on each subject's thorax over the distal third of the sternum. The HR receiver (Polar RS800CX monitor, Polar Electro OY, Kempele, Finland) was placed on the wrist.

In the first protocol, the subject remained 10 min seated at rest with spontaneous breathing. After 10 min, the volunteers quickly stood up from a seated position in up to 3 s according to verbal command and remained standing for 15 min. In the second protocol, the subject remained 10 min seated at rest with spontaneous breathing. Subsequently, the subject was exposed to a classical music auditory stimulation (Pachelbel-Canon in D), for 10 min seated at rest. After the music exposure, the volunteers quickly stood up from a seated position in up to 3 s according to verbal command and remained standing for 15 min. The sequence of the protocols was randomized.

Statistical analysis

Power analysis was applied and indicated a minimal number of 10 subjects. Standard statistical methods were used for the calculation of means and standard deviations. Normal Gaussian distribution of the data was verified by the Shapiro-Wilk goodness-of-fit test (Z > 1.0). For parametric distributions, we applied the ANOVA for repeated measures test followed by the posttest of Bonferroni. For non-parametric distributions, we used the Friedman test followed by the Dunn's test. We compared the HRV indices between the four moments in the first protocol (seated rest vs. 0-5 min after the volunteers stood up vs. 5-10 min after the volunteers stood up vs. 10-15 min after the volunteers stood up) and between the five moments in the second protocol (seated rest vs. 10 min musical auditory stimulation vs. 0-5 min after the volunteers stood up vs. 5-10 min after the volunteers stood up vs. 10-15 min after the volunteers stood up). Differences were considered significant when the probability of a Type I error was < 5% (P < 0.05). We used the Software GraphPad StatMate version 2.00 for Windows, GraphPad Software, San Diego California USA.


  Results Top


Data for baseline SAP and DAP, HR and mean RR interval, age, height, body weight and BMI are presented in [Table 1]. [Table 2] presents data related to the geometric domain indices at seated and after the volunteers stood up. We noted that all indices were reduced between 10 and 15 min after the subjects stood up compared with control (control vs. 10-15 min). The SD1/SD2 ratio was also reduced on the 1 st 5 min after the subjects stood up compared with seated (control vs. 0-5 min) [Table 3] displays results concerning the geometric indices at seated during music exposure and after the subjects stood up with no music exposure. We observed that only the SD1 index and SD1/SD2 ratio were decreased at 5-10 min after the subjects stood up following exposure to musical auditory stimulation compared to control (control vs. 5-10 min).
Table 1: Baseline DAP and SAP, HR, mean RR interval, weight, height and BMI of the volunteers

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Table 2: Mean and standard - deviation for time - domain indices between before and after the postural change maneuver

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Table 3: Mean and standard - deviation for time - domain indices between before and after the postural change maneuver in subjects exposed to auditory musical stimulation

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[Table 3] mean and standard-deviation for time-domain indices between before and after the PCM in subjects exposed to auditory musical stimulation. RRtri; TINNs; SD1; SD2; RR interval variability; SD1/SD2 ratio. *P < 0.05: Versus control.

[Figure 1] and [Figure 2] show an example of Poincaré plot patterns at seated rest [Figure 1]a and [Figure 2]a and at 10-15 min after the subject stood up [Figure 1]b and [Figure 2]b from one volunteer with no previous exposure to music [Figure 1] and from one volunteer previously exposed to musical auditory stimulation [Figure 2].
Figure 1: Visual pattern of Poincaré plot observed in one subject not exposed to music during control rest seated condition (a) and 10-15 min after the subject stood up (b)

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Figure 2: Visual pattern of Poincaré plot observed in one subject exposed to music during control rest seated condition (a) and10-15 min after the subject stood up (b)

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  Discussion Top


In this study, we aimed to investigate the response of the geometric indexes of HRV induced by the PCM in healthy women previously exposed to musical auditory stimulation of Pachelbel. As a main finding, we reported that this auditory stimulation attenuated the global cardiac autonomic responses induced by PCM. During the protocol without music, there was a decrease in all geometric indexes of HRV during the period from 10 to 15 min after the subjects stood up compared with control seated rest. In contrast, in the protocol with previous exposure to music, only SD1 and SD1/SD2 ratio reduced at 5-10 min after the subject stood up compared to the control condition.

According to our findings, previous exposure to classical baroque musical auditory stimulation attenuates the responses of the global HRV induced by an autonomic test. An elegant work performed by Goyal et al. [15] support our study, the authors examined the influence of stressful noise on tests of autonomic arousal. They divided 200 subjects into two distinct groups, a group working on metallurgical enterprises with excessive noise and the other group in normal working conditions, which went through several tests of autonomic arousal. The noise applied to individuals in the test group was approximately 90 dB for more than 8 h a day over a period of 6 months. The authors found that exposure to stressful noise intensified the responses of autonomic stimulation test, a significant increase was observed in sympathetic activity in individuals exposed to this type of noise compared to the control group, indicating thereby increased morbidity and mortality in these people. Based on our results and on the study mentioned above, we believe that the type of auditory stimulation is important in determining the response of the organism.

We observed that the global geometric indexes of HRV, i.e., SD2, RRtri and TINN were influenced by classical baroque musical auditory stimulation in response to the PCM. Those indices correspond to the global variability of the HR. The global indices of HRV in response to musical were reported to be chronically influenced by this stimulation. In a recent study by Chuang et al., [7] it was reported that chronic exposure to music during 10 weeks increased the standard deviation of NN interval index in patients with breast cancer treated with anthracyclines, a cardiotoxic antineoplasic drug, indicating an improvement in global HRV. The authors used a different style of music than the music used in our study; the music used in the first activity was popular Taiwanese songs with tempos, pleasant and moderate rhythms. Another activity included learning how to play musical instruments and featured different instruments in each session. The protocol was based on musical instruments that included hand-bells, egg shakers, metallophones, Cadeson bongos, recorders and ukuleles. We suggest that the global indices of HRV are more susceptible to be influenced by music.

We believe that the global indices of HRV (SD2, RRTri and TINN) were influenced by sound stimulus because the auditory stimulation possibly caused changes in the central nervous system activity and as a consequence, attenuated the cardiac autonomic responses to the PCM regarding the parasympathetic nervous system and partially the sympathetic component.

The SD1 index represents the transverse axis of the Poincaré plot and is defined by the standard deviation of the instantaneous HRV of beat-to-beat, this index shows the parasympathetic influence on the sinusal node. [4] During the analysis of the period from 5 to 10 min after the volunteers stood up in subjects previously exposed to music, this index presented statistically significant decrease compared to the seated control rest, suggesting reduced parasympathetic activity on the heart in healthy volunteers during this period. Comparing with the data presented by individuals previously exposed to musical auditory stimulation, this index was also reduced at the same period after the volunteer stood up. Although the global geometric indices of HRV in responses to the autonomic test were affected to music, we believe that classical baroque musical auditory stimulation does not influence the parasympathetic activity on the heart in response to the PCM in women, based on the geometric analysis of HRV.

These findings may be better explained by the qualitative analysis of the Poincaré plot after the PCM. In the protocol with no previous music exposure, it is observed at 10-15 min after the subjects stood up a lower dispersion of RR intervals both beat-by-beat and long-term compared to the period before music exposure, which characterizes reduction of HRV at 10-15 min. When the subjects were previously to music and performed the PCM we noted that there was no difference between the two moments (control vs. 10 and 15 min after the volunteers stood up). These graphical features were also observed by Vanderlei et al., [16] during the analysis of HRV in obese and eutrophic children. The authors showed greater dispersion of data in the Poincaré plot of the control group when compared with the obese group, indicating increased parasympathetic modulation of the heart in the eutrophic control group and thus, reduced HRV of obese children. The lower dispersion, causing an effect of flattening the shape formed by the points, is commonly found when there is a reduction of the SD1 index, just reaffirming influence of music on the parasympathetic geometric index of HRV in response to the PCM.

The equivalent sound level is a very important variable that may influence the cardiac autonomic responses during musical auditory stimulation. In our study, subjects were exposed to intensity between 70 and 80 dB. In this context, Nakamura et al. [17] investigated the effects of auditory stimulation at 50 dB with white noise or two distinct classical music on the renal sympathetic nerve activity in rats anesthetized with urethane. The authors reported that during exposure to two pieces of music (TM: "Träumerei" from Kinderszenen Op. 15-7, R. Schumann; ET: "Etude" Op. 12-10, Revolutionary from Etudes Op. 12, F. Chopin) renal sympathetic nerve activity and arterial blood pressure decreased, however, it was not observed when the rats were exposed to white noise. The authors suggested that some styles of music, but not all, may decrease sympathetic activity and arterial blood pressure. The response of sympathetic activity reduction during exposure to classical music is in agreement with our findings, in which the HRV responses to the PCM were attenuated by previous musical auditory stimulation.

Some physiological mechanisms involving the central nervous system are proposed to be related to the results presented in our study. Bernardi et al. [3] Observed that cerebral blood flow progressively fell with time during exposure to music variables such as harmonic, melodic or rhythmic structure (non-syncopated vs. syncopated) and tempo (rhythm speed). A study in animals showed that 21 days of exposure to a music protocol increased hypothalamus brain-derived neurotrophic factor and decreased nerve growth factor in the hypothalamus. [18] Furthermore, histaminergic receptors in the suprachiasmatic nucleus of the hypothalamus were also indicated to be involved in the acute responses of the sympathetic activity and arterial blood pressure induced by music stimulation. This mechanism was dependent on an intact cochlea and on the auditory cortex. Taken together, all those physiological mechanisms are hypothesized by our group to be involved in the effects of music on cardiac autonomic responses induced by on the PCM.

Some points in our study are important to be raised. Although we investigated only 11 volunteers, the statistical power analysis provided a minimal number of 10 subjects and we found statistical significance in the indices evaluated. We studied only women, since specific responses to music related to gender are an important topic that merits further evaluation. The literature suggested that women presented more intensity stress responses compared to men. [19] It was reported different reactivity responses in men and women. During heavy metal musical auditory stimulation, women exhibited a higher increase in the sympathetic nervous system responses compared to men. The sympathetic activity was evaluated through skin conductance and finger temperature measurements. It was observed that men presented increased autonomic responses after heavy metal exposure through salivary alpha-amylase measurement.


  Conclusion Top


Based on the above study it can be concluded that auditory stimulation with classical baroque music attenuates the responses of the global HRV induced by the PCM in health women. However, it presented no effect on the parasympathetic modulation of the heart in response to this autonomic test.


  Acknowledgment Top


We thank Dr. Hani Atrash for helping with English Grammar and Spelling review. This study received financial support from Foundation of Support to Research of São Paulo State.

 
  References Top

1.Valenti VE, Guida HL, Vanderlei LC, Roque AL, Ferreira LL, Ferreira C, et al. Relationship between cardiac autonomic regulation and auditory mechanisms: Importance for growth and development. J Hum Growth Dev 2013;23:94-8.  Back to cited text no. 1
    
2.Valenti VE, Guida HL, Frizzo AC, Cardoso AC, Vanderlei LC, Abreu LC. Auditory stimulation and cardiac autonomic regulation. Clinics (Sao Paulo) 2012;67:955-8.  Back to cited text no. 2
    
3.Bernardi L, Porta C, Casucci G, Balsamo R, Bernardi NF, Fogari R, et al. Dynamic interactions between musical, cardiovascular, and cerebral rhythms in humans. Circulation 2009;119:3171-80.  Back to cited text no. 3
    
4.Vanderlei LC, Pastre CM, Hoshi RA, Carvalho TD, Godoy MF. Basic notions of heart rate variability and its clinical applicability. Rev Bras Cir Cardiovasc 2009;24:205-17.  Back to cited text no. 4
    
5.Abreu LC. Heart rate variability as a functional marker of development. J Hum Growth Dev 2012;22:279-81.  Back to cited text no. 5
    
6.Ribeiro AL, Ferreira LM, Oliveira E, Cruzeiro PC, Torres RM, Rocha MO. Active orthostatic stress and respiratory sinus arrhythmia in Chagas global systolic function of the left ventricle preserved. Arq Bras Cardiol 2004;83:35-9.  Back to cited text no. 6
    
7.Chuang CY, Han WR, Li PC, Song MY, Young ST. Effect of long-term music therapy intervention on autonomic function in anthracycline-treated breast cancer patients. Integr Cancer Ther 2011;10:312-6.  Back to cited text no. 7
    
8.Roque AL, Valenti VE, Guida HL, Campos MF, Knap A, Vanderlei LC, et al. The effects of different styles of musical auditory stimulation on cardiac autonomic regulation in healthy women. Noise Health 2013;15:281-7.  Back to cited text no. 8
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9.Roque AL, Valenti VE, Guida HL, Campos MF, Knap A, Vanderlei LC, et al. The effects of auditory stimulation with music on heart rate variability in healthy women. Clinics (Sao Paulo) 2013;68:960-7.  Back to cited text no. 9
    
10.Lohman TG, Roche AF, Martorell R. Anthropometric Standardization Reference Manual. Champaign: Human Kinetics Books; 1998.  Back to cited text no. 10
    
11.Niskanen JP, Tarvainen MP, Ranta-Aho PO, Karjalainen PA. Software for advanced HRV analysis. Comput Methods Programs Biomed 2004;76:73-81.  Back to cited text no. 11
    
12.Dias de Carvalho T, Marcelo Pastre C, Claudino Rossi R, de Abreu LC, Valenti VE, Marques Vanderlei LC. Geometric index of heart rate variability in chronic obstructive pulmonary disease. Rev Port Pneumol 2011;17:260-5.  Back to cited text no. 12
    
13.Vanderlei FC, Rossi RC, de Souza NM, de Sá DA, Gonçalves TM, Pastre CM, et al. Heart rate variability in healthy adolescents at rest. J Hum Growth Dev 2012;22:173-8.  Back to cited text no. 13
    
14.Tulppo MP, Mäkikallio TH, Seppänen T, Laukkanen RT, Huikuri HV. Vagal modulation of heart rate during exercise: Effects of age and physical fitness. Am J Physiol 1998;274:H424-9.  Back to cited text no. 14
    
15.Goyal S, Gupta V, Walia L. Effect of noise stress on autonomic function tests. Noise Health 2010;12:182-6.  Back to cited text no. 15
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16.Vanderlei LC, Pastre CM, Freitas Jr IF, Godoy MF. Geometric indexes of heart rate variability in obese and eutrophic children. Arq Bras Cardiol 2010;95:35-40.  Back to cited text no. 16
    
17.Nakamura T, Tanida M, Niijima A, Nagai K. Effect of auditory stimulation on parasympathetic nerve activity in urethane-anesthetized rats. In Vivo 2009;23:415-9.  Back to cited text no. 17
    
18.Angelucci F, Ricci E, Padua L, Sabino A, Tonali PA. Music exposure differentially alters the levels of brain-derived neurotrophic factor and nerve growth factor in the mouse hypothalamus. Neurosci Lett 2007;429:152-5.  Back to cited text no. 18
    
19.Nater UM, Abbruzzese E, Krebs M, Ehlert U. Sex differences in emotional and psychophysiological responses to musical stimuli. Int J Psychophysiol 2006;62:300-8.  Back to cited text no. 19
    

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Correspondence Address:
Vitor E Valenti
Department of Speech-Language and Hearing Therapy, Faculty of Philosophy and Sciences, UNESP. Av. Hygino Muzzi Filho, 737, Marília 17525-000, SP
Brasil
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Source of Support: This study received financial support from Foundation of Support to Research of Sγo Paulo State,, Conflict of Interest: None


DOI: 10.4103/1463-1741.127857

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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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