© Mary Ann Liebert, Inc. Pp. 273–279
DOI: 10.1089/pho.2007.2235
Study of Autonomic Nervous Activity of Night Shift Workers
Treated with Laser Acupuncture
Jih-Huah Wu, Ph.D.,
1Hsin-Yang Chen, M.S.,
2Yu-Ju Chang, M.S.,
3Hung-Chien Wu, M.D.,
4Wen-Dien Chang, M.S.,
5,6Yi-Jing Chu, B.E.,
5and Joe-Air Jiang, Ph.D.
5Abstract
Objective:
The aim of this study was to evaluate the impact of laser acupuncture on the autonomic nervous
system (ANS) of the night shift worker. Background Data: Many articles have demonstrated that levels of
af-fective disorders and stress are high in night shift workers. We applied laser energy to the Neiguan point (PC6)
to examine the impact of laser acupuncture on the ANS of 45 healthy young males who were night shift
work-ers and evaluated their heart-rate variability (HRV). Materials and Methods: The laser group (n
15) received
laser acupuncture (9.7 J/cm
2, 830 nm) for 10 min, and the placebo group (n
15) received sham laser
treat-ment. The effects before and after this intervention on the HRV of the subjects were assessed, along with those
seen after 30 min of lying down. Results: After treatment and after the 30-min rest period, the
independent-sample t-test showed that both groups exhibited statistically significant differences in high-frequency (HF) HRV,
low-frequency (LF) HRV, and the LF:HF ratio of HRV (p
0.05). Compared with the placebo group, the
paired-samples t-test showed that after laser treatment the treatment group had a statistically significant improvement
in HF HRV (p
0.001), LF HRV (p 0.001), and the LF:HF HRV ratio (p 0.02). Conclusions: Laser
acupunc-ture stimulation applied to the Neiguan point increased vagal activity and suppression of cardiac sympathetic
nerves. This effect was positive and could be used to help patients who have circadian rhythm disorders.
273 Introduction
A
REPORT BY THESWISSINTERNATIONALINSTITUTEforMan-agement Development in 2004 revealed that the aver-age number of hours worked per year by workers in Taiwan 2327 hours, which was the third highest in the world.1
An-other survey of social trends in Taiwan showed that 82.18% of the population went to bed between 11 and 12 P.M. and that others did not get to bed until after midnight.2
There-fore, many people have difficulty getting up for work in the morning. They may be physically affected by this due to the disruption in their circadian rhythm. Patients with gastric disease, cardiac disease, cancer, diabetes mellitus, low fertil-ity, and sleeping disorders often also have circadian rhythm disorders.3Some researchers have reported that there is a
causal relation between working late and cardiovascular dis-ease in male workers4and female nurses.5
Heart rhythm is mainly controlled by the autonomic ner-vous system (ANS) centered in the brain. The sympathetic nervous system (SNS) releases norepinephrine to activate the sinoatrial (SA) node, while the parasympathetic nervous sys-tem (PNS) releases acetylcholine to inhibit it.6 In the past,
when reading an electrocardiogram (ECG), the focus was on changes in waveform and wavelength. Not until recently has the interval between heart beats, or heart-rate variability (HRV), been studied and considered to be clinically mean-ingful.7HRV is determined by measuring the changes in the
distance between two wave peaks on an ECG, and may be used as an indicator of SNS and PNS activity, and autonomic nervous activity.6HRVs in normal people may be influenced
by several factors, such as age,8,9gender,9race,8body fat,9
and posture.10The analysis of HRV has been developing for
more than 20 years, and many different methods have been proposed for data analysis. These methods can be roughly
1Department of Biomedical Engineering, Ming Chuan University, 2Department of Life Science, National Central University, Taoyuan, 3Graduate Institute of Acupuncture Science, China Medical University, 4Department of Traditional Chinese Medicine, Chung-Ho
Memo-rial Hospital, Taichung, 5Department of Bio-Industrial Mechatronics Engineering, National Taiwan University, Taipei, and 6Department of
classified into linear time domain analysis and frequency do-main analysis.11Our work adopts both analytic methods to
evaluate the effects of laser acupuncture on HRV of night shift workers.
Low-energy laser acupuncture that is non-invasive and painless was used in this study. Needle acupuncture usually causes psychological effects and may be painful, which would interfere with ANS regulation. Although there have been some studies in this area and HRV may change during needle acupuncture,13–17the influence of laser acupuncture
on changes in HRV has seldom been studied. Compared with needle acupuncture, laser acupuncture is painless, sterile, and safe, and there are no broken needles, no needle-induce illness, and the dose is easily controllable and it is easy to perform.18It thus has the advantages of safety and
measur-ability. The aim of this study was to apply laser acupuncture to the Neiguan point of the right hand, and to investigate its influence on ANS regulation and changes in long-term night shift workers.
Materials and Methods
For this double-blind study we recruited 45 healthy young males. Thirty young males worked on the night shift, and they were randomly assigned into laser and placebo groups. All volunteers were recruited in China Medical University Hospital, and the Institutional Review Board on Research on Human Subjects of Chung Shan Medical University Hospi-tal approved this study. Inclusion criteria were young males, aged between 18 and 30 years old, with a body mass index (BMI) between 19 and 25 kg/m2, who were night shift
work-ers. Night shift workers are defined as those working until 3 A.M. more than three times a week. Exclusion criteria were having cardiopulmonary or endocrine disease, being on medication, having a smoking history, and having drank al-coholic beverages in the 24 hours before testing.
Study design
The experiments were conducted in a quiet, closed, air-conditioned (27°C) room between 7 and 10 P.M. Subjects in
the laser-treated group laid down for 8 min (Fig. 1) and the non-invasive HRV analyzer were positioned on the left wrist to measure the radial pulse. Then 7 min of HRV were recorded just before the acupuncture treatment (Test 1). Laser energy was then applied continuously to the Neiguan point (PC6) of the subject’s right hand for 10 min. After treat-ment, HRV was again measured for 7 min (Test 2). Next, the subjects had a 30-min relaxation period during which they laid supine. Finally, HRV was measured for another 7 min (Test 3). For the placebo group, the subjects were subjected to the same procedure as those in the laser group, they re-ceived 10-min of placebo laser irradiation (the power to the laser was off, but the indicator light remained on). All
record-ings were saved inside the HRV analyzer and then trans-ferred to the database in a computer for statistical analysis. Assessment
The heart rate variability analyzer (ANS WATCH; Tai-wan Scientific Corp., Taipei, TaiTai-wan) was used to measure ANS activity. The power spectrum of the signal was esti-mated from 256 R-R intervals of the heartbeat, and all val-ues were analyzed with HRV analysis software. For the lin-ear time domain analysis, the R-R intervals of the ECG records were analyzed and the results were expressed in the form of normal-to-normal (NN) intervals. Then the standard deviation of the NN intervals (SDNN) was calculated. As for the frequency domain analysis, Fourier transform was applied to complex heartbeat signals so their duration could be determined. Three feature values were obtained, includ-ing a high-frequency (HF) value, representinclud-ing PNS activity, and a low-frequency (LF) value, representing the influence of SNS and PNS activity. Very-lowfrequency (VLF) activity has not yet been defined.12Linear time domain analysis has
rarely been used in spectral analysis, as frequency domain analysis is usually used. This is primarily because the fre-quency domain type is more appropriate for observing im-mediate changes in HRV. As established in 1996 by the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, the rel-evant indices and signals were defined and obtained as fol-lows:8
HF: the frequency band from 0.15–0.4 Hz, shown as a per-centage
HF (%) HF power/(HF power LF power)
LF: the frequency band from 0.04–0.15 Hz, shown as a per-centage
LF (%) LF power/(HF power LF power) LF:HF ratio: the ratio of LF to HF HRV
SDNN (ms): the standard deviation of the R-R intervals seen on the ECG
Physiological parameters: systolic blood pressure (SBP in millimeters of mercury), diastolic blood pressure (DBP in millimeters of mercury), and heart rate (HR) (in beats per minute [bpm]).
Treatment procedure
The suggested clinical treatment dosage for the low-en-ergy laser is 8–10 J/cm2, and it is used to hasten wound
heal-ing.19We used a low-energy laser device (Painless Light
PL-830; Advanced Chips & Products Corp., Hillside, NJ, USA), FIG. 1. Protocol used in our study.
TABLE1. DEMOGRAPHICDATA FOR THESTUDYGROUPS
Laser group Placebo group
n 15 n 15
Age (y) 20.27 2.55 21.80 3.08
Height (cm) 171.53 4.47 172.20 4.48 Weight (kg) 68.27 7.35 70.27 9.12 BMI (kg/m2) 23.20 2.36 23.62 2.25
consisting of two infrared diode lasers, ao apply the laser therapy. This device emits light at a wavelength of 830 nm, output frequency of 10 Hz, with an output power of 60 mW (2 30 mW), and a duty cycle of 50%, resulting in a treat-ment dose of 9.7 J/cm2. The irradiation was performed with
a distance of 2.5 cm between the two laser diodes. The laser treatments were all given by the same physician and were applied to the point of pericardium 6 (PC6), or the Neiguan point. The Neiguan point is located approximately 2 cm proximal to the middle point of the carpal fold between the tendons of the flexor carpi radialis muscle and the palmaris longus muscle.
Statistical analysis
The SPSS software (SPSS, Inc., Chicago, IL, USA) was used to perform the data analysis. The independent-sample t-test was used to check for differences between groups in the ba-sic data, such as age, height, weight, and BMI values. Before treatment, after treatment, and after a 30-min rest period, the SBP, DBP, HR, HRV, HF, LF, and LF:HF ratio of both groups were also analyzed using the independent-sample t-test. The paired-samples t-test was used to compare the parameters of each group before and after treatment. All the statistical tests were two-tailed.
Results
Basic data for our 30 subjects are shown in Table 1. There were no significant differences in height, weight, BMI, and
age between the groups (p 0.05). Baseline measurements (Test 1) of SBP, DBP, HR, HRV, HF, LF, and LF:HF ratio showed that there were no significant differences between the groups (p 0.05; Table 2).
Blood pressure
There were no significant differences in the mean blood pressure values between the two groups after treatment and after the 30-min rest period (p 0.05; Table 3). The compar-isons of SBP and DBP before and after treatment, and after the 30-min rest period in each group, are shown in Figs. 2 and 3. Compared with before treatment, there were no sig-nificant differences in SBP and DBP after treatment and af-ter the 30-min rest period between the two groups (p 0.05). Heart rate
The mean values of heart rate showed no significant differ-ences between both groups after treatment and after the 30-min rest period (p 0.05; Table 3). The comparisons of heart rate measurements after treatment and after the 30-min rest period in each group are shown in Fig. 4. A significant improvement was recorded after treatment in the treated group (p 0.05), but none was seen after the 30-min rest period (p 0.05). Heart rate variability
The comparisons between the two groups for HRV, in-cluding SDNN, HF, LF, and LF:HF ratio, are shown in Table TABLE2. BASELINEDATA FOR THETWOGROUPS
Laser group Placebo group
n 15 n 15 F value p Value SBP (mm Hg) 122.07 16.07 121.13 9.43 3.08 0.85 DBP (mm Hg) 76.67 3.24 75.13 2.61 0.72 0.17 HR (bpm) 71.67 11.91 74.07 9.22 1.01 0.54 SDNN (ms) 56.27 23.65 47.00 19.39 1.04 0.25 HF (%) 40.73 15.99 34.47 12.80 1.54 0.25 LF (%) 59.27 15.99 65.53 12.80 1.54 0.25 LFHF ratio 2.15 2.14 2.28 1.26 1.12 0.85
Data are expressed as means standard deviation. F value, Levene’s test for equality of variance.
TABLE3. THEANALYZEDPARAMETERS IN THETWOGROUPSAFTERTREATMENT
Test 2 Test 3
Laser group Placebo group F p Laser group Placebo group F p
(n 15) (n 15) value value (n 15) (n 15) value value SBP (mm Hg) 119.67 7.97 115.00 8.27 0.08 0.13 119.73 12.13 119.00 9.16 2.41 0.85 DBP (mm Hg) 75.87 3.44 76.13 3.16 0.35 0.83 76.60 3.42 76.33 3.04 0.05 0.82 HR (bpm) 66.00 10.60 70.33 8.00 1.13 0.22 65.00 8.90 69.53 8.98 0.003 0.18 SDNN (ms) 81.33 56.00 58.93 27.33 2.27 0.18 111.00 92.11 58.27 22.56 6.92b 0.05 HF (%) 55.33 16.15 35.60 16.26 0.001 0.002a 61.93 12.59 38.13 15.08 2.21 0.001a LF (%) 44.67 16.15 64.40 16.26 0.001 0.002a 38.07 12.59 61.87 15.08 2.21 0.001a LFHF ratio 1.02 0.76 2.35 1.35 7.01 0.003a 0.69 0.41 2.10 1.37 17.81b 0.001a ap 0.05 by independent-sample t-test. bp 0.05.
Data are expressed as means standard deviation.
3. Except for SDNN, comparisons of HF, LF, and LF:HF ra-tio between the laser group and the placebo group showed significant differences after treatment and after the 30-min rest period (p 0.05). A significant improvement in SDNN was not seen in two-point discrimination in either group (p 0.05; Fig. 5). However, there were significant improvements in HF, LF, and LF:HF ratio after treatment and after the 30-min rest period in the laser group (p 0.05), as shown in Figs. 6, 7, and 8, respectively.
Discussion
This study adopted laser acupuncture instead of tradi-tional needle acupuncture to assess the effects on the changes in HRV of long-term night shift workers. The results suggest that night shift workers need to regulate their biological clocks by manipulating their ANS. Schlager et al.20reported
that night shift workers had more highly activated sympa-thetic and parasympasympa-thetic nervous systems and higher heart rates. Night shift workers need more control and reg-ulation of their autonomic nervous system to accommodate their differing daytime and nighttime schedules. However, an over-excited ANS could be a risk factor for cardiovascu-lar disease.
Acupuncture is a method of physical stimulation of distal nerves in the skin and muscles that excites A and A nerve fibers.14The low-energy laser has been used for acupuncture
treatment, a method known as laser acupuncture.18 Odud
and Potapenko used laser beams to stimulate acupuncture points to treat hypertension.21 Later studies revealed that
laser energy in the spectrum from violet to orange (400–600 nm) is more easily absorbed by hemoglobin and melanin un-derneath the skin, while lasers with wavelengths over 1400 nm are more readily absorbed by water molecules in the skin. As a result, lasers in the red to infrared range (about 600–1400 nm) are the most suitable for acupuncture treatment, because they penetrate 2–5 mm into the skin. In addition, the pene-trating ability of laser energy into muscle is four times deeper
than that seen in the skin, and therefore the energy can reach nearly 1 cm underneath the skin to stimulate acupuncture points.18To date, neural pathways for laser acupuncture
re-main unknown, but a previous study proved that laser acupuncture can activate areas of the human cortical brain by stimulating acupuncture points. This may lead to a mod-ulation of the neuronal network.22HRV is a handy tool for
clinical evaluation, one that includes HF as an indicator of PNS activity, LF for the combination of SNS and PNS activ-ity, and LF:HF ratio for SNS activity. Nishijo et al. investi-gated the relationship between needle acupuncture and changes in HR, and found that acupuncture could decrease HR, increase vagal nerve activity, and decrease SNS activ-ity, which lead to increases in HF activactiv-ity, decreases in LF
FIG. 2. samples t-test results for SBP values before and af-ter inaf-tervention, and afaf-ter the 30-min rest period, for the three tests.
FIG. 3. Paired-samples t-test results for DBP values before and after intervention, and after the 30-min rest period, for the three tests.
FIG. 4. Paired-samples t-test results for HR values before and after intervention, and after the 30-min rest period, for the three tests.
activity, and a decreased LF:HF ratio.23The subjects in our
study also had higher HF activity, lower LF activity, and lower LF:HF ratios after laser acupuncture, which suggests that laser acupuncture may have the same effects as needle acupuncture. Adjustments in HR and BP in both groups were detected, but there were no significant differences in HR and BP after treatment and after the 30-min rest period. On the other hand, all subjects in our experiment had clear HR and BP changes after the nearly 1-h rest period, whether they re-ceived the laser acupuncture treatment or not. This suggests that lying down for 1 h may be the main contributing factor to the lower HR and BP seen in both groups.
Nishijo et al. found that healthy volunteers receiving nee-dle acupuncture at the Sen-Men point (HT7) had decreased
HR.23This again indicates that needle acupuncture may
reg-ulate the ANS by activating the PNS and inhibiting the SNS. A study by Haker et al. using needle acupuncture at the Hegu point (LI4) of healthy volunteers found that it activated the PNS and SNS. But they also found that only the PNS was activated by acupuncture treatment at the lung point of the ear.13Liou et al. found that non-acupoint acupuncture and
acupuncture at the Neiguan point were no different in changing HRV.24Huang et al. observed that the PNS was
excited by twirling the needle during acupuncture at the Neiguan point, while the SNS was not.14Chang et al. found
that electrical needling of the Zusanli point (ST36) could ac-tivate the SNS.15Li et al. found that both the PNS and the
SNS were activated by acupuncture needling at the Hegu
FIG. 6. Paired-samples t-test results for HF values before and after intervention, and after the 30-min rest period, for the three tests.
FIG. 8. Paired-samples t-test results for LF:HF ratio before and after intervention, and after the 30-min rest period, for the three tests.
FIG. 7. Paired-samples t-test results for LF values before and after intervention, and after the 30-min rest period, for the three tests.
FIG. 5. Paired-samples t-test results for SDNN values be-fore and after intervention, and after the 30-min rest period, for the three tests.
(LI4) and Neiguan points, regardless of whether the subjects were fatigued or not.16Hsu et al. observed that the PNS was
excited but the SNS was inhibited when subjects received acupuncture needling at the Xinshu point (BL15), and sug-gested a possible relaxing effect of stimulating this point.17
Needle acupuncture works by stimulation using mechan-ical impulses sent through connective tissue. This activates signal transduction pathways at acupuncture points and pro-duces changes in ANS modulation.25We used laser
acupunc-ture to cause similar results via its photobiostimulating effect.19 Though laser acupuncture has different a
physio-logical mechanism from that of needle acupuncture, it can also affect ANS modulation in night shift workers. In this study, we found that after laser acupuncture at the Neiguan point of night shift workers, the PNS was excited and the SNS was inhibited, and that after a 30-min rest period, exci-tation of the PNS and inhibition of the SNS were maintained. There were also changes in HRV. These results indicate that laser acupuncture at the Neiguan point of night shift work-ers can induce a new balance in the ANS, which is main-tained for at least 40 minutes. Thus laser acupuncture at the Neiguan point had effects on ANS modulation in night shift workers.
Conclusion
Working at night causes autonomic dysfunction, such as excitation of the SNS and inhibition of the PNS. Long-term imbalances in the ANS may lead to various cardiovascular and other chronic diseases. In this study we found that us-ing laser acupuncture at the Neiguan point (PC6) excites va-gal nerve activity and inhibits SNS activity of night shift workers, and helps to adjust autonomic nervous balance. The effect was maintained for at least 40 min after treatment. Thus laser stimulation of the Neiguan point appears to have an effect on ANS balance. We believe this phenomenon re-quires further investigation to clarify our knowledge of these effects.
Acknowledgements
The authors wish to thank Delta Electronics, Inc. for sponsoring this work. We are also grateful to the National Science Council of the Republic of China for financially supporting this research under contracts NSC 95-2218-E-002-073, NSC 96-2218-E-002-015, and NSC 96-2628-E-002-252-MY3.
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Address reprint requests to: Dr. Joe-Air Jiang, Ph.D. Associate Professor Department of Bio-Industrial Mechatronics Engineering National Taiwan University No. 1, Sec. 4, Roosevelt Road Taipei, 10617, Taiwan E-mail: [email protected]
