Preliminary Investigation: Acupoint-Skin Conductance in StrokeSurvivors

Yiu Ming Wong

� Springer Science+Business Media New York 2014

Abstract It has been reported that patients with rheuma-

toid arthritis or asthma have skin conductance over the

acupoints that is lower than that of their healthy counter-

parts; this has been regarded as indirect evidence of the

existence of acupoints and the energy-based model of dis-

eases. In order to investigate the potential application of

acupoint-skin conductance measurement that may reflect

pathology of ischemic stroke, the present study recruited 34

stroke survivors with hemiparesis, whose skin conductance

of a hand acupoint and an adjacent non-acupoint and the

finger temperature in both affected and unaffected hands

were simultaneously measured; the data revealed that the

skin conductance and finger temperature were statistically

higher in the unaffected hand than that of the affected, and

the skin conductance of the acupoint and the non-acupoint

were comparable in the affected and unaffected hands

respectively. We attribute the observed drop in the skin

conductance to the diminished peripheral blood flow of the

affected hand that is signified by relatively lower finger

temperature. As such, it should be advisable when studying

skin conductance over acupoints, monitoring the adjacent

non-acupoint skin and local vascular circulation is essential.

Keywords Skin conductance � Finger temperature �Stroke � Hand � Acupuncture

Introduction

While acupuncture is generally accepted as a useful non-

pharmacological method for pain reduction, the mechanism

of acupuncture treatments is uncertain (Melzack et al. 1980).

Acupuncture is described as an energy-based model of

therapy that an energy named ‘‘ki’’ travels through the body

along internal channels called ‘‘meridians’’ and the ‘‘acu-

points’’ are located along the meridians. Theoretically, the

ki obstructions in the meridians cause diseases in the body,

and acupuncture practitioners, by massaging or needling the

acupoints, can enhance the flow of ki and restore physical

wellbeing (Wagner 2010). However, this theory is not par-

allel to modern anatomy and physiology (Ramey 2000).

On the topic of the acupoint, some researchers reported

that patients with rheumatoid arthritis or asthma had rela-

tively lower skin conductance on certain acupoints as

compared to healthy counterparts; the findings were

regarded as indirect evidence of existence of the acupoints

and the ki obstruction, and the acupoint-skin conductance

measurement was proposed as diagnostically useful for

rheumatoid arthritis and asthma (Turner et al. 2013; Pro-

khorov et al. 2006; Ngai et al. 2011). Since these studies

were done without a measure of non-acupoint skin con-

ductance, it is open to doubt whether the alternation of skin

conductance is detectable only over the acupoints or may

be detectable globally over the patients’ skin.

In order to test the hypothesis that acupoint skin con-

ductance measurement may reflect pathology of stroke as

the ki obstruction in the theory of acupuncture (Cheng et al.

2013), the present study was to investigate the skin con-

ductance of a hand acupoint and an adjacent non-acupoint

and the index finger temperature in both affected and

unaffected hands among stroke survivors with hemiparesis.

We hypothesized that the skin conductance is lower over the

Y. M. Wong (&)

Health Science Unit (PEC), Hong Kong Physically Handicapped

and Able Bodied Association, S102, G/F, Lai Lo House,

Lai Kok Estate, Shamshuipo, Kowloon, Hong Kong

e-mail: pt@hkphab.org.hk

123

Appl Psychophysiol Biofeedback

DOI 10.1007/s10484-014-9249-6

acupoint than that of the non-acupoint, and the conductance

is relatively lowest over the acupoint of the affected side.

Methods

Subjects

Thirty-four male ischemic stroke survivors with hemipa-

resis between 46 and 69 years of age were recruited on a

volunteer basis through the Hong Kong Physically Hand-

icapped & Able Bodied Association. Their average age was

57 ± 6.9 years; weight was 70.4 ± 10.3 kg and height

was 163.7 ± 5 cm; all of them were left-limb affected.

Subjects were included if they suffering from stroke on

only one known occasion that occurred at least 1 year prior

to the study and their affected upper limb was graded

between 2 and 3 in muscle power testing. Subjects were

excluded if they had a cardiac pacemaker implanted, pre-

vious upper extremity surgery or disabilities, systemic

rheumatic or inflammatory diseases, high blood pressure

resistant to treatment or cognitive impairment that pre-

cludes protocol compliance. The Human Research Ethics

Committee of the Health Science Unit of the administrating

institution approved the study protocol; all the study pro-

cedures below were performed in compliance with the

relevant law and institutional guidelines in accordance with

the ethical standards of the Declaration of Helsinki.

Procedures

Firstly, the participants’ hands were washed according to

the guideline of Association for Professionals in Infection

Control (Larson 1995). After the hands were dried natu-

rally, the participant was seated with back and arm support,

and the hands were positioned neutrally. All the partici-

pants were assessed by a researcher with 10 years of

experience in clinical acupuncture and biofeedback who

measured the skin conductance on the acupoint LI-4, on a

neighboring non-acupoint skin, located about 2 cm later-

ally, as well as the temperature of the distal palmer index

finger (Fig. 1); the acupoint LI-4 was selected since it is

commonly used for post-stroke rehabilitation (Lin et al.

2009) and palpation diagnosis (Feely 2010). Both unaf-

fected and affected hands were measured simultaneously

for the skin conductance (four data acquisitions) and finger

temperature (two data acquisitions) using an FDA-

approved class I monitoring device (Flexcomp DSP,

Montreal, Canada). With a data-sampling rate at 100 Hz,

the static measurements lasted for 300 s and the mean of

the 300-s values was calculated. The unit for skin con-

ductance evaluation was the microsiemens (lS) in which

the higher the reading means the higher the electrical

conductivity as well as lower electrical resistance (Peek

2003). During the measurements, the room temperature,

humidity, and air velocity were kept constant in the range

of 22–23 �C, 52–55 % and 0.2–0.25 m/s respectively

(Lenzuni and Del Gaudio 2007).

Statistics and Results

Using SPSS Statistics 17.0 software (SPSS, Chicago, IL),

five separate within-group comparisons were conducted

using paired t tests, the P value for significance was set as

0.05 and was not adjusted due to the preliminary nature of

this investigation. The Cohen’s d was calculated in order to

Fig. 1 Left Acupoint LI4 of left

hand. Middle Corresponding

MRI that shows AP acupoint,

NAP non-acupoint. Right

Measurement setting contains

FT finger temperature, SC skin

conductance

Appl Psychophysiol Biofeedback

123

justify the adequateness of statistical power, the Cohen’s d

scoring 0.8 or higher was regarded as the large effect size.

The comparisons are listed in Table 1. The data revealed

that the skin conductance and finger temperature were

statistically higher in the unaffected hand than that of the

affected; the skin conductance on the acupoint and non-

acupoint were comparable in the affected and unaffected

hands respectively. The said significances were reported

with the effect size being large.

Discussion

To the author’s best knowledge, the present study is the

first investigation for the skin conductance of the stroke

survivors’ acupoint, though the findings did not demon-

strate the skin conductance being significantly different

between the acupoint and the adjacent non-acupoint on the

first finger web-space ipislaterally.

The only statistical significances noted were between the

skin conductance and between the finger temperature in the

unaffected and affected hand. The skin conductance mea-

surement was done by applying a current to the dermis and

quantifying the dermis’s ability to conduct electricity (Peek

2003). The dermal layer, which includes capillaries, arte-

rioles, and venules with blood moving inside them, is

electrically conductive (Hull et al. 1978); in turn, the skin

conductance is partially dependent to vasomotor activities

that could be vasodilatory or vasoconstrictory to the blood

vessels. It has been documented that there is an approxi-

mately 30 % reduction in peripheral blood flow in the

paretic limb compared to the unaffected side in stroke

survivors (Ivey et al. 2004). In this study, the most likely

explanation for the lowered skin conductance in the

affected hand is the local diminished blood flow that is

signified by relatively lower finger temperature; we tend to

attribute the observed drop in the skin conductance to the

vasomotor disturbance following disuse of the upper limb

from the consequence of stroke. We also believe there is a

positive relationship between the finger temperature and

skin conductance for the paretic hands (Adams and Immis

1983), thus it may be advisable when interpreting acupoints

as electrically distinguishable, simultaneously monitoring

the adjacent non-acupoint skin and local vascular circula-

tion is pre-required. For future studies involving stroke

survivors’ acupoint-skin conductance, the dermal water

contents and skin thickness should be evaluated to order to

clarify the potential role of metabolic or structural abnor-

malities in the tissue level that may develop following the

stroke.

The preliminary findings in the present study should be

taken cautiously as the use of male subjects between 46 and

69 years and only one acupoint was tested. The results

cannot be directly generalized to other age groups and

gender; a possibility still exists that the multiple-acupoints

skin conductance measurement could outperform than that

of the single acupoint for examining the energy-based

model of stroke. Secondly, different textbooks for teaching

acupuncture are various in number and placements of

acupoints; the present study is merely based on the acu-

point maps published by Taiwan authority (Lin et al. 2009).

Conclusion

Based on the present finding and preceding discussion, it

is likely that acupoint-skin conductance measurement does

not reflect pathology of the hemiparesis following ische-

mic stroke, but the hand skin conductance and finger

temperature measurements potentially act as a quantitative

tool for evaluating peripheral vaso-dynamics for stroke

survivors.

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Acupoint of unaffected

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1.87 ± 0.45 lS

Acupoint of affected hand

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P = 0.04*^

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* Statistical significance

^ Large effect size

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