A Comparison of the Thermal and Pressure Pain Thresholds of Arab and Western European Healthy Male Subjects
Abstract:
Background and objective:
Pain is a universal, personal and subjective experience. Many factors are involved in the interpretation of this unpleasant sensation, including past experience, ethnicity and culture. Understanding these factors plays an important role in a comprehensive and multidimensional approach to the assessment and management of acute and chronic pain. The aim of this study is to determine experimental pain perception differences between Arab and western European healthy male subjects.
Method:
Fifty-six healthy Arab and western European male volunteers from Queen Margaret University College recruited to examine pain threshold using the method of limits in Quantitative Sensory Test (TSA 2001) and a Dolorimeter. Thermal and pressure pain threshold was measured on the thenar eminence of the non-dominant hand. Both ethnic groups were analysed separately.
Result:
Total fifty-six subjects (28 Arab and 28 European) subjects completed the study. In depended t-test result indicates that no statistically significant difference was found between Arabs and Europeans hot [t (54) =1.150; p>0.05], cold [t (54) =0.568; p>0.05], and pressure [t (54) =-0.279; p>0.05] pain threshold.
Conclusion:
No significant statistical difference in pain thresholds between Arab and Western European healthy male subjects was evident. More research is warranted in this field to access the perceptual and psychological aspects associated with pain.
Introduction
Pain is a subjective experience (French, 1989) and the protective function of life (Turk and Melzack, 1992). A number of factors may influence pain perception, including psychological, sociological and biological. Pain is the most common symptom in people who seek medical help, and is an important growing problem in the world (Strong, 2002).
One of the most important factors affecting the pain perception is Culture. Research indicates that socio-cultural factors have a great influence on pain and it varies across different social situations. Hence, it is important to study pain reactions keeping the socio-cultural factors in mind (Zborowski, 1952). To be able to assess the pain and its effect of the patients, normative data needed for each ethnic group and recorded their normal behaviour in pain stimulation in laboratory setting.
Various methods have been used in the past to induce experimental pain in varied cultural background populations to determine the influence of culture on perception of pain of an individual (Bates et al, 1994; Juarez et al, 1999; woolf et al, 2003; Ibrahim et al, 2003; Rotheram et al, 2000, Zaidi, 1994, Zborowski, 1952, Dunn, 2004).
However, determining cultural differences was not the primary aim of the research in many of these studies. Thus, there is need for further studies to determine the influence of culture on the perception of pain in individuals. (Janal et al, 1994; Mimi et al, 2002). Culture affects the perception of pain and response to pain in different ways (Bates et al, 1993). However, to our knowledge, there has been no research to determine the effect of culture factor on the pain thresholds in respect of Western European and Arab populations. The case study by Chatuverdi et al (1997) portrays the need for this research.
In a study on medical practice in south London showed that there is a delay in South Asians receiving treatment for heart conditions (Chatuverdi et al 1997). This delay was found to be due to the failure to recognise patient behaviour as appropriate for their illness by the assessing clinicians. In other words, the clinicians did not know the normal behaviour of this group and thus failed to recognise the importance of their symptoms.
Cultural diversity is a known risk factor for the under treatment of pain (Kagawa-Singer & Blackhall, L.J 2001). Therefore, understanding the cultural factor in pain management plays an important role in successful modern pain management programs.
The areas of ethnicity and pain seem to have been less well researched than pain related age and gender. The influence of these two latter variables in pain experience has been studies in both healthy subjects and those with pain. Research concerning ethnicity is almost all limited to chronic pain.
Various studies surrounding this topic suggest that there are different components to pain but, generally, they focus their attention on the social and behavioural dimensions. Westbrook et al (1984) and Chatuverdi et al (1997) compared the pain behaviour of Swedes, Australians, South Asians, and Europeans respectively. Despite the use of different methodologies and populations, both observed differences in pain behaviour in the ethnic groups.
Bates (1993, 1994) suggested that the attitudes, beliefs and emotional and psychological state of an individual play an important role in the variation in chronic pain experience in different ethnic groups. These factors, which affect the pain perception, should be encountered in any pain assessment and its effect. Regardless of the design or methodology used in the different studies, the researchers point to the importance of considering ethnic particularities if these is to be a better understanding of patients.
Different methods have been used in the past to induce experimental pain. These include the use of ischemic pain (Rosche et al, 1984), pinch pain (Simmonds et al, 1992) mechanical pain (Simmonds et al, 1992; Walsh et al, 1995) and cold pain (Johnson & Tabasam, 1999). However, the sensitivity and magnitude of stimulus response is poorly estimated with these methods (Price, 1996). Quantitative sensory test and Dolorimeter was used because its show reliability and validity in pain thresholds assessing.
The study was designed to investigate a limited area of pain perception in a closely defined population using apparatus in which the stimulus eliciting a response is quantified.
· The premising aim of the study is to determine the difference, if any, in thermal and pressure pain thresholds of western Europeans and Arab healthy male population using Quantitative sensory test and a Dolorimeter.
· A secondary aim was to obtain subjects normative data from healthy male Arab and Western European subjects for pain threshold. This may be useful for further research.
Method:
Prior to main study pilot study was conducted in order to test various determinants of the study design and methodology. The pilot study was conducted a week prior to the research study to prevent any previous experience, which may cause bias of the result. Two subjects who would not be involved in the main study were selected. The methodology followed during the pilot study was similar to that used in the research study. The results of the pilot study were satisfactory and indicated the feasibility of a full-scale research study.
After obtaining approval from the university ethics committee, 56 healthy volunteer subjects were recruited from Queen Margaret University College. No examinee had a history of significant medical problems or chronic painful conditions. Informed consent was obtained from all subjects before thermal and pressure threshold measurement was carried out. Heat, cold pain thresholds were measured using a thermal sensory test (Verdugo & Ochoa, 1992). Pressure pain threshold was measured using a Dolorimeter. The apparatus employed was a thermal sensory analyser (model TSA-2001Medoc Ltd). The Quantitative sensory threshold test device was programmed such that it would discharge five hot and cold stimulations alternately to the non-dominant hand (the thenar aspect was used) (Yarnitsky et al, 1995 & Shy et al, 2003). In order to improve the reliability of the results a starting point for the Thermode was set as 32?C (Yarnitsky & Ochoa, 1991; Hagander et al, 2000). A range of 0°C to 50° C was used during the study. The rate of change in temperature was set to 1° C/sec as the stimulus moved away from the base line (Yarnitsky, 1997). To increase intrarater reliability the rate of temperature change was increased gradually (Palmer et al, 2000) and a temperature change of 3°C/sec was set as the stimulus returned to the base line of 32°C (Yarnitsky, 1997).
The sensory feedback data of the pain threshold levels was automatically recorded on the computer by a simple push-button response of the subject at the point where he deems the stimulus painful. The Peltier Thermode was firmly strapped against the thenar eminence by using a tourniquet approximately 20cm in length and 2cm in width (Hagander et al, 2000; Dyck et al, 1993), and to standardise the contact between the Peltier Thermode and thenar eminence surface, the tourniquet was expanded for 2 cm before fixation to the application site. The subject was blinded to the aim of the study and, to prevent the effect of optical feedback, the subjects were prevented from seeing the monitor displaying the information.
The pressure test was performed five minutes after the quantitative sensory test was conducted to avoid possibility of the false sensation and false reaction. The subjects were informed that they would be measured for pressure threshold and that they would feel pressure induced discomfort. The subjects were also informed that the pressure would be applied to the thenar aspect of the nondominant hand, and would be will gradually increased. They were instructed to say “Stop” at the point at which they felt pain; the pressure was then are released immediately (Fischer, 1986).
The subjects were positioned in comfortable seating and were advised to relax prior to the experiment. The non-dominant hand side and arm were supported on pillow placed on a table (Fischer, 1986). All subjects were ignorant of the aim of the study and to avoid optical biofeedback effect were prevented from seeing the pressure scale. The Pressure gauge was applied to the thenar eminence of the nondominant hand so that it was vertical and at 90° to the skin surface. To standardise the procedure, the pressure exerted by the Dolorimeter was increased at an even rate of about 1kg/sec. This was achieved by counting “one and thousand, two and thousand” and so on until the subject said, “STOP” at the point of unacceptable discomfort. The resulting reading from the Dolorimeter were then recorded (Fischer, 1986).
Statistical methods:
All statistical analysis was carried out using SPSS version 12.0 software.
Normality assumption for the primary response variable pain score was checked using the Kolmogorov-Smirnov test. In depended t-test was conducted for the differences in pain threshold scores between groups were used when normality of assumption was satisfied.
Result:
The results were derived separately for pain threshold and for the comparison of the age groups. The mean age of two ethnic groups was compared. It was found that the mean age of Arab was 24.2 years with SD of 3.3 years whereas, while the mean ± SD of the European was 23.1years ± 3.0 years (Table1).
Minimum
Maximum
Mean
Std. Deviation
Arab age
20 years
30 years
24.2 years
3.3 years
W.E Age
20 years
30 years
23.1 years
3.0 years
Table 1: descriptive statistics for the ages involved in the study.
Kolmogorov-Smirnov Test was conducted to test the normality of age’s distribution (Pallant, 2001). The result of the test indicates that there is no evidence against the claim that the distribution is normal: a Kolmogorov-Smirnov test for goodness-of-fit was insignificant: Kolmogorov-Smirnov Z=1.189; p>0.05 (Table2).
age
N
56
Normal Parameters
Mean
23.70
Std. Deviation
3.219
Kolmogorov-Smirnov Z
1.189
Asymp. Sig. (2-tailed)
.118
Table 2: Normal distribution of the involved ages
The result of independent t-test of involved ages were show that There were no statistically significant differences with a P value of 0.435 (P>0.05) between the two ethnic groups suggesting an equal variance could be assumed. The result of the independent t-test for equality of means for the involved ages are found 0.116 (P>0.05) (table 2).
Levene’s Test for Equality of Variances
t-test for Equality of Means of ages
F
Sig.
t
f
Sig. (2tailed)
95% Confidence Interval of the Difference
Lower
Upper
Equal variances assumed
.618
.435
1.209
54
.232
-.682
2.753
Table 3: Independent t-test values for the equality of means of ages of Arab and European.
Kolmogorov-Smirnov Test was conducted to test the distribution of hot, cold and pressure pain thresholds of Arab and western European subjects. The Result of Kolmogorov-Smirnov test for Hot Pain Thresholds was found with value of 0.094 at a significance of 0.200. The result of the present test shows that there is evidence that the distribution of hot pain threshold is normal distributed (p>0.05). The result of Kolmogorov-Smirnov test for Cold Pain Thresholds was found with value of 0.094 at a significance of 0.200. The result of the present test shows that there is evidence that the distribution of cold pain threshold is normal distributed (p>0.05). Finally, Result of Kolmogorov-Smirnov test for Pressure Pain Thresholds were found with value of 0.153 at a significance of 0.002. The result of the test shows the data is non-normal distributed, as the p value was less than 0.05. However, this result may due to biasing in sampling selecting (Pallant, 2001). Thus, the result was dealt as normal distributed (Table 5).
Kolmogorov-Smirnov test
Statistic
df
Sig.
Hot Pain Threshold
.094
56
.200(*)
Cold Pain Threshold
.094
56
.200(*)
Pressure Pain Threshold
.153
56
.002
Table 4: Normality test for data delivered from hot, cold and pressure pain threshold for both ethnic groups.
Using the in depended t-test test on the data for hot pain threshold (N=28), the result was found to be non-significant at P>0.05 for one tailed test, thus suggesting no statistically significant difference in the hot pain threshold between Arab and western European subjects [t (54) =1.150; p>0.05].
Levene’s Test for Equality of Variances
t-test for Equality of Means of Hot, Cold and Pressure pain thresholds
F
Sig.
t
df
Sig. (2-tailed)
95% Confidence Interval of the Difference
Lower
Upper
Hot Pain Threshold
Equal variances assumed
7.739
.007
1.150
54
.255
-.6135
2.2635
Cold Pain Threshold
Equal variances assumed
.995
.323
-.568
54
.572
-3.4112
1.9041
Pressure Pain Threshold
Equal variances not assumed
15.407
.000
.279
42.113
.782
-.5349
.7064
Table 5: The independent t-test result for hot, cold and pressure pain thresholds of Arab and European.
On using the in depended t-test on the data for cold pain threshold (N=28), the result was found to be non-significant at P>0.05 level for one tailed test, thus suggesting no statistically significant difference in the cold pain threshold between Arab and western European subjects [t (54) =0.568; p>0.05]. Finally, using the in depended t-test test on the data for pressure pain threshold for both ethnic groups (N=28), the result found to be non-significant at P>0.05 level for one tailed test, thus suggesting no statistically significant difference in pressure pain the threshold between Arabs and western European subjects [t (54) =-0.279; p>0.05](table 6).
Although the result of independent t-test for hot, cold, and pressure pain thresholds show that that statistically, there are no significant differences between Arab and western European healthy male subjects. However, there were differences in standard deviation (SD) between the ethnic groups.
The SD of Europeans hot, cold and pressure pain threshold was shown to have
greater discrepancy when compared to the Arab output, as shown in the Table 2.
N
Minimum
Maximum
Mean
Std. Deviation
Arabs Hot Pain Threshold
28
40.0ºC
46.4 ºC
42.6 ºC
1.9 ºC
W.European Hot Pain Threshold
28
3.1 ºC
47.8 ºC
43.4 ºC
3.2 ºC
Arabs Cold Pain Threshold
28
10.4 ºC
23.8 ºC
18.0 ºC
4.2 ºC
W.European Cold Pain Threshold
28
11.0 ºC
28.1 ºC
17.2 ºC
5.5 ºC
Arabs Pressure Pain Threshold
28
2.0kg
4.8kg
3.4kg
0.7kg
W.European Pressure Pain Threshold
28
2.1kg
6.2kg
3.4kg
1.4kg
Table6: The mean and SD of Arab and European hot, cold and pressure pain thresholds.
Discussion:
This study was unable to demonstrate differences in pain perception threshold between Arab and western European healthy male subjects. This is in agreement with studies examining other ethnic groups (Yosipovitch et al, 2004; Dimsdale, 2000; Greenwald, 1991). These studies, showed no significant difference in pain perception between ethnic groups. Although there are theories to explain possible threshold differences between ethnic groups (Juarez et al, 1999; Westbrook et al, 1984; and Chatuverdi et al, 1997) no significant difference was found in this study.
These results are in contrast with other studies, which show that there is a difference in pain perception between different ethnic groups (Bates et al, 1993; Elton, 1983; Melzack &Wall, 1982; McCaffery, 1999; Zborowski, 1952; Main & Spanswick, 2000; Juarez, 1999; Westbrook, 1984; Chaturvedi et al, 1997; Sheffield, 2000).
When comparing the mean values of the criteria, the Arab subjects in this study appeared more sensitive to painful stimuli than the Western European subjects. As the Arab subjects were African in origin, the result of present study is in agreement with a study by Edwards et al (1999, 2001) which suggested that African-American subjects showed increased unpleasantness ratings at the lowest temperatures when compared to white Americans, as well as enhanced sensitivity to noxious stimuli.
One interesting factor observed in this study is that a greater degree of homogeneity was displayed by the Arab subjects for hot, cold and pain thresholds when compared to the Western European subjects. The standard deviations for the Western European subjects for hot, cold and pressure pain threshold were higher than for the Arab subjects. This may be explained by two factors. The first is the origin of the Arab subjects: due to limitations in availability, they were taken from two African countries very close culturally and sociologically. The Western European subjects, however, were selected from a wider range group with many sub-groups and wide variation in cultural backgrounds. Previous studies have shown wide variations within different sub-groups of the same ethnic group (Zborowski, 1950). The second factor was the time of year at which the study was conducted. As it was shortly after the Christmas and New Year period, there is the possibility of alcohol intake by the Western European subjects being greater than at other times in the year (Jurgen Rehm and Gerhard Geml, 2002). Previous studies have shown that alcohol consumption may play a role in the degree of pain perception (Gustafson and Kallimén, 1988; Stewart et al, 2005). The greater consistency of results from Arab subjects could be explained by them being less likely to have consumed alcohol.
The present study disagrees with the studies by Juarez et al (1999); Westbrook et al (1984) and Chatuverdi et al (1997), which, demonstrate differences between the ethnic groups examined and indicate the need to include cultural considerations in acute and chronic pain management.
The present study agrees with the study done by Reed et al (1995), whose results suggested that subjects’ skin pigmented levels may play an important role in pain perception The skin of the Arab subjects was generally more pigmented, and they were more sensitive to hot pain stimulation than Western European subjects.
The present study is in agreement with those of Yosipovitch et al (2004) and Greenwald et al (1991), whose results suggest that there are no differences between ethnic groups in pain threshold.
Conclusion:
This study demonstrated thermal and pressure pain threshold is not affected by the ethnicity and culture of Arabs and western Europeans. Within ethnic groups, subject’s variability may be seen. Given that, the evidence from this limited study indicates little or no difference in pain thresholds between ethnic groups. Further research to investigate the psychological aspects of pain is justified.
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Pallant 2001
About the Author
1989-1993 BSc. in Physiotherapy and Rehabilitation, Istanbul/ Turkey.
2002-2005 PgDep. in Pain, Queen Margrate University, Edinburgh/ United Kingdom.
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