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Pain response during fasting and postprandial conditions in healthy young Indian males

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Abstract

terms of cardiovascular reactivity (CVR) (change in heart rate and blood pressure) and pain sensitivity (PS) (pain threshold, pain tolerance, and pain rating). [1,2] The utility of psychological and behavioral interventions in pain management is closely investigated due to the undesirable side effects associated with prolonged use of most analgesics. Methods of enhancing pain tolerance and decreasing pain rating without the use of drugs involve behavioral techniques, acute elicitation of the relaxation response, and mental distraction. Low blood glucose levels have been associated with aggression and frustration. [3] Therefore, this study compares CVR and PS in fasting and ½‑h postprandial (PP) conditions. Experimental pain was produced by performing CPT, in the fasting and ½‑h PP state. Abstract Background and Aim: The amount of pain perceived in response to a pain stimulus varies from person to person, and under different conditions in the same person. It can be estimated in terms of cardiovascular reactivity (CVR) and pain sensitivity (PS). The cold pressor task has been successfully used to induce experimental pain in human subjects. Low blood glucose levels have been associated with increased scores of anger and frustration. Therefore, in the present study we have compared the response to experimental pain produced, in subjects in their fasting and fed states. Methods: Cold pressor task was performed on 86 subjects in the fasting and ½-h postprandial (PP) states. The pain response was measured in terms of changes in pulse and blood pressure as CVR parameter and pain threshold, tolerance, and rating as PS parameters. Data were analyzed by comparing CVR and PS in fasting and ½-h PP condition by Student's t-test, Pearson's correlation and multiple regression analysis. Results: Pain threshold and tolerance increased significantly in the ½‑h PP state without significant change in the CVR. Significant positive correlation was obtained between blood glucose level and PS. Multiple regression analysis also showed significant independent contribution of blood glucose to pain threshold and tolerance. Conclusion: Increase in blood glucose levels in the ½-h PP state increases the pain threshold and tolerance, making it easier for the subjects to bear pain.
International Journal of Clinical and Experimental Physiology| Oct-Dec 2014 | Vol 1 | Issue 4 263
International Journal of Clinical and Experimental Physiology| Oct-Dec 2014 | Vol 1 | Issue 4 262 International Journal of Clinical and Experimental Physiology| Oct-Dec 2014 | Vol 1 | Issue 4 263
International Journal of Clinical and Experimental Physiology| Oct-Dec 2014 | Vol 1 | Issue 4 262
terms of cardiovascular reactivity (CVR) (change in heart
rate and blood pressure) and pain sensitivity (PS) (pain
threshold, pain tolerance, and pain rating).[1,2]
The utility of psychological and behavioral interventions
in pain management is closely investigated due to the
undesirable side effects associated with prolonged
use of most analgesics. Methods of enhancing pain
tolerance and decreasing pain rating without the use of
drugs involve behavioral techniques, acute elicitation
of the relaxation response, and mental distraction.
Low blood glucose levels have been associated with
aggression and frustration.[3] Therefore, this study
compares CVR and PS in fasting and ½‑h postprandial
(PP) conditions. Experimental pain was produced by
performing CPT, in the fasting and ½‑h PP state.
Access this article online
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Website:
www.ijcep.org
DOI:
10.4103/2348-8093.149752
Address for correspondence: Prof. Manoj Kumar, Department of Physiology, Teerthanker Mahaveer Medical College
and Research Centre, Teerthanker Mahaveer University, NH‑24, Pakbara, Moradabad, Uttar Pradesh ‑ 244 001, India.
E‑mail: premmanoj2001@yahoo.co.in
Abstract
Background and Aim: The amount of pain perceived in response to a pain stimulus varies from person to person, and under
different conditions in the same person. It can be estimated in terms of cardiovascular reactivity (CVR) and pain sensitivity (PS).
The cold pressor task has been successfully used to induce experimental pain in human subjects. Low blood glucose levels
have been associated with increased scores of anger and frustration. Therefore, in the present study we have compared the
response to experimental pain produced, in subjects in their fasting and fed states.
Methods: Cold pressor task was performed on 86 subjects in the fasting and ½-h postprandial (PP) states. The pain response
was measured in terms of changes in pulse and blood pressure as CVR parameter and pain threshold, tolerance, and rating as
PS parameters. Data were analyzed by comparing CVR and PS in fasting and ½-h PP condition by Student’s t-test, Pearson’s
correlation and multiple regression analysis.
Results: Pain threshold and tolerance increased signicantly in the ½‑h PP state without signicant change in the CVR.
Signicant positive correlation was obtained between blood glucose level and PS. Multiple regression analysis also showed
signicant independent contribution of blood glucose to pain threshold and tolerance.
Conclusion: Increase in blood glucose levels in the ½-h PP state increases the pain threshold and tolerance, making it easier
for the subjects to bear pain.
Key words: Cold pressor task, experimental pain, fasting, pain threshold, pain tolerance
INTRODUCTION
The intensity of pain perceived by an individual in
response to a painful stimulus depends on the biology of
the noxious event, and on physical, psychological, and
social factors related to the individual. Experimental pain
can be produced in human subjects by cold pressor task
(CPT), a simple noninvasive procedure.[1] The amount
of pain perceived by an individual can be estimated in
Original Article
Pain response during fasting and postprandial conditions
in healthy young Indian males
Indu Saxena, Manoj Kumar1, Anjali Verma1
Department of Biochemistry, All India Institute of Medical Sciences, Jodhpur, Rajasthan, 1Department of Physiology,
Teerthanker Mahaveer Medical College and Research Centre, Teerthanker Mahaveer University, Uttar Pradesh, India
Received: : 8th September, 2014; Revised: 24th October, 2014; Accepted: 14th November, 2014
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Saxena, et al.: Pain response and fasting
International Journal of Clinical and Experimental Physiology| Oct-Dec 2014 | Vol 1 | Issue 4 263
International Journal of Clinical and Experimental Physiology| Oct-Dec 2014 | Vol 1 | Issue 4 262
MATERIALS AND METHODS
Selection of volunteers
The study protocol was approved by the Institute’s
Ethics Committee. This study was carried out in
Teerthanker Mahaveer Medical College, Moradabad,
during a period of 6 months. Convenience sample of
subjects was selected from student volunteers enrolled
at Teerthanker Mahaveer University, Moradabad. Since
only 26 females volunteered for the study compared to
150 male volunteers, the study was conducted on male
volunteers only.
Subjects of age 18–25 years and body mass index
between 18.5 and 24.9 kg/m2 were selected. Subjects
with self‑report of acute/chronic illness, history of bone
injury in the nondominant hand, or on antipyretic or
analgesic medicines were excluded from the study.
Subjects with resting pulse >90/min and resting blood
pressure >140/90 mm Hg were also not included in
the study, to eliminate subjects with preexperiment
sympathetic stimulation. After screening the volunteers
according to the mentioned inclusion and exclusion
criteria, 110 subjects were selected for the study. Written
informed consent was obtained from selected volunteers
before beginning the study. The participants were asked
to report at 8 am, at least 8‑h after last meal.
Estimation of plasma glucose
Two milliliter venous blood sample was taken from
each subject, 5 min before performing the CPT in fasting
and PP condition. Plasma glucose was estimated using
estimation kit from Reactivos GPL based on glucose
oxidase‑peroxidase method.
Subjects with fasting plasma glucose values of 70 mg/dl
or less were not included in the study as sympathetic
stimulation occurs at this level of blood glucose. This
ensured that the increase in heart rate and blood pressure
was solely due to experimental pain produced by CPT.
Observations from subjects with fasting plasma glucose
higher than 110 mg/dl or with ½‑h PP (1/2‑h PP) plasma
glucose higher than 200 mg/dl were excluded from
statistical analysis as such high glucose levels may be
due to impaired glucose tolerance.
Cold pressor task
The CPT was performed by the method described by
Kumar et al.,[2] on each subject in the fasting condition and
again, ½‑h after ingestion of 75 g glucose in 300 ml water.
Heart rate and blood pressure were recorded manually,
before and immediately after performing the CPT. Time
of immersion, pain threshold (time duration in seconds
after which subject first reported feeling pain), pain
tolerance (time duration in seconds for which the subject
tolerated the pain) was recorded using two separate stop
watches and pain rating was obtained on visual analogue
scale (amount of pain reported by the subject at the end
of CPT on a scale of 0 [no pain] to 10 [maximum pain
bearable]) from each subject, immediately after CPT.[1]
On the basis of plasma glucose level and time of
immersion during CPT, follwing subjects were excluded
from the study.
• Subjects with fasting plasma glucose lower than
70 mg/dl (12 subjects were excluded), or higher than
110 mg/dl (2 subjects were excluded)
• Subjects with ½‑h PP glucose higher than
200 mg/dl (5 subjects were excluded)
• Subjects with a total time of immersion <10 s during
CPT (5 subjects were excluded).
Statistical analysis of data
Data analysis was carried out on observations obtained
from 86 subjects using Microsoft Excel version 2007
(Microsoft Office, United States), and Student’s t‑test
was used to compare the data obtained in the fasting
and ½‑h PP states. The data have been presented as
mean ± standard deviation. SPSS version 14 (SPSS
Software Inc., Chicago, IL, USA) was used. Pearson’s
correlation analysis and multiple regression to establish
a relationship between blood glucose and PS parameters.
P < 0.05 was considered as significant.
RESULTS
Basal parameters recorded before conducting the
CPT are presented in Table 1. There was a significant
increase in pulse in the ½‑h PP condition. The mean
value of systolic blood pressure (SBP) decreased in the
½‑h PP condition, but this decrease was not significant.
A slight but significant decrease in resting diastolic blood
pressure (DBP) was observed in the ½‑h PP condition.
Cardiovascular reactivity on subjection to CPT was
recorded in terms of change in pulse (dPulse), SBP
(dSBP) and DBP (dDBP). Table 2 depicts the CVR
along with the PS (in terms of pain threshold, pain
tolerance and pain rating) in the fasting and ½‑h PP
Table 1: Basal parameters before performing the cold
pressor task
Parameters Fasting ½-h postprandial P
Plasma glucose (mg/dl) 85.57±12.01 150.80±14.69 <0.001
Pulse (/min) 77.58±7.46 81.63±7.09 <0.001
SBP (mm Hg) 123.47±8.82 121.91±9.11 0.256
DBP (mm Hg) 80.93±5.65 77.63±5.94 <0.001
SBP: Systolic blood pressure, DBP: Diastolic blood pressure. The
values are expressed in mean±SD. P > 0.05 was considered signicant.
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Saxena, et al.: Pain response and fasting
in blood pressure also occurs in normal young men. The
PP hypotension may also contribute to tachycardia.
Pain sensitivity decreased in the ½‑h PP condition as the
subjects showed higher threshold and tolerance. Blood
glucose was positively and significantly correlated with
pain threshold and tolerance. However, since there was
no significant correlation between blood glucose and
pain rating, increase in blood glucose did not affect the
pain rating. Multiple regression analysis [Table 4] showed
independent significant contribution of blood glucose on
pain threshold and tolerance during fasting and ½‑h PP
condition. Apparently, subjects tolerated pain for a longer
time with no increase in pain rating. Decreased PS during
PP state is probably responsible for the decrease CVR in
this state. Although the subject tolerated pain for a longer
duration, heart rate and blood pressure did not increase
in that proportion.
The increased histamine in the PP condition could have an
analgesic effect via the H3 receptor.[6,7] Carbohydrate‑rich
meal results in increased insulin level in blood, promoting
protein synthesis and leading to decreased amino acid level
in blood. Consequently, the permeability of blood‑brain
barrier to tryptophan increases, causing increased synthesis
of serotonin.[8] Serotonin inhibits pain transmission in the
dorsal horn of the spinal cord by the raphe spinal pathway
and increases the pain threshold.[9] Since serotonin is
anxiolytic, it may also decrease PS by relieving anxiety in
the PP state. Recently, sweet taste‑induced analgesia has
been demonstrated in humans by functional magnetic
resonance imaging.[10] Any or all of these factors may
contribute to the decreased PS in the PP state.
Limitation of the study
Due to the lack of sufficient numbers of female subjects,
this study was conducted on young male subjects only.
However, since the PS is different in males and females,[2]
the study needs to be performed on a larger scale
including subjects of both sexes.
CONCLUSION
Comparison of pain response in fasting and ½‑h PP states
depicts decreased PS without any corresponding increase
condition. The CVR decreased significantly in the
½‑h PP condition. Pain threshold and pain tolerance
increased significantly, and pain rating decreased
significantly in the ½‑h PP state. The interrelationship
between blood glucose and PS parameters during
fasting and ½‑h PP condition is presented in Table 3.
Blood glucose levels and PS parameters (pain threshold
and pain tolerance) were positively and significantly
correlated during fasting and ½‑h PP condition. Pain
rating was negatively but not significantly correlated
with blood glucose. Result of multiple regression
analysis demonstrated significant and independent
contribution of blood glucose level to pain threshold
and pain tolerance [Table 4].
DISCUSSION
Significant increase in resting pulse rate in ½‑h PP condition
is in accordance with the histamine‑induced PP tachycardia
reported in vertebrates.[4] Decrease in blood pressure
during PP state was due to the vasodilation produced by
histamine. PP hypotension has been reported in normal
geriatric population.[5] This study shows that PP decrease
Table 4: Multiple regression analysis of pain sensitivity parameters (as dependent variables) with blood glucose
levels (as independent variable) in fasting and ½-h postprandial condition
Parameters Fasting ½-h postprandial
Standardized regression
coefcient beta
95% CI PStandardized regression
coefcient beta
95% CI P
Lower limit Upper limit Lower limit Upper limit
Pain threshold 0.406 0.156 0.453 <0.001 0.514 0.248 0.530 <0.001
Pain tolerance 0.491 0.673 1.516 <0.001 0.578 0.787 1.483 <0.001
Pain rating −0.024 −0.029 0.024 >0.05 −0.020 −0.024 0.020 >0.05
P<0.05 was considered as signicant. CI: Condence interval
Table 3: Correlation between blood glucose and pain
sensitivity parameters
Parameters Fasting ½-h postprandial
r P r P
Pain threshold 0.406** <0.001 0.514** <0.001
Pain tolerance 0.491** <0.001 0.578** <0.001
Pain rating −0.024 >0.05 −0.020 >0.05
P<0.05 was considered as signicant
Table 2: Cardiovascular reactivity and pain sensitivity
data in fasting and ½-h postprandial conditions
Parameter Fasting Postprandial P
dPulse (/min) 7.67±6.55 3.23±2.26 <0.001
dSBP (mm Hg) 5.72±4.93 3.53±2.62 <0.001
dDBP (mm Hg) 5.53±4.39 4.07±3.57 0.02
Pain threshold (s) 23.97±8.99 28.92±11.11 0.002
Pain tolerance (s) 62.69±26.78 72.97±28.35 0.01
Pain rating (VAS) 6.60±1.47 6.09±1.48 0.02
dPulse: Change in pulse, dSBP: Change in systolic blood pressure,
dDBP: Change in diastolic blood pressure, VAS: Visual analogue scale. The
values are expressed in mean±SD. P > 0.05 was considered signicant
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Saxena, et al.: Pain response and fasting
in CVR in the PP state, suggesting that it is more difficult to
bear pain on an empty stomach with low blood glucose.
Persons with high PS may be advised to avoid complete
fasts during episodes of chronic or acute pain.
ACKNOWLEDGMENTS
Mr Manoj Kumar, Social Worker, Department of Community
Medicine, is gratefully acknowledged for his technical help.
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How to cite this article: Saxena I, Kumar M, Verma A. Pain
response during fasting and postprandial conditions in healthy
young Indian males. Int J Clin Exp Physiol 2014;1:262-5.
Source of Support: Financial aid from Teerthanker Mahaveer
Medical College and Research Centre, Conict of Interest: Nil.
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Physiology of pain itch and temperature Text Book of Medical Physiology
  • Gk Pal
Pal GK. Physiology of pain itch and temperature. In: Pal GK, Pravati P, Nanda N, editors. Text Book of Medical Physiology. 2nd ed. New Delhi: Ahuja Publishing House; 2011. p. 811-20.