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Time of Test (NB; 1=24 hours)

■threshold (t) ■ threshold (m)

Where: 0.75 is equivalent to 21:00 (Start. Day 1) 1.0 is equivalent to 24:00 / 00:00 1.25 is equivalent to 06:00 1.50 is equivalent to 12:00

1.75 is equivalent to 21:00 (Start Day 2) 2.00 is equivalent to 24:00 / 00:00

This experiment showed that plantar T-P thresholds, in both subjects demonstrated diurnal variation. Both subjects showed very similar T-P thresholds, and similar time related threshold changes through the daytime period (07:00 -19:00). There were clear diumal differences between thresholds recorded at 07:00 (Female: 4.57 +/- 0.11 log units; Male: 4.58 +/- 0.04 log units) and those recorded at 21:00 hours (Female: 4.05 +/- 0.15 log units; Male: 4.10 +/- 0.05 log units) (p <0.005 for both subjects, paired ‘t ’ tests; Table 34).

T-P thresholds in both subjects followed the same, time-related patterns of circadian variation (p > 0.15), returning to the same late evening start threshold (p > 0.15 for both subjects, paired ‘t ’ tests. Table 34) after 25 hours. The partem of T-P threshold change indicated circadian rhythmicity. Greatest skin sensitivity (minimum T-P threshold) was observed in the evening, from which point thresholds rose (T-P sensitivity decreased) to a maximum insensitivity approximately 12 hours later, after which thresholds declined (sensitivity increased) to the same evening value.

There was less agreement for tests made during the night. The male showed little variability of thresholds at the repeat test times on subsequent Saturday / Sunday nights. His thresholds made a very steep rise from 23:00 to 03:00, and a clear acrophase in his threshold partem was seen at around 03:00. In contrast, the female showed much greater variability of thresholds at

the repeat tests, a less steep rise in threshold between 23:00 and 03:00, and no real difference between thresholds recorded at 03:00, 07:00 and 11:00. Mean T-P thresholds, across all tests, at all test times for the male were slightly higher than those of the female (male: 4.35 +/- 0.102; female 4.25 +/0 0.083, log units +/- s.e.m)

2.2 CIRCADIAN RHYTHMS IN PIN PRICK PAIN THREHSOLDS

2.2.1; The Pattern of Change in Pin Prick Pain Thresholds, from Morning to Late Afternoon

The plantar mid sole (MLA and LLA) and palmar (MP and LP) skin of 29 subjects were tested to pii^rick pain threshold throughout 8 hours, with tests being made in the morning, at lunch time, and at the end of the aftemoon on the same day. Tests were carried out in

November and December.

Approx. Test Times Pin Prick Test Areas

09:00 13:00 17:00 MLA LLA MP LP

*/

Where: MLA Glabrous skin of the instep: plantar medial longitudinal arch LLA Glabrous skin: plantar lateral longitudinal arch

MP Glabrous skin of the medial (radial) palm LP Glabrous skin of the lateral (ulnar) palm

The sample variables are shown in Table 35

The skin at the mid-sole o f the foot and the palm of the hand were tested to pin prick pain threshold using the range of modified (metal tipped) aesthesiometer filaments, in the manner described in the Methods chapter. Subjects were asked to identify pin prick pain threshold by reporting when the tip stimulus became distinctly ‘pricking’ in nature, rather than just provoking a sensation of innocuous touch, or pressure. Threshold tests were made in the moming, and repeated in the middle of the day, and again in the late aftemoon. As in the touch-pressure tests, each subject acted as his own control.

When the time-related data was examined, it was seen that the pin prick pain thresholds in the glabrous skin of the feet and hands followed a pattern of time-related change, throughout the day, similar to that noted in the touch-pressure threshold experiments (Table 36). There was a gradual decline in pin prick pain thresholds from a morning high, to a late afternoon low. This was more marked in the feet than the hands (p< 0.01) (Graph 8).

The time-related threshold change was most clearly marked in plantar skin. Plantar

thresholds changed from 5.60 +/- 0.05 log units in the morning, to 5.49 +/- 0.06 log units at midday, to 5.41 +/- 0.06 log units in the late afternoon. There was an overall

thresholds between both the morning - lunchtime, and lunchtime - late afternoon tests were of significance (p am-md< 0.001; p ^d.pm <0.01) (Table 36).

Graph 8: Pin Prick Pain Thresholds in Plantar and Palmar Skin (NB: The error bars show ‘between subjects’ differences)

Pin Prick Pain Thresholds in Glabrous^Skin

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Time of Test 09-22 _{13:05 17:26}

Palmar skin showed the same trend, changing from thresholds of 5.64 +/- 0.05 log units in the morning, to 5.60 +/- 0.06 log units at midday, to 5.55 +/- 0.06 log units in the late afternoon. There was an overall threshold change to 82% of the morning values by the late afternoon test (p < 0.01) although the differences in thresholds between moming - lunchtime and lunchtime - late afternoon tests were not significant (p > 0.1) (Table 36).

The mid-sole threshold data was subdivided, to differentiate between functionally dissimilar

plantar skin sites - the weight bearing [lateral longitudinal arch; LLA] and non-weight bearing [medial longitudinal arch; MLA]. The palmar data was similarly divided into medial / radial palm [MP] and lateral / ulnar palm [LP], to reflect similar topographical (but now functionally similar) areas. The pin prick pain threshold data for the 3 test times for the sub-divisions of the plantar and palmar skin is shown in Graph 9 and Table 37.

The sub-divisions within all glabrous test sites all showed significantly lower pin prick threshold values at the late aftemoon tests (p < 0.05, Table 37), and all showed a steady fell in threshold throughout the test time. Thus, there was a pattern of change in thresholds to pin prick pain at all glabrous skin sites tested, but Student-Newman-Keul’s analysis showed that there was no clear difference in the amount of time-related change in pin prick thresholds at the various test sites. The LLA / MP / LP were together less sensitive than the MLA (p < 0.05) and MLA / LP / MP were together more sensitive than the LLA (p < 0.05).

Graph 9: Diurnal Changes in Pin Prick Thresholds of Plantar (MLA and LLA) and Palmar (MP and LP) Skin

(NB: Error bars show ‘between subjects’ differences)

Pin Prick Pain Thresholds of Glabrous Skin

MLA LLA M P

Skin Test Site

109:22 13:05 17:26

2.2.2; The Pattern of Change in Pin Prick Pain Thresholds, from Morning to Late Evening

13 subjects gave plantar and palmar pin prick threshold data every 4 hours from 09:00 to 22:00 hours throughout the day and evening, to indicate the time of the acrophase of the pattern of threshold change.

n Test Times Pin Prick Test Areas

09:00 13:00 17:00 22:00 MLA LLA MP LP

13 s/ V"

The data from the four test times is shown in Graph 10, and Table 38

The fall in pin prick pain thresholds from moming to aftemoon was followed by a rise in thresholds during the evening, and this trend was seen in both feet and hands, but was most marked in plantar skin (Graph 10). The fall in plantar thresholds between morning and midday tests was significant (0.10 +/- 0. 04 log units, p < 0.05, paired ‘t’ test), and the rise in threshold between late afternoon and evening was also significant (- 0.11 +/- 0.04 log units, p < 0.02 paired ‘t’ test). There was no significant change in plantar thresholds between the midday and late afternoon tests, and the palmar trend was not of significance between any of the tests.

Graph 10: Time Related Pin Prick Threshold Changes in Hantar and Palmar Skin (n=13) NB: Error bars indicate ‘betvveen subjects’ differences

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