Cardiac cycle related modulation of electrocutaneous pain and tactile stimuli
thesisposted on 17.02.2014 by Mary Wilkinson
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Research suggests hypertension is associated with reduced somatosensory perception. Further, natural fluctuations in blood pressure (BP) across the cardiac cycle have been shown to modulate nociceptive responding, pain and tactile sensitivity, suggesting that arterial baroreceptors may be important moderators of somatosensation. This thesis further examined the influence of natural fluctuations in BP, and thus baroreceptor activity, across the cardiac cycle on electrocutaneous pain and tactile sensory thresholds and pain-related evoked potentials (PREPs) in normotensive individuals. Study 1 found pain thresholds were higher, i.e. pain was reduced, during systole compared to diastole. Further analysis revealed only participants with low-normal systolic BP displayed this cardiac cycle modulation, suggesting tonic BP may moderate cardiac cycle-related pain modulation. In the second study, tactile sensory thresholds did not vary across the cardiac cycle. However, when participants were split into high-normal and low-normal BP groups, interactions between BP and tactile sensory thresholds across the cardiac cycle were revealed. This finding suggests tonic BP may be an important factor determining the cardiac cycle modulation of tactile sensation. Study 3 found no variation in the N2 or P2 peak amplitudes, or N2-P2 peak-to-peak amplitudes across the cardiac cycle at scalp recording sites Cz, C3, or C4. Furthermore, BP median split analyses revealed no BP Group or interaction effect. As previous work reported a systolic dampening of PREPs, these data suggest the cardiac cycle-related modulation of PREPs may not be as robust as other measures of pain such as the nociceptive flexion reflex. Study 4 reported, in line with Study 3, no cardiac cycle related modulation of PREPs following stimulation of the right and left hands. However, a Hand × Scalp Electrode Site × Interval interaction was revealed for N2 peak amplitudes. These data suggest that the combination of side of stimulation and scalp recording site may be important in determining the patterning of PREPs across the cardiac cycle. Taken together, the findings of these studies suggest that pain perception, and to a lesser extent tactile sensation, are influenced by natural variations in BP across the cardiac cycle. However, modulation appears dependent on tonic BP. Conversely, pain-related brain activity across the cardiac cycle was not affected by tonic BP, but may be influenced by the combination of stimulation and recording sites.
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