Relatively few studies have examined the effects of nociception pe se on sympathetic nerve activity in awake healthy human subjects. Painful stimuli can produce differential responses from cutaneous and muscle postganglionic sympathetic neurones in the anaesthetised cat, and some animal and human studies suggest that nociceptive stimuli originating in different tissues may produce differential sympathetic effects- deep nociception causing vasodepressive and superficial nociception triggering an excitatory effect on cardiovascular state. It is important to understand how the sympathetic nervous system responds to nociception in healthy subjects in order to make more meaningful comparisons with the behaviour which occurs following damage to sympathetic pathways, e.g. nerve lesions (chronic regional pain syndromes) and spinal cord injury (autonomic dysreflexia (AD)). Additionally, it has been suggested that muscle spindles afferents may play a role in chronic pain, most notably the 'vicious cycle' of pain. While this has been investigated in animal studies, it has not been thoroughly investigated in healthy human subjects. Muscle spindle and sympathetic nerve activity from muscle and skin postganglionic neurones were directly recorded in healthy awake human subjects using microneurography; effector organ responses (blood pressure, heartrate, skin blood flow and sweat release) were recorded in both healthy and spinal cord injured subjects. Deep and superficial nociception was induced by intramuscular and subdermal injections of hypertonic saline given at unexpected times and in quasi-random order. Regardless of the origin of nociception (deep or superficial), general responses tended to be excitatory with increases seen in muscle and skin sympathetic nerve activity, heartrate, blood pressure and sweat release. A gender effect was noted regarding skin blood flow, with males largely showing decreases and females increases. No changes were noted in spindle firing rates and painful stimuli did not significantly increase effector organ responses in spinal cord injured subjects. Contrasting with previous studies, we did not see a differential sympathetic response or change in spindle firing rate to painful stimuli originating in different tissues. While it is believed that noxious stimuli trigger AD, we did not see exaggerated sympathetic responses in spinal cord injured subjects. More investigation is required regarding innocuous triggers of AD.
| Identifer | oai:union.ndltd.org:ADTP/258723 |
| Date | January 2009 |
| Creators | Burton, Alexander Robert, Clinical School - Prince of Wales Hospital, Faculty of Medicine, UNSW |
| Publisher | Awarded By:University of New South Wales. Clinical School - Prince of Wales Hospital |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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