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Objective Nociceptive Assessment in Ventilated ICU Patients: A Feasibility Study Using Pupillometry and the Nociceptive Flexion Reflex
Published on: July 4, 2018
Modulation of the human nociceptive flexion reflex by pleasant and unpleasant odors
Michelangelo Bartolo1, Mariano Serrao, Zurab Gamgebeli
1NeuroRehabilitation Unit, IRCCS Neurological Mediterranean Institute NEUROMED, Pozzilli, Isernia, Italy University Center for Adaptive Disorders and Head pain (UCADH), Pavia, Italy Neurorehabilitation Unit, "Sapienza" University of Rome Polo Pontino, Latina, Italy Rehabilitation Center, Policlinico Italia, Rome, Italy Laboratory of Nociceptive Psychophysiology, Casimiro Mondino National Institute of Neurology Foundation, IRCCS, Pavia, Italy Center of Audiology and Hearing Rehabilitation, Tbilisi, Georgia Tbilisi State Medical University, Tbilisi, Georgia IRCCS Neurological Mediterranean Institute NEUROMED, Pozzilli, Isernia, Italy Fondazione Don Gnocchi, Milan, Italy Headache Science Center, Casimiro Mondino National Institute of Neurology Foundation, IRCCS, Pavia, Italy Department of Public Health, Neuroscience, Experimental and Forensic Medicine, University of Pavia, Pavia, Italy.
Abstract:
The nociceptive withdrawal reflex (NWR), a defensive response that allows withdrawal from a noxious stimulus, is a reliable index of spinal nociception in humans. It has been shown that various kinds of stimuli (emotional, visual, auditory) can modulate the transmission and perception of pain. The aim of the present study was to evaluate, by means of the NWR, the modulatory effect on the spinal circuitry of olfactory stimuli with different emotional valence. The magnitude of the NWR elicited by electrical stimulation of the sural nerve was measured while 18 subjects (9 women, 9 men) smelled pleasant, unpleasant, or neutral odors. The NWR was conditioned by odor probe with interstimulus intervals (ISIs) of 500 ms and 1,500 ms. The magnitude of NWR was significantly greater after the unpleasant odor probe (P <.001) and reduced following the pleasant odor probe (P<.001) at both ISIs. A significant effect of olfactory stimuli on subjective pain ratings were found at both ISIs for pleasant vs unpleasant odors (P<.000), and for both pleasant and unpleasant odors vs neutral and basal conditions (P<.000). No statistical differences in subjective pain ratings at different ISIs were found. Consistent with the notion that NWR magnitude and pain perception can be modulated by stimuli with different emotional valence, these results show that olfactory stimuli, too, can modulate spinal nociception in humans.
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