Contact Heat Evoked Potentials in Knowledge Workers and Unskilled Labors
The study of contact heat evoked potentials (CHEPs) has gained significant attention in recent years due to its ability to evaluate the function of small nerve fibers, particularly Ad fibers. CHEPs are generated by applying heat-pain stimuli to the skin surface, which elicits cerebral electroencephalographic responses. These responses are characterized by parameters such as N2 latency, P2 latency, and N2-P2 amplitude. The technique is considered simpler, safer, and more objective compared to other methods like laser evoked potentials for assessing peripheral small nerve fiber function.
Small-fiber neuropathy (SFN) is a condition that affects small diameter unmyelinated C fibers and thinly myelinated Ad fibers, resulting from various etiologies. The assessment of intraepidermal nerve fiber density (IENFD) through skin biopsy has been a significant advancement in diagnosing SFN. CHEPs have been shown to correlate well with IENFD, making them an important diagnostic tool for SFN. Normal values of CHEPs have been established in several studies, facilitating the diagnosis of SFN. However, the impact of different factors such as gender, age, and body height on CHEP parameters remains controversial. Additionally, the effect of occupation on CHEP parameters has not been thoroughly investigated until now.
This study aimed to explore the differences in CHEP parameters between knowledge workers and unskilled laborers. The hypothesis was that occupation might influence CHEP results due to differences in physical activity, exposure to environmental factors, and habituation to pain. The study involved 137 healthy participants recruited between November 20, 2014, and December 31, 2016. Participants were divided into two groups: knowledge workers and unskilled laborers. Knowledge workers included teachers, physicians, college students, lawyers, accountants, and programmers, while unskilled laborers included builders, cleaners, chefs, soldiers, and lathemen.
All participants underwent a comprehensive evaluation, including neurologic examination, laboratory tests, and nerve conduction studies (NCS) to ensure eligibility. The CHEP test was performed on four body sites: the upper border of the distal third of the volar forearm, the upper border of the distal third of the lateral leg, the spinous process of the seventh cervical vertebrae (C7), and the spinous process of the 12th thoracic vertebrae (T12). The CHEP stimulator used a thermode to deliver heat pulses, increasing the temperature from 32°C to 51°C at a rate of 70°C/s. The electrodes were placed on Cz and Fz according to the international 10-20 system, and the recordings were analyzed using the Keypoint EMG system.
The results showed significant differences in CHEP parameters between knowledge workers and unskilled laborers. Specifically, the “N2 latency/height” and “P2 latency/height” on the volar forearm of unskilled laborers were significantly prolonged compared to those of knowledge workers. Similarly, the “N2 latency/height” and “P2 latency/height” in the distal leg of unskilled laborers were significantly prolonged, and the N2-P2 amplitude was significantly decreased compared to knowledge workers. However, no significant differences were observed at the spinous process of C7 and T12 between the two groups.
The study’s findings suggest that unskilled laborers may have a higher vulnerability to injury and a greater habituation to pain, leading to prolonged N2 and P2 latencies and decreased N2-P2 amplitudes. The thicker keratoderma in unskilled laborers could also contribute to the reduced N2-P2 amplitude. The differences in CHEP parameters were more pronounced in the distal forearm and leg, which are more exposed to external environmental factors compared to the C7 and T12 regions.
The study also discussed the potential reasons for these differences. Unskilled laborers, who are often exposed to more physical strain and environmental hazards, may have fewer activated Ad fibers or slower conduction velocities when confronted with nociceptive stimuli. Additionally, the activity of pain-related brain areas, such as the insula, thalamus, and secondary somatosensory cortices, might be reduced in unskilled laborers. These factors could collectively contribute to the observed differences in CHEP parameters.
The study’s findings have important implications for understanding the impact of occupation on small nerve fiber function. By highlighting the differences in CHEP parameters between knowledge workers and unskilled laborers, the study underscores the need for further research to explore the underlying mechanisms. Functional brain imaging studies could provide additional insights into the pain-related brain activity in different occupational groups.
In conclusion, this study is the first to investigate the effect of occupation on CHEP parameters. The results indicate that unskilled laborers have significantly prolonged N2 and P2 latencies and decreased N2-P2 amplitudes in the distal leg and volar forearm compared to knowledge workers. These findings suggest that occupation plays a role in influencing small nerve fiber function, as assessed by CHEPs. Further studies are needed to confirm these results and explore the potential mechanisms underlying these differences.
doi.org/10.1097/CM9.0000000000000681
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