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| 번호 | 제목 | 등록일 | 조회수 |
|---|---|---|---|
| 63 | Pudendal Nerve “Complete” Motor Latencies at Four Different Levels in the Anal Sphincter System in Young Adults [2002년 7월 DCR] | 2011-11-17 | 3474 |
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Tomoyuki Sato, M.D., Ph.D., Hideo Nagai, M.D., Ph.D.
From the Department of Surgery, Jichi Medical School, Tochigi-ken, Japan
PURPOSE: Pudendal nerve complete motor latency, or the sum of the conduction time from the root of the sacral nerve to the end of the pudendal nerve and the synaptic delay, varied in length (from shortest to longest) in the puborectalis, the deep external anal sphincter, and the superficial/subcutaneous
external anal sphincter, in that order, for middle-aged people. The aim of this study was to elucidate whether such a phenomenon was physiologic or pathologic. METHODS: In 20 young adults (21.9 +/- 1.37 years old, 10 females), pudendal nerve complete motor latencies were measured after magnetic stimulation to the sacral region. Electromyographic recordings
were taken at depths of 5, 3.8, 2.6, and 1.5 cm from the perineal skin using a needle electrode and at 3 cm from the anal verge using surface electrodes within the anal canal. The data were compared with the data of the middle-aged cohort (65.4 +/- 7.70 years old) in our previous study. RESULTS: The pudendal nerve complete motor latencies were 3.85 +/- 1.24 ms at 5 cm, 3.97 +/- 1.25 ms at 3.8 cm, 5.41 +/- 2.42 ms at 2.6 cm, 9.98 +/- 4.01 ms at 1.5 cm, and 3.45 +/- 0.52 ms while using
surface electrodes. The pudendal nerve complete motor latencies at 5, 3.8, and 2.6 cm were significantly shorter in the young adults than in the middle-aged subjects. The pudendal nerve complete motor latency using surface electrodes was significantly shorter than the pudendal nerve complete motor latency at 2.6 and 1.5 cm (mean +/- standard deviation). CONCLUSIONS: Because pudendal nerve complete motor latency was progressively longer at 5, 3.8, 2.6, and 1.5 cm, in that order, in young adults as well as in middle-aged people, this phenomenon was considered to be physiologic and may be mechanically reasonable and safe in shutting the anal canal and might be useful for milking the residual mucus out of the anal canal to prevent soiling. Aging disturbed the innervation of the upper three levels of the anal sphincter system. Pudendal nerve complete motor latency using intra-anal surface electrodes approximated that at the highest of the anal sphincters.
I nnervation of the anal sphincter skeletal muscle system is generally studied by the pudendal nerve
terminal motor latency (PNTML), which is recorded at the external anal sphincter (EAS) after an intrarectal electric stimulation of the pudendal nerve. The PNTML shows the sum of the conduction time of the terminal portion of the pudendal nerve distal to the ischial spine and the synaptic delay (the time of chemical transmission at the endplate) but cannot reflect the conduction time of the portion of the pudendal nerve proximal to the ischial spine. In addition, the PNTML cannot be recorded separately at the different parts of the anal sphincter skeletal muscle system, because various parts of the anal muscle system, including the puborectalis, the deep EAS, the superficial EAS, and the subcutaneous EAS, are studied together using surface electrodes inside the anal canal to measure the evoked potentials. We previously developed a method to measure the total conduction time from the root of the sacral nerve to the end of the pudendal nerve and the synaptic delay separately at four different levels of the anal sphincter skeletal muscle system using sacral magnetic stimulation and a concentric needle electrode.2 These motor latencies reflected the function of the complete length of the pudendal nerve and are thus called a pudendal nerve complete motor latency (PNCML), which can be measured separately at the puborectalis muscle, the deep EAS, the superficial EAS, and the subcutaneous EAS. These measurements are accomplished by using a concentric needle electrode in the anal sphincter skeletal muscle system that is appropriately withdrawn in a stepwise manner. In our previous study of normal middle-aged people, the PNCML varied depending on the level from
the perineal skin and was considered to be progressively longer in the puborectalis, the deep EAS, and the superficial/subcutaneous EAS. However, we did not know whether such variations in the PNCMLs were physiologic or pathologic, i.e., whether they indicated a subclinical deterioration in innervation induced by aging or not, because the data in that study were obtained only in middle-aged people. That article indicated that this question would be answered when healthy younger subjects were examined. Thus, the aim of this study is to answer this question using healthy young adult volunteers. DISCUSSION
PNTML can estimate the function of the terminal part of the pudendal nerve distal to the ischial spine. On the other hand, PNCML can estimate the function of the complete length of the pudendal nerve, given
that the root of the sacral nerve is stimulated by magnetic stimulation. Furthermore, PNCML can separately determine the conduction velocity present at each part of the anal sphincter system and thereby allow an estimation of the innervation to each part of this system,2 although the conduction velocity present at the puborectalis may reflect direct innervation from S-2–S-3 to the puborectalis (i.e., not through Alcock’s canal). In our previous study of middle-aged subjects, the PNCML was progressively longer in the puborectalis,
the deep EAS, and the superficial EAS/the subcutaneous EAS, in that order. One suspected reason was that the conduction velocity of neurons varies in accordance with their axonal diameter (specifically, the greater the diameter of the axon, the faster its conduction velocity)4 and that the branch neurons separately innervating parts of the anal sphincter system may have different diameters. Another reason was aging. In that study, however, we did not know whether the variation in PNCMLs indicated a subclinical deterioration in the state of the nerves induced by aging. Because the PNCML became progressively longer from level A to level D in younger adults as well as in
middle-aged subjects, this phenomenon must be physiologic and not pathologic. If the root of the nerves innervating the anal sphincter system was simultaneously excited, the anal sphincters would start to contract around the anal canal one after the other beginning with the puborectalis, the deep EAS, the superficial EAS, and continuing to the subcutaneous EAS within a few milliseconds, as if the anal sphincter functions to milk the residual mucus out of the anal canal. This mechanism may serve as a preventive action against soiling—a physiologic “sweeping brush.” We do not believe that the milking mechanism conflicts with the sampling reflex (which involves anal sphincter contraction to prevent matter leaking from the anal canal) because the sampling reflex occurs at the most superior portion of anal canal, whereas the milking mechanism occurs in the anal canal distal to the site of the sampling reflex. In addition, the sequential closure of the anal canal beginning with the puborectalis muscle may prevent the distal anal sphincter system from damage. That is, the distal sphincters might be destroyed by anal pressure to be released if the larger proximal sphincter such as the puborectalis muscle contracted after the distal sphincters had already contracted to close the lower level of the anal canal. Because PNCML was shorter at the upper three levels in young adults than in middle-aged people,
aging was believed to disturb the innervation of the upper three levels of the anal sphincter system. The manner of deterioration in PNCML induced by aging was not similar to that induced by vaginal delivery, which only damaged the upper two innervations of the anal sphincter system in our previous study. However, there was a similarity between the two events in that innervation to the lowest level or a sphincter considered to be the subcutaneous EAS was not disturbed. The above facts may also suggest that the two events share a similar mechanism, which for vaginal deliveries has previously been shown to be a stretching injury of the pudendal nerve. The pudendal nerve may be stretched daily and may be injured during normal defecation, in which the intensity of stretching of the pudendal nerve is much weaker than during vaginal delivery but is much more frequent. Thus, the manner of deterioration in the innervation between birth and aging may be similar in some respects and different in others. PNCML using the surface electrodes within the anal canal may represent the shortest PNCML or the
PNCML of the largest evoked potential within the pelvic floor musculature. That is why PNCML S approximated PNCML A. The PNCML procedure using surface electrodes may be the alternative to the PNCML at the largest muscle in the pelvic floor using a concentric needle electrode. The PNCML, using a concentric needle electrode, has the following characteristics and features. First,
PNCML can be a valuable tool to differentiate physiologic processes of the pelvic floor from pathologic conditions in some patients. Second, PNCML can index the severity of neurologic disturbance in the pelvic floor because PNCML can identify which innervation to the anal sphincter system was injured. Third, the above information might become useful for treating and preventing pelvic floor disturbances in the future. |
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