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Local thermal stimulation relaxes hypertonic anal sphincter

Evidence of somatoanal reflex


PURPOSE: Although it is generally believed that warm perineal baths reduce pain resulting from anal fissure, complicated hemorrhoids, or anal surgery, the exact mechanisms remain unclear. Because hypertonicity of the internal anal sphincter contributes to increasing pain in these conditions, it has been postulated that warm perineal baths could help to relax the anal sphincter, hence reducing pain. It is our purpose to demonstrate response of the anal sphincter to local thermal stimulationvia a somatoanal reflex. METHODS: Continuous anorectal manometry tracings were obtained from 15 healthy volunteers, 22 patients with hemorrhoid, and 20 patients with anal fissure. Local thermal stimulation was achieved by applying a heat pad on the right infragluteal region (local area), and subsequently on the right first interphalangeal region (control area). RESULTS: Obvious response to local thermal stimulation was shown by 13.3 percent of volunteers, 36.4 percent of patients with hemorrhoid, and 60 percent of patients with fissure. Heat-sensitive patients who responded to local thermal stimulation were divided to two groups, those with ultraslow waves and those without ultraslow waves. In patients with ultraslow waves, the amplitude of ultraslow waves decreased significantly after local thermal stimulation, with amplitude before local thermal stimulation, (mean ± standard deviation) 66.2±30.6 mmHg, and during local thermal stimulation, 43.2±22.3 mmHg, respectively,P=0.003. By contrast, in patients without ultraslow waves, the tonic pressure measured before local thermal stimulation and during local thermal stimulation was 74.2±23.5 and 60.5±18.5 mmHg, respectively,P=0.001. The response began at approximately three minutes after local thermal stimulation when the skin temperature was 42.1±0.3°C. No anal response was observed when the heat pad was applied to the control area. The maximum resting pressure of the heat-sensitive patients was significantly higher than that of the nonresponding patients (97.3±0.1vs. 76.9±23.3 mmHg;P=0.012). CONCLUSIONS: Local thermal stimulation evokes relaxation of the hypertonic internal anal sphincter through a somatoanal reflex, thus providing an easy and feasible method of clinical application.

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  1. 1.

    Corman ML. Colon and rectal surgery. 3rd ed. Philadelphia: JB Lippincott, 1993:121.

    Google Scholar 

  2. 2.

    Corman ML. Colon and rectal surgery. 3rd ed. Philadelphia: JB Lippincott, 1993:78.

    Google Scholar 

  3. 3.

    Gordon PH, Nivatvongs S. Principles and practice of surgery for the colon, rectum, and anus. St. Louis: Quality Medical Publishing, 1992;195–6

    Google Scholar 

  4. 4.

    Gibbons CP, Read NW. Anal hypertonia in fissure: cause or effect? Br J Surg 1986;73:443–5.

    Google Scholar 

  5. 5.

    Hancock BD. The internal sphincter and anal fissure. Br J Surg 1977;64:92–5.

    Google Scholar 

  6. 6.

    Waldron DJ, Kumar D, Hallan RI, Williams NS. Prolonged ambulatory assessment of anorectal function in patients with prolapsing hemorrhoids. Dis Colon Rectum 1989;32:968–74.

    Google Scholar 

  7. 7.

    Farouk R, Duthie GS, MacGregor AB, Bartolo DC. Sustained internal sphincter hypertonia in patients with chronic anal fissure. Dis Colon Rectum 1994;37:424–9.

    Google Scholar 

  8. 8.

    Pinho M, Correa JC, Furtado A, Ramos JR. Do hot baths promote anal sphincter relaxation? Dis Colon Rectum 1993;36:273–4.

    Google Scholar 

  9. 9.

    Shafik A. Role of warm-water bath in anorectal conditions. J Clin Gastroenterol 1993;16:304–8.

    Google Scholar 

  10. 10.

    Gowers WR. The autonomic action of the sphincter ani. Proc R Soc Med 1877;26:77–81.

    Google Scholar 

  11. 11.

    Shuster MM, Hookman P, Hendrix TR, Mendeloff AI. Simultaneous manometric recording of internal and external anal sphincter reflexes. Bull Johns Hopkins Hosp 1965;116:79–88.

    Google Scholar 

  12. 12.

    Kamm MA, Lennard-Jones JE, Nicholls RJ. Evaluation of the intrinsic innervation of the internal anal sphincter using electrical stimulation. Gut 1989;30:935–8.

    Google Scholar 

  13. 13.

    Ihre T. Studies on anal function in continent and incontinent patients. Scan J Gastroenterol 1974;25:1–64.

    Google Scholar 

  14. 14.

    Duthie GS, Miller R, Bartolo DC. Internal anal sphincter electromyographic frequency is related to anal canal resting pressure. Both are reduced in idiopathic faecal incontinence [abstract]. Gut 1990;31:A619.

    Google Scholar 

  15. 15.

    Vela AR, Rosenberg AJ, Anorectal manometry: a new simplified technique. Am J Gastroenterol 1982;77:468–90.

    Google Scholar 

  16. 16.

    Sangwan YP, Coller JA, Schoetz DJ Jr, Roberts PL, Murray JJ. Relationship between manometric anal waves and fecal incontinence. Dis Colon Rectum 1995;38:370–4.

    Google Scholar 

  17. 17.

    Schouten WR, Blankensteijn JD. Ultraslow wave pressure variations in the anal canal before and after lateral sphincterotomy. Int J Colorectal Dis 1992;7:115–8.

    Google Scholar 

  18. 18.

    Gordon PH, Nivatvongs S. Principles and practice of surgery for the colon, rectum, and anus. St. Louis: Quality Medical Publishing, 1992;13.

    Google Scholar 

  19. 19.

    Henry MM, Swash M. Coloproctology and the pelvic floor. Oxford: Butterworth-Neinemann, 1992;42–3.

    Google Scholar 

  20. 20.

    Wankling WJ, Brown BH, Collins CD, Duthie HL. Basal electrical activity in the anal canal in man. Gut 1968;9:457–60.

    Google Scholar 

  21. 21.

    Hancock BD. Measurement of the anal pressure and motility. Gut 1976;17:645–51.

    Google Scholar 

  22. 22.

    Frenckner B, von Euler C. Influence of pudendal block on the function of the anal sphincters. Gut 1975;16:482–9.

    Google Scholar 

  23. 23.

    Horvath KD, Whelan RL, Golub RW, Ahsan H, Cirocco WC. Effect of catheter diameter on resting pressures in anal fissure patients. Dis Colon Rectum 1995;38:728–31.

    Google Scholar 

  24. 24.

    Nagasaki A, Ikeda K, Sumitomo K. Rectoanal reflex induced by H2O thermal stimulation. Dis Colon Rectum 1989;32:765–8.

    Google Scholar 

  25. 25.

    Miller R, Lewis GT, Bartolo DC, Cervero F, Mortensen NJ. Sensory discrimination and dynamic activity in the anorectum: evidence using a new ambulatory technique. Br J Surg 1988;75:1003–7.

    Google Scholar 

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Correspondence to Jen-Hwey Chiu M.D., Ph.D..

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Jiang, JK., Chiu, JH. & Lin, JK. Local thermal stimulation relaxes hypertonic anal sphincter. Dis Colon Rectum 42, 1152–1159 (1999).

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Key words

  • Warm perineal bath
  • Local thermal stimulation
  • Anorectal manometry
  • Somatoanal reflex