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Supportive tissues of the vagina with special reference to a fibrous skeleton in the perineum: A review

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DOI: 10.4236/ojog.2014.43025    3,340 Downloads   4,910 Views   Citations

ABSTRACT

With the aid of immunohistochemistry, the present review attempts to demonstrate the composite fibers and nerve topographical anatomy in the vaginal supportive tissues. Along the tendinous arch of the pelvic fasciae, distal parts of the pelvic plexus extend antero-inferiorly and issue nerves to the internal anal sphincter as well as the cavernous tissues. At the attachment of the levator ani muscle to the rectum, smooth muscles in the endopelvic fascia lining the levator ani merge with the longitudinal smooth muscle layer of the rectum to provide the conjoint longitudinal muscle coat or the longitudinal anal muscle (LAM: smooth muscle). However, at the rectovaginal interface, the longitudinal smooth muscle layer of the rectum continues to the LAM without any contribution of the endopelvic fascia. The bilateral masses of the perineal smooth muscles (PSMs) are connected by the perineal body, and the PSMs receive 1) the longitudinal anal muscle, 2) the internal and external anal sphincters and, 3) the perineal membrane lining the vestibular wall. Tensile stress from the levator ani seems to be transferred to the PSMs via the LAM. Because of their irregularly arrayed muscle fibers, instead of a synchronized contraction in response to nerve impulses, the PSMs are likely to act as a barrier, septum or protector against mechanical stress because, even without innervation, such smooth muscle fibers resist (not absorb) pressure, in accordance with Bayliss’ rule. The external anal sphincter, a strong striated muscle, inserts into the PSMs and seems to play a dynamic role in supporting the rectovaginal interface to maintain the antero-posterior length of the urogenital hiatus. However, we do not think that smooth muscles play an active traction role without cooperation from striated muscle. The fibrous skeleton composed of smooth muscle in the female perineum is explained in terms of a “catamaran” model.

Conflicts of Interest

The authors declare no conflicts of interest.

Cite this paper

Sasaki, H. , Hinata, N. , Kurokawa, T. and Murakami, G. (2014) Supportive tissues of the vagina with special reference to a fibrous skeleton in the perineum: A review. Open Journal of Obstetrics and Gynecology, 4, 144-157. doi: 10.4236/ojog.2014.43025.

References

[1] DeLancey, J.O. and Starr, R.A. (1990) Histology of the connection between the vagina and levator ani muscles. Implications for urinary tract function. The Journal of Reproductive Medicine, 35, 765-771.
[2] De Lancey, J.O. (1992) Anatomic aspects of vaginal eversion after hysterectomy. American Journal of Obstetrics & Gynecology, 166, 1717-1728.
[3] DeLancey, J.O. (1993) Anatomy and biomechanics of genital prolapse. Clinical Obstetrics and Gynecology, 36, 897-909. http://dx.doi.org/10.1097/00003081-199312000-00015
[4] Oelrich, T.M. (1983) The striated urogenital sphincter muscle in the female. Anatomy & Physiology, 205, 223-232. http://dx.doi.org/10.1002/ar.1092050213
[5] Soga, H., Nagata, I., Murakami, G., Yajima, T., Takenaka, A., Fujisawa, M. and Koyama, M. (2007) A histotopographic study of the perineal body in elderly women: The surgical applicability of novel histological findings. International Urogynecology Journal and Pelvic Floor Dysfunction, 18, 1423-1430. http://dx.doi.org/10.1007/s00192-007-0380-2
[6] Hudson, C.N., Sohaib, S.A., Shulver, H.M. and Reznek, R.H. (2002) The anatomy of the perineal membrane: Its relationship to injury in childbirth and episiotomy. Australian and New Zealand Journal of Obstetrics and Gynaecology, 42, 193-196. http://dx.doi.org/10.1111/j.0004-8666.2002.00193.x
[7] Stein, T.A. and DeLancey, J.O. (2008) Structure of the perineal membrane in females: Gross and microscopic anatomy. Obstetrics & Gynecology, 111, 686-693. http://dx.doi.org/10.1097/AOG.0b013 e318163a9a5
[8] Kato, M., Matsubara, A., Murakami, G., Abe, S., Ide, Y., Sato, I. and Usui, T. (2008) Female perineal membrane: A study using pelvic floor semiserial sections from elderly nulliparous and multiparous women. International Urogynecology Journal and Pelvic Floor Dysfunction, 19, 1663-1670.
http://dx.doi.org/10.1007/s00192-008-0701-0
[9] Hinata, N., Murakami, G., Abe, S., Shibata, S., Morizane, S., Honda, M., Isoyama, T., Sejima, T. and Takenaka, A. (2013) Coexistence of elastic fibers with hyaluronic acid in the human urethral sphincter complex: A histological study. Journal of Urology, 190, 1313-1319. http://dx.doi.org/10.1016/j.juro. 2013.04.023
[10] Donker, P.J. (1986) A study of the myelinated fibres in the branches of the pelvic plexus. Neurourology and Urodynamics, 5, 185-202. http://dx.doi.org/10.1002/nau.1930050207
[11] Ball Jr., T.P., Teichman, J.M., Sharkey, F.E., Rogenes, V.J. and Adrian Jr., E.K. (1997) Terminal nerve distribution to the urethra and bladder neck: Considerations in the management of stress urinary incontinence. Journal of Urology, 158, 827-829. http://dx.doi.org/10.1016/S0022-5347(01)64329-5
[12] Niikura, H., Katahira, A., Utsunomiya, H., Takano, T., Ito, K., Nagase, S., Yoshinaga, K., Tokunaga, H., Toyoshima, M., Kinugasa, Y., Uchiyama, E., Murakami, G., Yabuki, Y. and Yaegashi, N. (2007) Surgical anatomy of intrapelvic fasciae and vesico-uterine ligament in nervesparing radical hysterectomy with fresh cadaver dissections. Tohoku Journal of Experimental Medicine, 212, 403-413.
http://dx.doi.org/10.1620/tjem.212.403
[13] Kinugasa, Y., Arakawa, T., Abe, H., Rodriguez-Vazquez, J.F., Murakami, G. and Sugihara, K. (2013) Female longitudinal anal muscles or conjoint longitudinal coats extend into the subcutaneous tissue along the vaginal vestibule: A histological study using human fetuses. Yonsei Medical Journal, 54, 778-784. http://dx.doi.org/10.3349/ymj.2013.54.3.778
[14] Trotter, J.A. (1993) Functional morphology of force transmission in skeletal muscle. A brief review. Acta Anatomica (Basel), 146, 205-222. http://dx.doi.org/10.1159/000147459
[15] Huijing, P.A. (1999) Muscle as a collagen fiber reinforced composite: a review of force transmission in muscle and whole limb. Journal of Biomechanics, 32, 329-345. http://dx.doi.org/10.1016/S0021-9290(98)00186-9
[16] Purslow, P.P. (2002) The structure and functional significance of variations in the connective tissue within muscle. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 133, 947-966. http://dx.doi.org/10.1016/S1095-6433(02)00141-1
[17] Osanai, H., Rodriguez-Vazquez, J.F., Abe, H., Murakami, G., Ohguro, H. and Fujimiya, M. (2011) Fetal check ligament connected between the conjunctiva and the medial and lateral recti. Investigative Ophthalmology & Visual Science, 52, 7175-7179. http://dx.doi.org/10.1167/iovs.11-7426
[18] Benjamin, M., Toumi, H., Ralphs, J.R., Bydder, G., Best, T.M. and Milz, S. (2006) Where tendons and ligaments meet bone: Attachment sites (‘enthuses’) in relation to exercise and/or mechanical load. Journal of Anatomy, 208, 471-490. http://dx.doi.org/10.1111/j.1469-7580.2006.00540.x
[19] Williams, P.L. (1995) Gray’s anatomy. Churchill Livingstone, New York.
[20] Arakawa, T., Murakami, G., Nakajima, F., Matsubara, A., Ohtsuka, A., Goto, T. and Teramoto, T. (2004) Morphologies of the interfaces between the levator ani muscle and pelvic viscera, with special reference to muscle insertion into the anorectum in elderly Japanese. Anatomical Science International, 79, 72-81. http://dx.doi.org/10.1111/j.1447-073x.2004.00069.x
[21] Hieda, K., Cho, K.H., Arakawa, T., Fujimiya, M., Murakami, G. and Matsubara, A. (2013) Nerves in the intersphincteric space of the human anal canal with special reference to their continuation to the enteric nerve plexus of the rectum. Clinical Anatomy, 26, 843-854. http://dx.doi.org/10.1002/ ca.22227
[22] Macchi, V., Porzionato, A., Stecco, C., Vigato, E., Parenti, A. and De Caro, R. (2008) Histo-topographic study of the longitudinal anal muscle. Clinical Anatomy, 21, 447-452. http://dx.doi.org/10.1002/ ca.20633
[23] Kannus, P. (2000) Structure of the tendon connective tissue. Scandinavian Journal of Medicine & Science in Sports, 10, 312-320. http://dx.doi.org/10.1034/j.1600-0838.2000.010006312.x
[24] Ritty, T.M., Ditsios, K. and Starcher, B.C. (2002) Distribution of the elastic fiber and associated proteins in flexor tendon reflects function. The Anatomical Record, 268, 430-440.
http://dx.doi.org/10.1002/ar.10175
[25] Stecco, C., Porzionato, A., Macchi, V., Tiengo, C., Parenti, A., Aldegheri, R., Delmas, V. and De Caro, R. (2006) Histological characteristics of the deep fascia of the upper limb. Italian Journal of Anatomy and Embryology, 111, 105-110.
[26] Ochala, J., Frontera, W.R., Dorer, D.J., Van Hoecke, J. and Krivickas, L.S. (2007) Single skeletal muscle fiber elastic and contractile characteristics in young and older men. Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 62, 375-381. http://dx.doi.org/10.1093/gerona/62.4.375
[27] Kono, R., Poukens, V. and Demer, J.L. (2002) Quantitative analysis of the structure of the human extraocular muscle pulley system. Investigative Ophthalmology & Visual Science, 43, 2923-2932.
[28] Miller, J.L., Watkin, K.L. and Chen, M.F. (2002) Muscle, adipose, and connective tissue variations in intrinsic musculature of the adult human tongue. Journal of Speech Language and Hearing Research, 45, 51-65. http://dx.doi.org/10.1044/1092-4388(2002/004)
[29] Murakami, G., Nakajima, F., Sato, T.J., Tsugane, M.H., Taguchi, K. and Tsukamoto, T. (2002) Individual variations in aging of the male urethral rhabdosphincter in Japanese. Clinical Anatomy, 15, 241-252. http://dx.doi.org/10.1002/ca.10015
[30] Hahn, M.S., Kobler, J.B., Starcher, B.C., Zeitels, S.M. and Langer, R. (2006) Quantitative and comparative studies of the vocal fold extracellular matrix. I: Elastic fibers and hyaluronic acid. Annals of Otology, Rhinology, and Laryngology, 115, 156-164.
[31] Korn, G.P., Martins, J.R., Park, S.W., Mendes, A., Kobayashi, E.Y., Nader, H.B. and De Biase, N.G. (2011) Concentration of hyaluronic acid in human vocal folds in young and old subjects. Otolaryngology—Head and Neck Surgery, 145, 981-986. http://dx.doi.org/10.1177/01945998114 19457
[32] Kawase, T., Shibata, S., Katori, Y., Ohtsuka, A., Murakami, G. and Fujimiya, M. (2012) Elastic fiber-mediated enthesis in the human middle ear. Journal of Anatomy, 221, 331-340.
http://dx.doi.org/10.1111/j.1469-7580.2012.01542.x
[33] Hirata, E., Fujiwara, H., Hayashi, S., Ohtsuka, A., Abe, S., Murakami, G. and Kudo, Y. (2011) Intergender differences in histological architecture of the fascia pelvis parietalis: A cadaveric study. Clinical Anatomy, 24, 469-477. http://dx.doi.org/10.1002/ca.21042
[34] Zhu, L., Lang, J., Feng, R., Chen, J. and Wong, F. (2004) Estrogen receptor in pelvic floor tissues in patients with stress urinary incontinence. International Urogynecology Journal and Pelvic Floor Dysfunction, 15, 340-343.
[35] Mauroy, B., Goullet, E., Stefaniak, X., Bonnal, J.L. and Amara, N. (2000) Tendinous arch of the pelvic fascia: Application to the technique of paravaginal colposuspension. Surgical and Radiologic Anatomy, 22, 73-79. http://dx.doi.org/10.1007/s00276-000-0073-8
[36] Delancey, J.O. (2002) Fascial and muscular abnormalities in women with urethral hypermobility and anterior vaginal wall prolapse. American Journal of Obstetrics and Gynecology, 187, 93-98.
[37] Pit, M.J., De Ruiter, M.C., Lycklama, A.N.A.A., Marani, E. and Zwartendijk, J. (2003) Anatomy of the arcus tendineus fasciae pelvis in females. Clinical Anatomy, 16, 131-137. http://dx.doi.org/10.1002/ ca.10102
[38] Albright, T.S., Gehrich, A.P., Davis, G.D., Sabi, F.L. and Buller, J.L. (2005) Arcus tendineus fascia pelvis: A further understanding. American Journal of Obstetrics and Gynecology, 193, 677-681.
[39] Tamakawa, M., Murakami, G., Takashima, K., Kato, T. and Hareyama, M. (2003) Fascial structures and autonomic nerves in the female pelvis: A study using macroscopic slices and their corresponding histology. Anatomical Science International, 78, 228-242. http://dx.doi.org/10.1046/j.0022-7722. 2003.00061.x
[40] Nagata, I., Murakami, G., Suzuki, D., Furuya, K., Koyama, M. and Ohtsuka, A. (2007) Histological features of the rectovaginal septum in elderly women and a proposal for posterior vaginal defect repair. International Urogynecology Journal, 18, 863-868. http://dx.doi.org/10.1007/s00192-006-0249-9
[41] Takenaka, A., Hara, R., Soga, H., Murakami, G. and Fujisawa, M. (2005) A novel technique for approaching the endopelvic fascia in retropubic radical prostatectomy, based on an anatomical study of fixed and fresh cadavers. BJU International, 95, 766-771.
[42] Hirata, E., Koyama, M., Murakami, G., Ohtsuka, A., Abe, S., Ide, Y., Fujiwara, H. and Kudo, Y. (2011) Comparative histological study of levels 1-3 supportive tissues using pelvic floor semiserial sections from elderly nulliparous and multiparous women. Journal of Obstetrics and Gynaecology Research, 37, 13-23. http://dx.doi.org/10.1111/j.1447-0756.2010.01298.x
[43] Zhai, L.D., Liu, J., Li, Y.S., Yuan, W. and He, L. (2009) Denonvilliers’ fascia in women and its relationship with the fascia propria of the rectum examined by successive slices of celloidin-embedded pelvic viscera. Diseases of the Colon & Rectum, 52, 1564-1571.
http://dx.doi.org/10.1007/DCR.0b013e3181a8f75c
[44] Kato, M., Niikura, H., Yaegashi, N., Murakami, G., Tatsumi, H. and Matsubara, A. (2008) Histotopography of the female cavernous nerve: A study using donated fetuses and adult cadavers. International Urogynecology Journal, 19, 1687-1695. http://dx.doi.org/10.1007/s00192-008-0713-9
[45] Lindsey, I., Guy, R.J., Warren, B.F. and Mortensen, N.J. (2000) Anatomy of Denonvilliers’ fascia and pelvic nerves, impotence, and implications for the colorectal surgeon. British Journal of Surgery, 87, 1288-1299.
[46] Kinugasa, Y., Murakami, G., Uchimoto, K., Takenaka, A., Yajima, T. and Sugihara, K. (2006) Operating behind Denonvilliers’ fascia for reliable preservation of urogenital autonomic nerves in total mesorectal excision: A histologic study using cadaveric specimens, including a surgical experiment using fresh cadaveric models. Diseases of the Colon & Rectum, 49, 1024-1032.
http://dx.doi.org/10.1007/s10350-006-0557-7
[47] Zhang, C., Ding, Z.H., Li, G.X., Yu, J., Wang, Y.N. and Hu, Y.F. (2010) Perirectal fascia and spaces: Annular distribution pattern around the mesorectum. Diseases of the Colon & Rectum, 53, 1315-1322. http://dx.doi.org/10.1007/DCR.0b013e3181e74525
[48] Hieda, K., Hinata, N., Sasaki, H., Morizane, S., Murakami, G., Abe, S. and Matsubara. A. (2014) Topohistology of sympathetic and parasympathetic nerve fibers in pelvic plexus branches: An immunohistochemical study using donated elderly cadavers. Anatomy & Cell Biology, in Press.
[49] Hoyle, C.H., Stones, R.W., Robson, T., Whitley, K. and Burnstock, G. (1996) Innervation of vasculature and microvasculature of the human vagina by NOS and neuropeptide-containing nerves. Journal of Anatomy, 188, 633-644.
[50] Hong, X., Huang, L. and Song, Y. (2008) Role of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide in the vaginal wall of women with stress urinary incontinence and pelvic organ prolapse. International Urogynecology Journal, 19, 1151-1157.
http://dx.doi.org/10.1007/s00192-008-0585-z
[51] Maggi, C.A., Giuliani, S., Santicioli, P., Patacchini, R., Said, S.I., Theodorsson, E., Turini, D., Barbanti, G., Giachetti, A. and Meli, A. (1990) Direct evidence for the involvement of vasoactive intestinal polypeptide in the motor response of the human isolated ileum to capsaicin. European Journal of Pharmacology, 185, 169-178. http://dx.doi.org/10.1016/0014-2999(90)90637-L
[52] Jacobson, E.D., Berguer, R., Pawlik, W.W. and Hottenstein, O.D. (1994) Mesenteric purinergic and peptidergic vasodilators. Physiology of the Gastrointestinal Tract, Raven, New York.
[53] De Lancey, J.O. (1999) Structural anatomy of the posterior pelvic compartment as it relates to rectocele. American Journal of Obstetrics & Gynecology, 180, 815-823. http://dx.doi.org/10.1016/ S0002-9378(99)70652-6
[54] Arakawa, T., Hayashi, S., Kinugasa, Y., Murakami, G. and Fujimiya, M. (2010) Development of the external anal sphincter with special reference to intergender difference: Observations of mid-term fetuses (15-30 weeks of gestation). Okajimas Folia Anatomica Japonica, 87, 49-58.
http://dx.doi.org/10.2535/ofaj.87.49
[55] Kinugasa, Y., Arakawa, T., Abe, S., Ohtsuka, A., Suzuki, D., Murakami, G., Fujimiya, M. and Sugihara, K. (2011) Anatomical reevaluation of the anococcygeal ligament and its surgical relevance. Diseases of the Colon & Rectum, 54, 232-237. http://dx.doi.org/10.1007/DCR.0b013e318202388f
[56] DeLancey, J.O. (1994) Structural support of the urethra as it relates to stress urinary incontinence: The hammock hypothesis. American Journal of Obstetrics and Gynecology, 170, 1713-1720.
[57] Hinata, N., Murakami, G., Abe, S., Honda, M., Isoyama, T., Sejima, T. and Takenaka, A. (2012) Detailed histological investigation of the female urethra: Application to radical cystectomy. Journal of Urology, 187, 451-456. http://dx.doi.org/10.1016/j.juro.2011.10.037
[58] Masumoto, H., Rodriguez-Vazquez, J.F., Verdugo-Lopez, S., Murakami, G. and Matsubara, A. (2011) Fetal topographical anatomy of the female urethra and descending vagina: A histological study of the early human fetal urethra. Annals of Anatomy, 193, 500-508. http://dx.doi.org/10.1016/j. aanat.2011.03.010
[59] Kurihara, M., Murakami, G., Kajiwara, M., Taguchi, K., Tsukamoto, T. and Usui, T. (2004) Lack of the complete circular rhabdosphincter and a distinct circular smooth muscle layer around the proximal urethra in elderly Japanese women: An anatomical study. International Urogynecology Journal, 15, 85-94. http://dx.doi.org/10.1007/s00192-003-1107-7
[60] Matsubara, A., Murakami, G., Arakawa, T., Yasumoto, H., Mutaguchi, K., Akita, K., Asano, K., Mita, K. and Usui, T. (2003) Topographic anatomy of the male perineal structures with special reference to perineal approaches for radical prostatectomy. International Journal of Urology, 10, 141-148. http://dx.doi.org/10.1046/j.1442-2042.2003.00585.x
[61] Uchimoto, K., Murakami, G., Kinugasa, Y., Arakawa, T., Matsubara, A. and Nakajima, Y. (2007) Rectourethralis muscle and pitfalls of anterior perineal dissection in abdominoperineal resection and intersphincteric resection for rectal cancer. Anatomical Science International, 82, 8-15.
http://dx.doi.org/10.1111/j.1447-073X.2006.00161.x
[62] Dingemans, K.P., Teeling, P., Lagendijk, J.H. and Becker, A.E. (2000) Extracellular matrix of the human aortic media: An ultrastructural histochemical and immunohistochemical study of the adult aortic media. Anatomical Record, 258, 1-14. http://dx.doi.org/10.1002/(SICI)1097-0185(20000101)258:1 <1::AID-AR1>3.0.CO;2-7
[63] Nelson, M.T. (1998) Bayliss, myogenic tone and volumeregulated chloride channels in arterial smooth muscle. Journal of Physiology, 507, 629. http://dx.doi.org/10.1111/j.1469-7793.1998.629bs.x
[64] Ji, G., Barsotti, R.J., Feldman, M.E. and Kotlikoff, M.I. (2002) Stretch-induced calcium release in smooth muscle. Journal of General Physiology, 119, 533-543. http://dx.doi.org/10.1085/jgp.20028514
[65] Petros, P. (2004) The female pelvic floor: Function, dysfunction and management according to the integral theory. Springer, Berlin. http://dx.doi.org/10.1007/978-3-662-05445-1
[66] Courtney, H. (1950) Anatomy of the pelvic diaphragm and anorectal musculature as related to sphincter preservation in anorectal surgery. American Journal of Surgery, 79, 155-173.
http://dx.doi.org/10.1016/0002-9610(50)90208-X
[67] Kinugasa, Y., Arakawa, T., Abe, H., Abe, S., Cho, B.H., Murakami, G. and Sugihara, K. (2012) Anococcygeal raphe revisited: A histological study using mid-term human fetuses and elderly cadavers. Yonsei Medical Journal, 53, 849-855. http://dx.doi.org/10.3349/ymj.2012.53.4.849
[68] Hinata, N. and Murakami, G. (2014) The urethral rhabdosphincter, levator ani muscle and perineal membrane: A review. BioMed Research International, 2014.
[69] Nakajima, F., Takenaka, A., Uchiyama, E., Hata, F., Suzuki, D. and Murakami, G. (2007) Macroscopic and histotopographic study of the deep transverse perineal muscle (musculus transversus perinei profundus) in elderly Japanese. Annals of Anatomy, 189, 65-74. http://dx.doi.org/10.1016/j.aanat. 2006.06.014
[70] Fritsch, H., Lienemann, A., Brenner, E. and Ludwikowski, B. (2004) Clinical anatomy of the pelvic floor. Advances in anatomy, embryology and cell biology. Vol. 175, Springer, Berlin, pp. 1-64.
http://dx.doi.org/10.1007/978-3-642-18548-9
[71] Oelrich, T.M. (1980) The urethral sphincter muscle in the male. American Journal of Anatomy, 158, 229-246. http://dx.doi.org/10.1002/aja.1001580211
[72] Oh, C. and Kark, A.E. (1973) Anatomy of the perineal body. Diseases of the Colon & Rectum, 16, 444-454. http://dx.doi.org/10.1007/BF02588867
[73] Myers, R.P. (2001) Practical surgical anatomy for radical prostatectomy. Urologic Clinics of North America, 28, 473-490. http://dx.doi.org/10.1016/S0094-0143(05)70156-7
[74] Mirilas, P. and Skandalakis, J.E. (2004) Urogenital diaphragm: An erroneous concept casting its shadow over the sphincter urethrae and deep perineal space. Journal of the American College of Surgeons, 198, 279-290. http://dx.doi.org/10.1016/j.jamcollsurg.2003.07.022
[75] Betschart, C., Scheiner, D., Maake, C., Vich, M., Slomianka, L., Fink, D. and Perucchini, D. (2008) Histomorphological analysis of the urogenital diaphragm in elderly women: A cadaver study. International Urogynecology Journal, 19, 1477-1481. http://dx.doi.org/10.1007/s00192-008-0669-9

  
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