Development of a Reversible Vas Deferens Occlusive Device. I. Anatomical Size of the Human and Dog Vas Deferens*

I

Vol. 25, No.8, August 1974 Printed in U.S.A

FERTILITY AND STERILITY

Copyright

© 1974 The American Fertility Society

DEVELOPMENT OF A REVERSIBLE V AS DEFERENS OCCLUSIVE DEVICE. I. ANATOMICAL SIZE OF THE HUMAN AND DOG VAS DEFERENS* ERICH E. BRUESCHKE, B.S.E.E., M.D., MARVIN BURNS, B.S.M.E., JOHN H. MANESS, B.S.E.E., JAMES R. WINGFIELD, B.S., KENNETH MA YERHOFER, AND LOURENS J. D. ZANEVELD, D.V.M., PH.D. Medical Sciences and Engineering Division, llT Research Institute, Chicago, Illinois 60616

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An effective mechanical contraceptive device for men would offer significant advantages over other techniques currently available and would hold promise of wide acceptance, particularly if the technique were truly reversible. We undertook this study to determine if the interposition of a reversible valve in the vas deferens of the dog could control sperm passage reversibly. If successful in dogs, the devices might ultimately be useful clinically. It is difficult to justify implantation of untried devices in humans without thorough animal studies of their safety and effectiveness. This is especially true in the case of male sterilization because a well developed surgical technique, vasectomy, has existed for many years and is itself an elective procedure. Experience with new medical devices of all types indicates that unforeseen problems are the rule. Therefore, we are extensively evaluating devices in dogs before using them in men. The eventual long-term sequelae of surgical vasectomy remain to be established. In the interim, it is apparent that surgical vasectomy procedures will probably increase in number. The morphologic side effects of vasectomy appear to be minimal as far as the testis is concerned,' although some changes can occur in the epididymis, Received September 28,1973. *Supported by the Contraceptive Development Branch, Center for Population Research, National Institutes of Child Health and Human Development, National Institutes of Health, Contract No. NIH-NICHD-71-2229.

659

notably in the ductuli efferentes. 2 Most of these alterations are apparently caused by sperm accumulation in the epididymis, resulting in distention and a great influx of phagocytes. 2,3 Another undesirable consequence of vasectomy may be the formation of sperm granuloma, but this is rare if a good technique is used. 4 The increased phagocytosis of spermatozoa is the most probable reason that 50% of vasectomized men develop sperm agglutinating and immobilizing antibodies within 6 months after vasectomy.5-8 Unquestionably, a major drawback of vasectomy is its relative irreversibility. Although vasovasotomy may be achieved in some cases, the surgery is relatively complex and its prospect for success is limited, especially if the original vasectomy was done in such a way as to prevent spontaneous reanastomosis.1,9,lO The permanence of the operation in the manner it is presently performed necessitates careful patient counseling. Special attention must be paid to the stability of the marriage, the number of children, other possible methods of birth control, and the patient's psychologic state. 11 - 14 In general, men who are not married or who have no children are advised against the operation. 14 Thorough counseling has resulted in the virtual absence of psychologic problems resulting from vasectomy (less than 3% of all tested) and in the general acceptance of this technique as a contraceptive method. However, some men who were in dire need of a depend-

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BRUESCHKE ET AL

able birth control method have been refused vasectomies. Many other men do not even discuss their problem with a physician, because they are uncertain that they would never want to have any more children. For them, a reversible method of vasectomy would be acceptable

August 1974

and desirable. A reversible vasectomy technique has been the object of considerable research. Several investigators have attempted vas occlusion using various intravasal materials and chemicals. Many of these studies have shown some promise; therefore, re-

FIG. 1. Vas sizing gauges in holder. The holder is made so that the size of the gauge can readily be determined. The holder and gauges are autoclavable.

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REVERSIBLE VAS DEFERENS OCCLUSIVE DEVICE: I

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versibility and selective control of fertility might be achieved with more highly developed devices and implantation techniques. For example, Lee 15 has used a surgical nylon or surgical silk suture material as an intravasal thread. However, in a number of the vasa, sperm passed around the intravasal thread. It is well known that after vasectomy the lumen of the testicular vas dilates; this is probably due to the sustained internal pressure. 10 Lee 17 has stated that devices placed in the vas lumen, such as the intra vasal thread, must be secured to prevent migration. Similar problems were noted by Laurence. 1s The use of silicone rubber to plug the vas was reported by Hrdlicka and associates. 1o Their results were encouraging; however, they did point out that long-term occlusion had not been

adequately established by their experiments. We were encouraged by reports that fertility can be restored even after years of vas occlusion. For example, Schmidt 20 reported a case where 20 years after vasectomy a patient had a vas reanastomosis procedure, produced viable sperm, and fathered a child. Djerassi 21 observed that contraception cannot be improved with any method which requires a conscious act. He has suggested development of a procedure which produces, by a single administration of a chemical birth control agent, indefinite (but reversible) sterility, which then could be overcome temporarily by a second "fertility producing" drug. This principle is somewhat analogous to that which would exist using reversible vas deferens occlusion devices. The general

FIG. 2. Individual gauges.

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BRUESdHJ{Fl E'i' AI,

state of the male popu.latlon (if su.ch de· vices prove to ba effective and lire widely used) would be Ohe of infertility; this state could be chang-ed only by a con· scious, rather than unconscious; I:u:~t. it has been established that sperm can move through Mnmuscular pOfiions of the vas deferens Or adjacent tissue. There is ample evidertce in tha literature thai the muscular contractions Mn bli! ifi~ tarrupted over a segment of the vas chan· nel while sperm pl:l!ilsage is maintaiMd. Schmidt I reported Cases of recanalization eveh wh/iJri a segment of the vas Was excised. He pOl5tull'ltecl that after ligation, presSure builds Up in thli! proximal vas,

August 1974

necrosis sets in, and the ligatures cut through the vas. Spermatozoa then leak into the area between the ends of the vas. A sperhil:1tic granuloma tlnd an epithelial lined tract subsequently develop between the ends of the vas, restoring its original pateh{jy. This observation is most significant when donsidering the potentials of an implantable device because from it we can infer that the Sperm transport process can be maintained intact over a transi· tional element in series with the VI:1S. In contrllst to the typical surgical VaS· ectomy, a reversible occlusive device would provide the medical community with flexibility in approaching male steril-

FIG. 3. A .gauge with its modified ogival tip inside the vas deferens.

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REVERSIBLE VAS 'DEFERENS OCCLUSIVE DEVICE: I

ization. For example, devices which would permit cycling of the vas obstruction from an occluded to a nonoccluded state may have a profound effect on minimiz· ing potential side effects and enchancing reestablishment of fertility. Ideally, one should be able to control the occlusion device externally (for instance, by mag· netic or electrical impulse). However, surgical intervention would not decrease the effectiveness of the device as a con· traceptive method, since most men would need the surgery for fathering children only once or twice in their lifetimes. Ex· ternal control would make the valve especially useful, however, because the previously described side effects caused by sperm accumulation might be prevented by infrequent reversal to the open position. This type of engineering problem

need be solved only after the practicality of such a valve has been demonstrated. From the start of our study, a number of complex questions arose., including those relating to: the dimensional properties and morphology of the vas, the mechanism of sperm transport and storage, the ability of the vas deferens to grow into a porous surface, the effect of materials on sperm motility and transport, the length and diameter of the tube through which sperm would pass, and the optimal type of material to use. Detailed answers to these questions were not available from the literature; an extensive effort was therefore made to obtain the necessary information. Some of the bioengineering aspects of this research have been previously presented. 22 - 24 An animal model which could be easily ejaculated, and hav-

TABLE 1. Exlernal and Internal Diameters of the Human Vas Deferens" Extema! diameter Specimen

no.

1. 2. 3. 4. 5.

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8. 9. 10. 11. 12. 13. 14. 15.

Specimen side

Length of specimen

1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 1 1 1 1

measurements in mm. bN.M. = not measured.

a All

20 10 15 15 15 8 22 21 10 8 12 13 14 10 24 10 19 14 20 17 25 25 15 N.M.b N.M.b

Intemal diameter

Measured range

Average

2.5 - 3.2 3.2 - 3.6 2.5 - 2.8 2.5 - 3.0 2.5 - 3.0 2.5 - 3.0 2.4 - 3.0 2.4 - 2.7 2.4 - 2.6 2.4 - 2.6 3.2 3.2 3.2 3.2 1.8 - 2.4 2.0 - 2.1 2.6 - 3.0 3.2 - 3.4 2.6 - 3.0 3.0 2.8 4.0 2.3 - 2.8 N.M.b N.M.b

2.85 3.4 2.65 2.75 2.75 2.75 2.8 2.55 2.5 2.5 3.2 3.2 3.2 3.2 2.1 2.05 2.8 3.3 2.8 3.0 2.8 4.0 2.55

No resistance

Significant resistance

0.9 0.9 0.8 0.8 0.8 0.9 0.9 0.7 0.8 0.8 0.8 0.8 0.8 0.9 0.8 0.9 0.8 0.9 0.9 1.0 0.9 1.0 0.9 0.8 0.9

1.1 1.1 1.0 1.0 1.0 1.1 1.1 0.9 0.9 0.9 1.1 1.0 1.0 1.2 0.9 1.0 1.0 1.1 1.2 1.3 1.3 1.3 1.0 1.0 1.1

664

BRUESCHKE ET AL

ing a vas similar to that of the human was required to conduct the necessary biologic experimentation. The dog appeared to be the experimental animal of choice (because of its cooperative nature, its ease of ejaculation and manageability, its rather large size, and its being a well established surgical model) and was used throughout our experimentation. The monkey was considered but it was rejected because it is somewhat difficult to handle and requires electroejaculation. Initially, observations were made to determine the comparative anatomy, morphology, physiology, and sperm output of the human and dog vas deferens. The design of any implantable device required knowledge of the size of the vas at the point where the device was to be implanted. This paper describes and compares the size of the scrotal portion of the vas deferens of the human and the dog. A sizing method specifically developed for this purpose was used. Succeeding papers will describe the effect of bilateral and uni-

August 1974 I

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0.856

0.71

0.99

FIG. 4. Frequency histogram for the "no resistance" luminal sizes of human vasa deferentia. Mean = 0.856 mm; standard deviation (SD) = 0.0715 mm.

lateral vasectomy on sperm counts of the dog (paper II), surface morphology of the lumen of the human and dog vas deferens (paper III), our experience with rigid reversible occlusive devices (paper IV), and

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FIG. 5. Frequency histogram for the "significant resistance" luminal SIzes of human vasa deferentia. Mean = 1.06 mm; standard deviation (SD) = 0.124 mm.

Vol. 25, No.8

our experience with flexible reversible occlusive devices (paper V) developed at this institute. MATERIALS AND METHODS

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665

REVERSIBLE VAS DEFERENS OCCLUSIVE DEVICE: I

Sections were excised from the vasa of 13 men undergoing vasectomy. These sections were taken from the scrotal area approximately 3 cm distal to the epididymis. This is the area where vasectomy is usually performed and where a valve can be implanted with greatest ease. In most cases, identical sections were obtained from both the right and left vasa. Eleven dogs were used for vas sizing. All were short-haired, mixed breed hounds from 1 to 4 years of age, weighing 16 to 21 kg, and measuring 18 to 22 cm at the shoulder. The dogs were purchased to these specifications from Pel-Freeze BioAnimals, Inc., Arkansas. The vas sizing experiments in this species were done in situ during unilateral vasectomy at an

area of the vas located 2.5 to 3 cm distal to the epididymis. The external diameter of the vas was measured with a scale; the internal diameter (lumen) was measured with a round gauge. Initially, stainless hypodermic needle tubing of known diameter was used; later, precision gauges were specifically devised for this purpose (Fig. 1). These gauges ranged in diameter from 0.5 mm to 1.5 mm, in increments of 0.10 mm. Each gauge had a flattened tab on one end, indicating the size of th~ gauge (Fig. 2). The end that was inserted into the vas had a short modified ogival point approximately 1.0 mm long and narrowing down to approximately half the size of the gauge. The gauges were inserted through the transected end of the vas (Fig. 3). Two observations were of importance: (1) The size of the largest gauge that

could be inserted into the vas without any

;

0.65 0.75 I

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0.85 0.95

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FIG. 6. Relative size distribution between the "no resistance" and "significant resistance" luminal sizes of the men. Central values indicate the mean for each population.

666

BRUESOHKE ET AL

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August 1974

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FIG. 7. Frequency histogram of the external size measurements of human vasa deferentia. Mean = 2.85 mm; standard deviation (SD) =0.43 mm.

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FIG. 8. Relationship of "significant resistance" luminal size to the external diameter of the same human vas deferens specimens. Bars denote ISD range.

VoL 25, No.8 I

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REVERSIBLE VAS PEF'ERENS OCCLUSIVE DEVICE: I

resistance ("no resistance") i and (2) Th~ size of the gauge that on insertion into the vas met with notable resistance ("significant resistance"). The data were gr9uped into two populations according to this classification and a frequency hist()gram was constructed for each. Standard deviations were calculated by standard statistical techniques for small samples. The gauging technique would alS() be applicable to vasa from which the mucosa has been removed to en.courage fibroblast ingrowth (this is applicable to certain device designs). The principles of anhnal (veterinary) care as promulgated in the Animal Welfare Act of 1970 (Public Law 91-579) were observed throughout the study. RESULTS

Table 1 lists the measurements of the internal and external diameters of 25 human vas specimens. Although 20 of the specimens were paired (ie, obtained from vasa of the left and right sides of ten men), the sides usually differed in their measurements. Of the ten paired specimens, six sides showed differences il) external diameter, six differed in the I'no resistance" internal diameter, and seven differed in the "significant resistance" internal diameter. The differences between the sides of each individual were as large

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667

as they were alJlong different individuals. Therefore, the specimens were treated as separate unit.s in computing the mean and standard deviations of the average vas size. The mean diameter of the largest gauge that could be entered into the human vas without any r!i)sistance was 0.85 ±0.071 mm (Fig. 4). The mean diameter of the probes that met with Gonsiderable resistance was 1.06 mm ±O.124 mm (Fig. 5) . The histograms constructed from the data in Table 1 (Figs. 4 and 5) suggest normal frequency distributions as indicated by the dashed curves superimposed on each figure. A visual assessment of the size distribution overlap among the classes is shown in Fig. 6. From these figures, one can see that the "no resistance" population has a smaller variance than the "significant resistance" population. Since various investigators were involved in obtaining the measurements, these results suggest that it is easier to obtain a general agreement as to what "no resistance" feels like, than what "significant resistance" feels like. Various specimens were first measured in situ. The results were usually identical to those of the excised specimens. Furthermore, gauging through a longitudinal incision produced results similar to gauging through the transected end. The external diameter of the excised specimen frequently varied along the length of the specimen (Table 1). Usually the middle section possessed a diameter smaller than the outer segment. The largest and smallest measurements were averaged and used in subsequent calculations. This average probably represents the best estimation of the normal diameter of the vas. The mean average diameter of 23 specimens was 2.85 ±0.43 mm (Fig. 7). A normal frequency distribution was obtained with only one sample falling outside the M ±2 SD range. In some cases (such as the design ap-

668

BRUESCHKE ET AL

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0.98

1.15

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FIG. 10. Frequency histogram for the "significant resistance" luminal sizes of dog vasa deferentia. Mean = 0.98 mm; standard deviation (SD) =0.085 Mm.

proach to a sutureless valve which will be reported on in future papers), a statistical characterization of the vas lumen may require an additional assessment of the size relationship between the vas luminal diameter and the outside diameter. Therefore, scale measurements of the vas outside diameter were made at the time of luminal gauging. The "significant resistance" class of gauge fit was selected and outside diameters were grouped in relation to this associated lumen size. A fairly linear relationship appears to exist between the means of these groups and its significant resistance gauge size (Fig. 8). Detailed external diameter measure-

August 1974

ments were not normally recorded in the dogs since all measurements were done in situ during unilateral vasectomy (Table 2). Of four vasa measured, however, the external diameters averaged approximately 2.5 mm, varying between 1.9 and 3.2 mm. For the same reason, only the internal diameters of one of the vasa were recorded so that the left and right vasa from the same dog could not be compared. It appeared, however, from visual observations that differences in sides also occurred in this species. The results were as consistent among individuals as could be expected from a highly selective population (Table 2). The frequency histoTABLE 2. Internal Diameter of the Dog Vas Deferens" Specimen

Internal diameter

number

No resistance

1

0.8 0.8 0.7 0.9 0.9 0.8 0.8 0.7 0.8 0.7 0.8

2 3 4 5 6 7 8 9 10 11 a All

Significant resistance

0.9

1.0 0.9 1.1 1.1

1.0 1.0 0.9

1.0 0.9

1.0

measurements in Mm.

"'

0.55 0.65 0.75 0.85 0.95 0.77

1.05

1.15

1.25

mm

0.98

FIG. 11. Relative size distribution between the "no -resistance" and "significant resistance" luminal sizes of the dogs.

Vol. 25, No.8

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grams showed normal distributions simi- incisions, depending on the particular lar to the human vas populations (Figs. 9 surgical technique associated with the and 10). The mean "no resistance" inter- device implant surgery. Some effort was nal diameter was 0.77 ±0.075 mm, where- made therefore to verify that the in vitro as the mean "significant resistance" fit data thus obtained were representative measured 0.98 ±0.085 mm. These mean in nature of in vivo luminal gauging and values differed from the mean sizes of the consequently, that the statistical results human vas respectively by 0.086 mm ("no obtained would be applicable in both resistance") and 0.084 mm ("significant instances. Additional gauging trials resistance" ), showing the consistency of through longitudinal incisions in vivo measurements. As with the human, the and in vitro and through the vas cut end "no resistance" dog population showed in vivo failed to show any significant smaller variance than the "significant re- difference between these various gauging sistance" dog population, although less situations. so, probably because of the selective samDISCUSSION pling of the dog population (Figs. 11 and 12). The overlap of the two luminal popI t is necessary to know the size of the ulations was also less extensive than that vas deferens in order to develop a suitable of the human vasa. intravasal valve. Ingrowth into the vas The human vas sizing data were ob- lumen or into the transected ends of the tained by gauging in vitro through the vas would necessitate a different fit for end of the vas. While this was the most optimal performance. If one has a device expeditious manner of obtaining this data, design wherein an exact fit is required, it was recognized that in practice, meas- the ideal fit would have to meet with urements of the vasal lumen must neces- enough resistance to promote tissue insarily be made in situ through both tran- growth but not enough to stretch the vas sected ends and through longitudinal excessively (we define this as "significant

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669

REVERSIBLE VAS DEFERENS OCCLUSIVE DEVICE: I

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0.35 0.45

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. 670

BRUESCHKE ET AL

August 1974

resistance") . This measurement defines smaller or larger size devices be needed. the external diameter of the end tubes of Devices not requiring a "significant rethe occlusive device required for implant- sistance" fit could greatly minimize the ing in the vas. Our technique for gauging number of device sizes. The dogs were is used before and after the mucosa has more consistent in their measurements been removed to promote tissue ingrowth in that they required device size increand to minimize sperm leakage. In con- ments of 0.1 mm, starting from 0.7 mm trast, the size of the largest gauge that to 1.1 mm. Therefore, dogs are excellent could be entered into the vas with "no experimental animals for contraceptive resistance" closely corresponds to the valve implantation studies, especially natural luminal diameter (for the human since the mean internal size of their vasa this averages 0.85 mm). This is the best varied less than 0.1 mm from that of fit for devices that only project into the the men. vas where tissue ingrowth is required to When sizing the vasa with the gauges, occur at the transected ends of the vas, the effect of occasional muscle spasms The gauges that have been devised (Figs. should be considered. Spontaneous mo1 and 2) allow an easy, rapid, and accur- tility, such as peristalsis, in the in situ ate assessment of the internal diameter of human or dog vasa were not observed the vas and may prove to be extremely in our studies, probably because of the valuable in the future when human vas anesthesia. 25 Muscle spasm of the vas implants are actually performed. does not permanently alter the luminal From a practical standpoint, it would size and the gauged result is always realso be desirable to know what size range producible if one begins gauging with of vas occlusion devices should be at hand smaller gauges and progresses to larger during surgery. An estimate can be ob- sizes. This is a very tolerable and rapid tained from the available data. Although procedure, and easily overcomes the subour sample is still limited, we can see that ject's neuromuscular tendencies to con· the "no resistance" (lumen) population tract the lumen. Although the size of the is distributed normally (Fig. 4). From external diameter varied in proportion to the mean (0.85 mm) and its variance the "significant resistance" luminal di(0.071 mm), it can be expected that only ameter, some variations from the mean 2.5% (M - 2 SD) of the vas lumen sizes were present (see bars denoting 1 SD would be less than 0.71 mm. Similarly, range in Fig. 11). The precise size for a judging from its size, only 2.5% (M + device cannot be obtained by measuring 2 SD) of the time will the "significant the external diameter of the vas and then resistance" exceed 1.31 mm. If we now estimating the lumiQal diameter. Gaugplot the "difference" population obtained ing the internal diameter of the vas is by subtracting the "no resistance" meas- therefore essential to successful contraurements from the "significant resistance" ceptive valve implantation. The mean measurements for each specimen in a luminal diameter of the human vasa rehistogram (Fig. 12), it can be seen that ported here was found to be about 0.85 only 2.5% of the time would a dilatation mm; this is significantly larger than that value of less than 0.05 mm (M - 2 SD) described by Hulka and Davis1 in their be expected. Therefore, we can conclude excellent review. They reported an averthat optimally the range of device sizes age luminal diameter of 0.55 rom. The required for human implantation would data and methods of measurement were start at 0.7 mm and increase in 0.05 mm not presented, however, so that theapincrements to 1.35 mm. Rarely would parent discrepancy cannot be explained

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REVERSIBLE VAS DEFERENS OCCLUSIVE DEVICE: I

at this time. These authors did not comment on the external diameter of the human vas, the mean of which we found to be 2.85 mm. This size is comparable to that reported by Popovic et al. 26 SUMMARY

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Considerations important to the development of reversible vas deferens occlusive devices have been presented. A system was developed to gauge the internal diameter of the vas deferens. The mean size (± the standard deviation) of the largest gauge that could be entered into the vas without resistance ("no resistance") was 0.85 ±0.071 mm for the human and 0.77 ±0.075 mm for the dog. The mean size of the gauge that on insertion into the vas met with notable resistance ("significant resistance") was 1.06 ±0.124 mm for the human and 0.98 +0.085 for the dog (M + 2 SD). A smaller variance was noted among the "no resistance" than among the "significant resistance" group. The mean outside diameter of the human vas was 2.85 ±0.43 mm. A relationship was found between the internal and external size of the vas but this relationship was not sufficient to predict luminal diameter based on vas deferens outside diameter. Size variations frequently occurred between the right and left vasa of the same individuals. From these studies, the dog appears to be an excellent candidate for reversible occlusive device implant experiments. Acknowledgments. The authors are grateful for suggestions and encouragement from Drs. Richard Blye, Gabriel Bialy, and Dolores Patanelli of the Contraceptive Development Branch of the National Institutes of Child Health and Human Development, and from Dr. Eugenia Rosemberg, formerly of the NICHD and now at the Worchester Institute. Human vas deferens specimens and data were obtained with the cooperation of Dr. Lonny Myers, Medical Director of the Midwest Population Center in

671

Chicago and Dr. Stanley Levine of the same center. Dr. C. W. deLannoy of the University of Illinois Medical Research Laboratory provided valuable assistance in the area of veterinary surgery. Richard Rodzen and Robert Mullins provided technical assis~nce. Consultations and suggestions were rec~ived from Drs. Joseph E. Davis and Matthew Freund of the New York Medical College. REFERENCES 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12. 13. 14.

Hulka JF, Davis JE: Vasectomy and reversible vasocclusion. Fertil Steril 23: 683, 1972 Alexander NJ: Vasectomy: long-term effects in the rhesus monkey. J Reprod Fertil 31: 399, 1972 Phadke AM: Fate of spermatozoa in cases of obstructive azoospermia and after ligation of vas deferens in man. J Reprod Fertil 7: 1, 1964 Schmidt SS: Technics and complications of elective vasectomy: the role of spermatic granuloma in spontaneous recanalization. Fertil SterilI7:467, 1966 Phadke AM, Padukone K: Presence and significance of autoantibodies against spermatozoa in the blood of men with obstructed vas deferens. J Reprod Fertil 7: 163, 1964 Rumke P: Sperm-agglutinating autoantibodies in relation to male infertility. Proc R Soc Med 61:275,1967 Ansbacher R: Sperm-agglutinating and sperm-immobilizing antibodies in vasectomized men. Fertil Steril 22: 629, 1971 Ansbacher R, Keung-yeung K, Wurster JC: Sperm antibodies In vasectomized men. Fertil Steril 23:640, 1972 Mehta KC, Ramani PS: A simple technique ofre-anastomosis after vasectomy. Br J UroI42:340, 1970 Phadke GM, Phadke AG: Experiences in the re-anastomosis of the vas deferens. J Urol 97: 888, 1967 Uehling DT, Wear JB: Patient attitudes towards vasectomy. Fertil Steril 23: 838, 1972 Nash JL, Rich JD: The sexual aftereffects of vasectomy. Fertil Steril 23: 715, 1972 Chaset N: Male sterilization. J Urol 87: 512, 1962 Greene LF: Bilateral partial vasectomy for elective sterilization. Am Fam Physician 4: 73, 1971

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16.

17.

18.

19.

20.

21.

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Lee HY: Experimental studies on reversible vas occlusion by intravasal thread. Fertil Steril 20: 735, 1969 Schmidt SS: Anastomosis of the vas deferens: an experimental study. III. Dilation of the vas following obstruction. J Urol 81: 206, 1959 Lee HY: Methods of temporary vas occlusion. Conference on Human Sterilization, Cherry Hill, New Jersey, October 2831, 1969 Laurence KA: Vas occlusion with plastic materials. Conference on Human Sterilization, Cherry Hill, New Jersey, October 28-31,1969 Hrdlicka JG, Schwartzman KH, Zinsser HH: New approaches to reversible seminal diversion. Fertil Steril 18: 289, 1967 Schmidt SS: Vas reanastomosis procedures. Conference on Human Sterilization, Cherry Hill, New Jersey, October 28-31, 1969 Djerassi C: Prognosis for the development of new birth-control agents. Science 166: 468, 1969

22.

23.

August 1974

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