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Dive into the research topics where J. P. Van Der Merwe is active.

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Featured researches published by J. P. Van Der Merwe.


Journal of Clinical Anesthesia | 2000

Moderate controlled hypotension with sodium nitroprusside does not improve surgical conditions or decrease blood loss in endoscopic sinus surgery

André P. Boezaart; J. P. Van Der Merwe; André Coetzee

Abstract Study Objective: To determine if moderate controlled hypotension can improve the dryness of the surgical field in endoscopic sinus surgery. Study Design: Randomized, prospective study. Setting: University-affiliated hospital. Patients: 32 ASA physical status I and II adult patients undergoing endoscopic sinus surgery. Interventions: All patients were premedicated orally with chlorazepate. Patients in Group H received 12.5 mg captopril orally prior to surgery. Anesthesia was provided using an intravenous (IV) technique supplemented with nitrous oxide (N 2 O); anesthesia was maintained with boluses of 2 μg/kg fentanyl and a propofol infusion at rates between 3 and 9 mg/kg/h at the discretion of the anesthetist. In Group H, sodium nitroprusside was infused at a rate of 1 to 2.5 μg/kg/min to maintain moderate controlled hypotension with mean blood pressure of 65 to 75 mm Hg. Measurements and Main Results: Arterial blood pressure was assessed via the radial artery. Readings were recorded prior to intubation, immediately after intubation, at the start of surgery, then at 5, 15, 30, 45, and 60 minutes intraoperatively, and at the end of surgery. Intraoperative blood loss, dryness of the surgical field, adrenocorticotropic (ACTH) hormone, arginin-vasopressin (AVP), cortisol, and the preoperative and postoperative psychomotoric function were examined. At the start of surgery and thereafter, MAP increased in Group N but not in Group H. Throughout surgery, MAP was significantly lower in Group H than in Group N. Blood loss, dryness of the surgical field, ACTH, AVP, and cortisol levels, and psychomotoric function were not significantly different between the groups. Conclusion: Intravenous anesthesia supplemented with N 2 is as effective as moderate controlled hypotension when blood loss, visibility in the surgical field, ACTH, AVP, and cortisol are examined.


Gynecologic and Obstetric Investigation | 2005

Effect of fibroids on fertility in patients undergoing assisted reproduction a structured literature review

C. Benecke; Thinus F. Kruger; T.I. Siebert; J. P. Van Der Merwe; D.W. Steyn

Objective: The aim of this study is to evaluate the current data to understand the impact of intramural leiomyomata on pregnancy outcome in assisted reproduction. Patients and Methods: In this review, articles were found by means of computerized Medline and Cochrane Library search using the key words uterine myomata, leiomyomata, fibroids, implantation, pregnancy, infertility and in vitro fertilization. Limitations were English, human, 1990–2002. Inclusion criteria were pregnancy data on in vitro fertilization, intramural myomata with no cavitary distortion and control groups without myomas for each patient with a myoma. Results: There was a significant negative impact on implantation rate in the intramural myomata groups versus the control groups, 16.4 vs. 27.7% OR 0.62 (0.48–0.8). The delivery rate per transfer cycle was also significantly lower (myomata vs. control), 31.2 vs. 40.9% OR 0.69 (0.50–0.95). Conclusion: Our study supports the notion that patients with intramural fibroids have a lower implantation rate per cycle. The studies did not shed new light on the size of intramural myomata that could affect the outcome. In previous failed in vitro fertilization cycles, microsurgical removal of myomata must be considered.


Andrologia | 2001

Stepwise regression analysis to study male and female factors impacting on pregnancy rate in an intrauterine insemination programme

M. Montanaro Gauci; Thinus F. Kruger; Kevin Coetzee; K. Smith; J. P. Van Der Merwe; Carl Lombard

Summary. The aim of this study was to evaluate the impact of male and female factors on the pregnancy rate in an intrauterine insemination (IUI) programme. Data on 522 cycles were retrospectively studied. All patients 39 years or younger were included in the study where data were available on male and female diagnosis, as well as on ovulation induction methodology. Regression analysis was possible on 495 cycles to study different factors affecting the pregnancy rate per treatment cycle. Logistic regression identified variables which were related to outcome and were subsequently incorporated into a statistical model. The number of follicles was found to have a linear association with the risk ratio (chance) of pregnancy. The age of the woman was also found to have a linear (negative) association with pregnancy. The percentage motility and percentage normal morphology (by strict criteria) of spermatozoa in the fresh ejaculate were the male factors that significantly and independently predicted the outcome. Percentage motility ≥ 50 was associated with a risk ratio of pregnancy of 2.95 compared to percentage motility < 50. Percentage normal sperm morphology > 14% was associated with a risk ratio of pregnancy of 1.8 compared to percentage normal morphology ≤ 14%. Female patients with idiopathic infertility were divided into three groups according to normal sperm morphology. The pregnancy rate per cycle was 2.63% (1/38) for the P (poor) pattern group (0–4% normal forms), 11.4% (17/149) for the G (good) pattern group (5–14%), and 24% (18/75) for the N (normal) pattern group (> 14% normal forms). A female diagnosis of endometriosis or tubal factor impacted negatively on the probability of pregnancy (risk ratio of 0.17), compared with other female diagnoses. Male and female factors contribute to pregnancy outcome, but the clinician can influence prognosis by increasing the number of follicles, especially in severe male factor cases.


Journal of Assisted Reproduction and Genetics | 1993

Follicle stimulating hormone levels on cycle day 3 predict ovulation stimulation response

A Ebrahim; G Rienhardt; S Morris; Thinus F. Kruger; Carl Lombard; J. P. Van Der Merwe

AimTo determine the value of basal follicle stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) levels on cycle day 3 in predicting the ovulation stimulation response in patients receiving exogenous gonadotropins for in vitro fertilization (IVF) or gamete intrafallopian transfer (GIFT).MethodsOne hundred eleven consecutive females with infertility due to various etiologies were investigated. Cycle day 3 serum levels of FSH, LH, and E2 were determined prior to ovulation induction with a combination of clomiphene citrate and human gonadotropins. Follicular growth was monitored ultrasonically, and when appropriate, oocytes were recruited, counted, graded, and then used, as prearranged, for either IVF or GIFT. Basal hormone levels were compared to the peak E2 concentration, the number of follicles aspirated, and the number of preovulatory oocytes recovered following drug therapy. Details of resulting pregnancies were also recorded.ResultsPatients with low basal FSH levels (<11.5 mIu/ml) yielded a higher mean number of preovulatory oocytes than those with high values (>11.5 mIu/ml), i.e., 6.7 oocytes per cycle vs 2.5 oocytes (P < 0.001). In the low group 97% of cycles yielded more than three fertilizable oocytes compared to 42% in the high group (P < 0.5). There were 16 term pregnancies (16%) in the low group and 1 (8.3%) in the high group. Basal LH and E2 levels did not improve on the ability to distinguish between different populations of infertile females who responded differently to ovulation induction.ConclusionCycle day 3 FSH levels are predictive of the ovulation response and probability of pregnancy in stimulated cycles and can be of value in patient selection and counseling in IVF and GIFT programs.


Journal of Assisted Reproduction and Genetics | 1987

The effect of serum supplementation on the cleavage of human embryos

Thinus F. Kruger; F. S. H. Stander; K. Smith; J. P. Van Der Merwe; Carl Lombard

The effect of serum supplementation was evaluated on 108 oocytes obtained from 29 patients. The oocytes were all mature and randomly distributed in two groups. Each ovum was paired with another ovum within the same patient. The experimental group contained no serum in the insemination and growth medium, but in the control group 10% serum was added to the insemination and growth medium. In the experimental group the cleavage rate was 66.7%, compared to 83.3% in the control group. The embryos from each patient were individually evaluated. The sign test was used for statistical analysis. A significant difference between the two groups (P=0.01) indicated that in this study the addition of serum to the medium gives better cleavage results. The effect of serum on embryos is discussed, as well as the practical implications of this finding.


International Journal of Oral and Maxillofacial Surgery | 1999

Eagle's syndrome: lesser cornu amputation: an alternative surgical solution?

A.J. van der Westhuijzen; J. P. Van Der Merwe; F.W. Grotepass

A case is reported of a 42-year-old female patient, who presented with clinical symptoms of Eagles syndrome, radiographic evidence of marginally elongated styloid processes as well as markedly elongated lesser cornua of the hyoid. The symptoms were successfully treated by amputating the lesser cornua of the hyoid. The patient has now been asymptomatic for more than 6 years.


Archives of Andrology | 1989

EFFECT OF SPERM WASHING AND SWIM-UP ON ANTIBODIES BOUND TO SPERM MEMBRANE: USE OF IMMUNOBEAD/SPERM CERVICAL MUCUS CONTACT TESTS

M.-L. Windt; R. Menkveld; Thinus F. Kruger; J. P. Van Der Merwe; J. A. Van Zyl

The direct immunobead test (IBT) and the sperm cervical mucus contact (SCMC) test were used to evaluate the effect of sperm washes and swim-up on antibodies bound to the sperm membrane in 11 patients with autosperm antibodies (30-100% IgA and 30-100% IgG) but otherwise normal semen measurements. The tests were performed on semen samples before and after a wash/swim-up procedure in Ham F10 + 10% human blood serum. Sperm-bound antibodies in washed spermatozoa that were able to swim into a layer of medium did not differ from those in unwashed samples. The IBT and the SCMC test on unwashed and washed spermatozoa were also not significantly different. However, all other washed semen parameters were improved. Correct washing of semen samples is important when performing the IBT to prevent false negative results. Eight of the 11 partners (73%) of the patients tested became pregnant after treatment with washed sperm. The ongoing pregnancy rate was 64%.


Archives of Andrology | 1996

A comparative study using prepared and unprepared frozen semen for donor insemination

L. R. Pistorius; T. F. Kruger; A. De Villiers; J. P. Van Der Merwe

The aim of this study was to compare the efficacy of pericervical insemination with unprepared semen With that of intrauterine insemination with prepared donor semen in a prospective, randomized, crossover clinical trial. Fifty-four subsequent patients who qualified for therapeutic donor insemination were randomized to receive alternately either an intrauterine insemination with thawed frozen donor semen, prepared by double wash and swim-up, or pericervical insemination with unprepared thawed frozen donor semen in subsequent treatment cycles, with each patient serving as her own control. Eleven pregnancies ensued from 54 cycles of intrauterine insemination (20.4% per cycle), and 2 pregnancies ensued from 58 cycles of pericervical insemination (3.4% per cycle, p = .005). Five pregnancies ensued during the first treatment cycle (13.2%), 4 during the second treatment cycle (17.4%), 2 during the third (13.2%), 1 during the fourth (7.1%), and 1 after the fourth treatment cycle (4.8%). The significantly better pregnancy rate from intrauterine insemination with prepared semen supports this treatment option. The decrease in pregnancy rate after the fourth treatment cycle confirms the need for alternative therapy after 4 failed cycles of therapeutic donor insemination.


IEEE Transactions on Electromagnetic Compatibility | 1998

S-parameter measurements yielding the characteristic matrices of multiconductor transmission lines

J. P. Van Der Merwe; Howard C. Reader; J.H. Cloete

A frequency-domain method is presented, which yields accurate characteristic matrices of uniform multiconductor transmission lines (MTLs). It uses simple two-port network analyzer S-parameter measurements of a set of open-circuit and short-circuited MTL configurations. The method eliminates the need for voltage and current probes, which introduce errors. Transversely inhomogeneous MTLs can be accurately characterized in their quasi-TEM propagation regime. The influence of the skin effect on the inductance matrix is taken into account. The technique was used to determine the inductance and capacitance matrices of a low-loss three-conductor ribbon cable above a ground plane. Comparisons with numerically and analytically obtained data are given. Measurements are found to be repeatable for lines of length /spl Lscr/</spl lambda//4. The /spl lambda//4 requirement is not found to be a restriction in the megahertz regime and only plays a role as line-end effects become significant at gigahertz frequencies. The obtained accuracy is significantly better than previously reported results.


Archives of Andrology | 1989

Effect of rapid dilution of semen on sperm-bound autoantibodies

M.-L. Windt; R. Menkveld; Thinus F. Kruger; J. P. Van Der Merwe; Carl Lombard

The effect of rapid dilution of autoantibody-positive semen on sperm-bound antibodies was studied in 12 male patients (0-100% IgA and 10-100% IgG). The direct immunobead test (IBT) and the sperm cervical mucus contact (SCMC) test were used to detect sperm-bound antibodies on spermatozoa before and after rapid dilution and swim up in HAM F-10 + 10% human blood serum. All patients tested had normal semen parameters. Sperm-bound antibodies detected after swim-up of semen samples ejaculated into 15 ml HAM F-10 + 10% serum (diluted) did not differ significantly from undiluted samples. Most values were lower (IBT and SCMC) but were not statistically significant. Sperm motility, forward progression, and morphology were statistically improved. Pregnancies resulting from washed semen (diluted) in combination with artificial insemination (AIH) or gamete intrafallopian tube transfer (GIFT) took place in spite of antibodies still present on the sperm membrane and can probably be attributed to improved semen quality, minimizing of ovum-sperm distance, and cervical mucus elimination.

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T. F. Kruger

Stellenbosch University

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Carl Lombard

South African Medical Research Council

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J. Basson

Stellenbosch University

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T.I. Siebert

Stellenbosch University

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C. Heyns

Stellenbosch University

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