PubMed Health⌕ Search

Biomedical subjects

L A Baker

Publications and source records attributed to L A Baker.

At least 19 recordsLinked to original sources
PubMed2001

Multicompartment ecosystem mass balances as a tool for understanding and managing the biogeochemical cycles of human ecosystems.

Nitrogen remains a ubiquitous pollutant in surface and groundwater throughout the United States, despite 30 years of pollution control efforts. A detailed multicompartment N balance for the Central Arizona-Phoenix ecosystem is used to illustrate how an ecosystem-level approach can be used to develop improved N management strategies. The N balance is used to demonstrate how nitrate in pumped groundwater used for crop irrigation could be used to reduce inputs of commercial fertilizer and decrease N leaching to aquifers. Effectively managing N pollution also will require an understanding of the complex factors that control the N balance, including targeted regulations, individual human behavior, land-use conversion, and other ecosystem management practices that affect the N balance. These sometimes countervailing factors are illustrated with several scenarios of wastewater treatment technology and population growth in the Phoenix area. Management of N eventually must be coupled to management of other elements, notably carbon, phosphorus, and salts. We postulate that an ecosystem framework for pollution management will result in strategies that are more effective, fairer, and less expensive than current approaches.

Arizona↗
PubMed2001

Combined bladder neck reconstruction and epispadias repair for exstrophy-epispadias complex.

PURPOSE: The achievement of satisfactory continence in the management of classic bladder exstrophy remains a surgical challenge. During the last 20 years a staged approach to the management of the exstrophy-epispadias complex has been used at many exstrophy centers to attain this goal. In select cases repairs can be combined to reduce the number of mandatory operations to achieve continence. We retrospectively review our experience with, and long-term results and complications of combined bladder neck reconstruction and epispadias repair. MATERIALS AND METHODS: A total of 19 boys with classic bladder exstrophy (17) and complete male epispadias (2) underwent combined bladder neck reconstruction and epispadias repair between 1982 and 1999. Primary closure was performed elsewhere in 16 cases and osteotomy was performed at primary closure in 8 (42%). All patients have undergone modified Cantwell-Ransley epispadias repair except for 2 who underwent a Young procedure. RESULTS: At the time of combined bladder neck and epispadias repair mean patient age was 5.2 years (range 2.5 to 10). Mean bladder capacity was 119 ml. (range 60 to 250). Of the 19 patients 13 (69%) are completely continent, and 2 (11%) are partially continent and 1 remained incontinent. Three patients did not gain satisfactory functional bladder capacity after combined repair, and underwent bladder augmentation and a continent diversion procedures. CONCLUSIONS: Combined bladder neck and epispadias repair is applicable in experienced hands but careful patient selection and long-term followup are the most important issues to develop criteria to select those best to undergo this procedure.

Bladder Exstrophy↗
PubMed2001

Modified Young-Dees-Leadbetter bladder neck reconstruction in patients with successful primary bladder closure elsewhere: a single institution experience.

PURPOSE: Achievement of urinary continence in patients with the exstrophy-epispadias complex remains a challenge. We reviewed our experience with the modified Young-Dees-Leadbetter bladder neck repair in patients with bladder exstrophy who underwent primary bladder closure elsewhere. MATERIALS AND METHODS: We retrospectively reviewed exstrophy charts and database of 57 male and 11 female with classic bladder exstrophy who underwent bladder neck repair at our institute and successful primary bladder closure elsewhere during the last 2 decades. Osteotomy was performed at primary closure in 14 (20%) cases and 9 (13%) patients at bladder neck repair in 9 (13%) to aid in stabilizing the urethra and pelvic ring, and to help reapproximate the pelvic floor musculature facilitating urinary continence. RESULTS: Primary closure was done within 72 hours of life elsewhere in 41 (60%) patients, and between ages 72 hours and 5 years (most during the first month of life) in 27. Paraexstrophy skin flaps were used in 33 (48%) cases, and the most common complication was bladder outlet obstruction of the posterior urethra secondary to the skin flaps. Of the 68 patients 57 (83%) are continent and voiding per urethra without need for augmentation or clean intermittent catheterization, 9 (13%) required clean intermittent catheterization including 7 who underwent continent urinary diversion after failed bladder neck repair, and 2 are still incontinent due to a severe posterior urethral stricture. Urinary retention was the most common symptom after bladder neck repair which resolved following catheter dilation or prolonged suprapubic catheter drainage. CONCLUSIONS: Successful early primary closure of a good bladder template is the most important determinant of eventual bladder capacity and compliance.

Adolescent↗
PubMed2001

Nitrogen transformations in a wetland receiving lagoon effluent: sequential model and implications for water reuse.

Constructed wetlands could be components of low-tech systems to treat and reuse wastewater in arid region. A key function of the wetland would be to provide additional N removal. To improve design criteria, a sequential model of nitrogen transformations (organic N --> ammonium: ammonium --> nitrate: nitrate --> nitrogen gas) was successfully calibrated and verified for a wetland in Kingman, Arizona. A sequential model has the ability to "recognize" species of nitrogen in the influent and predict species of nitrogen in the effluent. Model scenarios show that increasing nitrification rates in the summer and denitrification rates in the winter would improve nitrogen removal efficiencies. Several lines of evidence suggest that wintertime denitrification may be limited by carbon supply. Winter carbon supply could be augmented by routing a portion of the water through channels planted with dryland vegetation.

Carbon↗
PubMed2001

A multi-institutional analysis of laparoscopic orchidopexy.

OBJECTIVE: To combine and analyse the results from centres with a large experience of laparoscopy for the impalpable testis with small series, to determine the expected success rate for laparoscopic orchidopexy. METHODS: A questionnaire was distributed to participating paediatric urologists; each contributor retrospectively reviewed the clinical charts for their cases of therapeutic laparoscopy for an impalpable testis, detailing 36 variables for each patient. The data were collated centrally into a computerized database. For inclusion, the testis was intra-abdominal (including 'peeping' at the internal ring) at laparoscopic examination, was not managed through an open approach and did not undergo orchidectomy. Three surgical groups were assessed, with success defined as lack of atrophy and intrascrotal position: group 1, primary laparoscopic orchidopexy; group 2, a one-stage Fowler-Stephens (F-S) orchidopexy; and group 3, a two-stage F-S orchidopexy. RESULTS: Data were gathered from 10 centres in the USA, covering the period 1990-1999; 252 patients representing 310 testes were included and overall, 15.2% were lost to follow-up. There was no significant difference between success rates in the larger and smaller series. Atrophy occurred in 2.2% of 178 testes, 22.2% of 27 testes and 10.3% of 58 testes in groups 1-3, respectively. Testes were not in a satisfactory scrotal position in 0.6%, 7.4% and 1.7% of groups 1-3, respectively. The mean follow-up for each group was 7.7, 8.6 and 20.0 months, respectively. The overall success for all groups was 92.8% (97.2% group 1; 74.1% group 2; 87.9% group 3), with an atrophy rate of 6.1%. CONCLUSION: Laparoscopic orchidopexy for the intra-abdominal testis, in both large and small series, can be expected to have a success rate higher than that historically ascribed to open orchidopexy. Within this series, single-stage F-S laparoscopic orchidopexy resulted in a significantly higher atrophy rate than the two-stage repair. However, when considering both F-S approaches, the laparoscopic approach gave greater success than previously reported for the same open approaches. Despite the weaknesses inherent in a retrospective unrandomized study, we conclude that laparoscopic orchidopexy is, if not the procedure of choice, an acceptable and successful approach to the impalpable undescended testicle.

Child, Preschool↗
PubMed2001

The newborn exstrophy bladder inadequate for primary closure: evaluation, management and outcome.

PURPOSE: The surgical approach to the small newborn exstrophy bladder inadequate for primary closure remains undetermined. Various methods for long-term management have been implemented. We evaluated our experience with late primary closure of the small exstrophied bladder template. MATERIALS AND METHODS: Our institutional database of patients treated and followed for the exstrophy-epispadias complex was reviewed. Of these patients 19 had a bladder template that was too small to close in the newborn period. The treatment and outcome of these 19 patients were reviewed. RESULTS: Of the 19 children who had delayed closure due to a small bladder template 14 were males and 5 were females. Followup from birth ranged from 2 to 36 years (mean 18 years). Primary closure was performed at a mean patient age of 13 months (range 6 months to 2 years). Pelvic osteotomy was performed in 16 patients. Of the 19 patients 9 achieved continence after gaining a bladder capacity sufficient for bladder neck reconstruction, 4 required enterocystoplasty to augment bladder volume and perform clean intermittent catheterization (2 per stoma and 2 per urethra), 1 required a colon conduit for an extremely small bladder, and 1 underwent cystectomy and ureterosigmoidostomy for rhabdomyosarcoma. Four patients are currently incontinent, including 3 who are awaiting bladder neck reconstruction and 1 who has frequent nighttime incontinence that is medically managed. CONCLUSIONS: Delayed primary closure of the small bladder exstrophy template can allow the native bladder tissue adequate time to grow to a size feasible for successful closure. Epispadias repair can usually be performed at the same time and is facilitated by prior testosterone administration. Bladder neck reconstructive techniques have achieved continence without the need for augmentation or bladder replacement in 47% of the patients in our series. For patients who do not achieve adequate capacity for bladder neck reconstruction, preservation of the native bladder template facilitates future augmentation and ureteral reimplantation, thus requiring use of less bowel in the growing child.

Adolescent↗
PubMed2000

Multivariate models of mixed assortment: phenotypic assortment and social homogamy for education and fluid ability.

Phenotypic assortment is assumed to be the principal mechanism of spouse similarity in most biometrical studies. Other assortment mechanisms, such as social homogamy, may be plausible. Two models are presented that consider phenotypic assortment and social homogamy simultaneously (i.e., mixed assortment), where selective associations between social background factors (Model I) versus selective associations between total environments (Model II) distinguish the models. A series of illustrative analyses was undertaken for education and fluid ability available on a sample of 116 Swedish twin pairs and their spouses. On the basis of several fit criteria Model I was preferred over Model II. Both social homogamy and phenotypic assortment may contribute to spouse similarity for educational attainment and fluid ability. Furthermore, spouse similarity for fluid ability may arise indirectly from social homogamy and phenotypic assortment for educational attainment. Power analyses indicated greater observed power for Model I than Model II. Additional power analyses indicated that considerably more twin-spouse sets would be needed for Model II than Model I, to resolve social homogamy and phenotypic assortment. Effects of misspecification of mechanisms of spouse similarity are also briefly discussed.

Adult↗
PubMed2000

Open laparoscopic access using a radially dilating trocar: experience and indications in 50 consecutive cases.

BACKGROUND: Laparoscopy can be performed using needle access for initial insufflation or open access. PATIENTS AND METHODS: A technique for open laparoscopic access to the abdomen using a radially dilating cannula was used in 52 operations in 50 patients. Indications included age <2 years, severe kyphosis, and creation of an umbilical stoma. RESULTS: There was one case of minor leakage of carbon dioxide that did not affect the procedure being performed. There were two cases of preperitoneal placement, which were recognized immediately; in both, peritoneal access was easily obtained. CONCLUSION: Open laparoscopic access is safely and easily performed with a radially dilating trocar. This is the preferred technique at our institution for patients who meet the criteria for open access.

Child, Preschool↗
PubMed2000

The modified Cantwell-Ransley repair for exstrophy and epispadias: 10-year experience.

PURPOSE: We evaluate our experience with the modified Cantwell-Ransley epispadias repair technique to determine the complications and long-term results. MATERIALS AND METHODS: The modified Cantwell-Ransley epispadias repair was performed during the last 10 years in 93 males of whom 79 had classic bladder exstrophy and 14 had complete epispadias. Primary repair was performed in 65 boys with classic bladder exstrophy and 12 with epispadias, and secondary repair was done after prior failed reconstruction in 14 boys with classic exstrophy and 2 with complete epispadias. RESULTS: At mean followup of 68 months 87 patients had a horizontal or downward angled penis while standing. The incidence of urethrocutaneous fistulas was 23% in the immediate postoperative period and 19% at 3 months. A urethral stricture at the proximal anastomotic area developed in 7 patients and 5 (4 with exstrophy and 1 with epispadias) had minor skin separations of the dorsal penile skin closure. Catheterization or cystoscopy in 77 cases revealed an easily negotiable neourethral channel. CONCLUSIONS: The modified Cantwell-Ransley epispadias repair produces an excellent functional and cosmetic result.

Adolescent↗
PubMed2000

An analysis of clinical outcomes using color doppler testicular ultrasound for testicular torsion.

OBJECTIVES: To delineate the clinical outcomes of color Doppler ultrasound (US) in the equivocal torsion patient. METHODS: From 1992 to 1997, 130 patients (<23 years old) from 2 institutions underwent US imaging using a 7.5-mHz linear transducer to evaluate an acute scrotum equivocal, or of low suspicion, for torsion. The US reports and hospital charts of these patients were retrospectively reviewed. RESULTS: After clinical and radiologic evaluation, torsion was excluded in 110 patients without surgical exploration. In 3 patients, intermittent testicular torsion was diagnosed and in 17 patients, emergent exploration was performed for US diagnosis of testicular torsion. Twenty-five patients (22.7%) were subsequently lost to follow-up. Follow-up of 85 patients with US negative for torsion (mean length of follow-up = 466.9 days) revealed no testicular atrophy in 83. Two patients underwent delayed orchiectomy/contralateral orchiopexy for missed testicular torsion. Of 17 patients with US positive for torsion, 9 underwent orchiectomy for a necrotic torsed testis, 7 viable torsed testes were found, and 1 torsed appendix testis was found. Therefore, color Doppler US for the equivocal acute scrotum yielded a 1% false-positive rate, sensitivity of 88.9%, and specificity of 98.8%. CONCLUSION: When faced with ruling out testicular torsion, it is necessary to integrate the multiple pieces of patient data, knowing that each piece of data may have inaccuracies. With this in mind, this analysis of outcomes verifies that color Doppler US is an excellent adjunctive study in the clinically real situation in which the clinical evaluation is equivocal or low suspicion.

Adolescent↗
PubMed2000

Tmp21-I, a vesicular trafficking protein, is differentially expressed during induction of the ureter and metanephros.

PURPOSE: To identify genes participating in the reciprocal induction of the metanephros and ureter. MATERIALS AND METHODS: Embryonic day 14 Sprague-Dawley rat kidneys and ureters were microdissected into differentiating mesenchyme, ureteric buds, and extrarenal ureter and prepared for RT/PCR differential display. Differentially displayed cDNAs were reamplified, cloned, and sequenced. Expression was verified in the embryonic, newborn or adult kidneys by Northern blot hybridization or RT/PCR using sequence specific primers. A newborn rat kidney cDNA library was prepared and screened with probes of interest. Positive clones were screened, sequenced and compared to the GenBank/EMBL databases. A rabbit polyclonal antibody was raised to a synthetic peptide of the Tmp21-I protein and was used for immunohistochemistry. RESULTS: From the cDNAs differentially displayed by the ureteric buds cDNA B11, is 254 bp in length. The gene for B11 is expressed in adult and newborn kidneys as two transcripts (3.4 kb and 1.3 kb). More importantly, RT/PCR on E14 kidneys using B11 sequence specific primers identified expression in the embryonic kidney at the beginning of induction. B11 cDNA library screening yielded clones with inserts of 1.3 kb. This sequence encodes Tmp21-I, a vesicular trafficking protein. Immunohistochemistry demonstrates that Tmp21-I is abundant in the nephrogenic cortex of the newborn kidney and as a nephron matures, the protein levels decline. The protein is essentially absent in the adult rat kidney. CONCLUSIONS: Tmp21-I is a developmentally regulated gene expressed during kidney induction. Localized within the nephrogenic zone, it may direct the intracellular trafficking or secretion of proteins responsible for nephrogenesis.

Animals↗
PubMed2000

Radical bulbar dissection to correct severe chordee and proximal hypospadias.

PURPOSE: We describe a technique of proximal hypospadias correction that involves freeing the proximal normal bulbar urethra from perineal attachments to lengthen the ventral penis and decrease chordee. MATERIALS AND METHODS: Correction was performed in 9 patients with a mean age of 11.5 months who had proximal hypospadias and severe chordee that was perineal in 2, mid scrotal in 6 and penoscrotal in 1. After the penis was degloved the bulbar urethra was detethered to or beyond the perineal body without lifting the urethra from the corpora cavernosa. Any remaining penile chordee was corrected and the urethral plate was transected only when chordee persisted. When the urethral plate was intact and the penis straight, tubularized incised plate urethroplasty was done to correct hypospadias in 1 stage. Otherwise 2-stage repair was performed. RESULTS: Using this maneuver penile straightening was achieved in 2 of the 9 patients, resulting in a glanular urethral or penoscrotal meatus. Dorsal plication sutures required in 4 cases resulted in a mid shaft and penoscrotal meatus in 1 and 3, respectively. Residual chordee in the remaining 3 patients necessitated division of the urethral plate and 2-stage repair despite aggressive mobilization of the proximal urethra. Simultaneous tubularized incised plate urethroplasty was then performed in the 4 penoscrotal and 1 mid shaft meatus. All 6 patients who underwent a successful 1-stage procedure have excellent cosmetic results, while 1 required meatotomy. No fistula or chordee was present at a mean of 13.8 months of followup (range 3.9 to 27.1). CONCLUSIONS: This safe, rapid technique may compensate for significant penile tethering and chordee in a subpopulation of patients with proximal hypospadias, such as 6 of the 9 in our study. It also allows successful tubularized incised plate urethroplasty to be done simultaneously.

Humans↗
PubMed1999

Urethral obstruction after primary exstrophy closure: what is the fate of the genitourinary tract?

PURPOSE: We assessed the impact of posterior urethral obstruction after primary bladder exstrophy closure. MATERIALS AND METHODS: A review of the records of patients with classic bladder exstrophy at our institution identified 29 boys and 12 girls with a mean age of 11.75 years who had had posterior urethral outlet obstruction after closure was done in the neonatal period. RESULTS: Of these 41 patients 75% underwent closure elsewhere. At closure osteotomies were done in 13 patients and 23 were younger than 72 hours. Paraexstrophy skin flaps were used at primary closure in 27 cases (66%). Obstruction presented as recurrent urinary tract infection, upper tract deterioration with or without renal failure, bladder stones, difficult catheterization, urethral stitch erosion, a full bladder on ultrasound, a prolonged dry interval, urinary retention, inability to catheterize, bladder rupture, rectal prolapse and epididymitis or prostatitis. Usually the initial obstructive episode developed within 60 days of closure and it was recurrent. Therapy included suprapubic catheter placement, vesicostomy, ureterostomy, nephrostomy and multiple urethral manipulations, such as dilation with or without steroid injection, internal urethrotomy, urethral stitch removal, clean intermittent catheterization or open urethroplasty. All 6 patients who underwent long-term diversion via vesicostomy, ureterostomy or a conduit for greater than 6 months required permanent bowel segments for reconstruction, while in 5 of the 6 who underwent short-term diversion via nephrostomy or suprapubic tube placement for less than 6 months reconstruction was bowel-free. Of the 36 children in whom functional reconstruction was performed 9 are undergoing staged reconstruction, reconstruction failed in 14, 4 are socially dry and 9 are continent. CONCLUSIONS: Posterior urethral obstruction after exstrophy closure markedly decreases the success of staged bladder reconstruction, presents a significant risk to the upper urinary tract and should be detected early.

Bladder Exstrophy↗
PubMed1999

A multicenter outcomes analysis of patients with neonatal reflux presenting with prenatal hydronephrosis.

PURPOSE: Approximately 10 to 30% of prenatal cases of hydronephrosis result in the postnatal diagnosis of vesicoureteral reflux. Using a new generic prenatal-postnatal data sheet developed by the Society for Fetal Urology the characteristics, natural history and outcome of prenatal hydronephrosis confirmed postnatally to be vesicoureteral reflux were documented at 3 centers. MATERIALS AND METHODS: We performed a retrospective multicenter review of Society for Fetal Urology data sheets completed for each patient in whom prenatal hydronephrosis was proved to be postnatal vesicoureteral reflux from 1993 to 1998. RESULTS: In 56 male and 15 female patients with prenatal hydronephrosis a total of 116 refluxing renal units were confirmed postnatally. Of the 116 renal units 112 were hydronephrotic prenatally. During gestation increased hydronephrosis was noted with voiding in 4 cases. Of the 112 hydronephrotic renal units only 26 ureters in 15 patients were seen prenatally. The obstetrician considered the diagnosis of vesicoureteral reflux in only 24% of the cases. Postnatally 116 refluxing renal units were identified. Initial postnatal ultrasound was normal in 25% of the cases. Bilateral reflux was present in 36 male and 9 female patients. In 10 of the 19 uncircumcised patients (53%) urinary tract infection developed despite antibiotic prophylaxis. In 15 of the 74 renal units with grades III to V reflux the condition resolved at an average patient age of 0.9 and 2.1 years in boys and girls, respectively. A total of 27 refluxing renal units were reimplanted. CONCLUSIONS: The majority of prenatal reflux occurs in boys, and it is high grade and bilateral. The data sheets designed by the Society for Fetal Urology are useful data collection instruments. The presentation and natural history of vesicoureteral reflux are different in male and female individuals. In a significant number of renal units high grade reflux resolves spontaneously. Early circumcision may decrease the incidence of breakthrough urinary tract infection in this subpopulation. In addition, the effective management of prenatally detected reflux depends on multispecialty communication.

Female↗
PubMed1998

The staged approach to bladder exstrophy closure and the role of osteotomies.

Since the 1970's, the staged reconstruction of bladder exstrophy has yielded consistent surgical success. The Johns Hopkins Hospital approach begins with early pelvic ring approximation with abdominal wall, bladder, and posterior urethral closure. Within the first 72 hours of life, the malleable pelvis can sometimes be approximated without osteotomies. Beyond this age, the author's prefer a combined vertical iliac and horizontal innominate osteotomy. Second, we typically perform the epispadias closure at 1 year of age. A modified Cantwell-Ransley technique is performed, usually yielding an increase in bladder capacity and very satisfactory results. In the last phase, the modified Young-Dees-Leadbetter continence procedure along with transtrigonal/cephalotrigonal ureteroneocystostomies are performed when the urethra is catheterizable, the bladder capacity is 60 cc or greater, and the child will participate in a postoperative voiding program (typically 4-5 years of age). This applied approach usually results in a continent, voiding patient with pleasing external genitalia and preserved renal function.

Bladder Exstrophy↗
PubMed1998

Embryonic development of the ureter and bladder: acquisition of smooth muscle.

To delineate the temporal and spatial acquisition of the smooth muscle of the ureter, Sprague-Dawley rat embryos and newborn pups were immunostained with alpha-smooth muscle actin (alpha-SM actin) antibody. Alpha-SM actin expression was first detected in the urinary tract at 16 days of gestation (E16) in a thin subserosal zone about the urogenital sinus. At this time, the E16 ureter is composed of a simple cuboidal epithelium which is surrounded by 1 to 2 layers of condensed alpha-SM actin negative spindle shaped cells. No immunostaining was detected along the ureter or its intrarenal branches until the 20th day of gestation (E20). Alpha-SM actin expression in the E20 ureter exhibited regional differences. The number of alpha-SM actin positive smooth muscle cells was greatest in the distal ureter, intermediate in the mid ureter, and least in the proximal ureter near the kidney. While smooth muscle formation in the bladder was subserosal, in the ureter it was subepithelial. During postnatal life, alpha-SM actin expression increased in both organs as all periepithelial spindle cells stained positive and intensified their staining. Smooth muscle differentiation of the ureter and bladder occurs later in embryonic life than other visceral and vascular organs and occurs in an ascending fashion from the bladder to the intrarenal collecting system. It is likely that the activation of visceral smooth muscle myogenesis within the urinary tract is governed by positional information specific to the embryonic development of each organ.

Actins↗