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Biomedical subjects

R C Cohen

Publications and source records attributed to R C Cohen.

At least 19 recordsLinked to original sources
PubMed2006

Kinetics of NO and NO2 evolution from illuminated frozen nitrate solutions.

The release of NO and NO2 from frozen aqueous NaNO3 irradiated at 313 nm was studied using time-resolved spectroscopic techniques. The kinetic behavior of NO and NO2 signals during on-and-off illumination cycles confirms that NO2 is a primary photoproduct evolving from the outermost ice layers and reveals that NO is a secondary species generated deeper in the ice, whence it eventually emerges due to its inertness and larger diffusivity. NO is shown to be more weakly held than NO2 by ice in thermal desorption experiments on preirradiated samples. The partial control of gaseous emissions by mass transfer, and hence by the morphology and metamorphisms of polycrystalline ice, is established by (1) the nonmonotonic temperature dependence of NO and NO2 signals upon stepwise warming under continuous illumination, (2) the fact that the NO, NO2 or NOx (NOx identical with NO + NO2) amounts released in bright thermograms performed under various heating ramps fail to scale with photon dose, due to irreversible losses in the adsorbed state. Because present NO/NO2 ratios are up to 10-fold smaller than those determined over sunlit snowpacks, we infer that the immediate precursors to NO mostly absorb at lambda > lambda(max) (NO3-) approximately 302 nm.

Journal Article↗
PubMed2005

Local hydration environments of amino acids and dipeptides studied by X-ray spectroscopy of liquid microjets.

The nitrogen K-edge spectra of aqueous proline and diglycine solutions have been measured by total electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at neutral and high pH. All observed spectral features have been assigned by comparison to the recently reported spectrum of aqueous glycine and calculated spectra of isolated amino acids and hydrated amino acid clusters. The sharp preedge resonances at 401.3 and 402.6 eV observed in the spectrum of anionic glycine indicate that the nitrogen terminus is in an "acceptor-only" configuration, wherein neither amine proton is involved in hydrogen bonding to the solvent, at high pH. The analogous 1s --> sigma(NH) preedge transitions are absent in the NEXAFS spectrum of anionic proline, implying that the acceptor-only conformation observed in anionic glycine arises from steric shielding induced by free rotation of the amine terminus about the glycine CN bond. Anionic diglycine solutions exhibit a broadened 1s --> pi(CN) resonance at 401.2 eV and a broad shoulder resonance at 403 eV, also suggesting the presence of an acceptor-only species. Although this assignment is not as unambiguous as for glycine, it implies that the nitrogen terminus of most proteins is capable of existing in an acceptor-only conformation at high pH. The NEXAFS spectrum of zwitterionic lysine solution was also measured, exhibiting features similar to those of both anionic and zwitterionic glycine, and leading us to conclude that the alpha amine group is present in an acceptor-only configuration, while the end of the butylammonium side chain is fully solvated.

Glycine↗
PubMed2005

Photochemical production and release of gaseous NO2 from nitrate-doped water ice.

Temperature-programmed NO2 emissions from frozen aqueous NaNO3 solutions irradiated at 313 nm were monitored as function of nitrate concentration and heating rate, H, above -30 degrees C. Emissions increase nonmonotonically with temperature, displaying transitions suggestive of underlying metamorphic transformations. Thus, NO2 emissions surge at ca. -8 degrees C in frozen [NO3-] > 200 microM samples warmed at H = 0.70 degrees C min(-1) under continuous irradiation, and also in the dark from samples that had been photolyzed at -30 degrees C. The amounts of NO2 released in individual thermograms, SigmaN, increase less than linearly with [NO3-] or the duration of experiments, revealing the significant loss of photogenerated NO2. The actual SigmaN proportional, variant [NO3-]1/2 dependence (at constant H) is consistent with NO2 hydrolysis: 2NO2 + H2O --> NO3- + NO2- + 2H+, overtaking NO2 desorption, even below the eutectic point (-18 degrees C for aqueous NaNO3). The increasingly larger NO2 losses detected in longer experiments (at constant [NO3-]) are ascribed to secondary photolysis of trapped NO2. The relevance of present results to the interpretation of polar NO2 measurements is briefly analyzed.

Journal Article↗
PubMed2005

pH dependence of the electronic structure of glycine.

The carbon, nitrogen, and oxygen K-edge spectra were measured for aqueous solutions of glycine by total electron yield near-edge X-ray absorption fine structure (TEY NEXAFS) spectroscopy. The bulk solution pH was systematically varied while maintaining a constant amino acid concentration. Spectra were assigned through comparisons with both previous studies and ab initio computed spectra of isolated glycine molecules and hydrated glycine clusters. Nitrogen K-edge solution spectra recorded at low and moderate pH are nearly identical to those of solid glycine, whereas basic solution spectra strongly resemble those of the gas phase. The carbon 1s --> pi*(C=O) transition exhibits a 0.2 eV red shift at high pH due to the deprotonation of the amine terminus. This deprotonation also effects a 1.4 eV red shift in the nitrogen K-edge at high pH. Two sharp preedge features at 401.3 and 402.5 eV are also observed at high pH. These resonances, previously observed in the vapor-phase ISEELS spectrum of glycine, have been reassigned as transitions to sigma* bound states. The observation of these peaks indicates that the amine moiety is in an acceptor-only hydrogen bond configuration at high pH. At low pH, the oxygen 1s --> pi*(C=O) transition exhibits a 0.25-eV red shift due to the protonation of the carboxylic acid terminus. These spectral differences indicate that the variations in electronic structure observed in the NEXAFS spectra are determined by the internal charge state and hydration environment of the molecule in solution.

Glycine↗
PubMed2001

Urethral trauma in children.

We report our 12-year experience in the management of urethral injuries in nine children, six boys and three girls. The most common mechanisms of injury were motor vehicle accidents, followed by straddle injuries. All the injuries in boys involved the anterior urethra, and in girls the proximal or mid-urethra. There were associated injuries in five, including three pelvic fractures. All children were investigated with a retrograde urethrogram. Four were treated non-operatively with insertion of a urethral catheter. Of the remaining five, one had drainage of a penile haematoma, one cystourethroscopy, two insertion of urinary and suprapubic catheters, and one open cystotomy and passage of a guide wire with antegrade passage of a urethral catheter. Complications included one urinary tract infection, one urethral fistula, one urethrovaginal fistula, and two urethral strictures. Final outcome was satisfactory in all nine children.

Adolescent↗
PubMed2001

Laparoscopic varicocelectomy with preservation of the testicular artery in adolescents.

PURPOSE: The aim of this study was to determine if laparoscopic varicocelectomy (LV) with preservation of the testicular artery (TA) is a satisfactory alternative to standard open surgical techniques in adolescents. METHODS: Between June 1993 and June 1999 left LV was performed on 40 boys, median age, 12 years (range, 9 to 16 years). Selection for surgical correction included size of the varicocele, symptoms, and clinical or ultrasound assessment for testicular hypotrophy. Eight patients had undergone previous left-sided inguinal surgery, 5 of these for varicocele. Three laparoscopic ports were used. The TA was identified and preserved with the aid of a Doppler flow transducer ("Smart Needle"). All the testicular veins were ligated and divided. The inferior epigastric (IE) veins also were ligated in 19 patients. The operating time was a mean of 1 hour. The postoperative follow-up for a median of 19.5 months (range, 3 to 36 months) included clinical and ultrasound assessment. RESULTS: Preoperative assessment confirmed left-sided testicular hypotrophy 35 patients (88%). Thirty-eight varicoceles were stage 3, and 2 were stage 2. Testicular discomfort was present in 13 patients. Complete correction of the varicocele was achieved in 33 (83%). At a mean of 5 months after LV open repair in 7 patients confirmed a dilated cremasteric vein connecting to the IE veins. Ligation of the IE veins at the time of LV was associated with a persistent varicocele in 3 of 19 patients (16%), similar to the nonligated group, 4 of 21 patients (19%). Five patients (12.5%) had a mild hydrocele. The left testicular volume increased 30% to 50% in 28 patients (70%) at a median of 6.5 months after repair. Testicular atrophy did not occur in any patients. The majority of patients went home within 6 hours of surgery. CONCLUSIONS: The laparoscopic technique with preservation of the TA is an acceptable alternative to open surgical treatment of varicoceles. Further, it eliminates the risk of testicular atrophy and is the technique of choice when previous inguinal surgery has been performed. Ligation of IE veins was not associated with a decrease in the persistence of varicocele postoperatively.

Adolescent↗
PubMed1999

Laparoscopic bladder 'wrap' technique for repair of vesicoureteric reflux in a porcine model.

PURPOSE: The aim of this study was to determine if vesicoureteric reflux (VUR) can be successfully corrected laparoscopically by a bladder "wrap" technique in a pig model. METHODS: In 15 female piglets (mean weight, 22.5 kg) bilateral VUR was created by an open technique (11 grade 3, 2 each of grades 2 and 4). Eight weeks later (range, 4to 16 weeks) VUR was confirmed by fluoroscopic cystogram, and unilateral laparoscopic correction was performed. The contralateral ureter was used as a control. The bladder was emptied, and a 3F ureteric catheter was inserted on the repair side. Four 11-mm ports were inserted transperitoneally. The ureter was dissected to the ureterovesical junction (UVJ). Commencing at the UVJ, 2 (n = 9) or 3 (n = 6) black silk sutures were placed through the bladder muscle on either side of the ureter creating a bladder wrap around the distal 2 to 4 cm of ureter. At a mean of 16 weeks (range, 4 to 24 weeks) cystograms were repeated. The animals were killed the bladder and ureters underwent histopathology examination. RESULTS: VUR was corrected in 12 animals (80%). There was persistence of VUR in 2 and ureteric obstruction in 1. The wrap was intact in all animals. CONCLUSIONS: Laparoscopic correction of VUR by the bladder wrap technique is successful in pigs. Long-term follow-up studies will determine if this will be a satisfactory alternative surgical treatment for correction of VUR in children.

Animals↗
PubMed1999

Adverse outcome of congenital diaphragmatic hernia is determined by diaphragmatic agenesis, not by antenatal diagnosis.

BACKGROUND/PURPOSE: The authors studied their congenital diaphragmatic hernia (CDH) cases retrospectively to ascertain if classical CDH and diaphragmatic agenesis (DA) have separate clinical manifestations, whether antenatally diagnosed cases behave differently from those not diagnosed antenatally, and if antenatal diagnosis before 25 weeks carries a worse prognosis. METHODS: The authors performed a retrospective review of 23 infants with CDH treated at their institution between January 1996 and March 1999. The patients were divided into 3 groups that were analyzed: DA and classical CDH, antenatally diagnosed and nonantenatally diagnosed, and antenatally diagnosed before 25 weeks and after 25 weeks. RESULTS: There were 8 cases of DA and 11 cases of classical CDH. Four infants died without operation and could not be classified. Neonates with DA had significantly longer mean duration of preoperative stabilization compared with classical CDH (5.25+/-2.76 days v 1.36+/-1.0 days) and postoperative mechanical ventilatory support (15.7+/-3.0 days v 4.9+/-3.0 days). Fifty percent of DA patients died; all classical CDH patients survived. Twelve cases were diagnosed antenatally, 6 before 25 weeks' gestation. Antenatally diagnosed cases had no statistically significant difference in mortality rates from those not diagnosed antenatally; 50% of those diagnosed before 25 weeks survived. CONCLUSIONS: DA cases require more preoperative preparation and postoperative ventilation and have a bad prognosis compared with classical CDH. Antenatal diagnosis of CDH does not convey a different prognosis. Fifty percent of CDH patients with antenatal diagnosis before 25 weeks survive.

Diaphragm↗
PubMed1999

Cisapride in the control of symptoms in infants with gastroesophageal reflux: A randomized, double-blind, placebo-controlled trial.

OBJECTIVE: To evaluate the efficacy of cisapride in the treatment of uncomplicated gastroesophageal reflux in children younger than 36 months of age. STUDY DESIGN: A total of 95 patients satisfied the entry criteria and were randomly assigned to double-blind treatment with either cisapride (n = 50), 0.2 mg/kg 4 times daily, or placebo (n = 45) for 2 weeks. At the end of the 2-week treatment period, symptom diary and parental evaluation with repeat 24-hour pH study were performed. RESULTS: Sixty-eight patients completed the trial (38 in the cisapride group and 30 in the placebo group). There were no significant differences in the symptoms of crying, vomiting, or gagging; the overall symptom intensity score; or parental global evaluations. There was a significant difference (P <.03) in the percent time pH <4, the number of reflux episodes lasting more than 5 minutes, and the duration of the longest episode. No significant difference was demonstrated for the number of episodes with pH <4 or the reflux score. CONCLUSIONS: Cisapride was no better than placebo for relief of symptoms in children with uncomplicated gastroesophageal reflux. A beneficial effect was demonstrated in the cisapride group in relation to the measured parameters for esophageal acid exposure time.

Administration, Oral↗
PubMed1997

Ureteroceles in children: an ongoing challenge.

The treatment of ureteroceles in children requires an individualised approach. Antenatal diagnosis is the ideal, so that postnatal urinary antibiotic prophylaxis and appropriate investigations can be organised. Postnatal investigations should assess both upper and lower urinary tract. Renal and bladder ultrasound and radiographic micturating cystourethragraphy under antibiotic cover will both detect vesicoureteric reflux and assess any bladder outlet obstruction due to the ureterocele. Renal function, particularly of the upper moiety, is best evaluated by technetium Tc99m dimercaptosuccinic acid renal scan. Both function and obstruction can be quantitated by the Tc99m-mercaptoacetyltriglycine isotope scan with intravenous volume expansion (10 ml/kg) and furosemide diuresis (1 mg/kg). Intravenous urography provides the best anatomic information when the upper moiety is functional. The surgical management is based on the clinical situation, which is often variable, and therefore needs to be tailored for each patient. The general principles include restoration of anatomy to as near normal as possible and preservation of functional renal tissue.

Antibiotic Prophylaxis↗
PubMed1996

Endoscopic laser division of an esophageal web in a child.

The authors report the first successful endoscopic laser division of a congenital esophageal web in a child in whom dilatation had failed. Laser lysis is minimally invasive and should be attempted before surgery is considered.

Dilatation↗
PubMed1995

Intraneural ganglion of the common peroneal nerve in a 4-year-old boy.

The case history of a 4-year-old boy with an intraneural ganglion of the common peroneal nerve is presented. These lesions are rare, more commonly affect males, and typically present with a painful foot-drop. A mass is often palpable adjacent to the neck of the fibula. Our patient has made a good recovery after surgery.

Child, Preschool↗
PubMed1994

Postnatal diagnosis and outcome of urinary tract abnormalities detected by antenatal ultrasound.

OBJECTIVES: To determine the incidence of urinary tract abnormalities detected by antenatal ultrasound; the value of fetal renal measurements in predicting significant uropathy; and the nature and clinical outcome of fetal uropathy. DESIGN AND SETTING: A retrospective analysis of babies with urinary tract abnormalities detected before birth who were born at or referred to a teaching hospital. PATIENTS: One hundred and twenty-five babies born between June 1989 and November 1992. Sixty-nine babies were born at Westmead hospital and 56 were born elsewhere and referred to Westmead Hospital for investigation. RESULTS: The incidence of uropathy detected before birth among babies born at the teaching hospital was 5.1 per 1000 births. In 60% of these babies, significant abnormalities were confirmed after birth (3.1 per 1000 births). We found a significance of 71% and a specificity of 89% for fetal measurements in predicting significant uropathy. Among all 125 babies the most common abnormalities were pelviureteric junction (PUJ) anomalies (34%), minimal hydronephrosis (26%), ureteric reflux (18%) and multicystic kidney (7%). Pyeloplasty has been performed in 23 (46%) of the 52 kidneys with PUJ anomalies. Renal parenchymal abnormality was detected in four of 22 kidneys with ureteric reflux (18%). Of these four, all were exposed to Grade IV or V ureteric reflux but none had been infected. CONCLUSIONS: Antenatal ultrasound is a sensitive, though nonspecific, tool for the non-invasive identification of congenital abnormalities of the urinary tract, which are common and frequently asymptomatic after birth. Although ureteric reflux may not be predicted from renal measurements, the degree of fetal hydronephrosis indicates the likelihood of obstructive abnormality and, thus, the extent of postnatal investigation required.

Female↗
PubMed1993

Continuous epidural analgesia in newborn infants undergoing major surgery.

Providing safe, effective analgesia for newborn infants undergoing major surgery remains a challenge to pediatric anesthetists and surgeons. Continuous epidural analgesia (CEA) has been shown to provide safe and effective analgesia in infants and children; however, there is little reported use in neonates. We review our experience of CEA in 14 newborn infants (32 to 40 weeks gestation) aged 4 hours to 35 days undergoing major surgery, as well as a further 6 ex-preterm (25 to 29 weeks gestation) infants aged 2 to 5 months at time of surgery. In all cases effective analgesia was achieved for up to 69 hours without complication. All infants were awake and extubated uneventfully at the completion of surgery, which lasted 5 hours in one case. None of the infants developed respiratory depression or prolonged apnea. The technique has been widely accepted by surgeons, neonatal nursing staff, and neonatologists.

Analgesia, Epidural↗
PubMed1993

Splenic injury in children: a 10 year experience.

The aim of this report was to review retrospectively the management of splenic trauma at a major Australian tertiary referral centre (Westmead Hospital) over a 10 year period. Forty-nine patients (0-15 years of age) with documented blunt splenic trauma were identified. The causes of splenic injury were road trauma (73%) and falls (27%). There were 22 minor injuries (Injury severity score [ISS] < 16) and 27 severe injuries (ISS > or = 16). All nine deaths were related to road trauma (mean ISS = 59). The investigation most commonly used was CT scanning (47%). Peritoneal lavage was performed in six patients (12%). Management involved non-operative care in 29 patients (57%), exploratory laparotomy alone in 5 (10%), splenic salvage in 2 (4%) and splenectomy in 13 (26%). This experience supports the view that non-operative management of splenic injury in haemodynamically stable children is safe and is the preferred treatment. Experienced assessment and meticulous observation is necessary. Laparotomy is indicated if there is continuing haemodynamic instability despite resuscitation. Operative management is aimed at splenic salvage with splenectomy being reserved for uncontrolled haemorrhage.

Accidental Falls↗