Biomedical subjects

J R Buck

Publications and source records attributed to J R Buck.

At least 19 recordsLinked to original sources

PubMed2000

Stereocontrolled syntheses of deoxyribonucleosides via photoinduced electron-transfer deoxygenation of benzoyl-protected ribo- and arabinonucleosides.

The stereocontrolled, de novo syntheses of beta-2'-deoxy-, alpha-2'-deoxy-, beta-3'-deoxy-, and beta-2', 3'-dideoxyribonucleosides are described. Strategically protected ribose, arabinose, and xylose glycosylation precursors were synthesized bearing C2-esters capable of directing Vorbrüggen glycosylation. The key step is the regioselective deoxygenation of the desired hydroxyl group as either the benzoyl- or 3-(trifluoromethyl)benzoyl derivative. This deoxygenation is accomplished via a photoinduced electron-transfer (PET) mechanism using carbazole derivatives as the photosensitizer. The syntheses of the desired deoxynucleoside generally proceed in three steps from a common, readily available precursor.

Arabinonucleosides↗

PubMed2000

Control error statistics.

Control in general, and manual control in particular, are traditional topics in ergonomics. Numerous studies on these topics have focused on vehicular control or tracking, as experimenters have attempted to describe control performance in terms of control errors, typically using the 'root-mean-square' (RMS) error. The authors of this study believe that this and related statistics are not well understood by the ergonomics community and that additional or alternative performance measurements would be more appropriate as measurements of the particular criteria of concern. Accordingly, this paper shows some background of the RMS and similar statistics of control error, some new statistics, and their interrelationships. This development is intended as a guide to selection of criteria for use in tracking and manual control and their measurement.

Automobile Driving↗

PubMed2000

Synthesis and modification of the whistles of the bottlenose dolphin, Tursiops truncatus.

A signal-processing algorithm was developed to analyze harmonic frequency-modulated sounds, to modify the parameters of the analyzed signal, and to synthesize a new analytically specified signal that resembles the original signal in specified features. This algorithm was used with dolphin whistles, a frequency-modulated harmonic signal that has typically been described in terms of its contour, or pattern of modulation of the fundamental frequency. In order to test whether other features may also be salient to dolphins, the whistle analysis calculates the energies at the harmonics as well as the fundamental frequency of the whistle. The modification part of the algorithm can set all of these energies to a constant, can shift the whistle frequency, and can expand or compress the time base or the frequency of the whistle. The synthesis part of the algorithm then synthesizes a waveform based upon the energies and frequencies of the fundamental and first two harmonics. These synthetic whistles will be useful for evaluating what acoustic features dolphins use in discriminating different whistles.

Algorithms↗

PubMed1995

Effect of aminophylline on high-energy phosphate metabolism and fatigue in the diaphragm.

BACKGROUND: Diaphragmatic fatigue causes respiratory failure, for which aminophylline has been used as therapy. Because the mechanism of action of aminophylline in reversing diaphragmatic fatigue is unclear, we used in vivo 31P magnetic resonance spectroscopy (MRS) to determine the relation between diaphragmatic activation, force output, and aerobic metabolism. METHODS: Bilateral phrenic stimulation was used to pace the diaphragm in pentobarbital-anesthetized piglets (6-10 weeks old; n = 44). Esophageal and abdominal pressures were measured to calculate transdiaphragmatic pressure (Pdi) (Pdi = abdominal pressure-esophageal pressure) as an index of force output. Activation was determined by the amplitude of the compound action potential of the diaphragmatic electromyogram. Aerobic metabolism was assessed with a 31P MRS surface coil on the right hemidiaphragm with the animal in a 4.7-T magnet. The animals were divided into four groups based on aminophylline loading dose: saline, aminophylline 10 mg/kg (A10), aminophylline 20 mg/kg (A20), and aminophylline 40 mg/kg (A40). After aminophylline loading the diaphragm was paced for 25 min followed by a 10-min recovery. RESULTS: Aminophylline concentrations were 12.2 +/- 0.7, 21.9 +/- 2.4, and 44.9 +/- 3.6 mg/l in the A10, A20, and A40 groups, respectively. Compound action potential amplitude decreased in all groups by 30% after 25 min of pacing. Conversely, Pdi remained at 100 +/- 3% of the initial value after 5 min of pacing in the A40 group but decreased to 75 +/- 3% in the saline group. Pdi recovered completely (103 +/- 17%) in the A40 group but remained depressed (72 +/- 6%) in the saline group. Pdi values were intermediate in the A10 and A20 groups. MRS data revealed inadequate energy supply/demand ratio in the saline group such that the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) increased to 1.01 +/- 0.09 after 5 min of pacing. Pi/PCr remained unchanged in the A40 group and was intermediate in the A10 and A20 groups. beta-Adenosine triphosphate and intracellular pH did not differ among groups or as a function of pacing. Diaphragmatic blood flow increased from a resting value of 35-60 to 300-410 ml.min-1 x 100 g-1 during pacing in all groups and was not affected by aminophylline dose. CONCLUSIONS: Aminophylline, in a dose-dependent fashion, delays the onset of fatigue and improves recovery from fatigue. Delayed fatigue is associated with improved aerobic metabolism as reflected in a low Pi/PCr ratio.

Action Potentials↗

PubMed1995

Use of absorbable mesh as an aid in abdominal wall closure in the emergent setting.

A surgeon has many options available to aid in the closure of abdominal wall defects in the elective setting. In the emergent setting, active infection or contamination increases the likelihood of infection of permanent prosthetic material and limits the surgical options. In such settings, we have used absorbable mesh (Dexon) as an adjunct to fascial closure until the acute complications resolve. To evaluate the effectiveness of this technique, we reviewed the outcome of such closures in 26 critically ill patients. Between July 1987 and June 1993, 26 patients were identified who had placement of absorbable mesh as part of an emergent laparotomy at a major urban trauma center. Through a retrospective chart review, the incidence of complications and outcome of the closure were tabulated. Seven patients were initially operated on for trauma. Two of the patients had mesh placement at their initial procedure secondary to fascial loss from trauma. The remainder of the patients hd mesh placement during a subsequent laparotomy for complications related to their initial procedure. Indications for these laparotomies included combinations of wound dehiscence, intra-abdominal abscess, anastomotic disruption, and perforation. Mesh placement in patients with intra-abdominal infection created effectively open abdominal wounds that allowed continued abdominal drainage, but required extensive wound care. Despite the absorbable nature of the mesh and often prolonged hospital stay in these ill patients, none of them required reoperation for dehiscence, recurrence of intra-abdominal abscess, or infection of the mesh.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Abscess↗

PubMed1994

Primary common bile duct closure following exploration: an effective alternative to routine biliary drainage.

Primary closure of the common bile duct following exploration has been safely and effectively performed, as advocated by Halsted, provided no evidence of pancreatitis, cholangitis, or ampullary obstruction exists. Using this precedent, the operative management and clinical course of 29 patients undergoing common bile duct exploration (CBDE) for choledocholithiasis from 1986 to 1992 were reviewed. Ten patients had primary closure of the common bile duct (CBD) following choledochotomy and exploration, and 17 patients had t-tube placement. Two patients had CBDE through an enlarged cystic duct that was then ligated. Patients were selected for t-tube placement if they had pancreatitis, ascending cholangitis, evidence of retained stones, or ampullary obstruction. Two patients in this series died. No patient with primary closure of the CBD suffered a biliary complication including retained stones, biliary fistula, pancreatitis, or bile peritonitis. Serious systemic complications were comparable in both groups. The results of this series support the safety of primary common bile duct closure in selected cases.

Cholecystectomy↗

PubMed1993

A quantitative measure of similarity for tursiops truncatus signature whistles.

Bottlenose dolphins (tursiops truncatus) produce individually distinctive narrow-band "signature whistles." These whistles may be differentiated by the structure of their frequency contours. An algorithm is presented for extracting frequency contours from whistles and comparing two such contours. This algorithm performs nonuniform time dilation to align the contours and provides a quantitative distance measure between the contours. Two recognition experiments using the algorithm on three dolphin whistles from each of five individuals classified 15 out of 15 single-loop whistles correctly, and 14 out of 15 central loops for multiple-loop whistles correctly.

Algorithms↗

PubMed1993

Diaphragmatic fatigue assessed by 31P-magnetic resonance spectroscopy in vivo.

We tested whether fatigue of the piglet diaphragm is associated with inadequate oxidative metabolism as measured by magnetic resonance spectroscopy (MRS). An MRS measured ratio of inorganic phosphate to phosphocreatine (Pi/PCr) > or = 1 was taken as evidence of inadequate oxidative metabolism. Piglets (n = 10) underwent phrenic nerve pacing for 90 min with stimulation frequency of 30 Hz and duty cycle of 0.33. In a separate group of six piglets PCr, Pi, ATP, and intracellular pH were measured by in vivo MRS, and diaphragmatic blood flow was measured with radioactive microspheres at control, 2, 10, 45, 60, and 90 min of pacing. Transdiaphragmatic pressure fell from 25 +/- 3 to 15 +/- 2 mmHg (61 +/- 5%) at 2 min and remained depressed in a separate group of four piglets (P < 0.05). Conversely, compound action potential amplitude remained constant for the first 10 min of pacing and fell to 68 +/- 5% of control at 45 min (P < 0.05). Pi/PCr rose from a control value of 0.32 +/- 0.06 to 0.92 +/- 0.23 at 2 min and 0.79 +/- 0.03 at 10 min (P < 0.05) before returning toward control at 45-90 min. O2 delivery increased from 4.6 +/- 1.2 to 24.7 +/- 4.8 ml.min-1.100 g-1 at 2 min and 18.4 +/- 2.2 ml.min-1.100 g-1 at 10 min (P < 0.05) but then fell to lower levels at 45-90 min. ATP and intracellular pH remained constant except for a decline in pH to 6.98 +/- 0.09 at 45 min (P < 0.05) from the control value of 7.26 +/- 0.06.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1992

Severe pancreatico-duodenal injuries: the effectiveness of pyloric exclusion with vagotomy.

The operative management and clinical course of 17 patients treated for severe pancreatico-duodenal injuries from 1983 to 1990 was reviewed. The etiology of these injuries was gunshot wound in 15 patients; stab wound in 1 patient; and a motor vehicle accident in 1 patient. Seven patients presented in shock with a systolic blood pressure of less than 80. At exploration, 57 associated injuries were found in the 17 patients including 16 major vascular injuries. All patients were treated with pyloric exclusion and drainage. Vagotomy was performed in eight patients. None of these 17 patients were felt to have extensive enough damage to require pancreatico-duodenectomy. Two patients died in the immediate postoperative period of severe coagulopathy and two patients died of sepsis. Seven patients had complications related to the pancreatico-duodenal injury. All seven developed pancreatic fistulas; three also had pancreatitis and two developed multiple enterocutaneous fistulas. Systemic complications included pulmonary complications in eight patients and sepsis in five patients, including two patients with abdominal abscesses. Six patients bled in the immediate postoperative period secondary to coagulopathy. Three patients had complications related to pyloric exclusion. One developed afferent loop syndrome necessitating reoperation. The other two had marginal ulcers, which either perforated or bled and required reoperation. Of interest, neither of these two patients had vagotomy initially. The results of this series confirm the effectiveness of pyloric exclusion with vagotomy for severe pancreatico-duodenal injury.

Adolescent↗

PubMed1989

Prediction of successful primary closure of congenital abdominal wall defects using intraoperative measurements.

To determine whether intragastric pressure (IGP) and central venous pressure (CVP) would reliably predict successful primary closure of congenital abdominal wall defects (omphalocele/gastroschisis) in newborn infants, we developed the following prospective intraoperative management protocol. Following a temporary trial of fascial closure, infants who had an IGP less than 20 mm Hg or an increase in CVP of less than 4 mm Hg were primarily closed. If IGP was greater than 20 mm Hg or if CVP increased by more than 4 mm Hg, the temporary closure of the abdomen was reopened and a prosthetic silo was placed. Ten infants who were less than 24 hours old and averaged 2.7 kg (range, 1.4 to 4.2 kg) and 37-weeks gestation (range, 32 to 41 weeks) were studied. Eight infants met criteria for primary closure. Their IGP averaged 14 +/- 4 mm Hg (+/- SD) (range, 8 to 19 mm Hg), and their increase in CVP averaged 1 +/- 2 mm Hg (range, -2 to 3 mm Hg). In the two infants who required staged repair, IGP averaged 25 +/- 1 mm Hg (+/- SD) (range, 24 to 25 mm Hg), and the increase in CVP averaged 7 +/- 1 mm Hg (range, 6 to 8 mm Hg). All patients were anesthetized with fentanyl (12.5 micrograms/kg) and paralyzed with metocurine (0.3 mg/kg) intraoperatively. There were no postoperative complications in either group of patients related to increased intraabdominal pressure, and all patients were extubated within 48 hours of the initial surgery. We conclude that the intraoperative measurement of changes in IGP and CVP can serve as a guide to the operative management of congenital abdominal wall defects and can reliably predict successful outcome following repair.

Abdominal Muscles↗

PubMed1989

Relationship of diaphragmatic contractility to diaphragmatic blood flow in newborn lambs.

We determined the relationship of diaphragmatic contraction rate to diaphragmatic blood flow (Qdi), metabolism, and contractility in nine open-chested mechanically ventilated newborn lambs. The diaphragm was paced for 15 min at slow (20/min) and fast (100/min) contraction rates each followed by a 30-min rest period. There was a mild reduction in transdiaphragmatic pressure (Pdi) during the slow contraction period accompanied by a shift to the right of the curve relating stimulation frequency (10-100 Hz) to Pdi. Pdi returned to control at the start of the fast contraction period, but then fell by 30% within 2 min with continued fast contraction rates. The frequency-Pdi curve was significantly shifted to the right. Qdi, O2 transport, and O2 consumption increased during slow contraction and to an even greater extent during fast contraction. Fractional O2 extraction reached an apparent maximum during slow contraction. Lactate efflux from the right phrenic vein during slow contraction remained unchanged from control. During fast contraction lactate efflux rose proportionately more than did O2 consumption. We conclude that the energy demands at fast rates of diaphragmatic contraction in newborn lambs cannot be met by aerobic metabolism alone despite increasing O2 transport to the diaphragm.

Animals↗

PubMed1988

Hemodynamic effects of primary closure of omphalocele/gastroschisis in human newborns.

To determine whether they could establish reliable, objective criteria that would predict safe, primary closure of abdominal wall defects (omphalocele/gastroschisis) in newborn infants, the authors measured intraoperative changes in intra-gastric pressure (IGP), central venous pressure (CVP), cardiac index (CI), systolic arterial blood pressure (BP), and heart rate (HR). Eleven neonates, who averaged 2.7 kg (range 1.5-4.1 kg) and 36 weeks gestation (range 30-41 weeks) were anesthetized with fentanyl (7.5-12.5 micrograms/kg), metocurine (0.3 mg/kg), and oxygen. Three infants had defects that were too large to close primarily. Of the eight infants who underwent primary closure, four required re-operation within 24 h because of oliguria or poor peripheral perfusion. Infants who required re-operation had intra-gastric pressures of 20 mmHg or more, a decrease in CI of 0.78 1.min.m2 or more, and an increase in CVP of 4 mmHg or more. Heart rate, BP, and systemic vascular resistance did not differ in infants requiring and not requiring re-operation. The authors conclude that intraoperative measurement of changes in IGP, CVP, and/or CI can reliably predict success or failure of primary operative repair of abdominal wall defects in human neonates.

Abdominal Muscles↗

PubMed1988

Status reporting of "eyes on" and peripheral displays during tracking.

In response to external requests, pilots often orally report status information read from scattered visual displays while simultaneously controlling an aircraft. For an experimentally controlled "status-reporting" task, we found that the input frequency on a concurrent-tracking task and the task stream-related factors of the rate, uncertainty, and timing of requests showed few significant effects on mean performance times and standard deviations. Tracking performance did vary greatly between the different phases of the "status-reporting" task, the different types of displays and their locations, and the different tracking-input frequencies. An elementary manual control model produced conformal tracking error means and standard deviations when parameters corresponding to behavioral changes were varied. These results indicated that both the performance time statistics of the "status-reporting" task and the influence of concurrent performance on tracking error can be estimated using simple methods.

Adult↗

PubMed1987

Efficacy of emergency room thoracotomy in pediatric trauma.

With improved rapid transportation systems, an increasing number of children may arrive at the emergency room (ER) without detectable vital signs and may undergo vigorous resuscitation, including emergency room thoracotomy, aortic cross clamping, and open cardiac massage. Of 1,287 pediatric trauma admissions between 1980 and 1985, 101 deaths were recorded. Fifty (50%) of the deaths occurred in the ER. Thirty-three of the patients were pronounced dead with obvious irreversible injuries, while 17 (34%) with suspected thoracoabdominal injuries underwent ER thoracotomy during resuscitation. None of the 17 patients had detectable vital signs upon arrival to the ER. Fifteen patients had multisystem injuries associated with blunt trauma and two with isolated penetrating injuries. Despite maximal conventional resuscitation and ER thoracotomy, none of the 17 patients survived. In this group of pediatric blunt trauma victims who appear initially salvageable, and present in the ER with no detectable vital signs, ER resuscitative thoracotomy did not influence survival. ER thoracotomy in children, therefore, should be reserved for patients presenting with penetrating thoracic injuries or blunt injuries associated with detectable vital signs and deterioration despite maximal conventional therapy.

Adolescent↗

PubMed1987

The efficacy of computed tomography in evaluating abdominal injuries in children with major head trauma.

Physical examination may be unreliable in the evaluation of children with blunt abdominal trauma particularly in those with associated major head injuries. In the absence of obvious clinical signs or physical findings of intraabdominal injury, the usefulness of abdominal computed tomography in children is controversial. To test the efficacy of CT scans, a 12-month prospective study of computed tomography for the initial assessment of children with blunt abdominal trauma and major head injuries was carried out. Of 320 pediatric trauma admissions to our regional trauma center, 65 consecutive patients with Glasgow Coma Scores less than ten were managed with sequential head and abdominal computed tomography in the emergency room for (1) closed head injury and (2) suspected abdominal trauma. Fifteen patients (23%) were found to have significant intraabdominal injury. Only two required operative intervention. No patients died as a result of the abdominal injuries. In children with significant head trauma and suspected abdominal trauma, combined head and abdominal CT proved to be reliable.

Abdominal Injuries↗

PubMed1986

Hydroperoxide-dependent epoxidation of 3,4-dihydroxy-3,4-dihydrobenzo[a]anthracene by ram seminal vesicle microsomes and by hematin.

Addition of arachidonic acid to ram seminal vesicle microsomes oxidizes 3,4-dihydroxy-3,4-dihydrobenzo[a]anthracene (BA-3,4-diol) to five more polar products. Four of the products are identified by chromatographic and spectroscopic analysis as tetrahydrotetraols, which are solvolysis products of dihydrodiolepoxides. The fifth product is a 10-methyl ether formed by methanolysis of the anti-diolepoxide. Quantitation of the individual products indicates that anti-diolepoxides predominate over syn-diolepoxides by approximately 2:1. Identical product profiles are detected from the reaction of BA-3,4-diol with hematin and 13-hydroperoxy-octadecadienoic acid in the presence of Tween 20. No other products are detected in either system, which indicates that peroxyl radicals oxidize BA-3,4-diol exclusively by epoxidation of the 1,2-double bond. The stereochemical and regiochemical differences between oxidation of BA-3,4-diol by peroxyl radicals and cytochrome P-450 are dramatic and suggest that BA-3,4-diol is uniquely suited as a probe to quantitate peroxyl radical-dependent epoxidation in vitro and in vivo.

Animals↗

PubMed1985

A therapeutic trial of amniotic epithelial cell implantation in patients with lysosomal storage diseases.

To determine whether allografts of normal amniotic epithelium might provide a nonimmunogenic cellular source of exogenous lysosomal enzymes, subcutaneous implants of amniotic epithelium were performed in six children with clinically advanced storage diseases. The clinical and the biochemical status of each patient was observed for several weeks after amniotic epithelial cell implantation (AECI). Serial studies of blood samples from each patient in the post-AECI period did not demonstrate any increase in levels of deficient lysosomal hydrolase. In two patients, quantitative urinary excretion of substrate was also studied and did not show consistent alterations after AECI. No patient had objective improvement in clinical or neurodevelopmental status following AECI. Two patients died with progressive disease at 2 1/2 and 3 1/2 mo after AECI; no residual amniotic epithelium was found at postmortem examination. Four patients are alive with progressive disease at 6-14 mo after AECI. We conclude that allografts of normal human amnion do not provide sufficient replacement hydrolases for clinical or biochemical improvement in lysosomal storage diseases.

Amidohydrolases↗

PubMed1985

Life-threatening airway obstruction as a complication to the management of mediastinal masses in children.

Life-threatening airway obstruction from large mediastinal masses in children poses a difficult diagnostic and therapeutic dilemma, requiring the close coordination of a pediatric surgeon, anesthesiologist, radiologist, and oncologist. To focus on this problem, the anesthetic and surgical management of 50 consecutive children with mediastinal masses treated between 1978 and 1984 were reviewed. Thirty children presented with respiratory symptoms; nine had life-threatening respiratory compromise with dyspnea, orthopnea, and stridor. Thirteen of these symptomatic children had marked compression of the trachea and/or mainstem bronchi on radiographic studies. The tracheal cross-sectional area which was measured by computed tomography was decreased by 35% to 93% of the normal tracheal dimensions in these children. Nonresectable malignant neoplasms including lymphoma, Hodgkin's disease, rhabdomyosarcoma, and neuroblastoma were the eventual diagnoses in 10 of these patients. The other 3 patients were less than 4 years old and had benign lesions. General anesthesia was judged to be prohibitively risky in 5 of 13 patients. The diagnosis was established by node or needle biopsy under local anesthesia, and general anesthesia was deferred until the compromised airway was alleviated by radiation and chemotherapy. General anesthesia with endotracheal intubation was administered to 8 patients, 5 of whom developed total airway obstruction. Using a variety of maneuvers, ventilation was reestablished in all 5 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗