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Biomedical subjects

D E Cohen

Publications and source records attributed to D E Cohen.

At least 19 recordsLinked to original sources
PubMed1992

Effects of alfentanil on intracranial pressure in children undergoing ventriculoperitoneal shunt revision.

The effects of alfentanil on intracranial pressure in patients with diminished intracranial compliance has not been established. Ten patients with hydrocephalus of varying etiologies, ages 16 months to 20 yr, presenting for ventriculoperitoneal shunt revision were studied. Following induction of anesthesia with thiopental, nitrous oxide/oxygen, and isoflurane, the trachea was intubated and anesthesia was maintained with isoflurane (0.5%), nitrous oxide (70%), and oxygen. After a minimum of 30 min and after the new shunt was placed, alfentanil was administered in increments of 10, 20, and 40 micrograms/kg at 3-min intervals, and intracranial pressure was measured over 12 min via the new shunt. In these unstimulated, normocapnic (PETCO2 32-38 mmHg) patients, heart rate, mean arterial pressure, and cerebral perfusion pressure declined from 110 +/- 26 beats/min, 90 +/- 11 mmHg, and 71 +/- 14 mmHg, to 84 +/- 25 beats/min, 66 +/- 11 mmHg, and 45 +/- 16 mmHg (mean +/- SD), respectively, by 3 min after the third dose (P less than 0.001). Intracranial pressure did not change from baseline (19 +/- 14 mmHg vs. 21 +/- 11) after any dose of alfentanil. Contrary to earlier studies in adult patients with brain tumors, the authors found that alfentanil, in pediatric patients with hydrocephalus anesthetized with oxygen, nitrous oxide, and isoflurane, did not increase intracranial pressure within a 9-min study period. The significant decreases in cerebral perfusion pressure observed merit concern and further study.

Adolescent↗
PubMed1992

Bile salt hydrophobicity controls vesicle secretion rates and transformations in native bile.

After drainage of the bile salt pool, we infused unanesthetized bile fistula prairie dogs (Cynomys ludovicianus) intravenously with taurine-conjugated chenodeoxycholate (TCDC), cholate (TC), ursodeoxycholate (TUDC), and ursocholate (TUC) in concentrations that attained greater than 94% enrichment of biliary bile salts. With decreases in bile salt hydrophobicity, maximum steady state lecithin and to a lesser extent cholesterol secretion rates decreased in the rank order, TCDC greater than TC greater than TUDC greater than TUC. By phase analysis, TCDC-rich and TC-rich biles plotted inside their respective micellar zones, whereas TUDC-rich and TUC-rich biles plotted outside and were so-called "supersaturated" with cholesterol. Quasi-elastic light scattering and electron microscopy, when performed within 30 min of collection, revealed unilamellar vesicles in all biles. By 24 h, vesicles in TCDC-rich and TC-rich biles had dissolved into mixed micelles, whereas vesicles in TUDC-rich biles formed mixed micelles plus multilamellar liquid crystals, and vesicles in TUC-rich biles formed multilamellar liquid crystals exclusively. Because cholesterol/phospholipid molar ratios of multilamellar liquid crystals were less than or equal to 1, cholesterol monohydrate crystals did not form in these biles. We conclude that, despite drastic alterations in bile salt detergency, unilamellar vesicles are the final common pathway for lecithin and cholesterol secretion into bile. During equilibration of bile, the fate of unilamellar vesicles may be micellar, micellar plus liquid crystalline, or liquid crystalline only depending on the detergency (i.e., hydrophobic-hydrophilic balance) of the secreted bile salt.

Absorption↗
PubMed1992

Is outpatient tonsillectomy appropriate for young children?

The current literature suggests that outpatient tonsillectomy is a safe, cost-effective procedure. These reports have based their conclusions on the low rates of postoperative bleeding and dehydration. Generally, they have not examined other factors that may influence the postoperative course or identified groups of patients in whom outpatient management may not be appropriate. The literature regarding tonsillectomy in young children is conflicting. A retrospective analysis of the records of 223 children, 36 months of age and younger who had tonsillectomies, was performed. Postoperative airway complications including oxygen desaturation and airway obstruction developed in 115 patients. Seventeen (7.6%) children required postoperative care in an intensive care unit while an additional 117 (52.5%) patients received more than standard management. Preoperative apnea, an age of less than 12 months, and the presence of accompanying medical conditions were associated with a higher incidence of postoperative airway complications. It is recommended that tonsillectomy in patients under 36 months of age be planned as an inpatient procedure.

Age Factors↗
PubMed1991

Acyl chain unsaturation modulates distribution of lecithin molecular species between mixed micelles and vesicles in model bile. Implications for particle structure and metastable cholesterol solubilities.

We determined the distribution of lecithin molecular species between vesicles and mixed micelles in cholesterol super-saturated model biles (molar taurocholate-lecithin-cholesterol ratio 67:23:10, 3 g/dl, 0.15 M NaCl, pH approximately 6-7) that contained equimolar synthetic lecithin mixtures or egg yolk or soybean lecithins. After apparent equilibration (48 h), biles were fractionated by Superose 6 gel filtration chromatography at 20 degrees C, and lecithin molecular species in the vesicle and mixed micellar fractions were quantified as benzoyl diacylglycerides by high performance liquid chromatography. With binary lecithin mixtures, vesicles were enriched with lecithins containing the most saturated sn-1 or sn-2 chains by as much as 2.4-fold whereas mixed micelles were enriched in the more unsaturated lecithins. Vesicles isolated from model biles composed of egg yolk (primarily sn-1 16:0 and 18:0 acyl chains) or soy bean (mixed saturated and unsaturated sn-1 acyl chains) lecithins were selectively enriched (6.5-76%) in lecithins with saturated sn-1 acyl chains whereas mixed micelles were enriched with lecithins composed of either sn-1 18:1, 18:2, and 18:3 unsaturated or sn-2 20:4, 22:4, and 22:6 polyunsaturated chains. Gel filtration, lipid analysis, and quasielastic light scattering revealed that apparent micellar cholesterol solubilities and metastable vesicle cholesterol/lecithin molar ratios were as much as 60% and 100% higher, respectively, in biles composed of unsaturated lecithins. Acyl chain packing constraints imposed by distinctly different particle geometries most likely explain the asymmetric distribution of lecithin molecular species between vesicles and mixed micelles in model bile as well as the variations in apparent micellar cholesterol solubilities and vesicle cholesterol/lecithin molar ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile↗
PubMed1991

Experience of an interdisciplinary pediatric pain service.

This article is a report of our experience with an interdisciplinary pain service in a large tertiary care pediatric hospital. During the first 2 years of operation, we received 869 consultations and referrals from more than 19 hospital divisions. Postoperative pain was the most frequent reason for consultation (56% of patients). Patients with pain related to cancer and sickle cell disease comprised 25% of the consultations. The remaining patients had a wide variety of primary diagnoses and causes of pain. We calculated the time spent by pain service physicians in direct patient care. The majority (63%) of physician time was spent with a small number of patients (17%). Most of these patients had pain that was unrelated to surgery, cancer, or sickle cell disease, and many posed dilemmas in diagnosis and treatment. Physician time was correlated directly to the use of psychologic and physical therapies for the pain, involving multiple team members. This experience supports the demand for an interdisciplinary pain service in a tertiary care children's hospital. A significant amount of physician time is necessary to provide patient care and to maintain a team approach, however, and pediatricians and other health care professionals who aim to implement such services should be cognizant of the time required.

Child↗
PubMed1990

Rapid (1 hour) high performance gel filtration chromatography resolves coexisting simple micelles, mixed micelles, and vesicles in bile.

We describe the use and validation of Superose 6, a high performance gel filtration medium for rapid, high resolution separation and sizing of coexisting simple micelles, mixed micelles, and vesicles in bile. We fractionated model biles (1.7-4.2 g/dl total lipid concentration, 0.15 M NaCl) composed of lecithin (L), cholesterol (Ch), and the common bile salt taurocholate (TC) using Superose 6 gel filtration columns (1.0 cm diameter, 30 cm length, 0.5 ml model bile application, 1.0 ml fractions) pre-equilibrated and eluted with 2.5-10.0 mM TC. Lipid particle sizes were determined by quasielastic light scattering and lipid compositions by conventional analyses. In the absence of L and Ch, pure TC "biles" (32.2 mM), when eluted in the presence of 7.5 mM TC, yielded a single peak of particles (mean hydrodynamic radii, Rh values of 11-15 A), consistent with simple TC micelles. Model biles containing L and TC ([L] = 13.8 mM, [TC] = 32.2 mM) were fractionated with baseline resolution into TC-L mixed micelles, (Rh values of 30-40 A) and simple TC micelles. In agreement with the ternary TC-L-H2O phase diagram (Mazer, N. A., et al. 1980. Biochemistry. 19: 601-615), the proportions of simple and mixed micelles were inversely related to L concentrations ([L] = 0-32.2 mM) and correlated positively with eluant TC concentration. Superose 6 gel fractionation of model biles "super-saturated" with Ch (TC:L:Ch molar ratio 27:63:10, total lipid concentration 3 g/dl) yielded high resolution separation of vesicles (Rh value of 320 A) from mixed micelles of TC-L-Ch (Rh values of 40-50 A) and simple TC micelles (Rh values of 11-15 A). At an eluant TC concentration of 7.5 mM, Ch-rich vesicles (Ch/L molar ratio = 1.6) separated that contained 40% of total Ch, 9% of total L, and no TC, accurately reflecting predictions of the quaternary L-Ch-TC-H2O metastable phase diagram (Mazer, N. A., and M. C. Carey. 1983 Biochemistry. 22: 426-442). This suggested that a 7.5 mM TC concentration approximated the intermicellar concentration under the experimental conditions. We also fractionated an identical model bile using conventional Sephacryl S-300, a medium generally used to study model and native biles. Compared with Superose 6, the Sephacryl S-300 column of equivalent size yielded particle separations with lower resolution and speed (30 h v l h).(ABSTRACT TRUNCATED AT 400 WORDS)

Bile↗
PubMed1990

Principles of laser light-scattering spectroscopy: applications to the physicochemical study of model and native biles.

We present a nonmathematical treatment of the theoretical and experimental aspects of modern laser light-scattering techniques. We also describe the design of a "home-built" laser light-scattering apparatus used in the authors' laboratory for the physicochemical study of model and native biles. These powerful techniques provide nonperturbing measurements of the sizes, polydispersities and, in suitable cases, concentrations and shapes of simple micelles, mixed micelles, vesicles and large proteins in bile. the sizes of these aggregates (10 to 2,000 A) fall within limits resolvable by laser light and are conventionally expressed as mean hydrodynamic radii, Rh. Static light-scattering measurements of biliary lipid aggregates provide molecular weights and important information concerning particle shape, whereas quasielastic (also referred to as dynamic) light-scattering measurements assess particle sizes and polydispersities. Under favorable circumstances, quasielastic light scattering allows simultaneous determinations of sizes and concentrations of coexisting particle populations. The use of laser light-scattering technology in solving the solution properties and the physicochemical structures of model and native biles is detailed. In view of the extraordinarily diverse backgrounds of researchers in the gallstone field (e.g., internists, surgeons, biochemists, physicists), we believe that the present article (which relies heavily on graphical representations) will afford a better understanding of the usefulness and limitations of laser light-scattering techniques, particularly in their applications to the study of bile.

Bile↗
PubMed1990

Physical chemistry of biliary lipids during bile formation.

Present concepts suggest that the canalicular secretion of bile salts is monomeric, which in turn drives the hepatic secretion of lecithin and cholesterol presumably as unilamellar vesicles into bile. As biliary lipids are concentrated within the biliary tree and gallbladder, bile salts structurally alter lecithin-cholesterol vesicles to form a variety of metastable aggregates whose structures and phase transformations are predicted by phase equilibria considerations. These structural transformations ultimately result in the dispersion of biliary lipids as thermodynamically stable micelles or micelles plus thermodynamically unstable vesicles in common duct and gallbladder biles. The experiments reviewed herein represent experimental simulations of these processes. We used pure aqueous lipid systems to model the putative stages of biliary lipid aggregation on the basis of interactions of small unilamellar vesicles of lecithin-cholesterol with bile salts as the latter's concentrations were varied from below to well above the critical micellar concentration. With submicellar bile salt concentrations likely to be found within hepatocytes, vesicle structures are not appreciably altered. However, perimicellar bile salt concentrations possibly occurring in canaliculi and bile ductules induce the formation of a hexagonal rodlike phase. On further increases in bile salt concentration, the hexagonal rods (formed from lecithin-rich and cholesterol-poor vesicles) are dissolved into mixed micelles as bile salt concentrations exceed their critical micellar concentrations. In slightly cholesterol-"supersaturated" biles, the rapid dissolution of this intermediate phase results in the formation of cholesterol-supersaturated mixed micelles that, in time, give rise to a new population of cholesterol-rich vesicles that coexist with saturated micelles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Structural alterations in lecithin-cholesterol vesicles following interactions with monomeric and micellar bile salts: physical-chemical basis for subselection of biliary lecithin species and aggregative states of biliary lipids during bile formation.

Using complementary physical-chemical methods including turbidimetry, quasielastic light scattering, gel filtration, and phase analysis, we examined the interactions between dilute concentrations of the common bile salt, taurochenodeoxycholate (TCDC), and uni- and multilamellar vesicles (MLVs) composed of defined molecular species of lecithin (L) and varying contents of cholesterol (Ch). Dissolution rates of MLVs with micellar TCDC, as assessed by turbidimetry, were more rapid with vesicles composed of sn-1 palmitoyl species, typical of biliary L, compared with those composed of the more hydrophobic sn-1 stearoyl species. Incorporation of Ch retarded MLV dissolution rates in proportion to the Ch content, and only at high Ch contents were dissolution rates appreciably influenced by the sn-2 fatty acid composition of L. When MLVs contained Ch in amounts characteristic of intracellular membranes (Ch/L approximately 0.1), the dissolution rates of the individual L species by TCDC accurately predicted the steady state L composition of human bile. TCDC interacted with small unilamellar L/Ch vesicles (SUVs) at concentrations well below, as well as appreciably above, its critical micellar concentration. In accordance with the TCDC-egg yolk L-H2O phase diagram, perimicellar concentrations of TCDC interacted with SUVs to form aggregates that were approximately twice the size of the SUVs. These were consistent with the formation of a dispersed hexagonal (rod-like) phase, which co-existed with aqueous bile salt (BS) monomers and either micellar or unilamellar SUV phases. Micellar TCDC completely solubilized SUVs as mixed micelles, putatively via this transient hexagonal phase. With modest Ch-supersaturation, dissolution was followed by the reemergence of a new vesicle population that coexisted metastably with mixed micelles. With high Ch supersaturation, TCDC extracted L and Ch molecules from SUVs in different proportions to form Ch-supersaturated mixed micelles and Ch-enriched SUVs, in accordance with the metastable phase diagram. These experiments are consistent with the hypothesis that sn-1 palmitoyl L species are subselected for bile, in part, by physical-chemical interactions of intracellular BS concentrations with Ch-poor membranes and that the subsequent evolution of Ch-rich vesicles and Ch-saturated mixed micelles occurs via a transitional hexagonal (rod) phase. These liquid-crystalline states are likely to be transient in Ch-unsaturated biles, but may persist in Ch-supersaturated human biles because of their high Ch contents which retard or inhibit these phase transitions.

Bile↗
PubMed1989

Effect of intraoperative intervention on neurological outcome based on electroencephalographic monitoring during cardiopulmonary bypass.

Neurological complications of cardiopulmonary bypass procedures are well documented. The present two-part study was undertaken to (1) determine if on-line computerized electroencephalographic changes correlated with neurological outcome and (2) compare neurological outcome with that of a second group of patients who received intraoperative interventions based on electroencephalographic data. Part 1 consisted of monitoring 50 patients. A power drop index was developed that correlated with new global neurological deficits. New global deficits occurred in 44% of the patients. In part 2, this information was used to design intervention criteria. Treatment protocols used previously accepted methods of increasing cerebral blood flow, ie, increasing pump flow, raising mean arterial pressure, and increasing CO2 content in the ventilator blend. Global neurological deficits were reduced to 5% in a group of 41 clinically similar patients (p less than 0.001). Cerebral perfusion pressures were similar in both groups. The single correlating factor was the power drop index as identified by computerized EEG. Our conclusion is that simple intervention guided by computerized EEG can reduce global neurological deficits in patients having cardiopulmonary bypass procedures.

Aged↗
PubMed1989

Quasielastic light scattering evidence for vesicular secretion of biliary lipids.

We employed quasielastic light scattering, negative-stain, and freeze-fracture electron microscopy to study the time-dependent physicochemical behavior of biliary lipids in fresh rat bile. Three to five minutes after bile collection, the earliest light scattering measurements and electron microscopy revealed unilamellar vesicles (mean hydrodynamic radius, Rh = 430-740 A) coexisting with mixed micelles (Rh = 20-120 A) in all biles. Both percent biliary vesicles (1 to greater than 70%) and micellar sizes varied inversely with bile salt concentration (range 1.6-72 mM) both during endogenous pool drainage and sodium taurocholate infusion. With bile salt concentrations in the vicinity of or below the estimated critical micellar concentration, biliary vesicle concentrations remained constant or increased slightly with passage of time. However, with micellar bile salt concentrations, complete conversion of vesicles to micelles occurred at rates that were directly proportional to bile salt concentration. Back-extrapolation of weighted Rh averages of micelles plus vesicles as functions of time gave sizes of approximately 470 A at 1 min, suggesting the predominance of homogeneously sized unilamellar vesicles at the earliest stages of bile formation. After micellization of lipids, mixed protein aggregates of vesicle size were demonstrated in all biles. These experiments elucidate the dynamic coexistence of lipid vesicles and mixed micelles in cholesterol unsaturated biles and demonstrate that vesicle-to-micelle interconversions of biliary lipid aggregates are normal physiological phenomena within the biliary tree.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗