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Biomedical subjects

M Allen

Publications and source records attributed to M Allen.

At least 199 records · Page 11Linked to original sources
PubMed1991

Anterior sternal retraction for reoperative median sternotomy.

The incidence of reoperative median sternotomy for repeat cardiac surgery is increasing. Reoperative median sternotomy is associated with a higher morbidity and mortality than first-time cardiac surgery. A portion of this morbidity and mortality may be due to direct injury to the heart and great vessels in the process of reopening the sternum. We report a new technique utilizing anterior sternal retraction that allows division of adhesions between the undersurface of the sternum and the heart and great vessels under direct vision. This technique enables the surgeon to minimize the risk of serious injury to these underlying structures during reoperative cardiac surgery.

Cardiac Surgical Procedures↗
PubMed1991

Troposphere-stratosphere interactions in a one-dimensional model of Jovian photochemistry.

A simple one-dimensional model of the Jovian atmosphere including the coupling between a rapidly mixed troposphere and a stagnant stratosphere is presented. We treat analytically the case of a chemically unreactive species flowing downward through the stratosphere and troposphere with a constant flux. The calculated concentration profile has a maximum value approximately one atmospheric scale height above the tropopause. The corresponding mixing ratio rapidly decreases in the lower stratosphere. The contrast between the peak stratosphere and tropopause concentrations reflects the variation between the lower stratosphere and upper troposphere eddy diffusion coefficients. Numerical simulations of unreactive CO and C2H6, considering high-altitude photochemical sources (yielding downward fluxes to the troposphere) and deep troposphere thermochemical sources, demonstrate that upper troposphere abundances may have a large photochemical contribution. Recent observations of CO near 5 bar can be reproduced by a model using any one of three different tropospheric eddy diffusion profiles: a constant value of approximately 10(8) cm2 sec-1, a constant value of < or approximately 10(4) cm2 sec-1, or a two-layer model with a rapidly mixed (10(8) cm2 sec-1) layer below 20 bar and a slower mixing layer (10(4) cm2 sec-1) between 100 mbar and 20 bar. In the latter two scenarios, the photochemical source is an important and/or dominant source of upper tropospheric CO. However, the upper tropospheric C2H6 abundances are distinctly different among the three cases. These calculations suggest objectives for higher spectral resolution observations, critical vertical scales for planning experiments on future missions to Jupiter, and predictions that can be tested with the Galileo probe mass spectrometer.

Atmosphere↗
PubMed1991

Crafting a federal legislative framework for child welfare reform.

The nature and scope of the problems plaguing child welfare systems across the country make federal solutions especially urgent. A decade after enactment of the Adoption Assistance and Child Welfare Act (PL 96-272), legislation is pending that builds on its framework to enhance services and supports for vulnerable children and their families. The legislation reflects a growing consensus about the nature of the child welfare crisis and about the reform strategies that will be effective.

Adoption↗
PubMed1991

Baby walker related injuries--a continuing problem.

Baby walkers have been associated with burns, head trauma and other types of injury. A retrospective study of all infants under the age of two years attending an accident and emergency unit demonstrated 22 injuries associated with baby walkers from a total of 1049 attendances. The most serious injuries were three skull fractures, with the most common mechanism being of a fall downstairs in the walker. Injury while in a baby walker occurred with a similar frequency to injury due to road traffic accidents. We conclude that despite previous warnings Baby Walkers still represent a considerable hazard to infants.

Accidents, Home↗
PubMed1991

Modification of the thrombogenicity of a self-expanding vascular stent.

When placed in the iliac arteries of normal healthy animals, the Wall-stent self-expanding endovascular prosthesis exhibits minimal thrombogenicity, measured by 111In-labeled platelet uptake. Preliminary clinical reports suggest a greater thrombogenicity in diseased human arteries. When evaluated in an ex vivo shunt, these stents exhibit significant thrombogenicity. The ex vivo shunt may therefore provide a model to evaluate strategies to reduce thrombogenicity in the clinical setting. Stents were released into shunts and the uptake of In111-labeled platelets was measured by gamma imaging for 2 h at a flow rate of 100 mL/min. The effect of systemic heparin, 100 U/kg, oral aspirin, 325 mg, and local application of heparin-benzalkonium chloride complex were evaluated. At the end of each study the stents were fixed in situ and evaluated with scanning electron microscopy (SEM). Control stents exhibited a rapid, significant uptake of platelet associated 111In activity, which reached a maximum in approximately 1 h. Twenty-two percent of control stents occluded before 2 h. Aspirin reduced maximum platelet uptake by 46%. Systemic heparin, with a clotting time greater than five times control, reduced maximum platelet uptake by 86%. The benzalkonium-heparin complex coating, with no increase in clotting time, reduced maximum platelet uptake by 84%. No occlusions were observed with the anti-thrombotic regimes. SEM evaluation of the stents supports the results of the isotope uptake studies.

Animals↗
PubMed1991

Gestational age assessment in preterm neonates weighing less than 1500 grams.

Postnatal assessment of gestational age in preterm neonates traditionally has been performed using the methods of Dubowitz and Ballard. This study was designed to determine the accuracy of these methods in a sample of very low birth weight preterm neonates. Dubowitz and Ballard examinations were done on 110 preterm neonates within the first 72 hours of life by a neonatologist masked to the gestational age assessed antenatally. Mean birth weight was 1066 +/- 256 g (SD). These data were compared with gestational age assessments using last menstrual period and best obstetric estimate calculated by an obstetrician unaware of the neonatal examination. Mean gestational age using last menstrual period was 28.3 +/- 2.9 weeks. Mean differences between last menstrual period and Dubowitz/Ballard were -2.8 +/- 2.1 weeks and -2.6 +/- 2.2 weeks, respectively. Results using best obstetric estimate were similar. An ophthalmologist examined lens vessels of 89 neonates. A similar pattern toward overestimation of gestational age interval by Dubowitz/Ballard was seen at each lens vessel grade. The Dubowitz and Ballard examinations are inaccurate methods of assessing gestational age in preterm neonates with birth weights less than 1500 g.

Birth Weight↗
PubMed1990

Spatial variation of ozone depletion rates in the springtime Antarctic polar vortex.

An area-mapping technique, designed to filter out synoptic perturbations of the Antarctic polar vortex such as distortion or displacement away from the pole, was applied to the Nimbus-7 TOMS (Total Ozone Mapping Spectrometer) data. This procedure reveals the detailed morphology of the temporal evolution of column O3. The results for the austral spring of 1987 suggest the existence of a relatively stable collar region enclosing an interior that is undergoing large variations. There is tentative evidence for quasi-periodic (15 to 20 days) O3 fluctuations in the collar and for upwelling of tropospheric air in late spring. A simplified photochemical model of O3 loss and the temporal evolution of the area-mapped polar O3 are used to constrain the chlorine monoxide (ClO) concentrations in the springtime Antarctic vortex. The concentrations required to account for the observed loss of O3 are higher than those previously reported by Anderson et al. but are comparable to their recently revised values. However, the O3 loss rates could be larger than deduced here because of underestimates of total O3 by TOMS near the terminator. This uncertainty, together with the uncertainties associated with measurements acquired during the Airborne Antarctic Ozone Experiment, suggests that in early spring, closer to the vortex center, there may be even larger ClO concentrations than have yet been detected.

Antarctic Regions↗
PubMed1990

SME observations of O2 (1 delta g) nightglow: an assessment of the chemical production mechanisms.

Solar Mesosphere Explorer (SME) observations of the 3 a.m. 1.27 micrometers nightglow at 45 N latitude, averaged over the period 10-31 July 1984, are reported. From the deduced volume emission rates, we derive the O2(a1 delta g) night-time production rates for the 80-100 km altitude range. Utilizing the mean SME-acquired 3 p.m. ozone profile for the same latitude and time period and an updated photochemical model, we determine night-time O, O3, H, OH, HO2, and H2O2 profiles. These are used in calculating the rates of reactions which are sufficiently exothermic to produce O2(1 delta) or excited states of OH or HO2, which could transfer their energy to O2 to form O2(1 delta). Of these reactions, most have rates that are quite small compared with the observed night-time O2(1 delta) production rate. For several others, laboratory experiments have found O2(1 delta) yields which are insufficient for simulating the observed O2(1 delta). Using yields of O2(1 delta) based on published laboratory and observational studies, we find that the sum of two reaction sequences can approximate the SME measurements: (1) O+O+M and (2) H+O3 followed by OH*+O2.

Atmosphere↗
PubMed1990

Effects of membrane potential on electrically silent transport. Potential-independent translocation and asymmetric potential-dependent substrate binding to the red blood cell anion exchange protein.

Tracer anion exchange flux measurements have been carried out in human red blood cells with the membrane potential clamped at various values with gramicidin. The goal of the study was to determine the effect of membrane potential on the anion translocation and binding events in the catalytic cycle for exchange. The conditions were arranged such that most of the transporters were recruited into the same configuration (inward-facing or outward-facing, depending on the direction of the Cl- gradient). We found that the membrane potential has no detectable effect on the anion translocation event, measured as 36Cl(-)-Cl- or 36Cl(-)-HCO3- exchange. The lack of effect of potential is in agreement with previous studies on red cells and is different from the behavior of the mouse erythroid band 3 gene expressed in frog oocytes (Grygorczyk, R., W. Schwarz, and H. Passow. 1987. J. Membr. Biol. 99:127-136). A negative potential decreases the potency of extracellular SO4= as an inhibitor of either Cl- or HCO3- influx. Because of the potential-dependent inhibition by SO4=, conditions could be found in which a negative intracellular potential actually accelerates 36Cl- influx. This effect is observed only in media containing multivalent anions. The simplest interpretation of the effect is that the negative potential lowers the inhibitory potency of the multivalent anion by lowering its local concentration near the transport site. The magnitude of the effect is consistent with the idea that the anions move through 10-15% of the transmembrane potential between the extracellular medium and the outward-facing transport site. In contrast to its effect on extracellular substrate binding, there is no detectable effect of membrane potential on the competition between intracellular Cl- and SO4= for transport sites. The lack of effect of potential on intracellular substrate binding suggests that the access pathway leading to the inward-facing transport site is of lower electrical resistance than that leading to the extracellular substrate site.

Anion Transport Proteins↗
PubMed1990

Common peroneal nerve dysfunction after high tibial osteotomy.

We assessed 16 patients before and after high tibial osteotomy by electrophysiological recordings, creatine phosphokinase levels, radiographs and intracompartmental pressure monitoring. We found mild electrophysiological abnormalities pre-operatively in 12 of the 16 patients, but postoperatively these had deteriorated in 11 of the 14 patients studied. Creatine phosphokinase levels, compartment pressure and radiological deformity were not predictive of the development of postoperative common peroneal nerve palsy. Patients who also had a proximal fibular osteotomy had greater electrical abnormalities postoperatively and two of them developed common peroneal palsies. Proximal fibular osteotomy appears to be a causative factor in the development of common peroneal nerve palsy; more work is needed on the blood supply of the nerve.

Adult↗
PubMed1990

Myocardial preservation: a comparison of oxygenated crystalloid and blood cardioplegia.

The purpose of this experiment was to compare myocardial protective effect after global ischemia using oxygenated crystalloid (CCcO2) and an oxygenated blood (BCcO2) cardioplegic solutions. Post-ischemic ventricular performance was studied in 2 equal (n = 7) groups of dogs subjected to 120 min of global ischemia induced at average myocardial temperatures of 8 degrees C in the CCcO2 group and 18 degrees C in the BCcO2 group. Left ventricular (LV) function included analysis of LV systolic function (global and regional function), LV diastolic function (chamber and myocardial stiffness) and LV relaxation was measured by sonomicrometry and Millar micrometers. Data were processed with a Dec PDP-11/23 computer. In vitro oxygen content (Vol%) measured 3.2 +/- 1.0 (CCcO2) and 9.5 +/- 0.3 (BCcO2). Percent recoveries of LV global function (LVSP, loop area, % shortening, LV dp/dt, mean VCF and E max) in the CCcO2 group were approximately the same as those in the BCcO2 group. There were no significant differences in LV regional function (loop area and % shortening) after ischemia between the two groups. The chamber and myocardial stiffness after ischemia in the CCcO2 group were almost the same as the baseline values. Values in the BCcO2 group were reduced significantly compared to the baseline level. There were significant differences in post-ischemic chamber and myocardial stiffness between the two groups. Post-ischemic maximum negative LV dp/dt in both groups decreased significantly compared to the baseline values. However, the time constant and diastolic interval after ischemia in both groups were approximately the same as the baseline values. We conclude that there were no significant differences in myocardial protective effect between the CCcO2 and BCcO2 groups, and both methods preserved the ischemic myocardium well.

Animals↗
PubMed1990

Clinical management considerations in long-term survivors with trisomy 18.

As many as 90% or more of children with trisomy 18 die within the first year of life. A review of six patients with trisomy 18 documented by karyotype surviving past 1 year of age and of the trisomy 18 files of the Support Organization for Trisomy 18 and 13 indicated that a small number of children with trisomy 18 survive beyond their first year of life; a few live into their teens and twenties. In addition to medical problems that are unique to this chromosomal syndrome, these patients present complex medical problems common to all persons with chromosomal anomalies. The primary and tertiary care consultants who are able to provide knowledge and sensitive supportive care to children with trisomy 18 and to their parents are performing a service of significant benefit, no matter how brief the life span of the child may be.

Abnormalities, Multiple↗