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Biomedical subjects

A Cohen

Publications and source records attributed to A Cohen.

At least 523 records · Page 29Linked to original sources
PubMed1991

[Thrombosis of atrioventricular prosthesis. Contribution of transesophageal echocardiography].

The aim of this study was to assess the diagnostic value of transesophageal echocardiography for the detection of thrombosis of a mechanical mitral or tricuspid valve prosthesis. Twelve patients (mean age 54 +/- 12 years) out of a series of 39 patients operated between April 1988 and June 1989 for prosthetic valve dysfunction had valve thrombosis at operation (11 mitral and 1 tricuspid valve prosthesis). Transesophageal echocardiography was routinely performed preoperatively in addition to transthoracic Doppler echocardiography to search for an abdominal mass on the prosthetic valves. The largest diameter of the diastolic jet at the level of the prosthetic valve annulus was measured using transesophageal color flow Doppler in the 8 Starr-Edwards mitral valve prostheses and compared with 5 control valves. The results of transthoracic Doppler echocardiography and transesophageal echocardiography were compared with the operative findings. The specificity of transthoracic echocardiography for the positive diagnosis of prosthetic valve thrombosis was 18%. A thrombosis could be suspected in 10 of the 12 cases by transthoracic echocardiography giving a sensitivity of 83%. Eleven of the 12 abnormal masses on the prostheses were visualised by transesophageal echocardiography, a sensitivity of 91%. Detection of the masses on the arterial side was possible in all cases (10/10) but 5 of the 6 extensions of the thrombus into the ventricle could not be visualised. The diameter of the transprosthetic jet was less than 12 mm in 7 of the 8 thrombosed valves compared with greater than 15 mm in the 5 normal control prostheses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Heat stress on helicopter pilots during ground standby.

We attempted to use measurements of ambient thermal conditions to characterize and then predict thermal conditions in the cockpit before takeoff and during an hour standby period in Bell 206 and Bell 212 helicopters with a crew of two and with the cockpit doors opened. Dry bulb, wet bulb, and globe temperatures were measured on 28 separate summer days. The wet bulb globe temperature index (WBGT) was used to estimate heat stress. Ambient WBGT at time 0 ranged from 13 degrees C to 31 degrees C. There was a 2.9 +/- 3.7 degree difference in WBGT between ambient and cockpit conditions at time 0 which increased to 7.2 +/- 3.5 degrees after 1 h. Because of the cooling effect of opening the helicopter cockpit doors, the cockpit WBGT actually decreased over the standby period when cockpit WBGT values were 30 degrees C or more at time 0. Thus, there was an inverse correlation between cockpit WBGT at time 0 and the change in cockpit WBGT over the 1-h period (r = -0.767, p less than 0.001). The mean WBGT in the cockpit over the 1-h standby period was positively correlated with the ambient WBGT at time 0 (r = 0.783, p less than 0.001). We conclude that the greenhouse effect results in a cockpit WBGT which is significantly higher than ambient conditions. Subsequent changes in cockpit WBGT depend on the balance between heat transfer from the pilot's bodies to the cockpit and the loss of heat after the doors of the helicopters are opened. Ambient thermal conditions can be used to predict heat stress during the ground standby period.

Aerospace Medicine↗
PubMed1991

Relationship between neonatal excitability and respiratory habituation.

The Brazelton Neonatal Behavioral Assessment Scale was administered and analyzed in the cases of 25 full-term infants in order to assess the relationship between a behavioral measure of excitability and respiratory habituation. Sound and light stimuli were sequentially delivered, and prestimulus and poststimulus respiratory amplitude mean and standard deviation were analyzed. The stimulus with the least interperiod difference was considered as habituation. The correlation between arousal behavioral items and respiratory habituation ranged between 0.16 and 0.44. The two significant correlations were between peak of excitement and respiratory habituation to light (0.44) and between rapidity of buildup and respiratory habituation to sound (0.38). These results may indicate an interrelation in neonates between temperamental excitability attributes and respiratory regulation.

Acoustic Stimulation↗
PubMed1991

Sequential discontinuation of azathioprine and prednisone in renal transplantation.

We report the time course of rejections in 110 patients of first cadaver kidney grafts entered into a randomized controlled trial of induction ALG vs continuous IV CyA, with both groups receiving Aza for 30 days and Pred for 3 months. There was no difference in 1-year graft or patient survival in the two induction regimens. Despite a slight delay in time to first rejection, the number, severity, and outcome of rejections were the same in both. Fifty percent of patients never had a rejection, and 80% of these were on CyA monotherapy at 1 year vs only 22% in patients with rejections. Thirty-five percent had a rejection in the first month, and one fourth of these had a repeat in the second month. The risk of graft loss was 10% with a first, 38% with a second, and 50% with a third rejection. First rejections occurring after 30 days rarely caused graft loss and rejection after 90 days proved to be unusual.

Administration, Oral↗
PubMed1991

Diagnosis, transport, and outcome in fetuses with left ventricular outflow tract obstruction.

Between March 1986 and April 1990, 22 consecutive fetuses (at gestational ages of 21 to 38 weeks) with a suspected diagnosis of critical (ductus-dependent) left ventricular outflow tract obstruction on fetal echocardiogram were referred to our center for delivery and surgical treatment. Diagnoses were hypoplastic left heart syndrome (n = 16), valvular aortic stenosis (n = 2), common atrioventricular canal with subaortic stenosis (n = 3), and single ventricle with subaortic stenosis (n = 1). Postnatal echocardiography revealed that fetal echocardiography was correct in predicting left ventricular outflow tract obstruction to be critical in all but one patient, for a positive predictive value of 96%. Of the 21 patients with true, critical left ventricular outflow tract obstruction, 17 patients underwent cardiac surgery as neonates (birth to 6 days of age, median 2 days); 13 (or 77%) survived and were discharged from the hospital. In addition, one patient underwent successful balloon aortic valvotomy for critical valvular aortic stenosis but later died of sepsis. Lethal chromosomal and congenital abnormalities should be sought and are contraindications for this approach. In utero transport of fetuses with suspected critical left ventricular outflow tract obstruction to a neonatal cardiac surgical center can result in improved neonatal condition and may improve overall survival.

Echocardiography, Doppler↗
PubMed1991

Management of post-date pregnancy: a case control study.

Post-date pregnancy is associated with higher rates of perinatal mortality and morbidity. The purpose of the present study was to compare the outcome of 200 post-date pregnancies, managed according to our protocol, to a matched control group of 200 healthy pregnant women delivered at term. The management protocol was based mainly on the pelvic score and nonstress test. Higher rates of labor induction, meconium-stained amniotic fluid, fetal distress, instrumental deliveries and cesarean sections were found in post-date pregnancies than in the control group (40% vs. 3% P = 0.0001, 31% vs. 15.5% P = 0.00001, 18.5% vs. 9.5% P = 0.007, 8% vs. 3% P = 0.02, 12.5% vs. 4% P = 0.002 respectively). Neonatal birth weight in the study group was significantly higher than in the control group (3,484.3 +/- 410.7 vs. 3,218.4 +/- 407.8 g P less than 0.001). Despite these differences between the groups, the perinatal morbidity and mortality rates were similar. These results can be partially attributed to the early antenatal monitoring and intensive follow-up.

Apgar Score↗
PubMed1990

Oligodendrocyte cytotoxic factor associated with fish optic nerve regeneration: implications for mammalian CNS regeneration.

The limited capacity for regenerative axonal growth by adult mammalian central neurons has been attributed, at least in part, to the presence of mature oligodendrocytes, which are non-permissive for axonal growth. These cells do not interfere with growth during development, as developmental growth is largely completed before the maturation of the oligodendrocytes. Unlike mammals, fish central nervous system is endowed with a high regenerative capability. When soluble substances derived from regenerating fish optic nerves are applied to injured adult rabbit optic nerves, regenerative axonal growth is permitted. Therefore, in the present study, we tested whether the fish optic nerve, after injury, is endowed with a mechanism by which it avoids the possible inhibitory effect of the process-bearing mature oligodendrocytes. Specifically, we looked for the possible presence of soluble substances that can regulate the number of process-bearing mature oligodendrocytes. We found that soluble substances derived from regenerating fish optic nerve, when added to cultures of oligodendrocytes derived from newborn or injured adult rat optic nerves, caused a decrease in the number of process-bearing mature oligodendrocytes. Soluble substances derived from normal noninjured fish optic nerves, had a significantly lower effect. The observed decrease in the number of mature oligodendrocytes could not be mimicked by the addition of platelet-derived growth factor (PDGF), a known mitogen of oligodendrocyte progenitors which transiently inhibits their maturation. This study suggests a role to oligodendrocyte inhibitory/cytotoxic factor(s) in regeneration.

Animals↗
PubMed1990

Determination of serum uric acid by isotope dilution mass spectrometry as a new candidate definitive method.

A new isotope dilution mass spectrometric method for uric acid is described. A known weight of [1,3-15N2]uric acid is added to a known weight of serum, and the mixture is allowed to equillibrate. The serum is put through an anion-exchange resin, and the isolated uric acid is converted to the tetrakis-(tert-butyldlmethylsilyl) derivative of uric acid. For measurement, the derivative is injected into a gas chromatograph interfaced with a low-resolution, magnetic sector mass spectrometer. Isotope ratio measurements are made from the abundances of the [M - tert-butyl]+ ions at m/z 567 and 569. Bias is investigated by measuring the uric acid level in the same samples under different chromatographic conditions and with different ionization techniques. If these confirmatory measurements agree with the principal measurements, we have strong evidence for the absence of measurement bias. Uric acid was determined in three lyophilized human serum pools by this method. For Standard Reference Material (SRM) 909, four sets of six samples each were prepared. For Candidate SRM 909a, which consisted of two pools, each with a different level of uric acid, six sets of two samples of each level were prepared. The coefficient of variation for a single measurement ranged from 0.34% to 0.42%, while the relative standard error of the mean ranged from 0.08% to 0.14%. The results from the confirmatory measurements demonstrated that there was no significant bias in the measurements. The combination of high precision and absence of significant bias in the results qualifies this method as a candidate definitive method as defined by the National Committee for Clinical Laboratory Standards.

Humans↗
PubMed1990

Extrageniculate vision in hemianopic humans: saccade inhibition by signals in the blind field.

The functional competence of extrageniculate visual pathways in hemianopic humans was demonstrated by showing that distractor signals in the blind half of the visual field could inhibit saccades toward targets in the intact visual field. This inhibitory effect of unseen distractors in patients occurred only when distractors were presented in the temporal half of the visual field, was specific to oculomotor responses, and did not occur in normal subjects. These results show that a peripheral visual signal activates retinotectal pathways to prime the oculomotor system and that these pathways can mediate orienting behavior in hemianopic humans.

Analysis of Variance↗
PubMed1990

The expression of c-fos, c-jun, and c-myc genes is regulated by heat shock in human lymphoid cells.

The effect of heat shock on the expression of the nuclear protooncogenes c-fos, c-jun, and c-myc was studied in human lymphoid cells. Heat shock caused an increase in c-fos and c-jun mRNA levels and a decrease in c-myc mRNA levels in pre-B (Hyon) and T (DND-41) cell lines as well as in freshly isolated normal human thymocytes. The changes in the mRNA levels of these protooncogenes in Hyon cells were most pronounced at 42 and 43 degrees C; kinetic analysis demonstrated that the changes could be detected within 30 min of heat shock. Altered transcription of c-fos and c-myc genes was the primary effect of heat shock. Secondarily, heat shock of Hyon cells stabilized the c-myc mRNA level by increasing its half-life from 24 to 45 min. The overall effect of heat shock on c-myc mRNA level, however, was a marked inhibition of its transcription. These results demonstrate that the transcription of nuclear protooncogenes is regulated by heat shock indicating a role for nuclear protooncogenes in the stress response of lymphoid cells.

B-Lymphocytes↗
PubMed1990

[Hyperviscosity syndrome and eye involvement].

10 patients with serum hyperviscosity syndrome of different etiologies were examined by fluorescein angiography of the ocular fundus. There was no exact correlation between the pathological findings in the fundus of cases with plasma cell dyscrasia and blood viscosity. Only papilledema and retinal venous engorgement were improved by lowering serum viscosity by plasmapheresis. The abnormal circulating immunoglobulins are an important factor in the genesis of the pathological changes in the retina of patients with plasma cell dyscrasia.

Blood Viscosity↗