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Biomedical subjects

R Thomas

Publications and source records attributed to R Thomas.

At least 595 records · Page 33Linked to original sources
PubMed1986

Effects of varying electrode configuration with catheter-mediated defibrillator pulses at the coronary sinus orifice in dogs.

We compared two methods of delivering single damped sine-wave defibrillator pulses to the coronary sinus orifice in 20 dogs. Ten dogs had "unipolar" (coronary sinus to precordial disc) and 10 had "bipolar" (coronary sinus proximal to coronary sinus distal electrode) discharges. Delivered voltage, current, and energy were recorded during each pulse. Electrophysiologic testing was done before and 4 weeks after the procedure. Histologic examination of the atrioventricular groove was done at 1 mm serial sections. For the unipolar configuration a 200 J defibrillator pulse resulted in a peak voltage of 3370 +/- 125 V, a peak current of 21 +/- 4 A, and a delivered energy of 253 +/- 29 J as compared with 3010 +/- 99 V, 70 +/- 4 A, and 144 +/- 18 J, respectively, for the bipolar configuration (p less than .001). Three dogs (two with bipolar, one with unipolar pulses) had gross coronary sinus rupture and died from acute pericardial tamponade. In addition, irrespective of electrode configuration, all dogs showed microscopic rupture of the coronary sinus internal elastic membrane. Transmural atrial scarring occurred in all 10 dogs that received a unipolar pulse but in only two dogs that received a bipolar pulse (p = .0004). Unlike the atrium, injury to the left ventricle was limited in both groups. Similarly, injury to the periannular myocardium was inconsistent and not transmural in either group. No significant electrophysiologic changes were observed. With the present technique, unipolar rather than bipolar catheter-mediated defibrillator pulses result in transmural atrial injury that might prevent accessory pathway conduction. Regardless of electrode configuration, high-energy defibrillator pulses consistently cause some degree of coronary sinus rupture, most likely related to a barotraumatic mechanism.

Animals↗
PubMed1986

Blood anesthetic levels during surface-induced deep hypothermia under halothane-diethyl ether azeotrope anesthesia.

Blood anesthetic concentration and clinical indicators related to anesthetic management during surface-induced deep hypothermia were determined in seven adult mongrel dogs. The azeotrope of halothane and diethyl ether was assayed by gas chromatography. Blood concentration of halothane ranged from a pre-cooling control of 0.74 vol % to 0.11 vol % at 20 degrees C rewarming; ether ranged from 0.06 vol % at 20 degrees C rewarming to 0.22 vol % at 35 degrees C rewarming. Administration of anesthetic was reduced during cooling because of the spontaneous decrease in mean arterial pressure and heart rate. After elective circulatory arrest was induced, anesthetic was not required until after cardiac resuscitation at about 22 degrees C rewarming. Initial clinical signs indicating a need to increase administration of anesthetic included spontaneous respiration and an increase in mean arterial pressure. Blood azeotrope concentration was significantly lower during rewarming than at comparable temperatures during cooling. We conclude that blood concentration of halothane and ether changes as a function of body temperature and that anesthetic demand may be diminished following total circulatory arrest.

Anesthesia, Inhalation↗
PubMed1986

Cardiovascular response to rapid infusion of lactated Ringer's.

Cardiovascular response to rapid infusion of lactated Ringer's was investigated in 5 adult dogs (average body weight = 21.1 kg) under 1% halothane anesthesia. Following implantation of aortic flow probe and left atrial line, the chest was closed and splenectomy was performed prior to the experiment. Warmed lactated Ringer's was administered at five different infusion rates (2.5, 5, 10, 15 and 20 ml/kg/min in random sequence) to each dog until left atrial pressure (LAP) reached 20 mmHg or a maximum of 50 ml/kg had been infused. Subsequent infusions were done after stroke volume (SV) spontaneously returned to the control level. Cardiac output (CO), SV, heart rate (HR), mean arterial pressure (MAP), LAP and central venous pressure (CVP) were monitored simultaneously during infusions. HR was stable during infusions, whereas MAP increased by 39% of control. Response of LAP to volume infused was nearly linear at fast infusion rates (10, 15 and 20 ml/kg/min). Response of LAP to slow infusion rates (2.5 and 5 ml/kg/min) was curvilinear (decelerating curve). The relationship between CVP and volume infused was similar to LAP vs. volume infused. Ventricular function curves (SV, CO and stroke work vs. LAP) were also influenced by the rate of infusion with steeper curves at slow infusion rates than curves derived from fast infusion rates. However, initial changes in SV and CO curves were not significantly affected by the rate of infusion. We conclude that the cardiovascular response to rapid infusion of lactated Ringer's is rate dependent but initial changes in SV and CO curves are not significantly affected at infusion rates of 2.5, 5, 10, 15 or 20 ml/kg/min.

Animals↗
PubMed1986

[Apropos of Gilles de la Tourette's disease].

The observation of a young north african afflicted with a tic disorder suggests an underlying meaning in the apparently confused motoric discharges, thanks to psychodrama and to ethnopsychoanalytic consultations with the family. Thus, at a time when the Gilles de La Tourette syndrome is described as a neurological disorder, while recognizing the limited utility of chemotherapy, we believe that neurobiological studies, whatever their merit, do not exempt us from thinking about the specific psychopathology of tics and their evolving relationship with neurotic symptoms. That is, to go from motor discharge to the elaboration of conflicts.

Adolescent↗
PubMed1986

Histiocytosis-X in gynecology: a case presentation and review of the literature.

A patient is presented with persistent vulvar ulcerations of 15 months' duration. Biopsies of the lesions were diagnostic of histiocytosis-X. Chest x-ray revealed a honeycombed reticulonodular pattern consistent with pulmonary histiocytosis-X. The dehydration test indicated diabetes insipidus. Electron microscopy revealed Langerhan granules characteristic of histiocytes. This patient represents one of approximately two dozen cases in the world literature showing gynecologic manifestations of histiocytosis-X. The presentations, diagnosis, therapy, and prognosis of this disease are discussed.

Female↗
PubMed1986

Reversible and irreversible effects of retinol upon the phenotypic properties of embryonal carcinoma cells.

We have generated an embryonal carcinoma cell line, NR1, which is not growth-inhibited in response to retinol. Although the retinol-treated cells undergo morphological change, show reduced levels of the surface antigen SSEA-1 and possess increased surface reactivity with antifibronectin serum, the extent of phenotypic change of NR1 cells in response to retinol is not so great as that following treatment with retinoic acid. Furthermore, unlike cells from lines such as F9, the retinol-promoted morphological alterations appear to be reversible. The increased adherence of NR1 cells to glass coverslips in the presence of retinol suggests that stronger interaction with the substratum is responsible for the observed alteration in appearance of the cells. It is possible that NR1 cells exposed to retinol progress no further than a reversible, early stage of differentiation. Alternatively, retinol-treated cells might express a group of markers normally associated with, or accompanying, an irreversible, differentiated phenotype even though the cells are not, in fact, undergoing differentiation.

Animals↗
PubMed1986

Regional myocardial protection by retrograde coronary sinus infusion of cardioplegic solution.

Antegrade administration of a cardioplegic solution in the presence of a coronary artery stenosis may lead to the heterogeneous distribution of the agent and poor myocardial cooling distal to a vessel stenosis. To determine the effects of retrograde coronary sinus infusion of cardioplegic solution, coronary stenosis was created in the canine preparation by occluding the left circumflex artery (LCx) during cardioplegic arrest. Left ventricular global and regional function (assessed by sonomicrometry and solid-state micrometers) were studied after 60 min of ischemic arrest. Three groups (all n = 7) were studied: group I (control), cardioplegic solution infused via the aortic root without LCx occlusion; group II, same as group I except with LCx occlusion; group III, retrograde coronary sinus infusion of cardioplegic solution with LCx occlusion. Heart rate was controlled by atrial pacing. Statistically significant differences in global function between the three groups were seen at low filling pressures but were not seen during volume challenge. However, the recovery ratio of regional function in the LCx area at a left atrial pressure of 5 mm Hg in group II was 77.2% (% shortening) and 48.5% (segment work), which was significantly less (p less than .01) than recovery in group I (111.7% and 75.9%) and group III (108.3% and 81.5%). These differences persisted during volume loading, to a mean left atrial pressure of 15 mm Hg. Regional compliance in group II was also significantly (p less than .01) depressed after cardioplegic arrest but was well preserved in groups I and III.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Comparison of clinical effects and pharmacokinetics of once-daily Uniphyl and twice-daily Theo-Dur in asthmatic patients.

A pharmacokinetic study using theophylline syrup in adult asthmatic patients demonstrated a mean apparent volume of distribution of 0.38 liters/kg, mean elimination rate constant of 0.10 hours-1, and variable rates of clearance of theophylline (total body clearance of 0.38 to 0.96 ml/kg per minute). Subsequently, the asthmatic patients were compared using a cross-over design after maintenance Uniphyl (once daily at 8 a.m. or at 8 p.m.) and Theo-Dur (twice daily at 8 a.m. and 8 p.m.). Total daily maintenance theophylline dosage, calculated from the pharmacokinetic data, was identical in all three cross-over phases. At the end of each phase, plasma theophylline levels were measured every two hours and spirometric determinations were made every four hours (excluding 4 a.m.) for 24 hours. The following results were observed: highest peak and mean plasma theophylline concentration and area under the concentration-time curves with evening Uniphyl (p less than 0.05); prolonged time-to-peak theophylline concentration after nocturnal compared with daytime dosing; diurnal variation in pulmonary function and plasma theophylline concentrations; no significant differences between the three maintenance treatments in asthmatic symptoms or spirometric results.

Adult↗
PubMed1985

Towards a logical analysis of the immune response.

We present a new way to conceive, formalize and analyse models of the immune network. The models proposed are minimal ones, based essentially on the well-established negative feedback loop between helper and suppressor T cells. The occurrence of T-T interactions in both helper and suppressor circuits. These T-T interactions are represented here by autocatalytic feedback loops on TH and TS. The fact that immature B cells are sensitive to negative signaling, as was originally suggested by Lederberg (1959). There is a functional inactivation of immature B cells encountering antigen or anti-idiotypic antibody. This prevents further differentiation to a stage where the B cells become fully responsive. We describe the role of a logical method in the generation and analysis of the models, and the complementarity between this logical method and the more classical description by continuous differential equations. Logical analysis and numerical simulations of the differential equations show that the emerging model accounts for, the occurrence of multiple steady states (a virgin state, a memory state and a non-responsive state) in the absence of antigen, the kinetics of primary and secondary responses, high dose paralysis, low dose of paralysis. Its fit with real situations is surprisingly good for a model of this simplicity. Nevertheless, we give it as an example of what can now be done in the field rather than as a stable model.

Antibody Formation↗
PubMed1985

Computed tomography of xanthogranulomatous pyelonephritis.

The computed tomography findings in two cases of xanthogranulomatous pyelonephritis are presented. There was diffuse involvement of the kidney in one case, with correlation with the pathologic specimen and microscopic findings. In the second case there was focal involvement of the kidney. Computed tomography greatly assisted in making a correct preoperative diagnosis and in assessing the degree of extrarenal involvement.

Adult↗
PubMed1985

Two homologous genes coding for spore-specific proteins are expressed at different times during development of Myxococcus xanthus.

The ops and tps genes of Myxococcus xanthus have ca. 90% DNA and amino acid sequence homology and are in the same orientation separated by a spacer region of only 1.4 kilobases. The products of the two genes were found to cross-react immunologically, and both were capable of Ca2+-dependent self-assembly on the surface of myxospores. However, the ops and tps genes were expressed very differently during the developmental cycle of M. xanthus. The tps gene is induced early during fruiting body formation on a solid surface, and its product, protein S, is made in large quantities (up to 15% of total protein synthesis). When the cells turn into myxospores, protein S is assembled on the outer surface of the spore. We have now also found it in much smaller quantities inside the spores. The ops gene, on the other hand, appears to be induced later in development, after the cells have sporulated, since the ops gene product was found only inside the spores. When an ops gene under the control of a tps gene promoter was inserted into a wild-type strain, the ops gene product was synthesized at the same time as protein S and assembled onto the spore surface.

Bacterial Proteins↗
PubMed1985

Autotransplantation of skeletal muscle into myocardium.

In a series of 15 studies in dogs, sternocleidomastoid muscle was used to replace deficits created in left ventricular myocardium and sternohyoid muscle was used to replace portions of right myocardial wall. The five right ventricular autotransplants resulted in a 100% surgical success rate, with animals electively killed between 3 and 55 weeks after surgery. In 10 left ventricular studies excision of areas varying from 12 X 46 mm to 30 X 60 mm and incisions of from 40 mm to 70 mm in length were performed. Left ventricular studies resulted in a 60% surgical success rate, with clinically healthy animals being killed for study between 2 weeks and 50 weeks after surgery. Animals surviving the critical surgical recovery period showed no loss of weight or changes in activity. Gross findings at autopsy confirmed the viability of the skeletal muscle transplants. Borders were well healed and the grafted tissue was pliable. Histologic studies suggest that revascularization of skeletal muscle occurred from the myocardial side, and that there were healthy myocardial and skeletal muscle fibers at the junction, with evidence of regeneration.

Animals↗
PubMed1985

Catheter-mediated electrical ablation of the posterior septum via the coronary sinus: electrophysiologic and histologic observations in dogs.

In a series of 12 dogs, the electrophysiologic and histologic effects of a single damped sine-wave shock delivered via standard electrocatheters to the region of the coronary sinus orifice were investigated. Six dogs received 200 J and six received 360 J of stored energy. The shock was delivered to two consecutive proximal poles of a standard quadripolar catheter positioned at the coronary sinus orifice and connected to the positive output (anode) of a defibrillator. A disc electrode positioned on the anterior chest wall served as the cathode (negative pole). During the shock, voltage and current were recorded. Electrophysiologic testing was done before and 4 weeks after the shock. At 4 weeks, animals were killed and serial sections of the atrioventricular groove and conduction system were performed. No significant long-term change in atrioventricular conduction, spontaneous or induced atrial or ventricular arrhythmias was observed. However, transient atrioventricular block was seen in five and idioventricular rhythms in six animals in the short term. No persistent electrocardiographic changes were observed, and no sudden deaths occurred. Microscopically, transmural injury at the anulus proper or basilar ventricular epicardium was inconstant and infrequent. However, transmural atrial injury at the level of the coronary sinus was produced over a 10 +/- 5 mm length with the 200 J shock and a 21 +/- 6 mm length with the 360 J shock. Neither coronary artery injury nor damage to the conduction system was seen and cardiac tamponade did not occur. However, localized intramural atrial rupture of the coronary sinus wall (on the endocardial aspect only) was observed in each dog, consistent with barotrauma. With the present technique, atrial injury potentially capable of blocking the effects of accessory pathway conduction could be produced without other electrophysiologic alterations or complications. Injury to the anulus proper (and therefore to any accessory pathway per se) is probably unlikely. Barotrauma may play a significant role in the type of injury observed in this study.

Animals↗