Search PubMed⌕ Search

Biomedical subjects

M Leon

Publications and source records attributed to M Leon.

At least 91 records · Page 5Linked to original sources
PubMed1993

Elaboration of glial cell processes in the rat olfactory bulb associated with early learning.

Odor preference training early in life induces anatomical changes in focal areas of the glomerular layer of the rat main olfactory bulb. We examined the associated focal changes in glial cell morphology using immunohistochemistry for glial fibrillary acidic protein (GFAP) and found that the density of immunoreactive processes was higher in glomeruli responsive to an odor for which pups had developed a preference. The increase in process density in trained pups was specific to focal responsive regions of the bulb, revealed with [14C]2-deoxyglucose autoradiography. There was no change in the number of GFAP-immunoreactive cells between trained and control pups.

Aging↗
PubMed1993

Odor-induced increases in c-fos mRNA expression reveal an anatomical "unit" for odor processing in olfactory bulb.

Expression of the immediate-early gene c-fos was used to evaluate the coordinate activation of olfactory bulb neurons by brief exposure to specific odors in the alert rat. In situ hybridization to c-fos mRNA was compared to regional increases in 2-deoxy-D-[14C]glucose incorporation in an adjacent section analysis. Levels of c-fos mRNA in olfactory bulb were high in rats recently removed from their home cage but were low in animals placed in a relatively odor-free chamber for 30 min. Presentation of specific odors to alert rats for as little as 5 min increased c-fos mRNA in radially distributed neuronal ensembles that spanned the lamina of the main olfactory bulb. The complementary RNA (cRNA)-labeled neuronal collectives consisted of cells in the glomerular layer that precisely defined the borders of individual glomeruli and underlying tufted, mitral, and granule cells. The activated fields were much broader in the granule cell layer than in the overlying glomerular layer and thus exhibited a flask-like, as opposed to a columnar, contour. The bulbar distribution of cRNA-labeled cell arrays differed with different odors and, in the glomerular layer, corresponded to focal regions of high 2-deoxy-D-[14C]glucose uptake. Administration of the noncompetitive N-methyl-D-aspartate receptor antagonist MK801 did not attenuate the odor induction of c-fos but, instead, increased c-fos mRNA levels throughout the bulb. We propose that the neuronal ensembles expressing increased c-fos mRNA with odor stimulation represent principal functional units of sensory processing in the main olfactory bulb of the behaving rat.

Animals↗
PubMed1993

Detection of superior mesenteric and coeliac artery stenosis with colour flow Duplex imaging.

Measurements of blood velocity in the coeliac axis (CA) and the superior mesenteric artery (SMA) before and after a standard meal in normal people have been studied by several authors. However, information about the ability to detect stenotic lesions is lacking. The aim of our study was to determine the accuracy of Duplex scanning in detecting angiographically proven lesions. Twenty normal volunteers (13 males and seven females) and 24 patients (19 males and five females) with visceral artery stenosis on angiography were examined in the supine position (angle of insonation 60.5) with colour flow Duplex imaging (CFDI) (3.5 MHz probe), in the fasting state and after a standard meal at 15, 40, 60 and 90 min. Peak systolic velocity (PSV) and end diastolic velocity (EDV) were determined in both CA and SMA. The PSV was the best indicator of stenosis. After the meal, there was an increase in both PSV and EDV but neither of the postprandial measurements improved the accuracy of the test. The results indicate that CFDI can detect the presence of significant stenosis (> 50% in the CA and SMA with a sensitivity and specificity of > 80%.

Arterial Occlusive Diseases↗
PubMed1993

The effect of iloprost in patients with rest pain.

Thirty-four patients with ischaemic rest pain in 42 limbs and ankle pressure equal to or less than 50 mmHg have been treated with intravenous infusion of synthetic prostacyclin (iloprost) for eight days. Leg blood flow was measured with air plethysmography before treatment, on day 4 and day 8 of treatment. Total relief of pain for at least 6 weeks occurred in 91% of patients with leg blood flow > or = 40 ml/min, in 18% with leg flow 30-39 ml/min and in 11% with leg flow < 30 ml/min. Complete relief of pain for at least 6 weeks occurred in 92% of patients in whose limbs the blood flow on day 8 was greater than 50 ml/min but only in 6% with blood flow less than 50 ml/min. These results indicate that iloprost increases leg blood flow and that patients likely to respond can be identified from the baseline air plethysmographic measurement of leg blood flow.

Arteriosclerosis↗
PubMed1993

Excimer laser coronary angioplasty of aorto-ostial stenoses. Results of the excimer laser coronary angioplasty (ELCA) registry in the first 200 patients.

BACKGROUND: Percutaneous transluminal coronary angioplasty (PTCA) of aorto-ostial stenosis has been associated with a lower rate of acute success, a high risk of vessel closure, and late restenosis. The purpose of this report is to document a prospective multicenter trial of excimer laser coronary angioplasty (ELCA) of aorto-ostial stenosis involving the coronary arteries and saphenous vein grafts. METHODS AND RESULTS: Between December 1989 and May 1992, 206 aorto-ostial ELCA procedures were performed on 209 stenoses in 200 patients. Canadian Cardiovascular Society class III or IV angina was present in 76%. The distribution of stenosis locations was left main coronary (LM) in 26 (12%), right coronary (RCA) in 124 (59%), and vein grafts (VG) in 59 (28%). Adjunctive PTCA was performed in 72%. Procedure success defined as < or = 50% diameter stenosis without major complications was achieved in 90% (LM, 92%; RCA, 89%, VG, 90%). Quantitative angiographic analysis documented an improvement in stenosis diameter from 0.8 +/- 0.5 mm or 76 +/- 14% at baseline to 2.1 +/- 0.6 mm or 36 +/- 15% at completion (P < .01). The majority of the acute gain in diameter (1.0 +/- 0.6 mm) resulted from ELCA. A major complication during hospitalization occurred in 3.9% (death, 0%; Q-wave myocardial infarction, 0.5%; bypass surgery, 3.4%). The only logistic regression univariate and multivariate predictor of procedure failure was female gender. Six-month angiographic follow-up, available in 51% of eligible patients, documented an average lumen diameter of 1.7 +/- 1.0 mm and mean diameter stenosis of 46 +/- 26%. Restenosis (> 50% diameter stenosis) occurred in 39% (LM, 64%; RCA, 35%; VG, 35%). Restenosis was less likely when residual stenosis was < or = 35% (28% versus 53%, P < .05). Clinical events at follow-up were death, 2.7%; bypass surgery, 6.5%; myocardial infarction, 2.2%; and repeat angioplasty, 16.2%. Of the remainder, 78% were asymptomatic, class I or II for anginal symptoms. An adverse event during follow-up was more than twice as likely in the group with LM (50.0% versus 21.1%, P < .02). CONCLUSIONS: ELCA is acutely effective and safe therapy in patients with aorto-ostial stenosis. Six-month restenosis, adverse-event rates were higher and functional status was poorer in the group with LM stenosis. ELCA may be considered as an alternative to bypass surgery in carefully selected patients with isolated aorto-ostial stenosis of the RCA and saphenous vein grafts.

Adult↗
PubMed1993

Progression of carotid atherosclerosis. Three year follow-up and analysis of risk factors.

OBJECTIVE: To elicit the risk factors associated with increasing grades of stenosis in patients with carotid plaque. STUDY DESIGN: Retrospective review of serial duplex scans of the carotid bifurcation. Case note review for documented risk factors. SETTING: Irvine Laboratory of the Academic Department of Surgery, Vascular Section. PATIENTS AND RESULTS: Review of serial duplex scans of the carotid bifurcation was performed on 200 unselected patients who each had a follow-up of at least three years. Definite progression of carotid atherosclerosis was defined as an unequivocal increase in at least one grade by the criteria of Strandness, and was documented in 50 patients (25%). Even if the initial situation is normal or minimal disease (< 15% stenosis), once definite plaque progression is observed, the lesion will progress to a hemodynamically significant one (> 50%) in 67% of this patient population. The only risk factor for plaque progression that we defined is hypertension, and this may be spurious. There are no risk factors associated with the subgroup of plaques that progress rapidly above those that progress at a slower rate. CONCLUSIONS: There are no risk factors defined in this population which are associated with advancing carotid atherosclerosis.

Aged↗
PubMed1993

The effect of elastic stockings on the elasticity of varicose veins.

The aim of this study was to establish the long-term effect of graduated elastic compression on venous elasticity in patients with superficial or deep venous disease and to determine the possible relationship between elasticity and the duration of the disease. The elastic modulus of 29 patients, 19 with superficial vein incompetence and 10 with deep vein incompetence was assessed by the simultaneous measurement of calf volume (determined using strain gauge) and venous pressure (obtained via a dorsal foot vein) during venous occlusion. The measurements were obtained before and after 4 weeks of elastic compression stockings. The elastic modulus K, was defined as stress/strain when the veins were full and was calculated from the pressure/volume relationship. The results show a clear difference in elasticity before and after elastic stockings. Two groups of patients were identified: group 1 with increased elasticity and group 2 with decreased elasticity. There was a negative linear relationship (r = 0.88) between increase in elasticity after treatment and duration of venous disease.

Bandages↗
PubMed1992

The function relating the subjective magnitude of brain stimulation reward to stimulation strength varies with site of stimulation.

A two-lever choice paradigm with concurrent variable interval schedules of reward was used to measure the growth in the subjective magnitude of reward as a function of current, by finding the adjustment in the stimulating current required to offset a given difference in the rates at which two rewards were received. Increasing current by a factor of 2 increased subjective reward magnitude by a factor ranging from as little as 3 to as much as 4,000. This range was about as great between electrodes within one rat as between electrodes and rats. In the light of earlier findings regarding the equivalent effects of increments is current and pulse frequency, these large differences cannot readily be explained by differing fiber densities at the site of stimulation. It is suggested that the medial forebrain bundle terminates in more than one spatio-temporal integration mechanism. The magnitude of the spatio-temporally integrated effect of a barrage of action potentials in the reward-relevant axons depends on which subset of reward-relevant axons is excited by the stimulation.

Action Potentials↗
PubMed1992

Neuroethology of olfactory preference development.

Young mammals come to approach the odor of their mother, a response that facilitates their survival during early life. Young rats induce a cascade of events in their mother to induce the emission of her odor. The pups increase circulating prolactin levels, which increases food intake and the emission of large quantities of cecotrophe containing the maternal odor. This odor is synthesized by the action of cecal microorganisms and changes with maternal diet. The diet-dependence of the odor requires the pups to acquire their attraction to the odor postnatally. The acquisition of this preference occurs when an odor is paired with the tactile stimulation that pups receive during maternal care. The action of the tactile stimulation appears to be mediated by noradrenaline. The development of this type of olfactory attraction is accompanied by changes in the regions of the olfactory bulb that are responsive to the attractive odor. Metabolic, anatomical, and neurophysiological changes in response to the attractive odor emerge in such regions of the bulb after early olfactory preference training.

Animals↗
PubMed1992

The combination of liquid crystal thermography and duplex scanning in the diagnosis of deep vein thrombosis.

One hundred patients with clinically suspected deep vein thrombosis (DVT) were studied by liquid crystal thermography (LCT), duplex scanning and venography. Liquid crystal thermography was found to have a negative predictive value of 97% if performed within 1 week of the onset of symptoms. Duplex scanning had a sensitivity of 93% and specificity of 91% for all thrombi (proximal and calf). On the basis of these results a plan of investigation has been formulated that would avoid duplex scanning and venography in 39 of the 100 patients. Duplex scanning alone would be appropriate in 56 of the remaining 61 patients. Only six patients would be unsuitable for duplex scanning because of a very tense tender leg and require venography. The plan would miss one calf thrombus and result in treating three patients unnecessarily. This policy would be not only effective but also cost-effective.

Female↗
PubMed1992

Popliteal vein entrapment in the normal population.

The aim of this study was to determine the incidence and severity of popliteal vein compression by full knee extension in the normal population. The popliteal veins in 100 healthy volunteers (200 limbs) with no history of previous deep vein thrombosis (DVT) or venous obstruction were examined using duplex scanning with the knee slightly flexed and then fully extended. Knee extension produced complete obstruction in 17 subjects and severe obstruction (< 50% decrease in diameter) in a further 10 subjects. Thirteen subjects had unilateral compression and 14 bilateral. The 27 subjects were tested for functional venous outflow obstruction with air plethysmography. In flexion, the outflow fraction was normal (> 40%) in all subjects. With the knee fully extended, severe or complete venous obstruction (outflow fraction < 10%) was found in eight subjects. Moderate obstruction (outflow fraction 10-40%) was found in all the remaining 19 subjects. When digital compression of the long saphenous vein was performed, these subjects also demonstrated severe outflow obstruction. Although the incidence of symptoms of functional venous obstruction is rare in the general population, these findings have important implications for venous stasis for patients on the operating table and in those having prolonged bed rest. Studies investigating the association between popliteal vein compression and postoperative deep venous thrombosis are needed.

Adult↗
PubMed1992

The neurobiology of filial learning.

Early filial learning evokes clear neural changes in the developing brain. Anatomy and function in the developing olfactory, auditory, and visual systems change following early learning. Since this type of learning seems critical for the survival of the young, the mechanisms of such plasticity should be clear and reliable. In each sensory modality examined, both distinct changes in the brain and the reliable nature of learning through early experience have become evident with experimental analysis.

Animals↗
PubMed1992

Restenosis after placement of Palmaz-Schatz stents in native coronary arteries. Initial results of a multicenter experience.

BACKGROUND: Several metallic intracoronary stents are currently undergoing preliminary evaluation to ascertain potential benefit as means to reduce the 30-40% incidence of restenosis after balloon angioplasty. METHODS AND RESULTS: To determine the incidence and correlates of restenosis after placement of Palmaz-Schatz stents in native coronary arteries in the first group of patients selected for this procedure, clinical and quantitative angiographic data from 206 consecutive patients (221 stenoses) with successful stent placement (diameter stenosis < 50%) were analyzed. Six patients (2.9%) had thrombosis-mediated stent closure within 1 month after stent placement and were excluded from long-term angiographic follow-up. One hundred eighty-one (91%) of the remaining 200 patients had angiography at 5.8 +/- 2.1 months. Patients with and without follow-up did not differ in any baseline characteristic; in particular, history of restenosis at the site stented (73% versus 65%), placement of multiple overlapping stents (17% versus 20%), and mean poststent diameter stenosis (16 +/- 12% versus 14 +/- 12%). The overall incidence of restenosis (diameter stenosis > or = 50% at follow-up) in this group at high risk for restenosis was 36% (95% confidence interval, 29-43%) on a per-stenosis basis. The incidence of restenosis when a single stent was placed was 30% (95% confidence interval, 23-37%). Risk was dependent upon a history of restenosis (present versus absent 36% versus 16%, p = 0.02) and upon whether or not a poststent stenosis < or = 0% was achieved (6% versus 33%, p = 0.02). When multiple overlapping stents were placed, restenosis occurred at 64% of sites, and placement of multiple stents was discouraged during the later phases of this study as these results became apparent. CONCLUSIONS: Although multiple stents appear to yield a poor long-term result, placement of single stents may offer a benefit compared with standard coronary angioplasty, particularly if an excellent angiographic result can be obtained in patients without prior restenosis. Further randomized trials in such patients are needed.

Coronary Angiography↗
PubMed1992

Skin flow the venoarteriolar response and capillary filtration in diabetics. A 3-year follow-up.

Resting skin blood flow (RF) and the venoarteriolar response (VAR = the vasoconstrictor response on standing) have been studied in 100 patients with diabetic neuropathy, in 100 diabetics without neuropathy, and in 100 normal subjects by laser Doppler flowmetry. Capillary filtration was also studied with strain gauge plethysmography. The authors followed up these patients by evaluating their microcirculation again after three years. At the beginning of the study in patients with neuropathy, RF and capillary filtration were increased. The VAR and the microangiopathy index (MI = VAR/RF) were reduced in all diabetics, to a greater extent to those with neuropathy. After three years the authors observed an increase in capillary filtration associated with a further impairment in VAR and MI, suggesting progression of microangiopathy in both groups of diabetics. These results suggest that the postural control of blood flow in the skin of the foot is impaired in diabetic microangiopathy, particularly in neuropathics. Increased skin blood flow and capillary filtration and the impaired venoarteriolar response cause edema and may contribute to the thickening of capillary basement membranes and the progressive evolution of diabetic microangiopathy.

Adult↗
PubMed1992

Veno-arterial carbon dioxide gradient in human septic shock.

Recent reports have shown that venous hypercarbia, resulting in a widening of the veno-arterial difference in PCO2 (dPCO2), is related to systemic hypoperfusion in various forms of low-flow state. Although septic shock usually is a hyperdynamic state, other factors can influence the CO2 production and elimination, and thus dPCO2 in septic shock This study examined the dPCO2 and acid-base balance together with cardiac output measurements and oxygen-derived variables in 64 adult patients with documented septic shock. For a total of 191 observations, a significant exponential relation between dPCO2 and CO was found. At time of first measurement, 15 patients had an increased dPCO2 (above 6 mm Hg) and a higher mixed venous PCO2 (PvCO2) (47.2 +/- 10.0 vs 35.9 +/- 7.3 mm Hg, p less than 0.001). These patients had a lower cardiac index (2.9 +/- 1.3 vs 3.8 +/- 2.0 L/min.m2, p less than 0.01), a higher oxygen extraction ratio, but a similar VO2 than patients with normal dPCO2. The higher dPCO2 could also be related to an impaired CO2 elimination as indicated by a higher PaCO2 and a lower PaO2/FIO2 in these patients. Nonsurvivors had a significantly higher dPCO2 than survivors (5.9 +/- 3.4 vs 4.4 +/- 2.3 mm Hg, p less than 0.05) in the presence of similar cardiac output. The higher dPCO2 in these patients was probably related to the higher blood lactate levels (7.7 +/- 5.3 mmol/L vs 4.5 +/- 2.8 mmol/L, p less than 0.01) and the more severe pulmonary impairment (SaO2 90 +/- 8 percent vs 95 +/- 4 percent, p less than 0.001). Arteriovenous oxygen content difference (dAVO2) and VO2 were similar in survivors and nonsurvivors. In conclusion, dPCO2 patients with septic shock is related principally to cardiac output but apparently also to the degree of pulmonary impairment. Although dPCO2 is larger in nonsurvivors, its prognostic value is modest.

Adult↗
PubMed1992

Acute effects of hydroxyethylrutosides on capillary filtration in normal volunteers, patients with venous hypertension and in patients with diabetic microangiopathy (a dose comparison study).

The acute effects of hydroxyethylrutosides on capillary filtration were studied in 12 normal subjects, 25 patients with venous hypertension and 22 diabetics with microangiopathy. The two groups of patients randomly received a single oral dose (500 or 1000 mg) of hydroxyethylrutosides. A single dose of 500 mg was used for normal volunteers. In the following 6 hours capillary filtration was studied with straingauge plethysmography. The decrease in capillary filtration was evident within the first hour and was at its peak between the second and fourth hour. After 6 hours it was still significantly below baseline values in patients. The 1000 mg dose was significantly more effective in both groups of patients. This study confirms the efficacy of hydroxyethylrutosides in decreasing capillary filtration. It suggests that the effect of one dose lasts at least 6 hours and also that the higher dose is more effective.

Adult↗