Biomedical subjects

O Leroy

Publications and source records attributed to O Leroy.

At least 37 records · Page 2Linked to original sources

PubMed2000

On the polarization of light diffracted by ultrasound

If light is diffracted by ultrasound in an isotropic medium with acoustically induced birefringence, the state of polarization is modified in each order of diffraction with respect to the initial state of polarization of the incident light wave. In the present paper, some polarization effects are discussed in the case of normal light incidence. In general a rotation of the main polarization plane occurs, together with a change of the ellipticity. However, while the former effect always takes place, the latter only occurs in the case of ultrasonic light diffraction of the intermediate type. Some experimental measurements are included in case of argon laser light being diffracted by an ultrasonic wave propagating in fused silica (SiO2).

Journal Article↗

PubMed2000

Collinear acousto-optic diffraction using two nearby sound frequencies

Collinear acousto-optic spectrometers with sound consisting of one frequency have a spectral transfer function with many good characteristics, such as a narrow bandwidth, ... the side lobes, however, are rather high. To reduce these side lobes, one can try to apodize the sound in the acousto-optic cell by using a sound wave consisting out of two frequencies. At certain times, this produces a more smoothened sound field in the cell than in the one-frequency case. The resulting transfer function will contain lower side lobes. Also, the influence of all the sound field parameters--the amplitude, frequency difference, and time--on the transmission function is studied. Out of these results, better-performing collinear spectrometers can be designed.

Journal Article↗

PubMed2000

Schlieren photography study of energy absorption by uric acid nuclei.

Previous studies using microfocus x-ray radiography on concentric laminated uric acid calculi following in vitro extracorporeal shock-wave lithotripsy (ESWL) has demonstrated the enlargement of the matrix layers. The Schlieren technique was used to verify the hypothesis that the incident energy would be concentrated in the matrix layers by total internal reflection. Because of the rough surface of the stone, the ultrasonic beam (4 MHz) was incident at various angles. At the critical Rayleigh angle (45.9 degrees +/- 0.5 degrees ), the reflected beam consisted of a spectacularly reflected lobe and a reradiated leaky Rayleigh wave. Different critical Lamb angles, theta(L), of 30.8 degrees, 38.1 degrees and 50.8 degrees (experimental uncertainty 0.5 degrees ) were also determined. Depending on the angle of incidence on the stone surface, a Rayleigh wave can be produced and/or one or more layers, as a whole, are set into vibration (Lamb excitation), with the result that shell-like fragments consisting of one or more layers, break off the stones at sites of weaker bonding, as has been noted in previous in vitro lithotripsy experiments by our group.

Absorption↗

PubMed2000

Extension of the mode method for viscoelastic media and focused ultrasonic beams.

In the present study viscoelasticity is introduced in the mode model and the orthogonality condition is adapted for viscous media. The expansion of convergent acoustic Gaussian beams in terms of radiation modes for viscoelastic media is studied as well. The effects on the reflected and transmitted profiles of acoustic beams incident from an ideal liquid onto a viscoelastic plate are shown and physically explained. It is shown that focusing the incident beam can suppress divergence effects and gives the possibility to measure shear wave attenuation coefficients.

Acoustics↗

PubMed2000

Bounded beam interaction with thin inclusions. Characterization by phase differences at Rayleigh angle incidence.

A theoretical study of the reflection of a bounded Gaussian ultrasonic beam, incident onto a rectangular inclusion located near a fluid/solid half-space interface, is presented. The thickness of the inclusion is assumed to be much smaller than the ultrasonic wavelength in the solid. It is shown that, at critical Rayleigh angle incidence, the phase in the point of maximum amplitude of the shifted reflected lobe is very sensitive to dimension variations of the inclusion, and thus useful for inclusion characterization. The modelization of the problem is based on mode theory.

Acoustics↗

PubMed2000

Predisposing factors for nosocomial pneumonia in patients receiving mechanical ventilation and requiring tracheotomy.

STUDY OBJECTIVES: To assess the incidence of nosocomial pneumonia (NP) after tracheotomy in an ICU population and to determine NP risk factors during the ICU stay, particularly on the day of tracheotomy. DESIGN: A retrospective study using prospectively collected data. SETTING: A 16-bed multidisciplinary ICU. PATIENTS: One hundred thirty-five patients requiring tracheotomy for mechanical ventilation (MV) weaning. RESULTS: The mean (+/- SD) duration of MV before tracheotomy was 17.8 +/-13.4 days. Thirty-seven cases of NP occurred in 35 patients (25.9%), 8.7+/-7.3 days after the tracheotomy procedure. NP cases were classified as early NP (n = 19) if they occurred within 5 days after the procedure (mean, 2.7+/-1.1 days), and as late NP (n = 18) if they occurred beyond the fifth day (mean, 14.4+/-6.1 days). Multivariate analysis identified the following three independent factors associated with early NP: the presence of positive endotracheal aspirates (EAs) with pathogen levels of > or =10(5) cfu/mL (p = 0.0001); hyperthermia (temperature, > or =38.3 degrees C; p = 0.002) on the day of tracheotomy; and the continuation of sedation beyond 24 h after the tracheotomy (p = 0. 0001). Accountable pathogens of early NP were present in EA on the day of tracheotomy (p = 0.001). Cases of late NP were significantly associated with the duration of sedation before the procedure (p = 0. 002) and with hyperthermia (temperature, > or =38.3 degrees C) on the day of tracheotomy (p = 0.0005). The ICU admitting diagnosis, previous NP, duration of administration of antimicrobial agents and MV before tracheotomy, indication for tracheotomy, PO(2)/fraction of inspired oxygen ratio, and use of steroids on the day of the procedure were not associated with the occurrence of NP. The mortality rate of our population was 33.3%, and NP increased this percentage to 54.3%. CONCLUSIONS: Our results could suggest that tracheotomy should be delayed in mechanically ventilated patients with bronchial colonization and hyperthermia, when sedation cannot be discontinued after the procedure, to prevent occurrence of early NP.

Adult↗

PubMed1999

Dose dependency of antibody response in infants and children to pneumococcal polysaccharides conjugated to tetanus toxoid.

Three injections of tetravalent pneumococcal polysaccharide-tetanus toxoid conjugate vaccine (PncT) were given to infants at 2, 4 and 6 months of age simultaneously with diphtheria-tetanus-pertussis and Haemophilus influenzae type b-tetanus toxoid conjugate vaccines. Three doses (1, 3 or 10 microg) of polysaccharides were used. Children were boosted with unconjugated polysaccharide vaccine at 14 months of age. No dose dependency was seen after primary immunization. However, booster response to three vaccine serotypes was highest in the group primed with the lowest dose of conjugate vaccine. As the magnitude of the response to booster may be related to the number of polysaccharide-specific memory B cells, we hypothesize that the 10 microg dose of the tetravalent conjugate vaccine is too high for optimal induction of immunologic memory.

Antibodies, Bacterial↗

PubMed1999

Epidemiological features and prognosis of severe community-acquired pneumococcal pneumonia.

OBJECTIVE: To describe risk factors of severe pneumococcal community-acquired pneumonia and to study variables influencing outcome. DESIGN: Retrospective (1987-1992) and prospective (1993-1995) study. SETTING: Three participating ICUs from primary care hospitals. PATIENTS: Five hundred and five patients (mean age: 63 +/- 17 years) with severe community-acquired pneumonia (CAP). Three groups of patients were defined: pneumococcal CAP (group 1), CAP with microbial diagnosis other than Streptococcus pneumoniae (group 2), CAP from group 2 and CAP without microbial diagnosis (group 3). MEASUREMENTS AND RESULTS: Admission data and data on the disease's course were recorded. The mean Simplified Acute Physiologic Score (SAPS) was 12.5 +/- 5.4. On admission 288 (57 %) patients were mechanically ventilated (mv) and 82 (16.2 %) required inotropic support. A microbial diagnosis was established for 309 (61.2%) patients. S. pneumoniae was isolated in 137 (27.1%) patients. Severe pneumococcal CAP was independently associated with male sex (p = 0.01), lack of antibiotics use before admission (p = 0.0001), non-aspiration pneumonia (p = 0.01) and septic shock (p = 0.0001). The overall mortality rate was 27.5 % (29.2 % in group 1). In patients with severe pneumococcal CAP, multivariate analysis showed that leukopenia less than 3,500/mm3 (p = 0.0004), age over 65 years (p = 0.01), septic shock (p = 0.01), sepsis related complications (p = 0.0001), ICU complications (p = 0.001) and inadequacy of antimicrobial therapy (p = 0.002) worsened the prognosis. CONCLUSIONS: Few features facilitate the identification of pneumococcal CAP on ICU admission. The prognosis is mostly related to severity of illness (leukopenia, septic shock) while comorbidities do not seem to influence outcome. Sepsis-related disorders, ICU complications and adequate antimicrobial chemotherapy are the major variables affecting the outcome during an ICU stay.

APACHE↗

PubMed1999

Effect of hospital-acquired ventilator-associated pneumonia on mortality of severe community-acquired pneumonia.

PURPOSE: The purpose of this article is to evaluate, using two pairwise case-control studies, attributable mortality linked to hospital-acquired ventilator-associated pneumonia (HA-VAP) complicating the intensive care unit (ICU) stay of patients exhibiting severe community-acquired pneumonia (CAP). MATERIALS AND METHODS: Over an 11-year period, 498 patients with severe CAP were collected. Among them, 43 exhibited HA-VAP. In a first case-control study, these patients were matched with control on the basis of six confounding variables known to be general ICU prognosis factors. In a second case-control study, six variables specifically linked to CAP prognosis were used for matching. RESULTS: In the two case-control studies, each case patient was matched with one control patient. In the first analysis, success of matching was achieved in 198 of 258 (77%) variables used for matching. In the second analysis, matching was successful for 242 of 258 (94%) confounding variables used. Eighteen patients died, compared with, respectively, 6 (P = .003) and 7 (P = .01) controls. Attributable mortality of HA-VAP was similar in the two pairwise analyses, respectively, 28% (risk ratio = 3.0; 95% confidence interval, 1.32 to 6.82) and 26% (risk ratio = 2.57; 95% confidence interval, 1.2 to 5.52). CONCLUSION: When confounding factors were controlled, HA-VAP appeared to increase mortality of severe CAP requiring ICU admission.

Aged↗

PubMed1999

Pneumococcal conjugate vaccination in toddlers: mucosal antibody response measured as circulating antibody-secreting cells and as salivary antibodies.

BACKGROUND: Our previous studies have shown an antibody-secreting cell (ASC) response to pneumococcal vaccines in adults and suggested that a high IgA ASC response is an indicator of a secretory IgA response in saliva. We believe that the mucosal immune response is potentially an important characteristic of the pneumococcal vaccines and should thus be measured when the new pneumococcal conjugate vaccines are evaluated. OBJECTIVES: To study mucosal and serum antibody responses to pneumococcal conjugate vaccines in toddlers. METHODS: Each investigational vaccine, containing either 3 or 10 microg of pneumococcal PS serotypes 6B, 14, 19F and 23F conjugated to either diphtheria toxoid (PncD) or tetanus protein (PncT), was administered to 10 children (a total of 40 children). The ASC response was measured on Day 7 after immunization by enzyme-linked immunospot assay, and the salivary and serum antibodies were measured before and 7 and 28 days after the immunization by enzyme immunoassay. RESULTS: The vaccines studied induced ASC responses to the pneumococcal polysaccharides (PS) in all children vaccinated. The ASC responses to the PS components of the vaccine (the geometric mean number of ASCs varying from 120 to 160 ASC/10(6) cells) were lower than those seen earlier in adults after conjugate vaccine (240 to 2015 ASC/10(6) cells), but comparable with those seen earlier in adults after pneumococcal PS vaccine (113 to 136 ASC/10(6) cells). The ASC response was clearly dominated by IgA-secreting cells. Salivary IgA responses were detected in 35% of the children, but IgG was rarely detected in saliva. A positive correlation was demonstrated between the number of IgA ASCs and salivary IgA concentration (r = 0.70, P = 0.01), suggesting that a high number of IgA ASCs after parenteral immunization is an indicator of a secretory IgA response in saliva. On Day 28 after immunization increased serum concentrations of IgG were detected in most vaccinees (75 to 95%, depending on the serotype). CONCLUSIONS: Both mucosal and systemic antibody responses were induced by PncD and PncT vaccines in toddlers.

Antibodies, Bacterial↗

PubMed1999

Community-acquired pneumonia in the intensive care unit: epidemiological and prognosis data in older people.

OBJECTIVES: To compare epidemiological data, etiology, and prognosis of severe community-acquired pneumonia (CAP) in the intensive care unit (ICU) according to age (< or > or = 65 years) and to determine prognostic factors of CAP in older people. DESIGN: A retrospective (1987-1992) and prospective (1993-95) multicenter study. SETTING: Six ICUs in the north of France. PATIENTS: Five hundred five patients admitted to an ICU for severe CAP. MEASUREMENTS: Patient characteristics were compared with regard to age. Prognosis of CAP in older patients was studied by stepwise discriminant analysis. RESULTS: Two hundred seventy-eight patients (55%) were aged 65 years or older. Comparison of epidemiological data between older and younger patients revealed a higher prevalence of women (38% vs 29%), more severe underlying comorbidities (anticipated death within 5 years: 59% vs 26%), and more frequent chronic respiratory insufficiency (48% vs 33%) in the older patients. In this study group, 224 organisms were isolated from 172 patients (62%); those identified most frequently were Gram-negative bacilli (34%), S. pneumoniae (32%), and Staphylococcus sp. (19%). Compared with younger patients, no significant differences in bacteriological data were observed. However, crude and attributable mortality rates were significantly higher in the older patients (33% vs 21% and 30% vs 19%, respectively). Prognosis analysis identified four independent predictors of mortality in the older patients: initial septic shock (relative risk (RR) = 3), sepsis-related complications (RR = 4.3), hospital-acquired lower respiratory tract superinfections (RR = 2), and nonspecific pneumonia-related complications (RR = 2.8). CONCLUSION: The bacterial etiology provides some approaches to empirical therapy for older patients with severe community-acquired pneumonia. In addition, the inappropriateness of withholding intensive care for reasons of age alone is emphasized.

Age Factors↗

PubMed1999

Simplified prediction rule for prognosis of patients with severe community-acquired pneumonia in ICUs.

STUDY OBJECTIVES: To develop a simplified prognostic prediction rule for patients admitted to ICUs for severe community-acquired pneumonia (CAP). SETTING: Six ICUs in the north of France. PATIENTS: Five hundred five patients admitted to ICUs over a 9-year period (from 1987 to 1995) for severe CAP. INTERVENTIONS: Retrospective prognosis analysis and multivariate analysis using a credit scoring technique. MEASUREMENTS: The primary outcome measure was ICU mortality. RESULTS: Among the 505 patients, 472 were eligible for the prognosis study. The ICU mortality rate was 22.9%. Multivariate analysis identified, on the basis of the patient's medical history and initial examination on ICU admission, six independent predictors of mortality: age > or = 40 years, anticipated death within 5 years, nonaspiration pneumonia, chest radiograph involvement > 1 lobe, acute respiratory failure requiring mechanical ventilation, and septic shock. An initial risk score based on these factors classified patients into three risk classes of increasing mortality: 4% in class I, 25% in class II, and 60% in class III. Multivariate analysis of events occurring during ICU stay identified three independent predictors of mortality: hospital-acquired lower respiratory tract superinfections, nonspecific CAP-related complications, and sepsis-related complications. An adjustment risk score based on these factors was essential to accurately predict the final outcome of patients in the initial risk class II. CONCLUSIONS: As an aid to clinicians in stratifying the prognosis of patients with severe CAP, the simplified prediction rule used in this study could be useful for therapeutic decisions and appropriate care.

Community-Acquired Infections↗

PubMed1999

[Systemic manifestations and development of GPIIbIIIa antibodies in the course of staphylococcal endocarditis. Report of a case].

Immunological complications of staphylococcal endocarditis are rare but represent a serious event in this condition. The authors report the case of acute tricuspid valve endocarditis in a 38 year old drug addict. The diagnosis was suggested by the presentation of bilateral bacterial lung abscesses with a murmur of tricuspid regurgitation, and confirmed by transthoracic and transoesophageal echocardiography. Bacteriological cultures isolated a methicillin-sensitive staphylococcal aureus. The outcome was complicated by a nephrotic syndrome associated with a glomerulonephritis by deposition of immune complexes and an autoimmune thrombocytopaenic purpura due to acquired anti-glycoprotein IIb IIIa antibodies. Antibiotic therapy led to cure without sequellae of the endocarditis, the nephrotic syndrome and the thrombocytopaenia. This case illustrates the risk of immunological complications during acute staphylococcal tricuspid valve endocarditis and also illustrates the possibility of a favourable outcome with antibiotic therapy alone. However, the potential severity of these complications indicates the need for early diagnosis and strict surveillance of this condition.

Adult↗

PubMed1998

[Evaluation of prescription of antibiotics in an intensive care unit].

OBJECTIVES: In order to optimize prescriptions, we conducted a qualitative evaluation of antibiotic prescription in an intensive care unit. METHODS: A prospective observational study was performed on 100 consecutive prescriptions from 11/95 to 4/96. RESULTS: Among 14 documented cases, initial antibiotic therapy was in accordance with antimicrobial susceptibility patterns in all but one case. Among 86 empirical cases, 38 were secondarily documented, yielding 43 microorganisms. Of these 38, 27 were susceptible to 2 or more empirical antibiotics, 3 to only 1 and 8 to none. Antibiotics were modified in 23/38 (60%) cases, resulting in drug changes (n = 21) or drug addition (n = 2). In all cases, the new prescription was consistent with the antibiogram. In the 48 cases where no microorganism was isolated, antibiotic change was guided by clinical course and occurred in 6 (12.5%) cases. A switch to older, cheaper or more narrow spectrum antibiotics was possible in 18 cases, but was actually done in only 4 (22%). Dosage errors were observed in 5 cases of initial therapy. Second line therapy contained 8(21%) dosage errors. Most frequently, isolated organisms at admission were: Staphylococcus sp. (n = 15), P. aeruginosa (n = 11) and S. pneumoniae (n = 10). New pathogens emerged in 16 patients (16%) receiving antibiotics. The most frequent was P. aeruginosa in 4 patients receiving ofloxacin + amoxicillin +/- clavulanic acid. CONCLUSION: These results are encouraging, however, the use of guidelines and periodic evaluation of antibiotic prescription practices might improve the efficiency of empirical antibiotic prescriptions and reduce overall antibiotic costs.

Anti-Bacterial Agents↗

PubMed1998

Effect of spermine administration on pancreatic maturation in unweaned rats.

The effect of oral administration of spermine on pancreatic maturation was investigated in the suckling rat. The treatment consisted of 0.3-0.4 mmol spermine kg-1 body weight given orally once a day for 3 days starting at day 11 after birth. Spermine administration does not adversely affect the growth of the pancreas (wet weight, protein and DNA contents remain unchanged). The proliferating cell nuclear antigen (PCNA) index decreases significantly in spermine-treated rats, indicating that spermine slows down the proliferation rate of the organ. The enzymatic activities of trypsin, chymotrypsin and alpha-amylase are increased significantly in the pancreas of spermine-treated rats. The morphology of the organ seems affected as shown by hematoxylin-eosin staining: a cytoplasm indicative of higher synthetic activity is visible after spermine treatment. We conclude that spermine treatment of unweaned rats can induce precocious biochemical and morphological maturation of the exocrine pancreas, pushing the organ forward in the process of differentiation (closer to the adult stage).

Animals↗

PubMed1998

Streptococcus pneumoniae capsular polysaccharide-diphtheria toxoid conjugate vaccine is immunogenic in early infancy and able to induce immunologic memory.

BACKGROUND: Pneumococcal polysaccharide vaccines are not protective against the most common pneumococcal infections in infancy. The importance of pneumococcal diseases and emerging antimicrobial resistance emphasize the need for prophylaxis. METHODS: Pneumococcal conjugate vaccine, containing capsular polysaccharides from serotypes 6B, 14, 19F and 23F conjugated to diphtheria toxoid (PncD), was given to 75 infants at 2, 4 and 6 months of age. Three dosages (1, 3 or 10 microg of each) were used. A placebo group of 49 infants received physiologic saline. Children were given a booster dose of either polysaccharide or conjugate vaccine at 14 months of age; the placebo group received conjugate vaccine. Antibody concentrations were determined with an enzyme immunoassay. RESULTS: The highest dose induced the strongest response after primary immunization, but booster response was greatest in the group primed with the lowest dose. Polysaccharide and conjugate vaccines induced booster responses of the same magnitude. At 24 and 36 months of age the antibody concentrations were similar in children who had received the PncD in infancy and in children immunized at 14 months of age only. CONCLUSIONS: The PncD conjugate vaccine is immunogenic and able to induce immunologic memory.

Antibodies, Bacterial↗

PubMed1998

Reduced response to multiple vaccines sharing common protein epitopes that are administered simultaneously to infants.

The plethora of newly discovered vaccines implies that, in the future, many vaccines will have to be administered simultaneously to infants. We examined the potential interference with the immune response of several coadministered vaccines containing the same protein component, namely, tetanus toxoid (TT). Infants simultaneously receiving a tetravalent pneumococcal vaccine conjugated to TT (PncT) and a diphtheria-tetanus-pertussis-poliovirus-Haemophilus influenzae type b-tetanus conjugate vaccine showed significantly lower anti-H. influenzae type b polysaccharide (polyribosylribitol phosphate [PRP]) antibody concentrations than those receiving either a tetravalent pneumococcal vaccine conjugated to diphtheria toxoid or placebo. A dose range study showed that anti-PRP antibody concentrations were inversely related to the TT content of the PncT vaccines administered in infancy. Postimmunization antitetanus antibody concentrations were also affected adversely as the TT content of the coadministered vaccines was increased. This phenomenon, which we believe derives from interference by a common protein carrier, should be taken into account when the introduction of an immunization program including multiple conjugate vaccines is considered.

Antibodies, Bacterial↗

PubMed1997

Pulmonary disposition of vancomycin in critically ill patients.

Vancomycin penetration in epithelium lining fluid was studied in ten mechanically ventilated patients with methicillin-resistant Staphylococcus aureus pneumonia 24 hours after the onset of treatment. Vancomycin was given intravenously at a daily dose of 30 mg/kg. Vancomycin levels were detectable in four patients (range, 1-2.77 micrograms/ml). Concordance between high plasma concentrations (> 20 micrograms/ml) and detectable vancomycin levels in epithelium lining fluid was noted. These results suggest that the pulmonary disposition of vancomycin remains low for most patients 24 h after the onset of treatment compared with the minimum inhibitory concentrations for most gram-positive organisms. One therapeutic goal of vancomycin treatment could be to obtain through plasma levels of 20 micrograms/ml. Further studies are required to determine the clinical relevance of these observations.

Aged↗