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C Duvivier

Publications and source records attributed to C Duvivier.

At least 37 records · Page 2Linked to original sources
PubMed1997

Influence of external loading and assisted ventilation on chest wall mechanical properties.

Instantaneous respiratory effective elastance (Eteff) and tissue resistance (Rt) may be measured by studying the relationship between flow at the airway opening and at the chest during forced oscillations; using that method it has been shown that Rt varies little during breathing while Eteff presents much larger phasic variations than can be explained by the curvature of the static pressure-volume curve (Tomalak et a1., 1997). The aim of this study was to test the hypothesis that the large variations of Eteff were related to the activity of respiratory muscles. For this, we studied in six healthy subjects the changes in Eteff and Rt induced by inspiratory and expiratory elastic loading (IEL and EEL, respectively), resistive loading (REL) and assisted ventilation (ASV) while keeping lung volume, ventilation and breathing pattern as constant as possible. IEL and EEL predominantly increased Eteff during the inspiratory and expiratory phases, respectively; in contrast, ASV decreased Eteff during inspiration and almost completely abolished its positive volume dependence. The changes of Rt usually paralleled those of Eteff. We conclude that respiratory muscle activity is responsible for most of the variations of Eteff during spontaneous breathing.

Adult↗
PubMed1997

Respiratory tissue properties derived from flow transfer function in healthy humans.

Assuming homogeneity of alveolar pressure, the relationship between airway flow and flow at the chest during forced oscillation at the airway opening [flow transfer function (FTF)] is related to lung and chest wall tissue impedance (Zti): FTF = 1 + Zti/Zg, where Zg is alveolar gas impedance, which is inversely proportional to thoracic gas volume. By using a flow-type body plethysmograph to obtain flow rate at body surface, FTF has been measured at oscillation frequencies (f(os)) of 10, 20, 30 and 40 Hz in eight healthy subjects during both quiet and deep breathing. The data were corrected for the flow shunted through upper airway walls and analyzed in terms of tissue resistance (Rti) and effective elastance (Eti,eff) by using plethysmographically measured thoracic gas volume values. In most subjects, Rti was seen to decrease with increasing f(os) and Eti,eff to vary curvilinearly with f(os)2, which is suggestive of mechanical inhomogeneity. Rti presented a weak volume dependence during breathing, variable in sign according to f(os) and among subjects. In contrast, Eti,eff usually exhibited a U-shaped pattern with a minimum located a little above or below functional residual capacity and a steep increase with decreasing or increasing volume (30-80 hPa/l2) on either side. These variations are in excess of those expected from the sigmoid shape of the static pressure-volume curve and may reflect the effect of respiratory muscle activity. We conclude that FTF measurement is an interesting tool to study Rti and Eti,eff and that these parameters have probably different physiological determinants.

Adult↗
PubMed1997

Calcification of medial elastic fibers and aortic elasticity.

We tested the hypothesis that a simple change in wall composition (medial calcium overload of elastic fibers) can decrease aortic elasticity. Calcium overload was produced by hypervitaminosis D plus nicotine (VDN) in the young rat. Two months later, measurement of central aortic mean blood pressure in the unanesthetized, unrestrained rat showed that the VDN rat suffered from isolated systolic hypertension but that mean blood pressure was normal. Wall thickness and internal diameter determined after in situ pressurized fixation were unchanged, as was calculated wall stress. Wall stiffness was estimated from (1) elastic modulus (determined with the Moens-Korteweg equation and values for aortic pulse wave velocity in the unanesthetized, unrestrained rat and arterial dimensions) and (2) isobaric elasticity (= slope relating pulse wave velocity to mean intraluminal pressure in the phenylephrine-infused, pithed rat preparation). Both increased after VDN, and both were significantly correlated to the wall content of calcium and the elastin-specific amino acids desmosine and isodesmosine. Left ventricular hypertrophy occurred in the VDN model, and left ventricular mass was related to isobaric elasticity. In conclusion, elastocalcinosis induces destruction of elastic fibers, which leads to arterial stiffness, and the latter may be involved in the development of left ventricular hypertrophy in a normotensive model.

Analysis of Variance↗
PubMed1997

Vasodilators, aortic elasticity, and ventricular end-systolic stress in nonanesthetized unrestrained rats.

We evaluated the effect of different vasodilators on ventricular end-systolic stress by investigating the impact of sodium nitroprusside, nifedipine, and hydralazine on blood pressure, aortic stiffness, and wave reflection during drug-induced hypotension (to 80 mm Hg mean blood pressure) in normotensive (central aortic mean blood pressure, 116 to 119 mm Hg; systolic pressure, 133 to 137 mm Hg), nonanesthetized, unrestrained rats. Aortic stiffness was evaluated from the slope of the linear regression relating pulse wave velocity (PWV) to central aortic mean or pulse pressure. The fall in central aortic systolic blood pressure was less than the fall in mean pressure, especially after hydralazine (122+/-4 mm Hg; sodium nitroprusside, 107+/-2; and nifedipine, 112+/-3 mm Hg; P<.05). The PWV/mean pressure slope was linear, positive, and similar in all three groups (hydralazine, 3.3+/-0.2; sodium nitroprusside, 3.8+/-0.3; and nifedipine, 3.9+/-0.3 cm x s[-1]x mm Hg[-1]; P>.05). The PWV/pulse pressure slope was linear, negative, and less steep in the case of hydralazine (-4.9+/-0.6; sodium nitroprusside, -15.5+/-3.7; and nifedipine, -13.5+/-2.9 cm x s[-1] x mm Hg[-1]; P<.05). The travel time and augmentation index of the reflected wave were similar in all groups. In conclusion, sodium nitroprusside and nifedipine had a more beneficial effect on end-systolic stress than did hydralazine. This does not appear to be related to any specific effect on wave reflection or the "static" relationship between PWV and aortic mean blood pressure; it may be related to the effects of these drugs on the "dynamic" relationship between PWV and pulse pressure.

Animals↗
PubMed1996

[Pulmonary toxoplasmosis in patients with human immunodeficiency virus infection. 21 cases].

OBJECTIVES: Assess expression of pulmonary toxoplasmosis, the second most frequent localization after brain, in patients infected with the human immunodeficiency virus (HIV). METHODS: Twenty-one HIV-infected patients (18M, 3F) were admitted for pulmonary toxoplasmosis between September 1987 and February 1995. Mode of HIV transmission was unprotected homosexual sexual activity (n = 16), intravenous drug abuse (n = 3) and transfusion (n = 2). RESULTS: Isolated pulmonary toxoplasmosis was found in 11 patients. In 10 patients pulmonary toxoplasmosis was associated with cerebral (n = 4), bone marrow (n = 2), ocular (n = 1) and multifocal (n = 3) localizations. Seven patients were admitted for acute pulmonary distress. Fever (reported for 20 patients) and nonproductive cough (reported for 16 patients) were the most common clinical symptoms. Chest roentgenogram revealed bilateral pulmonary infiltrates in 16 (76%) patients. Mean absolute CD4 count was 25 +/- 57 (range 0-110). Serologic evidence of past infection was observed in 18 patients. Serology tests were not done for two patients and negative for one. Two patients presented co-infection with Pneumocystis carinii. Fourteen patients had elevated serum lactic dehydrogenase (LDH) concentration. Among those, 4 patients whose LDH concentration was elevated more than ten fold died of respiratory distress. Patients received pyrimethamine and sulfadiazine (n = 13) or clindamycin (n = 8). Seven patients died during the first month after diagnosis was made. For the other patients, mean survival was 8 months. No relapse of toxoplasmosis was observed. All the patients took a secondary prophylaxis. CONCLUSION: No difference between patient with isolated pulmonary toxoplasmosis and patients with associated extra-pulmonary localization was noted for clinical, biological, radiological presentations and outcome.

AIDS-Related Opportunistic Infections↗
PubMed1996

[Acid-alcohol-resistant bacilli detected by microscopic analysis of exhaled air from HIV-infected patients: tuberculosis or mycobacteriosis?].

OBJECTIVES: The incidence of atypical mycobacterial infections has increased with the AIDS epidemic. To present, microscopic examinations of airway specimens positive for acid-fast bacteria were highly suggestive of tuberculosis. However, since the AIDS epidemic, certain authors have reported an increase in Mycobacterium avium intracellulare found in respiratory specimens. The aim of this work was to determine what factors might distinguish between these two infections revealed discovery of an acid-fact bacilli. METHODS: Hospital files of all HIV seropositive patients seen between November 1992 and March 1995 and with at least one airway specimen positive for acid-fast bacilli were studied retrospectively. RESULTS: Mycobacterium tuberculosis was isolated in 19 patients, Mycobacterium avium intracellulare in 8 and culosis and M. avium intracellulare. There was no difference for age, sex, geographical origin, transmission mode, antigen positivity, radiologic findings or clinical signs between patients with the different types of mycobacterium. The CD4 count was however significantly lower in patients with an atypical mycobacteriosis (14.5/mm3) than in patients with tuberculosis (91.7 +/- 83.7) (p = 0.004). CONCLUSION: These findings show that in HIV-infected patients with a CD4 count under 100/mm3, the presence of acid-fact bacilli can indicate either M. tuberculosis or M. avium intracellulare. Combined anti-tuberculosis and antimycobacteriosis therapy thus would appear to be justified until the germ can be identified.

AIDS-Related Opportunistic Infections↗
PubMed1996

Correction of thermal artifacts in plethysmographic airway resistance measurements.

Specific airway resistance (sRaw) measured by body plethysmography without conditioning of the inspired air to BTPS exhibits a strong frequency dependence related to the fact that the warming and wetting of the gas in the airways is not instantaneous (R. Peslin, C. Duvivier, M. Vassiliou, and C. Gallina. J. Appl. Physiol. 79: 1958-1965, 1995). We have tested three methods in 21 healthy subjects to correct for that artifact by using a simple model, assuming a first-order thermal process characterized by a single time constant. The corrections required entering an assumed constant value for (methods 1 and 2) and/or for airway inertance (methods 1 and 3) and/or measuring the inspired gas temperature and water vapor saturation (methods 2 and 3). The frequency dependence of sRaw was measured from 0.5 to 3 Hz both with (sRawETPS) and without (sRawam) gas conditioning. With optimal values for and/or airway inertance, the mean difference between sRawam and sRawETPS was close to zero with all three methods, but the root mean square difference was significantly lower with method 2 (0.83 +/- 0.35 hPa.s compared with 1.21 +/- 0.54 and 1.20 +/- 0.49 hPa.s with methods 1 and 2, respectively). We conclude that the thermal artifact of sRaw measurements may be best corrected by using temperature measurements and an assumed time constant (0.152 s with our equipment).

Adult↗
PubMed1996

Separation of airway and tissue properties by transfer respiratory impedance and thoracic gas volume in reversible airway obstruction.

The aim of this study was to establish the ability to estimate separate airway and tissue properties from transfer respiratory impedance (Zrs,tr) data in the presence of airway obstruction. Zrs,tr, thoracic gas volume (TGV) and airway resistance (Raw,pleth) were measured in the presence of obstruction and after use of a bronchodilator (BD) in 13 normal or asymptomatic asthmatic adults and 28 children with symptomatic asthma. An analytical approach was used to solve the equations of a simplified variant of DuBois' model, including airway resistance (Raw*) and inertance (Iaw), tissue compliance (Ct) and resistance (Rt) and pulmonary gas compliance (Cg). The equations of the model could not be reliably solved in four children before BD. Mean Raw,pleth was not different from mean Raw* in adults before (mean +/- SEM) (3.4 +/- 0.5 vs 3.1 +/- 0.3 hPa.s.L-1) or after BD (1.4 +/- 0.2 vs 1.8 +/- 0.2 hPa.s.L-1), or in children after BD (2.9 +/- 0.3 vs 3.2 +/- 0.2 hPa.s.L-1, respectively). In children before BD, Raw* was significantly underestimated compared with Raw,pleth (3.8 +/- 0.4 vs 5.4 +/- 0.6 hPa.s.L-1). Overall, a significant positive correlation was found between the difference [Raw,pleth - Raw*] and Raw,pleth (r = 0.82). In adults, BD induced a decrease in Raw* and Rt, an increase in Ct, and no change in Iaw. In children after BD, there was no significant change in Raw* or Ct, whilst Rt decreased and Iaw increased. Taking Raw,pleth as the gold standard, it is concluded that coherent estimation of parameters of DuBois' model may be obtained from combined Zrs,tr and TGV measurements in normal subjects and moderately obstructed adults, but not in children with significant airway obstruction. This seems to be due to the systematic under-estimation of Raw*.

Adolescent↗
PubMed1996

Expiratory flow limitation during mechanical ventilation detected by the forced oscillation method.

We have previously observed large phasic variations of respiratory mechanical impedance in chronic obstructive pulmonary disease (COPD) patients mechanically-ventilated for acute respiratory failure, and postulated that they were due to expiratory flow limitation (EFL). The aim of this study was to test that assumption experimentally and to assess the value of impedance for automatic and noninvasive detection of EFL during mechanical ventilation. The study was performed: 1) in a mechanical analogue, including a flow-limiting element; and 2) in eight anaesthetized and paralysed rabbits, before and during histamine infusion. In both instances, EFL was obtained by lowering the expiratory pressure, using a computer-controlled ventilator; the absence of flow increase when expiratory pressure was further lowered was taken as evidence of EFL. Impedance was measured by applying 15 Hz oscillations at the airway opening. Its real (Re) and imaginary (Im) parts were measured separately during the inspiratory and the expiratory phases, and their differences were related to the mean inspiratory modulus. With the analogue, EFL was accompanied by large decreases both of Re and Im during the expiratory phase. In the rabbits, phasic variations of Re were variable in sign and were not significantly different with and without EFL. In contrast, EFL systematically and specifically decreased Im during the expiratory phase. A threshold of -50% provided a sensitivity of 96% and a specificity of 100% for detecting EFL. The observed phasic variations may be explained by airway wall shunt properties. The study suggests that a large decrease of the imaginary part of impedance during the expiratory phase is a sensitive and specific index of expiratory flow limitation during artificial ventilation.

Animals↗
PubMed1996

Frequency dependence of specific airway resistance in a commercialized plethysmograph.

Specific airway resistance (sRaw) measured by body plethysmography has been shown to decrease markedly with decreasing breathing frequency when the inspired air is not conditioned to body temperature, atmospheric pressure and saturation with water vapour (BTPS). The phenomenon has been attributed to noninstantaneous gas warming and wetting in the airways. The aim of this investigation was to assess whether the phenomenon was also present in a commercialized plethysmograph featuring an "electronic BTPS correction". Airway resistance (Raw) and sRaw were measured in 15 healthy subjects at six breathing frequencies ranging 0.25-3 Hz, using a constant volume plethysmograph in which a correction for non-BTPS gas conditions was applied by electronically flattening the box pressure-airway flow loop (Jaeger Masterscreen Body, version 4.0). The temperature and water vapour saturations in the box averaged 26.5 +/- 1.3 degrees C and 59 +/- 6%, respectively. Raw and sRaw exhibited a clear positive frequency dependence in all but one subject. From 0.25 to 3 Hz Raw increased from (mean+/-SD) 0.62 +/- 0.55 to 1.71 +/- 0.76 hPa x s x L-1 (p<0.001), and sRaw from 2.34 +/- 1.90 to 7.55 +/- 3.08 hPa x s (p<0.001). The data are consistent with a simple model, in which gas conditioning in the airways and external dead space occurred with a time constant of 0.39 s. We conclude that the electronic BTPS correction of the instrument was inadequate, probably because it is assumed that gas conditioning in the airways is instantaneous. We recommend that, with similar instruments, airway resistance be measured using as high a panting frequency as feasible.

Adult↗
PubMed1995

[Histoplasmosis, caused by Histoplasma capsulatum, and AIDS].

Histoplasma capsulatum histoplasmosis occurs frequently in endemic areas and with the AIDS outbreak, it appears as an opportunistic fungus involved in disseminated disease. We report the clinical, biological and treatment features of seven cases diagnosed in the CISIH of the Eastern part of Paris. Clinically, four patients were suffering from pulmonary symptoms, in three cases digestive disorders and in three cutaneous lesions. In all cases, the mycologic diagnosis was necessary. Amphotericin B and itraconazole were used as treatment for five patients (two died before the diagnosis was completed). Among these five subjects, four died (death was attributed to histoplasmosis in only one case). These observations emphasize the importance of this infection in HIV-infected patients coming from endemic areas.

AIDS-Related Opportunistic Infections↗
PubMed1995

Analysis of low-frequency lung impedance in rabbits with nonlinear models.

Lung mechanics was studied in six paralyzed tracheotomized rabbits ventilated with a specially devised computer-controlled ventilator. The target flow waveform contained noninteger multiple frequencies ranging from 0.83 to 6-10 Hz and met a neither-sum-nor-difference criterion to minimize the effects of nonlinearity (B. Suki and K. Lutchen. IEEE Trans. Biomed. Eng. 39: 1142-1151, 1992). The actual flow, however, contained harmonics of the two lowest frequencies. Measurements were performed at mean airway pressure (Paw) levels of 8 and 12 hPa and during histamine-induced bronchoconstriction. Smooth impedance curves were observed in unchallenged rabbits at low mean Paw levels. In contrast, unrealistic impedance fluctuations, suggestive of cross talk from the unwanted frequency components in the flow input, were seen at high mean Paw levels and during acute bronchoconstriction. Model analysis was performed by using the actual flow signal as an input to various nonlinear models. The impedance fluctuations observed at high mean Paw levels were well simulated by a model featuring a volume-dependent elastance, and those observed after histamine were almost perfectly reproduced by a model where resistance increased with the reciprocal of lung volume. We conclude that impedance data biased by cross talk may provide useful information on the presence and nature of respiratory system nonlinearities.

Airway Resistance↗
PubMed1995

Thermal artifacts in plethysmographic airway resistance measurements.

Measurements of airway resistance (Raw) by body plethysmography during unconditioned air breathing are implicitly based on the assumption that the warming and humidification of air in the airways are instantaneous. Simulation with a simple model suggests that Raw may be frequency dependent and substantially underestimated at most breathing frequencies if the time constant of gas conditioning (theta) is between 0.01 and 0.3 s. We measured the frequency dependence of the real (Re) and imaginary parts of the relationship between the plethysmographic signal and airway flow from 0.5 to 3 Hz in six healthy subjects in several situations. During breathing of unconditioned air through a heated pneumotachograph, Re increased by 47 +/- 70% between 2 and 3 Hz; the data were consistent with a theta of 0.087 +/- 0.023 s. Additional dead spaces moderately increased theta: 0.105 +/- 0.031 and 0.120 +/- 0.027 s with 50-cm-long polyvinyl chloride and copper tubes, respectively. During breathing of saturated air conditioned at 34, 36, 38, and 40 degrees C, Re exhibited a much smaller positive frequency dependence, most of which was probably due to a flow dependence of Raw. We conclude that unless the inspired gas is conditioned, plethysmographic Raw is likely to be substantially underestimated, particularly when measured during spontaneous breathing.

Adult↗
PubMed1995

A prospective evaluation of clinical criteria and polymerase chain reaction assay of cerebrospinal fluid for the diagnosis of cytomegalovirus-related neurological diseases during AIDS.

OBJECTIVE: To study the predictive value of clinical criteria and polymerase chain reaction (PCR) assay of cerebrospinal fluid (CSF) for the diagnosis of cytomegalovirus (CMV)-related neurological disorders during AIDS. SETTING: Four infectious diseases departments in two tertiary referral teaching hospitals in Paris, France. DESIGN AND PARTICIPANTS: One-year prospective study involving 164 consecutive immunosuppressed HIV-seropositive patients undergoing lumbar puncture (LP). METHODS: A tentative diagnostic classification, based on strict operational criteria and PCR assay of CSF, was performed at the time of LP. At the end of the study, tentative diagnoses and PCR results were blindly and independently compared with the firm diagnoses, based on central nervous system histology, clinical outcome and/or viral culture of CSF. RESULTS: The tentative diagnosis showed CMV-related neurological disease in 38 patients, and CMV DNA was detected in 42. Among the 88 patients for whom a firm diagnosis was possible, 26 had a diagnosis of CMV-related neurological disease. The concordance between the tentative and firm diagnoses was 61%, with a kappa index of 0.40. In contrast, the sensitivity and specificity of PCR were respectively 92 and 94%, with positive and negative predictive values of 86 and 97%. The presence of CMV DNA in CSF was associated with an increased risk of death (P < 0.0001). CONCLUSIONS: Unlike clinical criteria, PCR detection of viral DNA in CSF can be used reliably for antemortem diagnosis of CMV-related neurological disease, a frequent complication of AIDS in this study. This rapid method should make a major impact on the management of these patients.

AIDS-Related Opportunistic Infections↗
PubMed1994

Two-frequency analysis of respiratory mechanics in artificially ventilated rabbits.

The frequency dependence of respiratory mechanical properties was studied in 10 paralyzed, artificially ventilated rabbits, by superimposing a single sinusoidal signal with a frequency of 10, 20 or 30 Hz upon the ventilator waveform. The tracheal pressure and flow signals were analyzed both with the usual first order model, which provided total respiratory elastance (Ers) and resistance (Rrs), and by Fourier analysis, which provided respiratory impedance (Zrs) at the breathing frequency (0.85 Hz) and at the superimposed oscillation frequency. The real part of Zrs (Re(Zrs)) decreased by 30% from 0.85 to 10 Hz (P < 0.001), but did not vary significantly from 10 to 30 Hz. This finding is satisfactorily explained by tissue viscoelasticity. Following a histamine aerosol, the frequency dependence of Re(Zrs) changed very little in three out of four rabbits, but increased substantially in the fourth. In that instance, assuming that lung hysteresivity was not markedly modified by histamine, the results suggest inhomogeneous airway obstruction and/or airway wall shunting.

Airway Resistance↗
PubMed1994

Comparative effects of laryngeal mask and tracheal tube on total respiratory resistance in anaesthetised patients.

We compared the effects of the laryngeal mask and tracheal tube on total respiratory resistance in 10 anaesthetised, mechanically ventilated patients undergoing otological microsurgery. The subjects were randomly divided into two groups. In the first group, the tracheal tube (Rüsch) was inserted for the first series of measurements. This was then replaced by a laryngeal mask (Intavent) and a second series of measurements was made during the first hour of operation. In the second group, the same protocol was applied with inverse order in the use of the devices. From the measurement of respiratory flow and pressure at the airway opening, total respiratory resistance was calculated by multiple linear regression. The data were corrected to eliminate the previously determined nonlinear resistance of the two devices. Arterial blood pressure, electrocardiogram, oxygen saturation and end-tidal carbon dioxide concentration were continuously monitored. With the laryngeal mask and the tracheal tube, mean (SE) minute ventilation was 9.4(0.9)l.min-1 and 8.1(0.9)l.min-1, respectively for end-tidal carbon dioxide concentrations between 3.6 and 4.1%. Although the glottic resistance was included in the measurement performed with the laryngeal mask but not with the tracheal tube, mean (SE) total respiratory resistance was not significantly different with the two devices (0.61(0.32) and 0.69(0.35) kPa.l-1.s, respectively). Leakage was avoided with the laryngeal mask because the insufflation pressure never exceeded 1.7 kPa except in one patient suffering from severe chronic obstructive pulmonary disease who had a total respiratory resistance of 1.45 kPa.l-1.s. During the first hour of the operation all respiratory variables remained stable irrespective of the device used.

Adult↗
PubMed1994

Small-amplitude pressure oscillations do not modify respiratory mechanics in rabbits.

Changes in respiratory mechanics have occasionally been observed during high-frequency ventilation. In this study we investigated whether small pressure oscillations such as those used for respiratory impedance measurements modified total respiratory resistance (Rrs) and total respiratory elastance (Ers). The latter were measured in six paralyzed artificially ventilated rabbits with and without superimposed pressure oscillations at the airway opening. Rrs and Ers were obtained by least square fitting of low-pass filtered tracheal pressure and flow to the usual first-order model. Pressure oscillations of 2-4 hPa peak-to-peak at 10, 20, and 30 Hz applied for periods of 10 min had virtually no effect on Ers (changes ranging from -2.5 to 2.6%) and Rrs (0-8.2%). Analysis of variance did not show a significant difference on the pooled data. Pressure oscillations were also applied every other minute after a histamine aerosol. Ers and Rrs were similarly unchanged. We conclude that the small pressure oscillations used in respiratory impedance measurements do not modify lung mechanical properties and lung response to bronchomotor agents.

Air Pressure↗