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Biomedical subjects

P Baconnier

Publications and source records attributed to P Baconnier.

At least 19 recordsLinked to original sources
PubMed2004

Dynamic echo-planar MR imaging of the diaphragm for a 3D dynamic analysis.

The purpose of this study was to prove the feasibility of 3D reconstructions of the diaphragm during the respiratory cycle using EPI sequences (EPI acquisition, 270 ms/image, on a healthy subject breathing spontaneously and at 0.1 Hz). Continuously recorded respiratory signal allowed for retrospective synchronization with respiratory phases for reconstruction of successive diaphragm surfaces using a specifically designed software. Displacements, area and volume changes of the diaphragm were quantified. Our measurements were comparable with the data in the literature. Reconstructed surfaces allowed in vivo diaphragm dynamic evaluation in terms of displacements, area and volume variations. EPI has adequate spatial and temporal resolution for studying diaphragm dynamics during natural breathing.

Diaphragm↗
PubMed2004

Identification of a non-linear model as a new method to detect expiratory airflow limitation in mechanically ventilated patients.

Expiratory flow limitation (EFL) can occur in mechanically ventilated patients with chronic obstructive pulmonary disease and other disorders. It leads to dynamic hyperinflation with ensuing deleterious consequences. Detecting EFL is thus clinically relevant. Easily applicable methods however lack this detection being routinely made in intensive care. Using a simple mathematical model, we propose a new method to detect EFL that does not require any intervention or modification of the ongoing therapeutic. The model consists in a monoalveolar representation of the respiratory system, including a collapsible airway that is submitted to periodic changes in pressure at the airway opening: EFL provokes a sharp expiratory increase in the resistance Rc of the collapsible airway. The model parameters were identified via the Levenberg-Marquardt method by fitting simulated data on the airway pressure and the flow signals recorded in 10 mechanically ventilated patients. A sensitivity study demonstrated that only 8/11 parameters needed to be identified, the remaining three being given reasonable physiological values. Flow-volume curves built at different levels of positive expiratory pressure, PEEP, during "PEEP trials" (stepwise increases in positive end-expiratory pressure to optimize ventilator settings) have shown evidence of EFL in three cases. This was concordant with parameter identification (high Rc during expiration for EFL patients). We conclude from these preliminary results that our model is a potential tool for the non-invasive detection of EFL in mechanically ventilated patients.

Adult↗
PubMed2001

[Selective activation of blood pressure monitoring alarms: effect of noise pollution in the intensive care unit].

OBJECTIVE: To evaluate a selective activation of sounding alarms on non-invasive blood pressure (BP) monitoring according to the patient haemodynamic status. STUDY DESIGN: Prospective study. METHODS: Activation of alarms on BP was regulated with a protocol. Sounding alarms were either inactivated when patient's haemodynamic status was stable (group 1), or activated when it was unstable (group 2). The frequency of BP measurement was one every 15 min. For all mean BP value recorded, the following criteria were analyzed: 1) normality of the value compared to ranges 65-115 mmHg in group 1 or compared to alarm thresholds in group 2; 2) consequences on the care and therapeutic; 3) delay when an abnormal value was detected and managed after more than 15 min. RESULTS: 1,674 hours of monitoring from 42 patients, allowed the analysis of 6,695 measurements of mean BP, 3,092 in group 1 and 3,603 in group 2. In group 1, 2,822 measurements were considered as normal and 3,094 measures in group 2. Eight measurements had consequences on therapeutic in group 1, with only one with delay in care giving. 287 measurements had consequences on therapeutic in group 2, 8 with delay in care giving. Six per cent of abnormal measurements in group 2 were managed with delay. This protocol reduced by 52% the production of sounding alarms on BP, without noxious effects for the patients. CONCLUSION: Selective activation of sounding alarms on BP, according to the patient haemodynamic status, reduced noise pollution and could be one solution to improve monitoring efficiency in intensive care unit.

France↗
PubMed2001

Positive end expiratory pressure and expiratory flow limitation: a model study.

Patients suffering from chronic obstructive pulmonary diseases, frequently exhibit expiratory airflow limitation. We propose a mathematical model describing the mechanical behavior of the ventilated respiratory system. This model has to simulate applied positive end-expiratory pressure (PEEP) effects during expiration, a process used by clinicians to improve airflow. The proposed model consists of a nonlinear two-compartment system. One of the compartments represents the collapsible airways and mimics its dynamic compression, the other represents the lung and chest wall compartment. For all clinical conditions tested (n=16), the mathematical model simulates the removal of expiratory airflow limitation at PEEP lower than 70-80% of intrinsic end-expiratory pressure (PEEPi), i.e. the end-expiratory alveolar pressure (PAet) without PEEP. It also shows the presence of an optimal PEEP. The optimal PEEP contributes to decrease PAet from 7.4+/-0.9 (SD) to 5.4+/-0.9 hPa (p < 0.0001; mild flow limitation) and from 11.8+/-1.1 to 7.8+/-0.7 hPa (p < 0.0001; severe flow limitation). Resistance of the collapsible compartment is decreased from 53+/-7 to 8.2+/-5.9 hPa.L(-1).s (p < 0.0001; mild flow limitation) and from 80+/-11 to 6.9+/-5.4 hPa.L(-1).s (p < 0.0001; severe flow limitation). This simplistic mathematical model gives a plausible explanation of the expiratory airflow limitation removal with PEEP and a rationale to the practice of PEEP application to airflow limited patients.

Airway Resistance↗
PubMed2000

[Clinical evaluation of alarm efficieny in intensive care].

OBJECTIVE: To evaluate the efficiency of haemodynamic and respiratory monitoring system by a clinical analysis of the alarms. STUDY DESIGN: Observational prospective study. PATIENTS: 25 patients who presented acute respiratory distress syndrome and who were monitored with haemodynamic and respiratory monitoring. METHODS: Each minute, a bedside clinical observer analysed alarms from the monitoring according to detection or absence to clinical events. Four situations were defined to statistical descriptive analysis: a) false positive (FP); b) true positive (TP); c) false negative (FN); and d) true negative (TN). True positive alarm which induced consequences on patients care were also analysed. RESULTS: 15,013 minutes allowed the recordings of 3,665 alarms, 44% from arterial pressure, 17% from SpO2 and 12% from airways maximal pressure. 46% were false positive alarms inducing a noisy pollution. The positive predictive value PPV = TP/(TP + FP) of these alarms were respectively 51% for arterial pressure, 18% for SpO2 and 100% for Paw. Only 5% of true positive alarms induced consequences on patients care. CONCLUSION: This protocol allowed the evaluation of monitoring efficiency. This kind of evaluation may help to improve monitoring capacity with reducing noisy pollution from false positive alarms.

Adolescent↗
PubMed1999

[Relationships between air conditioning, airborne microorganisms and health].

Concurrently with the increase of air-conditioning, potentially severe or frequent new diseases have emerged, giving rise to social and economical consequences. The first part of this work is a state of the art review of the relationships between air-conditioning, airborne microorganisms and health, through a technical, metrological and medical approach. The second part presents four studies performed in this field. Two of them deal with the relationship between airborne microorganisms and technical features of air-conditioning. Measurements performed on actual sites demonstrated the benefit of using high efficiency filters and low risk components in air-conditioning systems. The third study was aimed to look for a relationship between airborne microorganisms and sick building syndrome symptoms. Statistical analyses of individual data revealed significant associations between airborne bacteria or fungi and symptoms. These results may be the first step in determining a dose-response relationship, in order to define threshold limit values in this field. In the fourth study, the contribution of particle counting in assessing exposure to airborne microorganisms was explored by monitoring simultaneous variations of microbial and particle concentrations. The results showed that associating particle counting may allow to detect microbial variations instantaneously, and therefore improve the assessment of exposure to airborne microorganisms.

Air Conditioning↗
PubMed1998

Respiratory mechanics during laparoscopic cholecystectomy: the effects of the abdominal wall lift.

UNLABELLED: The abdominal wall lift (AWL) has been proposed for laparoscopic cholecystectomy to reduce hemodynamic effects caused by carbon dioxide (CO2) and high intraabdominal pressures (IAP). Data concerning effects of AWL on respiratory mechanics are scant. We therefore used a noninvasive method to evaluate whether the AWL could offset these effects. The PETCO2, airflow, and airway pressure were continuously measured in nine patients undergoing laparoscopic cholecystectomy using an AWL with minimal CO2 insufflation. We used a least-squares method to calculate maximal airway pressure (Pmax), elastance (Ers), and resistances (Rrs) of the respiratory system. After CO2 insufflation, the initiation of AWL resulted in a significantly decreased IAP (from 13 to 6 mm Hg; P < 0.001) and Rrs (from 20.6 to 17.8 cm H2O.L(-1).s(-1); P = 0.029), whereas Ers was partly modified (34.0 to 33.3 cm H2O/L; not significantly different). With AWL, we hypothesized that the diaphragm remained flat and stiff, outweighing the beneficial effect of the decrease of IAP on Ers. PETCO2 significantly increased after AWL and at the end of the procedure. We conclude that AWL partly reverses the impairment of the respiratory mechanics induced by CO2 insufflation during laparoscopic surgery. IMPLICATIONS: The abdominal wall lift (AWL), acting on the abdominal chest wall, had some benefits during laparoscopic surgery by limiting CO2 peritoneal insufflation and several side effects, such as hemodynamics. We examined the consequences of this technique on respiratory mechanics in nine patients undergoing laparoscopic cholecystectomy. Our findings suggest that the AWL decreases intraabdominal pressure and respiratory resistances without a significant effect on respiratory elastance.

Abdomen↗
PubMed1997

[Correction to the airflow measurement in the presence of a leak between the trachea and endotracheal tube].

PURPOSE: To estimate the leak between the endotracheal tube and the trachea in newborns in order to compensate for errors in airflow measurement and to monitor mechanical variables from pressure and flow signals. METHODS: Assuming that the leak resistance (Rf) is constant during a respiratory cycle, the resistive properties of the endotracheal tube were evaluated. The method was validated in the intensive care unit with a mechanical test lung and assessed on recordings of three newborns during mechanical ventilation for RDS. We have used a least squares method for the estimation of positive end expiratory pressure (PEEP) on both newborns and simulated data. RESULTS: Direct measurements of simulated leak resistances on the mechanical lung are in agreement with our estimation of leak resistances. In newborns, the success of flow correction is evidenced on end inspiratory pauses: corrected flow drops to zero while raw data show a constant nonzero flow. On the simulated lung, the PEEP underestimation with uncorrected flow ranges from 10 to 20 cm H20 while the corresponding, underestimation with corrected flow is less than 2 cm H2O. In newborns, the flow correction shifts the estimated PEEP from negative values (-0.3 +/- 1.3 cm H2O before correction) to positive values (3.6 +/- 0.7 cm H2O after correction) higher than the imposed PEEP (2 cm H2O). CONCLUSIONS: The efficiency of this simple method has been demonstrated. It could be used successfully on adult patients, as there will not be flow correction in the absence of leaks.

Humans↗
PubMed1997

Evaluation of respiratory inductive plethysmography: accuracy for analysis of respiratory waveforms.

OBJECTIVE: To assess the accuracy of respiratory inductive plethysmography (RIP) waveforms to those obtained with whole body plethysmograph (BP) as this device gives a plethysmographic signal and a pneumotachograph (PNT). DESIGN: Randomized controlled trial. SETTING: Physiologic laboratory in a university hospital. PARTICIPANTS: Eleven subjects from the laboratory staff. INTERVENTIONS: This study was achieved during four consecutive periods in subjects breathing spontaneously and through different added resistive loads. Using the least square method calibration, two RIP waveforms, VRIP.BP(t) and VRIP.PNT(t), were simultaneously calculated with coefficients obtained from BP and from PNT volume waveforms, respectively VBP(t) and VPNT(t). For each recording, to compare volume waveforms, we calculated their differences in term of distances, DRIP-BP and DRIP-PNT, between the normalized RIP volume signal (respectively, VRIP.BP[t] and VRIP.PNT[t]) and its normalized reference (respectively, VBP[t] and VPNT[t]). We also calculated the distance DPNT-BP between the two normalized references VBP(t) and VPNT(t). RESULTS: No significant effect of load or time on the distance occurred. Including all the recordings, the mean distance DRIP-BP (3.4+/-1.1%) appears significantly lower than both the mean distance DRIP-PNT (4.5+/-1.3%; p<0.04) and the mean distance DPNT-BP (4.6+/-0.9%; p<0.008). For each period or load level, DRIP-BP appears to be lower than DRIP-PNT and DPNT-BP. CONCLUSION: The RIP seems reasonably accurate for analysis of respiratory waveform while subjects subsequently breathe against resistive loads.

Adult↗
PubMed1992

Entrainment of respiratory rhythm by periodic lung inflation: effect of airflow rate and duration.

In anesthesized, paralyzed, and mechanically ventilated rabbits, the rate and duration of airflow were varied to investigate the effect on the central respiratory rhythm during 1:1 entrainment (1 phrenic nerve burst for 1 pump inflation). Our results showed that 1) the largest range of 1:1 entrainment was obtained with the longest inflation durations associated with the lowest flow rates and 2) both inspiratory (TI) and expiratory (TE) durations (as estimated by the period of phrenic nerve activity and phrenic nerve silence, respectively) increased when total respiratory duration (TT = TI+TE) increased. The phase relationships we studied were DI (the time elapsing between the onset of phrenic activity and the beginning of pump inflation) and DE (the time between the end of phrenic activity and the end of pump inflation). Both DI and DE increased when the total ventilatory period increased. However, for constant ventilatory period, DI changed with the rate and duration of airflow, whereas DE remained constant. In addition, under these conditions, TI, TE, and the integrated phrenic nerve activity remained constant independently of airflow rate and duration. The present results are discussed with regard to the pulmonary receptors (slowly and rapidly adapting receptors and C fibers) that are stimulated during mechanical ventilation, and hypotheses are drawn regarding their possible contribution to rhythm generation and the mechanism through which they may act.

Animals↗
PubMed1989

Assessment of induced bronchoconstriction in anesthetized cats by the end-inflation occlusion method.

Airway occlusion during constant flow inflation allows rapid determination of frequency-dependence of pulmonary resistance by estimating its extreme values: RL,max (zero frequency) and RL,min (high frequency). RL,max represents the maximum resistance value that can be obtained with the prevailing time constant inequalities and stress relaxation, while RL,min represents the resistance that would be obtained in the absence of time constant inequalities and stress relaxation. In 5 anesthetized, tracheostomized, paralyzed, and artificially ventilated cats, RL,min, RL,max, and static pulmonary elastance (EL,st) have been measured following airway occlusion at the end of constant flow tidal inflations. Measurements were made before and during continuous infusion of increasing doses of serotonin (10-100 micrograms/kg/min IV). The development of intrinsic positive end-expiratory pressure (PEEPi) was also assessed. Cats varied greatly in their responsiveness to serotonin, but RL,min, RL,max, and EL,st increased and PEEPi developed in all cats. Increases in RL,max did not always parallel increases in RL,min but were similar to those in EL,st, suggesting that altered viscoelastic properties of the lung contributed to the increases in RL,max. We conclude that time-constant inequalities, changes in the lung periphery, and hyperinflation probably all contribute to the observed increases in RL,max and will influence conventional methods of measuring RL. Measuring RL,min potentially provides a better method for assessing the reduction in caliber of the conducting airways in isolation.

Airway Obstruction↗
PubMed1989

Entrainment of the respiratory rhythm by periodic lung inflation during vagal cooling.

The aim of this study was to determine whether pulmonary receptors other than slowly adapting stretch receptors are capable of entraining the respiratory rhythm when periodically stimulated during artificial ventilation. Experiments were performed on anaesthetised (urethane, 1.5 g/kg) and paralysed (pancuronium bromide, 0.1 mg/kg) rabbits. Vagi were cooled in order to block conduction in the myelinated fibres innervating slowly adapting receptors. The effectiveness of this cooling was assimilated to the absence of the Hering-Breuer inflation reflex and the presence of the deflation reflex. Our results indicate that under such conditions: (1) harmonic entrainment (one phrenic burst for one pump period) can be observed, (2) the range of harmonic entrainment is more limited when the vagi are cooled, and (3) during harmonic entrainment the inspiratory duration and phrenic activity are similar to what is observed at the same period with intact vagi, whereas vagal cooling modifies the phase difference between the phrenic burst and the pump. We have concluded that periodic input from rapidly adapting receptors and/or vagal C-fibres can entrain the respiratory rhythm as does input from slowly adapting receptors but with different patterns as evidenced by phase relationship.

Animals↗
PubMed1989

Individuality of breathing patterns in adults assessed over time.

Sixteen healthy adult subjects underwent two studies separated by 4-5 years to test whether their resting pattern of breathing was reproducible over time. From breath-by-breath analysis of airflow, measured with a pneumotachometer, the pattern of breathing was quantified in terms of individual respiratory variables; inspiratory time (TI), expiratory time (TE), total breath duration (TTOT), tidal volume (VT), VT/TI, TI/TTOT, and by taking TI, TE and VT all together (TRIAD). Also, the shape of the entire airflow profile was quantified by harmonic analysis (ASTER). A statistical analysis was designed to compare differences between the 1st and the 2nd recording within individuals with those differences observed between random pairs of recordings from the two studies in the same 16 individuals. It was found that all variables were significantly more similar within-individuals than between-individuals; this is best demonstrated when considering the ASTER and/or the TRIAD. It was concluded that the individuality of breathing pattern is maintained over a long period despite changes in smoking habit, weight, mild respiratory diseases, and other changes which occurred between the two studies in our subjects.

Adult↗
PubMed1988

A theoretical analysis of interrupter technique for measuring respiratory mechanics.

The application of the flow interrupter technique to series and parallel models of the respiratory system is examined theoretically, assuming instantaneous transmission of pressures and incompressible gases in the lung air spaces. The initial pressure change observed immediately after occlusion divided by the preocclusion flow gives an initial resistance (Rinit) equal to that of the airway tree when the model consists of compartments connected in parallel. When the compartments are connected in series, Rinit is the resistance of the most proximal airway only. In general, the initial pressure change is followed by a second slower change, reflecting equilibration of pressures between the compartments. The total postocclusion pressure change divided by the flow gives a steady-state resistance (Rss) whose value depends on the ventilation history before occlusion. When this history consists of a relaxed expiration Rss asymptotes from Rinit to a value higher than the zero-frequency resistance of the model as the expiratory time increases. However, the relative contributions of serial and parallel pendelluft and viscoelasticity to Rss cannot be determined from pressure and flow measurements made at the airway opening. Therefore in disease, the interrupter method does not permit one to say whether ventilation inhomogeneity or alteration in lung tissue properties is the predominant abnormality.

Airway Resistance↗
PubMed1986

A program for cycle-by-cycle shape analysis of biological rhythms. Application to respiratory rhythm.

A computer program for cycle-by-cycle analysis and quantification of biological rhythms, written for an Apple II microcomputer with 48k RAM is described. The program comprises 4 steps: (1) file constitution suitable for biological data collecting; (2) signal digitalization at a sampling rate up to 1 kHz with storage in central memory; (3) determination of each cycle's limits (delimitation parameters being defined by the user; following delimitation, cycles may be dropped or saved for further analyses); (4) cycle-by-cycle harmonic analysis (fast Fourier Transform algorithm). The program is written in BASIC Applesoft, hardware-dependent functions (analog inputs, graphic display and random access disk storage) are implemented in subroutines (partly assembler) which may be easily modified. The program, consisting of 4 chained procedures is run interactively, although procedure (4) may be run automatically. Analysis of human ventilatory airflow signal with this program is given as an example of cycle-by-cycle shape analysis of a biological rhythm.

Humans↗