High-resolution respiratory inductive plethysmography in rats: validation in anesthetized conditions.

Respiratory monitoring is often required in experimental physiological and pharmacological studies in rodents. Currently, the mostly used techniques are direct measurement of airflow on intubated animals and whole body plethysmography. OBJECTIVE: Although the reliability of these methods has been broadly demonstrated, they also have several drawbacks such as invasiveness, high cost of use or confinement of the animals. Respiratory inductive plethysmography (RIP) is a non-invasive technique already used in medium-sized mammals that has not yet been evaluated in small rodents. The implementation of inductive plethysmography in rats represents an instrumental challenge because of the small inductances that are expected. APPROACH: A rodent-specific RIP apparatus has been developed and compared to direct airflow measurement provided by a pneumotachograph (PNT) considered as the invasive gold standard for respiratory monitoring. The experiments were carried out on anesthetized rats artificially ventilated at different levels of tidal volumes (V T) covering the whole physiological range. MAIN RESULTS: Based on the Euclidian distance between signals, this study shows that after calibration, signals from RIP fit at 93% with PNT values. The Bland and Altman plot evidences differences between RIP and PNT lower than 20% and the values obtained are highly correlated (R = 0.98, p < 0.001). SIGNIFICANCE: This study demonstrates that it is possible to design RIP systems suitable for measurement of tidal volumes and airflow in anesthetized rats. Further studies will now be focused on the validation in extended physiological conditions.

Detecting variations of blood volume shift due to heart beat from respiratory inductive plethysmography measurements in man.

The simultaneous study of the cardiac and respiratory activities and their interactions is of great physiological and clinical interest. For this purpose, we want to investigate if respiratory inductive plethysmography (RIP) can be used for cardiac functional exploration. We propose a system, based on RIP technology and time-scale approaches of signal processing, for the extraction of cardiac information. This study focuses on the monitoring of blood volume shift due to heart beat, noted ▵Vtr_c and investigates RIP for the detection of ▵Vtr_c variations by comparison to stroke volume (SV) variations estimated by impedance cardiography (IMP). We proposed a specific respiratory protocol assumed to induce significant variations of the SV. Fifteen healthy volunteers in the seated and supine positions were asked to alternate rest respiration and maneuvers, consisting in blowing into a manometer. A multi-step treatment including a variant of empirical mode decomposition was applied on RIP signals to extract cardiac volume signals and estimate beat-to-beat ▵Vtr_c. These were averaged in quasi-stationary states at rest and during the respiratory maneuvers, and analysed in view of SV estimations from IMP signals simultaneously acquired. Correlation and statistical tests over the data show that RIP can be used to detect variations of the cardiac blood shift in healthy young subjects.

Sequentiality of daily life physiology: an automatized segmentation approach.

Based on the hypotheses that (1) a physiological organization exists inside each activity of daily life and (2) the pattern of evolution of physiological variables is characteristic of each activity, pattern changes should be detected on daily life physiological recordings. The present study aims at investigating whether a simple segmentation method can be set up to detect pattern changes on physiological recordings carried out during daily life. Heart and breathing rates and skin temperature have been non-invasively recorded in volunteers following scenarios made of "daily life" steps (13 records). An observer, undergoing the scenario, wrote down annotations during the recording time. Two segmentation procedures have been compared to the annotations, a visual inspection of the signals and an automatic program based on a trends detection algorithm applied to one physiological signal (skin temperature). The annotations resulted in a total number of 213 segments defined on the 13 records, the best visual inspection detected less segments (120) than the automatic program (194). If evaluated in terms of the number of correspondences between the times marks given by annotations and those resulting from both physiologically based segmentations, the automatic program was better than the visual inspection. The mean time lags between annotation and program time marks remain <60 s (the precision of annotation times marks). We conclude that physiological variables time series recorded in common life conditions exhibit different successive patterns that can be detected by a simple trends detection algorithm. Theses sequences are coherent with the corresponding annotated activity.

Swallowing disorders, pneumonia and respiratory tract infectious disease in the elderly.

Swallowing disorders (or dysphagia) are common in the elderly and their prevalence is often underestimated. They may result in serious complications including dehydration, malnutrition, airway obstruction, aspiration pneumonia (infectious process) or pneumonitis (chemical injury caused by the inhalation of sterile gastric contents). Moreover the repercussions of dysphagia are not only physical but also emotional and social, leading to depression, altered quality of life, and social isolation. While some changes in swallowing may be a natural result of aging, dysphagia in the elderly is mainly due to central nervous system diseases such as stroke, parkinsonism, dementia, medications, local oral and oesophageal factors. To be effective, management requires a multidisciplinary team approach and a careful assessment of the patient's oropharyngeal anatomy and physiology, medical and nutritional status, cognition, language and behaviour. Clinical evaluation can be completed by a videofluoroscopic study which enables observation of bolus movement and movements of the oral cavity, pharynx and larynx throughout the swallow. The treatment depends on the underlying cause, extent of dysphagia and prognosis. Various categories of treatment are available, including compensatory strategies (postural changes and dietary modification), direct or indirect therapy techniques (swallow manoeuvres, medication and surgical procedures).

[Swallowing disorders, pneumonia and respiratory tract infectious disease in the elderly]. / Troubles de la déglutition du sujet âgé et pneumopathies en 14 questions/réponses.

Swallowing disorders (or dysphagia) are common in the elderly and their prevalence is often underestimated. They may result in serious complications including dehydration, malnutrition, airway obstruction, aspiration pneumonia (infectious process) or pneumonitis (chemical injury caused by the inhalation of sterile gastric contents). Moreover the repercussions of dysphagia are not only physical but also emotional and social, leading to depression, altered quality of life, and social isolation. While some changes in swallowing may be a natural result of aging, dysphagia in the elderly is mainly due to central nervous system diseases such as stroke, parkinsonism, dementia, medications, local oral and oesophageal factors. To be effective, management requires a multidisciplinary team approach and a careful assessment of the patient's oropharyngeal anatomy and physiology, medical and nutritional status, cognition, language and behaviour. Clinical evaluation can be completed by a videofluoroscopic study which enables observation of bolus movement and movements of the oral cavity, pharynx and larynx throughout the swallow. The treatment depends on the underlying cause, extent of dysphagia and prognosis. Various categories of treatment are available, including compensatory strategies (postural changes and dietary modification), direct or indirect therapy techniques (swallow manoeuvres, medication and surgical procedures).

Berkeley-Madonna implementation of Ikeda's model.

Starting from one model, we check the possibility of using Berkeley-Madonna software to transpose and simulate some existing biological integrated models. The considered model is the one of Ikeda et al., proposed in 1979, which treats of fluid regulation and which is very well described mathematically in the original paper. Despite a few mistakes or bugs, the model has been easily and successfully implemented under Berkeley-Madonna. We recover the same simulation results as Ikeda and new simulations can now easily be carried out, thanks to the user-friendly qualities of Berkeley-Madonna.

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.

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.

[Selective activation of blood pressure monitoring alarms: effect of noise pollution in the intensive care unit]. / Activation sélective des alarmes sur le monitoring de la pression artérielle: effet sur la pollution sonore en réanimation.

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.

Mechanical output impedance of the lung determined from cardiogenic oscillations.

The beating heart naturally oscillates the lung because of the close juxtaposition between these organs producing cardiogenic oscillations in flow that can be measured at the mouth when the glottis is open. Correspondingly, if the mouth is occluded, the same phenomenon produces cardiogenic pressure oscillations that can be measured just distal to the site of occlusion. The Fourier-domain ratio of these oscillations in pressure and flow constitutes what we call cardiogenic respiratory impedance (Zc). We calculated Zc between about 1.5 and 10 Hz in relaxed normal subjects at functional residual capacity with open glottis. Zc was insensitive to heart rate changes induced by exercise and had an imaginary part close to zero at all frequencies investigated. Its real part was similar to or smaller than resistance determined by the forced oscillation technique. We speculate that Zc measures the flow resistance of the central and upper airways of the lung. Zc may be useful as a means of obtaining information about lung mechanics without the need for an external source of flow perturbations.

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.

[Clinical evaluation of alarm efficieny in intensive care]. / Evaluation clinique de la pertinence des alarmes en réanimation.

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.

[Relationships between air conditioning, airborne microorganisms and health]. / Etude des relations entre climatisation, micro-organismes aéroportés et santé.

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.

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.

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.

[Correction to the airflow measurement in the presence of a leak between the trachea and endotracheal tube]. / La correction du débit en présence d'une fuite entre trachée et sonde endotrachéale.

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.

Simulation of pulmonary damages induced by inhaled Cl2 on the bronchial tree.

We have measured the change of lung mechanical parameters on isolated rabbit lungs exposed to chlorine gas (Cl2). Experimental results show parallel increase in elastance and resistance of impaired lungs. We tried to determine whether this may be explained by a reduction of the ventilated areas in the lung, consecutive to closure of some airways. We have been tried to simulate these experimental results by studying the effects of various airways occlusions imposed on two concurrent models (symmetrical and dissymmetrical) of the tracheo-bronchial tree. For each model, we successively evaluated the resistance of the normal lung, simulated a partial peripheral airways occlusion and estimated the induced changes in total resistance. Analytical expressions of the "occluded lung" elastance and resistance have been found for the symmetrical model but not for the dissymmetrical model (a graphical approach is proposed). With the symmetrical model, simulated results are comparable to experimental ones when the occlusion level is proximal. Whatever the dissymmetry level (delta) of the fractal tree model, we could not simulate the expected increase in resistance with the observed increase in elastance. We conclude that either the occlusion in non homogeneous or the lung impairment is not only a reduction in ventilated areas.