A simple dynamic model of respiratory pump.

To study the interaction of forces that produce chest wall motion, we propose a model based on the lever system of Hillman and Finucane (J Appl Physiol 63(3):951-961, 1987) and introduce some dynamic properties of the respiratory system. The passive elements (rib cage and abdomen) are considered as elastic compartments linked to the open air via a resistive tube, an image of airways. The respiratory muscles (active) force is applied to both compartments. Parameters of the model are identified in using experimental data of airflow signal measured by pneumotachography and rib cage and abdomen signals measured by respiratory inductive plethysmography on eleven healthy volunteers in five conditions: at rest and with four level of added loads. A breath by breath analysis showed, whatever the individual and the condition are, that there are several breaths on which the airflow simulated by our model is well fitted to the airflow measured by pneumotachography as estimated by a determination coefficient R(2) > or = 0.70. This very simple model may well represent the behaviour of the chest wall and thus may be useful to interpret the relative motion of rib cage and abdomen during quiet breathing.

Variability of end-expiratory lung volume in premature infants.

BACKGROUND: Analysis of breath-to-breath variability of respiratory characteristics provides information on the respiratory control. In infants, the control of end-expiratory lung volume (EELV) is active and complex, and it can be altered by respiratory disease. The pattern of EELV variability may reflect the behavior of this regulatory system. OBJECTIVES: We aimed to characterize EELV variability in premature infants, and to evaluate variability pattern changes associated with respiratory distress and ventilatory support. METHODS: EELV variations were recorded using inductance plethysmography in 18 infants (gestational age 30-33 weeks) during the first 10 days of life. An autocorrelation analysis was conducted to evaluate the 'EELV memory', i.e. the impact of the characteristics of one breath on the following breaths. RESULTS: In infants without respiratory symptoms, EELV variability was high, with large standard deviations of EELV. Autocorrelation was found to be significant until a median lag of 7 (interquartiles: 4-8) breaths. Autocorrelation was markedly prolonged in patients with respiratory distress or ventilatory support, with a higher number of breath lags with significant autocorrelation (p < 0.01) and higher autocorrelation coefficients (p < 0.05). Conventional assisted ventilation does not re-establish a healthy EELV profile and is associated with lower respiratory variability. CONCLUSIONS: In premature infants, EELV variability pattern is modified by respiratory distress with a prolonged 'EELV memory', which suggests a greater instability of the control of EELV.

Calibration of respiratory inductance plethysmograph in preterm infants with different respiratory conditions.

Respiratory inductance plethysmography (RIP) is a method for respiratory measurements particularly attractive in infants because it is noninvasive and it does not interfere with the airway. RIP calibration remains controversial in neonates, and is particularly difficult in infants with thoraco-abdominal asynchrony or with ventilatory assist. The objective of this study was to evaluate a new RIP calibration method in preterm infants either without respiratory disease, with thoraco-abdominal asynchrony, or with ventilatory support. This method is based on (i) a specifically adapted RIP jacket, (ii) the least squares method to estimate the volume/motion ribcage and abdominal coefficients, and (iii) an individualized filtering method that takes into account individual breathing pattern. The reference flow was recorded with a pneumotachograph. The accuracy of flow reconstruction using the new method was compared to the accuracy of three other calibration methods, with arbitrary fixed RIP coefficients or with coefficients determined according to qualitative diagnostic calibration method principle. Fifteen preterm neonates have been studied; gestational age was (mean +/- SD) 31.7 +/- 0.8 weeks; birth weight was 1,470 +/- 250 g. The respiratory flow determined with the new method had a goodness of fit at least equivalent to the other three methods in the entire group. Moreover, in unfavorable conditions--breathing asynchrony or ventilatory assist--the quality of fit was significantly higher than with the three other methods (P < 0.05, repeated measures ANOVA). Accuracy of tidal volume measurements was at least equivalent to the other methods, and the breath-by-breath differences with reference volumes were lower, although not significantly, than with the other methods. The goodness of fit of the reconstructed RIP flow with this new method--even in unfavorable respiratory conditions--provides a prerequisite for the study of flow pattern during the neonatal period.

Use of computer and respiratory inductance plethysmography for the automated detection of swallowing in the elderly.

Deglutition disorders can occur at any age but are especially prevalent in the elderly. The resulting morbidity and mortality are being recognized as major geriatric health issues, Because of difficulties in studying swallowing in the frail elderly, a new, non-invasive, user-friendly, bedside technique has been developed. Ideally suited to such patients, this tool, an intermediary between purely instrumental and clinical methods, combines respiratory inductance plethysmography (RIP) and the computer to detect swallowing automatically, Based on an automated analysis of the airflow estimated by the RIP-derived signal, this new tool was evaluated according to its capacity to detect clinical swallowing from among the 1643 automatically detected respiratory events, This evaluation used contingency tables and Receiver Operator Characteristic (ROC) curves, Results were all significant (chi2(1,n=1643)>100, p<0.01). Considering its high accuracy in detecting swallowing (area under the ROC curve greater than 0.9), this system would be proposed to study deglutition and then deglutition disorders in the frail elderly, to set up medical supervision and to evaluate the efficiency of a swallowing disorder remedial therapeutic.

Use of respiratory inductance plethysmography for the detection of swallowing in the elderly.

It is essential to have a user-friendly, noninvasive bedside procedure at our disposal in order to study swallowing and swallowing disorders in the elderly in view of the frailty of this age group. In the present work, respiratory inductance plethysmography (RIP) is proposed as an appropriate clinical tool for such studies. An automated process for the detection of swallowing is used involving the derivative of the respiratory volume signal. The accuracy of the automated detection is given by the area under the Receiver Operating Characteristic (ROC) curve and is found to be greater than 0.9. At the optimal threshold, RIP constitutes a reliable and objective bedside clinical tool for studying swallowing in the elderly, as well as being user-friendly and noninvasive. In addition, RIP can be used to monitor swallowing in order to analyze swallowing disorders and put in place medical supervision of swallowing for individuals who might aspirate.

Enhanced cardiac vagal efferent activity does not explain training-induced bradycardia.

Studies of heart rate variability (HRV) have so far produced contradictory evidence to support the common belief that endurance training enhances cardiac parasympathetic tone. This may be related to the fact that most studies failed to specifically isolate the vagally mediated influence of respiration. This study used a cross-sectional comparison of endurance athletes (n=20; ATHL) exhibiting resting bradycardia and age-matched nonathletes (n=12; CRTL) to indirectly assess training effects on amplitude and timing characteristics of respiratory sinus arrhythmia (RSA). Continuous electrocardiogram (ECG) and ventilatory flows were recorded during spontaneous breathing (SP), as well as during breathing at four cycles less than (M4) or more (P4) than SP, to also examine potential repercussions of training on the sensitivity of the cardiac vagal responses to breathing. A fast Fourier transform procedure was used to quantify the standard spectral high-frequency (HF) and low-frequency (LF) components and a respiratory-centered frequency (RCF) component of HRV. RSA was assessed using a breath-by-breath quantification of the amplitude and timing of the maximum change in instantaneous heart rate. Under baseline SP conditions, heart rate was lower in ATHL (62.6+/-6.5 vs. 75.2+/-9 beats/min; p<0.05) while blood pressure (BP), breath cycle duration, tidal volume, and ventilatory drive were similar in both groups. HRV total spectral power density, LF, HF, or RCF was not different between groups at either the SP, M4, or P4 conditions. Changes in total breath duration similarly affected RSA amplitude in all groups, while HR and BP remained unchanged from SP. RSA phase was not affected by training status or by changes in total breath duration. RSA amplitude was negatively related to breathing frequency in all groups (p<0.05), while the mean slope of the relationship (sensitivity) was not different between groups. In as much as RSA is an adequate marker of cardiac vagal efferent activity, these results add support to a contribution of a decrease in intrinsic heart rate to explain training-induced bradycardia.

Individual differences in respiratory sinus arrhythmia.

To investigate the interindividual differences in respiratory sinus arrhythmia (RSA), recordings of ventilation and electrocardiogram were obtained from 12 healthy subjects for five imposed breathing periods (T(TOT)) surrounding each individual's spontaneous breathing period. In addition to the spectral analysis of the R-R interval signal at each breathing period, RSA characteristics were quantified by using a breath-by-breath analysis where a sinusoid was fitted to the changes in instantaneous heart rate in each breath. The amplitude and phase (or delay = phase x T(TOT)) of this sinusoid were taken as the RSA characteristics for each breath. It was found that for each subject the RSA amplitude-T(TOT) relationship was linear, whereas the delay-T(TOT) relationship was parabolic. However, the parameters of these relationships differed between individuals. Linear correlation between the slopes of RSA amplitude versus T(TOT) regression lines and 1) mean breathing period and 2) mean R-R interval during spontaneous breathing were calculated. Only the correlation coefficient with breathing period was significantly different from zero, indicating that the longer the spontaneous breathing period the lesser the increase in RSA amplitude with increasing breathing period. Similarly, only the correlation coefficient between the curvature of the RSA delay-T(TOT) parabola and mean breathing period was significantly different from zero; the longer the spontaneous breathing period the larger the curvature of RSA delay. These results suggest that the changes in RSA characteristics induced by changing the breathing period may be explained partly by the spontaneous breathing period of each individual. Furthermore, a transfer function analysis performed on these data suggested interindividual differences in the autonomic modulation of the heart rate.

Cardioventilatory changes induced by mentally imaged rowing.

Mentally imaged but unexecuted physical activity has been reported to induce a cardiorespiratory change. In order to test whether the previous experience of the performed exercise was a prerequisite to observe these changes, ventilation and heart rate were recorded during mental imagination of a rowing race in four groups of volunteers: 12 competitive rowers, 10 non-rower athletes, 12 students (22-30 years old) and 12 senior subjects (50-60 years old). Recordings were performed at rest, during the viewing of a rowing race and during mental imagination of this race. Analysis of variance revealed significant condition effect for all cardiorespiratory variables. All subjects increased their breathing rate (mean increase: 16 breaths.min(-1) in rowers, 8 breaths.min(-1) in athletes, 8 breaths.min(-1) in students, and 6 breaths.min(-1) in seniors), 29 decreased their tidal volume (mean decrease: 100 ml in rowers, 102 ml in athletes, 120 ml in students and 26 ml in seniors), with an increase in the resulting ventilation in 38 subjects (mean increase: 14 l.min(-1) in rowers, 3.6 l.min(-1) in athletes, 2.8 l.min(-1) in students, 2.6 l.min(-1) in seniors). Heart rate was increased in 34 subjects (mean increase: 12 beats.min(-1) in rowers, 5 beats.min(-1) in athletes, 6 beats.min(-1) in students and 5 beats.min(-1) in seniors). The number of subjects who exhibited changes was evenly distributed among the four groups. However, mean values of the changes were higher in rowers than in the three other groups, mainly due to three rowers who exhibited extremely large increases in cardioventilatory variables. Analysis of variance showed no significant group effect for heart rate and breathing rate. These results suggest that rowing experience may not be necessary for changes in heart rate and ventilation to be elicited by mentally imagining a rowing race.

Multi-sensors acquisition, data fusion, knowledge mining and alarm triggering in health smart homes for elderly people.

We deal in this paper with the concept of health smart home (HSH) designed to follow dependent people at home in order to avoid the hospitalisation, limiting hospital sojourns to short acute care or fast specific diagnostic investigations. For elderly people the project of such a HSH has been called AISLE (Apartment with Intelligent Sensors for Longevity Effectiveness). For this purpose, system having three levels of automatic measuring (1) the circadian activity, (2) the vegetative state, and (3) some state variables specific of certain organs involved in precise diseases, has been developed within the framework of a 'Health Integrated Smart Home Information System' (HIS2). HIS2 is an experimental platform for technologic development and clinical evaluation, in order to ensure the medical security and quality of life for patients who need home based medical monitoring. Location sensors are placed in each room of the HIS2, allowing the monitoring of patient's successive daily activity phases within the patient's home environment. We proceed with a sampling in an hourly schedule to detect weak variations of the nycthemeral rhythms. Based on numerous measurements, we establish a mean value with confidence limits of activity variables in normal behaviour permitting to detect for example a sudden abnormal event (like a fall) as well as a chronic pathologic activity (like a pollakiuria), allowing us to define a canonical domain within which the patient's activity is qualified to be 'predictable'. Alerts are set off if the patient's activity deviates from a predictable canonical domain. Moreover, we can follow the cardio-respiratory state by measuring the intensity of the respiratory sinusal arrhythmia in order to quantify the integrity of the bulbar vegetative system, and we finally propose to carefully watch abnormal symptoms like arterial pressure or presence of plasma proteins in the expired air flow for early detecting respectively hypertension or pulmonary oedema.

Ventilatory support: a dynamical systems approach.

Misunderstanding of the dynamical behavior of the ventilatory system, especially under assisted ventilation, may explain the problems encountered in ventilatory support monitoring. Proportional assist ventilation (PAV) that theoretically gives a breath by breath assistance presents instability with high levels of assistance. We have constructed a mathematical model of interactions between three objects: the central respiratory pattern generator modelled by a modified Van der Pol oscillator, the mechanical respiratory system which is the passive part of the system and a controlled ventilator that follows its own law. The dynamical study of our model shows the existence of two crucial behaviors, i.e. oscillations and damping, depending on only two parameters, namely the time constant of the mechanical respiratory system and a cumulative interaction index. The same result is observed in simulations of spontaneous breathing as well as of PAV. In this last case, increasing assistance leads first to an increase of the tidal volume (VT), a further increase in assistance inducing a decrease in VT, ending in damping of the whole system to an attractive fixed point. We conclude that instabilities observed in PAV may be explained by the different possible dynamical behaviors of the system rather than changes in mechanical characteristics of the respiratory system.