Biomedical subjects

Philippe Micheau

Publications and source records attributed to Philippe Micheau.

4 recordsLinked to original sources

PubMed2006

Postnatal maturation of laryngeal chemoreflexes in the preterm lamb.

Laryngeal chemoreflexes (LCR) are triggered by the contact of liquids with the laryngeal mucosa. In the mature organism, LCR trigger lower airway protective responses (coughing, effective swallowing, and arousal) to prevent aspiration. General belief holds that LCR are responsible for apnea and bradycardia in the newborn mammal, including humans. Our laboratory has recently shown that LCR in full-term lambs are consistently analogous to the mature LCR reported in adult mammals, without significant apneas and bradycardias (St-Hilaire M, Nsegbe E, Gagnon-Gervais K, Samson N, Moreau-Bussiere F, Fortier PH, and Praud J-P. J Appl Physiol 98: 2197-2203, 2005). The aim of the present study was to assess LCR in nonsedated, newborn preterm lambs born at 132 days of gestation (term = 147 days). The preterm lambs were instrumented for recording glottal adductor electromyogram, electroencephalogram, eye movements, heart rate, respiration, and oximetry. A chronic supraglottal catheter was used for injecting 0.5 ml of saline, distilled water, and HCl (pH 2) during quiet sleep, active sleep, and wakefulness on postnatal days 7 (D7) and 14 (D14). Laryngeal stimulation by water or HCl on D7 induced significant apneas, bradycardia, and desaturation, which, at times, appeared potentially life-threatening. No significant apneas, bradycardias, or desaturation were observed on D14. No consistent effects of sleep state could be shown in the present study. In conclusion, laryngeal stimulation by liquids triggers potentially dangerous LCR in preterm lambs on D7, but not on D14. It is proposed that maturation of the LCR between D7 and D14 is partly involved in the disappearance of apneas/bradycardias of prematurity with postnatal age.

Adaptation, Physiological↗

PubMed2006

Decentralized harmonic active vibration control of a flexible plate using piezoelectric actuator-sensor pairs.

We have investigated decentralized active control of periodic panel vibration using multiple pairs combining PZT actuators and PVDF sensors distributed on the panel. By contrast with centralized MIMO controllers used to actively control the vibrations or the sound radiation of extended structures, decentralized control using independent local control loops only requires identification of the diagonal terms in the plant matrix. However, it is difficult to a priori predict the global stability of such decentralized control. In this study, the general situation of noncollocated actuator-sensor pairs was considered. Frequency domain gradient and Newton-Raphson adaptation of decentralized control were analyzed, both in terms of performance and stability conditions. The stability conditions are especially derived in terms of the adaptation coefficient and a control effort weighting coefficient. Simulations and experimental results are presented in the case of a simply supported panel with four PZT-PVDF pairs distributed on it. Decentralized vibration control is shown to be highly dependent on the frequency, but can be as effective as a fully centralized control even when the plant matrix is not diagonal-dominant or is not strictly positive real (not dissipative).

Journal Article↗

PubMed2003

Evaluation of the lambda model for human postural control during ankle strategy.

An accurate modeling of human stance might be helpful in assessing postural deficit. The objective of this article is to validate a mathematical postural control model for quiet standing posture. The postural dynamics is modeled in the sagittal plane as an inverted pendulum with torque applied at the ankle joint. The torque control system is represented by the physiological lambda model. Two neurophysiological command variables of the central nervous system, designated lambda and micro, establish the dynamic threshold muscle at which motoneuron recruitment begins. Kinematic data and electromyographic signals were collected on four young males in order to measure small voluntary sway and quiet standing posture. Validation of the mathematical model was achieved through comparison of the experimental and simulated results. The mathematical model allows computation of the unmeasurable neurophysiological commands lambda and micro that control the equilibrium position and stability. Furthermore, with the model it is possible to conclude that low-amplitude body sway during quiet stance is commanded by the central nervous system.

Adult↗

PubMedDate not supplied

A prototype of volume-controlled tidal liquid ventilator using independent piston pumps.

Liquid ventilation using perfluorochemicals (PFC) offers clear theoretical advantages over gas ventilation, such as decreased lung damage, recruitment of collapsed lung regions, and lavage of inflammatory debris. We present a total liquid ventilator designed to ventilate patients with completely filled lungs with a tidal volume of PFC liquid. The two independent piston pumps are volume controlled and pressure limited. Measurable pumping errors are corrected by a programmed supervisor module, which modifies the inserted or withdrawn volume. Pump independence also allows easy functional residual capacity modifications during ventilation. The bubble gas exchanger is divided into two sections such that the PFC exiting the lungs is not in contact with the PFC entering the lungs. The heating system is incorporated into the metallic base of the gas exchanger, and a heat-sink-type condenser is placed on top of the exchanger to retrieve PFC vapors. The prototype was tested on 5 healthy term newborn lambs (<5 days old). The results demonstrate the efficiency and safety of the prototype in maintaining adequate gas exchange, normal acido-basis equilibrium, and cardiovascular stability during a short, 2-hour total liquid ventilator. Airway pressure, lung volume, and ventilation scheme were maintained in the targeted range.

Algorithms↗