Daniel Dalle

The ventilatory response to hypoxia in the newborn lamb after carotid body denervation

Neonates of various species including lambs respond to hypoxia by a transient hyperventilation followed by a VE depression (diphasic response). To better delineate the role of the carotid chemoreceptors and that of the central depressive/inhibitive effect of hypoxia on minute ventilation, we have studied the VE response of 4-day-old carotid body-deprived lambs (CBD) during successive exposure to moderate and severe (0.12 and 0.07 FIO2) hypoxia. The carotid body denervation was done to abolish most of the chemoreceptor stimulating effect on VE during hypoxia and to allow for central depression/inhibition of VE during hypoxia. In the CBD lambs, baseline VE was 461 +/- 81 (SE) ml X (kg X min)-1. It increased to 532 +/- 79 ml X (kg X min)-1 and to 541 +/- 75 ml X (kg X min)-1, to 0.12 FIO2 and 0.07 FIO2. These VE increases did not reach level of significance (P greater than 0.05). After 2-5 min of both levels of hypoxia VE dropped respectively to 460 +/- 60 ml X (kg X min)-1 and to 459 +/- 38 ml X (kg X min)-1. No marked ventilatory depressions were noted but VE had only returned to baseline. It is concluded that, in the denervated newborn lamb, the centrally mediated depressive effect of hypoxia is small and not sufficient to explain the diphasic VE response of the intact lamb to steady state hypoxia. Analysis of the magnitude of the hyperventilation and the VE damping pre-hypoxic levels occurring with sustained hypoxia in newborns of various species suggests that the immaturity of the O2-sensitive chemoreceptor rather than the central effect of hypoxia is the determinant factor of the diphasic response of newborn mammals to hypoxic hypoxia.

Computer analysis of bowel sounds

Abstract An automatic method of analysis of bowel sound recordings has been developed. A PDP8/I computer, equipped with DECtape and interfaced with a TR48 analog computer was used for the analysis. It was found that the probability of a sound occurring followed a law similar to that of Poissons phenomenon. Mean energy, sound duration and silence duration in the postmeal situation were respectively, 0·1589 V R.M.S., 4·5 msec, and 31·7 msec. No frequency exceeded 3000 Hz. This method of analysis was applied to experimental situations to study the importance of various parameters influencing the genesis of bowel sounds.

Problem-based and Project-based Learning in Engineering and Medicine: Determinants of Students’ Engagement and Persistance

This paper presents results of a study conducted with undergraduate students involved in either problemor project-based curricula (Medicine and Engineering, respectively) at the Université de Sherbrooke, Canada. The objective of the present research was to measure the impact of these innovative curricula on students’ engagement and persistence in higher education. Our research question was: What determinants better predict students’ engagement and persistence in innovative curricula such as PBL? Nine variables were examined as potential predictors of both factors (engagement and persistence). Results showed a variation in variables predicting engagement and persistence, with the most significant predictor being stress related.

Prolonged active glottic closure after barbiturate-induced respiratory arrest in lambs

We recently showed that the glottis is actively closed throughout post-hyperventilation, hypocapnic central apnea in lambs. The present study was designed to test whether the glottis is also closed in non-hypocapnic central apnea. Twenty-seven lambs aged 2 to 30 days were intravenously injected with 325 mg of sodium pentobarbital, so as to obtain breathing arrest. Airflow was recorded via a facial mask and pneumotachograph, along with the electromyographic activity (EMG) of the thyroarytenoid muscle (TA, a glottic adductor). With the onset of apnea, continuous TA EMG appeared in a few seconds and rose rapidly. Brief inspiratory gasps were observed in eight lambs, and TA EMG was abruptly inhibited for the exact duration of the gasps. The continuous TA EMG then disappeared after 115 to 230 sec. We conclude that the glottis is actively closed during fatal non-hypocapnic central apnea in lambs. Our data suggest that active glottic closure occurs with major depression of central inspiratory drive.

Laryngeal Response to Hypoxia in Awake Lambs during the First Postnatal Days

ABSTRACT: We recently showed that hypoxia does not induce active expiratory glottic adduction in awake lambs more than 10 d old. To reconcile our results with previous data from other researchers, we hypothesized that an active expiratory glottic closure might still be part of the response to hypoxia in the very first postnatal days. The present study was undertaken to test this hypothesis. We studied 22 awake, nonsedated lambs during hypocapnic hypoxia (fraction of inspired O2 = 0.08 during 15 min) induced during the first 72 h of postnatal life. We recorded airflow via a facial mask and pneumotachograph, along with the electromyographic activity (EMG) of the thyroarytenoid muscle (a glottic adductor) in 10 lambs. We also recorded the EMG of both the posterior cricoarytenoid (n= 4) and cricothyroid (n= 5) muscles (glottic abductors), as well as the abdominal muscles (n= 4). We identified typical expiratory airflow braking on the breath-by-breath computed flow-volume loop and thyroarytenoid muscle expiratory EMG as evidence of active expiratory glottic adduction. We found that hypoxia induced a biphasic ventilatory response, with an early peak and a subsequent decrease, and that active expiratory glottic adduction was absent during baseline room-air breathing and hypoxia. We also found that the glottic abductor phasic inspiratory and tonic expiratory EMG as well as the abdominal muscle phasic expiratory EMG, all of which were present during baseline recording, increased during hypoxia. We conclude that hypoxia does not induce expiratory glottic closure in the very first days of life in awake lambs. Apparently, the ventilatory response to hypoxia in this period already involves an increase in the inspiratory and expiratory glottic aperture, thereby facilitating the high levels of airflow created by the contracting thoracic pump muscles.

Postprandial Bowel Sounds

Bowel sounds were recorded under standard conditions for 30 minutes before, and for 90 minutes after a standard meal in 12 healthy human volunteers. The sounds were analyzed with the aid of a computer, and the evolution in time of specific parameters obtained as a quantitative printout. The number, total duration, and mean energy of sounds totaled for ten minute periods were found to be markedly influenced by the ingestion of the meal. A peak of activity occurred immediately after the meal; the activity then decreased to 85% of premeal value 60 minutes later, and a second peak followed after a further 60 minutes. An excellent correlation (correlation coefficient better than 0.9) was found at two recording sites between the three analyzed parameters, taken in pairs. For any given parameter, a correlation was also found between its value at the two sites (k better than 0.9),but the actual value were significantly different (p <0.001). When bowel sounds are interpreted, therefore, food ingestion should be taken into consideration.

Artificial neural network simulator with integrated learning supervision

In recent years, there has been a growing interest in the field of Artificial Neural Networks (ANNs). But at present, there is no rule or formula that can give adequate ANN design parameters for a given task. To find these parameters, the developer has to rely on his expertise, on simulation results and on analysis of the learning behaviour of different ANN configurations. Current ANN simulators offer various tools to assist the developer in analyzing the state of the ANN during or after training. The ANN simulator presented in this paper supervises directly the learning behaviour of the ANN, as the human developer does. It has the ability to detect critical situations during the training, and it gives meaningful results to help guide the developer in making the proper design choices. The simulator is intended to be used in collaboration with an expert system that will automatically choose the design parameters, in an attempt to automate the design process of ANNS. This article is intended to present this aspect of ANN simulator design in particular.

EFFECT OF CAFFEINE ON VENTILATION DURING POST-NATAL MATURATION OF BREATHING IN AWAKE LAMBS

Caffeine is an efficient respiratory stimulant during the neonatal period, but its action on respiration beyond this period remains unclear. This study was performed to evaluate the effect of caffeine on ventilation in relation to post-natal maturation. Nineteen lambs divided in 3 groups of different ages were studied;I: 7 lambs with a mean age of 1 week;II: 6 lambs, mean age of 2 1/2 months and III: 6 sheep, 6 months old. After a baseline period, saline (as a control infusion) then, 10 minutes later, caffeine 10 mg/kg I.V. were injected to the animals. Ventilation was measured using a mask adapted to the animals facial contour and connected to a pneumotachograph; on-line values of VE (minute ventilation), Vt/Ti, (mean inspiratory flow) and Ti/Ttot (timing of respiration) were derived from the flow signal using a computerized system.No response was seen after saline;but in all three groups, VE (ml/min/kg) increased significantly after caffeine; this increase was 36% in group I; 46% in group II; and was 48% in group III. This increase in VE was due mainly to an increase in Vt/Ti (ml/sec/kg), which increased in groups I,II,III by 36,41 and 26%. Ti/Ttot did not change significantly at any time. The plasma concentrations were 9.7,8.8,10.0 mg/1 in groups I,II,III. We conclude that: the magnitude of the ventilatory response and the strategy of breathing in response to the therapeutic blood concentration of caffeine persists without major difference between 1 week to 6 months of age in lambs.