Patrick Létourneau

Radiotelemetry system for apnea study in lambs.

Neonatal apneas are being studied in the laboratory using polysomnographic recordings in lambs. Standard equipment, requiring animal restraint, disrupts sleep and prevents development of spontaneous apneas. The aim of the current work was to develop and validate a wireless recording equipment to study freely moving lambs. Firstly, a radiotelemetry equipment composed of a multichannel FM transmitter and a receiver was developed. Secondly, to test the telemetry equipment, each biopotential - [electroencephalogram (EEG), electrooculogram (EOG), electrocardiogram (ECG), electromyograms (EMGs), nasal airflow] - was recorded simultaneously by standard equipment and by telemetry (5 lambs). The results indicated an excellent concordance between signals obtained by both systems. Finally, the 8-channel telemetry prototype was tested for polysomnographic recordings (16 lambs). Results obtained confirmed the possibility of recording frequent REM sleep periods and spontaneous apneas. In conclusion, this radiotelemetry polysomnographic equipment brings new possibilities for research on neonatal apneas.

Non-nutritive swallowing and respiration coordination in full-term newborn lambs.

Swallowing is a powerful inhibitor of respiratory rhythm in infants. The present study was aimed at investigating the influence of states of alertness on non-nutritive swallowing (NNS) frequency, on NNS and respiration coordination, and on bursts of NNS frequency in newborn lambs. Six full term newborn lambs were instrumented for electroencephalogram, eye movement, diaphragm and thyroarytenoid muscle electromyogram, nasal flow and electrocardiogram. Polysomnographic recordings were performed in non-sedated lambs, using radiotelemetry. NNS frequency was significantly higher during quiet wakefulness (W) and active sleep (AS) than during quiet sleep (QS). NNS mainly interrupted inspiration and the transition phases between expiration and inspiration, especially in W and AS. Bursts of NNS occurred significantly more often during AS. This study highlights the relevance of the ovine model to study ontogeny of NNS during sleep, and documents the influence of sleep on NNS and respiration coordination.

Active glottal closure during anoxic gasping in lambs

The present study was aimed at assessing laryngeal dynamics and their consequences during anoxic gasping in ketamine-sedated lambs. We first verified that the glottis was closed between gasps during anoxic gasping in seven chronically instrumented lambs, aged 11-15 days. Recording of glottal constrictor muscle electrical activity, subglottal pressure and lung volume, together with endoscopic observation, confirmed the presence of active glottal closure with maintenance of a high lung volume between gasps. Secondly, we tested whether maintenance of a high lung volume between gasps improved autoresuscitation efficiency. Six sedated lambs aged 8-11 days underwent two anoxic runs, including one with an open tracheostomy to prevent maintenance of a high lung volume. Access back to air was allowed for gasping. No significant difference was found in time to eupnea resumption, hemodynamic parameters or arterial blood gases. We conclude that a high lung volume is actively maintained by glottal closure between anoxic gasps in sedated lambs. Further studies are however needed to define the importance of laryngeal dynamics during gasping.

A radiotelemetry system for polysomnographic recordings in lambs.

The use of telemetry in biomedical research is rapidly increasing and is soon likely to be standard in research fields where prolonged recordings of multiple physiologic variables are necessary in freely moving animals. We describe our experience with a radiotelemetry system designed in our laboratory for polysomnographic recordings in newborn lambs. The system comprises eight channels: four channels for electromyographic activity of respiratory muscles, and one channel each for electrocorticogram, eye movement, electrocardiogram, and nasal flow. Using this system, we report our experience on the study of respiration and spontaneous apneas in the various states of consciousness, based on more than 500 h of recordings. Addition of radiotelemetry to our armamentarium has proven to be of invaluable help for the study of neonatal apneas and has now become routine in our laboratory.

Influence of 24-Hour Sleep Deprivation on Respiration in Lambs

The aim of this study was first to examine the effects of 24-h sleep deprivation on apnea index and duration in lambs. The effects on sleep architecture and sigh and swallowing indices were also studied. The impact of postnatal maturation on all measured variables was assessed by studying two different age groups. Twelve lambs (six aged 1–2 d and six aged 23–24 d on the day of surgery) were chronically instrumented for polysomnographic recordings including sleep state assessment, nasal flow, diaphragm electromyogram, and glottal constrictor muscle electromyogram. Two recordings, one control and one after 24-h sleep deprivation, were performed in all lambs. Results show that the effects of sleep deprivation predominate in rapid eye movement sleep in the younger group, with increased rapid eye movement sleep proportion and apnea, sigh, and swallowing index. Our results in lambs suggest that the consequences of sleep deprivation upon respiration are predominant early after birth. Although the potential relationship of these observations to neonatal apneas and sudden infant death syndrome has yet to be defined, awareness of the effects of sleep deprivation is important for neonatal care.

C-fiber blockade influence on non-nutritive swallowing in full-term lambs

Systemic C-fiber blockade (CFB) has been reported to inhibit induced swallowing in adult guinea pigs. The aim of this study was to investigate the effects of CFB on spontaneous, non-nutritive swallowing (NNS) frequency and NNS-respiration coordination in the neonatal period. Seven CFB lambs and seven control lambs aged 2+/-1 days were chronically instrumented for recording electroencephalogram, eye movements, diaphragm EMG, thyroarytenoid muscle EMG, nasal airflow and electrocardiogram. Polysomnographic recordings were performed in non-sedated lambs, using radiotelemetry transmission. CFB lambs spent more time in active sleep than controls (p=0.02). Frequency of non-nutritive swallowing was not different in CFB and control lambs, whatever the state of alertness. In addition, CFB did not disrupt the overall respiratory-swallowing coordination, inspiratory-related NNS being the most frequent and expiratory-related NNS the least in both CFB and control lambs. Further analyses revealed that CFB had no effect on baseline respiratory and heart rate, and apnea and sigh frequency, whatever the state of alertness. Our results suggest that, in the neonatal period, C-fibers are not involved in NNS frequency and have no influence on the overall respiratory-swallowing coordination.

USEFULNESS OF RADIOTELEMETRY SYSTEM FOR STUDYING SLEEP APNEAS IN LAMBS 1819

Our research program on upper airway dynamics during neonatal apneas utilizes polysomnographic recordings in non-sedated newborn lamb. Standard equipment, however, consists of numerous sensors attached to the lamb and requires animal restraint that disrupts sleep and prevents development of normal, spontaneous apneas. In order to perform recordings in more natural conditions, we have recently develop a radiotelemetry equipment composed of an implantable 8 channel transmitter and a FM receiver. The transmitter (23× 35 × 8 mm) is supplied with a lithium battery connected in series with a magnetically activated switch to extend battery life. Studied biopotentials (EEG, EOG, EMG, nasal flow) can be transmitted to a maximal distance of 8 m. The aim of the present study was to validate this telemetry equipment in vivo. Five non-sedated lambs, aged 5 to 25 days, were studied. The first validation step was to record each biopotential simultaneously by the standard equipment and by telemetry. Results obtained confirmed the reliability and reproducibility of the signals transmitted by telemetry. The second validation step was to test the usefulness of the telemetry equipment for repeated and simultaneous recording of several signals in one lamb (EEG, EOG, ECG, diaphragm EMG, pharyngeal and laryngeal constrictor muscle EMG). Results obtained confirmed the possibility to record signals during more than 30 days. Moreover, we were able to record longer sleep periods (especially REM sleep) with more spontaneous central apneas. In conclusion, radiotelemetry is an exciting tool for research on neonatal apneas (including fetal lamb in utero, preterm or term newborn lamb). A Sa02 sensor is being developped and will soon be added. Finally, radiotelemetry has several potential clinical applications, including cardiorespiratory home monitoring of infants at risk for sudden infant death syndrome, and adult or children polysomnographic studies. Funded by MRC 7137.