Irenej Kianicka

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.

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.

Influence of Sleep States on Laryngeal and Abdominal Muscle Response to Upper Airway Occlusion in Lambs

This study was aimed at describing abdominal and laryngeal muscle responses to upper airway occlusion (UAO) in early life and the effect of sleep states on these responses. Twelve nonsedated, 9-26-d-old lambs were studied. We simultaneously recorded 1) airflow (pneumotachograph + face mask);2) sleep states (electrocorticogram and electrooculogram);3) abdominal muscle (external obliquus) electromyogram (EMG); and 4) glottic constrictor (thyroarytenoid) and dilator (posterior cricoarytenoid and cricothyroid) muscle EMGs. The pneumotachograph was repeatedly occluded for 15-30 s in wakefulness and natural sleep. We analyzed 90 occlusions during wakefulness (11 lambs), 28 during non-rapid eye movement(nREM) sleep (six lambs), and 23 during rapid eye movement (REM) sleep (five lambs). A phasic expiratory external obliquus EMG was present during baseline and progressively increased throughout UAO in wakefulness and nREM sleep, but not in REM sleep. Phasic thyroarytenoid EMG progressively increased during inspiratory efforts throughout UAO in wakefulness and nREM sleep, paralleling the increase in glottic dilator (posterior cricoarytenoid and cricothyroid) EMG. In contrast, glottic muscle response to UAO in REM sleep was severely blunted or disorganized by frequent swallowing movements. We conclude that UAO triggers complex and coordinated laryngeal and abdominal muscle responses during wakefulness and nREM sleep in lambs; these responses are largely absent, however, in REM sleep. These unique results, together with the defective arousal response in REM sleep, suggest that vulnerability to airway occlusion could be increased during REM sleep in early life. Possible implications for understanding severe postnatal apneas are discussed.

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.

Abolition of breathing rhythmicity in lambs by CO2 unloading in the first hours of life

The mechanisms responsible for the maintenance of regular breathing after initiation of breathing at birth are still poorly understood. This study was designed to test the hypothesis that removing the chemical CO2 drive would abolish breathing rhythmicity in lambs in the first hours of life. A technique of graded CO2 removal through a veno-venous extracorporeal circuit was used in five unanesthetized lambs aged from 4 to 12 hours. In all lambs, CO2 unloading invariably resulted in sustained central apnea, after a decrease in Paco, of 6.9 +/- 5.7 Torr. We were unable to find a significant relationship between the decrease in PaCO2 and PaO2 (range 35-275 Torr) at onset of apnea. During apnea, the passage from behavioral quiet sleep to arousal or to active sleep was marked by transient and weak breathing movements. We conclude that the CO2 drive, but not the behavioral states, is a major factor for maintaining breathing rhythmicity in lambs in the first hours of life.

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.