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Biomedical subjects

S J England

Publications and source records attributed to S J England.

At least 37 records · Page 2Linked to original sources
PubMed1988

Importance of vagal afferents in determining ventilation in newborn rats.

We studied the effect of acute bilateral vagotomy on ventilation and ventilatory pattern in rats. In 1- to 6-day-old unanesthetized rats, vagotomy resulted in a substantial decrease (38%) in ventilation during air breathing. After vagotomy there was a threefold increase in tidal volume (VT), inspiratory time (TI) doubled, and expiratory time (TE) was six times longer. When studied under isoflurane anesthesia, newborn rats showed decreases in ventilation similar to that observed without anesthesia, whereas anesthetized adult rats had no consistent changes in ventilation. Adult and newborn rats had nearly identical proportionate increases in VT and TI after vagotomy, but TE lengthened to a greater extent in the newborns. Additionally, we demonstrated a significant decrease in ventilation when 100% O2 rather than air was supplied to nonvagotomized unanesthetized newborn rats. Ventilation decreased by 19% after vagotomy under hyperoxic conditions. We conclude that vagal afferent input, probably of pulmonary mechanoreceptor origin, provides positive feedback to respiration in newborn rats and that newborn rats greater than 24 h old also have a degree of peripheral chemoreceptor drive during air breathing.

Afferent Pathways↗
PubMed1988

Comparison of diaphragmatic fatigue in newborn and older rabbits.

The ability to maintain occlusion pressure (i.e., fatigability) during activation of the diaphragm via phrenic nerve stimulation was compared in newborn (less than 14 days old) and older (greater than 30 days old) rabbits. The younger animals had lower maximum inspiratory pressures (MIP) and markedly greater falls in pressure during sustained diaphragmatic contractions at greater than 40% MIP than did the older animals. Histological analysis showed a paucity of high-oxidative type I fibers in the diaphragms of the young animals. We therefore conclude that the newborn rabbit diaphragm is extremely susceptible to fatigue and that this susceptibility correlates with the distribution of muscle fiber types.

Age Factors↗
PubMed1987

Tracheomalacia: an experimental animal model for a new surgical approach.

Tracheomalacia was created by removing the posterior 50% of the circumference of eight cartilage rings (5-6 cm in length) from the intrathoracic trachea in each of 12 piglets while leaving the mucosa intact. In 6 animals an autologous, free tibial periosteal graft was applied over the defect (graft group). The remaining 6 piglets served as the control group. In all animals, a silastic stent was left in the trachea for 2 weeks to prevent immediate tracheal collapse. The presence of tracheomalacia was assessed 6-8 weeks after surgery. At bronchoscopy total tracheal collapse during coughing occurred only in the controls. As the animals went from quiet breathing to coughing, mean intrathoracic pressure increased from 5 to 80 cm H2O in both groups, and average sagittal tracheal diameter decreased by 10% in the graft group and 71% in the controls. During coughing, mean resistance to airflow across the defect increased by 0.005 +/- 0.002 cm H2O/liter/min in the graft group, by 0.083 +/- 0.96 cm H2O/liter/min in the controls (P less than 0.005), and by 0.027 cm H2O/liter/min at the same tracheal level in two normal pigs. At sacrifice 12 weeks postoperatively, bone and collagenized fibrous tissue had been produced by all grafts, without evidence of stricture. This study shows that experimentally induced tracheomalacia can be treated successfully by the application of an autologous periosteal tibial graft, which becomes incorporated into the weakened tracheal wall.

Airway Resistance↗
PubMed1987

Role of upper airway in ventilatory control in awake and sleeping dogs.

We examined the role of the upper airway in the regulation of the pattern of breathing in six adult dogs during wakefulness and sleep. The dogs breathed through a fenestrated endotracheal tube inserted through a tracheostomy. The tube was modified to allow airflow to be directed either through the nose or through the tracheostomy. When airflow was diverted from nose to tracheostomy there was an abrupt increase in the rate of expiratory airflow, resulting in prolongation of the end-expiratory pause but no change in overall expiratory duration or respiratory frequency. Furthermore, electromyogram recordings from implanted diaphragmatic and laryngeal muscle electrodes did not show any changes that could be interpreted as an attempt to delay expiratory airflow or increase end-expiratory lung volume. The effects of switching from nose to tracheostomy breathing could be reversed by adding a resistance to the endotracheal tube so as to approximate upper airway resistance. The findings indicate that under normal conditions in the adult dog upper airway receptors play little role in regulation of respiratory pattern and that the upper airway exerts little influence on the maintenance of end-expiratory lung volume.

Animals↗
PubMed1987

Diaphragmatic work of breathing in premature human infants.

Present methods of assessing the work of breathing in human infants do not account for the added load when intercostal muscle activity is lost and rib cage distortion occurs. We have developed a technique for assessing diaphragmatic work in this circumstance utilizing measurements of transdiaphragmatic pressure and abdominal volume displacement. Eleven preterm infants without evidence of lung disease were studied. During periods of minimal rib cage distortion, inspiratory diaphragmatic work averaged 5.9 g X cm X ml-1, increasing to an average of 12.4 g X cm X ml-1 with periods of paradoxical rib cage motion (P less than 0.01). Inspiratory work was strongly correlated with the electrical activity of the diaphragm as measured from its moving time average (P less than 0.05). Assuming a mechanical efficiency of 4% in these infants, the caloric cost of diaphragmatic work may reach 10% of their basal metabolic rate in periods with rib cage distortion. When lung disease is superimposed, the increased metabolic demands of the diaphragm may predispose preterm infants to fatigue and may contribute to a failure to grow.

Diaphragm↗
PubMed1987

Comparison of calibration methods for respiratory inductive plethysmography in infants.

In infants under the age of 6 mo respiratory inductive plethysmograph (RIP)-calculated tidal volumes (VT) were compared with simultaneously measured volumes using a pneumotachograph (PNT) to 1) assess whether using multiple points (MP) along the inspiratory profile of a breath is superior to using only VT when calculating volume-motion (VM) coefficients, 2) verify the assumption of independent contributions of the abdomen and rib cage to VT, which was accomplished by extending the normal RIP model to include a term representing interaction between these two compartments, and 3) investigate whether VM coefficients are sleep-state dependent. Neither use of multiple points nor inclusion of the interacting term improved the performance of the RIP over that observed using a simple two-compartment model with VT measurements. However, VM coefficients obtained during quiet sleep (QS) were not reliable when used during rapid-eye-movement (REM) sleep, suggesting that coefficients obtained during one sleep state may not be applicable to another state where there is a substantial change in the relative abdominal/rib cage contributions to VT.

Humans↗
PubMed1987

Evaluation of respiratory inductive plethysmography in infants weighing less than 1,500 grams.

Calibration of the respiratory inductive plethysmograph (RIP) was performed in premature infants weighing less than 1,500 g. In only 25% of the studies was an acceptable calibration achieved, as assessed by statistical comparison of simultaneously measured pneumotachygraph and RIP tidal volumes. In 6 infants, dead space loading or air injection was performed in an attempt to alter abdominal and rib cage volume contributions and thereby improve the calibration. Neither of these maneuvers resulted in an improvement of the accuracy of the RIP calibration coefficient. We conclude that, when calibrated by the least squares technique, the reliability of inductive plethysmography in measuring tidal volume in small infants is low. This is presumably because they have very small tidal volumes and highly compliant rib cages.

Female↗
PubMed1987

Comparison of methods of measurement of compliance of the respiratory system in children.

Compliance of the respiratory system (Crs) was compared using 2 previously described methods, namely, the passive expiratory flow and multiple occlusion techniques. These 2 methods have the advantage of being totally noninvasive, but both have limitations precluding their use in some circumstances. The results of this study of 10 intubated patients, who varied widely in age (premature newborn to adolescence) and diseases, showed no significant difference between the Crs obtained by the 2 methods. The Crs measurements can therefore be used interchangeably, the choice of technique being dependent on the subjects' clinical state.

Child↗
PubMed1986

Influence of the upper airway on breathing pattern and expiratory time constant in unanesthetized dog pups.

Unanesthetized dog pups (2 to 31 days old) respond to sudden opening of a tracheal cannula to atmospheric pressure with a marked increase in breathing frequency. This response is achieved with a 25% decrease in inspiratory and 40% decrease in expiratory times. Expiratory thyroarytenoid muscle activity increased concomitantly, while inspiratory diaphragmatic and posterior cricoarytenoid muscle activities were reduced. These responses are interpreted as a compensatory mechanism for maintenance of an elevated end-expiratory lung volume with functional loss of the upper airway. The changes in expiratory time and thyroarytenoid muscle activity were not observed when positive pressure was applied at the trachea. The expiratory time constant was assessed during spontaneous breathing. The mean value was twice as long during nasal breathing than during tracheal breathing. The nasal value was substantially increased when the thyroarytenoid muscle was active during expiration.

Animals↗
PubMed1986

Respiratory activity of laryngeal muscles in awake and sleeping dogs.

Experiments were conducted in adult dogs to determine the respiratory activity of laryngeal muscles during wakefulness and sleep. We studied the EMG activity of three laryngeal muscles in five trained dogs, two of which were completely intact, and three of which had a previously-formed side-hole tracheal stoma. Pairs of electrodes were implanted chronically into the posterior cricoarytenoid muscle (PCA), a laryngeal dilator, cricothyroid (CT), and thyroarytenoid (TA), a laryngeal adductor. EMG electrodes were also inserted into the costal portion of the diaphragm. In wakefulness (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep the EMGs of the PCA and CT muscles increased in intensity during diaphragm activation, with varying levels of basal activity during expiration. However, the greatest levels of inspiratory activity in PCA and CT during sleep were found in REM sleep, usually in the absence of augmented diaphragm EMG activity. This laryngeal muscle activity was associated with laryngeal dilation. There were also marked state-related changes in the level of activity of CT during expiration, suggestive of changes in the degree of expiratory adduction of the larynx. The adductor muscles (TA) were not active during expiration, except during alert W. There were no consistent differences in respiratory activity of the laryngeal muscles between the two intact dogs and those with a tracheal stoma (whether or not an endotracheal tube was in place), nor was laryngeal muscle activity affected by the subsequent creation of a tracheal stoma in the two intact dogs. The findings indicate that sleep-wakefulness state exerts important influences on the respiratory activity of laryngeal muscles in the adult dog.

Airway Resistance↗
PubMed1986

Laryngeal muscle activities during progressive hypercapnia and hypoxia in awake and sleeping dogs.

Laryngeal, intercostal and diaphragmatic muscle activities were recorded during progressive hypercapnia and hypoxia in dogs with chronically implanted electrodes. As ventilation increased during progressive chemoreceptor stimulation, inspiratory activity of the posterior cricoarytenoid muscle, a laryngeal abductor, and of the cricothyroid muscle were augmented. When expiratory flow rates reached 2-3 times resting levels, both of these muscles were also active during expiration and recruitment of the internal intercostal muscles was observed. The thyroarytenoid muscle, a laryngeal adductor, was active only rarely and no consistent activation of this muscle was observed with either hypercapnia or hypoxia. The patterns of muscle activation in response to respiratory stimulation were not different during wakefulness, slow wave sleep, and rapid eye movement sleep. The results indicate that the laryngeal muscles are activated during hypercapnia and hypoxia in a manner which reduces both inspiratory and expiratory airflow resistance regardless of sleep-wakefulness state.

Animals↗
PubMed1985

Laryngeal muscle and diaphragmatic activities in conscious dog pups.

A new chronic animal preparation (i.e. puppies) for the study of respiratory laryngeal muscle activity is described. Posterior cricoarytenoid (PCA), thyroarytenoid (TA) and diaphragmatic activities were monitored in conscious puppies (13-43 days old) using chronically implanted electrodes. PCA activity was prominent during inspiration in all behavioral states. TA and post-inspiratory diaphragmatic activities were consistently high during expiration in quiet wakefulness and quiet sleep, but expiratory TA activity decreased dramatically and post-inspiratory diaphragmatic activity became highly variable in rapid eye movement sleep. There was also a tendency for these expiratory muscle activities to become less pronounced with increasing postnatal age. When a chronically implanted, low resistance T-tube tracheal cannula was suddenly opened, thus effectively eliminating the effects of upper airway resistance on airflow, respiratory frequency dramatically increased. These results indicate that the puppy exhibits muscle activities consistent with the maintenance of an elevated end-expiratory lung volume achieved by the retardation of expiratory airflow using the larynx and diaphragm.

Animals↗
PubMed1985

State-related incidence of spontaneous breathing during high frequency ventilation.

Previous reports indicate that apnea is induced by high frequency ventilation (HFV) in anesthetized animals. We have studied conscious dogs ventilated with HFV during sleep and wakefulness to determine if this apnea is state related. Eucapnic apnea or very low breathing frequencies were observed during quiet wakefulness, quiet sleep and tonic REM sleep. However, spontaneous breathing at nearly normal rates was invariably seen during phasic REM sleep. We conclude that HFV as administered induces apnea or near apnea in conscious animals and that the inhibitory pathways causing this apnea are probably disabled during phasic REM sleep.

Animals↗
PubMed1985

Laryngeal constriction in normal humans during experimentally induced bronchoconstriction.

Changes in the size of the glottis with bronchoconstriction were assessed in six normal subjects following inhalation of histamine or methacholine. Measurements were made during both tidal breathing and panting at 2-3 Hz. The midexpiratory size of the glottis was decreased by a mean of 8% during bronchoconstriction compared with control during tidal breathing. Changes in midinspiratory size were inconsistent. During panting, the glottic size was unchanged from inspiration to expiration but decreased in 7 of 15 studies during bronchoconstriction. The decreases in expiratory size of the glottis during quiet breathing would lead to an elevated laryngeal resistance coupled with an increased lower airway resistance. Although this seems to be a paradoxical laryngeal response, it may contribute to maintaining hyperinflation during bronchoconstriction, thereby effectively enlarging the lower airways.

Adult↗
PubMed1984

Total resistance of the respiratory system in preterm infants with and without an endotracheal tube.

The passive compliance and resistance of the respiratory system were measured in 12 spontaneously breathing newborn infants before and after endotracheal extubation. End-inspiratory airway occlusions were used to relax the respiratory muscles, allowing occlusion pressure to be measured and respiratory system compliance and resistance to be calculated from the flow volume relationship of the subsequent passive expiration. Airway pressure was measured from an endotracheal tube or a face mask, expiratory flow from a pneumotachograph, and expiratory volume from the integrated flow signal. In six of the infants, diaphragmatic electromyography was also performed before and after extubation. Resistance and EMG findings were both decreased by extubation (mean decrease 43.9%, P less than 0.001 and 27.3%, P less than 0.05, respectively), but compliance was unchanged. Thus, by substantially increasing resistance, an endotracheal tube causes the diaphragm to increase its activity to maintain ventilation.

Airway Resistance↗
PubMed1984

Neuromuscular blockade enhances phrenic nerve activity during high-frequency ventilation.

Phrenic nerve activity was monitored in anesthetized cats during high-frequency ventilation (HFV). Rhythmic phrenic discharge disappeared during HFV in all animals at normal arterial PCO2 levels. Rhythmic activity returned after neuromuscular blockade in the vagally intact animal. Although vagotomy alone also restored phrenic discharge, this activity was further enhanced by subsequent neuromuscular blockade. Therefore we suggest that apnea during HFV results from inspiratory inhibition mediated by both chest wall and vagal afferent mechanisms.

Animals↗