Maintenance of an elevated FRC in the newborn. Paradox of REM sleep.
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Functional Residual Capacity↗
Biomedical subjects
A C Bryan
Publications and source records attributed to A C Bryan.
Passive respiratory mechanics in newborns and children.
When the Hering-Breuer reflex is used to relax the respiratory muscles, the passive compliance (Crs), resistance (Rrs), and time constant (Trs) of the respiratory system can be measured from the subsequent expiration. We used this method to assess 22 newborns with respiratory illness. Passive expirations were also recorded in 6 paralyzed, ventilated children. Using a simple slide valve, airway occlusion pressure was measured from a face mask or endotracheal tube, and expiratory flow was measured from a pneumotachygraph. In all subjects, there was a linear function of expiratory flow versus its integral, volume; by extrapolating the linear function to zero flow and zero volume (i.e., initial volume at time zero) Crs, Rrs, and Trs could be calculated; Crs was significantly reduced in mechanically ventilated versus spontaneously breathing infants, and Rrs was significantly higher in intubated versus extubated infants. During passive expiration in newborns, inspiration occurred at a volume above passive functional residual capacity. The passive expiratory flow-volume technique is simple, noninvasive, and appears to provide accurate measurements of respiratory mechanics in the newborn and in paralyzed children.
Child, Preschool↗
Ultrastructure of carotid bodies in sudden infant death syndrome.
Recent studies have implicated an abnormality in carotid body structure and function in the pathogenesis of sudden infant death syndrome (SIDS). In the present investigation, the light and electron microscopic findings in carotid bodies from ten victims of SIDS were compared with those in six control infants and five infants dying of congenital heart disease. The cross-sectional area of carotid body chemoreceptor cells and the frequency, distribution, and size of neurosecretory granules were assessed morphometrically. The area of carotid body occupied by chemoreceptor cells (the functional area) was comparable in SIDS victims, control infants, and infants with congenital heart disease. By electron microscopy, the carotid body chief cells from all groups contained numerous electron-dense neurosecretory granules. Distribution, frequency, and size of neurosecretory granules in SIDS victims and control infants did not differ significantly. Morphology of carotid bodies from SIDS victims was found to be normal. The presence of neurosecretory granules in chemoreceptor cells of SIDS victims suggests that the cellular mechanism of neurotransmitter synthesis and storage is not altered.
Carotid Body↗
Total airway resistance and respiratory muscle activity during sleep.
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Adult↗
Comparison of conventional and high-frequency ventilation: oxygenation and lung pathology.
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Animals↗
Influence of chest wall distortion on esophageal pressure.
The caudocephalad profile of esophageal pressure swings was studied in 10 preterm and 5 full-term infants, and the effect of chest wall distortion on esophageal pressure swings was analyzed in 12 preterm infants. Esophageal pressure was measured with a fluid-filled catheter, tidal volume with a pneumotachograph, mouth pressure with a face mask and pressure transducer, and rib cage and abdominal motion with magnetometers. In preterm infants the profile of esophageal pressure swings fell very steeply in the caudocephalad direction. In full-term infants it was flat during quiet sleep and steep during rapid-eye-movement sleep. When breaths, standardized for pleural pressure, were compared between a period with maximal and a period with minimal chest wall distortion, esophageal pressure swings for both spontaneous and occluded breaths were higher in the former period. We conclude that the complaint preterm rib cage results in an uneven distribution of pleural pressure and that this distribution varies with changes in chest wall distortion. Esophageal pressure measurements are therefore an unreliable estimate of mean pleural pressure in the preterm infant and can be unreliable in the term infant.
Esophagus↗
Effect of chest wall distortion on occlusion pressure and the preterm diaphragm.
We studied the effect of chest wall distortion (CWD) on transdiaphragmatic pressure (Pdi) and/or mouth pressure during end-expiratory airway occlusions in seven preterm infants. We measured mouth occlusion pressure (Pmo) with a face mask and pressure transducer, gastric pressure (Pga) with a fluid-filled catheter, diaphragmatic electromyogram (Edi) using surface electrodes, and rib cage and abdominal motion using magnetometers. We reasoned that Pdi = Pmo - Pga on airway occlusion. Periods with maximal and periods with minimal CWD were compared. We found that 1) when CWD was minimal, an increase in Edi produced an increase in Pmo and Pdi in all infants; when CWD was greatest, large increases in Edi produced no increase in Pmo or Pdi in four infants; 2) when breaths with the same Pmo or Pdi from each period in each infant were compared, those from the period with greatest CWD had an increased Edi (mean increase 76%, P less than 0.005, and 144%, P less than 0.01, for Pmo and Pdi, respectively). We conclude that in preterm infants, Pmo can be a poor indicator of respiratory drive, and CWD markedly limits the effectiveness of the diaphragm as a force generator.
Diaphragm↗
Myelination of the human vagus nerve from 24 weeks postconceptional age to adolescence.
Significant changes in respiratory reflexes occur with maturation. The vagus nerve, the pathway for the Hering-Breuer and irritant-receptor reflexes, was studied quantitatively in 33 infants and 5 adolescents. In the infants, total myelinated vagus fibers increased linearly (r m0.682, p less than 0.001) with postconceptional age (PCA), and by 40 weeks after conception, total counts were comparable to those of adolescent group. Counts of total myelinated vagus fibers in 16 term infants (greater than 41 weeks PCA) were comparable to those in the adolescent group (p less than 0.40), whereas 17 preterm infants (less than 38 weeks PCA) showed significantly fewer total myelinated vagus fibers than term or adolescent groups (p less than 0.001). Smaller-diameter (less than 2 micrometer) myelinated vagus fibers depended upon PCA in the preterm group (p less than 0.005), but were independent of PCA in the term group (p less than 0.5). Preterm infants have a higher percentage of small to total myelinated vagus fibers than term infants (p less than 0.1).
Adolescent↗
High-frequency oscillation compared with standard ventilation in pulmonary injury model.
Hemorrhagic pulmonary edema was induced by intra-atrial infusion of 0.04--0.1 ml/kg of oleic acid into six anesthetized dogs. Gas exchange and cardiac outputs were then compared at identical mean airway pressures during randomized ventilation with either a volume-cycled ventilator with positive end-expiratory pressure (conventional positive-pressure ventilation, tidal volume 16--21 ml/kg, frequency 15--20 cycles/min) or a variable volume piston pump operating at 15 Hz (high-frequency oscillation). The fractional inspired oxygen concentration was maintained at 0.5 throughout. During 17 data sets matched for intratracheal mean airway pressures over a range of 7.5--27 cmH2O, measurements of systemic arterial pressure, arterial blood gas tensions, thermodilution cardiac outputs, and pulmonary arterial and capillary wedge pressures were identical (P less than 0.05) during ventilation with conventional positive-pressure ventilation and high-frequency oscillation. With both forms of ventilation, arterial oxygen tension progressively improved as mean airway pressure increased. In a shunt model of acute lung injury we were unable to show significant differences in oxygenation or cardiac output when high-frequency oscillation was compared with conventional positive-pressure ventilation with positive end-expiratory pressure at equivalent mean airway pressures.
Animals↗
Oxygenation during high-frequency ventilation compared with conventional mechanical ventilation in two models of lung injury.
Oxygenation and mean lung volume were investigated during high frequency oscillation (HFO) and conventional mechanical ventilation (CMV) in two models of lung disease and related to the lung mechanics of the lesions. Oleic acid (n = 10) or lung lavage (n = 12) pulmonary injury was induced in a series of rabbits. Each animal was alternately ventilated with HFO (15 Hz sinusoidal wave form) and CMV (flow generator I:E, 1:2; f, 30 breaths/min; VT, 10 to 15 ml/kg) at matched mean airway pressure. Pao2 was measured 5 minutes after onset of ventilation. In the lung lavage model Pao2 was significantly greater during HFO than CMV (Pao2 228 +/- 116 torr vs 71 +/- 42 torr) provided that mean airway pressure was greater than the distinct opening pressure characteristic of this lesion. In the oleic acid model oxygenation was again superior during HFO (Pao2 269 +/- 116 torr vs 110 +/- 83 torr), but only if HFO was preceded by a sustained inflation. Plethysmography in a subset of six rabbits from each group revealed that the improvements in oxygenation were associated with significantly higher mean lung volumes during HFO than CMV (58 +/- 30 ml vs 29 +/- 14 ml lung lavage model, 45 +/- 15 ml vs 30.9 +/- 13 ml on the oleic acid model). The importance of a sustained inflation in rapidly optimizing gas exchange during HFO but not CMV was demonstrated. A sustained inflation resulted in immediate and sustained increases in Pao2 (from 134 +/- 102 torr to 274 +/0 124 torr in the oleic acid model; from 115 +/- 105 torr to 291 +/- 143 torr in the lung lavage model) and mean lung volume (41.8 +/- 11 to 53.8 +/- 9.7 ml in the oleic acid model, 30.9 +/- 7.7 ml to 42.8 +/- 5 ml in the lung lavage model). It is suggested that in these two particular models of lung disease, HFO, when combined with a sustained inflation (to provide opening forces), can more fully exploit the pressure volume hysteresis of unstable lung units than CMV, thereby resulting in the larger mean lung volumes and better oxygenation observed during HFO.
Animals↗
Treatment of RDS by high-frequency oscillatory ventilation: a preliminary report.
The feasibility of high-frequency oscillatory ventilation was investigated in eight neonates with severe RDS. Low-volume, high-frequency flow oscillations were generated by a piston pump and delivered through standard endotracheal tubes. Oscillatory frequencies ranged from 8 to 20 Hz and mean airway pressure from 9 to 20 cm H2O. Heart rate, airway pressures, and arterial blood gases and blood pressure were monitored during both continuous positive pressure ventilation and HFO. During HFO mean PaCO2 was 44.0 +/- 4.8 mm Hg. During CPPV immediately prior to oscillation an FIO2 of 0.66 +/- 0.15 resulted in a PaO2 of 59.6 +/- 17.0 mm Hg. Oxygenation improved during HFO such that a mean FIO2 of only 0.41 +/- 0.11 was needed for similar oxygenation. Improvements in oxygenation correlated directly with increases in mean airway pressure. Based on an animal model the phasic pressure swings during HFO are estimated to be 5 to 7 cm H2O in the trachea, much less than conventional ventilation. We conclude that HFO shows great promise in the support of gas exchange in infants with RDS. The use of small phasic volume and pressure swings should minimize pulmonary barotrauma. HFO should also permit the use of lower inspired oxygen fractions.
Humans↗
The vagus nerve and sudden infant death syndrome: a morphometric study.
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Age Factors↗
Tonic inspiratory muscle activity as a cause of hyperinflation in asthma.
We studied tonic activity of the inspiratory muscles during exacerbation of asthma in five female and two male patients. Exacerbation was provoked by withholding bronchodilatory medication for 12 h prior to the study. Thoracic gas volume (TGV) at the end of resting expiration was determined before and after albuterol (salbutamol) inhalation with a body plethysmograph. Intercostal muscle electromyogram (EMG) was recorded with surface electrodes and diaphragmatic EMG with esophageal electrodes. Tonic activity was defined as electrical activity in the EMG present throughout expiration. After salbutamol the TGV decreased 13.4 +/- 2.9% (mean +/- SE) (P less than 0.01). This decrease in TGV was accompanied by a proportional reduction in tonic intercostal (r = 0.78, P less than 0.05) and diaphragmatic activity (r = 0.84, P less than 0.05). These findings suggest that the hyperinflation present during exacerbation of asthma is at least in part due to active inspiratory muscle activity present throughout expiration.
Adult↗
Synergistic behavior of inspiratory muscles after diaphragmatic fatigue in the newborn.
We studied diaphragmatic and intercostal muscle activity and the pattern of motion of rib cage and abdomen after diaphragmatic muscle fatigue in 15 newborn infants (birth wt 1,251 +/- 424 g, mean +/- SD). Rib cage and abdominal motion were monitored with magnetometers and intercostal and diaphragmatic electromyograms (EMG's) with surface electrodes. Twelve infants showed a total of 66 episodes of muscle fatigue identified by EMG frequency spectrum analysis. Two patterns of responses to fatigue were observed. In the first case, five infants consistently recruited their intercostal muscles; this was followed by a normalization of the diaphragmatic frequency spectrum. In these infants, recruitment of intercostal muscles successfully prevented any clinical deterioration. In the second, seven infants showed no change in their intercostal muscle activity, and diaphragmatic fatigue was followed by apnea. We conclude that in newborn infants the synergistic behavior of the diaphragm and intercostal muscles can maximize the performance of these muscles and, in some infants, seems to prevent development of apnea.
Apnea↗
Changes in ventilation and chest wall mechanics during sleep in normal adolescents.
The effect of sleep state on ventilation and the mechanics of breathing was studied in nine normal adolescents by use of a respiratory inductive plethysmograph and surface electromyogram electrodes. Minute ventilation was state dependent (P less than 0.01), decreasing by a mean of 8% from wakefulness to nonrapid-eye-movement (NREM) sleep and increasing 4% from NREM to rapid-eye-movement (REM) sleep. These changes were caused by changes in respiratory rate. Tidal volume (VT) was not affected by sleep state (P greater than 0.10). The pattern of breathing during wakefulness was similar to that of REM sleep. During NREM sleep intercostal and diaphragmatic muscle activity increased by a mean of 34% and 11%, respectively, as compared with wakefulness, indicating an increase in the respiratory work load. This was accompanied by a substantial increase in rib cage contribution to VT. REM sleep was associated with a marked decrease in intercostal muscle activity (P less than 0.05) and a diminished rib cage contribution; VT was maintained due to a mean increase of 34% in diaphragmatic muscle activity (P less than 0.05).
Adolescent↗
Importance of inspiratory muscle tone in maintenance of FRC in the newborn.
The importance of inspiratory muscle tone in the maintenance of functional residual capacity (FRC) in newborns was studied in eight premature infants with birth weights of 1,166 +/- 217 g and gestational age 29 +/- 1.9 wk (mean +/- SD). Rib cage and abdominal anteroposterior diameters were monitored with magnetometers, and electromyograms of the diaphragm and intercostal muscles were recorded with surface electrodes. Sleep state was monitored using electrooculogram and behavioral criteria. We assessed the decrease in tonic activity of the inspiratory muscles and the fall in end-expiratory lung volume during apnea compared with the period just preceding apnea. A total of 98 apneas were analyzed. In all instances a decrease in diaphragmatic and intercostal tone was associated with a decrease in the anteroposterior diameter of both rib cage and abdomen, indicating a fall in FRC. These changes were more marked during quiet sleep than during rapid-eye-movement sleep (P less than 0.01). Our results suggest that inspiratory muscle tone is a major determinant of FRC in the newborn.
Apnea↗
Vagotomy reverses apnea induced by high-frequency oscillatory ventilation.
Apnea has been observed in both animals and patients during high-frequency oscillatory ventilation. The effects of vagotomy were studied during periods of oscillator-induced apnea in 11 pentobarbital-anesthetized dogs. The animals were intubated and breathing spontaneously. An arterial cannula was inserted for monitoring blood pressure and blood gases. Intratracheal airway pressure was measured, and respiratory activity was assessed using either an intrapleural catheter or esophageal balloon. The dogs then underwent high-frequency ventilation at 15 Hz. Apnea was induced by appropriate selection of volume displacement of the piston pump and the distal airway pressure in eucapnic animals. Segments of right and left vagus nerves were exposed in the neck, bathed in local anesthetic, and transected. Spontaneous ventilation resumed immediately in nine animals and could not be suppressed at the same CO2 partial pressure despite continuation of oscillation. We conclude that the apnea observed during high-frequency ventilation is mediated by active vagal inhibition of central respiratory activity and is usually reversed by vagotomy.
Animals↗