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Biomedical subjects

A R Stark

Publications and source records attributed to A R Stark.

At least 37 records · Page 2Linked to original sources
PubMed1989

Action of the inspiratory muscles of the rib cage during breathing in newborns.

To determine whether the rib cage muscles actively contribute to tidal volume change in infancy, we measured tidal volume (VT), using a pneumotachograph, respiratory gastric pressure swings (Pga), using a liquid-filled gastric catheter, and rib cage and abdominal volume, using respiratory inductive plethysmography in 15 newborns, both before and during 2% CO2-induced hyperventilation. Active rib cage expansion produced by phasic contraction of the inspiratory muscles of the rib cage should reduce respiratory abdominal pressure fluctuations by moving the anterior abdominal wall outward and cephalad, thereby having an expanding influence on the abdominal cavity. During quiet sleep (n = 13), CO2-induced hyperventilation was associated with significant increases in VT, Pga, rib cage volume (Vrc), and abdominal volume (Vab). Increments in Pga were small relative to VT, as shown by an increase in the slope of the VT versus Pga respiratory loop (VT/Pga) in all subjects (p less than 0.001, paired t test). CO2 breathing was associated with an increase in the contribution of the rib cage compartment to total volume change (Vrc/Vrc + Vab) in all infants studied (p less than 0.001, paired t test), and the total volume response to hyperventilation was more strongly related to changes in rib cage volume (slope = 0.62, r = 0.90) than to abdominal volume (slope = 0.31, r = 0.60). During REM sleep (n = 6), mean VT/Pga did not change significantly, and the rib cage contribution to tidal breathing decreased in three of six infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdomen↗
PubMed1989

Management of neonatal emergencies in the delivery room.

Emergencies in the delivery room are best handled by anticipation and a team approach. Basic principles of resuscitation should be applied in all cases by a team skilled in airway management and ventilatory and circulatory support. Specialized management schemes are described for rapid treatment and effective stabilization of infants with air leak syndromes, hydrops fetalis, disorders of the airway, and diaphragmatic and abdominal wall defects.

Delivery, Obstetric↗
PubMed1988

Diaphragmatic movement in newborn infants.

Axial movement of the right hemidiaphragm during tidal breathing was recorded using real-time ultrasonography in 46 healthy term infants. Displacement was 2.6 +/- 0.1, 3.6 +/- 0.2, and 4.5 +/- 0.2 mm (mean +/- SEM) for the anterior, middle, and posterior thirds, respectively. Diaphragmatic movement was significantly greater in the middle and posterior segments than in the anterior segment (P less than 0.0001). Excursion of the diaphragm was similar in sleeping and awake infants, and during quiet and active sleep, as identified by behavioral criteria. Diaphragmatic movement was also assessed in nine infants who required mechanical ventilation and pharmacologic paralysis because of respiratory disease. In these infants, axial movement of the right hemidiaphragm was less in the middle and posterior thirds (P less than 0.05 and P less than 0.01, respectively) than in spontaneously breathing infants, and posterior movement was not predominant. Normative data for axial diaphragmatic movement may be of clinical value in the assessment of defects of the diaphragm, rib cage, or abdomen in newborn infants and may allow further understanding of the direct effects of therapeutic interventions on the respiratory system in infancy.

Diaphragm↗
PubMed1988

Posterior cricoarytenoid and diaphragm activities during tidal breathing in neonates.

To investigate airflow regulation in newborn infants, we recorded airflow, volume, diaphragm (Di), and laryngeal electromyogram (EMG) during spontaneous breathing in eight supine unsedated sleeping full-term neonates. Using an esophageal catheter electrode, we recorded phasic respiratory activity consistent with that of the principal laryngeal abductors, the posterior cricoarytenoids (PCA). Sequential activation of PCA and Di preceded inspiration. PCA activity typically peaked early in inspiration followed by either a decrescendo or tonic EMG activity of variable amplitude during expiration. Expiratory airflow retardation, or braking, accompanied by expiratory prolongation and reduced ventilation, was commonly observed. In some subjects we observed a time interval between PCA onset and a sudden increase in expiratory airflow just before inspiration, suggesting that release of the brake involved an abrupt loss of antagonistic adductor activity. Our findings suggest that airflow in newborn infants is controlled throughout the breathing cycle by the coordinated action of the Di and the reciprocal action of PCA and laryngeal adductor activities. We conclude that braking mechanisms in infants interact with vagal reflex mechanisms that modulate respiratory cycle timing to influence both the dynamic maintenance of end-expiratory lung volume and ventilation.

Diaphragm↗
PubMed1988

Control of inspiratory duration in premature infants.

We used single-breath mechanical loads and airway occlusions in premature infants to determine whether maturation influences the reflex control of inspiratory duration. We measured flow, volume, airway pressure, and surface diaphragmatic electromyogram (EMG) in 10 healthy preterm infants [33 +/- 1 (SD) wk gestation], 2-7 days of age. Three resistive and two elastic loads and occlusions were applied to the inspiratory outlet of a two-way respiratory valve. Application of all loads resulted in inspired volumes significantly decreased from control (P less than 0.001), and these decreases were progressive with increasing loads. Inspiratory duration (TI) was prolonged from control by all loads and occlusions when measured from the diaphragmatic EMG (neural TI) and by all but the smaller elastic load when measured from the flow tracing (mechanical TI). Similar decreases in inspired volume at the end of neural TI produced by application of both elastic and resistive loads resulted in comparable prolongation of neural TI. In contrast, for comparable volume decrements, resistive loading prolonged mechanical TI more than elastic loading (P less than 0.001). Mechanical and neural TI values of the breath after the loaded breath were unchanged from control values. Comparison of the neural volume-timing relationship in premature infants with our data in full-term infants suggests that the strength of the timing response to similar relative decrements in inspired volume is comparable. We conclude that reflex control of neural TI in premature infants depends on the magnitude of inspired volume and is independent of the volume trajectory.(ABSTRACT TRUNCATED AT 250 WORDS)

Diaphragm↗
PubMed1987

Regulation of end-expiratory lung volume during sleep in premature infants.

To investigate the regulation of end-expiratory lung volume (EEV) in premature infants, we recorded airflow, tidal volume, diaphragm electromyogram (EMG), and chest wall displacement during sleep. In quiet sleep, EEV during breathing was 10.8 +/- 3.6 (SD) ml greater than the minimum volume reached during unobstructed apneas. In active sleep, no decrease in EEV was observed during 28 of 35 unobstructed apneas. Breaths during quiet sleep had a variable extent of expiratory airflow retardation (braking), and inspiratory interruption occurred at substantial expiratory flow rates. During active sleep, the expiratory flow-volume curve was nearly linear, proceeding nearly to the volume axis at zero flow, and diaphragm EMG activity terminated near the peak of mechanical inspiration. Expiratory duration (TE) and inspiratory duration (TI) were significantly shortened in quiet sleep vs. active sleep although tidal volume was not significantly different. In quiet sleep, diaphragmatic braking activity and shortened TE combined to maintain EEV during breathing substantially above relaxation volume. In active sleep, reduced expiratory braking and prolongation of TE resulted in an EEV that was close to relaxation volume. We conclude that breathing strategy to regulate EEV in premature infants appears to be strongly influenced by sleep state.

Diaphragm↗
PubMed1986

Respiratory distress syndrome.

Increasing knowledge of the pathophysiology of respiratory distress syndrome has led to improvements in clinical management. Future advances in prevention and therapy, including administration of agents to prevent prematurity or to accelerate lung maturation, provision of surfactant replacement, and new techniques of mechanical ventilation, will further decrease mortality and morbidity.

Animals↗
PubMed1986

Reflex control of inspiratory duration in newborn infants.

We applied graded resistive and elastic loads and total airway occlusions to single inspirations in six full-term healthy infants on days 2-3 of life to investigate the effect on neural and mechanical inspiratory duration (TI). The infants breathed through a face mask and pneumotachograph, and flow, volume, airway pressure, and diaphragm electromyogram (EMG) were recorded. Loads were applied to the inspiratory outlet of a two-way respiratory valve using a manifold system. Application of all loads resulted in inspired volumes decreased from control (P less than 0.001), and changes were progressive with increasing loads. TI measured from the pattern of the diaphragm EMG (TIEMG) was prolonged from control by application of all elastic and resistive loads and by total airway occlusions, resulting in a single curvilinear relationship between inspired volume and TIEMG that was independent of inspired volume trajectory. In contrast, when TI was measured from the pattern of airflow, the effect of loading on the mechanical time constant of the respiratory system resulted in different inspired volume-TI relationships for elastic and resistive loads. Mechanical and neural inspired volume and duration of the following unloaded inspiration were unchanged from control values. These findings indicate that neural inspiratory timing in infants depends on magnitude of phasic volume change during inspiration. They are consistent with the hypothesis that termination of inspiration is accomplished by an "off-switch" mechanism and that inspired volume determines the level of vagally mediated inspiratory inhibition to trigger this mechanism.

Airway Obstruction↗
PubMed1985

Neonatal effects of maternal nadolol therapy.

Described is the case of an infant, exposed during gestation to the beta-blocker nadolol, who experienced cardiorespiratory depression, mild hypoglycemia, and growth retardation. The longer duration of action of nadolol and the fact that it is only 30% protein bound make it less desirable than propranolol for use as a beta-blocker during pregnancy.

Female↗
PubMed1985

Reflex control of expiratory duration in newborn infants.

We investigated the effect on expiratory duration (TE) of application of graded resistive and elastic loads and total airway occlusions to single expirations in 9 full-term healthy infants studied on the 2nd or 3rd day of life. The infants breathed through a face mask and pneumotachograph, and flow, volume, airway pressure, and diaphragm electromyogram (EMG) were recorded. Loads were applied to the expiratory outlet of a two-way respiratory valve using a manifold system. Application of all loads resulted in expired volumes (VE) decreased from control (P less than 0.05), and changes were progressive with increasing loads. As VE became smaller, end-expiratory volume (EEV) became greater. TE, measured either from the pattern of airflow or airway pressure, or from diaphragm EMG activity, progressively increased with increasing loads and was greatest with total occlusions (P less than 0.05, compared with control). Resistive loading resulted in a greater accumulated VE history than elastic loading to the same EEV. For equivalent changes in EEV, TE was more prolonged with resistive than with elastic loading. Expiratory loading did not change the inspiratory duration determined from the diaphragm EMG activity of the breath immediately following each loaded expiration. These findings in infants are consistent with an integrative neural mechanism that modulates TE in response to the accumulated VE history, including both EEV and rate of lung deflation.

Airway Resistance↗
PubMed1984

Effect on ventilation of change to the upright posture in newborn infants.

We have investigated the effect of postural change on tidal volume (VT), inspiratory (TI) and expiratory (TE) duration, minute ventilation (VI), and end-tidal PCO2 in a group of 11 healthy full-term sleeping infants, 2-4 days of age. During tilts from the supine to upright posture, the average volume increase was 4.3 +/- 4.4 (SD) ml or 1.2 ml/kg in the maneuvers unassociated with sighs. In the 20% of tilts in which sighs occurred, the average volume change was slightly higher. Transition from supine to upright posture resulted in statistically significant increases in VT (6.45 +/- 0.06 to 6.72 +/- 0.06 ml/kg), TI (554 +/- 7 to 604 +/- 7 ms), and TE (629 +/- 12 to 777 +/- 14 ms), and decrease in VI (328 +/- 5 to 288 +/- 4 ml X kg-1 X min-1) (all means +/- SE, P less than 0.0005). Return to supine position resulted in statistically significant changes in the opposite direction. Tilting to the upright posture brought about a small (0.4 +/- 0.1 Torr, means +/- SE) but consistent statistically significant increase in end-tidal PCO2, which persisted through the first minute when the infant was returned to the supine position. The expiratory prolongation observed with tilting appears to minimize changes in end-expiratory lung volume, obviating the need for an effective compensatory muscle response to defend ventilation. Thus it appears that infants, in contrast to adults, adopt a breathing strategy to limit the extent of change in absolute lung volume, rather than to defend ventilation at increased lung volume.

Carbon Dioxide↗
PubMed1984

Apnea duration is related to ventilatory oscillation characteristics in newborn infants.

The occasional short apneas seen in full-term infants within the first postnatal week are related to the minimum phase of oscillatory breathing patterns. To determine the relationship between breathing patterns and the longer and more frequent apneas seen in premature infants, we monitored respiration in 14 premature infants using a face mask and pneumotachograph. Tidal volume, breath duration, and ventilation were calculated on a breath by breath basis, converted to time-axis data strings, and filtered with a comb of zero phase shift digital band pass filters to detect breathing patterns. Compared with full-term infants, premature infants had breathing patterns that occurred more often and had twice the average amplitude. Of 182 apneas greater than or equal to 3 s long, 94% occurred at the minimum phase of oscillatory breathing patterns. All of the 38 apneas greater than or equal to 10 s long occurred at the minimum phase of oscillatory breathing patterns. Duration of apnea was related to breathing pattern characteristics, e.g., longer apneas were related to stronger, longer cycle-time breathing patterns. Apnea in the premature infant is not an isolated event but is one aspect of an underlying pattern.

Apnea↗
PubMed1984

Dynamic maintenance of end-expiratory lung volume in full-term infants.

We recorded airflow, tidal volume, respiratory muscle electromyogram (EMG), and chest wall configuration in eight normal newborn infants to investigate the determination of end-expiratory lung volume (EEV). The expiratory flow-volume representation was nearly linear and EMG evidence of respiratory muscle activity was absent during the latter part of expiration in both supine and upright postures, consistent with passive expiration. Occasional breaths were associated with marked retardation of expiratory airflow (braking). During unobstructed apnea, expiration proceeded to the relaxation volume (Vr) with no change in slope of the flow-volume curve. During breathing, EEV was greater than Vr observed during apnea. We calculated the difference between EEV and Vr estimated by extrapolation of the linear portion of the expiratory flow-volume curve as 14.4 +/- 5.4 ml (supine) and 11.8 +/- 2.4 ml (upright). When infants were tilted from supine to upright, expiratory duration (TE) and the expiratory time constant (tau) increased significantly. Since the increases in tau and TE offset each other, the EEV-Vr difference was similar in both postures. We propose that while braking plays a major role in the early part of expiration, as long as the final portion of expiration is passive, the dynamic maintenance of EEV above Vr depends on the relative values of tau and TE. Expiratory braking mechanisms interact with the passive mechanical properties of the respiratory system to modulate the balance between tau and TE. These mechanisms provide a neonatal breathing strategy to maintain EEV above a low Vr until the chest wall stiffens with maturity.

Functional Residual Capacity↗
PubMed1984

Hemodynamic response to high-frequency ventilation in infants following cardiac surgery.

The hemodynamic response to high-frequency ventilation was compared with conventional ventilation in six infants following cardiac surgery. While undergoing high-frequency ventilation, adequate gas exchange was maintained in all infants. High frequency ventilation allowed a reduction of peak ventilatory pressure at the airway opening by 19%, and peak tracheal pressure by 42%. No clinically important changes in heart rate, systemic and pulmonary arterial pressure, cardiac index, or systemic and pulmonary vascular resistance were noted when high-frequency ventilation was compared with conventional ventilation.

Blood Pressure↗
PubMed1983

Respiratory system impedance from 4 to 40 Hz in paralyzed intubated infants with respiratory disease.

To describe the mechanical characteristics of the respiratory system in intubated neonates with respiratory disease, we measured impedance and resistance in six paralyzed intubated infants with respiratory distress syndrome, three of whom also had pulmonary interstitial emphysema. We subtracted the effects of the endotracheal tube after showing that such subtraction was valid. Oscillatory flow was generated from 4 to 40 Hz by a loudspeaker, airway pressure was measured, and flow was calculated from pressure changes in an airtight enclosure mounted behind the flow source (speaker plethysmograph). After subtraction of the endotracheal tube contribution, resistance ranged from 22 to 34 cmH2O liter-1 s; compliance from 0.22 to 0.68 ml/cmH2O; and inertance from 0.0056 to 0.047 cmH2O liter-1 s2. Our results indicate that, for these intubated infants, the mechanics of the respiratory system are well described as resistance, compliance, and inertance in series. Most of the inertance, some of the resistance, and little of the compliance are due to the endotracheal tube. When the contribution of the endotracheal tube is subtracted, the results are descriptive of the subglottal respiratory system. These data characterize the neonatal respiratory system of infants with respiratory distress syndrome (with or without pulmonary interstitial emphysema) in the range of frequencies used during high frequency ventilation.

Airway Resistance↗
PubMed1983

High-frequency ventilation in premature infants with lung disease: adequate gas exchange at low tracheal pressure.

The technique of high-frequency ventilation (HFV) was used in ten infants with severe respiratory distress syndrome and five infants with pulmonary interstitial emphysema (PIE). The mean frequency used was 12 Hz (720/min). Peak tracheal pressure for the infants with respiratory distress syndrome was 28 +/- 4 (SD) cm H2O on conventional ventilation, and 22 +/- 4 cm H2O on HFV (P less than .05). For the infants with PIE, peak tracheal pressure decreased from 38 +/- 11 to 24 +/- 5 cm H2O (P less than .05). Mean tracheal pressure was the same for the two types of ventilation. No adverse clinical or pathologic side effects were seen. Clinical and radiologic improvements were seen in the infants with PIE after initiation of HFV. It is believed that these improvements in the patients with PIE were secondary to the decrease in tracheal pressure and that HFV may have a role in treatment of preexisting barotrauma and its prevention. These studies contribute to the preliminary data necessary before controlled trials of HFV in infants with respiratory distress syndrome and PIE can be carried out.

Humans↗
PubMed1983

Apnea monitoring by acoustic detection of airflow.

An acoustic monitor to detect apnea in infants has been developed. Recordings of a signal derived from breath sounds at the nose were made in eight premature infants and compared with observation of the infant and with transthoracic impedance and ECG monitoring. The acoustic monitor detected 26 episodes of apnea lasting 15 seconds or longer which were confirmed by observation and by heart rate slowing of at least 20 beats per minute. Only seven of these episodes were detected by the impedance monitor. The ECG monitor alarmed during the nine spells in which heart rate dropped below 100 beats per minute, 27.5 +/- 9.7 seconds after breath sounds ceased. Inasmuch as the acoustic device detects absent airflow during central or obstructive apnea before bradycardia occurs and is insensitive to body movements, it represents an improved monitoring technique for infants with apnea.

Acoustics↗