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Biomedical subjects

A R Stark

Publications and source records attributed to A R Stark.

At least 19 recordsLinked to original sources
PubMed1990

Chest wall motion of infants during spinal anesthesia.

To test the extent to which diaphragmatic contraction moves the rib cage in awake supine infants during quiet breathing, we studied chest wall motion in seven prematurely born infants before and during spinal anesthesia for inguinal hernia repair. Infants were studied at or around term (postconceptional age 43 +/- 8 wk). Spinal anesthesia produced a sensory block at the T2-T4 level, with concomitant motor block at a slightly lower level. This resulted in the loss of most intercostal muscle activity, whereas diaphragmatic function was preserved. Rib cage and abdominal displacements were measured with respiratory inductance plethysmography before and during spinal anesthesia. During the anesthetic, outward inspiratory rib cage motion decreased in six infants (P less than 0.02, paired t test); four of these developed paradoxical inward movement of the rib cage during inspiration. One infant, the most immature in the group, had inward movement of the rib cage both before and during the anesthetic. Abdominal displacements increased during spinal anesthesia in six of seven infants (P less than 0.05), suggesting an increase in diaphragmatic motion. We conclude that, in the group of infants studied, outward rib cage movement during awake tidal breathing requires active, coordinated intercostal muscle activity that is suppressed by spinal anesthesia.

Anesthesia, Spinal↗
PubMed1990

Changes in the contribution of the rib cage to tidal breathing during infancy.

As the shape, compliance, and deformability of the rib cage (RC) change during infancy, RC participation in quiet breathing may increase. We used respiratory inductive plethysmography (RIP) to determine the relative contributions of the RC and abdomen (AB) to tidal volume (VT) in 20 studies in 14 healthy infants 1 to 26 months of age during quiet natural sleep. RIP was calibrated with simultaneous flow measurements (anesthesia mask and pneumotachograph) by the least squares method of statistical analysis. We analyzed segments of breathing with and without flow measurement for RIP-derived VT, change in RC volume (Vrc) and AB volume (Vab) with each breath and the RC contribution to tidal breathing (%RC = Vrc/Vrc + Vab). The %RC increased with age: %RC = 1.4 age (months) + 33 (r = 0.69, p less than 0.01). After 9 months of age, %RC resembled that found in quietly sleeping adolescents. Mask placement increased VT in all but one subject (mean increase, 29 +/- 23% of baseline +/- SD; p less than 0.001, paired t test). In infants younger than 10 months of age, mask placement also increased %RC (without mask, 40 +/- 9%; with mask, 46 +/- 10% p less than 0.02). We conclude that by 1 yr of age, the RC contribution to tidal breathing during quiet sleep is similar to that of the adolescent, suggesting that major developmental changes in RC shape, compliance, and deformability take place during infancy.

Abdominal Muscles↗
PubMed1989

Mixed and obstructive apneas are related to ventilatory oscillations in premature infants.

In our previous study of 14 premature infants, apnea occurred at the minimum phase of ventilatory oscillations. The apneas corresponded to cessation of airflow at the nose and mouth and were not distinguished as central, mixed, or obstructive. Changes in heart rate associated with the apneas were not identified. To determine whether ventilatory pattern characteristics might predict either the type of apnea or heart rate changes during the apnea, we analyzed measurements of chest wall movement and heart rate that were made during the earlier studies. Chest wall movement measured by magnetometers was compared with airflow measured with 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. Of 182 apneas greater than or equal to 3 s duration, 55% were central, 31% were mixed, and 14% were obstructive. All three types of apnea were related to ventilatory oscillations. Multiple linear and logistic regressions showed that an apnea was more likely to be obstructive when it was long and when the underlying ventilatory oscillation was due primarily to an oscillation in breath duration. Multiple linear and logistic regressions showed that decreases in heart rate were related primarily to the duration of apnea and secondarily to the characteristics of the underlying breathing patterns.

Airway Obstruction↗
PubMed1989

Effect of changes in lung volume on respiratory system compliance in newborn infants.

Total respiratory system compliance (Crs) at volumes above the tidal volume (VT) was studied by use of the expiratory volume clamping (EVC) technique in 10 healthy sleeping unsedated newborn infants. Flow was measured with a pneumotachograph attached to a face mask and integrated to yield volume. Volume changes were confirmed by respiratory inductance plethysmography. Crs measured by EVC was compared with Crs during tidal breathing determined by the passive flow-volume (PFV) technique. Volume increases of approximately 75% VT were achieved with three to eight inspiratory efforts during expiratory occlusions. Crs above VT was consistently greater than during tidal breathing (P less than 0.0005). This increase in Crs likely reflects recruitment of lung units that are closed or atelectatic in the VT range. Within the VT range, Crs measured by PFV was compared with that obtained by the multiple-occlusion method (MO). PFV yielded greater values of Crs than MO (P less than 0.01). This may be due to braking of expiratory airflow after the release of an occlusion or nonlinearity of Crs. Thus both volume recruitment and airflow retardation may affect the measurement of Crs in unsedated newborn infants.

Humans↗
PubMed1989

Transition from dynamically maintained to relaxed end-expiratory volume in human infants.

Newborn infants, in contrast to adults, dynamically maintain end-expiratory lung volume (EEV) above relaxation volume. The purpose of this study was to determine at what age children develop a breathing strategy that is relaxed, i.e., determined by the mechanical characteristics of the lung and chest wall. Forty studies were performed in 27 healthy infants and children aged 1 mo to 8 yr during natural sleep. Volume changes were recorded with the use of respiratory inductance plethysmography (RIP). The volume signal was differentiated to yield flow. Flow-volume representations were generated for a random sample of the recorded breaths to determine the predominant breathing strategy utilized, i.e., relaxed, interrupted, or indeterminate. The respiratory pattern was predominantly interrupted below 6 mo of age and predominantly relaxed over 1 yr of age. Mixed patterns were observed in children 6-12 mo of age. The number of breaths that could not be classified (indeterminate) decreased with age. Respiratory frequency measured from the sample of breaths decreased with age and was accompanied by an increase in expiratory time. We conclude that a relaxed EEV develops at the end of the first year of life and may be related to changes in the mechanical properties of the chest wall associated with growth as well as changes in respiratory timing.

Analog-Digital Conversion↗
PubMed1989

Changes of time constants during infancy and early childhood.

We used respiratory inductance plethysmography to record tidal respiration in 27 healthy unsedated infants and children 1 mo to 8 yr of age during sleep. Rib cage and abdominal outputs were present at approximately equal gains and summed to obtain an estimate of volume. Flow-volume curves were generated from the uncalibrated volume signal and its flow derivative. Expiratory time constants (tau) were obtained by visually drawing a line through the linear portion of the expiratory flow-volume relationship. tau increased significantly during the first 10 mo of life. After 10 mo, the estimated rate of increase of tau for older children was less than 5% of the estimated initial rate and not significantly different from zero. Prolongation of tau was paralleled by an increase in expiratory time (Te), and no changes in Te/tau were observed in the first 2 yr of life. These changes in tau likely reflect the increase in lung compliance induced by rapid alveolar growth during infancy. After the first year, expiratory time constants appear to remain relatively constant and may be consistent with balanced changes in compliance and resistance beyond infancy.

Aging↗
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↗
PubMed1979

Muscle relaxation in mechanically ventilated infants.

We evaluated the effect of muscle paralysis on gas exchange and incidence of pneumothorax in 35 severely ill infants on mechanical ventilation. Pancuronium (0.1 mg/kg) was given repeatedly until spontaneous respirations ceased in infants with inadequate gas exchange with FIO2 greater than 0.60, or peak inspiratory pressure greater than 30 cm H2O, or who were breathing out of phase with the respirator. Of 27 infants who had an alveolar-arterial oxygen gradient greater than 300 torr before paralysis, AaDO2 improved by greater than 100 torr within one hour of paralysis in only two infants; it worsened in two infants within the same period. By six hours postparalysis, 12 of 27 infants had improved, five of whom had had a worsening AaDO2 before administration of pancuronium. Changes in oxygenation were unrelated to changes in arterial carbon dioxide tension in most infants. Peak transpulmonary pressures after paralysis were lower than during spontaneous breathing, and may explain the low incidence of pneumothorax (3 of 35) during paralysis. Since those who improved could not be distinguished by birth weight, gestational age, or diagnosis, pancuronium might be worthy of trial in a mechanically ventilated infant with severe lung disease who is at risk for pneumothorax.

Carbon Dioxide↗