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Biomedical subjects

A R Stark

Publications and source records attributed to A R Stark.

53 records · Page 3Linked to original sources
PubMed1982

High-frequency ventilation does not affect pulmonary surfactant, liquid, or morphologic features in normal cats.

Effects on pulmonary surfactant, liquid, and morphologic features were compared in normal cats ventilated with conventional and high-frequency ventilators for 4 h. Normal blood gases and comparable mean airway pressures (approximately 7 cm H2O) were maintained with the two techniques. Peak tracheal pressure during conventional ventilation (16.5 +/- 0.9 cm H2O) was significantly greater than that during high-frequency ventilation (8.5 +/- 1.1 cm H2O, p less than 0.00001). Pressure-volume curves were identical in control, conventional, and high-frequency ventilation groups. There was no effect on pulmonary lavage surfactant, whether measured functionally or biochemically. Likewise, lung liquid and morphologic aspects examined by both light and electron microscopy were not affected. These results provide evidence that high-frequency ventilation under these conditions does not cause pulmonary damage.

Animals↗
PubMed1981

Diabetic nephropathy and perinatal outcome.

We studied the effect of diabetic nephropathy on the course of pregnancy, perinatal outcome, and infant development and determined the influence of pregnancy on maternal hypertension and renal function. Maternal proteinuria usually increased during pregnancy (greater than 3 gm/24 hours in 69%), and hypertension was present by the third trimester in 73%. The degree of proteinuria correlated with diastolic pressure and creatinine clearance. After pregnancy, proteinuria declined in 65% of the mothers, hypertension was absent in 43.5%, and the expected rate of fall in creatinine clearance was not accelerated. Among 35 patients, abortion occurred spontaneously or was performed electively in 25.7%, and 71% of the remainder underwent delivery before 37 weeks. Birth weight was related to maternal blood pressure and creatinine clearance. Neonatal morbidity was common, but the perinatal survival rate was 89%. Infants seen at follow-up without congenital anomalies had normal development at 8 to 36 months of age. We concluded that perinatal outcome has significantly improved for diabetic women with nephropathy.

Adult↗
PubMed1981

Recovery of airway patency after obstruction in normal infants.

We examined the characteristics of spontaneous restoration of airflow after airway obstruction during neck flexion in normal sleeping infants. In 22 of 27 episodes of complete airway obstruction in 5 of 8 infants, there was some resumption of airflow, although the angle of neck flexion was maintained. The airway reopening was usually delayed, after 1 to 3 obstructed inspiratory efforts, and usually without evidence of behavioral arousal. The time course of this delayed response suggested chemoreceptor mediation. In those trials where arousal was observed, airflow resumed immediately. Our observations suggested that activation of the genioglossus and other airway-maintaining muscles leads to airway reopening neck flexion in infants and that tonic genioglossus activity maintains airway patency. These observations represented the first description of restoration of airway patency after airway occlusion in infants.

Adult↗
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↗
PubMed1979

Spontaneous neck flexion and airway obstruction during apneic spells in preterm infants.

Forty-three apneic episodes were observed in eight preterm infants, four of whom had a history of spells. Measurements of expiratory airflow and respiratory effort indicated that 36 of 43 spells were mixed, consisting of central apnea preceded or followed by airway obstruction. The episodes occurred more frequently during periods of spontaneous neck flexion. This association can be related to previous studies indicating that neck flexion interferes with neuromuscular regulation of pharyngeal patency and can produce intermittent airway obstruction. Our observations suggest that airway obstruction may be an important factor in the pathogenesis of apnea in certain preterm infants.

Airway Obstruction↗
PubMed1979

Lung volume changes, occlusion pressure and chest wall configuration in human infants.

UNLABELLED: Measurements of respiration were compared in normal, full term and premature infants before and after application of 5 cm H2O continuous negative pressure (CNEG) around the body below the neck. Mean minute ventilation in the full term infants decreased when CNEG was applied, secondary to a decrease in respiratory rate, with tidal volume relatively unchanged. The premature infants showed no consistent ventilatory response to CNEG. There were variable changes in occlusion pressure at increased lung volume. Observation with rib cage and abdomen anterior-posterior (A-P) magnetometers showed that the increase in end-expiratory lung volume was accounted for largely by expansion of the rib cage so that the configuration of the diaphragm and its mechanical advantage were maintained. These results suggest that the diaphragm is the major determinant of mask occlusion pressure in infants. SPECULATION: The effects of increased lung volume on the configuration of the chest wall may relate to the success of continuous distending pressure in the treatment of respiratory disorders in infants, including apnea of prematurity.

Humans↗
PubMed1979

Prolonged expiratory duration with elevated lung volume in newborn infants.

UNLABELLED: End-expiratory lung volume increased 17.5 +/- 5.4 ml (mean +/- SD) in full term infants and 7.7 +/- 2.1 ml in premature infants when 5--7 cm H2O continuous negative pressure (CNEG) was applied around the thorax. In the full term infants, respiratory rate decreased from 52--43 min-1 (P less than 0.001), mean inspiratory duration (ti) was unchanged, and mean duration of expiration (te) increased from 0.62 +/- 0.14 (SE)-0.84 +/- 0.22 sec (P less than 0.001) after application of CNEG. Te of occluded efforts on CNEG was also prolonged (P less than 0.005), although less than te of spontaneous breaths on CNEG (P less than 0.005). Te increased in four of eight premature infants when CNEG was applied. We conclude that phasic vagal feedback regulates Ti and te is controlled by tonic vagal activity. SPECULATION: Premature infants may have an optimum functional residual capacity (FRC) which can be achieved with continuous distending pressure, resulting in regularization of respiration.

Humans↗
PubMedDate not supplied

Increased muscularization of small pulmonary arteries in preterm infants of diabetic mothers: a morphometric study in noninflated, noninjected, routinely fixed lungs.

We attempted to identify a structural correlate of the pulmonary hypertension observed in newborn infants of diabetic mothers (IDM) by performing a morphometric analysis of pulmonary arteries at the transition of terminal to respiratory bronchiolus (TRB) in postmortem lungs of 20 IDM and 14 control infants. Although there was no readily apparent microscopic difference between the lungs of newborn IDM and controls, the degree of muscularization, as measured by mean medial area (MMA) of 10 TRB arteries, was significantly greater in preterm IDM (gestational age < or = 37 weeks) than in age-matched controls (502 versus 341 microns 2; P = .0038). Among infants of gestational age > 37 weeks, there was no significant difference between MMA in IDM (508 microns 2) and MMA in controls (598 microns 2). These findings point at an accelerated muscularization of the TRB arteries in IDM, apparent early in the third trimester. The pathogenesis of this hypermuscularization is not understood, but smooth muscle growth promoters such as insulin may play a role. The abnormal timing of TRB artery muscularization could be a manifestation of the basic disturbance in development that contributes to the pulmonary hypertension observed in newborn IDM and to the respiratory difficulties commonly experienced by these infants.

Bronchi↗
PubMedDate not supplied

Apnea monitors--1982.

Breathing cessation happens frequently among infants in neonatal intensive care units, particularly among premature infants. Most instances are benign respiratory pauses; however, some are significant apneic spells--breathing pauses longer than 20 sec or associated with bradycardia or cyanosis. These apneic spells must be recognized promptly and the infants stimulated to breathe to avoid brain damage or death from hypoxia. Apnea monitors now in use can detect some types of apneic spells, but not those in which airflow has been occluded but breathing motions continued. Monitors that measure air flow have been developed, but are not yet perfected for clinical use. An acoustic air-flow monitor has been developed that registers apneic spells more reliably than monitors now in use, and does not affect the infant's normal breathing.

Apnea↗