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Biomedical subjects

M H Bryan

Publications and source records attributed to M H Bryan.

At least 55 records · Page 3Linked to original sources
PubMed1978

Functional immaturity of pulmonary irritant receptors and apnea in newborn preterm infants.

Absence of cough and gag reflexes has been noted in premature infants, but pulmonary irritant reflexes have not been studied. Irritant receptors respond to deflation, direct stimulation, or inhalation of irritant gases, resulting in an increased inspiratory effort. We have studied the responses of 28 intubated infants to direct bronchial mucosal stimulation with a fine catheter. Six of ten infants whose gestation was 35 weeks or more consistently showed a "mature" response, with an increase in inspiratory effort, while only one of 18 infants less than 35 weeks consistently showed this response. The premature infants showed variable responses. Fifty-eight of 93 stimulations produced an increased inspiratory effort, followed by marked slowing or apnea, while 20 stimulations resulted in slowing or apnea alone. These paradoxical responses to irritant stimulation may be related to immaturity of vagal myelination, and may be an important factor in the frequency of silent aspiration and apnea in premature infants.

Apnea↗
PubMed1977

The effect of gestational age on intralipid tolerance in newborn infants.

Tolerance to intravenously administered Intralipid was studied in 18 newborn infants aged 4 to 8 days and gestation 27 to 40 weeks. Clearance of a bolus injection of Intralipid from plasma was an exponential function following first order kinetics. Less mature infants had a clearance rate less than half that seen in more mature infants. Free fatty acids rose more rapidly and were maintained above fasting levels throughout the study in the immature group, probably because of impaired utilization of free fatty acid. The slower clearance of Intralipid in immature infants may be related to lipoprotein lipase deficiency secondary to their limited adipose tissue mass.

Clinical Trials as Topic↗
PubMed1977

Neonatal chest wall afferents and regulation of respiration.

We have studied two groups of eight preterm infants, relating chest wall afferent information to respiratory timing. Rib cage and abdominal motion were monitored by magnetometers and flow and tidal volume via a face mask. In the first group, studies were done in REM sleep when spontaneously occurring distortion of the rib cage occurred and a significant linear relationship between the rate of distortion of the chest wall and shortening of the inspiratory time (Ti) was found in all infants. Reduction in this distortion by the use of continuous positive airway pressure (CPAP) or continuous negative pressure at the body surface (CNeg) was associated with a significant (P less than 0.01) lengthening of Ti. Absence of changes in Ti when pressure was applied in quiet sleep suggested that lung volume or chemical changes were not involved. In the second group of infants we artificially generated the afferent inflow by using vibratory stimuli applied in one intercostal interspace and produced a significant (P less than 0.05) shortening in Ti. We suggest that the distortion of the rib cage in REM sleep generates afferent information from intercostal muscle spindles that is related to the rate of distortion and this, via a supraspinal reflex, inhibits phrenic motoneuron discharge. It may then be of importance in the etiology of apneic episodes in these infants. Applied pressure may be of benefit because it reduces an inhibitory afferent inflow.

Afferent Pathways↗
PubMed1977

Mechanics of the rib cage and diaphragm during sleep.

The pattern of motion of the rib cage and abdomen/diaphragm was studied in three normal subjects during sleep. Sleep state was monitored by electroencephalograph and electrocculograph. Intercostal electromyographs (EMG's) were recorded from the second interspace parasternally. Abdominothoracic motion was monitored with magnetometers and these signals calibrated by isovolume lines either immediately before going to sleep, or if there was movement, on awakening. Respiration was recorded using a jerkin plethysmograph. In the awake subject in the supine position, the rib cage contributed 44% to the tidal volume and had essentially the same contribution in quiet sleep. However, in active or rapid eye movement sleep the rib cage contribution fell to 19% of the tidal volume. This was accompanied by a marked reduction in the intercostal EMG. With the subject in the upright position the rib cage appears to be passively driven by the diaphragm. However, the present data suggest that active contraction of the intercostal muscles is required for normal rib cage expansion in the supine position.

Abdomen↗
PubMed1976

A simple method of measuring total respiratory system compliance in newborn infants.

A new method of measuring the static compliance of the respiratory system in the awake, non-paralysed infant is described. The static compliance was measured by this method in 12 healthy premature infants aged from 1 day to 30 weeks. In addition, the dynamic compliance was measured by the oesophageal balloon technique. The static compliance was significantly higher than the dynamic, and this difference was related to the respiratory rate. These infants therefore demonstrated frequency dependence of dynamic compliance.

Compliance↗
PubMed1976

The effect of Intralipid on the estimation of serum bilirubin in the newborn infant.

After noting rises in measured serum billirubin in premature infants undergoing parenteral nutrition, a series of experiments was designed to ascertain the effect of the presence of Intralipid on the actual laboratory analysis. It has been shown that the most commonly used spectrophotometric analysis of bilirubin and the estimation of direct bilirubin by micromethods are affected by the presence of Intralipid in the specimens. Centrifugation of the blood samples at 15,000 rpm for 10 minutes and analysis of the aqueous layer overcomes, in both methods, the interference and error introduced by the presence of Intralipid chylomicrons in patient sera. Alternatively spurious bilirubin measurements due to hyperlipidemia may be avoided by using a bilirubinometer equipped with a filter which eliminates the effect of Intralipid interference.

Bilirubin↗
PubMed1976

Effect of premature delivery on the maturation of the Hering-Breuer inspiratory inhibitory reflex in human infants.

The Hering-Breuer inspiratory inhibitory reflex was studied serially in a group of premature infants and in a group of term infants in the immediate postnatal period. The premature infants had a stronger inspiratory inhibitory reflex than did the term infants at birth; this reflex decreased with maturation of the premature. Development in the extrauterine environment significantly delayed the rate of disappearance of this reflex. This may indicate that premature delivery retards the neurologic maturation of the human infant. The term infant showed no change in the activity of the inspiratory inhibitory reflex in the first five days of life.

Female↗
PubMed1976

Respiratory load compensation in infants.

We have studied the respiratory compensation for elastic loads in 15 term and preterm infants. Elastic loads, approximately equal to the infant's effective elastance, were applied to the airway for five breaths while tidal volume and mask pressure were monitored. Motion of the rib cage and abdomen were monitored simultaneously with magnetometers. The studies were done both in active or REM sleep and in quiet or non-REM sleep. During quiet sleep the load immediately reduced the tidal volume by about 50% but a progressive increase in tidal volume occurred over the next four loaded breaths. During active sleep load compensation was disorganized with respect to both tidal volume and frequency, and compensation was significantly less. Active sleep was also characterized by marked rib cage distortion. We suggest that during active sleep there is tonic inhibition of the intercostal muscles, allowing the diaphragm to distort the rib cage. This distortion impairs load compensation by a direct mechanical effect and indirectly by initiating an intercostal-phrenic reflex.

Abdomen↗
PubMed1975

A new method of evaluating the chemosensitivity of the respiratory center in children.

Decreased ventilatory response to carbon dioxide is often present in lung disease. This can be due to a reduction in the output of the respiratory center or an inability of the respiratory pump to respond to a normal output because of the size or impedence of the pump. To separate these mechanisms we have measured the isometric force developed by the respiratory muscle during brief airway occlusion, by measuring the pressure generated at 100 msec (Pm100). We studied 43 subjects ranging in age from 6 to 50 years, and nine neonates. We found a linear rise of Pm100 with rising PAco2 during carbon dioxide rebreathing maneuvers. Our results also show that although there are wide variations in slopes of Pm100 to carbon dioxide tension (SPm100/PAco2) between individuals, in a given subject this slope remains constant even following repeated studies. It also remains constant for age and size, indicating that the neuromechanical output of the respiratory apparatus does not change with growth. In contrast the ventilatory response either assessed as Ve/PAco2 or Vt/PAco2 depended on age and lung size. The results suggest that throughout growth, comparison of Pm100/PAco2 and Ve/PAco2 can distinguish between abnormalities of neuromuscular output from other causes of ventilatory impairment.

Adolescent↗