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Biomedical subjects

A C Bryan

Publications and source records attributed to A C Bryan.

At least 91 records · Page 5Linked to original sources
PubMed1978

Developmental pattern of muscle fiber types in human ventilatory muscles.

Premature infants tolerate respiratory loads poorly. This may reflect incomplete development of the ventilatory muscles (VM) causing poor resistance to fatigue. To study the developmental pattern of human VM, 31 postmortem specimens of diaphragm and intercostal muscles were obtained. Individual muscle fibers were classified as type I (slow-twitch, high-oxidative) or type II (fast-twich, low-oxidative) using histochemical staining methods for myofibrillar adenosine triphosphatase (M-ATPase) (pH 10.30) and nicotinamide adenine dinucleotide (NADH) tetrazolium reductase. In the diaphragm, premature infants (less than 37 wk gestation) had only 9.7 +/- 1.3% type I fibers, full-term newborns 25.0 +/- 1.1%, and older subjects (greater than 2 yr of age) 54.9 +/- 1.3%. There was no further increase after 8 mo postpartum. In the intercostal muscles, premature infants had only 19.0 +/- 4.8% type I fibers, full-term newborns 45.7 +/- 1.3%, and older subjects 65.2 +/- 2.6%. There was no further increase after 2 mo postpartum. These findings suggest the ventilatory muscles of newborn infants are more susceptible to fatigue than those of older subjects. This may contribute significantly to respiratory problems in the neonate.

Adenosine Triphosphatases↗
PubMed1978

VA/Q inhomogeneity and AaDO2 in man during exercise: effect of SF6 breathing.

Pulmonary gas exchange was studied in five normal subjects both at rest and during moderate steady-state exercise on a bicycle ergometer while breathing a) room air and b) a mixture of 20.9% O2-balance sulfur hexafluoride (SF6). The alveolar-arterial oxygen pressure differences (AaDO2) widened significantly from rest to exercise. Breathing the O2-SF6 mixture reduced the AaDo2 significantly from 10.9 to 4.2 Torr at rest and from 15.5 to 10.1 Torr during exercise (P less than or equal to 0.01). There were no concurrent changes in metabolism, cardiac output, or heart rate during the SF6 breathing. Possible changes in the anatomic shunt fraction, alveolar-end-capillary equilibration, or the distribution of blood flow cannot account for these observations. We conclude that the AaDO2 increase during exercise reflects an inhomogeneity of ventilation-perfusion ratios (VA/Q) most probably arising within regions of the lung (intraregional inhomogeneity) rather than between regions (interregional inhomogeneity).

Adult↗
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

Contributions of changing rib cage--diaphragm interactions to the ventilatory depression of halothane anesthesia.

The ventilatory response to CO2 was subdivided into that portion due to increasing rib cage expansion, and that due to increased diaphragmatic descent. Five children were studied, awake, and anesthetized with halothane, 0.8-0.9%. During anesthesia there was a 67+/-8% reduction (mean+/-SE) in the slope of the response of overall ventilation to an increase in CO2. This was primarily due to an 89+/-8% reduction in the recruitment of rib cage ventilation (P less than .001). There was no significant change in the slope of the diaphragmatic response (anesthetized value 19+/-21% less than control), although the response curve was shifted to the right so that a higher CO2 concentration was needed to stimulate a given level of diaphragmatic excursion. Additional measurements of the inspiratory intercostal electromyogram in three adult subjects documented a rapid, profound depression of intercostal activity with halothane anesthesia that was associated with a marked decrease in rib cage ventilation. The authors conclude that a major component of the ventilatory depression associated with halothane anesthesia results from the preferential suppression of intercostal muscle function with relative sparing of diaphragmatic activity.

Adolescent↗
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

Relationship of lung recoil to lung volume and maximum expiratory flow in normal children.

Thirty-one normal children, aged 6--18 yr, were studied by measurements of static lung volumes, static expiratory pressure-volume (PV) curves, and maximum expiratory flow-volume (MEFV) curves. A theoretical standard volume was used to compare children of differing size and this showed that total lung capacity (TLC) is also a valid standard volume. The shape of the PV curve was found to change so that static elastic recoil at a fixed proportion of TLC was higher in older than in younger children. This was also true of static recoil at functional residual capacity (FRC) and an associated increase in the ratio of FRC to TLC was interpreted as evidence for increase in outward recoil of the chest wall during childhood. Since static recoil at "closing capacity" (CC) remained constant, a decrease in the ratio of CC to TLC was quantitatively explained by the PV shift during childhood. Although maximum expiratory flow at various lung volumes increased in constant proportion to TLC, "upstream conductance" decreased relative to TLC. It was concluded that maturation of the respiratory system is disproportionate in several features during childhood and that these disproportions are likely to be even more prominent during infancy and early childhood.

Adolescent↗
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↗
PubMed1977

Volume dependence of instantaneous time constants derived from the maximal expiratory flow-volume curve. A new approach to the analysis of forced expiration.

A simple expansion of the information in the maximal expiratory flow-volume curve was used to measure the convexity to the volume axis of maximal expiratory flow-volume curves produced by 11 asymptomatic smokers and 11 asymptomatic nonsmokers. The ratio of remaining volume to maximal flow was equal to the product of upstream resistance and chord compliance. This "instantaneous time constant" increased more near residual volume in the smokers. Using this method, plethysmographically obtained maximal expiratory flow-volume curves were more sensitive than spirometrically obtained maximal expiratory flow-volume curves. This method compared favorably with moment analysis and helium response of maximal expiratory flow as a separator of asymptomatic smokers and nonsmokers.

Adult↗
PubMed1977

Ventilatory muscle endurance training in normal subjects and patients with cystic fibrosis.

Ventilatory muscles can become fatigued, and this can contribute to respiratory failure. Patients with chronic obstructive lung disease may benefit from improving their ventilatory muscle endurance to improve resistance to fatigue. Ventilatory muscle endurance was measured in 30 normal subjects and 55 patients with cystic fibrosis by finding the highest level of normocapnic hyperpnea that could be sustained for 15 min. Subjects with cystic fibrosis had 36 per cent higher ventilatory muscle endurance than normal subjects, reflecting the chronic training stress of breathing against increased respiratory loads. Four normal subjects and 4 subjects with cystic fibrosis participated in a specific ventilatory muscle endurance training program consisting of 25 min per day of maximal normocapnic hyperpnea 5 days per week for 4 weeks. The cystic fibrosis patients who trained improved their ventilatory muscle endurance by 51.6 per cent, whereas the normal subjects who trained showed a 22.1 per cent increase in ventilatory muscle endurance. Seven subjects with cystic fibrosis participated in a 4-week physical activity training program consisting of at least 1.5 hours per day of intensive swimming and canoeing at summer camp. They increased their ventilatory muscle endurance by 56.7 per cent. There were no other pulmonary function changes. Ventilatory muscle endurance can be readily improved in cystic fibrosis equally well by specific ventilatory muscle endurance exercise.

Adolescent↗
PubMed1977

Pulmonary function abnormalities in symptom-free children after bronchiolitis.

Twenty-three children less than 18 months old who had clinical and radiological evidence of bronchiolitis and remained symptom-free thereafter were studied to determine pulmonary function ten years later. Abnormal Pao2, Viso V and RV/TLC ratio were found in the majority of subjects, and 31.3% had abnormalities in all three tests; four and one-half percent had exercise-induced bronchospasm. These changes indicate a residual parenchymal or airways lesion following bronchiolitis.

Asthma↗
PubMed1977

Nitrogen washout studies in acute mountain sickness.

We assessed the severity of Acute Mountain Sickness (A.M.S.), indices of pulmonary gas exchange and nitrogen washout curves in healthy volunteers acutely exposed to high altitude. Symptoms of A.M.S. ranged from malaise to vomiting with intractable headache. The slope of phase III of the nitrogen washout curve increased most in those subjects with the most severe A.M.S. and who were most hypoxemic. The sickest subject also had the greatest increase in (A-a)DO2 and the largest increase in the slope of phase III. These abnormalities in gas exchange and nitrogen washout curves in the subjects with the most marked A.M.S. suggest that the manifestations of cerebral and pulmonary dysfunction at altitude develop simultaneously, although not necessarily by identical mechanisms.

Adolescent↗
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

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

Transit time analysis of the forced expiratory spirogram in growth.

In the search for more sensitive indicators of airway obstruction Fish et al. (Am. Rev. Respirat. Diseases 109: 700, 1974) have proposed a transit time analysis of the forced expiratory spirogram. In this method the forced vital capacity (FVC) is divided into volumes of air and each volume is assigned a transit time; the nature of the FVC can be described by the transit times' mean, standard deviation, and index of skewness. In a group of 48 healthy nonsmoking subjects between the ages of 9 and 22 yr we found that all three quantities decreased with increasing age. This demonstrates an improvement in the function of the peripheral airways with lung growth. In contrast to the increase in flow rates with lung growth, none of this improved function can be attributed to increased lung volume.

Adolescent↗
PubMed1976

An intercostal-phrenic inhibitory reflex in human newborn infants.

An effect of phasic distortion of the rib cage on inspiratory time was studied in thirty sleeping newborn infants. Distortion was produced by both manual compression of various rib cage diameters, and by occluding the airway at functional residual capacity, allowing diaphragmatic contraction to alter rib cage shape. With rapid distortion produced by these maneuvers, inspiration was often terminated prematurely. The effect was dependent upon there being a rapid rate of distortion, and was most readily elicited when inward motion involved the lower lateral rib cage. The results indicate a potent inspiratory inhibitory reflex, originating most probably from the spindles of intercostal muscles. This reflex acts to decrease tidal volume and ventilation when rates of rib cage retraction are high during spontaneous breathing.

Airway Obstruction↗