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Biomedical subjects

B T Thach

Publications and source records attributed to B T Thach.

At least 91 records · Page 5Linked to original sources
PubMed1980

Upper airway patency in the human infant: influence of airway pressure and posture.

We have determined the influence of transmural pressure and neck posture on upper airway patency in infants after death. In natural resting postures, the airway was closed at transmural pressures not exceeding those normally seen during peak inspiratory airflow in the living infant, implying that a neuromuscular mechanism is necessary to maintain airway patency during life. Neck flexion raised closing pressure, making the airway more susceptible to collapse, whereas neck extension lowered closing pressure, making the airway more resistant to collapse. When the angle of flexion was kept constant, closing pressure was not significantly altered by turning the head or positioning the infant prone. Pressures above the corresponding closing pressure were required to reopen the closed airway, suggesting that the walls of the closed airway tended to adhere and implying that surface forces can impose an added load to airway-maintaining musculature during obstructive apnea in the living infant.

Humans↗
PubMed1980

A self-retaining nasal flowmeter for preterm infants.

A nasal flowmeter suitable for preterm infants is described. It is made from a commercially available nasal cannula and 400-mesh stainless steel screen. Low dead space (0.35 ml) and low resistance (1.3 cmH2O . 100 ml-1 . s) are advantages. Light weight and compact design have eliminated the need for extensive restraint of the subject. Also, the investigator need not hold the flowmeter in place. These features make accurate measurement of respiratory airflow and tidal volume possible during polygraphic monitoring studies lasting several hours.

Humans↗
PubMed1980

Control of genioglossus muscle inspiratory activity.

Tonic and phasic inspiratory genioglossus (GG) electromyographic activity (EMG) was recorded from 13 anesthetized rabbits during unstimulated breathing. Integrated GG EMG peaked earlier in inspiration and presented a more rounded contour than integrated diaphragmatic (DIA) EMG. Spontaneous augmented deep inspirations (sighs) showed a biphasic pattern in both GG and DIA EMGs. Hyperventilation abolished phasic inspiratory activity in the GG before the DIA, suggesting that the GG has a higher CO2 apneic point. Hypercapnia increased both EMGs; however, GG EMG increased more, as a percent of base line, than did DIA EMG. Oxygen breathing decreased GG more than DIA EMG; sodium cyanide injection and brief nitrogen breathing increased GG more than DIA EMG; carotid body denervation abolished these responses. Vagotomy abolished the Hering-Breuer inflation-inhibition reflex in both muscles, and tactile, visual, and auditory stimulation increased GG more than DIA EMG. Thus, the GG responses to chemoreceptor input and to nonspecific respiratory stimuli are qualitatively similar but quantitatively different from DIA responses. The relevance to mixed and obstructive apnea is discussed.

Acoustic Stimulation↗
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

A neuromuscular mechanism maintaining extrathoracic airway patency.

The ability of the extrathoracic airway (ETA) to remain open when exposed to negative pressure was investigated in rabbits. Postmortem, the ETA collapsed at -6.3 +/- 0.6 cmH2O whereas, during airway occlusion maneuvers in lightly anesthetized animals, it remained patent at pressures as low as -80 cmH2O. This discrepancy suggested that a neuromuscular mechanism maintains ETA patency. Four findings indicated that the genioglossus and geniohyoid muscles, which pull the tongue and hyoid bone anteriorly, help maintain ETA patency: 1) anterior movement of the hyoid bone increased the negative pressure at which the ETA collapsed postmortem, 2) ETA closure during occluded inspirations occurred after 12th nerve section abolished electromyographic activity in these muscles and 3) after deep anesthesia depressed such activity, and 4) closing pressure was linearly related to peak integrated electromyograms of the two muscles. After 12th nerve section, ETA closing pressure became more negative with progressive asphyxia greatly exceeding postmortem closing pressure, which suggests that other muscles also help maintain ETA patency. Blood gas tensions, respiratory system mechanoreceptors, and depth of anesthesia appear to influence genioglossus and geniohyoid activity.

Anesthesia↗
PubMed1978

Maturation of respiratory control in unanesthetized newborn rabbits.

The maturation of control of breathing was studied in unanesthetized rabbit pups breathing room air in a body plethysmograph during the first 8 postnatal days. Measurements include pulmonary ventilation (VE), tidal volume (VT), inspiratory (TI) and total breathing cycle (Ttot) durations, TI/Ttot, mean inspiratory flow (VT/TI), and tracheal pressure developed by the inspiratory muscles 0.1 and 0.2 s after the onset of inspirations with airways occluded at functional residual capacity (P0.1 and P0.2). All of the above variables increased progressively from the 1st to the 8th day, except for P0.1, P0.2, and TI/Ttot which remained constant. The constancy of TI/Ttot implies that the increase in VE with age was due entirely to increased VT/TI. The constancy of P0.1 and P0.2 implies that the increase in VT/TI with age was due to decreased "effective" impedance of the respiratory system. The latter probably mainly reflects increased compliance and decreased flow resistance with growth. The results also show that during the first 8 days of life there is a progressive shift to the right in the VT vs. TI relationship.

Aging↗
PubMed1977

Respiratory patterns during progressive asphyxia in newborn rabbits.

During acute progressive asphyxia an abrupt transition occurs from regular respiratory efforts to primary apnea and gasping. To study this transition we measured inspiratory duration (TI), expiratory duration (TE), maximal inspiratory tracheal pressure (Pmax), electromyographic activity (EMG) of different muscle groups, and the electrocorticogram (ECoG) of 3- to 5-day-old rabbits following airway occlusion at functional residual capacity (FRC). The onset of primary apnea was associated with other central nervous system events as indicated by decerebrate posture and maximal EMG activity which were followed by relaxation, loss of EMG activity, and an isoelectric ECoG. Indices of inspiratory drive (Pmax and Pmax/TI) were preserved or accentuated following primary apnea despite a reduction of overall respiratory activity (frequency X Pmax). The onset of primary apnea appears to be due to interruption of the respiratory cycling controls rather than failure of the respiratory center which regulates inspiratory force. Gasping appears to be linked with progressive changes in respiratory patterns which are observed prior to primary apnea. These findings do not support the concept of a "gasping" center.

Airway Obstruction↗
PubMed1976

Quantitative assessment of oral tactile sensitivity in pre-term and term neonates, and comparison with adults.

The tongues of 34 infants between 31 and 40 weeks estimated gestational age were stimulated with filament esthesiometers. Stereotyped ipsilateral movements of the tongue were elicited in all infants. An assessment of tactile sensitivity based on this reflex is minimally affected by infant activity state and habituation to repeated stimulation. Small pre-term infants (31 to 35 weeks gestation) and infants born near term (37 to 40 weeks gestation) were more sensitive to tactile stimulation than an intermediate group (35 to 37 weeks gestation). In infants followed longitudinally, a transient decrement in sensitivity occurred at two weeks postnatal age. The tactile sensitivity in 12 adults (as measured by their correct reports of stimulus location) was far greater than the sensitivity of the infants.

Adult↗
PubMed1976

Effect of ether on control of rate and depth of breathing in newborn rabbits.

The effect of ether anesthesia on Hering-Breuer inflation reflexes of newborn rabbit pups was investigated. Studies were done at a level of anesthesia at which an apneustic pattern of respiration is seen in vagotomized animals. The hypothesis that increase in vagal influence on respiratory frequency is accompanied by increase in influence on contractile force of the inspiratory muscles was tested. Two aspects of the Hering-Breuer reflex, breath duration and airway pressure developed with an elastic load, were evaluated simultaneously. This was done by performing airway occlusions at FRC--the results expressed as percent slowing on occlusion and as effective elastance (E'rs). The animals were studied with and without anesthesia, before and after vagotomy. Anesthesia resulted in a marked increase in vagal influence on inspiratory duration (34% increase) and on total breath duration (36% increase). In contrast E'rs was decreased (20%) after anesthesia whereas passive elastance was slightly increased. The vagal contribution to E'rs was essentially the same before and after anesthesia (36-38%). Thus ether anesthesia increases one aspect of the Hering-Breuer reflex without changing the other. These findings are likely due to depression of the central nervous system rather than due to peripheral effects of ether.

Airway Obstruction↗
PubMed1976

Maturational changes of effective elastance in the first 10 days of life.

The effective elastance of the respiratory system (E'rs) is a measure of its ability to resist a change in tidal volume under conditions of changing elastic loads. E'rs was measured while subjects breathed air and 2% CO2 and 4% CO2 in air in two groups of premature infants of different gestational ages at 1 day 3-4 days, and 7-10 days of age. E'rs was shown to decrease with increasing maturation and was independent of changes in control tidal volume. The decrease of E'rs with increased gestational age could be accounted for by differences in calculated thoracic gas volumes in all but one instance, where E'rs was lower in one group on the 3rd day of life. The activity of the Hering-Breuer reflex, as measured by the degree of slowing of inspiratory time after occlusion at FRC, has been previously reported to be normal to increased in similar infants. This suggests that differences related to size account for most of the maturational changes of E'rs in newborns.

Age Factors↗
PubMed1976

Maturational effects on respiratory responses to carbon dioxide in premature infants.

The respiratory responses of 18 premature infants to breathing steady-state levels of carbon dioxide were quantified by conventional minute ventilation measurements and by measuring the pressure generated after end-expiratory airway occlusions. Since no flow or volume changes occur following airway occlusion, the CO2 response obtained by this measurement is independent of vagal stretch receptor influence and mechanical changes in the lungs. When studied at 3-4 days of postnatal age, a group of 29-32-wk gestation infants had a mean slope of ventilatory response to CO2 of 10.8 +/- 5.6 ml-min-1-kg-1-mmHg-1 as compared to 53.5 +/- 10.8 ml-min-1-kg-1-mmHg-1 (P less than 0.005) for a group of 33-36 wk. When these infants were restudied at 7-10 days of age, the slopes were 21.6+/- 6.6 and 58.4 +/- 10.6 ml-min-1-kg-1-mmHg-1 (P less than 0.01), respectively. The mask pressure response paralleled minute ventilation. We conclude that the increase in ventilatory response to carbon dioxide seen with maturation is not due only to changing mechanical features of the lungs, but to increased sensitivity of respiratory centers to carbon dioxide.

Age Factors↗
PubMed1976

Sighing in newborn human infants: role of inflation-augmenting reflex.

To investigate the reflex mechanisms of sighs (spontaneous large breaths) (VT greater than 2 X control VT) in infants, recordings of respiratory flow and tidal volume (VT) were made during sleep. The frequency of sighs was greater at 1 than at 5 days of age, while respiratory frequency and control VT did not change. Most sighs (93%) had a biphasic pattern of inspiratory flow characterized by an inspiratory duration nearly twice that of control breaths, with an abrupt change in flow rate halfway through inspiration. Interruption of ventilation (3-7 s of airway occlusion) appeared to generate a stimulus for biphasic sighs, since sighs occurred during the first breath after termination of airway occlusion more frequently after long than after brief occlusions. However, a biphasic inspiratory pattern in airway pressure was rarely observed while the airways were occluded, regardless of occlusion duration. This suggests that increase in lung volume during the initial part of the biphasic inspiration following occlusion is a stimulus for the second part. Thus the underlying reflex mechanism of sighs in human infants appears to be the same as occurs in the so-called Head's paradoxical response to lung inflation.

Airway Obstruction↗
PubMed1976

Respiratory response to airway occlusion in infants: sleep state and maturation.

The progressive respiratory response to occlusion of the airway at FRC was measured in a group of full-term and premature human infants. The sleep state of the full-term infants was shown to affect the response primarily through variations in the phase of thoracic and abdominal movements. The weakest responses were seen in those infants who demonstrated parodoxical respiration prior to occlusion. Most infants developed paradoxical respiratory movements after occlusion, but this did not affect the strength of the load-compensatory response. An increase in response related to both gestational and postnatal age was observed. This increase could not be accounted for by variations in the amount of paradoxical and in-phase respiration and thus may represent an increase in the sensitivity of infants to chemical stimuli with maturation.

Aging↗
PubMed1976

Behçet syndrome with "aphthous colitis".

A 46-year-old man with Behçet syndrome and a long history of recurrent bouts of colitis was studied by sigmoidoscopy, barium enema x-ray film, and colon biopsy. A nonspecific colitis characterized by shallow mucosal ulcerations and submucosal mononuclear infiltration in the absence of meaningful roentgenolographic changes was seen. A histopathological comparison was made between the oral and colonic lesions. The aphthous colitis appears, therefore, to be a colonic manifestation of Behçet syndrome, differing from typical chronic nonspecific ulcerative colitis in terms of clinical course, severity, and histologic appearance. The simultaneous occurrence of Behçet syndrome and inflammatory disease of the colon was discussed in terms of the differential diagnosis of colitis.

Adult↗
PubMed1975

Experimental meconium aspiration: Effects of glucocorticoid treatment.

An animal model of meconium aspiration was developed to determine the efficacy of glucocorticoids in its treatment. Rabbit pups were made to aspirate either meconium or saline prior to the onset of respiration. Cortisol was administered in a random, blind fashion. Slight decrease in respiratory rate and less severe histopathologic changes in the lungs were seen in corticosteroid-treated animals. Survival was significantly decreased, without definite cause, in the glucocorticoid-treated animals whether or not they had aspirated meconium. Because of this decreased survival and the relatively insignificant improvement in clinical course and histopathology found with glucocorticoid treatment, we cannot recommend cortisol for the treatment of meconium aspiration.

Animals↗