Search PubMed⌕ Search

Biomedical subjects

B T Thach

Publications and source records attributed to B T Thach.

At least 73 records · Page 4Linked to original sources
PubMed1984

Frequency and significance of swallowing during prolonged apnea in infants.

To better document and describe the phenomenon of swallowing during apneic spells, we compared the frequency of swallowing during epidsodes of prolonged apnea with nonapnea control periods in 9 preterm and 1 term infant. Infants with a history of idiopathic prolonged apnea were studied for 2 to 3 h by monitoring, electrocardiogram, nasal air flow, oral CO2, abdominal respiratory movements, chin electromyogram, pharyngeal pressure, and pH. In 7 of the infants, additional observations were performed without the intrapharyngeal recording devices. One or more swallows occurred during 75% of the 100 spells observed. Swallows were far more common during apneic spells than during nonapnea control periods, and were more frequent during mixed and obstructive apnea than during central apnea (p less than .01). Asphyxia, regurgitation, and the intrapharyngeal recording devices did not appear to cause the increased frequency of swallows during apneic spells. Swallowing was temporally related to spontaneous recovery from apnea, with a swallow usually preceding recovery by 5 to 6 s. During apneic spells, we observed that swallows were often associated with a brief obstructed inspiratory effort ("swallow-breath"), a normal component of nonfeeding swallows in infants. These swallow-breaths were interspersed with higher amplitude "ordinary" obstructed breaths during apneic episodes. Thus, 2 distinctly different types of obstructed inspiratory efforts were identified during mixed and obstructive apnea episodes in infants. The sequence of events during apneic spells in the term and preterm infants was similar.

Apnea↗
PubMed1984

Regulation of upper airway maintaining muscles during progressive asphyxia.

The electromyographic activity of an upper airway muscle (genioglossus, GG) and the diaphragm were studied in 10 adult and three young anesthetized rabbits during progressive asphyxia induced by airway occlusion. Results were similar for both age groups. Peak inspiratory activity of GG muscle increased more than that of the diaphragm during both the hyperpnea and gasping (P less than 0.05). The increase in GG activity during gasping was not significantly different from that during hyperpnea even though an important stimulus, arousal, was absent during gasping. During end stage asphyxia, as the strength of gasps grew weaker, the rate of loss of GG muscle activity was greater than that of the diaphragm. However, GG activity remained greater than that of the diaphragm at the time of the last spontaneous gasp. As asphyxia progressed, inspiratory duration and the inspiratory contour of integrated electromyogram activity of both muscles changed. These data indicate differences in the control mechanism of the genioglossus and diaphragm during acute severe asphyxia. Increased upper airway muscle activity seen during gasping should help preserve upper airway patency and facilitate autoresuscitation by gasping. These observations of coordinated changes in timing and activity of two functionally different respiratory muscles support the concept that gasping is a highly organized function of the respiratory centers.

Airway Resistance↗
PubMed1984

Interferences with potentiometry of CO2 in the Ektachem 400 Analyzer.

We have investigated the Kodak Ektachem 400 Analyzer procedure for CO2 for interferences from benzyl alcohol, benzoic acid, and several compounds structurally similar to benzoic acid. Benzoic acid in plasma, at concentrations found in neonates intoxicated with benzyl alcohol, caused a large increase in the results for CO2, as did substantially above-normal concentrations of certain fatty acids and keto-acids, and toxic concentrations of aspirin. We observed a correlation between increasing benzoic acid concentrations (up to 17 mmol/L) and falsely increasing CO2 values (greater than 47 mmol/L) obtained with the Ektachem Analyzer for samples from a neonate in the intensive-care unit, who was receiving benzyl alcohol-preserved saline solutions. Although the Ektachem CO2 procedure is simple and rapid, and in most cases accurate, questionable results are occasionally encountered, as indicated by a low anion gap or a measured CO2 exceeding that calculated from blood gas measurements. Such results require the use of another method for verification.

Benzoates↗
PubMed1982

Influence of upper airway pressure changes on respiratory frequency.

Influences of pressure changes within the upper airway on respiratory frequency were studied in anesthetized rabbits. These reflex effects were investigated in two ways: (1) by applying sustained negative or positive pressures to isolated upper airway in vagally intact animals during tracheostomy breathing, and (2) by briefly occluding the nasal airways of vagotomized animals at end expiration. Negative pressure applied to isolated upper airway decreased the respiratory frequency (P less than 0.01). Decrease in respiratory frequency correlated with magnitude of pressure change. In contrast, positive pressures produced an increase in respiratory frequency (P less than 0.05). But, the increase in frequency correlated poorly with magnitude of positive pressure change. A post-stimulus effect lasting several breaths was seen following the release of both negative and positive pressures (P less than 0.01). Nasal occlusion in vagotomized animals was associated with an increase in Ti and Ttot of the first nasally occluded breath (P less than 0.05). Increase in Ti was not associated with an increase in peak diaphragmatic activity. This would result in decreased inspiratory load on the upper airway patency maintaining muscles by reducing the mean inspiratory pressure. Hence, these reflex responses to airway pressure could play a functional role in the maintenance of upper airway patency.

Animals↗
PubMed1982

Pharyngeal airway obstruction in preterm infants during mixed and obstructive apnea.

The site of upper airway obstruction during mixed and obstructive apnea was investigated in nine preterm infants with clinical apnea. The level of obstruction was determined using a saline-filled pharyngeal catheter that detects respiratory pressure changes. High pharyngeal obstruction was found in 87 of 94 spells. These data suggest that the mechanism of upper airway obstruction in infants with apnea may be similar to that seen in older children and adults with obstructive sleep apnea.

Airway Obstruction↗
PubMed1982

Influence of upper airway pressure changes on genioglossus muscle respiratory activity.

The effects of change in pharyngeal airway pressure on electromyographic (EMG) activity of a pharyngeal dilating muscle (genioglossus) were investigated in 20 anesthetized rabbits. In vagotomized animals, upper airway loading maneuvers (nasal occlusion) increased the peak inspiratory activity of the genioglossus (GG) muscle on the first occluded breath. In contrast, "unloading" maneuvers (switching from nose to tracheostomy breathing) decreased GG activity. To further characterize the GG response, sustained pressure changes were produced within the isolated upper airway. Negative pressure increased GG activity; positive pressure decreased it. A poststimulus effect consisting of increased GG activity compared with control was seen following both negative- and positive-pressure stimuli. Cyclical pressure changes applied to the isolated upper airway increased the GG activity. These observations indicate the presence of reflex pathways that regulate GG muscle activity in response to upper airway pressure loads. This reflex system appears to play a role in regulating GG activity during tidal breathing and could be important in ensuring pharyngeal airway patency.

Animals↗
PubMed1982

Genioglossus muscle responses to upper airway pressure changes: afferent pathways.

The afferent pathway of an upper airway reflex in which genioglossus muscle electromyographic (GG EMG) activity is influenced by pharyngeal pressure changes was investigated in 20 anesthetized rabbits. We took advantage of the fact that the upper airway was separated into two compartments by pharyngeal closure occurring when the animals breathe through a tracheostomy. This allowed pressure to be delivered selectively either to the nose and nasopharynx or to the larynx and hypopharynx. Midcervical vagotomy did not eliminate the GG EMG response to pressure stimuli. On the other hand high cervical vagotomy or superior laryngeal nerve section eliminated the response in the laryngeal compartment, but not in the nasopharyngeal compartment. Topical anesthesia of the mucosa of the nose, pharynx, and larynx abolished the response in both compartments. Therefore we conclude that more than one afferent pathway exists for this upper airway pressure reflex; the primary afferent pathway from the laryngeal compartment is the superior laryngeal branch of the vagus nerve, whereas the primary afferent pathway for the nasopharynx is nonvagal. Trigeminal nerve, glossopharyngeal nerve, and/or nervus intermedius carry nonvagal afferents from the nasopharynx and nose. The topical anesthetic and nerve section studies suggest that superficial receptors mediate this response. The occurrence of swallowing in response to upper airway pressure changes and its elimination by topical anesthesia or superior mechanoreceptors may mediate both genioglossus respiratory responses and swallowing responses.

Afferent Pathways↗
PubMed1982

Breathing pattern and transcutaneous oxygen tension during motor activity in preterm infants.

We studied breathing pattern and transcutaneous oxygen tension (TcPO2) during episodes of sustained generalized motor activity in 18 hospitalized preterm infants. We used a newly developed quantitative method for assessing minute ventilation in infants during vigorous motor activity. We recorded respiratory air flow, tidal volume, esophageal pressure, TcPO2, and electromyograms of various muscle groups. We observed a distinctive pattern of breathing ("exertional breathing pattern") that was invariably associated with episodes of "squirming" motor activity. This breathing pattern is characterized by reduced minute volume, intermittent Valsalva maneuvers, and obstructed inspiratory effects (obstructive apnea). Episodes of squirming with the accompanying altered breathing pattern were usually followed by a decrease in TcPO2. These episodes occurred spontaneously or could be induced by sensory stimulation. They appear to be a significant cause of obstructive apnea and TcPO2 instability in hospitalized preterm infants, and were responsible for 30% of sudden decreases in TcP[O2 of 10 mmHg or greater.

Heart Rate↗
PubMed1981

Coordination of breathing and swallowing in human infants.

Spontaneous nonfeeding swallows taken during wakefulness and sleep were identified in nine preterm infants by characteristic patterns in pharyngeal pressure, submental electromyogram, and respiratory airflow. Two hundred and seventeen swallows during ongoing respiration interrupted either inspiratory or expiratory airflow with airway closure for approximately 1 s. The duration of airway closure was independent of respiratory rate. A brief "swallow-breath" was associated with swallow onset in most instances. The respiratory nature of this movement was confirmed by simultaneous recording of a fall in pharyngeal or esophageal pressure and outward movement of the abdomen. Prolongation of the respiratory cycle was generally observed when a swallow interrupted ventilation at higher lung volumes, i.e., in late inspiration or early expiration. When the swallow interrupted ventilation at lower lung volume, i.e, in late expiration or early inspiration, the subsequent inspiratory effort was usually obstructed as it preceded airway opening at the end of the swallow synergism.

Deglutition↗
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↗
PubMed1981

Evaluation of response time of a transcutaneous oxygen tension electrode.

Response characteristics of a transcutaneous PO2 electrode to step changes in PaO2 were determined. In vitro lag time and 95% response time of a transcutaneous PO2 monitor were compared to in vivo response. Release of arterial occlusion was used to produce rapid local PaO2 changes in human infants and adults. In vitro lag time and 95% response time varied according to whether an increment or decrement in PO2 was produced. In vivo 95% response time of this electrode was two to six times slower than previous estimates, and it varied significantly with the magnitude of the step change, subject age, anatomic location, and local hemodynamic factors. Also, we found that in vivo lag time is two to three times faster than previously reported.

Adult↗
PubMed1980

Hiccups in infants: characteristics and effects on ventilation.

Twenty-seven polygraphic recordings of respiration were obtained on 20 infants, providing data on the frequency, distinguishing features, and medical significance of hiccupping episodes. Eight hiccupping episodes were recorded in seven subjects. The mean duration of the spells was 8.4 +/- 4.2 (SD) minutes. Unintubated subjects, not selected because they were hiccupping, hiccupped 2.5% of the time that they were monitored. Each hiccup was a brief, powerful inspiratory muscle contraction. In unintubated subjects, hiccups were marked by upper airway obstruction, whereas in intubated patients, hiccups were unobstructed inspirations. In unintubated subjects, hiccups were associated with an increase in obstructed eupneic breaths and with decreases in respiratory frequency and minute ventilation; in three subjects hiccups precipitated episodes of mixed apnea. In intubated patients, hiccupping spells were characterized by hyperventilation and respiratory alkalosis. Two types of ECG artifacts were seen with hiccups: high-frequency spikes, mimicking abnormal QRS complexes, and low-frequency waves. From these studies, it appears that hiccups occur frequently in young infants and may affect breathing in clinically significant ways.

Alkalosis, Respiratory↗
PubMed1980

Intercostal muscle reflexes and sleep breathing patterns in the human infant.

Breathing variability and apnea characteristic of rapid eye movement (REM) sleep was investigated in a newborn infant with complete interruption of intercostal to phrenic neural pathways due to intrapartem transection of the cervical spinal cord. Breath-to-breath variability in inspiratory duration (TI), breath duration (Ttot), tidal volume (VT), and ventilation (VI) was significantly greater in REM than in quiet sleep and was similar to the variability in these parameters seen in normal infants. In addition, brief periods of diaphragmeatic apnea were observed during REM sleep. The phenomenon of shortened TI during airway occlusion previously attributed to intercostal-to-phrenic reflexes was examined in the quadriplegic infant and in seven healthy term infants. The frequency of this response was increased when airway occlusion was delayed until after onset of inspiration. Shortening of TI by occlusion occurred no less frequently in the quadriplegic than in the control infants. The constant paradoxical inward movement of the rib cage during inspiration observed in the quadriplegic infant suggests that supraspinal innervation of intercostal muscle limits such paradoxical movements in the normal infant. The quadriplegic infant's end-expiratory volume was consistently above his passive functional residual capacity, as inferred from respiratory volume and pressure measurements.

Birth Injuries↗