PubMed Health⌕ Search

Biomedical subjects

S T Kuna

Publications and source records attributed to S T Kuna.

At least 19 recordsLinked to original sources
PubMed1991

Pathophysiology of upper airway closure during sleep.

While the upper airway normally remains patent during quiet breathing in wakefulness and sleep, patients with obstructive sleep apnea have repetitive periods of upper airway closure during sleep. The upper airway closures usually occur at various sites in the pharynx. The patency of the potentially collapsible pharynx during inspiration depends on the balance between subatmospheric pressure in the pharyngeal airway and airway dilating forces generated by pharyngeal muscles. The pressure required to collapse the upper airway in the absence of upper airway muscle activity, ie, closing pressure, is normally subatmospheric. In obstructive sleep apnea, positive pressures are required to maintain patency of the passive upper airway. The pathophysiologic mechanisms underlying upper airway closures during sleep form the basis for the treatment of obstructive sleep apnea. In general, these treatment modalities attempt to (1) raise the pharyngeal pressure above the closing pressure, (2) decrease the closing pressure, or (3) increase upper airway muscle activity.

Airway Obstruction↗
PubMed1991

Posterior cricoarytenoid activity in normal adults during involuntary and voluntary hyperventilation.

The effect of isocapnic hypoxia and hyperoxic hypercapnia on the electrical activity of the posterior cricoarytenoid (PCA) muscle was determined in eight normal adult humans by use of standard rebreathing techniques and was compared with PCA activity during voluntary hyperventilation performed under isocapnic and hypocapnic conditions. PCA activity was recorded with intramuscular hooked-wire electrodes implanted through a fiberoptic nasopharyngoscope. During quiet breathing in all subjects, the PCA was phasically active on inspiration and tonically active throughout the respiratory cycle. At comparable increments in respiratory output, hypercapnia, hypoxia, and voluntary hyperventilation appeared to be associated with similar increases in phasic or tonic PCA activity. During quiet breathing, the onset of phasic PCA activity usually occurred before inspiratory airflow and extended beyond the start of expiratory airflow. The duration of phasic PCA preactivation and postinspiratory phasic PCA activity remained unchanged during progressive hypercapnia and progressive hypoxia. The results, in combination with recent findings for vocal cord adductors, suggest that vocal cord position throughout the respiratory cycle during hyperpnea is actively controlled by simultaneously acting and antagonistic intrinsic laryngeal muscles.

Adult↗
PubMed1991

Arytenoideus muscle activity in normal adult humans during wakefulness and sleep.

The respiratory-related activity of the arytenoideus (AR) muscle, a vocal cord adductor, was investigated in 10 healthy adults during wakefulness and sleep. AR activity was measured with intramuscular hooked-wire electrodes implanted by means of a fiber-optic nasopharyngoscope. Correct placement of the electrodes was confirmed by discharge patterns during voluntary maneuvers. The AR usually exhibited respiratory-related activity during quiet breathing in all awake subjects. Tonic activity was frequently present throughout the respiratory cycle. The pattern of phasic discharge during wakefulness exhibited considerable intrasubject variability both in timing and level of activity. Phasic activity usually began in midinspiration and terminated in mid- to late expiration. Periods of biphasic discharge were observed in four subjects. Phasic discharge primarily confined to expiration was also commonly observed. During quiet breathing in wakefulness, the level of phasic AR activity appeared to be directly related to the time of expiration. The AR was electrically silent in the six subjects who achieved stable periods of non-rapid-eye-movement sleep. Rapid-eye-movement sleep was observed in three subjects and was associated with sporadic paroxysmal bursts of AR activity. The results during wakefulness indicate that vocal cord adduction in expiration is an active phenomenon and suggest that the larynx may have an active role in braking exhalation.

Adult↗
PubMed1991

Thyroarytenoid muscle activity during loaded and nonloaded breathing in adult humans.

Previous fiber-optic studies in humans have demonstrated narrowing of the glottic aperture in expiration during application of expiratory resistive loads. Nine healthy subjects were studied to determine the effect of expiratory resistive loads on the electromyographic activity of the thyroarytenoid (TA) muscle, a vocal cord adductor. Four of the nine subjects also underwent the application of inspiratory resistive loads and voluntary prolongation of either inspiratory (TI) or expiratory (TE) time. TA activity was recorded by intramuscular hooked-wire electrodes. During quiet breathing in all subjects, the TA was phasically active on expiration and often tonically active throughout the respiratory cycle. TA expiratory activity progressively increased with increasing levels of expiratory load. Inspiratory loads resulted in increased TA "inspiratory" activity. Voluntary prolongation of TE to times similar to those reached during loaded breathing induced increases in TA expiratory activity similar to those reached during the loaded state. Voluntary prolongation of TI was associated with an increase in TA inspiratory activity. Similar increases in TI during inspiratory loading or voluntary conditions were associated with comparable increases in TA inspiratory activity in three of the four subjects. In conclusion, increased activation of TA during the application of expiratory resistive loads implies that the reported narrowing of glottic aperture during expiratory loading is an active phenomenon. Changes in activation of the TA with resistive loads appear to be related to changes in respiratory pattern.

Adult↗
PubMed1991

Obstructive sleep apnea.

Obstructive sleep apnea is diagnosed with the use of polysomnography by documenting repetitive periods of upper airway closure during sleep. Apneic episodes can compromise gas exchange and disrupt the sleep pattern. The challenge to the clinician is to suspect this diagnosis when evaluating the awake patient. The history of loud snoring plus daytime hypersomnolence or multiple awakenings during sleep justifies ordering a polysomnogram. The importance of diagnosing obstructive sleep apnea is underscored by the resolution of its sequelae with effective medical or surgical treatment.

Airway Obstruction↗
PubMed1990

Progressive exercise testing in closed head-injured subjects: comparison of exercise apparatus in assessment of a physical conditioning program.

Progressive exercise tests were performed on 12 closed head-injured subjects to determine 1) whether results differ when tests are performed on a treadmill, a bicycle ergometer, or mechanical stairs and 2) whether a 3-month general physical conditioning program results in an improvement in exercise performance. The subjects performed progressive exercise tests on each apparatus on entry into a residential transitional rehabilitation program and approximately 3 months later following participation in a physical conditioning program. On both the initial and 3-month exercise tests, maximal oxygen consumption (VO2 max) was significantly greater on the treadmill and the mechanical stairs than on the bicycle ergometer. The mean VO2 max was 74% of the predicted value on the initial exercise test and rose to 85% of the predicted value after the 3-month physical conditioning program. Oxygen consumption per kilogram of body weight at a given power output on a given apparatus showed no statistically significant difference between the initial and 3-month tests, indicating no change in exercise efficiency. On the 3-month test, a statistically significant decrease was noted in heart rate at rest and after the 4-minute period of recovery from maximal exercise on any given apparatus. The data obtained in this study indicate that 1) the treadmill and mechanical stairs are more suitable than the bicycle ergometer for assessing maximal exercise performance and 2) improved physical fitness following a physical conditioning program is associated with an improvement in cardiovascular function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Intramuscular and esophageal electrode recordings of posterior cricoarytenoid activity in normal subjects.

Six normal human subjects were studied to compare intramuscular and esophageal electrode recordings of posterior cricoarytenoid (PCA) muscle activity. A new electromyographic technique was developed to implant hooked wire electrodes into the PCA via a nasopharyngoscope. The esophageal electrode was similar to that used by other investigators to record PCA activity (P. C. Kosch et al. J. Appl. Physiol. 64: 1968-1978, 1988). Simultaneous recordings from the intramuscular and esophageal electrodes were obtained during wakefulness and sleep. Changes in esophageal electrode activity were compared with changes in intramuscular electrode activity under four conditions: 1) voluntary maneuvers, 2) differences in state, 3) nasal airway occlusion during non-rapid-eye-movement sleep, and 4) spontaneous variations in respiratory efforts during non-rapid-eye-movement or rapid-eye-movement sleep. Although similar results were obtained from the esophageal and intramuscular electrodes, differences were present between the two recordings during both wakefulness and sleep. The esophageal electrode recorded activity from surrounding muscles during voluntary maneuvers, vocalization, and quiet breathing in wakefulness. Discrepancies between the two electrode recordings during sleep occurred under conditions of increased and decreased respiratory motor output. The data suggest that the esophageal electrode may not give an accurate assessment of PCA activity during many conditions in wakefulness and sleep.

Adult↗
PubMed1990

Posterior cricoarytenoid muscle activity during wakefulness and sleep in normal adults.

Six normal adults were studied 1) to compare respiratory-related posterior cricoarytenoid (PCA) muscle activity during wakefulness and sleep and 2) to determine the effect of upper airway occlusions during non-rapid-eye-movement (NREM) sleep on PCA activity. A new electromyographic technique was developed to implant hooked-wire electrodes into the PCA by using a nasopharyngoscope. A previously described technique was used to induce upper airway occlusions during NREM sleep (Kuna and Smickley, J. Appl. Physiol. 64: 347-353, 1988). The PCA exhibited phasic inspiratory activity during quiet breathing in wakefulness and sleep in all subjects. Discounting changes in tonic activity, peak amplitude of PCA inspiratory activity during stage 3-4 NREM sleep decreased to 77% of its value in wakefulness. Tonic activity throughout the respiratory cycle was present in all subjects during wakefulness but was absent during state 3-4 NREM sleep. In this sleep stage, PCA phasic activity abruptly terminated near the end of inspiration. During nasal airway occlusions in NREM sleep, PCA phasic activity did not increase significantly during the first or second occluded effort. The results, in combination with recent findings for vocal cord adductors in awake and sleeping adults, suggest that vocal cord position during quiet breathing in wakefulness is actively controlled by simultaneously acting antagonistic intrinsic laryngeal muscles. In contrast, the return of the vocal cords toward the midline during expiration in stage 3-4 NREM sleep appears to be a passive phenomenon.

Adult↗
PubMed1990

Thyroarytenoid muscle activity during hypoxia, hypercapnia, and voluntary hyperventilation in humans.

Intramuscular electromyographic activity of the thyroarytenoid (TA) muscle, a vocal cord adductor, was recorded in nine normal adult humans during progressive isocapnic hypoxia and hyperoxic hypercapnia. Four of the nine subjects also performed voluntary isocapnic hyperventilation. During quiet breathing of room air, the TA exhibited phasic activity in expiration and often tonic activity throughout the respiratory cycle. Both phasic and tonic TA activity progressively decreased with either increasing hypoxia or hypercapnia. Tonic activity appeared to decrease more rapidly than phasic activity with increasing chemical stimulation. At comparable tidal volume increments, the relative decrease in phasic TA activity appeared to be greater under hypoxic than under hypercapnic conditions. During voluntary isocapnic hyperventilation, phasic TA activity decreased without significant change in tonic activity. At tidal volumes approximately double those of base line, the relative decrease in TA activity was similar during both hypercapnia and voluntary hyperventilation, although differences appeared at higher tidal volumes. The results, in combination with recent findings in humans regarding the posterior cricoarytenoid muscle, a vocal cord abductor, suggest that vocal cord position is dependent on the net balance of counteracting forces not only during quiet breathing but also during involuntary and voluntary hyperpnea.

Adult↗
PubMed1990

Hypercarbic periodic breathing during sleep in a child with a central nervous system tumor.

A 4-yr-old girl with a ganglioglioma involving the cerebellum and pons presented with CO2 retention and arterial O2 desaturation during wakefulness and sleep. Despite the presence of a regular respiratory pattern during wakefulness, NREM sleep was associated with the appearance of a sustained periodic respiratory pattern characterized by clusters of usually two breaths separated by an 8 to 10-s expiratory pause. At sleep onset, this Biot's respiratory pattern appeared immediately after a sigh. Breathing frequency during NREM sleep became regular with administration of supplemental O2 and an attendant increase in end-tidal CO2. Shortly after withdrawal of supplemental O2 during NREM sleep, the periodic pattern resumed and was again immediately preceded by a sigh. The observations during NREM sleep in this patient with a central nervous system abnormality indicate that Biot's type respiratory pattern may be reversed by administration of supplemental oxygen. The results in this patient suggest: (1) the presence of a very elevated CO2 apnea threshold, and (2) that the pons may play a role in determining the effect of hypercapnic hypoxia on respiratory pattern during sleep.

Brain Neoplasms↗
PubMed1989

Specificity of esophageal electrode recordings of posterior cricoarytenoid muscle activity.

Esophageal electrodes have been used for recording the electromyographic (EMG) activity of the posterior cricoarytenoid muscle (PCA). To determine the specificity of this EMG technique, esophageal electrode recordings were compared with intramuscular recordings in eight anesthetized mongrel dogs. Intramuscular wire electrodes were placed in the right and left PCA, and the esophageal electrode was introduced through the nose or mouth and advanced into the upper esophagus. On direct visualization of the upper airway, the unshielded catheter electrode entered the esophagus on the right or left side. Cold block of the recurrent laryngeal nerve (RLN) ipsilateral to the esophageal electrode was associated with a marked decrease in recorded activity, whereas cold block of the contralateral RLN resulted only in a small reduction in activity. After supplemental doses of anesthesia were administered, bilateral RLN cold block essentially abolished the activity recorded with the intramuscular electrodes as well as that recorded with the esophageal electrode. Before supplemental doses of anesthesia were given, especially after vagotomy, the esophageal electrode, and in some cases the intramuscular electrodes, recorded phasic inspiratory activity not originating from the PCA. Therefore, one should be cautious in interpreting the activity recorded from esophageal electrodes as originating from the PCA, especially in conditions associated with increased respiratory efforts.

Animals↗
PubMed1988

Response of genioglossus muscle activity to nasal airway occlusion in normal sleeping adults.

To determine the combined effect of increased subatmospheric upper airway pressure and withdrawal of phasic volume feedback from the lung on genioglossus muscle activity, the response of this muscle to intermittent nasal airway occlusion was studied in 12 normal adult males during sleep. Nasal occlusion at end expiration was achieved by inflating balloon-tipped catheters located within the portals of a nose mask. No seal was placed over the mouth. During nose breathing in non-rapid-eye-movement (NREM) sleep, nasal airway occlusion resulted in multiple respiratory efforts before arousal. Mouth breathing was not initiated until arousal. Phasic inspiratory genioglossus activity was present in eight subjects during NREM sleep. In these subjects, comparison of peak genioglossus inspiratory activity on the first three occluded efforts to the value just before occlusion showed an increase of 4.7, 16.1, and 28.0%, respectively. The relative increases in peak genioglossus activity were very similar to respective increases in peak diaphragm activity. Arousal was associated with a large burst in genioglossus activity. During airway occlusion in rapid-eye-movement (REM) sleep, mouth breathing could occur without a change in sleep state. In general, genioglossus responses to airway occlusion in REM sleep were similar in pattern to those in NREM sleep. A relatively small reflex activation of upper airway muscles associated with a sudden increase in subatmospheric pressure in the potentially collapsible segment of the upper airway may help compromise upper airway patency during sleep.

Adult↗
PubMed1988

Thyroarytenoid muscle activity during wakefulness and sleep in normal adults.

To determine the respiratory-related activity of the thyroarytenoid (TA) muscle in normal adults, intramuscular electromyographic recordings were performed in eight normal adult males during wakefulness and sleep. Phasic expiratory TA activity was present during normal tidal breathing in all subjects during wakefulness. Tonic activity was frequently present during inspiration. After an initial rapid rise in activity near the onset of expiration, phasic TA activity generally exhibited one of three different discharge patterns: a plateau, a progressive increase, or, less commonly, a progressive decrease in activity. In four of five subjects examined, peak TA activity during quiet breathing in wakefulness appeared to be directly related to time of expiration. At a particular lung volume above end-expiratory volume during wakefulness, measurements of expiratory resistance were directly related to the level of TA activity. TA activity disappeared during stable periods of non-rapid-eye-movement sleep and exhibited paroxysmal bursts of activity during rapid-eye-movement sleep. The results during wakefulness indicate that the TA contributes to an active adduction of the vocal cords in expiration and suggest the presence of an active laryngeal braking mechanism during exhalation.

Adult↗
PubMed1988

Effect of laryngeal anesthesia on pulmonary function testing in normal subjects.

Pulmonary function tests (PFT) were performed on 11 normal subjects before and after topical anesthesia of the larynx. The PFT consisted of flow volume loops and body box determinations of functional residual capacity and airway resistance, each performed in triplicate. After the first set of tests, cotton pledgets soaked in 4% lidocaine were held in the pyriform sinuses for 2 min to block the superior laryngeal nerves. In addition, 1.5 ml of 10% cocaine was dropped on the vocal cords via indirect laryngoscopy. PFT were repeated 5 min after anesthesia. Besides routine analysis of the flow volume loops, areas under the inspiratory (Area I) and expiratory (Area E) portions of the loops were calculated by planimetry. Area I, peak inspiratory flow (PIF), as well as forced inspiratory flow at 25, 50, and 75% forced vital capacity (FVC), decreased after anesthesia. Peak expiratory flow decreased after anesthesia, but Area E and forced expiratory flow at 25, 50, and 75% FVC were unchanged. This protocol also was performed in 12 normal subjects with isotonic saline being substituted for the lidocaine and cocaine. In this group, no significant differences were observed when flow volume loop parameters were compared before and after topical application of saline. In 5 spontaneously breathing anesthetized dogs, posterior cricoarytenoid muscle and afferent superior laryngeal nerve activity were recorded before and after laryngeal anesthesia performed with the same procedure used in the human subjects. Laryngeal anesthesia resulted in a substantial decrease or a complete disappearance of afferent SLN activity recorded during unobstructed and obstructed respiration. The data suggest that laryngeal receptors help modulate upper airway patency in man.

Adult↗
PubMed1988

Effect of nasal airway positive pressure on upper airway size and configuration.

The effect of nasal airway positive pressure (NAPP) on upper airway size and configuration during wakefulness was studied by computerized tomography in 12 obese subjects with obstructive sleep apnea (OSA), seven weight- and age-matched subjects without OSA, and 12 normal subjects. NAPP of 10 to 12 cm H2O was associated with a significant increase in airway area throughout the upper airway in all three groups. The change in airway area per cm H2O NAPP increased from nasopharynx to hypopharynx. The change in airway area per cm H2O NAPP was significantly smaller in the OSA than in the normal subjects in the region of the soft palate. Electromyographic recordings of the genioglossus and alae nasi muscles with and without NAPP during wakefulness in five of the OSA and five of the normal subjects showed either a decrease or no change in phasic and tonic activity with NAPP. In a separate series of experiments in an additional five OSA and five normal subjects, NAPP of zero, 5, 10, and 15 cm H2O was associated with a linear increase in airway area at a given airway level. These results indicate that (1) the increase in pharyngeal cross-sectional area with application of NAPP during wakefulness is smaller in OSA than in normal subjects in the region of the soft palate and (2) changes in upper airway muscle activity may accompany changes in upper airway size and configuration.

Electromyography↗
PubMed1987

Interaction of hypercapnia and phasic volume feedback on motor control of the upper airway.

The effect of hypercapnia on the suppression of efferent hypoglossal and recurrent laryngeal nerve activity by phasic volume feedback was studied in decerebrate paralyzed intubated cats ventilated with a phrenic-driven servo-respirator. The gain of the respirator was altered for single inspirations, and the resulting changes in neural activities were quantified by comparison with respective neural activities without phasic volume feedback. This maneuver was performed when the end-tidal CO2 concentration was 5, 7, and 9%. Changes in the level of CO2 did not alter the slope or position of the volume thresholds for suppression of hypoglossal and recurrent laryngeal activities. The slope of the volume-time isopleths for specific levels of graded suppression also remained constant for each nerve at the different levels of CO2. Under hypercapnic conditions, greater volumes were required at a given time into inspiration to achieve any particular level of suppression, but these differences generally did not reach statistical significance. These data demonstrate a lack of effect of the CO2 stimulus on the suppression of upper airway motoneuron activity by phasic volume feedback. Despite the absence of this interaction, a CO2-induced increase in central inspiratory activation of upper airway motoneurons, in the presence of a very sensitive volume feedback system, would help maintain airway patency in the face of upper airway narrowing or closure.

Animals↗
PubMed1986

Inhibition of inspiratory upper airway motoneuron activity by phasic volume feedback.

The effects of phasic volume feedback on efferent hypoglossal, recurrent laryngeal and phrenic nerve activity were studied in decerebrate, paralyzed intubated cats ventilated with a phrenic-driven servo-respirator. The gain of the respirator was altered for single inspirations, and the resulting changes in neural activities were quantified by comparison with respective neural activities without phasic volume feedback. The volume thresholds for suppression of hypoglossal and recurrent laryngeal activities were time independent. Above these two thresholds and extending over a substantial range, volume feedback caused graded inhibition of upper airway motoneuron outputs. At any particular time during inspiration the relationships between hypoglossal or recurrent laryngeal inhibition and volume were concave to the volume axis. Rate of airflow appeared to exert an effect on upper airway motoneuron activity independent of volume. These results indicate that for hypoglossal and recurrent laryngeal efferent activity 1) volume feedback can cause a sustained graded inhibition throughout inspiration; 2) the volume thresholds are time independent; and 3) partial inhibition decreases susceptibility to additional inhibition. These actions of volume feedback on upper airway motoneuron output differ from those on phrenic efferent discharge and show that phasic vagal volume feedback has a marked and differential effect on upper airway motoneuron activity. The vagus, in this preparation, appears to play a critical role in the regulation of upper airway motoneuron activity and therefore maintenance of upper airway patency.

Animals↗