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Biomedical subjects

S T Kuna

Publications and source records attributed to S T Kuna.

At least 37 records · Page 2Linked to original sources
PubMed1994

Cricothyroid muscle activity during sleep in normal adult humans.

Previous investigators reported that cricothyroid (CT) muscle usually exhibits phasic inspiratory activity in normal adult humans during wakefulness. The purpose of this study was to determine respiratory-related CT activity in normal adult humans during sleep. Nighttime polysomnograms were performed in 16 subjects. Hooked-wire electrodes were percutaneously implanted in CT with 21-gauge needle-catheter unit that allowed artifact-free monopolar recordings during electrode placement. During wakefulness, CT was usually phasically active on inspiration, with tonic activity throughout the respiratory cycle. Phasic inspiratory activity was present throughout sleep in all subjects, even those without respiratory-related CT activity during wakefulness. Compared with non-rapid-eye-movement (NREM) sleep, phasic CT activity uniformly increased in rapid-eye-movement (REM) sleep. No differences were apparent in height of phasic CT activity between phasic and tonic REM sleep. Application of nasal continuous positive pressure in stage 3/4 NREM sleep was associated with a decrease in phasic CT activity. Passively induced hypocapnia with positive-pressure ventilation via a nose mask in stage 3/4 NREM sleep was associated with a disappearance of phasic CT activity. Cessation of positive-pressure ventilation under hypocapnic conditions frequently resulted in apnea. Phasic CT activity remained absent during apnea but reappeared coincident with or soon after resumption of spontaneous respiration. In summary, CT's phasic inspiratory activity and respiratory-related response to various stimuli during sleep were very similar to those of posterior cricoarytenoid muscle, the principal vocal cord abductor.

Adult↗
PubMed1994

Effect of hypercapnia on laryngeal airway resistance in normal adult humans.

Laryngeal airway resistance (Rlar) was measured in eight normal adult humans during progressive hyperoxic hypercapnia. In most subjects, the translaryngeal pressure-flow relationship appeared linear under normocapnic conditions. During hypercapnia, the pressure-flow relationship on inspiration and expiration was curvilinear with increasing translaryngeal pressure associated with progressively smaller increments in flow. Translaryngeal pressure-flow relationships at different CO2 levels were compared over their common flow ranges by performing a least-squares linear regression on data throughout inspiration and expiration. During normocapnia, the mean slope, i.e., mean Rlar, was 0.50 +/- 0.21 (SD) cmH2O.l-1.s. A moderately significant decrease in Rlar was present at 9% end-tidal CO2 (P = 0.08). In a separate series of experiments, subjects breathed oxygen- and helium-based gas mixtures through a face mask attached to a pneumotachograph. Data analysis over the flow range present during normocapnia revealed no difference in Rlar between nose and mouth breathing and similar decreases in Rlar under hypercapnic conditions with the oxygen- and helium-based gas mixtures. The decrease in Rlar from normocapnic to hypercapnic conditions found over common, but relatively low, ranges of flow predicts that even greater increases in Rlar would occur at high flow rates in the absence of increasing glottic aperture.

Adult↗
PubMed1994

Laryngeal response during forced vital capacity maneuvers in normal adult humans.

Previous investigators have reported that transient forced expiration is accompanied by abduction of the vocal cords. To further investigate the laryngeal response during voluntary forced vital capacity maneuvers, intramuscular electromyographic recordings were obtained in 25 normal adult humans from three intrinsic laryngeal muscles: the posterior cricoarytenoid (PCA), a vocal cord abductor, and the thyroarytenoid (TA) and arytenoideus (AR), both vocal cord adductors. All three muscles exhibited sustained activation throughout most of forced expiration from total lung capacity. Forced inspiration from residual volume was associated with a further increase in PCA activity and a marked decrease in adductor muscle activity. To determine the net effect of these electromyographic changes on vocal cord position, simultaneous fiberoptic recordings of vocal cord movement were obtained in five of the subjects. The angle formed by the vocal cords at the anterior commissure was used to assess glottic aperture size. Glottic angle progressively decreased from peak expiratory flow to the end of forced expiration. The angle was 56 +/- 13 degrees (SD) at peak expiratory flow, 34 +/- 4 degrees after forced expiration of 90% of the vital capacity, and 7 +/- 7 degrees at end-expiration. The results indicate that forced expiration is associated with marked activation of not only the PCA but also laryngeal adductor muscles. During forced expiration, the glottis does not decrease below its size during quiet breathing until exhalation of about 75% of forced vital capacity.

Adult↗
PubMed1993

Thyroarytenoid muscle activity in sleep apneas.

In normal subjects the thyroarytenoid muscle (TA), a vocal cord adductor, has phasic expiratory activity during wakefulness that disappears during non-rapid-eye-movement (NREM) sleep. Fiber-optic studies have reported absent or irregular vocal cord movements during obstructive apneas and vocal cord adduction during central apneas. This study was designed to investigate TA activity during NREM sleep in 14 subjects with sleep apnea by means of intramuscular wire electrodes. During central apneas, which were recorded in three subjects, continuous TA activity was observed. During obstructive apneas, which were recorded in all subjects, two different patterns of TA activity were observed: 1) absence of any activity until arousal and 2) phasic activity throughout the apnea. The first pattern was detected in six subjects, whereas both patterns were observed in the remaining eight subjects. No correlation was found between obstructive apnea characteristics and presence or absence of TA activity. In all subjects TA underwent a marked activation during arousal. While nasal continuous positive airway pressure was applied during NREM sleep TA activity was always absent. The persistence of TA activity during central apneas suggests that they may represent an extreme prolongation of neural expiratory discharge. We speculate that a variable interaction of different stimuli acting during obstructive apnea may activate TA, which, in turn, may contribute to glottic narrowing.

Adult↗
PubMed1993

Laryngeal response to passively induced hypocapnia during NREM sleep in normal adult humans.

Passively induced hypocapnia in animals activates vocal cord adductor muscles and decreases the glottic aperture. The purpose of this study was to determine if passively induced hypocapnia has similar effects in normal adult humans in stage 3/4 non-rapid-eye-movement (NREM) sleep. Hypocapnia was induced by hyperventilating the subjects with a positive-pressure ventilator via a nose mask. At hypocapnic levels below the CO2 apneic threshold, abrupt cessation of mechanical ventilation was followed by an apnea. In protocol 1, intramuscular electromyographic recordings of intrinsic laryngeal muscles were obtained in nine subjects. Activity of the posterior cricoarytenoid muscle, a vocal cord abductor, disappeared during passive hyperventilation. The muscle remained electrically silent during an apnea, but phasic inspiratory activity reappeared with the first respiratory effort. The thyroarytenoid and arytenoideus muscles, both vocal cord adductors, were electrically silent during spontaneous breathing in NREM sleep. Hypocapnia was frequently associated with activation of both adductor muscles. Once activated, the adductor muscles remained tonically active during an ensuring apnea. In protocol 2, a fiber-optic scope was advanced transnasally into the hypopharynx to determine glottic aperture size during passively induced hypocapnic apnea. In the seven subjects who achieved stable NREM sleep, the glottic aperture during an apnea was smaller than at any time throughout the respiratory cycle during spontaneous breathing just before positive-pressure ventilation. The results suggest that the decrease in glottic aperture observed during an induced hypocapnic apnea is due to suppression of the posterior cricoarytenoid muscle and/or activation of vocal cord adductor muscles.

Apnea↗
PubMed1993

Effect of hypercapnia and hypoxia on arytenoideus muscle activity in normal adult humans.

The electrical activity of the arytenoideus muscle, a vocal cord adductor, was measured in 14 normal adult humans during progressive isocapnic hypoxia and progressive hyperoxic hypercapnia. Electromyograms of the arytenoideus were obtained 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. In three of the subjects, respiratory-related arytenoideus activity was not present during quiet breathing or chemical stimulation. During quiet breathing in the 11 other subjects, the arytenoideus exhibited phasic activity during expiration and usually tonic activity throughout the respiratory cycle. Phasic and tonic arytenoideus activity decreased under hypoxic and hypercapnic conditions. At higher levels of chemical stimulation in many subjects, short abrupt bursts of activity were frequently present at the transitions between inspiration and expiration. To determine the mechanical effect of the latter electromyographic findings, arytenoideus activity and fiber-optic images of the glottic aperture were simultaneously recorded in nine additional normal adult human subjects during progressive hyperoxic hypercapnia. The short abrupt bursts of arytenoideus activity were usually associated with a decrease in glottic aperture, although no change and an increase in glottic aperture were observed in individual subjects. The results suggest that the arytenoideus muscle may have an important role in the control of ventilation in normal human subjects.

Adult↗
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↗