Occluded Effort Research Articles

Evaluation of diaphragmatic fatigue in obstructive sleep apnoeas during non-REM sleep.

BACKGROUND: Resistive load applied to the airways may induce diaphragmatic fatigue, and hypoxaemia has been shown to predispose to the development of fatigue. Inspiratory muscle fatigue may occur in patients...

Role of chemosensitivity in intrathoracic pressure changes during obstructive sleep apnea.

We tested the hypothesis that the awake ventilatory response to hypoxia and hypercapnia may contribute to the variability of respiratory effort developed in response to upper airway obstruction in obstructive sleep apnea syndrome. The polygraphic recordings of 38 patients diagnosed as having obstructive sleep apnea on the basis of an apnea+hypopnea index greater than 10 were examined. All subjects received hypoxic and hypercapnic ventilatory tests the day before the nocturnal polysomnography. Thirty apneas during non-rapid eye movement (NREM) sleep and at least 10 apneas during rapid eye movement sleep were analyzed. For each considered apnea, we measured esophageal pressure (Pes) swings during the first three breaths preceding apnea and during the first three and last three occluded efforts occurring during the apnea. We considered as indices of respiratory effort the overall increase from the minimum to the maximum Pes (delta Pes), the rate of increase of Pes during apnea (RPes), and the maximal respiratory effort at the end of apnea (Pes max fin). In NREM sleep, all three indices of respiratory effort were correlated positively with the awake ventilatory response to hypoxia or hypercapnia and with the apnea index. No correlation was found between the indices of respiratory effort and body mass index, age, pulmonary function tests, awake blood gases, apnea duration, and apnea desaturation. In rapid eye movement sleep, none of the considered variables predicted the degree of respiratory effort. In conclusion, our results suggest that the degree of ventilatory response to upper airway occlusion in obstructive sleep apnea may be influenced by the sensitivity of central neural drive to chemical stimuli.

Effect of oxygenation on breath-by-breath response of the genioglossus muscle during occlusion

We investigated the effect of different levels of O2 tension (hypoxia, normoxia, and hyperoxia) on the breath-by-breath onset and peak electromyographic (EMG) activity of the genioglossus (GG) muscle during a five-breath end-expiratory tracheal occlusion of 20- to 30-s duration. GG and diaphragmatic (DIA) EMG activity were measured with needle electrodes in eight anesthetized tracheotomized adult cats. In response to occlusion, the increase in the number of animals with GG EMG activity was different during hypoxia, normoxia, and hyperoxia (P = 0.003, Friedman). During hypoxia, eight of eight of the animals had GG EMG activity by the third occluded effort. In contrast, during normoxia, only four of eight and, during hyperoxia, only three of eight animals had GG EMG activity throughout the entire five-breath occlusion. Similarly, at release of the occlusion, more animals had persistent GG EMG activity on the postocclusion breaths during hypoxia than during normoxia or hyperoxia. Breath-by-breath augmentation of peak amplitude of the GG and DIA EMGs on each occluded effort was accentuated during hypoxia (P less than 0.01) and abolished during hyperoxia (P = 0.10). These results suggest that hypoxemia is a major determinant of the rapidity of onset, magnitude, and sustained activity of upper airway muscles during airway occlusion.

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.

Genioglossus and diaphragm activity during obstructive apnea and airway occlusion in infants.

To document mechanisms contributing to upper airway collapse, we compared the electromyographic activity of the genioglossus (GG) and diaphragm (DIA) during spontaneous mixed and obstructive apnea and during induced end-expiratory airway occlusion in 11 premature infants. In addition to ventilation and esophageal pressure measurements, we obtained DIA and GG electromyograms (EMG) from subcostal and sublingual surface electrodes, respectively. Amplitude of the DIA EMG and the frequency of occurrence of the GG EMG were determined for: 1) the breath preceding apnea or occlusion, 2) the initial and last obstructed inspiratory efforts, and 3) the first breath at resolution of both apnea and occlusion. During spontaneous apnea with airway obstruction amplitude of the DIA, EMG decreased on the initial obstructed inspiratory effort and did not exceed that of the breath preceding apnea until reestablishment of flow. In contrast, during end-expiratory airway occlusion, the amplitude of the DIA EMG increased both during and at release of occlusion. In 18 +/- 6% of the spontaneous apneic episodes, GG EMG was present with the breath preceding apnea and this frequency did not increase significantly until resolution of the apnea. During induced airway occlusion, GG EMG was not present with the breath preceding occlusion but its frequency did increase to 58 +/- 8 and 42 +/- 8% with the last occluded inspiratory effort and the first breath after release of occlusion, respectively. The decreased presence of the GG EMG from the last occluded effort to the breath at release of occlusion (58 +/- 8 versus 42 +/- 8%, p less than 0.05) was probably due to the greater mechanoreceptor-mediated inhibition associated with reestablishment of flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Diaphragm Strength in the Shrinking Lung Syndrome of Systemic Lupus Erythematosus

The cause of the reduced lung volume in the 'shrinking lung' syndrome of systemic lupus erythematosus (SLE) was investigated in 12 patients with the condition. Nine patients described persistent episodes of pleuritic chest pain. Narrow section (3 mm) computed tomography of the thorax revealed no interstitial fibrosis or significant pleural disease. Assessment of diaphragmatic function using manoeuvres more reliable than the maximal occluded efforts previously used alone to assess respiratory muscle strength, showed that diaphragm strength was unequivocally normal in nine of 12 patients. In three, maximum transdiaphragmatic pressure was moderately reduced, but phrenic nerve stimulation demonstrated that this was due to incomplete activation of the diaphragm during a maximal voluntary effort, rather than to a primary abnormality of the diaphragm. Results of maximum lung recoil pressures and dynamic compliance, and analysis of the 12-s maximum voluntary ventilation, suggested a restriction in chest-wall expansion, although it was not possible to identify the underlying cause of this on the basis of our results. We conclude that the 'shrinking lung' syndrome of SLE is not explained by a primary abnormality of the diaphragm.

Upper airway muscle activity during nasal occlusion in newborn babies.

Submental electromyorgams (SM EMG) were recorded from 20 preterm babies (gestational age 30 +/- 2 wk, postmenstrual age at study 35 +/- 2 wk) (mean +/- SD) and 3 full-term infants (7-14 days old). SM EMG was evaluated during eupnea and brief experimental airway occlusion. Phasic inspiratory SM EMG was rarely seen during eupnea. SM EMG tended to increase on the first occluded effort, although this increase was not statistically significant in most babies. All infants showed progressive breath-by-breath augmentation of phasic SM EMG during occlusions in rapid-eye-movement (REM) as well as quiet (QS) sleep; phasic increases in SM EMG were similar during REM and QS occlusions in the majority (16/22) of babies. Periods of airway closure were detected during 24 occlusions in 5 infants; phasic SM EMG was reduced on these occasions. The results are consistent with the idea that recruitment of upper airway muscles contributes to the stability of the airway of the preterm human.

Genioglossus and breathing responses to airway occlusion: effect of sleep and route of occlusion.

We examined the effect of sleep state on the response of genioglossus muscle (EMGgg) activity to total airway occlusion applied at 1) nasal (N) airway [and thus exposing the upper airway (UAW) to pressure changes] and 2) tracheal (T) airway (thus excluding UAW from pressure changes). A total of 233 tests were performed during wakefulness (W), 98 tests in slow-wave sleep (SWS), and 72 tests in rapid-eye-movement (REM) sleep. Prolongation of inspiratory time (TI) of the first occluded effort occurred in all tests irrespective of behavioral state, with the greatest increase seen in awake N tests. Nasal tests augmented EMGgg activity in the first occluded breath and produced a linear increase in EMGgg during occlusion. The EMGgg activity at any given time during nasal occlusion in SWS was less than that recorded during W tests. There was a marked reduction in EMGgg response to N occlusion during REM sleep. The EMGgg activity during awake T tests was significantly less than that of N tests at any given time during occlusion. There was no relationship between the level of EMGgg activity and asphyxia in T tests performed during SWS and REM sleep. Nasal tests decreased the force generated by the inspiratory pump muscles and the central drive to breathing compared with T tests. These results confirm the important role of the UAW in regulating breathing pattern and indicate that both immediate and progressive load-compensating responses during nasal occlusion are influenced by information arising from the UAW.

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.

Breathing pattern in rats with chronic section of the superior laryngeal nerves

In a first set of experiments we registered the integrated afferent activity of the superior laryngeal nerve (SLN) in adult anaesthetized rats. The activity increased with positive upper airway pressure (Pua); with progressively more negative Pua, the SLN activity at first declined then increased again. A second set of adult rats underwent bilateral section of the SLN (SLN denervated) or a sham operation (controls). Both groups appeared to recover promptly from the operation and 6 days later their resting breathing pattern was recorded by the barometric method. SLN denervated rats had a shorter inspiratory time (80%), hence higher frequency and mean inspiratory flow, than controls. During hypoxia (10 min at 10% O 2) both groups hyperventilated with an almost identical pattern. The rats were then again anaesthetized and the right vagus cut in an attempt to reduce the afferent component from the lower airways, which may have masked the SLN regulatory contribution. One week after this second operation both SLN denervated and controls breathed more deeply and slowly than before vagotomy, but the pattern was not significantly different between the two groups, either in normoxia or hypoxia. Finally, the rats were anaesthetized and integrated diaphragm activity recorded during spontaneous breathing and the first effort against closure of the nostrils. With both vagi cut, the duration of the occluded effort was slightly longer in SLN denervated than in controls. These results suggest that in adult awake rats laryngeal afferent activity tends to decrease mean inspiratory flow. However, this regulatory contribution is small during eupnea and insignificant during hypoxic hyperventilation.

Differential response of respiratory muscles to airway occlusion in infants.

The effect of end-expiratory occlusion on respiratory muscle activity was studied in 10 unsedated preterm infants during sleep. Electromyograms (EMG) of the upper airway were recorded from surface electrodes placed over the submental (SM) area; diaphragm (DIA) EMGs were obtained with identical electrodes over the right subcostal margin. Phasic SM EMG accompanied 56 +/- 36% of breaths during spontaneous breathing and increased to 80 +/- 26% (P less than 0.05) on the first inspiratory effort after occlusion. Occlusion increased peak amplitude (P less than 0.001) and total duration (P less than 0.005) of the SM EMG without significant changes in its initial rate of rise. In contrast, only the total duration of the DIA EMG increased (P less than 0.005) during occlusion. Inspiratory time increased from 470 +/- 120 to 720 +/- 210 ms (P less than 0.001) during the first occluded effort, but expiratory time did not change. With sustained occlusion, peak amplitude of the SM EMG progressively increased, but DIA EMG only significantly increased by the third occluded effort. Pharyngeal patency was invariably maintained throughout the induced airway occlusions. Sharp bursts of SM EMG activity coincided with resolution of spontaneous obstructive apneic episodes in four infants. The immediate increase in SM EMG associated with airway occlusion may be a mechanism that prevents the development of obstructive apnea.

1861 PROLONGATION OF INSPIRATORY TIME BY LOWER AIRWAY OCCLUSION IN CHILDREN

Inspiration is strongly inhibited by volume-related vagal afferents in human neonates and animals but this reflex is not as active in human adults during normal breathing. To determine if volume-related inspiratory inhibition occurs beyond the neonatal period we performed 10±1 end expiratory occlusions in 5 patients (3-17mos.) with cuffed tracheostomy or endotracheal tubes. Occlusion pressure and surface diaphragm electromyogram (DIA EMG) were simultaneously recorded. DIA EMG duration (TIDIA) was measured from the raw signal, and peak amplitude, time to peak and rate of rise of DIA EMG were quantified from moving average signals. Inspiratory time (Ti) was measured from flow signal during the breath immediately preceding occlusion and from occlusion pressure (JAP 38:335, 1975) during the first occluded effort. During control breaths TIDIA was longer than Ti from flow (790±110vs 550±130ms, p<0.01). Occlusion consistently increased Ti (550±1130 to 710±230ms, p<0.05) and TIDIA (790±110 to 990±130ms, p<0.001). Peak amplitude and time to peak DIA EMG increased by 22±6%, p<0.005 and 30±4%, p<0.001, respectively, during occlusion but rate of rise did not change. In summary, in patients with isolated lower airways, end expiratory occlusions prolonged inspiratory efforts and DIA EMG. These findings indicate that during normal breathing volume-related afferents shorten inspiration in children. Isolation of lower airways suggests that these reflexes are not mediated by upper airway mechanoreceptors. Thus, the Hering-Breuer reflex may he present beyond the neonatal period. (Supp. NIH HL31173 and HL25830)

Respiratory afferent activity in the superior laryngeal nerves

This study evaluates the afferent activity in the superior laryngeal nerve (SLN) during breathing as well as during occluded inspiratory efforts. Experiments were performed in 11 anesthetized and spontaneously breathing dogs. Electroneurographic activity was recorded from the peripheral cut end of the SLN and, in 3 dogs, also from the contralateral vagus nerve. A tracheal cannula with a side arm allowed the bypass of the larynx during breathing and occluded efforts. A clear inspiratory modulation was present in all experimental conditions. Both peak and duration of the SLN activity decreased (87% and 89%) when breathing was diverted from the upper airway to the tracheostomy. Peak and duration of the SLN activity (as % of upper airway breathing) increased during occluded efforts; however, the increase was greater when the larynx was not by-passed (peak = 118% vs 208%, duration = 143% vs 178%). Section of the ipsilateral recurrent laryngeal nerve reduced the inspiratory modulation. Vagal afferent activity increased equally during tracheostomy and upper airway breathing and decreased markedly during tracheal and upper airway occlusions. Our results indicate that collapsing pressure in the larynx is the major stimulus in activating laryngeal afferents.

RELEASE OF UPPER AIRWAY MUSCLE INHIBITION DURING AIRWAY OCCLUSION

Control of upper airway(UA) muscles appears essential for maintenance of pharyngeal patency. Animal studies indicate that volume-related vagal inhibition during inspiration modulates UA muscles more than the diaphragm(DIA). To determine if preferential inhibition of UA muscles occurs in neonates during normal inspiration, we studied 9 infants (GA 30±3 wks, age 15±8 days, Wt 1.1±0.2 kg) by performing 9 (range 5-16) end expiratory nasal occlusions during sleep. We recorded UA EMG (via surface submental electrodes), surface DIA EMG, ventilation, esophageal and mask pressures.Phasic inspiratory EMG occurred in 52±36% of unoccluded breaths and increased to 78±27%(p<.02) in the first occluded effort. Peak UA EMG during unoccluded breathing was 58±28% of that during the first occluded effort (p<.001). This increase in UA EMG activity during occlusion was accompanied by an increase in time to peak UA EMG from 250±91 to 612±63 MS (p<.001), while the rate of rise did not change. In contrast, peak activity, time to peak, and rate of rise of DIA EMG were unchanged during the first occluded effort. Esophageal pressures were consistently transmitted to the nasal mask during occlusion, indicating UA patency. These data indicate that feedback associated with lung inflation inhibits UA EMG more than DIA EMG during normal breathing. Release of this inhibition during airway obstruction, with the concomitant increase in UA muscle activity, may be a major mechanism for maintenance of pharyngeal patency in preterm infants. Supported by NIH HL31173 and HL25830