Genioglossus Activity Research Articles

Transition from suckling to drinking at weaning: a kinematic and electromyographic study in miniature pigs.

The movements of the tongue, hyoid, and jaw were recorded cineradiographically in preweaning pigs as they suckled bariumized milk from a veterinary teat or drank it from a bowl. The movements were quantified by measuring the X, Y coordinates of radioopaque markers embedded in the tongue and attached to both jaws and to the hyoid. EMG activity in masseter, anterior digastric, geniohyoid, genioglossus, hyoglossus, sternohyoid, stylohyoid, and omohyoid muscles was recorded synchronously with cineradiography at 100 frames/sec. In both suckling and drinking, the movements were characterized by minimal movements of the jaw and hyoid but extensive movements of the tongue. In suckling, the movements were largely confined to the midposterior part of the tongue. A seal was formed between the posterior tongue and soft palate while a depression formed in the mid-tongue; this was associated with fluid moving into the depression probably because of a reduced intraoral pressure. The depression was associated with increased EMG activity in the genioglossus muscle and overlapping activity in digastric, geniohyoid, hyoglossus, and sternohyoid muscles. In drinking cycles, significant movement occurred in all parts of the tongue; milk ingestion was associated with tongue movements that combined elements characteristic both of suckling (mid-tongue depression with a posterior seal) and of lapping (extensive anteroposterior movements within the tongue itself). In drinking, compared to suckling, there was a major reduction in EMG activity in masseter, digastric, geniohyoid, and sternohyoid muscles. After milk had accumulated in the valleculae, swallows usually occurred in every other cycle during suckling and in every third or fourth cycle during drinking. The emptying of the valleculae was an event that was embedded in the early jaw-opening phase of an otherwise normal suckling or drinking cycle. Emptying of the valleculae was associated with posteriorly directed movement of the back of the tongue and increased EMG activity in hyoglossus, styloglossus, and omohyoid muscles. No differences were noted in the kinematics associated with swallowing in the two activities, but, in the normalized and averaged EMG data, there were significant differences in the timing of genioglossus activity and in the relative balance of hyoglossal and stylohyoid activity.

Modulation of respiratory-related genioglossus motor unit activity associated with changes in head position in humans.

There is little information available regarding how respiratory-related activity of the genioglossus motor unit is modulated in various head positions. The present study was undertaken to investigate what type of genioglossus motor unit contributes to the respiratory-related activity of the genioglossus muscle and how its activity is modulated with various head positions in 8 awake adult males. Single genioglossus motor unit activity and nasal airflow were simultaneously recorded in the natural head position during nasal breathing. Forty-five genioglossus motor units were classified into three types: inspiratory motor unit, inspiratory-expiratory motor unit and non-respiratory motor unit. The duration and instantaneous firing frequency of the inspiratory motor unit during inspiration significantly increased in the 30° headup position while it decreased in the 30° head-down position (p<0.05). The intantaneous firing frequency of the inspiratory-expiratory motor unit also significantly increased in the 30° head-up position while it decreased in the 30° head-down position (p<0.05), however, there was no significant difference between respiratory phases. These findings suggest that there are two types of respiratory-related genioglossus motor unit, which show different responses to various head positions. These genioglossus motor units may alleviate tongue collapse in altered head positions by different mechanisms.

A Longitudinal Study of the Upper Airway Negative Pressure Reflex in Newborn Lambs. 1498

It has been previously shown that the activity of the neonatal Genioglossus(GG) muscle reflexly increases only in response to large amounts of upper airway negative pressure (UANP) in lambs (Duara, Ped Res: 4:331A,1994), in comparison to the small amounts needed to activate the GG in adults. In order to evaluate maturation of the UANP reflex in lambs, we hypothesized that onset of the adult pattern would coincide with the onset of another developmental marker, namely rumination, at 3-4 weeks of age. Because hypoxia increases respiratory muscles activity, we also hypothesized that hypoxia would potentiate the UANP reflex. Therefore, we studied seven chronically instrumented lambs shortly after birth (study 1: mean±SD age 10.6±0.48 days & weight 5.47±0.43 kg) and again at approximately 1 month of age (study 2: mean±SD age 25.1 ± 0.7 days & weight 8.14 ± 0.43 kg). During surgery, EMG wires were placed in the diaphragm and GG and a mid-cervical tracheal stoma was created. The animals were allowed to recover for 24-48 hours prior to study 1. Isolated upper airways (UA) were evaluated while awake lambs were allowed to breathe through tracheostomies. End-expiratory NP of different magnitudes (-5, -10,-20, -40 cm H2O) were randomly applied to the isolated UA for 3 breaths, or 3 seconds if apnea was induced, in room air (RA) and hypoxia (10% O2 through the tracheostomy for 7-10 min). EMG activity of the GG was quantified as average activity (AvAc, area under the curve/duration) derived from the moving time average of phasic EMG output. Results revealed that there was a significant increase in the GG response in relationship to increasing magnitudes of UANP in both study 1 and study 2 (p<0.05). Hypoxia induced a significant increase in GG activity in both studies (<0.05). However, there was no significant increase in GG activity with small amounts of NP (-5 cm H2O) in either study, and hypoxia did not potentiate augmentation of GG at this level of NP. We conclude that the UANP reflex remains relatively immature in ruminating lambs, and that the adult response to low magnitude NP must occur later in development. Hypoxia augmented GG muscle activity above basal values in both studies, but did not potentiate its response to low magnitude NP. We speculate that the immature UANP reflex in neonates contributes to impaired oropharyngeal airway reopening in the event of its closure, and the failure to augment reflex activation with hypoxia may be a contributory factor in certain instances of SIDS.

Long-term facilitation of upper airway muscle activities in vagotomized and vagally intact cats.

The primary purpose of the present investigation was to determine whether long-term facilitation (LTF) of upper airway muscle activities occurs in vagotomized and vagally intact cats. Tidal volume and diaphragm, genioglossus, and nasal dilator muscle activities were recorded before, during, and after one carotid sinus nerve was stimulated five times with 2-min trains of constant current. Sixty minutes after stimulation, nasal dilator and genioglossus muscle activities were significantly greater than control in the vagotomized cats but not in the vagally intact cats. Tidal volume recorded from the vagotomized and vagally intact cats was significantly greater than control during the poststimulation period. In contrast, diaphragm activities were not significantly elevated in the poststimulation period in either group of animals. We conclude that 1) LTF of genioglossus and nasal dilator muscle activities can be evoked in vagotomized cats; 2) vagal mechanisms inhibit LTF in upper airway muscles; and 3) LTF can be evoked in accessory inspiratory muscles because LTF of inspired tidal volume was greater than LTF of diaphragm activity.

How and why should we stabilize the upper airway?

This review focuses on the evidence for upper airway instability during sleep and on the methods used to correct this instability. Upper airway patency during sleep is determined by the balance between the forces tending to constrict the pharynx (i.e. negative suction force generated by the diaphragm) and those tending to dilate in the pharynx (i.e. force acting on the tongue, soft palate and pharyngeal dilator muscles). The evidence for reduction in genioglossus activity and tensor palatini activity, failure of compensatory mechanisms to maintain these activities, and increase in upper airway resistance during sleep in reviewed. Coupled with abnormal pharyngeal anatomy to start with, the above events lead to abnormal pharyngeal function and cause repetitive episodes of airway occlusion, that is, sleep apnea. It is concluded that abnormal airway function in sleep apnea is a diffuse, rather than a localized process, that may involve the entire airway from the nasopharynx to the larynx. Methods to improve abnormal pharyngeal anatomy and pharyngeal function, such as nasal continuous positive airway pressure (CPAP), oral appliances, posture, weight loss, medications, and surgery are discussed. Given the pathophysiology of sleep apnea, that is, diffuse abnormality of the upper airway, it is reasonable to expect that only those approaches that exert a beneficial effect on the entire upper airway, as opposed to the approaches that modify only a short segment of it, may be expected to be of benefit in treatment of sleep apnea.

Control of epiglottic position in dogs: role of negative upper airway pressure

We investigated the influence of negative upper airway pressure (NUAP) on hyoepiglotticus and genioglossus muscle electromyographic (EMG) activity in anaesthetised (sodium pentobarbitone/chloralose) dogs breathing via a tracheostomy. Changes in pressure were not transmitted through the entire upper airway, thus confirming airway occlusion during NUAP. When NUAP was applied at the larynx, peak inspiratory and tonic EMG activity of the genioglossus and HE both increased significantly ( p < 0.05) and reached a plateau at NUAP of −10 to −20 cmH 2O. Nasal NUAP at any level failed to influence either genioglossus or HE EMG activity. Following bilateral section of the internal branches of the superior laryngeal nerves (SLNin), resting levels of HE and genioglossus EMG activity decreased to virtually zero. Moreover, NUAP applied at the larynx now failed to recruit EMG activity for either muscle. These findings suggest active control of epiglottic position in dogs during NUAP.

Tongue, jaw, and lip muscle activity and jaw movement during experimental chewing efforts in man.

The electromyographic (EMG) activity of the human genioglossus (GG) muscle during chewing efforts is not fully understood. In this study, the EMG activity of the human GG muscle during unilateral gum chewing was illustrated and correlated with the activities in the anterior temporalis (AT), the anterior digastric (DG), and the inferior orbicularis oris (OI) muscles. GG muscle activity was measured with customized surface electrodes, while other muscles were recorded with conventional surface electrodes. EMG activities during tongue displacement and the articulation of long vowels, recorded by the customized electrodes, were consistent with the recordings obtained by fine wire electrodes placed in the GG muscle. Jaw displacement was monitored by means of a kinesiograph with a transducer attached to the mandibular central incisors. Mean normalized GG muscle activity showed an onset in the last one-fifth of the intercuspal phase, gradually increasing during jaw-opening, and at its greatest immediately before the maximum jaw-opening position. It then decreased during jaw-closing and ceased in intercuspation but showed a small rebound in the third fifth of the intercuspal phase. The GG muscle burst showed phase lags with the DG and OI muscles and an opposite phase with the AT muscle (all P < 0.0001). All correlations were statistically significant (all P < 0.0001, r values between 0.88 and 0.97). The results suggest central coordination of the timing of the activities of the jaw, lip, and tongue muscles in chewing.

Influence of sleep onset on upper-airway muscle activity in apnea patients versus normal controls.

Current evidence suggests that patients with obstructive sleep apnea (OSA) may have augmented pharyngeal dilator muscle activity during wakefulness, to compensate for deficient anatomy. However, the isolated effect of sleep on the activity of these muscles (comparing OSA patients with controls) has not been studied. We therefore determined waking levels of genioglossus (GG) and tensor palatini (TP) muscle activity (% of maximum electromyographic [EMG] activity) in 10 OSA patients and eight controls, and then assessed the impact of the first two breaths of sleep (theta electroencephalographic [EEG] activity) following a period of stable wakefulness. Apnea patients demonstrated greater genioglossal (27.4 +/- 4.0 versus 10.7 +/- 2.1%) and tensor palatini (31.9 +/- 6.5 versus 10.6 +/- 1.9%) EMG activity than did controls during wakefulness. This augmented muscle activity in apnea patients could be reduced to near control levels during wakefulness with the application of continuous positive airway pressure (CPAP) to the upper airway. At sleep onset, control subjects demonstrated small but consistent decrements in the activity of both the TP and GG muscles. On the other hand, apnea patients demonstrated large, significantly greater decrements in TP EMG at sleep onset than did the control subjects. The effect of sleep on GG EMG in apnea patients was inconsistent, with most (n = 7) demonstrating large (significantly larger than controls) decrements in genioglossal activity. However, three OSA patients demonstrated small increments in GG EMG at sleep onset despite falling TP EMG and obstructive apnea or hypopnea. We conclude that sleep onset is associated with significantly larger decrements in TP muscle EMG activity in OSA patients than in controls, which may represent a loss of neuromuscular compensation that is present during wakefulness. However, our results for the GG muscle were more variable, and did not always support this hypothesis.

Characteristics of the genioglossus and musculus uvulae in sleep apnea hypopnea syndrome and in snorers.

Genioglossus (GG) activity has been extensively studied by electromyographic recordings in the investigation of the pathophysiology of sleep apnea-hypopnea syndrome (SAHS). However, the effective force developed by this upper airway (UA) dilator muscle depends on its metabolic and histochemical characteristics. The aim of this study was to compare the metabolic and fiber type characteristics of two UA dilator muscles, musculus uvulae (MU) and GG, in 17 patients with SAHS and in 11 nonapneic snorers. MU and GG samples were obtained during uvulopalatopharyngoplasty. Anthropomorphic characteristics were similar in snorers and patients with SAHS, who differed only in the presence of sleep-related breathing abnormalities. MU glycolytic, glycogenolytic, and anaerobic enzyme activities were significantly greater in patients with SAHS than in snorers. These differences were not observed for GG. MU and GG enzyme activities differed only in snorers. The proportion of type I muscle fiber was greater in GG than in MU, but it was similar in patients with SAHS and snorers for each muscle. Type IIA and IIB muscle fibers were, respectively, in greater and smaller proportions in patients with SAHS than in snorers. We conclude that (1) the differences in metabolic characteristics between patients with SAHS and snorers are not observed in all UA muscles, and (2) similar histochemical differences are observed in GG and MU between these two groups, thus suggesting that these differences may be implicated in the pathophysiology of SAHS.

Effects of genioglossal response to negative airway pressure on upper airway collapsibility during sleep

Continuous negative airway pressure (CNAP) trials can be used to measure upper airway (UA) collapsibility. This procedure can be accompanied by an increase in UA muscle activity. The purpose of this study was to evaluate the influence of CNAP-induced increase in genioglossal (GG) activity on UA collapsibility in 10 healthy sleeping men. UA collapsibility was measured on two occasions; each recording was preceded by the administration of a placebo or diazepam (0.15 mg/kg) in a randomized double-blind crossover design. In seven subjects, the decrease in mask pressure (Pmask) was associated with an increase in mean GG electromyographic (EMG) activity during the placebo trial, with a significant negative relationship between these two variables. This relationship was still observed with diazepam. In six subjects, the slope of the relationship between mean EMG and Pmask was less negative with diazepam. This was associated with an increase in critical pressure (Pcrit). With the placebo, a positive relationship was found between Pcrit and the slope of the mean EMG/Pmask relationship. We conclude that Pcrit is influenced by the GG response to the decrease in Pmask during CNAP.

Inspiratory coactivation of the genioglossus enlarges retroglossal space in laryngectomized humans

To investigate the relationship between the electrical activity of the genioglossus (GG-EMG) and associated tongue movement, seven laryngectomized subjects breathing through a tracheal stoma (without pressure or flow change in the upper airway) were studied in the supine position. Tongue movement, with the use of lateral fluoroscopy, and GG-EMG expressed as a percentage of maximum voluntary genioglossal activation were monitored simultaneously during 1) spontaneous inspiration (SI), 2) resistive loaded inspiration (LI), and 3) rapid inspiration (RI). Tongue position during each maneuver was compared with its position during spontaneous expiration. Peak GG-EMG during the three maneuvers was significantly different from each other (SI: 5.4 +/- 1.6, LI: 11.9 +/- 1.8, and RI: 51.6 +/- 9.4 (SE) %, respectively). Associated forward movement of the posterior aspect of the tongue was minimum during SI; however, significant movement was observed during LI, and this was increased during RI. Significant covariance existed between peak GG-EMG and this movement. Genioglossal coactivation with inspiration enlarges the glossopharyngeal airway, particularly in its caudal part. In subjects with intact upper airways, this activation may protect or enhance upper airway patency in an effort-dependent manner.

Electrophysiological brainstem investigations in obstructive sleep apnoea syndrome.

Phasic inspiratory genioglossus activity prevents pharyngeal airway collapse in healthy subjects during sleep and is diminished or absent in obstructive sleep apnoea syndrome (OSAS), thus leading to pharyngeal obstruction. Case reports of OSAS after pontomedullary lesions indicate that impaired inspiratory genioglossal activity may result from brainstem lesions. We therefore investigated brainstem functions in 18 awake patients with OSAS using brainstem auditory evoked potentials, blink reflex, masseter reflex, masseter inhibitory reflex (in 11 of 18 patients), magnetic evoked potentials of the tongue and electrooculography with vestibular testing. Fifteen of 18 patients showed no electrophysiological abnormalities. One patient had a left pontine and two patients a bilateral pontomesencephalic lesion, although a causal connection with OSAS was not conclusively confirmed. Our results do not support the assumption of a relevant structural brainstem lesion in OSAS patients with normal neurological findings.

Central and reflex neural control of genioglossus in subjects who underwent laryngectomy

Inspiratory activation of the genioglossus (GG) may occur by central drive or as a reflex to negative airway pressure. To distinguish between these, we studied seven laryngectomy patients who breathe via tracheal stomas. Negative pressure stimuli (-15 and -25 cmH2O for 500 ms) were applied 1) at functional residual capacity and 2) during early inspiration via (i) the upper airway (UA) and (ii) the tracheal stoma. Intraoral surface GG electromyogram was quantified, as described previously (R. L. Horner, J. A. Innes, K. Murphy, and A. Guz, J. Physiol. Lond. 436: 15-29, 1991). Phasic GG activity was also measured from an integrated electromyogram during spontaneous and inspiratory loaded breathing. Reflex GG activation occurred with negative UA pressure both at functional residual capacity and during inspiration (P < 0.001), but pressure stimuli at the stoma caused no significant activation (P = 0.07). Phasic inspiratory activation occurred in four patients at rest and in all seven patients during inspiratory loading (P < 0.02). These patients demonstrate 1) reflex activation of the GG by negative UA pressure without airflow or respiratory effort and 2) central inspiratory GG activation that is not mediated by negative airway pressure.

Changes in upper airway resistance during progressive normocapnic hypoxia in patients with obstructive sleep apnoea syndrome

The responses of the upper airway to progressive normocapnic hypoxia were studied in 6 healthy men and in 6 patients with obstructive sleep apnoea syndrome (OSAS). The upper airway resistance was calculated by the ratio of the laryngeal pressure (measured using a catheter introduced into oesophagus) to the inspiratory flow. Additionally, genioglossal EMG activity (GG-EMG) was measured and analysed. The changes of all variables were analysed individually for each subject. The OSAS patients showed reduced ventilatory response, GG-reactivity and changes in upper airway resistance during progressive hypoxia. It is concluded that impaired reactivity to hypoxic activation (probably due to the process of adaptation of carotid chemoreceptors to nocturnal hypoxia), might reduce the defence abilities of OSAS patients against episodes of obturation in upper airway and obstructive apnoea events.

An electromyographic analysis of orofacial motor activities during trained tongue-protrusion and biting tasks in monkeys

This study sought to characterise the electromyographic (EMG) activity patterns of orofacialmuscles during trained tongue-protrusion and biting tasks in two awake monkeys ( Macaca fascicularis). Chronic or acute EMG electrodes were placed in the anterior digastric (DIG), genioglossus (GG), masseter (MASS), platysma (PLAT), zygomaticus major (ZYGO), orbicularis oris superior (OOS), and orbicularis oris inferior (OOI) muscles and their EMG activity as well as the force signals of the tongue-protrusion and biting tasks were recorded. A total of 327 tongue-protrusion task trials and a total of 210 biting-task trials were successfully completed in several recording sessions and the EMG patterns were generally consistent between the different sessions. For the tongue task, the mean onset time of increase in GG activity significantly ( p < 0.0001) led the mean onset time of increase in the force. The DIG, GG, and OOI (and also the OOS in one of the monkeys) showed a significant ( p < 0.0001) increase in mean EMG amplitude during the holding phase, but the GG in both monkeys had the highest mean EMG amplitude ratio (MAR), i.e. the mean EMG amplitude during the holding or dynamic phase divided by the mean EMG amplitude during the pre-trial period. A similar EMG pattern was documented for different directions of the tongue-protrusion task (right, symmetrical, and left) and changes in the levels of EMG activities occurred in GG and OOI as the direction of the tongue-protrusion task changed from left to right. The task at different forces was associated with no apparent change in MAR for the holding phase for each muscle recorded. However, during the dynamic phase, only the GG showed a significant increase in EMG activity as the forces were increased. For the biting task, the mean onset times of the MASS activity and force were not significantly different. The MASS and ZYGO muscles (and the PLAT in one of the monkeys) showed a significant increase in mean EMG amplitude during the holding phase compared with the pre-trial period, and the MASS showed the highest MAR. It was also the only muscle showing a significant increase in the EMG activity when the bite-force level was increased. These findings reveal that certain orofacial muscles are selectively recruited during the two different orofacial tasks. Based on the EMG activity pattern during different directions or force levels of the task, the data suggest that, of the muscles recorded, the principal agonist for the tongue task is the GG and that for the biting task is the MASS; the other muscles that may be active appear to serve as accessories to the task.

Upper Airway Muscle Activity During REM and Non-REM Sleep of Patients With Obstructive Apnea

We measured electromyograms (EMGs) of genioglossus muscle (GG) and inspiratory intercostal muscle (IIM) in both rapid eye movement (REM) sleep and non-REM sleep of 12 patients with obstructive sleep apnea (OSA) to examine the influence of different sleep stages on upper airway muscle activity during sleep apnea. Quantifications of both muscle activities were assessed by their individual peak amplitude of integrated inspiratory EMG. Genioglossus and IIM activities showed a qualitatively similar cyclic change with an alteration of apneic and ventilatory phases during both non-REM and REM sleep. Both muscle activities increased gradually in the late apneic phase and reached each peak at the opening of the upper airway and, subsequently, decreased gradually. There were no significant differences in both muscles activities in either the ventilatory or early apneic phase between non-REM sleep and REM sleep. On the other hand, GG and IIM activities in the late apneic phase during REM sleep were significantly lower than those during non-REM sleep. The relative activity of GG to IIM in the late apneic phase was significantly lower during REM sleep than that during non-REM sleep. These results indicate that upper airway and intercostal muscle activation in the later apneic phase during REM sleep were inhibited compared with those during non-REM sleep and that this inhibition was observed predominantly in upper airway muscles.

Brain stem integration of vocalization: role of the midbrain periaqueductal gray

1. The contribution of the midbrain periaqueductal gray (PAG) to the central regulation of vocalization was investigated by analyzing the electromyographic (EMG) changes in respiratory, laryngeal, and oral muscles evoked by microinjection of D,L-homocysteic acid (DLH) in the PAG of unanesthetized, precollicular decerebrate cats. Moderate to large (6-40 nmol) doses of DLH evoked natural-sounding vocalization as well as increases in inspiratory depth and respiratory rate. 2. Two basic types of vocalization were evoked, each associated with a distinct and characteristic pattern of respiratory, laryngeal and oral EMG changes. Type A vocalization (voiced sounds such as howl/mew/growl) was characterized by excitation of the cricothyroid (CT) and thyro-arytenoid (TA) muscles, and inhibition of the posterior crico-arytenoid (PCA) muscle, whereas type B vocalization (unvoiced hiss sounds) was characterized by excitation of the PCA and TA muscles and no significant activation of the CT muscle. In addition, stronger expiratory (external oblique, internal oblique, internal intercostal) EMG increases were associated with type A responses, and larger increases in genioglossus and digastric muscle activity were associated with type B responses. 3. Microinjections of small doses of DLH (300 pmol-3 nmol), also evoked patterned changes in muscle activity (usually without audible vocalization) that, although of lower amplitude, were identical to those evoked by injections of moderate to large DLH doses. In no such experiments (175 sites) were individual muscles activated by small dose injections of DLH into the PAG. Further, type A vocalization/muscle patterns were evoked from PAG sites caudal to those at which type B vocalization/muscle patterns were evoked. 4. Considered together these results indicate: that the PAG contains topographically separable groups of neurons that coordinate laryngeal, respiratory, and oral muscle patterns characteristic of two fundamental types of vocalization and that the underlying PAG organization takes the form of a representation of muscle patterns, rather than individual muscles. 5. The patterns of EMG activity evoked by excitation of PAG neurons were strikingly similar to previously reported patterns of EMG activity characteristic of major phonatory categories in higher species, including humans (e.g., vowel phonation, voiceless consonant phonation). These findings raise the possibility that the sound production circuitry of the PAG could well be utilized by cortical and subcortical "language structures" to coordinate basic respiratory and laryngeal motor patterns that are necessary for speech.

Genioglossus muscle activity and inspiratory timing in obstructive sleep apnea

Atypical tongue muscle activity during sleep may contribute to the development of obstructive sleep apnea (OSA). Inspiratory genioglossus (GG) muscle activity was investigated in 10 OSA adults and 4 symptom-free controls. On the basis of overnight monitoring during nonREM sleep, the duration of the inspiratory GG activity and the total GG activity cycle is shorter in patients with OSA. The duration of inspiration and the duration of one total respiratory cycle is also shorter in patients with OSA. The commencement time lag between inspiratory GG activity and the onset of inspiration is shorter in patients with OSA during nonapneic breathing which indicates that inspiratory GG activity is activated relatively later in these patients. Furthermore, the inspiratory GG activity occurs after inspiration during an apnea, but the timing of GG activity onset progressively advances during the apnea. Earlier GG reactivation occurs before inspiration during the first nonoccluded breath at the end of an apnea. During subsequent tidal breathing, the timing of the GG onset progressively decreases after the onset of inspiration until the next obstructive apnea occurs. This observation suggests that the timing relationship between GG inspiratory activity and inspiratory effort is of physiologic importance in the pathogenesis of OSA. Furthermore, it may explain why dental appliances, such as the tongue retaining device, are highly effective in the resolution of OSA in selected patients.

Changes in serotonin metabolism may elicit obstructive apnoea in the newborn rat.

1. Experiments were performed on anaesthetized newborn rats (aged 3-10 days) to know whether an increase in central serotonin levels might favour the occurrence of obstructive apnoeas as previously suggested by in vitro results from our group. 2. The levels of serotonin (5-HT), its precursor 5-hydroxytryptophan (5-HTP) and its metabolite, 5-hydroxyindole-acetic acid (5-HIAA), were analysed in cerebrospinal fluid samples collected at the level of the obex prior to and after intraperitoneal injection of L-tryptophan (50 mg kg-1) in sixty-eight anaesthetized newborn rats (control rats prior to injection and injected rats 15, 30 and 45 min after the injection). A significant increase in 5-HT and 5-HTP levels occurred 30 min after the injection, attesting to the activation of 5-HT biosynthesis. 3. The EMG activity of both the genioglossus and the diaphragm was recorded before and after L-tryptophan load (50 mg kg-1) in twenty-two newborn rats. After the injection of L-tryptophan, the amplitude of the integrated genioglossus activity decreased, or was even abolished, either during a few respiratory cycles or for long periods in twenty-one out of twenty-two animals. Recovery of the genioglossus activity occurred within 45-60 min. 4. The thoracic respiratory movements and the resulting upper airway pressure changes were recorded before and after L-tryptophan injection (50 mg kg-1) in sixty-two animals. In some litters (n = 7), most of the animals (21/25) displayed, within 20-40 min of the injection, recurrent episodes of obstructive apnoea often followed by central ones. These respiratory difficulties became severe and drastic, and led in two instances to respiratory distress and death. Lower doses of L-tryptophan (10 mg kg-1) did not induce any respiratory disorders unless these were potentiated by pargyline treatment (50 mg kg-1, n = 7). The obstructive apnoeas liable to occur after an L-tryptophan load (50 mg kg-1) were prevented by blocking the 5-HT receptor with methysergide (50 mg kg-1, n = 5) or by blocking the 5-HT biosynthesis by applying p-chlorophenylalanine (PCPA) pretreatment at birth (300 mg kg-1, n = 7). In other litters (n = 6), none of the eighteen newborn rats tested were affected by L-tryptophan, however, In five young adult rats, L-tryptophan again had no effect.4+ ĕ

Control of segmental upper airway resistance in patients with obstructive sleep apnea

We sought to determine if the upper airway response to an added inspiratory resistive load (IRL) during wakefulness could be used to predict the site of upper airway collapse in patients with obstructive sleep apnea (OSA). In 10 awake patients with OSA, we investigated the relationship between resistance in three segments of the upper airway (nasal, nasopharyngeal, and oropharyngeal) and three muscles known to influence these segments (alae nasi, tensor veli palatini, and genioglossus) while the patient breathed with or without a small IRL (2 cmH2O.l-1.s). During IRL, patients with OSA exhibited increased nasopharyngeal resistance and no significant increase in either the genioglossus or tensor veli palatini activities. Neither nasal resistance nor alae nasi EMG activity was affected by IRL. We contrasted this to the response of five normal subjects, in whom we found no change in the resistance of either segment of the airway and no change in the genioglossus EMG but a significant activation of the tensor palatini. In six patients with OSA, we used the waking data to predict the site of upper airway collapse during sleep and we had limited success. The most successful index (correct in 4 of 6 patients) incorporated the greatest relative change in segmental resistance during IRL at the lowest electromyographic activity. We conclude, in patients with OSA, IRL narrows the more collapsible segment of the upper airway, in part due to inadequate activation of upper airway muscles. However, it is difficult to predict the site of upper airway collapse based on the waking measurements where upper airway muscle activity masks the passive airway characteristics.