Effect of sleep/wake state on arterial blood pressure in genetically identical mice

Genetic determinants may contribute to the large variability in arterial blood pressure responses to changes in sleep/wake state in humans. In this study, we developed techniques to examine the relationship between sleep/wake state and mean arterial pressure (MAP) in unrestrained, genetically identical mice (C57BL/6J; n = 9). The left common carotid artery was catheterized, and arterial blood gases were analyzed 24-48 h postsurgery to verify normal respiratory and metabolic function. The animals were then allowed to cycle naturally through sleep/wake states over a 3- to 4-h period while continuous polysomnography and arterial pressure measurements were made. The MAP decreased from quiet wakefulness to non-rapid-eye-movement sleep (9.8 +/- 1.3 mmHg; P < 0.001) and further decreased from non-rapid-eye-movement to rapid-eye-movement sleep (9.7 +/- 1.8 mmHg; P < 0.001). We conclude that the inbred strain of C57BL/6J mice exhibits significant and consistent changes in MAP related to sleep/wake state. Future studies can compare responses in this strain of mice with those in other inbred or transgenic mice to determine whether specific genes regulate arterial blood pressure responses to sleep/wake state.

Effect of alae nasi activation on maximal nasal inspiratory airflow in humans

The upper airway is a complicated structure that is usually widely patent during inspiration. However, on inspiration during certain physiological and pathophysiological states, the nares, pharynx, and larynx may collapse. Collapse at these locations occurs when the transmural pressure (Ptm) at a flow-limiting site (FLS) falls below a critical level (Ptm'). On airway collapse, inspiratory airflow is limited to a maximal level (VImax) determined by (-Ptm')/Rus, where Rus is the resistance upstream to the FLS. The airflow dynamics of the upper airway are affected by the activity of its associated muscles. In this study, we examine the modulation of VImax by muscle activity in the nasal airway under conditions of inspiratory airflow limitation. Each of six subjects performed sniffs through one patent nostril (pretreated with an alpha agonist) while flaring the nostril at varying levels of dilator muscle (alae nasi) EMG activity (EMGan). For each sniff, we located the nasal FLS with an airway catheter and determined VImax, Ptm', and Rus. Activation of the alae nasi from the lowest to the highest values of EMGan increased VImax from 422 +/- 156 to 753 +/- 291 ml/s (P < 0.01) and decreased Ptm' from -3.6 +/- 3.0 to -6.0 +/- 4.7 cmH2O (P < 0.05). Activation of the alae nasi had no consistent effect on Rus. VImax was positively correlated with EMGan, and Ptm' was negatively correlated with EMGan in all subjects. Our findings demonstrate that alae nasi activation increases VImax through the nasal airway by decreasing airway collapsibility.

The hypotonic upper airway in obstructive sleep apnea: role of structures and neuromuscular activity

The structural properties of the upper airway determine its collapsibility during periods of muscle hypotonia. Both rapid-eye-movement (REM) sleep and increases in nasal pressure (PN) produce hypotonia, which persists even after nasal pressure is abruptly reduced. To determine the factors that influence the collapsibility of the hypotonic airway, the critical pressure (Pcrit) and nasal resistance upstream to the site of pharyngeal collapse (RN) were measured in the first three breaths after abrupt reductions in PN during non-REM and REM sleep. PN was reduced abruptly from 15.2+/-3.2 cm H2O (mean +/- SD) for three breaths in 19 apneic patients. Upper-airway pressure-flow relationships were analyzed to determine Pcrit for each breath in non-REM and REM sleep. We found that Pcrit rose (collapsibility increased, p < 0.001) and RN fell (p = 0.02) between the first and third breath after the decrease in PN, whereas no difference in Pcrit was detected between sleep stages. In six patients, genioglossus-muscle electromyograms (EMGs) were recorded. Peak phasic activity rose between the first and third breath (p = 0.03), but tonic and peak phasic EMG activity fell in REM as compared with non-REM sleep (p < 0.001). We conclude that the hypotonic upper airway becomes most collapsible by the third breath after an abrupt decrease in PN, regardless of sleep stage and despite an increase in genioglossus-muscle activity. Our findings suggest that predominantly mechanical rather than neuromuscular factors modulate the properties of the pharynx after abrupt reductions in nasal pressure.

Relief of upper airway obstruction with hypoglossal nerve stimulation in the canine

Hypoglossal nerve stimulation was investigated as a method to relieve an induced upper airway obstruction. Six dogs were implanted with a cuff electrode applied to each hypoglossal nerve and a pulse generator. After 4 weeks, the hypoglossal nerve was stimulated (50% duty cycle) for up to 8 weeks. At 12 weeks a double tracheotomy was placed, with a negative pressure intermittently applied to the upper limb, simulating inspiratory airway pressure. Unilateral hypoglossal nerve stimulation improved peak upper airway flow from an average of 0.1 L/s to 1.6 L/s (P = 0.0001). Seventy-seven percent of the maximum possible flow (explanted tracheotomy tube) was obtained with unilateral stimulation. Histopathological evaluation revealed no nerve damage secondary to chronic stimulation. This study provides support for clinical trials of hypoglossal stimulation for obstructive sleep apnea.

Systemic and pulmonary hemodynamic responses to normal and obstructed breathing during sleep

We examined the hemodynamic responses to normal breathing and induced upper airway obstructions during sleep in a canine model of obstructive sleep apnea. During normal breathing, cardiac output decreased (12.9 +/- 3.5%, P < 0.025) from wakefulness to non-rapid-eye-movement sleep (NREM) but did not change from NREM to rapid-eye-movement (REM) sleep. There was a decrease (P < 0.05) in systemic (7.2 +/- 2.1 mmHg) and pulmonary (2.0 +/- 0.6 mmHg) arterial pressures from wakefulness to NREM sleep. In contrast, systemic (8.1 +/- 1.0 mmHg, P < 0.025), but not pulmonary, arterial pressures decreased from NREM to REM sleep. During repetitive airway obstructions (56.0 +/- 4.7 events/h) in NREM sleep, cardiac output (17.9 +/- 3.1%) and heart rate (16.2 +/- 2.5%) increased (P < 0.05), without a change in stroke volume, compared with normal breathing during NREM sleep. During single obstructive events, left (7.8 +/- 3.0%, P < 0.05) and right (7.1 +/- 0.7%, P < 0.01) ventricular outputs decreased during the apneic period. However, left (20.7 +/- 1.6%, P < 0.01) and right (24.0 +/- 4.2%, P < 0.05) ventricular outputs increased in the post-apneic period because of an increase in heart rate. Thus 1) the systemic, but not the pulmonary, circulation vasodilates during REM sleep with normal breathing; 2) heart rate, rather than stroke volume, is the dominant factor modulating ventricular output in response to apnea; and 3) left and right ventricular outputs oscillate markedly and in phase throughout the apnea cycle.

An instrument to measure functional status outcomes for disorders of excessive sleepiness

This article reports the development of the functional outcomes of sleep questionnaire (FOSQ). This is the first self-report measure designed to assess the impact of disorders of excessive sleepiness (DOES) on multiple activities of everyday living. Three samples were used in the development and psychometric analyses of the FOSQ: Sample 1 (n = 153) consisted of individuals seeking medical attention for a sleep problem and persons of similar age and gender having no sleep disorder; samples 2 (n = 24) and 3 (n = 51) were composed of patients from two medical centers diagnosed with obstructive sleep apnea (OSA). Factor analysis of the FOSQ yielded five factors: activity level, vigilance, intimacy and sexual relationships, general productivity, and social outcome. Internal reliability was excellent for both the subscales (alpha = 0.86 to alpha = 0.91) and the total scale (alpha = 0.95). Test-retest reliability of the FOSQ yielded coefficients ranging from r = 0.81 to r = 0.90 for the five subscales and r = 0.90 for the total measure. The FOSQ successfully discriminated between normal subjects and those seeking medical attention for a sleep problem (T157 = -5.88, p = 0.0001). This psychometric evaluation of the FOSQ demonstrated parameters acceptable for its application in research and in clinical practice to measure functional status outcomes for persons with DOES. Thus, the FOSQ can be used to determine how disorders of excessive sleepiness affect patients' abilities to conduct normal activities and the extent to which these abilities are improved by effective treatment of DOES.

Neuromuscular activity and upper airway collapsibility. Mechanisms of action in the decerebrate cat

We have shown that tracheal and tongue displacement represent two basic mechanisms by which upper airway collapsibility can be altered. In this study, we investigated whether hypercapnia, which activates upper airway muscles, alters upper airway collapsibility by a mechanism similar to tracheal or tongue displacement. To answer this question, we utilized a feline isolated upper airway preparation in which maximal inspiratory airflow (Vimax), the pharyngeal critical pressure (Pcrit) and the nasal resistance (Rn) upstream to the flow-limiting site (FLS) were measured. In protocol #1, upper airway airflow dynamics were studied at two levels of trachea displacement under either hypo- or hypercapnic conditions. We found that the increase in Vimax with 1 cm of caudal tracheal displacement was attenuated by hypercapnia (44 +/- 12 ml/s versus 81 +/- 7 ml/s during hypocapnia, p = 0.048), as was the decrease in Pcrit (-2.4 +/- 1.1 cm H2O versus -5.2 +/- 1.1 cm H2O, p = 0.001). In protocol #2, we investigated the effect of transecting the cervical strap muscles and hypoglossal nerves on airflow dynamics during hypercapnia. Vimax, Pcrit, and Rn did not change after transecting either the strap muscles or the hypoglossal nerves. We conclude that the primary mechanism for changes in Pcrit during hypercapnia is similar to trachea displacement and is mediated by muscles other than the straps or tongue.

Night-to-night variability in CPAP use over the first three months of treatment

The purpose of this study was to examine the relationship between night-to-night variability and nightly duration of continuous positive airway pressure (CPAP) therapy over the first 9 weeks of treatment and to determine when patients begin to establish a nonadherent pattern of use. Data were analyzed from a study of daily CPAP use covertly monitored in 32 diagnosed patients with obstructive sleep apnea (OSA) using a microprocessor monitor encased in a CPAP machine. Patterns of CPAP use were bimodal, based on the frequency of nightly use. Approximately half the subjects were consistent users of CPAP, applying it > 90% of the nights for an average of 6.22 +/- 1.21 hours per night, while the other half comprised intermittent users who had a wide range of daily use averaging 3.45 +/- 1.94 hours per night on the nights CPAP was used. The percent of days skipped was significantly correlated with decreased nightly duration (rho = -0.73, p < 0.0001). Analysis of the night-to-night pattern of use revealed that the two groups differed significantly in the nightly duration of CPAP use by the fourth day of treatment (p = 0.001). Exploration of factors that potentially differentiate the two groups revealed no reliable predictors. However, intermittent users continued to report significantly greater OSA symptoms (snoring, snorting, and apnea) posttreatment, suggesting that they continued to experience sleep disordered breathing.

Direct hypoglossal nerve stimulation in obstructive sleep apnea

OBJECTIVES

To determine the motor responses resulting from direct electrical stimulation of the hypoglossal (HG) nerve and to correlate these responses to changes in upper airway patency during sleep.

DESIGN

The motor effects of direct electrical stimulation of the main trunk of the HG nerve and the branch that supplies the genioglossus muscle during anesthesia and wakefulness were assessed visually. Responses in airflow during sleep to HG nerve stimulation were assessed with standard polysomnographic techniques.

SETTING

University medical center.

PATIENTS

Fifteen patients undergoing a surgical procedure that involved the neck that exposed the HG nerve and 5 volunteer patients with obstructive sleep apnea constituted the study population.

INTERVENTIONS

The main trunk (n = 3) and genioglossus branch (n = 2) of the HG nerve were stimulated electrically with a half-cuff tripolar electrode.

RESULTS

Stimulation of the branch of the HG nerve that innervates the genioglossus muscle caused protrusion and contralateral deviation of the tongue. Stimulation of the main trunk of the HG nerve caused slight ipsilateral deviation and retrusion of the tongue. The arousal threshold for stimulation exceeded the motor recruitment threshold by 0.8 +/- 0.4 V. Inspiratory airflow increased in all patients by 184.5 +/- 61.7 mL/s (mean +/- SD; P = .02, analysis of variance) with stimulation.

CONCLUSION

Direct HG nerve stimulation below the arousal threshold can improve airflow in patients with obstructive sleep apnea.

Electrical stimulation of upper airway musculature

Investigators have postulated that pharyngeal collapse during sleep in patients with obstructive sleep apnea (OSA) may be alleviated by stimulating the genioglossus. The effect of electrical stimulation (ES) of the genioglossus on pharyngeal patency was examined in an isolated feline upper airway preparation and in apneic humans during sleep. We found that stimulation of the genioglossus (n = 8) and of the hypoglossal nerve (n = 1) increased maximum airflow through the isolated feline upper airway in humans during sleep. Additional findings in the isolated feline upper airway suggest that such increases in airflow were due to decreases in pharyngeal collapsibility. The evidence suggests that improvements in airflow dynamics with electrical stimulation are due to selective recruitment of the genioglossus, rather than due to nonspecific activation of the pharyngeal musculature or arousal from sleep. The implications of these results for future therapy with ES are discussed.

Structural basis for alterations in upper airway collapsibility

To determine the structural basis for alterations in upper airway (UA) collapsibility, the pharyngeal critical pressure (Pcrit) was measured in an isolated feline upper airway preparation. The effect of airway elongation and dilation was explored by displacing the trachea caudally and the tongue anteriorly, respectively. With caudal-tracheal displacement, Pcrit fell progressively, a result that can be attributed to increased tension within the pharyngeal mucosa. In contrast, anterior-tongue displacement decreased Pcrit when the trachea had been caudally displaced but not with the trachea in the neutral position. These findings suggest that longitudinal tension within the airway mucosa modulates both Pcrit and the response in Pcrit to dilating forces. A mechanical model to account for these findings is discussed.

Reflex stimulation of renal sympathetic nerve activity and blood pressure in response to apnea

The purpose of this study was to examine the role of afferent input in the reflex modulation of renal sympathetic nerve activity (SNA) in response to apnea. Apneas of 20-, 40-, and 60-s duration were induced in the anesthetized, paralyzed cat (n = 7) ventilated with either room air or 100% oxygen. While receiving room air, there were increases (p < 0.005) in renal SNA of 34.5 +/- 4.2%, 53.3 +/- 6.4%, and 59.9 +/- 7.2% of maximum during the 20-, 40-, and 60-s apneas, respectively. There were corresponding increases (p < 0.025) in mean arterial pressure (Pa) of 9 +/- 3, 30 +/- 9, and 45 +/- 12 mm Hg during the 20-, 40-, and 60-s apneas while receiving room air, respectively. The effect of 100% oxygen was to reduce (p < 0.0001) the renal SNA response to apnea, at a matched level of PaCO2, by at least 80%, and to eliminate any increase in Pa. During the first breath of the postapneic period, there was a partial inhibition of renal SNA. During the second and third breaths of the postapneic period, there was a marked fall in renal SNA that was associated with a precipitous decline in directly recorded carotid chemoreceptor activity (n = 2). The magnitude of the fall in renal SNA after apnea was related to the degree of postapneic hypertension. We conclude that hypoxic chemoreceptor stimulation is the predominant factor generating the renal SNA response to apnea, with modulating inputs from thoracic afferents and arterial baroreceptors likely contributing to the marked inhibition of renal SNA immediately after the apnea.

Peripheral course of genioglossal motor axons within the hypoglossal nerve of the rat

The spatial compartmentalization of motor axons in cranial nerves has not been previously demonstrated. In the present study, motor axons in the medial lingual ramus of the hypoglossal nerve of rats were labeled using horseradish peroxidase and diaminobenzidine staining methods. Neuronal axons were segregated into fascicles within the main nerve trunk (average total length: 10.4 mm). Light microscopic examination of stained nerve sections revealed reaction product within individual axons and showed that the grouping of labeled nerve fibers in the medial ramus was maintained for at least the peripheral half of the nerve before the stain faded. The authors propose that the fascicular anatomy of the rat hypoglossal cranial nerve resembles that of peripheral spinal nerves in humans. This functional and structural compartmentalization may have a clinical impact on the repair and treatment of cranial nerve pathologies.

The study of maximal nasal inspiratory flow in humans

During inspiration through one nostril, airflow becomes limited to a maximal level (VImax) when the transmural pressure (Ptm) at a flow-limiting site (FLS) falls below a critical level (Ptm'). We compared two methods for measuring the Ptm' of the nasal FLS. Each of six subjects (four normal and two with allergic rhinitis out of season) performed multiple inspirations through one nostril as we varied the resistance at the nasal opening. Studies were performed after application of a topical decongestant without activation of the alae nasi. We determined Ptm' by regressing the resulting values of VImax on the corresponding transnasal pressure gradients (Regression Method). We also measured Ptm' directly using pressure catheters to measure the pressure surrounding the FLS and the lateral pressure near the FLS at VImax (Catheter Method). The mean value of Ptm' by the Regression Method was -3.8 +/- 3.2 (SD) cmH2O. The value by the Catheter Method with the catheter just downstream from the nasal FLS was -3.5 +/- 2.9 cmH2O, which correlated closely with the Ptm by the Regression Method (r = 0.98). Our findings suggest that the Ptm' of the nasal airway can be determined by either method. The Catheter Method, however, requires only one inspiratory effort for each determination and simultaneously localizes the nasal FLS.

Electrical stimulation of the lingual musculature in obstructive sleep apnea

The influence of lingual muscle activity on airflow dynamics in the upper airway was examined in nine patients with obstructive sleep apnea. Muscles that retract the tongue (hyoglossus and styloglossus) and protrude the tongue (genioglossus) were selectively stimulated electrically during sleep with fine wire electrodes placed intramuscularly transorally. We confirmed that stimulation with 50 Hz and 40-microseconds pulse duration did not elicit changes in electroencephalographic patterns or heart rate or alter airflow after the stimulation burst had ceased. The highest stimulus intensity that did not arouse patients from sleep was then utilized to examine the effect of lingual muscle recruitment on airflow dynamics during steady-state periods of inspiratory airflow limitation. When applying a stimulus burst during single inspirations, maximal inspiratory airflow decreased by 239 +/- 177 ml/s (P < 0.05) during retractor stimulation, whereas maximal inspiratory airflow increased by 217 +/- 93 ml/s during protrusor stimulation (P < 0.001) compared with breaths immediately before and after the stimulated breath. When consecutive inspirations were stimulated repeatedly, protrusor stimulation decreased the frequency of obstructive breathing episodes in four patients breathing at 3.9 +/- 3.4 (SD) cmH2O nasal pressure. The findings suggest that stimulation of the lingual muscles can increase or decrease airflow depending on the specific muscles stimulated without arousing patients from sleep.

Obstructive sleep apnea presenting during infantry field exercises: does the Army Weight Control Program protect soldiers from obstructive sleep apnea?

We report two cases of obstructive sleep apnea (OSA) that presented during infantry field exercises as snoring so loud as to risk betraying the unit's position. Both patients exceeded the height-weight standards of the Army Weight Control Program (AWCP). Since high body mass is a strong risk factor for OSA, we asked whether the AWCP reduces the risk of OSA. We found that it should for women in all age groups and for men over 40, but it is less protective for younger men (who constitute a large portion of Army personnel). In light of this and of previous estimates that up to 1.5% of all Army personnel exceed the AWCP standards, we conclude that there may be a significant number of unrecognized cases of OSA in the Army. Additionally, tightening of the AWCP standards may be warranted for women under 30 and men under 50, who currently are permitted to significantly exceed ideal body weight.

Effect of tracheal and tongue displacement on upper airway airflow dynamics

We have previously shown that caudal tracheal displacement alters the airflow dynamics of the upper airway. In the present study, we specifically examined the effects of tongue and tracheal displacement on upper airway airflow dynamics. To determine how tongue and tracheal displacement modulate maximal inspiratory airflow (VImax), we analyzed the pressure-flow relationships obtained in the isolated upper airway of paralyzed cats. VImax and its determinants, the pharyngeal critical pressure (Pcrit) and the nasal resistance (Rn) upstream to the flow-limiting site, were measured as tongue displacement and tracheal displacement were systematically varied. Four results were obtained: 1) there was no independent effect of tongue displacement on VImax, Pcrit, or Rn; 2) there was an increase in VImax with 2 cm of tracheal displacement, which was associated with a decrease in Pcrit and an increase in Rn; 3) there was an interactive effect of tongue and tracheal displacement on VImax and Pcrit but not on Rn; and 4) there was a large increase in VImax with tongue displacement > 2.5 cm with the trachea nondisplaced, which was associated with a large decrease in Pcrit and a large increase in Rn. We conclude that tongue and tracheal displacement exert differing influences on airflow dynamics and present a mechanical model of the upper airway that explains these results.

Airway obstruction during sleep increases blood pressure without arousal

Recent studies suggest that arousal is the dominant factor acutely increasing blood pressure in obstructive sleep apnea and that neither stimulation of chemoreceptors nor mechanical factors associated with large negative swings in intrapleural pressure substantially contribute to the rise in blood pressure associated with each obstructive apneic event. A canine model of obstructive sleep apnea was used to examine the relative contributions of these mechanisms in the blood pressure response to induced airway obstruction during non-rapid-eye-movement sleep. In part A of the study, the arousal response was eliminated from an obstructive event by restoring airway patency just before the expected arousal, allowing blood pressure responses to be compared between obstructive events with and without arousal. In part B of the study, the protocol of Part A was repeated after pharmacological blockade of the autonomic nervous system with hexamethonium (20 mg/kg iv), eliminating neurally mediated responses due to arousal, stimulation of chemoreceptors, or other reflexes, while maintaining any mechanical effects on blood pressure related to swings in intrapleural pressure. The results of part A (n = 4 dogs) show that obstructive apneic events of 28.5 +/- 3.1 s duration, with arterial hemoglobin desaturation to 92.9 +/- 0.8% and airway pressure swings of -37.6 +/- 6 mmHg, significantly increased mean arterial pressure (MAP) by 13.8 +/- 1.5 mmHg in the absence of arousal (P < 0.005). In comparison, when arousal was allowed to occur, MAP increased by a further 11.8 +/- 1.2 mmHg (P < 0.01). In part B (n = 3 dogs), there was no change in MAP during the obstructive apneic event, and MAP fell by > 10 mmHg in the postobstruction period whether or not arousal occurred (P < 0.05). We conclude that neural reflexes, but not mechanical factors, substantially contribute to the acute blood pressure response to an obstructive apneic event and that arousal produces a separate, additional acute hypertensive response.

Effect of blood pressure changes on air flow dynamics in the upper airway of the decerebrate cat

BACKGROUND

Previous studies suggest that upper airway neuromuscular activity can be affected by changes in blood pressure via a baroreceptor-mediated mechanism. It was hypothesized that increases in blood pressure would increase upper airway collapsibility predisposing to airway obstruction at a flow-limiting site in the hypopharynx.

METHODS

To examine the effect of blood pressure on upper airway function, maximal inspiratory air flow was determined through the isolated feline upper airway before, during, and after intravenous infusion of phenylephrine (10-20 micrograms.kg-1.min) in six decerebrate, tracheotomized cats. Inspiratory flow, hypopharyngeal pressure, and pressure at the site of pharyngeal collapse were recorded as hypopharyngeal pressure was rapidly decreased to achieve inspiratory flow limitation in the isolated upper airway. Pressure-flow relationships were used to determine maximal inspiratory air flow and its mechanical determinants, the upper airway critical pressure (a measure of pharyngeal collapsibility), and the nasal resistance upstream to the site of flow limitation.

RESULTS

An increased mean arterial blood pressure of 71 +/- 16 mmHg (mean +/- SD) was associated with significant decrease in maximal inspiratory air flow from 147 +/- 38 ml/s to 115 +/- 27 ml.sec-1 (P < 0.01). The decrease in maximal inspiratory air flow was associated with an increase in upper airway critical pressure from -8.1 +/- 3.8 to -5.7 +/- 3.7 cm H2O (p < 0.02), with no significant change in nasal resistance. When blood pressure was decreased to baseline by discontinuing the phenylephrine infusion, maximal inspiratory air flow and upper airway critical pressure returned to their baseline values.

CONCLUSIONS

Increased blood pressure increased the severity of upper airway air flow obstruction by increasing pharyngeal collapsibility. Previous studies relating baroreceptor activity to neuromuscular regulation of upper airway tone, are consistent with this effect being mediated by afferent activity from baroreceptors. These findings warrant further study because they suggest the possibility that upper airway obstruction in postoperative patients could either be caused or exacerbated by an increase in blood pressure.

The effects of selective nerve stimulation on upper airway airflow mechanics

OBJECTIVE

To evaluate the effect of electrical stimulation of hypoglossal nerve branches and ansa cervicalis nerve branches on upper airway patency.

DESIGN

Pressure-flow relationships obtained during supramaximal stimulation of hypoglossal nerve branches and ansa cervicalis nerve branches were analyzed in the isolated feline upper airway to determine the maximum inspiratory airflow as well as to determine pharyngeal collapsibility (upper airway critical pressure) and nasal resistance upstream from the site of pharyngeal collapse. Comparisons were performed between baseline and stimulation conditions with paired two-tailed t tests.

RESULTS

Stimulation of the proximal hypoglossal nerve trunk, distal medial hypoglossal nerve branch, nerve branches to the suprahyoid muscles, the infrahyoid muscles, and the suprahyoid and infrahyoid muscles simultaneously increased maximum inspiratory airflow significantly by decreasing airway collapsibility. A greater reduction in airway collapsibility was observed with stimulation of the tongue muscles compared with stimulation of the strap muscles.

CONCLUSIONS

Stimulation of specific hypoglossal and ansa cervicalis nerve branches consistently increased maximum inspiratory airflow by decreasing airway collapsibility. The major decrease in airway collapsibility from hypoglossal nerve stimulation is dependent on the action of the genioglossus muscle.

A dog model to investigate the relationship between obstructive sleep apnoea and blood pressure regulation

Patients exhibiting obstructive sleep apnoea (OSA) do not display a normal circadian pattern of blood pressure. It is not clear whether this disruption of the circadian blood pressure pattern is a result of the intermittent airway obstruction during sleep or is the result of confounding factors, such as obesity and age, which are common in OSA and may independently affect blood pressure. To determine if a cause and effect relationship exists between repetitive airway obstruction during sleep and blood pressure regulation a chronically instrumented canine model of OSA has been developed. This canine model has been shown to reproduce the characteristic apnoea and hypersomnolence of human OSA. Furthermore, in this model a 12-h nocturnal period of repetitive airway obstruction during sleep caused an increase in baseline blood pressure of more than 10 mmHg that was sustained for at least two hours following the restoration of normal airway patency. These results imply that there is a cause and effect relationship between intermittent airway obstruction during sleep and elevated blood pressure.

Effect of hypertension on upper airway function and sleep apnoea

Current evidence suggests that elevations in blood pressure during obstructive apnoeic episodes increase pharyngeal collapsibility and the severity of obstructive sleep apnoea.

A survey screen for prediction of apnea

Questionnaire data from patients presenting at three sleep disorders centers were used to develop and assess a screening tool for sleep apnea based on the reporting of the frequency of various symptoms of sleep apnea and other sleep disorders plus age, body mass index (BMI) and gender. Patients were not specifically referred for suspicion of sleep apnea. Separate factor analyses of survey responses from 658, 193 and 77 respondents from the first, second and third sites, respectively, each yielded four orthogonal factors, one of which accounted for all the questions concerned with the frequency of disordered breathing during sleep. The survey was shown to be reliable in a subset of patients from one of the sites (test-retest correlation = 0.92). Survey data were then compared to a clinical measure of sleep apnea (respiratory disturbance index) obtained from polysomnography. A multivariable apnea risk index including survey responses, age, gender and BMI was estimated using multiple logistic regression in a total sample of 427 respondents from two of the sites. Predictive ability was assessed using receiver operating characteristic (ROC) curves. The area under the ROC curve was 0.79 (p < 0.0001). For BMI alone, it was 0.73, and for an index measuring the self-report of the frequency of apnea symptoms, it was 0.70. The multivariable apnea risk index has potential utility in clinical settings.

Diagnosis and treatment of obstructive sleep apnea of the larynx

To determine the mechanism for obstructive sleep apnea in two patients with clinical abnormalities of laryngeal function, airflow dynamics during sleep were analyzed. The site of airway obstruction was assessed by examining pressure gradients across specific airway segments. The relation between maximal inspiratory airflow and nasal pressure was analyzed to determine (1) the critical pressure, a measure of the collapsibility of the laryngeal airway, and (2) the effect of nasal continuous positive airway pressure on airflow during sleep. Large inspiratory pressure gradients developed during sleep between the supraglottic and pleural spaces, indicating that collapse had occurred in the larynx. Elevated critical pressures of -6.4 and +1.2 cm H2O, respectively, occurred in the two patients. When the nasal pressure was raised to 10 cm H2O, normal levels of tidal airflow occurred, and obstructive apneas were eliminated. These findings indicate that sleep apnea was caused by laryngeal airflow obstruction that resulted from elevations in the collapsibility of the larynx. The response to nasal continuous positive airway pressure suggested that laryngeal sleep apnea was similar to pharyngeal sleep apnea in pathophysiologic characteristic and response to treatment.