Differences in Predicted Therapeutic Outcome of Mandibular Advancement Determined by Remotely Controlled Mandibular Positioner in Canadian and Chinese Apneic Patients.

Background: In-lab mandibular protrusive titration using a remotely controlled mandibular positioner (RCMP) could predict the success rate of mandibular advancement device (MAD) and reliably determine the Optimal Protrusive Position (OPP) for obstructive sleep apnea (OSA) patients. The aim of this study was to compare MAD success rate using in-lab RCMP manual titration performed in Caucasian and Chinese OSA patients. Methods: Manual RCMP titration was performed during an in-lab sleep study using the same procedure that had been previously reported in untreated Caucasian and Chinese OSA patients. Success rate was determined according to classical success criteria or to those previously used for RCMP titration. Results: A total of 160 subjects were included in this study, and conclusive data were obtained from 141 (71 Chinese and 70 Caucasian OSA patients). Chinese patients were significantly younger, with lower BMI and more severe OSA disease than the Canadian counterparts. Among patients with predicted success, the OPP expressed in % of full protrusion position did not differ between the two ethnic groups. Chinese ethnicity, younger age and lower baseline AHI were significant determinants of RCMP success. In a multivariate analysis, only ethnicity and AHI were found to significantly account for success, the odds ratio for success in Chinese compared to Caucasians corrected for AHI being 3.7 and 4.6 depending on criteria used to define success. Conclusion: Although the OSA disease was more severe in Chinese patients, the predicted success rate of MAD according to RCMP titration was higher in Chinese than in Caucasians. This study was registered on ClinicalTrials.gov (NCT03231254).

Association of insomnia and short sleep duration, alone or with comorbid obstructive sleep apnea, and the risk of chronic kidney disease.

STUDY OBJECTIVES: Obstructive sleep apnea (OSA), sleep fragmentation, and short sleep duration (SD) have been associated with chronic kidney disease (CKD). However, these potential mechanisms for CKD have not been compared in the same cohort. This study investigated the independent and combined impact of OSA and insomnia with short sleep duration on the risk of CKD progression in a sleep clinic population. METHODS: In a cross-sectional study design, adults with suspected OSA completed an overnight sleep study and a questionnaire that included the Insomnia Severity Index (ISI) and Pittsburgh Sleep Quality Index (PSQI). They also provided blood and urine samples for measurement of the glomerular filtration rate and urine albumin:creatinine ratio, from which the risk of CKD progression was determined. RESULTS: Participants (n = 732, 41% female, 55 ± 13 years) were categorized into four groups: no/mild OSA without insomnia (NM-OSA, n = 203), insomnia with SD without OSA (Insomnia-SD, n = 104), moderate-to-severe OSA without insomnia (MS-OSA, n = 242), and comorbid insomnia and OSA with SD (COMISA-SD, n = 183). After stratification, 12.8% of NM-OSA, 15.4% of Insomnia-SD, 28.9% of MS-OSA, and 31.7% of the COMISA-SD participants had an increased risk of CKD progression. Compared to NM-OSA, the odds ratio (OR) for an increased risk of CKD progression was not increased in Insomnia-SD (OR 0.95, confidence interval [CI]: 0.45-1.99) and was increased to the same degree in MS-OSA (OR 2.79, CI: 1.60-4.85) and COMISA-SD (OR 3.04, CI: 1.69-5.47). However, the ORs were similar between the MS-OSA and COMISA-SD groups across all statistical models (p ≥ .883). CONCLUSIONS: In a sleep clinic population, insomnia with short sleep duration does not increase the risk of CKD progression; nor does it further increase the risk of CKD progression associated with moderate-to-severe OSA.

Risk of chronic kidney disease in patients with obstructive sleep apnea.

STUDY OBJECTIVES: Chronic kidney disease (CKD) is a global health concern and a major risk factor for cardiovascular morbidity and mortality. Obstructive sleep apnea (OSA) may exacerbate this risk by contributing to the development of CKD. This study investigated the prevalence and patient awareness of the risk of CKD progression in individuals with OSA. METHODS: Adults referred to five Canadian academic sleep centers for suspected OSA completed a questionnaire, a home sleep apnea test or in-lab polysomnography and provided blood and urine samples for measurement of estimated glomerular filtration rate (eGFR) and the albumin:creatinine ratio (ACR), respectively. The risk of CKD progression was estimated from a heat map incorporating both eGFR and ACR. RESULTS: 1295 adults (42% female, 54 ± 13 years) were categorized based on the oxygen desaturation index (4% desaturation): <15 (no/mild OSA, n = 552), 15-30 (moderate OSA, n = 322), and >30 (severe OSA, n = 421). After stratification, 13.6% of the no/mild OSA group, 28.9% of the moderate OSA group, and 30.9% of the severe OSA group had a moderate-to-very high risk of CKD progression (p < .001), which was defined as an eGFR <60 mL/min/1.73 m2, an ACR ≥3 mg/mmol, or both. Compared to those with no/mild OSA, the odds ratio for moderate-to-very high risk of CKD progression was 2.63 (95% CI: 1.79-3.85) for moderate OSA and 2.96 (2.04-4.30) for severe OSA after adjustment for CKD risk factors. Among patients at increased risk of CKD progression, 73% were unaware they had abnormal kidney function. CONCLUSION: Patients with moderate and severe OSA have an increased risk of CKD progression independent of other CKD risk factors; most patients are unaware of this increased risk.

Assessment of tongue mechanical properties using different contraction tasks.

Inadequate upper airway (UA) dilator muscle function may play an important role in the pathophysiology of obstructive sleep apnea (OSA). To date, tongue mechanical properties have been assessed mainly using protrusion protocol with conflicting results. Performance during elevation tasks among patients with OSA remains unknown. This study aimed at assessing tongue muscle strength, strength stability, endurance time, fatigue indices, and total muscle work, using elevation and protrusion tasks with repetitive isometric fatiguing contractions in 12 normal plus mild, 17 moderate, and 11 severe patients with OSA, and to assess the influence of body mass index (BMI) and age. Endurance time was longer in protrusion than elevation task (P = 0.01). In both tasks, endurance time was negatively correlated with baseline value of strength coefficient of variation (P < 0.01). Compared with other groups, patients with moderate OSA had the lowest total muscle work for protrusion (P = 0.01) and shortest endurance time (P = 0.04), regardless of the type of task. Additionally, in patients with moderate-severe OSA, the total muscle work for both tasks was lower in nonobese compared with obese (P < 0.05). Total muscle work for protrusion was positively correlated with apnea hypopnea index (AHI) in obese subjects (P < 0.01). Endurance time was shorter (P < 0.01) and recovery time longer (P = 0.02) in the old compared with young subjects. In conclusion, the tongue is more prone to fatigue during the elevation task and in patients with moderate OSA. Obesity appeared to prevent alteration of tongue mechanical properties in patients with OSA. Baseline strength stability and endurance were related, illustrating the role of central neuromuscular output in tongue resistance to fatigue.NEW & NOTEWORTHY To our knowledge, this is the first study to assess and compare tongue function using both elevation and protrusion tasks with repetitive isometric fatiguing contractions in subjects with different OSA status. Tongue mechanical performance seemed to differ between protrusion and elevation tasks and depend on the severity of OSA.

Effects of repetitive transcranial magnetic stimulation of upper airway muscles during sleep in obstructive sleep apnea patients.

We tested the hypothesis that stimulating the genioglossus by repetitive transcranial magnetic stimulation (rTMS) during the ascendant portion of the inspiratory flow of airflow-limited breaths would sustain the recruitment of upper airway dilator muscles over time and improve airway dynamics without arousing obstructive sleep apnea (OSA) patients. In a cross-sectional design, nine OSA patients underwent a rTMS trial during stable non-rapid eye movement (NREM) sleep. Submental muscle motor threshold (SUB) and motor-evoked potential were evaluated during wakefulness and sleep. During NREM sleep, maximal inspiratory flow, inspiratory volume, inspiratory time, shifts of electroencephalogram frequency, and pulse rate variability were assessed under three different stimulation paradigms completed at 1.2 sleep SUB stimulation output: 1) 5Hz-08 (stimulation frequency: 5 Hz; duration of train stimulation: 0.8 s); 2) 25Hz-02 (stimulation frequency: 25 Hz; duration of train stimulation: 0.2 s); and 3) 25Hz-04 (stimulation frequency: 25 Hz; duration of train stimulation: 0.4 s). SUB increased during NREM sleep (wakefulness: 23.8 ± 6.1%; NREM: 26.8 ± 5.2%; = 0.001). Two distinct airflow patterns were observed in response to rTMS: with and without initial airflow drops, without other airflow variables change regardless the stimulation paradigm applied. Finally, rTMS-induced cortical and/or autonomic arousal were observed in 36, 26, and 35% of all delivered rTMS trains during 5Hz-08, 25Hz-02, and 25Hz-04 stimulation paradigms, respectively. In conclusion, rTMS does not provide any airflow improvement of flow-limited breaths as seen with nonrepetitive TMS of upper airway dilator muscles. However, rTMS trains were free of arousals in the majority of cases.

Diaphragm and genioglossus corticomotor excitability in patients with obstructive sleep apnea and control subjects.

Corticomotor excitability of peripheral muscles appears to be altered in patients with obstructive sleep apnea. However, there is no evidence of such alteration for upper airway/respiratory muscles that are involved in the pathophysiology of this disease. The aim of this study was to compare the effects of hypercapnic stimulation on diaphragm and genioglossus corticomotor excitability in awake healthy subjects versus patients with obstructive sleep apnea. Corticomotor excitability was assessed by transcranial magnetic stimulation in 12 untreated apneic men (48 ± 10 years; body mass index = 28.9 ± 4.7 kg m(-2); apnea-hypopnoea index = 41 ± 23 events per hour) and nine control men (45 ± 10 years; body mass index = 27.3 ± 3.3 kg m(-2); apnea-hypopnoea index = 7 ± 4 events per hour). Assessments included diaphragm and genioglossus expiratory motor thresholds, and transcranial magnetic stimulation-induced motor-evoked potential characteristics obtained while breathing room air or 5% CO2 (random order) and then 7% CO2 both balanced with pure O2. Transcranial magnetic stimulation twitches were applied during early inspiration and end expiration. Diaphragm motor-evoked potential amplitudes increased and expiratory diaphragm motor-evoked potential latencies decreased during CO2-induced increase in ventilatory drive, with no difference in these responses between patients with obstructive sleep apnea and control subjects. Expiratory genioglossus motor-evoked potential amplitudes were significantly lower in patients with obstructive sleep apnea than in control subjects. Baseline activity of the genioglossus increased with increasing FiCO2, this effect being significantly higher in patients with obstructive sleep apnea than in control subjects. However, neither genioglossus motor-evoked potential amplitudes nor latencies were significantly modified with increasing FiCO2 both in patients with obstructive sleep apnea and in control subjects. Corticomotor excitability of genioglossus and diaphragm are not altered during CO2-induced increase in ventilatory drive in patients with obstructive sleep apnea.

Effects of one-week tongue task training on sleep apnea severity: A pilot study.

The aim of the present study was to assess the effects of one-week tongue-task training (TTT) on sleep apnea severity in sleep apnea subjects. Ten patients with sleep apnea (seven men, mean [± SD] age 52 ± 8 years; mean apnea-hypopnea [AHI] index 20.9 ± 5.3 events/h) underwent 1 h TTT in the authors' laboratory on seven consecutive days. A complete or limited recording and tongue maximal protruding force were assessed before and after one-week TTT. One-week TTT was associated with a global AHI decrease (pre-TTT: 20.9 ± 5.3 events/h; post-TTT: 16.1 ± 5.1 events/h; P<0.001) and AHI decrease during rapid eye movement sleep (pre-TTT: 32.2 ± 18.4 events/h; post-TTT: 16.7 ± 6.6 events/h; P=0.03), while protruding force remained unchanged. The authors consider these results to be potentially clinically relevant and worthy of further investigation in a large randomized trial.

Mechanical effects of repetitive transcranial magnetic stimulation of upper airway muscles in awake obstructive sleep apnoea subjects.

NEW FINDINGS: What is the central question of this study? Can repetitive transcranial magnetic stimulation (rTMS) of the genioglossus enhance the beneficial effects observed with transcranial magnetic stimulation single twitches on upper airway mechanical properties? What is the main finding and its importance? We found that both inspiratory and expiratory rTMS protocols induce a different activation pattern of upper airway muscles, with evidence for an increase in genioglossus corticomotor excitability in response to rTMS. This is of major importance because it might open the door for rTMS protocols with the goal of increasing corticomotor excitability and, thus, possibly increasing the tonic genioglossus activity, which is known to be diminished during sleep in subjects with sleep apnoea. ABSTRACT: Stimulation of upper airway (UA) muscles during sleep by isolated transcranial magnetic stimulation (TMS) twitch can improve airflow dynamics without arousal, but the effect of repetitive TMS (rTMS) on UA dynamics is unknown. Phrenic nerve magnetic stimulation (PNMS) can be used to produce painless experimental twitch-induced flow limitation during wakefulness. The aim of this study was to quantify the effects of rTMS applied during wakefulness on UA mechanical properties using PNMS in subjects with obstructive sleep apnoea (OSA). Phrenic nerve magnetic stimulation was applied to 10 subjects, with and without simultaneous rTMS, during inspiration and expiration. Flow-limitation characteristics and UA obstruction level were determined [maximal (V̇I,max)and minimal inspiratory airflow (V̇I,min),V̇I,max-V̇I,min flow drop (ΔV̇I),oropharyngeal (POro,peak ) and velopharyngeal peak pressures, oropharyngeal k1 /k2 ratios with k1 and k2 determined by the polynomial regression model between instantaneous flow and pharyngeal pressure and UA resistance]. Both genioglossus and diaphragm root mean squares and motor-evoked potential amplitudes (geniolossus, GGAmp ) and latencies were computed. A flow-limitation pattern always occurred after PNMS. A decrease in V̇I,max and an increase in ΔV̇I occurred following rTMS applied during inspiration, and POro,peak values were more negative with both inspiratory and expiratory rTMS. The GGAmp also increased significantly from the second to the last rTMS expiratory train twitch. All other parameters remained unchanged. These results suggest the following conclusions: (i) rTMS does not improve UA mechanical properties in awake subjects with OSA; (ii) the activation pattern of UA muscles differs following isolated twitch and repetitive cortical stimulation of the genioglossus; and (iii) rTMS applied during expiration induces corticomotor facilitation.

Impact of stepwise mandibular advancement on upper airway mechanics in obstructive sleep apnea using phrenic nerve magnetic stimulation.

Mandibular advancement devices (MAD) represent a potential treatment for obstructive sleep apnea (OSA). However, their mechanisms of actions are not completely understood. This study was aimed to explore the effects of MAD-induced mandibular protrusion on upper airway mechanics. 25 men commencing treatment for OSA with MAD were recruited. Phrenic nerve magnetic stimulation (PNMS) was used to measure flow/pressure relationship during progressive protrusion in three conditions (without MAD, MAD at minimum protrusion, and MAD at maximum tolerable protrusion). Pressures were recorded simultaneously at three different upper airway segments (naso-, velo-, and oro-pharynx). Without MAD, PNMS twitches induced flow-limitation at the velopharyngeal level in 19 subjects and six of them experienced a shift in the flow-limitation site to the lower segment with MAD at maximum protrusion. An association was found between having a velopharyngeal limitation site without MAD and the increase in maximum flow with the advanced MAD. These data suggest that mandibular advancement devices are acting predominantly at the velopharyngeal level.

Consecutive transcranial magnetic stimulation twitches reduce flow limitation during sleep in apnoeic patients.

NEW FINDINGS: What is the central question of this study? A transcranial magnetic stimulation (TMS)-induced twitch applied on isolated single breaths over the motor cortex somatotopic representation of the tongue briefly recruits submental muscles and improves airflow dynamics of flow-limited respiratory cycles without arousing sleep apnoea patients. However, the mechanical impact of the TMS-induced twitch applied during consecutive breathing cycles on airflow dynamics remains unknown. What is the main finding and what is its importance? Our results show that application of TMS with the stimulator output set at the sleep submental motor threshold intensity on consecutive respiratory cycles increases inspiratory flow and reduces the turbulent airflow component. These results indicate an improvement of airflow pattern after two single consecutive TMS-induced twitches without arousing sleep apnoea patients. Transcranial magnetic stimulation (TMS)-induced twitches applied on isolated breaths briefly recruit upper airway dilator muscles and improve airflow and inspiratory volume without arousing apnoeic patients from sleep, but the effects of applying such twitches consecutively on airflow dynamics is unknown. The objective of this study was to quantify the effects of five consecutive TMS-induced twitches applied on sleep-induced obstructive hypopnoeic breaths in 10 obstructive sleep apnoea patients. Submental muscle motor threshold (SUBMT) and motor-evoked potential were measured during wakefulness and sleep. The TMS-induced twitches were applied during stable non-rapid eye movement (NREM) sleep, at the beginning of inspiration of consecutive flow-limited respiratory cycles, with the stimulator output set at sleep SUBMT. Maximal inspiratory flow, inspiratory volume, inspiratory time, shifts of electroencephalogram frequency and pulse rate variability were assessed. During sleep, SUBMT increased (wakefulness, 25.3 ± 4.9%; NREM sleep, 27.0 ± 6.2%; P = 0.02). During each series of stimulations there was a rise in maximal inspiratory flow (from 306.7 ± 123.2 to 359.8 ± 154.1 ml s(-1); P = 0.0002) and in inspiratory volume (from 346.1 ± 128.1 to 414.9 ± 171.2 ml; P = 0.02) without differences in thoraco-abdominal efforts and inspiratory time. These responses were observed in the absence of arousals and ceased immediately after TMS interruption. Transcranial magnetic stimulation-induced cortical and/or autonomic arousal was observed in 30.2% of all series of stimulation. Consecutive twitch TMS of submental muscles may lead to arousals in a minority of patients but can be applied on consecutive respiratory cycles during sleep and can significantly improve maximal inspiratory flow and inspiratory volume of flow-limited cycles.

Acute upper airway muscle and inspiratory flow responses to transcranial magnetic stimulation during sleep in apnoeic patients.

Transcranial magnetic stimulation (TMS) can activate the corticobulbar system and briefly recruit upper airway dilator muscles, improving the inspiratory airflow dynamics of flow-limited respiratory cycles during sleep. The purpose of this investigation was to quantify the effects of TMS-induced twitches applied during sleep on flow-limited respiratory cycles in 14 obstructive sleep apnoea patients. Submental muscle motor threshold (SUB(MT)) and motor-evoked potential (SUB(MEP)) were examined during wakefulness and sleep. The TMS-induced twitches were applied during stable non-rapid eye movement (NREM) sleep, during non-consecutive flow-limited respiratory cycles at the beginning of inspiration, with intensities varying from sleep SUB(MT) up to maximal stimulation without arousal. Maximal inspiratory flow, inspiratory volume, shifts of electroencephalogram frequency and pulse rate variability were assessed. Cortical and/or autonomic arousal after TMS was observed in only 13.8% of all twitches applied. The SUB(MT) increased during NREM sleep (wakefulness, 24.8 ± 9.3%; and NREM sleep, 28.3 ± 9.5%; P = 0.003). Augmenting stimulator output from SUB(MT) to maximal stimulation before arousal enhanced SUB(MEP) peak-to-peak amplitude (from 0.09 ± 0.05 to 0.4 ± 0.3 mV; P = 0.005) with a concomitant rise in maximal inspiratory flow (from 376.2 ± 107.9 to 411.9 ± 109.3 ml s(-1); P = 0.008) and inspiratory volume (from 594.8 ± 189.2 to 663.7 ± 203.1 ml; P = 0.001) in all but one patient. Corticobulbar excitability of submental muscles decreases during NREM sleep. Brief recruitment of submental muscles with TMS during sleep improves upper airway mechanics without arousing patients from sleep.

Impact of CPAP interface and mandibular advancement device on upper airway mechanical properties assessed with phrenic nerve stimulation in sleep apnea patients.

Oronasal mask (ONM) can be used when mouth leaks impair nasal-CPAP effectiveness. However, ONM's constraint on the chin and straps' traction may alter upper airway (UA) mechanical properties. In contrast, mandibular advancement device associated with nasal-CPAP (NM+MAD) may reduce UA resistance. The aim of this exploratory study was to compare the effects of ONM, NM, and NM+MAD on UA mechanical properties. The three interface modalities were assessed in 11 OSAS patients at 6, 8, 10 cmH(2)O CPAP using a phrenic nerve magnetic stimulation (PNMS) protocol. PNMS-twitches' related flow, pharyngeal pressures (nasopharynx, velopharynx, oropharynx) and UA resistances were determined. Regardless of CPAP level, twitch-induced maximum flow was higher with NM+MAD than with ONM. Velopharyngeal resistance was higher with ONM than with NM+MAD. Oropharyngeal resistance was higher with ONM than with NM. In conclusion, NM+MAD reduced velopharyngeal resistance compared to those measured with ONM and NM alone. We hypothesize that this strategy may help reducing the effective pressure level and thus further limit the risk for mouth leaks.

Influence of negative airway pressure on upper airway dynamic and impact on night-time apnea worsening.

BACKGROUND: Negative airway pressure loading such as seen during obstructive apnea/hypopnea may influence upper airway (UA) mechanical properties. We measured the effects of such loading on UA mechanical properties during wakefulness and assessed the potential link with night-time apnea worsening. METHODS: Twitch stimulations of the phrenic nerve were applied before and after a step-by-step increase in UA suction flow in 10 sleep apnea and 10 control males. RESULTS: Inspiratory closing pressure was lower in control than in apneic subjects. No consistent changes were observed in UA mechanical properties before and after the trial. In apneic patients, changes in the apnea index from the beginning to the end of the night correlated with changes in inspiratory closing pressure following suction flow. CONCLUSION: (1) Apnea phenotype does not influence the impact of negative airway pressure on UA dynamic properties during wakefulness and (2) worsening of sleep apnea frequency during the night may relate to the exposure to recurrent UA negative pressure.

Assessment of upper airway dynamics by anterior magnetic phrenic stimulation in conscious sleep apnea patients.

Phrenic nerve magnetic stimulation (PNMS) performed anterolaterally at the base of the neck (BAMPS) and cervical magnetic stimulation are common techniques for assessing upper airway (UA) mechanical properties in conscious humans. We considered that if NMS performed at the sternal level (a-MS) could induce a similar percentage of flow-limited twitches as BAMPS in conscious subjects, gauging UA dynamic properties by PNMS would be simplified. Instantaneous flow, pharyngeal and esophageal pressures, as well as thoraco-abdominal motion were recorded in 10 conscious sleep apnea patients. BAMPS and a-MS were applied at end expiration. The percentage of flow-limited twitches, maximal tolerated intensity, and minimal stimulator output associated with flow-limited twitches were similar between BAMPS and a-MS. Examining the effects of stimulation site, stimulation intensity and site*intensity interaction on the characteristics of flow-limited twitches, the former was responsible for more negative peak esophageal pressure (BAMPS: -11.5 ± 0.9 cmH(2)O; a-MS: -6.5 ± 1.1 cmH(2)O; P = 0.002) and UA closing pressure (BAMPS: -7.7 ± 0.5 cmH(2)O; a-MS: -5.8 ± 0.6 cmH(2)O; P = 0.02) as well as for lower mean linear upper airway resistance (UAR) (BAMPS 3.5 ± 0.4 cmH(2)O·l(-1)·s(-1); a-MS 2.2 ± 0.4 cmH(2)O·l(-1)·s(-1); P = 0.02). a-MS systematically evoked outward/inward thoracic displacement, although this movement pattern was observed in only 50% of patients when they were subjected to BAMPS. Linear UAR of BAMPS-induced flow-limited twitches was lower in the presence of initial outward thoracic movement (2 ± 0.05 cmH(2)O·l(-1)·s(-1)) than with inward motion (4.3 ± 1.5 cmH(2)O·l(-1)·s(-1); P = 0.03). We conclude that a-MS represents a practical and functional technique to evaluate UA mechanical properties in conscious sleep apnea patients.

Influence of CO2 on upper airway muscles and chest wall/diaphragm corticomotor responses assessed by transcranial magnetic stimulation in awake healthy subjects.

RATIONALE: Functional interaction between upper airway (UA) dilator muscles and the diaphragm is crucial in the maintenance of UA patency. This interaction could be altered by increasing respiratory drive. The aim of our study was to compare the effects of hypercapnic stimulation on diaphragm and genioglossus corticomotor responses to transcranial magnetic stimulation (TMS). METHODS: 10 self-reported healthy men (32 ± 9 yr; body mass index = 24 ± 3 kg/m(-2)) breathed, in random order, room air or 5% and then 7% Fi(CO(2)), both balanced with pure O(2). Assessments included ventilatory variables, isoflow UA resistance (at 300 ml/s), measurement of lower chest wall/diaphragm (LCW/diaphragm), and genioglossus motor threshold (MT) and motor-evoked potential (MEP) characteristics. TMS twitches were applied during early inspiration and end expiration at stimulation intensity 30% above LCW/diaphragm and genioglossus MT. RESULTS: Compared with room air, CO(2) inhalation significantly augmented minute ventilation, maximal inspiratory flow, tidal volume, and tidal volume/respiratory time ratio. UA resistance was unchanged with CO(2) inhalation. During 7% CO(2) breathing, LCW/diaphragm MT decreased by 9.6 ± 10.1% whereas genioglossus MT increased by 7.2 ± 9%. CO(2)-induced ventilatory stimulation led to elevation of LCW/diaphragm MEP amplitudes during inspiration but not during expiration. LCW/diaphragm MEP latencies remained unaltered both during inspiration and expiration. Genioglossus MEP latencies and amplitudes were unchanged with CO(2). CONCLUSION: In awake, healthy subjects, CO(2)-induced hyperventilation is associated with heightened LCW/diaphragm corticomotor activation without modulating genioglossus MEP responses. This imbalance may promote UA instability during increased respiratory drive.

Assessment of upper airway dynamic properties using sternal phrenic nerve magnetic stimulation in awake subjects.

To assess upper airway (UA) dynamic properties, magnetic stimulation of the phrenic nerves (MSPN) is usually performed at cervical level or anterior-laterally at the neck base. We hypothesized that UA dynamic properties could be effectively assessed by MSPN performed at the sternal level. Instantaneous flow, pharyngeal and mask pressures were recorded in 12 healthy awake subjects. End-expiratory MSPN were applied in random order with a non-focal coil placed behind the 7th cervical vertebrae (C7-MS) and at the sternal level (a-MS). The percentage of flow-limited twitches was greater with a-MS (a-MS: 33% and C7-MS: 2%; P<0.0001). For the non flow-limited twitches, maximal inspiratory flow was 36% greater (P<0.001) and isoflow UA resistance was lower with a-MS (0.6±0.1 and 0.9±0.1 cmH2Ol(-1)s; P=0.02). Maximal inspiratory flow of flow-limited twitches was 78% greater (P=0.05) and isoflow UA resistance tended to be lesser with a-MS (0.9±0.3 and 1.8±0.7 cmH2Ol(-1)s; P=0.09). a-MS could be a practical approach for assessing UA dynamic properties in awake subjects.