Suppression of spontaneous breathing during high-frequency jet ventilation

The effect of ventilatory frequency of high-frequency jet ventilation (HFJV) from 1 to 5 Hz, apart from changes in thoracic volume, on spontaneous breathing activity was studied in Yorkshire piglets under pentobarbital anesthesia. The highest P_aCO₂ at which the animals did not breathe against the ventilator (apnea point) was established either by changing minute volume of ventilation or by adding CO₂ to the respiratory gas. The higher the apnea point, the higher the suppression of spontaneous breathing activity was assumed to be. If the apnea point was searched for by changing minute volume a progressive increase of suppression of spontaneous respiratory activity was found at ventilatory rates of 3 Hz or more, concomitantly with a rise in end-expiratory pressure (P_EE). In case the tidal volume was kept constant, increase of ventilatory rate resulted in a tremendous increase of lung volume, together with considerably higher levels of P_EE. When under these conditions the apnea point was searched for by adding CO₂ to the respiratory gas a much higher CO₂-drive was needed for spontaneous breathing and therefore a much stronger inhibition of spontaneous breathing was concluded. By placing the animals in a body box in which pressure could be varied, thoracic volume could be kept constant during HFJV. When thoracic volume was kept constant in this way a constant tidal volume at increasing jet frequencies resulted in only a slight increase in suppression of spontaneous breathing.We conclude that the increase in lung volume is a major factor in suppressing central respiratory activity during HFJV. Jet frequency by itself might be an additional suppressive factor. Airway CO₂ did not seem to have an important effect.     

Common sleep problems in ICU: heart failure and sleep-disordered breathing syndromes

Ventilation during sleep is under tight metabolic control, and can be destabilized by upper airway obstruction leading to snoring or obstructive apneas, inadequate respiratory pump muscle activity leading to hypoventilation, and central control instability leading to changes in metabolic feedback and loop gain. These three physiologic disturbances can lead to obstructive sleep apnea hypopnea syndrome (OSAHS), hypoventilation syndromes, and periodic breathing. OSAHS places a strain on the cardiac output by virtue of hypoxemia, large negative intrathoracic pressures, and high swings in systemic blood pressure. Periodic breathing, also known as central sleep apnea with Cheyne-Stokes pattern of respiration, is likely to be a product of advanced heart failure.     

快速预氧在妇产科门诊手术中的应用

目的 观察术前快速预氧对妇产科门诊手术中因呼吸抑制缺氧患者的预防作用。方法 采用电脑产生随机序列，将拟接受静脉全身麻醉的120例妇产科患者，将病人随机分为快速预氧（试验）组和常规吸氧（对照）组，每组各60例。快速预氧组患者在麻醉前做8次深呼吸，常规吸氧组保持自然呼吸，麻醉方法均为咪唑安定1mg、芬太尼1μg/kg、丙泊酚2mg／kg，术中间断推注丙泊酚。观察麻醉时间、异丙酚总量、术中呼吸抑制和呼吸暂停发生率及呼气末二氧化碳浓度（PetCO2）和SpO2变化情况。结果 两组的一般情况、麻醉时间和丙泊酚用量差异无统计学意义。两组间呼吸抑制和呼吸暂停的发生率差异无统计学意义（P〉0．05）。与快速预氧组相比，常规吸氧组中SpO2值下降更明显，缺氧的发生率更高（P〈0．05）。结论 麻醉前快速预吸氧能增加机体氧储备，提高对缺氧的耐受性，可有效避免门诊手术中呼吸抑制所致的缺氧。     

Suppression of spontaneous breathing during high-frequency jet ventilation

Conditions which suppress spontaneous breathing activity during high-frequency jet ventilation (HFJV) were analysed in Yorkshire piglets under pentobarbital anesthesia. The highest P_aCO₂ at which the animals did not breathe against the ventilator (apnea point) was established during different patterns of ventilation, either by changing the minute volume or by adding CO₂ to the inspiratory gas. Arterial oxygen tension was maintained throughout the study above 80 mm Hg. An elevation of ventilatory rate increased the apnea point, suggesting a progressive suppression of spontaneous breathing. This suppression did not depend on the amount of lung stretch during insufflation, because at higher rates lower tidal volumes were used. Suppression also appeared to be independent of insufflatory flow, i.e. the velocity of lung stretch. At higher frequencies end-expiratory airway pressure (P_EE) increased and there appeared to be a positive relationship between the apnea point and P_EE. In a separate series this positive relationship between the apnea point and P_EE was confirmed. A hysteresis effect in this relationship, however, suggests that other than jet frequency, lung volume rather than positive end-expiratory pressure (PEEP) is a major determinant of suppression of spontaneous breathing activity during HFJV.     

Continuous in vivo oxygen saturation in newborn infants with pulmonary disease: a new fiberoptic catheter oximeter.

We measured the in vivo oxygen saturation of hemoglobin in the arterial blood of 34 sick newborn infants with a new, rapidly responding, continuously recording, catheter oximeter. The oxygen saturation, SaO2, was found to fluctuate between 85 and 95% in infants with pulmonary disease who are in a stable condition and breathing spontaneously. Severe disaturation occurred during apnea and after procedures such as chest percussion and suctioning of the endotrachael tube. The effects of changes in respiratory therapy were quickly manifested by changes in SaO2. This was particularly useful in guiding resuscitation of newborn infants who were asphyxiated at birth. Blood sampling for measurement of PaO2 can be done less frequently, reducing the need for blood transfusions in small infants.     

七氟醚全身麻醉保留自主呼吸在输尿管下激光碎石术的应用

目的探讨全程七氟醚全身麻醉保留自主呼吸在输尿管下激光碎石术的可行性和安全性。方法选择ASA分级Ⅰ～Ⅱ级择期在全身麻醉下实施输尿管下激光碎石术的患者60例,随机分为自主通气组(S组,n=30)和机械通气组(M组,n=30)。S组应用七氟醚诱导,待下颌松弛后插入喉罩,保留自主呼吸并维持至术毕;M组应用七氟醚及维库溴铵全麻诱导后插入喉罩并予以机械通气。记录两组患者诱导时间,清醒时间及麻醉诱导前(T0)、喉罩置入即刻(T1)、喉罩置入后3min(T2)、喉罩置入后30min(T3)、喉罩拔除即刻(T4)、喉罩拔除后20min(T5)的血流动力学及经皮氧饱和度(SpO2)、呼末二氧化碳(PetCO2)。同时记录吸气末七氟烷浓度(CINSEV)和呼气末七氟烷浓度(CETSEV)并抽取动脉血行血气分析。结果 S组和M组各有2例和3例患者因中转进腹退出研究。两组患者均获得满意的插管条件,但S组的麻醉诱导时间明显长于M组,两组的差异有统计学意义(t=28.43,P<0.05),且喉罩置入前所需的的CENSEV明显高于M组,S组间清醒时间短于M组,诱导期及术中PetCO2高于M组,两组的差异均有统计学意义(t分别=27.61、2.78、4.34、3.10,P均<0.05),但均在允许范围内。结论七氟醚全身麻醉保留自主呼吸可提供充分的氧供,不引起危害性的二氧化碳潴留。但需要较高的吸气末七氟烷浓度获得满意的插管条件。术中及术后血流动力及呼吸功能均能维持接近生理状态,在肌松要求不高的手术全麻中可免用机械通气。     

Breathing circuit respiratory work in infants recovering from respiratory failure

OBJECTIVE: To compare cardiopulmonary function during spontaneous breathing with three continuous-flow breathing circuits. The major difference between these circuits was the degree of flow resistance offered by the exhalation valve. DESIGN: Randomized crossover trial. PATIENTS: Twelve infants less than 12 months of age recovering from respiratory failure of variable etiology. Only patients weighing 3 to 10 kg were studied. INTERVENTIONS: The patients were connected to each respiratory circuit in a random sequence, with 15 min allowed for equilibration before assessment of cardiopulmonary function. Airway pressure (Paw) and FIO2 were maintained unchanged. MEASUREMENTS AND MAIN RESULTS: Ventilation, gas exchange, or circulatory function were not altered significantly by changing the breathing circuit. However, Paw and esophageal pressure fluctuations were altered and were largest during breathing with the circuit that had an exhalation valve with high-flow resistance. The Paw fluctuation recorded while the patient was breathing with the flow-resistor circuit increased with weight and exceeded 2 cm H2O in all patients weighing greater than 4.5 kg. Paw fluctuation could be decreased by greater than 2 cm H2O in ten of 12 patients by using the threshold-resistor circuit. CONCLUSIONS: The results indicate a need for evaluating the characteristics of respiratory circuits used for spontaneous breathing in infants and children, to avoid unnecessary equipment-related increase in respiratory work.     

Adaptive mechanical backup ventilation for preterm infants on respiratory assist modes – a pilot study

Background Mechanical respiratory-assist modes, such as assist/control, low-rate intermittent mandatory ventilation, continuous positive airway pressure, or proportional assist ventilation (PAV), require a continuous respiratory effort. Because of the frequent occurrence of periodic breathing and/or apnea, mechanical backup ventilation must be initiated during episodes of reduced or absent respiratory drive to maintain gas exchange. The common approach to this problem is a regular conventional mechanical ventilation, which is initiated and withdrawn in an “on/off” function. Objective To develop and evaluate a mechanical backup ventilation mode that is adaptive to the rapidly changing breathing pattern of preterm infants. Design Prospective randomized clinical crossover trial. Setting Neonatal intensive care unit at the University of Munich, Germany. Patients Preterm infants undergoing PAV. Interventions The infants were ventilated with PAV using a newly developed adaptive backup support, with and without pulse-oximetry-guided operation (SpO₂-sensitive backup). Each infant was ventilated with both modes of backup support on 2 consecutive days, with the sequence randomized. Measurements and results The analysis on 11 preterm infants showed a statistically significant and clinically relevant reduction of the incidence (33%) and duration of oxygen desaturations (52%) when SpO₂-sensitive adaptive backup support was used. Conclusions SpO₂-sensitive adaptive backup proved safe and effective in reducing the incidence and duration of oxygen desaturation in this short-term trial. This technology is potentially applicable to other assisted modalities of ventilation, such as noninvasive nasal ventilation.     

机械通气中呼吸拮抗时药物治疗对血流动力学及呼吸功能的影响

目的研究机械通气中呼吸拮抗时应用咪唑安定和潘可罗宁对血流动力学及呼吸功能的影响。方法将30例机械通气中发生呼吸拮抗的患者随机分成3组,组1使用潘可罗宁,组2联合使用咪唑安定和潘可罗宁,组3使用咪唑安定。分别观察3组用药前及用药后5、15、30和60min时人机协调情况,并监测血压、心率、呼吸频率及脉搏血氧饱和度(SpO2)的动态变化。结果3组患者用药前均存在人机对抗,自主呼吸频率快SpO2下降。组2患者用药后呼吸改善最明显,人机协调一致率高,用药30min内达100%,且持续时间长;血压、心率变化小,呼吸改善及低氧血症纠正好。组1用药后5min人机协调一致率即达100%,但持续时间短;血压和心率显著升高,自主呼吸频率及低氧血症有所改善。组3人机协调一致率最低;血压、心率、呼吸频率及低氧血症均无明显变化。结论咪唑安定和潘可罗宁合用能保持循环功能稳定,维持合适的通气功能,是一种能够合理改善机械通气中呼吸拮抗的药物治疗方法。     

Noninvasive positive pressure ventilation in infants with upper airway obstruction: comparison of continuous and bilevel positive pressure

Objective This study evaluated the efficacy of noninvasive continuous positive pressure (CPAP) ventilation in infants with severe upper airway obstruction and compared CPAP to bilevel positive airway pressure (BIPAP) ventilation.Design and setting Prospective, randomized, controlled study in the pulmonary pediatric department of a university hospital.Patients Ten infants (median age 9.5 months, range 3—18) with laryngomalacia (n=5), tracheomalacia (n=3), tracheal hypoplasia (n=1), and Pierre Robin syndrome (n=1)Interventions Breathing pattern and respiratory effort were measured by esophageal and transdiaphragmatic pressure monitoring during spontaneous breathing, with or without CPAP and BIPAP ventilation.Measurements and results Median respiratory rate decreased from 45 breaths/min (range 24–84) during spontaneous breathing to 29 (range 18–60) during CPAP ventilation. All indices of respiratory effort decreased significantly during CPAP ventilation compared to unassisted spontaneous breathing (median, range): esophageal pressure swing from 28 to 10 cmH₂O (13–76 to 7–28), esophageal pressure time product from 695 to 143 cmH₂O/s per minute (264–1417 to 98–469), diaphragmatic pressure time product from 845 to 195 cmH₂O/s per minute (264–1417 to 159–1183) During BIPAP ventilation a similar decrease in respiratory effort was observed but with patient-ventilator asynchrony in all patients.Conclusions This short-term study shows that noninvasive CPAP and BIPAP ventilation are associated with a significant and comparable decrease in respiratory effort in infants with upper airway obstruction. However, BIPAP ventilation was associated with patient-ventilator asynchrony.     

不同护理体位对鼻饲喂养早产儿的影响

目的 探讨不同体位护理对于鼻饲喂养早产儿临床效果及安全性的影响。方法 选择2015年3月至2017年9月我院新生儿科收治的早产儿66例为研究对象, 随机将其分成A、B、C、D 4组。A组(16例)采用15°仰卧位,B组(17例)采用30°仰卧位,C组(15例)采用15°俯卧位,D组(18例)采用30°俯卧位。比较4组心率(HR)、呼吸频率(RR)、经皮血氧饱和度(TcPO₂)、血压(Bp)等指标的变化,并观察早产儿胃内潴留及呼吸暂停、周期性呼吸的发生情况。结果 4组的HR、RR、TcPO₂及平均动脉压均维持在正常范围以内,C、D组HR、RR、平均动脉压较A、B组降低,而TcPO₂较A、B组升高,B、D组各指标分别优于A、C组;C、D组胃潴留量较A、B组显著减少;仅A组发生2例呼吸暂停,4组护理发生周期性呼吸的差异无统计学意义(χ²=2.269,P=0.519)。结论 仰卧、俯卧位护理对于鼻饲喂养早产儿的生命体征影响均较小,而取俯卧位、头部抬高体位进行护理,更有利于早产儿呼吸及胃部排空,减少并发症发生。     

The impact of spontaneous breathing during mechanical ventilation

PURPOSE OF REVIEW: In patients with acute respiratory distress syndrome, controlled mechanical ventilation is generally used in the initial phase to ensure adequate alveolar ventilation, arterial oxygenation, and to reduce work of breathing without causing further damage to the lungs. Although introduced as weaning techniques, partial ventilator support modes have become standard techniques for primary mechanical ventilator support. This review evaluates the physiological and clinical effects of persisting spontaneous breathing during ventilator support in patients with acute respiratory distress syndrome. RECENT FINDINGS: The improvements in pulmonary gas exchange, systemic blood flow and oxygen supply to the tissue which have been observed when spontaneous breathing has been maintained during mechanical ventilation are reflected in the clinical improvement in the patient's condition. Computer tomography observations demonstrated that spontaneous breathing improves gas exchange by redistribution of ventilation and end-expiratory gas to dependent, juxtadiaphragmatic lung regions and thereby promotes alveolar recruitment. Thus, spontaneous breathing during ventilator support counters the undesirable cyclic alveolar collapse in dependent lung regions. In addition, spontaneous breathing during ventilator support may prevent increase in sedation beyond a level of comfort to adapt the patient to mechanical ventilation which decreases duration of mechanical ventilator support, length of stay in the intensive care unit, and overall costs of care giving. SUMMARY: In view of the recently available data, it can be concluded that maintained spontaneous breathing during mechanical ventilation should not be suppressed even in patients with severe pulmonary functional disorders.     

BIPAP用于全身麻醉气管拔管后短期呼吸支持可行性分析

目的：比较和分析BIPAP用于全身麻醉气管拔管后短期呼吸支持的可行性。方法：60例成年择期手术病人随机分为3组（n=20），全麻气管导管拔除后分别予以BIPAP（B组）、CPAP＋PSV（C组）、SIMV＋CPAP（S组）面罩无创机械通气，记录并比较3组予以面罩无创通气后不同时刻血流动力学、血气参数、呼吸参数、并发症发生率及耐受性。结果：（1）3组无创通气后15min血压、心率较基础值明显增加（P＜0．01），S组比B组、C组增加更为明显（P＜0．01），B组、C组在30min以后血流动力学逐渐恢复至基础值，而S组在60分钟时才恢复至无创通气前水平；（2）分钟通气量相同时，B组、C组气道最高压力及平均压低于S组（P＜0．05）、且随无创通气逐渐降低，而S组变化不明显，B组自主呼吸恢复比S组明显（P＜0．05）；（3）3组无创通气后PaO2均显著增加（P＜0．01），PaCO2均在正常生理范围，但S组有升高（P＜0．05）；（4）三组并发症发生率及胃肠减压气体引流量无明显差异（P＞0．05）：（5）B组、C组比S组耐受性更好（P＜0．01）。结论：BIPAP对血流动力学、呼吸功能影响小、允许任何时相的自主呼吸、耐受性良好、并发症少、适用范围广，应用于全身麻醉后短期呼吸支持具有可行性。     

Relationship between breath-synchronous arterial pressure and heart rate variations during orthostatic stress

It has recently been shown that the phase relationship between respiration-induced changes in arterial pressure (AP) and heart rate (HR) are different in supine and upright postures. We wanted to further analyse the coupling between respiration, arterial blood pressure and HR in the time domain, and how this coupling was altered during orthostatic stress. Nine healthy subjects were studied. Respiration-induced changes in AP and HR were recorded during frequency- and volume-controlled breathing. This was done during supine rest with and without lower body negative pressure (-50 mmHg) (LBNP). All experiments were performed after beta1-blockade. Responses were averaged breath-by-breath to enhance the time resolution and to eliminate noise. The respiration-induced changes in arterial pulse pressure (PP) were different between control and LBNP: The peak in PP during the respiratory cycle occurred 0.9 +/- 0.8 (mean +/- SD) s before the onset of inspiration during supine control and 0.8 +/- 2.1 s after the onset of inspiration during LBNP (P = 0.03). These changes in the timing of peak PP significantly distorted the cyclic systolic AP and mean AP fluctuations during LBNP. Despite the altered AP response with LBNP, HR fluctuations closely correlated in time with respiration in all conditions, albeit with a significantly reduced amplitude during LBNP (-49%, P = 0.01). The results points to a lack of coupling between AP and HR during paced breathing and thus suggest that respiratory sinus dysrhythmia at least, to a large extent, is independent of the arterial baroreflex.     

Capnography for the Nonintubated Patient in the Emergency Setting

Background

Multiple studies illustrate the benefits of waveform capnography in the nonintubated patient. This type of monitoring is routinely used by anesthesia providers to recognize ventilation issues. Its role in the administration of deep sedation is well defined. Prehospital providers embrace the ease and benefit of monitoring capnography. Currently, few community-based emergency physicians utilize capnography with the nonintubated patient.

Objective

This article will identify clinical areas where monitoring end-tidal carbon dioxide is beneficial to the emergency provider and patient.

Discussion

Capnography provides real-time data to aid in the diagnosis and patient monitoring for patient states beyond procedural sedation and bronchospasm. Capnographic changes provide valuable information in such processes as diabetic ketoacidosis, seizures, pulmonary embolism, and malignant hyperthermia.

Conclusions

Capnography is a quick, low-cost method of enhancing patient safety with the potential to improve the clinician's diagnostic power.     

Feasibility of non-invasive pressure support ventilation in infants with respiratory failure after extubation: a pilot study

Objective  To evaluate the feasibility and effects of non-invasive pressure support ventilation (NIV) on the breathing pattern in infants developing respiratory failure after extubation. Design  Prospective pilot clinical study; each patient served as their own control. Setting  A nine-bed paediatric intensive care unit of a tertiary university hospital. Patients  Six patients (median age 5 months, range 0.5–7 months; median weight 4.2 kg, range 3.8–5.1 kg) who developed respiratory failure after extubation. Interventions  After a period of spontaneous breathing (SB), children who developed respiratory failure were treated with NIV. Measurements and results  Measurements included clinical dyspnoea score (DS), blood gases and oesophageal pressure recordings, which were analysed for respiratory rate (RR), oesophageal inspiratory pressure swing (dPes) and oesophageal pressure-time product (PTPes). All data were collected during both periods (SB and NIV). When comparing NIV with SB, DS was reduced by 44% (P < 0.001), RR by 32% (P < 0.001), dPes by 45% (P < 0.01) and PTPes by 57% (P < 0.001). A non-significant trend for decrease in PaCO₂ was observed. Conclusion  In these infants, non-invasive pressure support ventilation with turbine flow generator induced a reduction of breathing frequency, dPes and PTPes, indicating reduced load of the inspiratory muscles. NIV can be used with some benefits in infants with respiratory failure after extubation.     

Detection of Ventricular Tachycardia and Fibrillation Using Coronary Sinus Blood Temperature: A Feasibility Study

This study investigated the potential of coronary sinus blood temperature to detect ventricular arrhythmias. A rapid-response, thermistor-tipped catheter placed in the coronary venous system of anesthetized dogs was used to record the blood temperature during periods of induced bradycardia, tachycardia, and ventricular fibrillation. A second catheter was used to measure blood temperature in the aortic arch during these same episodes. A pulsatile component of venous blood temperature, typically 40 m°C in amplitude, was well correlated with the cardiac cycle, while another, slightly larger, pulsatile component was well correlated with respiration. The cardiac component peaked during ventricular systole, and the respiratory component peaked during expiration. As compared with sinus rhythm, the cardiac signal diminished during hradycardia and tachycardia and nearly disappeared during asystole and ventricular fibrillation. The baseline component of venous blood temperature rose during periods of tachycardia and fibrillation, while respiration proved to be an important factor in the baseline temperatures. The presence of small, cyclic, thermal variations in the coronary venous system was verified, and the concept of measuring metabolic activity to assess ventricular function was substantiated. These studies show promise that this concept could be incorporated into medical devices that use these temperature signals for diagnosis of ventricular arrhythmias.     

Thoracocardiography: Noninvasive monitoring of left ventricular stroke volume

Thoracocardiography noninvasively monitors global stroke volume by inductive plethysmographic recording of ventricular volume curves as previously validated by thermodilution. Our purpose was to investigate the potential of thoracocardiography to individually assess stroke volume of the left ventricle. We hypothesized that curves predominantly reflecting left ventricular volume could be obtained by recording waveforms from thoracocardiographic transducers placed at various levels around the chest, and by identifying their origin as the left ventricle if mean expiratory exceeded mean respiratory stroke volumes during spontaneous breathing. Stroke volumes obtained by thoracocardiography in normal subjects were compared beat by beat with estimates derived from simultaneous measurements of left ventricular cavity stroke area by echocardiography with automatic boundary detection. Changes in respiratory variations of stroke volumes were analyzed during spontaneous breathing at fixed rate and tidal volume, during mechanical ventilation, and resistive loaded breathing. In 170 comparisons of beat-by-beat stroke volumes, 89% of thoracocardiographic fell within ±20% of echocardiographic estimates. Changes in tidal volume, resistive loaded breathing, and mechanical ventilation induced respiratory variations of thoracocardiographic derived stroke volumes consistent with the known effect of respiratory changes in intrapleural pressure on left ventricular stroke volumes. The results suggest that thoracocardiography noninvasively tracks changes in left ventricular stroke volumes. Their absolute value may also be monitored if an initial calibration by an independent technique, such as echocardiography, is performed.     

Cuffed oropharyngeal airway: a new tool for airway management

The aim of the study was to evaluate the use of cuffed oropharyngeal airway (COPA) in spontaneously breathing patients (n = 162) under total anesthesia and to compare the new method with the laryngeal mask (LM) (n = 172). COPA provided adequate well-hermetized airway in operations under total anesthesia on spontaneously breathing patients. COPA can serve as an alternative to LM in patients with spontaneous respiration, as no appreciable differences in the incidence and type of complications in the two groups were observed. COPA extends the anesthesiologist's potentialities in ensuring reliable patency of airways, is simple, and requires no special training.     

Implementation of a Wearable Ultrasound Device for the Overnight Monitoring of Tongue Base Deformation during Obstructive Sleep Apnea Events

Obstructive sleep apnea (OSA) is a breathing disorder characterized by the repeated collapse of the pharyngeal airway during sleep. Previous studies have reported that tongue base deformation may be a major contributing factor. However, overnight monitoring of tongue motion in patients with OSA has previously been impracticable. We developed a wearable ultrasound device for prolonged recording during natural sleep of the changes in tongue base thickness (TBT) in patients with OSA. The maximum TBT was fed into a polysomnography system so that physiologic signals and TBT data were simultaneously monitored. Subject trials revealed that TBT increased significantly during snoring, hypopnea and apnea events during natural sleep in patients with OSA. Moreover, the data revealed that the location of the maximum TBT during normal breathing was significantly different compared with the location during obstructive respiratory events, which implies a posterior or inferior displacement of the tongue base during sleep apnea.