Preload Dependence Is Associated with Reduced Sublingual Microcirculation during Major Abdominal Surgery.

BACKGROUND: Dynamic indices, such as pulse pressure variation, detect preload dependence and are used to predict fluid responsiveness. The behavior of sublingual microcirculation during preload dependence is unknown during major abdominal surgery. The purpose of this study was to test the hypothesis that during abdominal surgery, microvascular perfusion is impaired during preload dependence and recovers after fluid administration. METHODS: This prospective observational study included patients having major abdominal surgery. Pulse pressure variation was used to identify preload dependence. A fluid challenge was performed when pulse pressure variation was greater than 13%. Macrocirculation variables (mean arterial pressure, heart rate, stroke volume index, and pulse pressure variation) and sublingual microcirculation variables (perfused vessel density, microvascular flow index, proportion of perfused vessels, and flow heterogeneity index) were recorded every 10 min. RESULTS: In 17 patients, who contributed 32 preload dependence episodes, the occurrence of preload dependence during major abdominal surgery was associated with a decrease in mean arterial pressure (72 ± 9 vs. 83 ± 15 mmHg [mean ± SD]; P = 0.016) and stroke volume index (36 ± 8 vs. 43 ± 8 ml/m; P < 0.001) with a concomitant decrease in microvascular flow index (median [interquartile range], 2.33 [1.81, 2.75] vs. 2.84 [2.56, 2.88]; P = 0.009) and perfused vessel density (14.9 [12.0, 16.4] vs. 16.1 mm/mm [14.7, 21.4], P = 0.009), while heterogeneity index was increased from 0.2 (0.2, 0.4) to 0.5 (0.4, 0.7; P = 0.001). After fluid challenge, all microvascular parameters and the stroke volume index improved, while mean arterial pressure and heart rate remained unchanged. CONCLUSIONS: Preload dependence was associated with reduced sublingual microcirculation during major abdominal surgery. Fluid administration successfully restored microvascular perfusion.

Sublingual microcirculatory blood flow and vessel density in Sherpas at high altitude.

Anecdotal reports suggest that Sherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitude, despite exhibiting lower arterial oxygen content than acclimatized lowlanders. This study tested the hypothesis that Sherpas exposed to hypobaric hypoxia on ascent to 5,300 m develop increased microcirculatory blood flow as a means of maintaining tissue oxygen delivery. Incident dark-field imaging was used to obtain images of the sublingual microcirculation from 64 Sherpas and 69 lowlanders. Serial measurements were obtained from participants undertaking an ascent from baseline testing (35 m or 1,300 m) to Everest base camp (5,300 m) and following subsequent descent in Kathmandu (1,300 m). Microcirculatory flow index and heterogeneity index were used to provide indexes of microcirculatory flow, while capillary density was assessed using small vessel density. Sherpas demonstrated significantly greater microcirculatory blood flow at Everest base camp, but not at baseline testing or on return in Kathmandu, than lowlanders. Additionally, blood flow exhibited greater homogeneity at 5,300 and 1,300 m (descent) in Sherpas than lowlanders. Sublingual small vessel density was not different between the two cohorts at baseline testing or at 1,300 m; however, at 5,300 m, capillary density was up to 30% greater in Sherpas. These data suggest that Sherpas can maintain a significantly greater microcirculatory flow per unit time and flow per unit volume of tissue at high altitude than lowlanders. These findings support the notion that peripheral vascular factors at the microcirculatory level may be important in the process of adaptation to hypoxia.NEW & NOTEWORTHY Sherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitude, yet the physiological mechanisms underlying this tolerance remain unknown. In our prospective study, conducted on healthy volunteers ascending to Everest base camp (5,300 m), we demonstrated that Sherpas have a higher sublingual microcirculatory blood flow and greater capillary density at high altitude than lowlanders. These findings support the notion that the peripheral microcirculation plays a key role in the process of long-term adaptation to hypoxia.

A Study of Healthy Adults' Oro-lingual Effort During Swallowing Using OroPress, A New Portable Wireless Measurement Tool.

OroPress is a new, low profile, portable, wireless tool that enables stable measurement of tongue pressure during isometric ('pushing') tasks and, more importantly, during swallowing. Using this tool, a pressure-time product, the OroPress Absolute (OPA) parameter, has been developed as a representative measure of lingual effort during swallowing. In a sample of 57 adults aged 20-80+ years, of both sexes and without dysphagia, tongue-palate contact pressures generated while swallowing 5 ml, 10 ml of water and 5 ml custard, were recorded using OroPress. Data were examined for effects of gender, age and bolus condition (consistency, volume). OPA was tested for stability of measure and then correlated with the criterion standard, peak pressure recorded when swallowing (PMax(SW)). Swallowing pressures (PMax(SW), OPA) were positively correlated with bolus viscosity. No significant age and gender differences were found. Excellent stability of measure (test, re-test reliability) was demonstrated and OPA was positively correlated with PMax(SW). OroPress produces valid, reliable and reproducible measurements and improved accuracy of oro-lingual pressure measurement during swallowing. With such a tool, interventions/therapy can be proactive and principled as outcomes are better validated. To enhance specificity of intervention, measurement parameters need to reflect the pressure and temporal qualities of swallow function. OPA has the potential to describe differences in effort made, and ability to sustain pressures, in adults without dysphagia. The results of these studies will enable more accurate examination of the oral phase of swallowing as we establish this highly accurate sensor as a criterion standard for oro-lingual pressure measurement in clinical populations.

Monitoring Microcirculatory Blood Flow with a New Sublingual Tonometer in a Porcine Model of Hemorrhagic Shock.

Tissue capnometry may be suitable for the indirect evaluation of regional hypoperfusion. We tested the performance of a new sublingual capillary tonometer in experimental hemorrhage. Thirty-six anesthetized, ventilated mini pigs were divided into sham-operated (n = 9) and shock groups (n = 27). Hemorrhagic shock was induced by reducing mean arterial pressure (MAP) to 40 mmHg for 60 min, after which fluid resuscitation started aiming to increase MAP to 75% of the baseline value (60-180 min). Sublingual carbon-dioxide partial pressure was measured by tonometry, using a specially coiled silicone rubber tube. Mucosal red blood cell velocity (RBCV) and capillary perfusion rate (CPR) were assessed by orthogonal polarization spectral (OPS) imaging. In the 60 min shock phase a significant drop in cardiac index was accompanied by reduction in sublingual RBCV and CPR and significant increase in the sublingual mucosal-to-arterial PCO2 gap (PSLCO2 gap), which significantly improved during the 120 min resuscitation phase. There was significant correlation between PSLCO2 gap and sublingual RBCV (r = -0.65, p < 0.0001), CPR (r = -0.64, p < 0.0001), central venous oxygen saturation (r = -0.50, p < 0.0001), and central venous-to-arterial PCO2 difference (r = 0.62, p < 0.0001). This new sublingual tonometer may be an appropriate tool for the indirect evaluation of circulatory changes in shock.

A systematic review of goal directed fluid therapy: rating of evidence for goals and monitoring methods.

PURPOSE: To review the literature on goal directed fluid therapy and evaluate the quality of evidence for each combination of goal and monitoring method. MATERIALS AND METHODS: A search of major digital databases and hand search of references was conducted. All studies assessing the clinical utility of a specific fluid therapy goal or set of goals using any monitoring method were included. Data was extracted using a pre-determined pro forma and papers were evaluated using GRADE principles to assess evidence quality. RESULTS: Eighty-one papers met the inclusion criteria, investigating 31 goals and 22 methods for monitoring fluid therapy in 13052 patients. In total there were 118 different goal/method combinations. Goals with high evidence quality were central venous lactate and stroke volume index. Goals with moderate quality evidence were sublingual microcirculation flow, the oxygen extraction ratio, cardiac index, cardiac output, and SVC collapsibility index. CONCLUSIONS: This review has highlighted the plethora of goals and methods for monitoring fluid therapy. Strikingly, there is scant high quality evidence, in particular for non-invasive G/M combinations in non-operative and non-intensive care settings. There is an urgent need to address this research gap, which will be helped by methodologies to compare utility of G/M combinations.

Electrical cardioversion for atrial fibrillation improves microvascular flow independent of blood pressure changes.

OBJECTIVE: This study tested the hypothesis that there is a discrepancy between global hemodynamic parameters and microvascular flow in patients before and after successful elective electrical cardioversion (ECV) for atrial fibrillation (AF). DESIGN: Prospective observational study. SETTING: Preanesthesia holding area in a teaching hospital. PARTICIPANTS: Adult patients who underwent successful elective ECV for AF. INTERVENTIONS: ECV. MEASUREMENTS AND MAIN RESULTS: Routine measurements of heart rate and noninvasive blood pressure were recorded and the sublingual microcirculation was visualized by sidestream darkfield imaging before and after the conversion of AF to sinus rhythm by elective ECV. The conversion to sinus rhythm significantly improved the microvascular flow index for smaller and larger microvessels. For smaller microvessels, perfused vessel density did not reach significance after conversion to sinus rhythm, whereas the proportion of perfused vessels was significantly larger and indices of heterogeneity for microvascular flow index decreased significantly. No correlation could be identified for the changes in mean blood pressure, perfused vessel density, and microvascular flow index for smaller microvessels. CONCLUSIONS: Successful ECV in patients with AF improves indices of sublingual microvascular perfusion. This change has no clear relation to the change in blood pressure and cannot be predicted from it. It may be prudent not to rely solely on global hemodynamic parameters to assess end-organ perfusion in this setting.

Temperature of periimplant tissues in clinically successful implants: an observational clinical study in humans.

OBJECTIVE: The aim of this study was to evaluate periimplant tissue temperature in a successful implant. It has been shown that periimplant disease and mucositis are inflammatory diseases. As such, one of the main clinical signs is the change in temperature. We try to establish normal values of temperature with an easy to use appliance. DESIGN: Fifty-one individuals were enrolled in this study. Only 1 implant per patient was included. The implants were clinically and radiographically examined and diagnosed as clinical successful implants. An infrared ear thermometer was used to measure periimplant temperature (PIT) and the difference with the sublingual temperature (ΔT). These data were analyzed using the Student t test, analysis of variance, and cluster analysis. RESULTS: Statistically significant differences in PIT were observed between the second sextant and the fourth and fifth sextants. These differences were not significant on considering ΔT. In addition, for the clinically and radiographically successful implants, ΔT for all sextants showed a mean of 0.81 (CI, 0.57-1.04). CONCLUSIONS: We have found a difference in outcome between periimplant temperature and the temperature differential. PIT depends on the anatomical location, though ΔT is an independent measurement with a value of 0.81°C.

Direct observation of the human microcirculation during cardiopulmonary bypass: effects of pulsatile perfusion.

OBJECTIVES: Possible benefits of pulsatile perfusion during cardiopulmonary bypass often are attributed to enhanced microvascular flow. However, there is no evidence to support this in humans. Therefore, the authors assessed whether pulsatile perfusion alters human microvascular flow. DESIGN: A prospective, randomized observational crossover study. SETTING: A tertiary cardiothoracic surgery referral center. PARTICIPANTS: Sixteen patients undergoing routine cardiopulmonary bypass for cardiac surgery. INTERVENTIONS: All patients underwent both pulsatile and nonpulsatile perfusion in random order. MEASUREMENTS AND MAIN RESULTS: The authors used sidestream dark-field imaging to record video clips of the sublingual human microcirculation. Perfusion was started either in the pulsatile (n = 8) or the nonpulsatile mode. After 10 minutes, microvascular recordings were made. The perfusion mode was then switched, and after 10 minutes, new microvascular recordings were taken. The authors quantified pulsatile perfusion-generated surplus hemodynamic energy by calculating pulse pressure and energy-equivalent pressure. Microvascular analysis included determination of the perfused vessel density (mean ± standard deviation). This did not differ between nonpulsatile and pulsatile perfusion (6.65 ± 1.39 v 6.83 ± 1.23 mm(-1), p = 0.58, and 2.16 ± 0.64 v 1.96 ± 0.48 mm(-1), p = 0.20 for small and large microvessels, respectively, cutoff diameter = 20 µm). Pulse pressure and energy-equivalent pressure was higher during pulsatile perfusion. However, there was no correlation between the difference in energy-equivalent pressure or pulse pressure and perfused vessel density (r = -0.43, p = 0.13, and r = -0.09, p = 0.76, respectively). CONCLUSION: Pulsatile perfusion does not alter human microvascular perfusion using standard equipment in routine cardiac surgery. Changes in pulse pressure or energy-equivalent pressure bear no obvious relationship with microcirculatory parameters.

Microcirculatory dysfunction in sepsis.

This article discusses the role of microcirculatory dysfunction in the pathophysiology of sepsis, reviewing the role of the endothelium in modulating microcirculatory flow, discussing the function of nitric oxide in mediating microcirculatory blood flow, and outlining means of evaluating microcirculatory function in septic patients. Finally, potential novel therapies and challenges in treating microcirculatory dysfunction in septic patients are discussed.

Microvascular perfusion measured by orthogonal polarization spectral imaging is well maintained during exposure to high altitude in trained mountaineers.

The objective of this study was to examine microvascular perfusion during hypobaric hypoxia and physical exercise. We used orthogonal polarization spectral imaging for the non-invasive visualization and assessment of the sublingual mucosal microcirculation in twelve healthy altitude acclimatized mountaineers. Red blood cell velocity (RCV), microvascular diameter (Dia), functional capillary density (FCD) and the number of rolling leukocytes were studied at baseline and after (I) a climb to an altitude of 3196 m, (II) a passive ascent to the same altitude by helicopter and (III) an exercise program at an altitude below 2100 m in the European Alps. Exposure to high altitude and exercise resulted in an increased heart rate (Trial I: 64 (54-66) vs. 95 (84-100); median (interquartile range); P<0.05) and decreased oxygen saturation (Trial I: 98 (98-99) vs. 90 (88-92); P<0.05). However, RCV, Dia and FCD did not change significantly. Furthermore, no enhanced rolling of leukocytes in postcapillary venules could be observed (Trial I: 6.2 (4.4-6.8) vs. 7.8 (4.3-6.7)). In the pooled data of all three trials of this study we could show a significant positive correlation between oxygen saturation and red blood cell velocity (r = 0.25; P = 0.02). These results indicate that orthogonal polarization spectral imaging can be a useful tool for the microcirculatory assessment of man under hypoxic conditions. We could show that in trained, acclimatized subjects microvascular perfusion is well maintained during hypobaric hypoxia at an altitude of 3196 m and no evidence for an increased postcapillary leukocyte adhesion was seen.

Results of electromyostimulation therapy in obstructive sleep apnea.

Innovative muscle stimulation techniques have become alternatives for therapy of obstructive sleep apnea syndrome breathing disorders. In group I, an individually shaped mouth floor electrode (IME) and in group II, an individually adaptable multi-point electrode (MPE) on a silicone carrier has been used for electromyostimulation (EMS) therapy in patients with obstructive sleep apnea. The enoral-cutaneous EMS was carried out with the low-frequency stimulation apparatus I-pulse over a period of 8 weeks, two times daily for 30 min during daytime hours only. In group III, the patients used EMS therapy for half a year continuously. Before and after stimulation treatment, three-dimensional volumetric sonographical measurement of the geniohyoid muscle was carried out. All patients (n = 14) totally applied the EMS therapy. Under IME and MPE application after 4 weeks of EMS therapy, a median volume increase of 19.6% (minimum 9.7%, maximum 27.9%) was registered, the median after 8 weeks IME was 27.6% and in MPE 24.0%). No significant difference (analysis of variance type: P > 0.05) between electrodes could be found. In all groups, a reduction of the muscle length of 4.7% was proved. In groups I and II after 26 weeks, the volume was near baseline before stimulation (+4.3%). In the third group, the increase of volume persisted (+29.4%) over the observation period of 12-26 weeks. Opposed to established stimulation techniques, a threefold effectiveness enhancement could be verified by using both individually adaptable electrodes. The EMS therapy should be carried out as continuous long-term therapy or as interval therapy.

Quantitative contributions of the muscles of the tongue, floor-of-mouth, jaw, and velum to tongue-to-palate pressure generation.

PURPOSE: The purpose of this investigation was to evaluate the relationship between tongue-to-palate pressure and the electromyography (EMG) measured from the mylohyoid, anterior belly of the digastric, geniohyoid, medial pterygoid, velum, genioglossus, and intrinsic tongue muscles. Methods Seven healthy adults performed tongue-to-palate pressure tasks at known percentages of their maximum pressure while intramuscular EMG was recorded from the muscles stated above. Multiple regression analysis was performed. RESULTS: Predictors of pressure included the posterior fibers of the genioglossus, mylohyoid, anterior belly of digastric, medial pterygoid, and intrinsic tongue. CONCLUSIONS: Increasing tongue-to-palate pressure coincides with increased muscle activity. Activation of the floor-of-mouth, tongue, and jaw closing muscles increased tongue-to-palate pressure. These findings support the use of a tongue-press exercise to strengthen floor-of-mouth muscles, tongue, and jaw-closing muscles.

Bilateral comunications of the paralingual space / Comunicaciones bilaterales del espacio paralingual

Paralingual Space is a region located on the floor of the oral cavity. The cavity has great importance in communications and for the spread of infectious diseases. This study investigated the level of dissemination of 0.2 ml of an oily pigment solution, into paralingual space of 20 heads of male Sprague Dawley rats. The results can be seen by the spread of the solution in the three segments of paralingual space, being higher in the middle third of the region, although the differences were not significant (p<0.05). With these observations, the discussion is about the possibility that an infection may spread into paralingual space opposite the muscles of the medial wall of this space.

El espacio paralingual es una región ubicada en el piso de la cavidad oral con comunicaciones de gran importancia para la difusión de procesos infecciosos. El presente estudio investigó el nivel de difusión de 0,2 ml de una solución oleosa pigmentada, hacia el espacio paralingual opuesto en 20 cabezas de ratas Sprague Dawley. En los resultados obtenidos se observa la difusión de la solución en los tres segmentos del espacio paralingual, siendo mayor en el tercio medio de la región, aunque las diferencias no resultaron significativas (p<0,05). Con estas observaciones se discute acerca de la posibilidad de que un proceso infeccioso pueda difundir hacia el espacio paralingual opuesto a través de la musculatura de la pared medial del espacio.

Monitoring of the sublingual microcirculation in cardiac surgery using orthogonal polarization spectral imaging: preliminary results.

BACKGROUND: The recent introduction of orthogonal polarization spectral imaging enables the direct visualization of the microcirculation of man without imaging enhancing dyes. The authors studied the changes in microvascular perfusion of sublingual mucosa during cardiac surgery with the use of cardiopulmonary bypass (CPB) using this optical method. METHOD: Orthogonal polarization spectral images were recorded in 47 patients after skin incision (T1), after the start of CPB (T2), in the late phase of CPB (T3), and 1 h after the discontinuation of CPB (T4). The images were analyzed for microvascular diameter, erythrocyte velocity, and functional capillary density using an established analysis routine for intravital microscopy studies. In a subpopulation (n = 8), the expression of the adhesion molecules CD18 on circulation leukocytes was compared with the number of visualized rolling leukocytes. RESULTS: Preoperatively, no significant changes of the microvascular diameter and erythrocyte velocity were seen. The functional capillary density was significantly reduced at T3 to 90% of the values observed before CPB but recovered at T4 and showed a weak but significant correlation with body temperature (r = 0.38, P < 0.01) and hemoglobin concentration (r = 0.20, P < 0.05). Expression of CD18 was significantly increased in the late phase of CPB (T3) only, whereas the numbers of rolling leukocytes increased during CPB and revealed a significant threefold increase 1 h after termination of CPB. CONCLUSIONS: Orthogonal polarization spectral imaging revealed no major changes of microvascular perfusion during uncomplicated hypothermic CPB. The slightly reduced functional capillary density during CPB may be caused by several factors all present during CPB, including hypothermia, the artificial extracorporeal perfusion, surgical trauma, hemodilution, and inflammatory reaction. The current data do not allow differentiation between the effects of those possible causes.

Movement-related cortical potentials associated with saliva and water bolus swallowing.

The purpose of this study was to document the movement-related cortical potentials associated with saliva and water bolus swallowing in seven right-handed healthy humans. As the subjects performed a saliva or water bolus swallowing task, electroencephalograms with electrodes at C3, Cz, and C4 and an electromyogram of the mylohyoid muscle complex were recorded. The early slope, referred to as the Bereitschafts potential, before saliva swallowing was significantly steeper than that before water bolus swallowing. Positive potential amplitude during water bolus swallowing was significantly larger than that during saliva swallowing. Negative slope and motor potential were not clearly present during performance of either swallowing task. Those findings imply that the features of movement-related cortical potential associated with pharyngeal swallowing are different from those associated with limb movement, and that both the cortical process associated with sensory information of pharyngeal swallowing and the cortical preparatory process of pharyngeal swallowing depend on the type of swallowing task.

Tissue capnometry: does the answer lie under the tongue?

Increases in tissue partial pressure of carbon dioxide (PCO(2)) can reflect an abnormal oxygen supply to the cells, so that monitoring tissue PCO(2) may help identify circulatory abnormalities and guide their correction. Gastric tonometry aims at monitoring regional PCO(2) in the stomach, an easily accessible organ that becomes ischemic quite early when the circulatory status is jeopardized. Despite substantial initial enthusiasm, this technique has never been widely implemented due to various technical problems and artifacts during measurement. Experimental studies have suggested that sublingual PCO(2 )(P(sl)CO(2)) is a reliable marker of tissue perfusion. Clinical studies have demonstrated that high P(sl)CO(2) values and, especially, high gradients between P(sl)CO(2) and arterial PCO(2) (DeltaP(sl-a)CO(2)) are associated with impaired microcirculatory blood flow and a worse prognosis in critically ill patients. Although some questions remain to be answered about sublingual capnometry and its utility, this technique could offer new hope for tissue PCO(2) monitoring in clinical practice.

Functional rehabilitation following resection of the floor of the mouth: the nasolabial flap revisited.

INTRODUCTION: The aim of this study was to analyse the results of treatment following reconstruction of intraoral soft tissue using a nasolabial flap, with particular consideration of functional aspects. MATERIAL AND METHODS: In 26 patients (over a period of 10 years), the intraoral repair of the defect was carried out in the anterior floor of the mouth, 19 have received a unilateral and seven a bilateral nasolabial flap. The defects were caused by resection of squamous cell carcinomas (T1-T2) of the intraoral mucosa in 24 cases and osteoradionecrosis with soft tissue loss in two cases. RESULTS: Complications of local wound healing were observed in three cases. In 23 patients the subsequent prosthetic rehabilitation was successful and allowed a return of masticatory function. In the other three cases, a secondary operation for flap remodelling would have been preferred, but the patients declined these operations. CONCLUSION: The nasolabial flap for replacement of soft tissue in the floor of the mouth represents a functional and aesthetically satisfactory alternative to reconstruction by microsurgically anastomosed flaps in cases with defects of up to 5 x 5 cm in size, especially in older, medically compromised patients who are therefore of poorer surgical risk.

Regeneration of intraoral defects after tumor resection with a bioengineered human dermal replacement (Dermagraft).

The experiences of seven patients with squamous cell carcinomas of the oral cavity who underwent reconstruction with a bioengineered human dermal replacement (Dermagraft) are examined. The human dermal replacement consists of fibroblasts seeded onto a three-dimensional polymer scaffold to create a living dermal structure. In this setting, the fibroblasts secrete a mixture of growth factors and matrix proteins in physiological concentration that is essential for wound healing and epithelization. The fibroblast tissue remains metabolically active after cryopreservation and can be used as an off-the-shelf tissue to cover medium-sized defects and avoid donor-site morbidity. In the first series of patients treated with this tissue, defect closure was achieved without functional problems, allowing optimal postoperative monitoring for tumor recurrence.

Sublingual electrical stimulation of the tongue during wakefulness and sleep.

Pharyngeal obstruction in patients with obstructive sleep apnea (OSA) is thought to result from decreased upper airway muscle tone during sleep. The goal of the present study was to estimate the role of the tongue muscles in maintaining pharyngeal patency during sleep. Using non-invasive, sub-lingual surface electrical stimulation (ES), we measured tongue protrusion force during wakefulness and upper airway resistance during sleep in seven healthy subjects and six patients with OSA. During wakefulness, ES produced similar protrusion forces in healthy subjects and patients with OSA. ES of the anterior sublingual surface, causing preferential contraction of the genioglossus, resulted in smaller effects than combined ES of the anterior and lateral surface, which also stimulated tongue retractors. During sleep, trans-pharyngeal resistance decreased and peak inspiratory flow rate increased from 319+/-24 to 459+/-27 and from 58+/-16 to 270+/-35 ml/sec for healthy subjects and OSA patients, respectively (P<0.001). However, ES was usually unsuccessful in reopening the upper airway in the presence of complete apneas. We conclude that non-invasive ES of the tongue improves flow dynamics during sleep. Combined activation of tongue protrusors and retractors may have a beneficial mechanical effect. The magnitude of responses observed suggests that in addition to the stimulated muscles, other muscles and/or forces have a substantial impact on pharyngeal patency.