Therapeutic electrical stimulation of the hypoglossal nerve in obstructive sleep apnea.

BACKGROUND: Hypoglossal nerve stimulation has been demonstrated to relieve upper airway obstruction acutely, but its effect on obstructive sleep apnea is not known. OBJECTIVE: To determine the response in obstructive sleep apnea to electrical stimulation of the hypoglossal nerve. METHODS: Eight patients with obstructive sleep apnea were implanted with a device that stimulated the hypoglossal nerve unilaterally during inspiration. Sleep and breathing patterns were examined at baseline before implantation and after implantation at 1, 3, and 6 months and last follow-up. RESULTS: Unilateral hypoglossal nerve stimulation decreased the severity of obstructive sleep apnea throughout the entire study period. Specifically, stimulation significantly reduced the mean apnea-hypopnea indices in non-rapid eye movement (mean +/- SD episodes per hour, 52.0 +/- 20.4 for baseline nights and 22.6 +/- 12.1 for stimulation nights; P<.001) and rapid eye movement (48.2 +/- 30.5 and 16.6 +/- 17.1, respectively; P<.001) sleep and reduced the severity of oxyhemoglobin desaturations. With improvement in sleep apnea, a trend toward deeper stages of non-rapid eye movement sleep was observed. Moreover, all patients tolerated long-term stimulation at night and did not experience any adverse effects from stimulation. Even after completing the study protocol, the 3 patients who remained free from stimulator malfunction continued to use this device as primary treatment. CONCLUSION: The findings demonstrate the feasibility and therapeutic potential for hypoglossal nerve stimulation in obstructive sleep apnea.

Is the atrial high rate episode diagnostic feature reliable in detecting paroxysmal episodes of atrial tachyarrhythmias?

The atrial high rate episode diagnostic in the Thera pacemaker reports frequency, duration, and date/time of atrial tachyarrhythmias according to programmed criteria. The aim of the study was to validate the atrial high rate episode diagnostic feature. Episodes of atrial fibrillation recorded by Holter monitoring were compared to episodes detected by the pacemaker. Forty five ambulatory (Holter) recordings were used for evaluation. Thirty of 45 ambulatory (Holter) recordings showed sinus rhythm. On 4 of these 30 ambulatory (Holter) recordings, the Thera detected 12 episodes of atrial tachyarrhythmias as false-positives (sinus rhythm was detected as atrial tachyarrhythmia). The main reason was far-field R and T was oversensing. On 15 of 45 ambulatory (Holter) recordings, 125 episodes of atrial tachyarrhythmias were recorded. Ninety-three of these events also were detected by the pacemaker, while for 32 events the Thera reported sinus rhythm. The main reason was that the episodes were of too short duration. Therefore, the Thera (programmed with detection rate 160 beats/min, detection beats 40, termination beats 10) was unable to detect atrial tachycardias. Software simulation of the diagnostic algorithm under several programming settings using the digitized Holter files demonstrated highly reliable detection of atrial tachyarrhythmias (sensitivity 98%, specificity 100%) when programmed as follows: detection rate 220 beats/min, detection beats 10, termination beats 20. It can be concluded that Thera's high rate episode monitor is a reliable tool for detection of atrial tachyarrhythmias, if programmed as recommended.

Dynamic control of location-specific information in tactile cutaneous reflexes from the foot during human walking.

The purpose of the present study was to determine whether tactile cutaneous reflexes from the skin of the foot contain location-specific information during human walking. Muscular responses to non-nociceptive electrical stimulation of the sural, posterior tibial, and superficial peroneal nerves, each supplying a different skin area of the foot, were studied in both legs during walking on a treadmill. For all three nerves the major responses in all muscles were observed at a similar latency of approximately 80-85 msec. In the ipsilateral leg these reflex responses and their phase-dependent modulation were highly nerve-specific. During most of the stance phase, for example, the peroneal and tibial nerves generally evoked small responses in the biceps femoris muscle. In contrast, during late swing large facilitations generally occurred for the peroneal nerve, whereas suppressions were observed for the tibial nerve. In the contralateral leg the reflex responses for the three nerves were less distinct, although some nerve specificity was observed for individual subjects. It is concluded that non-nociceptive stimulation of the sural, posterior tibial, and superficial peroneal nerves each evokes distinct reflex responses, indicating the presence of location-specific information from the skin of the foot in cutaneous reflexes during human walking. It will be argued that differentially controlled reflex pathways can account for the differences in the phase-dependent reflex modulation patterns of the three nerves, which points to the dynamic control of this information during the course of a step cycle.

Modulation of the mandibular stretch reflex sensitivity during various phases of rhythmic open-close movements in humans.

The muscle spindles of the jaw elevator muscles provide positive feedback to the alpha motoneurons. It is generally assumed that the feedback is modulated during chewing so that counterproductive forces of the jaw elevator muscles can be avoided during jaw opening. Our aim was to investigate the modulation of the muscle spindle input to the alpha motoneurons during various phases of open-close movements in man. To that end, subjects made rhythmic open-close movements at their natural chewing frequency. A force impulse (5 N, 10 ms), eliciting a jaw-jerk reflex, was unexpectedly applied. The impulse was applied to the mandible at 8 different phases during an open-close cycle, but only 1 impulse per cycle. Jaw movement and surface EMG of the masseter and temporal muscles on both sides were recorded during 3 cycles without an impulse and 3 succeeding cycles with an impulse. To examine whether the modulation of the mandibular stretch reflex sensitivity depends on the food resistance, we applied an additional external force on the mandible, counteracting closing of the jaw each cycle. Two experimental sessions were performed in random order, i.e., without force and with an additional force of 20 N. We observed pronounced reflexes at the onset of jaw closing, during the closing phase, and at occlusion. No or only weak jaw-jerk reflexes were present during jaw opening. The reflex amplitudes at occlusion were larger when an external force was present. This increase in reflex amplitude may be the result of an adjusted gamma motoneuron activity, from pre-motor inhibition, or from both. The reflex amplitudes elicited during jaw closing were not correlated with the phase of the movement.

Long-term recording of cardiac output via an implantable haemodynamic monitoring device.

Long-term monitoring of central haemodynamics with implanted monitoring systems might be valuable in managing heart failure patients. Such systems offer an opportunity for repeated 'semi-invasive' cardiac output determinations according to the Fick principle. Five patients, four with chronic heart failure and one with chronic pulmonary disease, underwent supine exercise testing during cardiac catheterization at 0, 2, 6 and 11 months after implantation of a right ventricular mixed venous oxygen saturation sensor connected to an implantable haemodynamic monitor. The monitor provided a continuous measure of oxygen saturation via a radio-telemetry link to a metabolic cart capable of measurement of breath-by-breath oxygen consumption. Cardiac output was computed using oxygen consumption, mixed venous oxygen saturation, arterial oxygen saturation by pulse oximetry and haemoglobin oxygen capacity. Biosensor-derived oxygen saturation compared to blood samples from the pulmonary artery showed an excellent correlation over time, r2 = 0.94 (implant), r2 = 0.91 (6-11 months). There was a strong correlation between semi-invasive-determined cardiac output using the biosensor and the invasive technique, which persisted over the entire follow-up period. Repeated semi-invasive cardiac output measurements using an implanted haemodynamic monitoring system in chronic heart failure patients is feasible and the data may be of value for optimizing therapy.

The relationship between jaw elevator muscle surface electromyogram and simulated food resistance during dynamic condition in humans.

In six human subjects, electromyograms (EMGs) of the masseter and temporal muscles were recorded bilaterally during experiments in which the subjects made rhythmic open-close movements. The closing phase was counteracted by a variable external force on the mandible. Variables of the force (amplitude, time integral and work) and variables of the corresponding EMG bursts (duration, peak amplitude and time integral) were computed for each open-close cycle. Linear regression analyses were used to determine the strength of the relationship between each EMG variable and each force variable. By step-wise multiple regression analysis the EMG variables predicting the force variables were determined. Although there was a highly significant and positive correlation (P < 0.0005), the average coefficients of linear correlation varied from 0.46 to 0.82. The strongest relationship was observed between the time integrals of the force and EMG in the interval between the onset of the burst and the onset of occlusion. It was suggested that to assess muscle force during chewing, the time integral of EMG bursts should be computed.

The role of sensory information in the control of rhythmic open-close movements in humans.

Chewing requires a low level of muscle activity for jaw movement. Additional muscle activity is required to overcome the resistance of the food. The additional muscle activity consists of two contributions, an anticipating contribution before food contact and a peripherally induced contribution, about 23 ms after food contact. The amounts of both contributions depend on the information about food resistance obtained in preceding chewing cycles. It is not known whether this information is preserved if the resistance is absent during only a limited number of chewing cycles. Our aim was to investigate the extent to which information about food resistance obtained during chewing is used during subsequent cycles to generate anticipating and peripherally induced muscle activity. Subjects made rhythmic open-close movements at their natural chewing frequency, controlled by a metronome. Food resistance was simulated by an external force acting on the jaw in a downward direction during part of the closing movement. Jaw movement and surface EMG of the masseter and suprahyoid muscles were recorded during experiments in which sequences of at least 20 cycles with the force were alternated with a small, random number (from 1 to 10) of cycles without the force. The amount of anticipating muscle activity as well as the peripherally induced muscle activity in the first cycle with the force gradually decreased as a function of the number of preceding forceless cycles. About 30% of the additional muscle activity had an anticipatory origin, whereas the rest of the activity was evoked by the force regardless of the number of preceding forceless cycles.

Thoracic electrical bioimpedance: suitable for monitoring stroke volume during pregnancy?

To obtain normal values for maternal stroke volume and cardiac output during pregnancy, a non-invasive, accurate and reproducible method is required. The thoracic electrical bioimpedance (TEB) method may be suitable. However, this method is as yet only qualified for short-term trend recordings, since it assumes that body dimensions such as height, weight and thoracic circumference remain constant during the study. This may not be the case in long-term studies, especially during pregnancy. In this paper it is argued that changes in stroke volume (SV) during pregnancy are reflected most strongly when using the formula: SV = P VET (dZ/dt)max/Z0, where P is a personal factor to be determined at the beginning of pregnancy; VET the ventricular ejection time; (dZ/dt)max the maximum of the first derivative of the thoracic impedance during the cardiac cycle and Z0 the time average of this impedance during the cardiac cycle. Indexed parameters should not be used as this reduces sensitivity. Commercial equipment, based upon other algorithms, can be used by feeding the right parameters for each series of measurements. This enables calculation, trends in stroke volume and cardiac output for longitudinal studies for instance during pregnancy.

A computer-controlled experimental set-up enabling the quantification of motor performance in man, applied to mastication.

This paper describes a computer-controlled experimental set-up, which enables the simulation and manipulation of the resistance of food, the bolus size and reflex evoking events during chewing in man. Food resistance was simulated by an external downward directed force on the mandible during the closing phase. The force was supplied by a magnet-coil system. A coil, rigidly attached to the subject's mandible, was located in a permanent magnetic field. By varying the current through the coil, the force on the coil and thus on the mandible could be adjusted. The current was on line computed as a function of the jaw gape. Food resistance and bolus size could be simulated and manipulated by varying the amplitude of the force and the jaw gape at which the force started, respectively. The possibility of varying these parameters could be used simultaneously and independently. Reflex evoking events were simulated by an additional loading or unloading force pulse, superimposed on the food-simulating force. The set-up has been tested during experiments in which food resistance, bolus size and reflex evoking events were simulated. Examples of these experiments are presented in this paper.

Control of human jaw elevator muscle activity during simulated chewing with varying bolus size.

During chewing, a small part of the observed muscle activity is needed for the basic open-close movements of the mandible, and additional muscle activity (AMA) is needed to overcome the resistance of the food. The AMA consists of two contributions: a large peripherally induced contribution, starting after food contact and a small anticipating contribution, starting before food contact. We investigated whether the latencies of these contributions depend on the expected or actual bolus size. Subjects made rhythmic open-close movements near their natural chewing frequency controlled by a metronome. This frequency was determined while the subjects were chewing gum. Food resistance was simulated by an external force, acting on the jaw in a downward direction during part of the closing movement. Bolus size was simulated by the jaw gape at which the force started. Jaw movement and surface EMG of the masseter and anterior temporal muscles on both sides and the suprahyoid muscles were recorded during experiments in which the jaw gape at which the force started was varied. The peripherally induced contribution to the AMA started about 20 ms after the onset of the force, irrespective of the jaw gape at which the force started. It is concluded that the onset of this contribution depends solely on food contact in the actual cycle. The function of the observed mechanism for jaw elevator muscle control may be to enable a highly automatic control of the muscle activity required to overcome the resistance of food of different hardness and different size. The onset of the anticipating contribution to the AMA showed neither a relationship with the actual jaw gape at which force onset occurred nor with the expected jaw gape of force onset. It is suggested that the onset of the anticipating AMA is related to the jaw gape at the onset of closing. The function of this contribution may be the regulation of the mechanical response of the jaw after an expected disturbance of the closing movement by food contact, by tuning the muscle stiffness to the expected hardness of the food.

Control of elevator muscle activity during simulated chewing with varying food resistance in humans.

1. During chewing, a small part of the observed muscle activity is needed for the basic open-close movements of the mandible, and much additional muscle activity (AMA) is needed to overcome the resistance of the food. In chewing cycles in which a counteracting force is expected, the AMA is mainly generated by peripheral induction with a latency of approximately 23 ms. It was investigated whether an open-loop or closed-loop mechanism is involved in the control of the AMA in these cycles. 2. Subjects made rhythmic open-close movements at their natural chewing frequency controlled by a metronome. Food resistance was simulated by an external force, acting on the jaw in a downward direction during part of the closing movement. Sequences of cycles with a force were unexpectedly alternated with sequences of cycles with a different force. The force changed from 19 to 0 N and vice versa, and from 25 to 6 N and vice versa. Jaw movement and surface electromyogram of the masseter, temporalis, and suprahyoid muscles on both sides were recorded during cycles before and after the transition from one force condition to another. 3. The movement trajectory and AMA of the second and following cycles with a new force appeared to be similar. Thus adaptation to the changed circumstances occurred within two open-close cycles. 4. In the first cycle with 0 or 6 N in the 19----0 N and 25----6 N experiments respectively, a large part of the AMA had disappeared. The AMA in this cycle started to differ from the AMA in the previous cycle approximately 23 ms after the moment the force in this cycle started to differ from the previous cycle. 5. In the first cycle with 19 or 25 N in the reverse experiments, the AMA increased 120-136 ms after the moment the force in this cycle started to differ from the previous cycle. 6. During the closing phase of each open-close cycle, no muscle activity of the suprahyoid muscles was observed; thus co-contraction with the elevator muscles did not occur. 7. It was concluded that the AMA is under control of a closed-loop mechanism with a latency of approximately 23 ms. However, the reflex output has a maximum, depending on information about the food resistance gained in previous cycles.(ABSTRACT TRUNCATED AT 400 WORDS)

Peripherally induced and anticipating elevator muscle activity during simulated chewing in humans.

1. During chewing, little muscle activity is required to make open-close movements with the mandible, and much additional muscle activity (AMA) of the closing muscles is needed to overcome the resistance of food. The neuromuscular control of the AMA was investigated. 2. Subjects made rhythmic open-close movements at their natural chewing frequency controlled by a metronome. Food resistance was simulated by an external force, acting on the jaw in a downward direction during part of the closing movement. Sequences of cycles with a force were unexpectedly alternated with sequences of cycles without a force. Jaw movement, and surface electromyograph (EMG) of the masseter, temporalis, and digastric muscles on both sides were recorded during cycles before and after the transition from force to no force (Disappear experiment) and vice versa (Appear experiment). 3. The movement trajectory of the second and following cycles after the transition from force to no force or vice versa were similar. Thus adaptation to the changed circumstances occurred in both types of experiments within two open-close cycles. 4. In the first cycle with force in the Appear experiments, the AMA started, on average, 129 ms after the onset of the force. In all other cycles with force, the AMA started, on average, 70 ms before the onset of the force at a low level and steeply increased 23 ms after the onset of the force. 5. In the first cycle without force in the Disappear experiments, the AMA started, on average, 69 ms before the moment at which the force would have started. However, the large contribution to the AMA had disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

On the origin of the presaccadic spike potential.

The spike potential (SP) accompanying the onset of saccadic eye movements has been reported to originate near the orbital region. Its dependence on saccade size, however, does not correlate with the behaviour of any of the possible sources of the potential available in the orbital region. The exact size dependence cannot be studied from results obtained with classical ENG methods to detect the saccadic onset and furthermore without removal of the artefact in the signal caused by the corneo-retinal potential. We recorded the SP by monitoring the eye movements with an infrared scleral reflection method (IRIS), and carefully studied the SP amplitude as a function of saccade size, and revealed a more realistic function. Furthermore, removal of the artefact of the corneo-retinal potential revealed a biphasic wave shape of the SP instead of the usually observed monophasic peak. These results support the hypothesis that this electrical activity accompanying the onset of saccadic eye movements originates in the oculomotor neurones innervating the ocular muscle units.