Predicting the recovery of ventilatory activity in central respiratory paralysis

OBJECTIVE

To assess the value of the diaphragmatic response to transcranial magnetic stimulation (TMS) in predicting the recovery of ventilatory activity after CNS lesions responsible for central respiratory paralysis.

METHODS

The authors studied 11 long-term ventilator-dependent patients with central respiratory paralysis (description group: spinal trauma 10, medullary ischemia 1) and 16 patients with central respiratory paralysis for less than 10 weeks (prognostic group, evaluated after a 1-year follow-up: spinal trauma 8, medullary ischemia 4, radiation myelitis 1, subdural hematoma 1, complication of neurosurgery 2).

RESULTS

In the description group, all the patients had a bilaterally abolished diaphragm response. In the prognostic group, six patients were fully ventilator dependent because of a complete absence of ventilatory activity at follow-up time. They lacked any diaphragm response. The 10 other patients had recovered ventilatory activity and full (n = 9) or partial (n = 1) ventilatory autonomy. In nine cases, diaphragm response was present at least on one side, with a normal latency (right: 15.6 +/- 1.5 milliseconds; left: 16.2 +/- 2.2 milliseconds). The test had 100% specificity (95% CI 52 to 100) and 90% sensitivity (95% CI 54 to 99) to predict the recovery of ventilatory activity.

CONCLUSION

Electrophysiologic studies of the diaphragm in response to transcranial magnetic stimulation may help predict the recovery of central respiratory paralysis within 1 year.

Vivid dreams, hallucinations, psychosis and REM sleep in Guillain–Barré syndrome

We conducted a prospective controlled study of the clinical and biological determinants of the mental status abnormalities in 139 patients with Guillain-Barré syndrome (GBS) and 55 patients without GBS placed in the intensive care unit (ICU controls). There were mental status changes in 31% of GBS patients and in 16% of controls (odds ratio = 2.3; P = 0.04). In GBS patients, they included vivid dreams (19%), illusions (30%, including an illusory body tilt), hallucinations (60%, mainly visual) and delusions (70%, mostly paranoid). They appeared a median 9 days after disease onset (range 1-40 days, during the progression or the plateau of the disease), and lasted a median 8 days. Seven (16%) patients experienced the symptoms before their admission to the ICU. Hallucinations were frequently hypnagogic, occurring as soon as the patients closed their eyes. Autonomic dysfunction, assisted ventilation and high CSF protein levels were significant risk factors for abnormal mental status in GBS patients. CSF hypocretin-1 (a hypothalamic neuropeptide deficient in narcolepsy) levels, measured in 20 patients, were lower in GBS patients with hallucinations (555 +/- 132 pg/ml) than in those without (664 +/- 71 pg/ml, P = 0.03). Since the mental status abnormalities had dream-like aspects, we examined their association with rapid eye movement sleep (REM sleep) using continuous sleep monitoring in 13 GBS patients with (n = 7) and without (n = 6) hallucinations and 6 tetraplegic ICU controls without hallucinations. Although sleep was short and fragmented in all groups, REM sleep latency was shorter in GBS patients with hallucinations (56 +/- 115 min) than in GBS patients without hallucinations (153 +/- 130 min) and in controls (207 +/- 179 min, P < 0.05). In addition, sleep structure was highly abnormal in hallucinators, with sleep onset in REM sleep periods (83%), abnormal eye movements during non-REM sleep (57%), high percentages of REM sleep without atonia (92 +/- 22%), REM sleep behaviour disorders and autonomic dysfunction (100%), reminiscent of a status dissociatus. The sleep abnormalities, that were almost absent in non-hallucinated GBS patients, were not exclusively related to ICU conditions, since they also appeared out of ICU, and were reversible, disappearing when the mental status abnormalities vanished while the patients were still in ICU. In conclusion, the mental status abnormalities experienced by GBS patients are different from the ICU delirium, are strongly associated with autonomic dysfunction, severe forms of the disease and possibly with a transitory hypocretin-1 transmission decrease. Sleep studies suggest that mental status abnormalities are wakeful dreams caused by a sleep and dream-associated disorder (status dissociatus).

[Initiation and management of home mechanical ventilation]

INTRODUCTION

Effective initiation and optimal monitoring of treatment are essential elements for successful home mechanical ventilation (HMV).

STATE OF KNOWLEDGE

Ventilation is best initiated in a hospital setting. There is an enormous range of equipment available but there is little evidence pointing to the superiority of one device over another. Many problems can arise that lead to an interruption in HMV but often these can be resolved simply as discussed in this article.

PERSPECTIVES

Unfortunately a number of pitfalls in management remain, the main one being the absence of accurate data about the sleep of patients on ventilators, which hinders optimal nocturnal management. Another problem is the lack of adaptation of equipment for use by handicapped patients. Finally the transfer of responsibility and workload to home carers including family members with disengagement by the hospital can also be a major milestone.

CONCLUSION

Successful initiation and supervision is the key to effective home mechanical ventilation. Treatment is often abandoned because of pitfalls, mistakes and lack of knowledge. This article proposes means to improve these two important areas.

Unaltered respiratory-related evoked potentials after acute diaphragm dysfunction in humans

Respiratory muscles play an important role in the origin of respiratory sensations. Data dissecting the role of the diaphragm and other inspiratory muscles are scarce. This study aimed to determine the impact of diaphragm dysfunction following inspiratory resistive loading on respiratory-related evoked potentials considered as a neurophysiological substrate of certain types of respiratory sensations. Altogether, nine subjects aged 25-50 yrs (six females) participated in the study. Transdiaphragmatic pressure output of cervical magnetic stimulation (with subdivision in oesophageal and gastric component), and respiratory-related evoked potentials (C3 and C4 derivations in the international 10-20 system) following mid-inspiratory occlusions were studied before and after an inspiratory-resistive loading challenge. Predominant diaphragm dysfunction was observed in seven subjects (average 28% reduction in transdiaphragmatic pressure, from 27.25-19.91 cmH2O, with increased oesophageal-to-gastric pressure ratio). The latencies and amplitudes of all the components of the respiratory-related evoked potentials were unchanged. The study concluded that predominant diaphragm fatigue does not affect respiratory-related evoked potentials.

[What perception have smokers of nicotine and tar yields of cigarettes?]

INTRODUCTION

Advertising information on cigarette package participate to the reduction of health risks from smoking. Impact on smokers has been poorly studied. This study intended to determine the smoker perception of nicotine and tar yields of cigarettes.

METHODS

Consulting in an outpatient smoking cessation clinic, 171 smokers answered freely and spontaneously to a questionnaire evaluating their perception of nicotine and tar yields, cigarette consumption (number and brand), nicotine dependence. Simultaneously, biological tobacco markers were measured.

RESULTS

The number of cigarettes, nicotine dependence and specific tobacco markers were not significantly different according to the cigarette type: "full savour", "light" or "ultra light". Women smoked less than men and 54% preferred "light" cigarettes versus 37% of men. These smokers were entering a tobacco cessation program, it was assumed they had lead a prior reflection about their smoking habits. Only 8% of them gave the correct values of nicotine and tar yields and 14% gave approximate values. Tar levels were highly underestimated.

CONCLUSIONS

This study shows that smokers have actually no interest for nicotine and tar yields. As the new decree which modifies manufacture's obligation concerning the legal mentions, is applicable in January 2004 in France; our conclusion may change in the future.

Acute fungal pustulosis on a bedridden patient's back

We report a particular dermatophytosis due to Trichophyton rubrum. A 61-year-old woman presented an eruption which quickly evolved within 48 h, consisting of papular annular patches surrounded by creamy white pustules, which sometimes coalesced. The eruption was exclusively located on the back. The rest of the body and skin examination was normal, and the patient had no temperature. The mycological sample revealed mycelial filaments in the direct microscopic examination and T. rubrum in the mycological culture. Only a few cases of pustular lesions due to T. rubrum are reported in the literature. The extensive character, the site and the inflammatory aspect of the lesions were very surprising. This clinical presentation is more frequent with geophilic and zoophilic organisms than with anthropophilic dermatophytes such as T. rubrum.

Alveolar lymphocytosis in patients with chronic uveitis: relationship to sarcoidosis

Bronchoalveolar lavage (BAL) is frequently performed in patients with suspected ocular sarcoidosis. This study describes the immunogenetical, immunological, radiological, and functional features of a subclinical alveolar lymphocytosis unrelated to sarcoidosis in patients with chronic uveitis. Two hundred and ten patients with chronic uveitis of unknown origin, who underwent fiber-optic bronchoscopy with BAL as part of a prospective protocol over a three-year period, were evaluable for retrospective analysis. Sixty-five patients had alveolar lymphocytosis: Sarcoidosis was diagnosed in 13 (6%) patients, whereas alveolar lymphocytosis was considered unrelated to sarcoidosis in 52 (25%). Alveolar lymphocytosis unrelated to sarcoidosis was not associated with radiologically detectable interstitial lung disease or pulmonary function impairment. CD4/CD8 lymphocyte ratio was 3.7 +/- 3.0. Total cell count, total lymphocyte, and CD4 lymphocyte percentage were significantly lower when compared with sarcoidosis-related alveolitis (129,000 +/- 80,000 vs. 218,000 +/- 117,000, p <0.05; 33.1% +/- 13.2 vs. 39.7% +/- 13.2, p <0.05; and 54.3% +/- 18.2 vs. 65.4% +/- 10.1, p <0.05, respectively). Patients with alveolar lymphocytosis unrelated to sarcoidosis were older (47.8 +/- 17.7 years vs. 42.7 +/- 14.2 years, p <0.05) and more likely to carry the HLA-B51 allele (19.7% vs. 7.1%, p <0.01) than patients with chronic uveitis without alveolar lymphocytosis. They did not appear to be at risk of developing clinically apparent interstitial lung disease on followup. We conclude that alveolar lymphocytosis is frequently observed in patients with chronic uveitis. It is generally unrelated to sarcoidosis and may then be associated with a distinctive immunogenetic phenotype.

Parkinson's disease and sleepiness: an integral part of PD

OBJECTIVE

To investigate the potential causes of excessive daytime sleepiness in patients with PD-poor sleep quality, abnormal sleep-wakefulness control, and treatment with dopaminergic agents.

METHODS

The authors performed night-time polysomnography and daytime multiple sleep latency tests in 54 consecutive levodopa-treated patients with PD referred for sleepiness, 27 of whom were also receiving dopaminergic agonists.

RESULTS

Sleep latency was 6.3 +/- 0.6 minutes (normal >8 minutes), and the Epworth Sleepiness score was 14.3 +/- 4.1 (normal <10). A narcolepsy-like phenotype (> or = 2 sleep-onset REM periods) was found in 39% of the patients, who were sleepier (4.6 +/- 0.9 minutes) than the other 61% of patients (7.4 +/- 0.7 minutes). Periodic leg movement syndromes were rare (15%, range 16 to 43/h), but obstructive sleep apnea-hypopnea syndromes were frequent (20% of patients had an apnea-hypopnea index >15/h; range 15.1 to 50.0). Severity of sleepiness was weakly correlated with Epworth Sleepiness score (r = -0.34) and daily dose of levodopa (r = 0.30) but not with dopamine-agonist treatment, age, disease duration, parkinsonian motor disability, total sleep time, periodic leg movement, apnea-hypopnea, or arousal indices.

CONCLUSIONS

In patients with PD preselected for sleepiness, severity of sleepiness was not dependent on nocturnal sleep abnormalities, motor and cognitive impairment, or antiparkinsonian treatment. The results suggest that sleepiness-sudden onset of sleep-does not result from pharmacotherapy but is related to the pathology of PD.

[Respiratory disorders during sleep in degenerative diseases of the brain stem]

Sleep-disordered breathing may be present in patients with degenerative diseases affecting the brainstem. Indeed, this last structure contains the executive system of rapid eye movement (REM) sleep (tegmentum of the pons), of respiratory drive (medulla oblongata and pons) and motor neurons of upper airways dilators (fifth, seventh, ninth, tenth and twelfth cranial roots). Patients with Parkinson's disease suffer frequently from insomnia, partly caused by nocturnal motor disability, and from REM sleep behavior disorder. In 20 percent of the patients, excessive daytime sleepiness is caused by a sleep apnea syndrome, with a partly levodopa-dependent upper airway dysfunction. In 40 percent of the patients, sleepiness mimics a secondary narcolepsy and may be associated with hypnagogic hallucinations. During supranuclear palsy, REM sleep is progressively curtailed with rare sleep-disordered breathing. Patients with multiple systemic atrophy may present a nocturnal stridor caused by laryngeal palsy and benefit from tracheotomy or continuous nasal positive airway pressure. Seldom sleep and respiratory studies in genetic ataxic diseases suggest a normal respiratory drive, occasional diaphragmatic dysfunction and night hypopneas. During amyotrophic lateral sclerosis, the progressive loss of phrenic nerve leads to a diaphragmatic dysfunction, dyspnea and a lesser survival. Adequate ventilation is jeopardized during REM sleep with a consequent loss of this state.

Effects of muscle group recruitment on sniff transdiaphragmatic pressure and its components

Measuring maximal sniff pressures is an easy way of assessing inspiratory muscle strength. During a static manoeuvre, the pattern of inspiratory muscle recruitment during a sniff can vary from one individual to another. We therefore assessed how voluntarily changing muscle recruitment would affect sniff oesophageal, gastric and transdiaphragmatic pressures (Pes,sn, Pga,sn and Pdi,sn, respectively). Ten normal subjects (age 27-38 years) performed natural sniff manoeuvres ("nat"), and preferentially diaphragmatic ("dia") or extradiaphragmatic ("extradia") sniff manoeuvres, after having learnt to dissociate between the inspiratory muscle groups. Abdominal displacements were monitored using a belt-mounted strain gauge. Natural patterns of muscle recruitment varied among subjects. On average, Pes,sn,nat was [median (range)] 81 (21-105) cmH2O. All of the subjects were able to modify inspiratory muscle recruitment voluntarily. Pes,sn was not significantly affected by the type of manoeuvre performed, as opposed to Pdi,sn, which, as expected, increased with both the diaphragmatic and extradiaphragmatic manoeuvres [Pdi,sn,dia 132 (99-157) cmH2O, Pdi,sn,extradia 96 (50-146) cmH2O, P<0.05]. Whatever the manoeuvre, there was no correlation between Pes and Pdi, but Pga and Pdi were correlated during both the diaphragmatic (r = 0.82, P < 0.05) and the extradiaphragmatic manoeuvre (r = 0.70, P < 0.05). Pes,sn may have limitations as an index of diaphragm function, but by showing its independence from inspiratory muscle recruitment, this study contributes to its validation as a robust index of global inspiratory muscle strength that is particularly well suited for follow-up studies. This should extend to Pes,sn substitutes measured at the airway opening.

Dysfunction of phrenic pacemakers induced by metallic rescue blankets

Phrenic pacing can restore diaphragmatic contractions in patients with central respiratory paralysis. It relies on radiofrequency transmission of energy from an external unit to implanted receivers through circular coil antennas. The case of a patient is reported in whom severe hypoventilation occurred following the use of a metallic rescue blanket. The phenomenon was confirmed in two subsequent patients and during benchmark tests. Possible mechanisms include reflection and diffusion of high frequency waves by a Faraday-like effect. Patients with implanted devices relying on telemetric control or powering, and their care givers, should be warned against the use of metallic rescue sheets.

Improvement of sleep architecture in PD with subthalamic nucleus stimulation

High-frequency stimulation of the subthalamic nucleus (STN) was used to investigate the relationship of sleep disorders with motor handicap in PD. In 10 insomniac patients with PD, stimulation reduced nighttime akinesia by 60% and completely suppressed axial and early morning dystonia, but did not alleviate periodic leg movements (n = 3) or REM sleep behavior disorders (n = 5). Total sleep time increased by 47%; wakefulness after sleep onset decreased by 51 minutes. Insomnia in patients with PD may predominantly result from nighttime motor disability.

Pulmonary blood flow distribution in stage 1 chronic obstructive pulmonary disease

We investigated the hypothesis that lung blood flow distribution is modified in stage 1 chronic obstructive pulmonary disease (COPD). We compared patients with stage 1 COPD (n = 11) with restrictive patients with comparable blood gases (n = 7), to patients with low cardiac index with normal lungs (n = 11) and to control subjects (n = 11). Distribution of transit time (DTT) was computed by deconvolution from first pass radioactivity curves (albumin (99m)Tc) reconstructed from right and left ventricular regions of interest. Distribution descriptors, mean transit time (p < 0.05), standard deviation (p < 0.001), relative dispersion (p < 0.001), and kurtosis (p < 0.001) differed between groups (ANOVA). Cardiac index was the same in COPD and low CI groups but lower compared with normal subjects (p < 0.05). After normalization for cardiac output, the DTT of patients with COPD remained different from low CI and restrictive patients (p < 0.001). Therefore changes in DTT in patients with COPD compared with patients without COPD could not be explained on the basis of difference in cardiac output. Because P(O(2)), PC(O(2)), and pH were similar in COPD and restrictive groups, difference in distribution could not be explained either on the basis of blood gas data. We conclude that changes in DTT occurs in stage 1 COPD and cannot be explained by hypoxemia, hypercapnia, or acidosis alone but must relate to other structural or regulatory responses.

Traumatic coronary-pulmonary artery fistula, 23 years after a stab wound

We describe a 50-year-old man with onset of severe hemoptysis and anemia. Twenty-three years earlier, he had undergone a surgical procedure for a left thoracic wound as a result of a knife injury. Current diagnosis of aneurysm of the left ventricle and coronary-pulmonary artery fistula was made after coronary arteriography. The patient underwent resection of the aneurysm and repair of the fistula.

Assessment of upper airway dynamics in awake patients with sleep apnea using phrenic nerve stimulation

Phrenic nerve stimulation can reproduce during wakefulness the dissociation between upper airway and inspiratory muscles that is associated with obstructive sleep-related breathing disorders. This could provide a useful management tool in the study of passive upper airway (UA) dynamics during wakefulness in patients with the obstructive sleep apnea-hypopnea syndrome (OSAHS). To assess the feasibility of the technique in this setting, we studied the dynamics of diaphragm twitch-associated inspiratory flow in eight patients with OSAHS. Cervical magnetic stimulation (CMS) and bilateral anterior magnetic phrenic stimulation (BAMPS) were applied at end-expiration during exclusive nasal breathing. Electrical phrenic nerve stimulation (ES) proved not feasible. The driving pressure and the respiratory resistance at peak twitch esophageal pressure obtained at maximal stimulation intensity were significantly higher with BAMPS than with CMS. A twitch-flow limitation pattern was observed in seven of eight subjects; VI(max) values of flow-limited twitches obtained at 100% stimulation intensity was 0.81 +/- 0.5 L/s with BAMPS and 0.87 +/- 0.5 L/s with CMS (p = 0.4). The number of flow-limited BAMPS twitches dropped from an average 77.5% to 18.4% with nasal continuous positive airway pressure (CPAP) levels corresponding to the patient's home treatment. We conclude that (1) BAMPS is potentially a useful tool to evaluate the dynamics of flow through the passive UA in awake OSAHS patients, (2) BAMPS may be superior to CMS in evaluating UA properties in OSAHS.

Hallucinations, REM sleep, and Parkinson's disease: a medical hypothesis

BACKGROUND

Patients with PD can have disabling visual hallucinations associated with dopaminergic therapy. Sleep disorders, including vivid dreams and REM sleep with motor behaviors (RBD), are frequent in these patients.

METHODS

The association of hallucinations and REM sleep both at night and during the day was examined in 10 consecutive nondemented patients with long-standing levodopa-responsive PD and hallucinations. Seven patients presented with paranoia and paranoid delusions. Overnight sleep recordings and standard multiple daytime sleep latency test were performed. The results were compared to those of 10 similar patients with PD not experiencing hallucinations.

RESULTS

RBD was detected in all 10 patients with hallucinations and in six without. Although nighttime sleep conditions were similar in both groups, hallucinators tended to be sleepier during the day. Delusions following nighttime REM period and daytime REM onsets were observed in three and eight of the hallucinators, and zero and two of the others. Daytime hallucinations, coincident with REM sleep intrusions during periods of wakefulness, were reported only by hallucinators. Postmortem examination of the brain of one patient showed numerous Lewy bodies in neurons of the subcoeruleus nucleus, a region that is involved in REM sleep control.

CONCLUSION

The visual hallucinations that coincide with daytime episodes of REM sleep in patients who also experience post-REM delusions at night may be dream imagery. Psychosis in patients with PD may therefore reflect a narcolepsy-like REM sleep disorder.

Multiple organ failure complicating probable scrub typhus

This report describes a case of life-threatening acute respiratory distress syndrome with multiple organ failure complicating probable scrub typhus. Favorable outcome was associated with fluoroquinolone therapy. Scrub typhus should be suspected in travelers returning from Southeast Asia presenting with unexplained respiratory manifestations.

Linkage of hiccup with heartbeat

We explored a possible link between the cardiac cycle and the timing of recurrent hiccups in 10 patients with chronic, intractable hiccups. Recordings made during daytime naps in a sleep laboratory included sleep state; electrocardiogram; and respiration by means of a thermistor to detect airflow, bands around the rib cage and abdomen to assess expansion, and a bipolar surface electrode electromyogram over parasternal intercostal muscles. Hiccups could be detected on the abdominal bands and the parasternal electromyogram. The time of occurrence of each hiccup and each R wave in a continuous tracing of 100 or more hiccups were recorded and analyzed together with semiquantitive estimates of the phase of hiccup respiration. Whereas the hiccup rate ranged from approximately one-third to one-eighth of heart rate and was more variable than heart rate, hiccups showed a tendency, stronger in some subjects than others, to occur in midsystole. Variation in R-wave-R-wave (R-R) interval in association with hiccups was found in five patients. In three of these patients, hiccups were synchronized with respiration so that the cyclic change in R-R interval posthiccup could be explained as sinus arrhythmia, but, in two patients, the hiccups were not synchronized with respiration, so that hiccups are most likely responsible for the variation in heart rate. Also, the variation of R-R interval with hiccups suggests that there is some phasic autonomic efferent activity associated with hiccups.

Diaphragm and chest wall: assessment of the inspiratory pump with MR imaging-preliminary observations

Magnetic resonance (MR) imaging of the thorax with three-dimensional (3D) reconstruction and functional quantification was evaluated as a tool for structure-function evaluation of chest-wall mechanics. Good agreement was found between the corresponding spirometric and MR imaging values of lung volumes. Fast MR imaging of the thorax with 3D reconstruction should improve the ability to evaluate the inspiratory pump in clinical and research investigations.

Expiratory flow limitation as a determinant of orthopnea in acute left heart failure

OBJECTIVES

To assess the contribution of expiratory flow limitation (FL) in orthopnea during acute left heart failure (LHF).

BACKGROUND

Orthopnea is typical of acute LHF, but its mechanisms are not completely understood. In other settings, such as chronic obstructive pulmonary disease, dyspnea correlates best with expiratory FL and can, therefore, be interpreted as, in part, the result of a hyperinflation-related increased load to the inspiratory muscles. As airway obstruction is common in acute LHF, postural FL could contribute to orthopnea.

METHODS

Flow limitation was assessed during quiet breathing by applying a negative pressure at the mouth throughout tidal expiration (negative expiratory pressure [NEP]). Flow limitation was assumed when expiratory flow did not increase during NEP. Twelve patients with acute LHF aged 40-98 years were studied seated and supine and compared with 10 age-matched healthy subjects.

RESULTS

Compared with controls, patients had rapid shallow breathing with slightly increased minute ventilation and mean inspiratory flow. Breathing pattern was not influenced by posture. Flow limitation was observed in four patients when seated and in nine patients when supine. In seven cases, FL was induced or aggravated by the supine position. This coincided with orthopnea in six cases. Only one out of the five patients without orthopnea had posture dependent FL. Control subjects did not exhibit FL in either position.

CONCLUSIONS

Expiratory FL appears to be common in patients with acute LHF, particularly so when orthopnea is present. Its postural aggravation could contribute to LHF-related orthopnea.

Effect of low and high frequency thalamic stimulation on sleep in patients with Parkinson's disease and essential tremor

Continuous high frequency stimulation of the ventral intermediate nucleus of the thalamus (Vim), delivered through surgically implanted quadripolar electrodes, alleviates tremor in Parkinson's disease (PD) and essential tremor (ET). The Vim is adjacent to the thalamic reticular nuclei, where sleep spindles originate according to animal models. In order to determine whether Vim stimulation affects sleep spindles, six patients (4 PD, 2 ET), aged 60-69 years, were recorded on a control night and a stimulation night (130 Hz, 2-3 V; right stimulation in five patients and bilateral stimulation in one patient). Stimulation did not modify sleep quality or architecture. Sleep spindles were present and symmetrical in five out of six patients under stimulation. However, in one patient with a sustained 'thalamotomy-like effect' that abolished tremor, spindles were asymmetrical even without stimulation. In each patient, spindle density was similar on both nights (mean+/- SEM: 2.25+/-0. 61 spindles per min of stage 2 sleep vs. 1.84+/-0.31). In an attempt to promote sleep two different patterns of stimulation were applied in the region of ventrooralis posterior and reticularis nuclei in five patients in the awake state. Continuous low frequency stimulation (5 Hz, 0.1 V), and repeated trains of 15 Hz for 1 s every 15 s mimicking the pattern of physiological spindles, each failed to induce sleep or cortical synchronization. We conclude that Vim stimulation, unlike thalamotomy, selectively reduces tremor without altering sleep or sleep spindles. Our results also suggest that low frequency stimulation applied in the region of the reticular nuclei does not induce sleep.