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Biomedical subjects

T Similowski

Publications and source records attributed to T Similowski.

At least 19 recordsLinked to original sources
PubMed1997

Putative projection of phrenic afferents to the limbic cortex in humans studied with cerebral-evoked potentials.

Respiratory sensations may rely in part on cortical integration of respiratory afferent information. In an attempt to study such projections, we recorded evoked potentials at scalp and cervical sites in 10 normal volunteers undergoing transcutaneous phrenic stimulation (0.1-ms square pulses, intensity liminal for diaphragmatic activation, series of 600 shocks at 2 Hz). A negative cerebral component of peak latency (12.79 +/- 0.54 ms; N13) was constant, and a negative spinal component (7.09 +/- 1.04 ms; N7) could also be recorded, all results being reproducible over time. Monitoring of cardiac frequency, skin anesthesia, and stimulation adjacent to the phrenic nerve made the phrenic origin of N7 and N13 the foremost hypothesis. Increasing stimulation frequency and comparison with median nerve stimulation provided arguments for the neural nature of the signals and their cerebral origin. Recordings from intracerebral electrodes in a patient showed a polarity reversal of the evoked potentials at the level of the cingulate gyrus. In conclusion, phrenic stimulation could allow one to study projections of phrenic afferents to the central nervous system in humans. Their exact site and physiological meaning remain to be clarified.

Adult↗
PubMed1997

Comparison of magnetic and electrical phrenic nerve stimulation in assessment of phrenic nerve conduction time.

Cervical magnetic stimulation (CMS), a nonvolitional test of diaphragm function, is an easy means for measuring the latency of the diaphragm motor response to phrenic nerve stimulation, namely, phrenic nerve conduction time (PNCT). In this application, CMS has some practical advantages over electrical stimulation of the phrenic nerve in the neck (ES). Although normal ES-PNCTs have been consistently reported between 7 and 8 ms, data are less homogeneous for CMS-PNCTs, with some reports suggesting lower values. This study systematically compares ES- and CMS-PNCTs for the same subjects. Surface recordings of diaphragmatic electromyographic activity were obtained for seven healthy volunteers during ES and CMS of varying intensities. On average, ES-PNCTs amounted to 6.41 +/- 0.84 ms and were little influenced by stimulation intensity. With CMS, PNCTs were significantly lower (average difference 1.05 ms), showing a marked increase as CMS intensity lessened. ES and CMS values became comparable for a CMS intensity 65% of the maximal possible intensity of 2.5 Tesla. These findings may be the result of phrenic nerve depolarization occurring more distally than expected with CMS, which may have clinical implications regarding the diagnosis and follow-up of phrenic nerve lesions.

Adult↗
PubMed1996

Impairment of central motor conduction to the diaphragm in stroke.

Respiratory complications are common in patients with stroke, but the involvement of the diaphragm in this setting is not completely understood. The purpose of this study was to assess corticodiaphragmatic pathways in patients with vascular hemiplegia. Fifteen patients were studied, nine with a capsular type of hemiplegia. Seven age-matched subjects served as the control group, and eight healthy young volunteers were studied to validate the methods by comparison with the literature. Diaphragm electromyogram was recorded bilaterally, using surface electrodes. Abductor pollicis brevis electromyogram was also recorded. After having checked the integrity of peripheral conduction, corticofugal pathways were studied using cortical magnetic stimulation, a reproducible and patient-independent stimulus. Left and right conduction times to the diaphragm were symmetrical in the control subjects, the young volunteers, and the six patients with hemiplegia but without capsular lesion (16.5 to 20.1 ms). Conversely, they were markedly asymmetrical in patients with capsular hemiplegia, diaphragm response on the plegic side being abolished or markedly delayed. Although the clinical impact of these findings remains to be determined, this study confirms that "central diaphragm paralysis" can be present in stroke. It also indicates that there is no bilateral motor representation of each hemidiaphragm.

Adult↗
PubMed1996

Facilitation-independent response of the diaphragm to cortical magnetic stimulation.

Neural diseases are often associated with respiratory muscle disorders. Assessment of the motor pathway from the central nervous system to the diaphragm is therefore highly clinically relevant from a diagnosis and follow-up point of view. Cortical magnetic stimulation (CxMS) combined with surface diaphragm electromyogram (EMGdi) has to date been limited in this application by the need of an underlying voluntary contraction to obtain a diaphragm response (facilitation). This study was performed to verify this point with high-powered stimulators and to describe the pattern of diaphragm response to CxMS. In nine subjects, EMGdi was compared with EMG of the abductor pollicis brevis (APB). CxMS was applied on relaxed muscles. The effects of its decreasing intensity and those of a voluntary contraction were studied. In three subjects, transdiaphragmatic pressure was also measured. CxMS consistently provoked a contraction of the relaxed diaphragm (16.06 +/- 0.64 ms, mean +/- SD). Decreasing stimulation intensity decreased the amplitude and increased the latency of this response. Underlying contractions had opposite effects. Respective behaviors of the diaphragm and APB were similar. It is concluded that CxMS gives access to central motor conduction to the diaphragm without the need for subject cooperation.

Adult↗
PubMed1996

Assessment of the voluntary activation of the diaphragm using cervical and cortical magnetic stimulation.

The twitch occlusion technique is a promising tool for use in accessing central drive to the diaphragm and determining maximal transdiaphragmatic pressure (Pdi) from submaximal efforts. It clinical use is limited by difficulties inherent to bilateral electrical stimulation (BES) of the phrenic nerves. This study was designed to revisit the technique using cervical magnetic stimulation (CMS). In addition, the effects of a voluntary contraction on diaphragm response to magnetic stimulation of the cortex (CxMS) were studied. Seven volunteers aged 23-33 yrs were studied. Pdi was determined at relaxed functional residual capacity (FRC) in response to BES (Pdi,P-ES) and CMS (Pdi,p-CMS), and the effects of an increasing voluntary contraction (Pdi, vol) were assessed, The same procedure was applied to CxMS. Pdi,p-CMS at relaxed FRC was 27.5 +/- 2.2 cmH2O (mean+/-SEM), about 20% higher than Pdi,p-ES, and reported previously. Pd,p-CMS linearly decreased with Pdi, vol, and six out of seven subjects were capable of producing voluntary contractions sufficient to extinguish the twitch. More complex patterns were observed with CxMS. Cervical magnetic stimulation provides diaphragmatic twitch occlusion data very similar to bilateral electrical phrenic stimulation. Magnetic stimulation, be it cervical or cortical, could probably be helpful for the assessment of central and peripheral mechanisms of diaphragmatic dysfunction in the clinical setting.

Adult↗
PubMed1996

Assessment of the motor pathway to the diaphragm using cortical and cervical magnetic stimulation in the decision-making process of phrenic pacing.

BACKGROUND: Phrenic nerve pacing is a recognized substitute to positive pressure ventilation via tracheotomy in patients with high cervical cord lesions or central hypoventilation. Although its indications are infrequent, reliable strategies need to be used in the determinations of patients who may benefit from this treatment; contraindications should be carefully respected. STUDY OBJECTIVES: To determine whether modern and noninvasive means to study the motor pathway to the diaphragm, namely cortical magnetic stimulation (CxMS) and cervical magnetic stimulation (CMS), can contribute to the selection of patients who may benefit from phrenic pacing. DESIGN AND SETTING: Prospective study (18 months), on a consecutive basis, of patients referred for possible phrenic pacing to a 10-bed ICU associated with a respiratory neurophysiology laboratory. PATIENTS: Seven patients (high cervical cord injury, n = 5; central hypoventilation following neurosurgery, n = 1; idiopathic acquired central hypoventilation, n = 1). INTERVENTION, MEASUREMENTS, AND RESULTS: Electromyography of the diaphragm and transdiaphragmatic pressure were assessed in response to CxMS and CMS. In three cases, no interruption of the corticodiaphragmatic pathway was evidenced, the decision of pacing was postponed, and the patients eventually recovered a spontaneous breathing activity. In two cases, the diagnosis of irreversible peripheral phrenic dysfunction was reached and pacing was denied. In two cases, complete interruption of the corticodiaphragmatic pathway and integrity of peripheral conduction led to the decision of phrenic pacemaker implantation. CONCLUSION: CxMS and CMS can be used to refine the assessment of patients proposed for phrenic pacing. CxMS can possibly identify those in whom there is a possibility for eventual recovery, and therefore substantiate a decision to postpone the pacing.

Adolescent↗
PubMed1996

[Iatrogenic disorders in the active respiratory systems (respiratory center and its performance].

Amongst the undesirable effects of medical intervention which touch on the respiratory apparatus one can distinguish schematically those disorders which affect the "passive respiratory system" (lungs, pleura, bronchi and vessels) and those which concern the "active respiratory system (SRA)" (nerve centres, respiratory muscles) which are less often described. After a brief reminder of the principles and limits of the available methods of investigation, this chapter reviews the different iatrogenic disorders of SRA according to their level and their aetiology. Peripheral disorders are touched on such as alterations of phrenic conduction (with particular mention of satellite lesions from cardiac surgery), those of neuromuscular transmission (most often induced by medication) and of intrinsic muscular properties (mainly steroid induced myopathies). Central disorders are described principally as the respiratory effects of neurotropic and non-neurotropic medications and the harmful effects of different substances on the sleep/respiration interaction. The secondary effects of therapy on SRA are all the more marked if there are underlying respiratory or neuromuscular disturbances which allow a large place for preventive measures. The diagnosis is made difficult by the complexity of the structures and functions involved and it is clear that the development of pathophysiological studies, which are still too scarce, should enable better understanding of their clinical significance.

Diagnosis, Differential↗
PubMed1995

[Diagnosis and treatment of acute respiratory failure in chronic obstructive respiratory insufficiency].

Acute respiratory failure of chronic obstructive pulmonary disease is a common event. Vital prognosis is seldom directly engaged, and careful management generally allows patients to resume their prior respiratory status, and long term therapeutic procedures such as oxygen therapy or home ventilation to be discussed. Diagnosis is often simple, and evaluation of severity, therapeutic strategy, and etiology research are carried out simultaneously. The first step of treatment is controlled oxygen therapy. When conservative treatment fails to achieve safe level of PaO2 without inducing threatening hypercapnia, mechanical ventilation is required. Recent data strongly suggest that non invasive inspiratory pressure support brings major benefits in terms of morbidity and mortality.

Acute Disease↗
PubMed1995

Baclofen therapy for chronic hiccup.

Chronic hiccup is a rare but potentially severe condition, that can be symptomatic of a variety of diseases, or idiopathic. Many therapeutic interventions have been reported, most often as case reports. Among other drugs, baclofen has been suggested as a therapy for chronic hiccup. In a large series of patients, we have evaluated its therapeutic position. In patients with chronic hiccup, defined as hiccup spell or recurring hiccup attacks lasting more than 7 days, investigation of the upper gastro-oesophageal tract (fibroscopy, manometry, and pH monitoring) was systematically performed. Most patients had tried numerous drugs in the past, without success. Baclofen was used as a first treatment in patients without evidence of any gastro-oesophageal disease (n = 17), and was undertaken only after full treatment of such disease (n = 55) had failed to solve the hiccup problem (n = 20). Baclofen has, therefore, been administered to 37 patients with chronic hiccup (average duration 4.6 yrs). Baclofen produced a long-term complete resolution (18 cases) or a considerable decrease (10 cases) of hiccups in 28 of the 37 patients. There was no significant difference between patients with or without gastro-oesophageal disease. We conclude that so-called idiopathic chronic hiccup often results from gastro-oesophageal abnormalities. Also, if controlled studies confirm our encouraging results, baclofen can be a major element in the treatment of chronic hiccup that is idiopathic, or that cannot be helped by treatment of gastro-oesophageal diseases.

Anti-Ulcer Agents↗
PubMed1995

Physical examination of the adult patient with respiratory diseases: inspection and palpation.

Inspection of the thorax identifies the breathing position adopted by the patient, the shape of the thorax, the dynamics of respiration (breathing pattern, symmetry of expansion, mechanics and synchrony of rib cage and abdominal movements). Inspection of the neck adds useful information, particularly with respect to the dynamics of breathing. Palpation ascertains the signs suggested by inspection with respect to the mechanics of breathing. It also assesses the state of the pleura and pulmonary parenchyma by studying the tactile fremitus. It integrates extrarespiratory signs, such as enlarged lymph nodes or breast abnormalities. Extrathoracic respiratory signs should also be systematically looked for, including cyanosis, finger deformation, pulsus paradoxus, and pursed lips breathing. Interobserver agreement about respiratory signs has repeatedly been studied, and generally found to be low, as are clinical-functional correlations. However, some data on chronic obstructive pulmonary disease (COPD), asthma or pulmonary embolism are available. From the description of some signs and the current knowledge about their operative values, it appears that much clinical research remains necessary to better define the precise diagnostic value of a given sign. The impact of training on diagnostic performance also has to be defined. Both of these aspects should allow clinicians to optimize the way in which they use their hands and eyes to conduct respiratory diagnosis, as well as the way they teach respiratory symptomatology.

Adult↗
PubMed1995

[Bibliometry of biomedical periodicals].

Bibliometry or the science citation index is a quantitative evaluation of periodical literature, biomedical or others. It depends above all on an analysis of citations which allows for a calculation of different indices characterising and classifying journals (number of articles published, frequency of citation, impact, topicality...). The applications of bibliometry are varied from the administration of library collections to the appreciation of the significance of a review in its own speciality area. By extension the bibliometry index are sometimes used to evaluate the importance of a discipline in the literature, the place of a nation within a discipline, the significance of certain opinions or the quality of research. The intrinsic limits of bibliometry are such that this last application should be handled with caution. In effect, various biases can mechanically affect the value of different indices and particularly the fact that an article appearing in a prestigious review should not prejudge its quality such as the relevance of the question posed, the validity of the methodology employed or the accuracy of the results. For this, the study of citations is insufficient and some qualitative or semi-quantitative criteria bearing on the contents of the article should be used (critical reading, gate analysis, etc.) This general review has, as its aim, to expose both the definitions and limits of bibliometry illustrating them with some information calculated from the principal respiratory journals.

Bias↗
PubMed1994

Late CD8+ lymphocytic alveolitis after allogeneic bone marrow transplantation and chronic graft-versus-host disease.

Late-onset interstitial pneumonitis following allogeneic bone marrow transplantation (BMT) is a rare condition usually caused by a variety of infective agents, although in some cases these are idiopathic. We investigated noninfectious late interstitial pneumonitis with lymphocytic alveolitis in seven allogeneic BMT recipients using bronchoalveolar lavage (BAL), lymphocyte phenotyping analysis, CT lung scans, and pulmonary function tests. The results were compared with those of a control group composed of similar patients with no pulmonary symptoms. Of 65 long-term survivors, seven were included in the study. All had chronic graft-versus-host disease (GVHD) and developed interstitial pneumonitis a median of 210 d (range 120 to 445 d) after BMT. BAL revealed lymphocytosis, with an overall expansion of CD8+ subsets (38 to 90%). Lymphocytic alveolitis was not observed in the control group. Pulmonary function tests revealed a restrictive syndrome, and biopsy samples obtained from 2 patients showed interstitial lymphoid infiltration with fibrosis of the alveolar walls. Of the 7 patients, six were cured by starting immunosuppressive drugs or increasing the dosage with a drastic improvement in respiratory symptoms within 1 mo. These findings suggest that CD8+ alveolitis may be observed in late interstitial pneumonitis in allogeneic BMT recipients and may be a pulmonary manifestation of chronic GVHD.

Adult↗
PubMed1994

Inspiratory muscle testing in stable COPD patients.

Exploration of inspiratory muscles in stable chronic pulmonary disease patients can be important in the investigation of a respiratory handicap unsatisfactorily explained by alterations of the passive respiratory system, or in the follow-up of patients undergoing treatments that can interfere with muscle function. Compensatory mechanisms tend to counterbalance the deleterious effects of hyperinflation in these patients, and precise clinical data are needed in order to avoid mistakes due to underverified hypotheses. Investigation of inspiratory muscle function requires the study of output data under various states of activity of the system. As outputs, volume displacement lacks specificity, pressure measurements can be more specific but are at times invasive and should be associated with lung volume measurements, electromyography is methodologically complex, nonquantitative and of poor reproducibility. Voluntary manoeuvres depend upon subject co-operation, and do not allow partitioning of output between the action of different muscle groups. Transcutaneous electrical phrenic nerve stimulation is devoid of these inconveniences, but it explores only one muscle (the diaphragm) under conditions that are not "natural" (relaxed rib cage). Recently, perspectives for easier clinical assessment of inspiratory muscle function in chronic obstructive pulmonary disease patients have been opened by cervical magnetic stimulation, better understanding of the meaning of mouth pressure in relationship to phrenic stimulation, and development of noninvasive tests, such as nostril pressure during sniff or phonomyography. If validated, such tests should provide a reasonably limited panel of clinical tools to better appreciate muscle function in this setting.

Diaphragm↗