Biomedical subjects

C Straus

Publications and source records attributed to C Straus.

At least 37 records · Page 2Linked to original sources

PubMed2000

Developmental disinhibition: turning off inhibition turns on breathing in vertebrates.

Development requires age-dependent changes in essential behaviors. While the mechanisms determining the developmental expression of such behavior in vertebrates remain largely unknown, a few studies have identified permissive mechanisms in which the appearance of promoting signals activates pre-established networks. Here we report a different developmental process. Specifically, we show that the neuronal substrate that produces putative lung breathing in tadpoles is formed early in development, but remains more or less inactive until metamorphosis because of suppression mediated by a GABA(B) receptor-dependent mechanism. Blocking this suppression using 2-hydroxy-saclofen, a GABA(B) receptor antagonist, results in the precocious production of the putative lung breathing motor pattern. This blocker failed to augment putative lung breaths after metamorphosis. Thus, our results suggest that loss of an inhibitory signal during development (i.e., developmental disinhibition) is responsible for the developmental expression of air breathing.

Action Potentials↗

PubMed2000

Baclofen eliminates cluster lung breathing of the tadpole brainstem, in vitro.

Intermittent lung ventilation is a respiratory pattern wherein breaths occur in clusters. Intermittent lung ventilation is common in amphibians and can occur in mammals. Isolated brainstems from postmetamorphic tadpoles exhibiting episodic lung ventilatory bursts were superfused with baclofen, a potent gamma-aminobutyric acid (GABA)(B) receptor agonist. At moderate concentrations (0.125 to 0.5 microM), the number of lung bursts per episode decreased but their overall frequency was unchanged. At 0.5 microM, only 1.22+/-0.24 lung bursts occurred per episode, indicating virtually no clustering. Only at higher concentrations was overall breathing frequency decreased. Therefore, at moderate concentrations of baclofen continuous ventilation replaced episodic ventilation, suggesting that a GABA(B) receptor-dependent pathway may regulate the clustering of lung breaths.

Animals↗

PubMed2000

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.

Adult↗

PubMed2000

A computed tomographic scan assessment of endotracheal suctioning-induced bronchoconstriction in ventilated sheep.

This study was directed at assessing changes in bronchial cross-sectional surface areas (BCSA) and in respiratory resistance induced by endotracheal suctioning in nine anesthetized sheep. Cardiorespiratory parameters (Swan-Ganz catheter), respiratory resistance (inspiratory occlusion technique), BCSA, and lung aeration (computed tomography) were studied at baseline, during endotracheal suctioning, and after 20 consecutive hyperinflations. Measurements performed initially at an inspired oxygen fraction (FI(O(2))) of 0.3 were repeated at an FI(O(2)) of 1.0. At an FI(O(2)) of 0.3, endotracheal suctioning resulted in atelectasis, a reduction in BCSA of 29 +/- 23% (mean +/- SD), a decrease in arterial oxygen saturation from 95 +/- 3% to 87 +/- 12% (p = 0.02), an increase in venous admixture from 19 +/- 10% to 31 +/- 19% (p = 0. 006), and an increase in lung tissue resistance (DR(rs)) (p = 0. 0003). At an FI(O(2)) of 1.0, despite an extension of atelectasis and an increase in pulmonary shunt from 19 +/- 5% to 36 +/- 2% (p < 0.0001), arterial O(2) desaturation was prevented and BCSA decreased by only 7 +/- 32%. A recruitment maneuver after endotracheal suctioning entirely reversed the suctioning-induced increase in DR(rs) and atelectasis. In three lidocaine-pretreated sheep, the endotracheal suctioning-induced reduction of BCSA was entirely prevented. These data suggest that the endotracheal suctioning-induced decrease in BCSA is related to atelectasis and bronchoconstriction. Both effects can be reversed by hyperoxygenation maneuver before suctioning in combination with recruitment maneuver after suctioning.

Airway Resistance↗

PubMed2000

Radiologic gastrostomy placement: pigtail- versus mushroom-retained catheters.

OBJECTIVE: Two different types of percutaneous fluoroscopic gastrostomy procedures were prospectively evaluated. SUBJECTS AND METHODS: Between January 1, 1998, and August 10, 1999, 127 percutaneous gastrostomy catheters were placed in 128 patients in 128 attempts. Seventy-five 12- or 14-French pigtail-retained catheters and fifty-two 20-French mushroom-retained catheters were inserted. Catheters were generally placed on the basis of operator preference except pigtail-retained tubes were preferentially placed in patients with head and neck or esophageal malignancies and mushroom-retained catheters were preferentially placed in neurologically compromised or combative patients. The technical success, procedural complications, and catheter complications were recorded. Statistical analysis was performed. RESULTS: Ninety-nine percent (127/128) of the procedures were successful, and there were no procedural complications. One catheter was not placed because the colon intervened between the abdominal wall and stomach. In patients who received pigtail-retained catheters, the major complication rate was 3% (2/75), the minor complication rate was 8% (6/75), and the tube complication rate was 36% (27/75). The following complications were seen: tube occlusion (n = 12), inadvertent catheter removal (n = 8), peristomal tube leakage (n = 7), superficial cellulitis (n = 4), aspiration pneumonia (n = 2), and T-fastener cellulitis (n = 2). In patients who received mushroom-retained catheters, the major complication rate was 0%, the minor complication rate was 2% (1/52), and the tube complication rate was 2% (1/52). Complications were superficial cellulitis (n = 1) and partial catheter fracture (n = 1). There were no significant differences in major and minor complications between procedures. Pigtail-retained catheters had a significantly higher rate of tube complications (p < 0.001) CONCLUSION: Compared with pigtail-retained catheters, mushroom-retained gastrostomy catheters are more durable and secure and are less prone to tube dysfunction. These catheters should be preferentially placed when possible.

Adolescent↗

PubMed2000

[Ontogeny of respiratory muscle control. Evidence from the amphibian model].

The mechanisms which control the cyclic contraction of the respiratory muscles remain uncertain. The ontogenic approach is attractive but difficult in mammals. The bullfrog larva, the tadpole, provides a model easier to study as its brainstem can be isolated in vitro. The tadpole undergoes a development from exclusive gill ventilation to bimodal breathing and, eventually, to exclusive lung ventilation. During the metamorphic stages, lung ventilation is not dependent upon inhibitory mechanisms, suggesting that pacemaker neurones may possibly drive the lung rhythm. This is not the case for the gill ventilation. However, inhibitory mechanisms are probably involved in the shape of the lung discharge in the adult frog. During the development of the tadpole, the regions of the brainstem responsible for the lung rhythm migrate rostrally, the sensitivity to hypoxia shifts from gill ventilation to lung ventilation and the sensitivity to hypercapnia develops with the lung ventilation. The ontogenic particularities of tadpole breathing and the study of its isolated brainstem provide a unique model for the investigation of the ventilatory rhythm generation.

Animals↗

PubMed1999

Efficacy of a low volume recirculating superfusion chamber for long term administration of expensive drugs and dyes.

We have characterized the efficacy of a low volume (2 ml) two-compartment experimental chamber in which a gas inflow equilibrates and recirculates the bathing fluid. This type of chamber is suitable for experiments employing en bloc preparations that require the administration of expensive molecular probes. The fluid in the chamber is pumped from a compartment holding the preparation to an elevated reservoir compartment using gas bubbles. The fluid returns via gravity along a different path. The flow rate of superfusate in the chamber was 30 ml min(-1). To determine the effectiveness of the chamber in dissolving gas, we filled the chamber with bicarbonate-buffered physiological saline and measured pH and P(O(2)) with ion-selective and Clark-style microelectrodes. Steady state values of pH and P(O(2)) in the chamber were almost identical to those in an external tonometer bubbled vigorously with the same gas mixture. When CO(2) was increased from 2 to 4.4%, the chamber pH fell with a time constant of 56 s (about twice that of the tonometer). To determine the effectiveness of gas exchange between a brain preparation and the fluid in the chamber we measured pH and P(O(2)) depth profiles of the in vitro tadpole brainstem. We found virtually no unstirred layer owing to excellent mixing and the high flow created by the recirculating mechanism. We demonstrate that despite the high flow rates, preparations are mechanically stable allowing intracellular electrophysiological recordings.

Animals↗

PubMed1999

Pressure-volume curves and compliance in acute lung injury: evidence of recruitment above the lower inflection point.

Measuring elastic pressure-volume (Pel-V) curves of the respiratory system and the volume recruited by a positive end-expiratory pressure (PEEP) allows one to study the pressure range over which recruitment occurs in acute lung injury (ALI), and to explain how recruitment affects the compliance. Pel-V curves were measured with the low flow inflation technique in 11 patients mechanically ventilated for ALI. Curve I was recorded during inflation from the volume attained after a prolonged expiration (6 s) at PEEP (9.0 +/- 2.2 cm H2O), and Curve II after expiration to the elastic equilibrium volume at zero end-expiratory pressure (ZEEP). By using the end-expiratory volume of the breaths, the curves were aligned on a common volume axis to determine the effect of a single complete expiration. In each patient, Curve II (from ZEEP) was shifted toward lower volumes than Curve I. The volume shift, probably due to derecruitment, was 205 +/- 100 ml at 15 cm H2O (p < 0.01) and 78 +/- 93 ml at 30 cm H2O (p < 0.01); thus, during inflation from ZEEP, the volume deficit was successively regained over a pressure range up to at least 30 cm H2O. At any pressure, compliance was higher on the curve from ZEEP than from PEEP, by 10.0 +/- 8.7 ml/cm H2O at 15 cm H2O (p < 0.01), and by 5.4 +/- 5.5 at 30 cm H2O (p < 0.01). It is concluded that in ALI, a single expiration to ZEEP leads to lung collapse. High compliance during insufflation from ZEEP indicates that lung recruitment happens far above the lower inflection point of the Pel-V curve.

Adolescent↗

PubMed1998

Cervical magnetic stimulation as a method to discriminate between diaphragm and rib cage muscle fatigue.

Inspiratory muscle fatigue can probably determine hypercapnic respiratory failure. Diaphragm fatigue is detected by electrical phrenic stimulation (ELS), but there is no simple tool to assess rib cage muscle (RCM) fatigue. Cervical magnetic stimulation (CMS) costimulates the phrenic nerves and RCM. We reasoned that changes in transdiaphragmatic pressure twitch (Pdi,tw) with CMS and ELS should be different after selective diaphragm vs. RCM fatigue. Five volunteers performed inspiratory resistive tasks while voluntarily uncoupling diaphragm and RCM. Baseline Pdi,twELS and Pdi,twCMS were 28.57 +/- 1.68 and 32.83 +/- 2.92 cmH2O. After selective diaphragm loading, Pdi,twELS and Pdi,twCMS were reduced by 39 and 26%, with comparable decreases in gastric pressure twitch (Pga,tw). Esophageal pressure twitch (Pes,tw) was better preserved with CMS. Therefore Pes,tw/Pga,tw was lower with ELS than CMS (-1.24 +/- 0.16 vs. -1.73 +/- 0.11, P = 0.05). After selective RCM loading, there was no diaphragm fatigue, but Pes,twCMS was significantly reduced (-30%). These findings support the role of rib cage stiffening by CMS-related RCM contraction in the ELS-CMS differences and suggest that CMS can be used to assess RCM fatigue.

Adult↗

PubMed1998

Contribution of the endotracheal tube and the upper airway to breathing workload.

The influence of the endotracheal tube (ETT) during a T-piece trial remains controversial. Our aim was to compare the work of breathing of 14 successfully extubated patients at the end of a 2-h trial (T) and after extubation (E) of the trachea, and to assess, using the acoustic reflection method, the resistance of the endotracheal tube and of the supraglottic airway as well as their related work. We found that the work of breathing of the patients was identical between T and E (1.72 +/- 0.59 versus 1.63 +/- 0.45 J/L; p = 0.50 and 23.5 +/- 10.6 versus 22.6 +/- 9.7 J/min; p = 0.70). There was no significant difference between the beginning and the end of the T-piece trial (1.57 +/- 0.53 versus 1.72 +/- 0.59 J/ L, p = 0.10). The work caused by the ETT amounted to 11.0 +/- 3.9% of the total work of breathing. The supraglottic airway resistance was in the normal range and was significantly smaller than the endotracheal tube resistance (0.79 +/- 0.4 versus 1.43 +/- 0.31 cm H2O x s/L; p = 0.008, flow = 0.25 L/s). We conclude that a 2-h trial of spontaneous breathing through an endotracheal tube well mimics the work of breathing performed after extubation, in patients who pass a weaning trial and do not require reintubation.

Acoustics↗

PubMed1997

Neuromuscular blockade with acute respiratory failure in a patient receiving cibenzoline.

Cibenzoline is a class Ic antiarrhythmic agent that can be used to treat supraventricular arrhythmias. A case is reported of cibenzoline overdose in a patient with impaired renal function, leading not only to the usual cardiac and metabolic symptoms (bradycardia and hypoglycaemia), but also to a myastheniform syndrome with acute respiratory failure. Neuromuscular blockade was demonstrated by repetitive supramaximal stimulation of the median nerve, and diaphragmatic involvement was evidenced by applying the same protocol to the phrenic nerve. Muscle strength recovered as serum cibenzoline levels decreased, allowing the patient to be weaned from the ventilator. This observation suggests that cibenzoline, like other antiarrhythmic agents, can be responsible for neuromuscular blockade, and should therefore be used with caution in patients with neuromuscular and respiratory diseases or with impaired renal function.

Acute Disease↗

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↗

PubMed1997

Influence of neck muscles on mouth pressure response to cervical magnetic stimulation.

Measurement of mouth pressure (Pm) in response to electrical phrenic nerve stimulation (Es) provides a simple noninvasive means to assess diaphragm function. An even simpler measure would be to use the Pm twitch response (Pm,t) to cervical magnetic stimulation (CMS) rather than to Es. Because CMS coactivates the diaphragm and inspiratory neck muscles (INM), CMS-Pm,t accurately reflects diaphragm function only if the corresponding INM contraction does not produce inspiratory pressures by itself. In patients with recent-onset bilateral diaphragm paralysis, it has been demonstrated that CMS-Pm,t was indeed zero; however, INM hypertrophy could change this situation and lead CMS-Pm,t to overestimate the performance of the diaphragm. To address this issue, we studied nine patients with amyotrophic lateral sclerosis (ALS) who had evidence of diaphragmatic paralysis and compensatory hypertrophy and hyperactivity of inspiratory neck muscles. The response to CMS was described in terms of diaphragm electromyogram (EMG), Pm, and abdominal (AB) and rib cage (RC) motion. No EMG response to CMS could be observed in most cases, and CMS was always associated with AB paradox. Nevertheless, a negative Pm,t swing was recorded with an amplitude of -2.6 +/- 1.0 cm H2O (mean +/- SD). We conclude that inspiratory neck muscle hypertrophy can significantly influence the Pm response to CMS. This should be taken into account when using the CMS-Pm combination in patients with possible chronic diaphragm dysfunction.

Aged↗

PubMed1997

Destructive polyarthritis due to a group B streptococcus.

A new case of destructive polyarthritis due to a Group B streptococcus is reported. The patient was a 55-year-old male whose predominantly axial manifestations in the absence of evidence of an infection initially suggested psoriatic arthritis. Although rare, Group B streptococcal arthritis has been reported outside the postpartal and neonatal periods. Monoarthritis with a favorable outcome has been the most common clinical pattern. Several cases of destructive polyarthritis with axial involvement have been reported in which the joint destruction and longer time to diagnosis as compared with monoarticular forms resulted in permanent functional impairment.

Arthritis, Infectious↗

PubMed1997

Chemodectoma of the cauda equina.

We report a new case of chemodectoma of the cauda equina, in a 52-year-old male who presented with low back pain and sciatica, then rapidly developed cauda equina syndrome. Magnetic resonance imaging demonstrated a tumor at the L2-L3 level. Complete excision was performed and the tumor was found to be a chemodectoma. Chemodectomas are rare neural crest tumors that are usually located at the neck. About 70 cases involving the cauda equina have been reported. Most are benign, although local recurrences occur in 4% of cases. A case with a cerebellar metastasis has been reported. Long-term follow-up should be provided.

Cauda Equina↗

PubMed1997

Spontaneous epidural hematoma discovered upon evaluation of a calcified disk herniation.

A female renal transplant recipient had intractable femoral neuralgia due to a large calcified disk herniation. She then developed an anterior epidural hematoma above the herniation, from T12 to L2, in the absence of clotting disorders. Spontaneous resorption of the hematoma occurred. The femoral neuralgia resolved after surgical treatment of the herniation. The location of the hematoma suggests that the calcified disk may have torn the fragilized epidural venous network.

Calcinosis↗

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↗