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Biomedical subjects

C Straus

Publications and source records attributed to C Straus.

At least 19 recordsLinked to original sources
PubMed2005

Diffusional screening in real 3D human acini--a theoretical study.

Gas exchange at the acinar level involves several physico-chemical phenomena within a complex geometry. A gas transport model, which takes into account both the diffusion into the acinus and the diffusion across the alveolar membrane, is used to understand gas mixing in realistic systems. It is first shown that the behaviour of the system, computed on model geometries in 3D, only depends on the topological structure of the acinus. Taking advantage of this property, a new efficient method based on random walks on a lattice is used to compute gas diffusion in structures taken from real morphological data. This approach shows that, at rest, the human acinus efficiency is only 30-40%. These results provide a new evidence of the existence of diffusional screening at the acinar level. This implies permanent spatial inhomogeneity of oxygen and carbon dioxide partial pressure. The notion of an "alveolar gas" is reinterpreted as a spatial average of the gas distribution. This model casts new light on the respiratory properties of other gas mixtures, such as helium-oxygen.

Cell Membrane Permeability↗
PubMed2005

[Primary central nervous system lymphoma presenting with central neurogenic hyperventilation. A case report and review of the literature].

INTRODUCTION: Central neurogenic hyperventilation (CNH) in an awake patient is a rare entity. OBSERVATION: We report here a 54-year-old patient who developed central neurogenic hyperventilation as the initial presentation of a primary central nervous system lymphoma located in the brainstem. CONCLUSION: The patient's hyperventilation resolved completely with chemotherapy for primary CNS lymphoma. Most of the cases reported in the literature are related to a diffuse tumor of the brainstem with an intriguing overrepresentation of primary CNS lymphoma. The pathogenesis of CNH is discussed.

Brain Stem Neoplasms↗
PubMed2005

Effects of upper airway anaesthesia on respiratory-related evoked potentials in humans.

Cortical potentials evoked by mid-inspiratory occlusion arise from numerous receptors, many of which are probably within the upper airway. Their precise nature is not known. The aim of the current study was to improve knowledge of this by studying the effects of topical upper airway anaesthesia on respiratory-related evoked potentials. Respiratory-related evoked potentials were described through the averaging of electroencephalogram (EEG) epochs following mid-inspiratory occlusions (C3-CZ; C4-CZ). A total of 21 healthy volunteers (13 male, aged 22-52 yrs) were studied during mouth breathing, before and after topical upper airway anaesthesia (lidocaine). Moreover, 15 subjects were studied during nose breathing with and without anaesthesia. Six subjects were studied whilst inhaling L-menthol. Typical potentials were present in all the subjects, their components featuring normal amplitudes and latencies. The route of breathing and upper airway anaesthesia did not modify the EEG responses to inspiratory occlusions, qualitatively or quantitatively, during mouth or nose breathing. L-menthol had no effect. Upper airway receptors sensitive to topical anaesthesia are unlikely to contribute significantly to mid-inspiratory occlusion-evoked potentials. On the contrary, deeper receptors, such as joint and muscle receptors, could contribute dominantly to these potentials.

Administration, Inhalation↗
PubMed2004

Facilitation of the diaphragm response to transcranial magnetic stimulation by increases in human respiratory drive.

The human respiratory neural drive has an automatic component (bulbospinal pathway) and a volitional component (corticospinal pathway). The aim of this study was to assess the effects of a hypercapnia-induced increase in the automatic respiratory drive on the function of the diaphragmatic corticospinal pathway as independently as possible of any other influence. Thirteen healthy volunteers breathed room air and then 5 and 7% hyperoxic CO2. Cervical (cms) and transcranial (tms) magnetic stimulations were performed during early inspiration and expiration. Transdiaphragmatic pressure (Pdi) and surface electromyogram of the diaphragm (DiEMG) and of the abductor pollicis brevis (apbEMG) were recorded in response to cms and tms. During inspiration, Pdi,cms was unaffected by CO2, but Pdi,tms increased significantly with 7% CO2. During expiration, Pdi,cms was significantly reduced by CO2, whereas Pdi,tms was preserved. DiEMG,tms latencies decreased significantly during early inspiration and expiration (air vs. 5% CO2 and air vs. 7% CO2). DiEMG,tms amplitude increased significantly in response to early expiration-tms (air vs. 5% CO2 and air vs. 7% CO2) but not in response to early inspiration-tms. DiEMG,cms latencies and amplitudes were not affected by CO2 whereas 7% CO2 significantly increased the apbEMG,cms latency. The apbEMG,tms vs. apbEMG,cms latency difference was unaffected by CO2. In conclusion, increasing the automatic drive to breathe facilitates the response of the diaphragm to tms, during both inspiration and expiration. This could allow the corticospinal drive to breathe to keep the capacity to modulate respiration in conditions under which the automatic respiratory control is stimulated.

Adaptation, Physiological↗
PubMed2003

A phylogenetic hypothesis for the origin of hiccough.

The occurrence of hiccoughs (hiccups) is very widespread and yet their neuronal origin and physiological significance are still unresolved. Several hypotheses have been proposed. Here we consider a phylogenetic perspective, starting from the concept that the ventilatory central pattern generator of lower vertebrates provides the base upon which central pattern generators of higher vertebrates develop. Hiccoughs are characterized by glottal closure during inspiration and by early development in relation to lung ventilation. They are inhibited when the concentration of inhaled CO(2) is increased and they can be abolished by the drug baclofen (an agonist of the GABA(B) receptor). These properties are shared by ventilatory motor patterns of lower vertebrates, leading to the hypothesis that hiccough is the expression of archaic motor patterns and particularly the motor pattern of gill ventilation in bimodal breathers such as most frogs. A circuit that can generate hiccoughs may persist in mammals because it has permitted the development of pattern generators for other useful functions of the pharynx and chest wall muscles, such as suckling or eupneic breathing.

Animals↗
PubMed2003

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.

Acute Disease↗
PubMed2002

Evidence that ventilatory rhythmogenesis in the frog involves two distinct neuronal oscillators.

In Rana catesbeiana the upper airways are used for two distinct yet highly coordinated ventilatory behaviours: buccal ventilation and lung inflation cycles. How these behaviours are generated and coordinated is unknown. The purpose of this study was to identify putative rhythmogenic brainstem loci involved in these ventilatory behaviours. We surveyed the isolated postmetamorphic brainstem to determine sites where local depolarization, produced by microinjecting the non-NMDA glutamate receptor agonist, AMPA, augmented the ventilatory motor patterns. Two sites were identified: a caudal site, at the level of cranial nerve (CN) X, where AMPA injections caused increased buccal burst frequency but abolished lung bursts, and a rostral site, between the levels of CN VIII and IX, where injections increased the frequency of both types of ventilatory bursts. These two sites were further examined using GABA microinjections to locally inhibit cells. GABA injected into the caudal site suppressed the buccal rhythm but the lung rhythm continued, albeit at a different frequency. When GABA was injected into the rostral site the lung bursts were abolished but the buccal rhythm continued. When the two sites were physically separated by transection, both rostral and caudal brainstem sections were capable of rhythmogenesis. The results suggest the respiratory network within the amphibian brainstem is composed of at least two distinct but interacting oscillators, the buccal and lung oscillators. These putative oscillators may provide a promising experimental model for studying coupled oscillators in vertebrates.

Animals↗
PubMed2001

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.

Abdominal Muscles↗
PubMed2001

Which came first, the lung or the breath?

Lungs are the characteristic air-filled organs (AO) of the Polypteriformes, lungfish and tetrapods, whereas the swimbladder is ancestral in all other bony fish. Lungs are paired ventral derivatives of the pharynx posterior to the gills. Their respiratory blood supply is the sixth branchial artery and the venous outflow enters the heart separately from systemic and portal blood at the sinus venosus (Polypteriformes) or the atrium (lungfish), or is delivered to a separate left atrium (tetrapods). The swimbladder, on the other hand, is unpaired, and arises dorsally from the posterior pharynx. It is employed in breathing in Ginglymodi (gars), Halecomorphi (bowfin) and in basal teleosts. In most cases, its respiratory blood supply is homologous to that of the lung, but the vein drains to the cardinal veins. Separate intercardiac channels for oxygenated and deoxygenated blood are lacking. The question of the homology of lungs and swimbladders and of breathing mechanisms remains open. On the whole, air ventilatory mechanisms in the actinopterygian lineage are similar among different groups, including Polypteriformes, but are distinct from those of lungfish and tetrapods. However, there is extreme variation within this apparent dichotomy. Furthermore, the possible separate origin of air breathing in actinopterygian and 'sarcopterygian' lines is in conflict with the postulated much more ancient origin of vertebrate air-breathing organs. New studies on the isolated brainstem preparation of the gar (Lepisosteus osseus) show a pattern of efferent activity associated with a glottal opening that is remarkably similar to that seen in the in-vitro brainstem preparation of frogs and tadpoles. Given the complete lack of evidence for AO in chondrichthyans, and the isolated position of placoderms for which buoyancy organs of uncertain homology have been demonstrated, it is likely that homologous pharyngeal AO arose in the ancestors of early bony fish, and was pre-dated by behavioral mechanisms for surface (water) breathing. The primitive AO may have been the posterior gill pouches or even the modified gills themselves, served by the sixth branchial artery. Further development of the dorsal part may have led to the respiratory swimbladder, whereas the paired ventral parts evolved into lungs.

Animals↗
PubMed2001

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.

Adult↗
PubMed2001

Comparison of balloon- and mushroom-retained large-bore gastrostomy catheters.

OBJECTIVE: We conducted a retrospective study to evaluate two different types of percutaneous fluoroscopic gastrostomy procedures and catheters. MATERIALS AND METHODS: Between July 8, 1999, and August 4, 2000, 80 percutaneous gastrostomy catheters were placed in 80 patients in 80 attempts. Twenty-five 16-, 18-, or 20-French balloon-retained catheters and 55 20-French mushroom-retained catheters were inserted. Typically, the type of catheters placed was based on operator preference. However, balloon-retained tubes were preferred for use in patients with obstructive head and neck or esophageal malignancies, and mushroom-retained catheters were preferred for use in demented or combative patients. Follow-up was conducted through chart reviews and telephone interviews. The technical success, procedural complications, and catheter complications were recorded. Chi-square statistical analysis was performed. RESULTS: Technical success was 100% (80/80 patients), and no procedural complications occurred. In patients who received balloon-retained catheters, the major complication rate was 0%, the minor complication rate was 8% (2/25 patients), and the tube complication rate was 68% (17/25 patients). The following complications occurred: catheter dislodgment (n = 17), superficial cellulitis (n = 1), and bleeding gastric ulcer (n = 1). In patients who received mushroom-retained catheters, the major complication rate was 0%, the minor complication rate was 3.6% (2/55 patients), and the tube complication rate was 3.6% (2/55 patients). The following complications occurred: superficial cellulitis (n = 2), tube occlusion (n = 1), and peristomal tube leakage (n = 1). No significant differences in major or minor complications were found between the gastrostomy procedures. Balloon-retained catheters had a significantly higher rate of tube complications (p < 0.001). CONCLUSION: Compared with balloon-retained catheters, mushroom-retained gastrostomy catheters are significantly more durable, more secure, and less prone to tube dysfunction. Mushroom-retained catheters should be the preferred type of gastrostomy catheter to place in patients whenever possible.

Catheterization↗
PubMed2001

Superselective microcoil embolization of colonic hemorrhage.

OBJECTIVE: We evaluated therapeutic microcoil embolization in a group of patients with severe colonic hemorrhage. MATERIALS AND METHODS: Twenty-seven patients with severe colonic bleeding due to diverticular disease (n = 19), angiodysplasia (n = 6), cecal ulcer (n = 1), or unknown cause (n = 1) underwent attempted microcoil embolization (n = 25). Microcatheters were used in all procedures, and embolization was performed at the level of the vasa recta or the marginal artery of Drummond. Branches of the superior mesenteric artery were embolized in 12 patients, branches of the inferior mesenteric artery were embolized in 12 patients, and branches of both the superior and inferior mesenteric arteries were embolized in one patient. RESULTS: Technical success was achieved in 93% (25/27) of the procedures. However, immediate hemostasis occurred in 96% (26/27) of patients because in one failed procedure, an occlusive dissection of the inferior mesenteric artery arrested bleeding. Three patients rebled within 24 hr. One patient was treated with endoscopic cauterization, and two patients underwent right hemicolectomy. One patient who underwent right hemicolectomy for rebleeding had ischemic changes found on pathologic analysis of the resected specimen, and a second patient who underwent embolization of branches of the superior and inferior mesenteric arteries developed bowel infarction requiring left hemicolectomy. Prolonged clinical success occurred in 81% (22/27) of patients. CONCLUSION: Therapeutic microcoil embolization for severe colonic hemorrhage is an effective and well-tolerated procedure.

Aged↗
PubMed2001

Oxygen sensitive chemoreceptors in the first gill arch of the tadpole, Rana catesbeiana.

Spike frequency was recorded in the nerve of the isolated superfused first gill arch of the bullfrog larva, Rana catesbeiana and the response to different superfusate PO2 was evaluated. In the metamorphic tadpole, spike frequency increased significantly when the superfusate PO2 was decreased (mean +/- SEM): 8.5 +/- 1.6 Hz at 650 Torr, 11.7 +/- 1.9 Hz at 140 Torr, 13.3 +/- 1.8 Hz at 65 Torr, 14.8 +/- 2.4 Hz at 0 Torr (ANOVA, p = 0.0002). The O2 sensitive chemoreceptor stimulants NaCN and almitrine also increased the spike frequency. This study demonstrates the presence of O2 sensitive chemoreceptors in the first gill arch of the tadpole.

Animals↗