The effect of breathing an ambient low-density, hyperoxic gas on the perceived effort of breathing and maximal performance of exercise in well-trained athletes

BACKGROUND

The role of the perception of breathing effort in the regulation of performance of maximal exercise remains unclear.

AIMS

To determine whether the perceived effort of ventilation is altered through substituting a less dense gas for normal ambient air and whether this substitution affects performance of maximal incremental exercise in trained athletes.

METHODS

Eight highly trained cyclists (mean SD) maximal oxygen consumption (VO(2)max) = 69.9 (7.9) (mlO(2)/kg/min) performed two randomised maximal tests in a hyperbaric chamber breathing ambient air composed of either 35% O(2)/65% N(2) (nitrox) or 35% O(2)/65% He (heliox). A ramp protocol was used in which power output was incremented at 0.5 W/s. The trials were separated by at least 48 h. The perceived effort of breathing was obtained via Borg Category Ratio Scales at 3-min intervals and at fatigue. Oxygen consumption (VO(2)) and minute ventilation (V(E)) were monitored continuously.

RESULTS

Breathing heliox did not change the sensation of dyspnoea: there were no differences between trials for the Borg scales at any time point. Exercise performance was not different between the nitrox and heliox trials (peak power output = 451 (58) and 453 (56) W), nor was VO(2)max (4.96 (0.61) and 4.88 (0.65) l/min) or maximal V(E) (157 (24) and 163 (22) l/min). Between-trial variability in peak power output was less than either VO(2)max or maximal V(E).

CONCLUSION

Breathing a less dense gas does not improve maximal performance of exercise or reduce the perception of breathing effort in highly trained athletes, although an attenuated submaximal tidal volume and V(E) with a concomitant reduction in VO(2) suggests an improved gas exchange and reduced O(2) cost of ventilation when breathing heliox.

Functional dissociation of saccade and hand reaching control with bilateral lesions of the medial wall of the intraparietal sulcus: Implications for optic ataxia

The posterior parietal cortex (PPC) is essential for the integration of visuomotor information during visually guided reaching. Studies in macaque monkeys have demonstrated a functional specialisation around the intraparietal sulcus (IPS) with a more medial representation of hand movements ("parietal reach region") and a more lateral representation of saccadic eye movements (lateral intraparietal area, LIP). Here we present evidence for the validity of this concept with respect to the human parietal cortex. We recorded isolated and combined goal-directed eye-hand movements in normal control subjects and in a patient with bilateral parieto-occipital lesions and incomplete Balint's syndrome including severe optic ataxia (misreaching to visual targets). Brain lesions in the patient were caused by acute posterior leucoencephalopathy in association with aortic surgery because of Takayasu's arteritis. MRI scans showed bilateral line-shaped hemorrhagic lesions, restricted to the cortex at the medial banks of the intraparietal sulcus, but leaving its lateral banks largely intact. In the patient visually guided reaching was significantly dysmetric, whereas the metrics of visually guided saccades were within normal limits. Dysmetria was more pronounced for the right visual field, with a gross hypermetria. Variability of the movement improved when a delay of 5 or 10 s was introduced between target presentation and movement execution. Lesion data support the concept of a functional specialisation around the human IPS: The cortex medial to the IPS predominantly controls rapid goal-directed reaching movements, comparable to the parietal reach region in monkeys, whereas saccadic eye movements appear to be controlled rather by the cortex lateral to the IPS.

Accumulation of ammonium in Norway spruce (Picea abies) seedlings measured by in vivo 14N-NMR

(14)N-NMR and (31)P-NMR have been used to monitor the in vivo pH in roots, stems, and needles from seedlings of Norway spruce, a typical ammonium-tolerant plant. The vacuolar and cytoplasmic pH measured by (31)P-NMR was found to be c. pH 4.8 and 7.0, respectively, with no significant difference between plants growing with ammonium or nitrate as the N-source. The (1)H-coupled (14) NH 4+ resonance is pH-sensitive: at alkaline pH it is a narrow singlet line and below pH 4 it is an increasing multiplet line with five signals. The pH values in ammonium-containing compartments measured by (14)N-NMR ranged from 3.7 to 3.9, notably lower than the estimated pH values of the P(i) pools. This suggests that, in seedlings of Norway spruce, ammonium is stored in vacuoles with low pH possibly to protect the seedlings against the toxic effects of ammonium ( NH 4+) or ammonia (NH3). It was also found that concentrations of malate were 3-6 times higher in stems than in roots and needles, with nitrate-grown plants containing more malate than plants grown with ammonium.

Analysis of mouse brain using a clinical 1.5 T scanner and a standard small loop surface coil

With increasing numbers of in vivo experiments in the field of neuroscience, the interest in methods for in vivo imaging of animal brains as small as those of mice has increased. Because highly specialized small bore scanners with high field strengths are not commonly available, clinical magnetic resonance imaging (cMRI) scanners have been used in the past to image rat and more recently also mouse brains in combination with specifically developed RF coils. These studies have demonstrated that imaging of small animal brains is feasible, and that tumor volumes measured by cMRI correlate well with histological tumor volume analysis. This protocol describes the cMRI settings at 1.5 T for imaging of mouse brain with resolutions up to 120 x 120 microm using an inexpensive, commercially available small loop surface coil. This allows easy establishment of a small animal MRI facility without the need for cost intensive dedicated small animal scanners or special custom made coils. In this study, we demonstrate high-resolution imaging of intracranial xenografts in a mouse glioma model and monitor the treatment effect of external field irradiation by cMRI.

Ring vortex solitons in nonlocal nonlinear media

We study the formation and propagation of two-dimensional vortex solitons, i.e. solitons with a phase singularity, in optical materials with a nonlocal focusing nonlinearity. We show that nonlocality stabilizes the dynamics of an otherwise unstable vortex beam. This occurs for either single or higher charge fundamental vortices as well as higher order (multiple ring) vortex solitons. Our results pave the way for experimental observation of stable vortex rings in other nonlocal nonlinear systems including Bose-Einstein condensates with pronounced long-range interparticle interaction.

Idiopathic necrotizing dermatitis: current management

OBJECTIVES

To identify and demonstrate necrotizing dermatitis in infancy; an uncommon, puzzling syndrome, in which anecdotal reporting and personal experience indicates that one third of cases may require skin grafting. Much informed discussion about the pathogenesis of this distressing syndrome centres on the role of spider envenomation; and in particular on the speculative role of the Australian White-tailed spider, Lampona cylindrata.

METHODS

We present here six cases of necrotizing dermatitis treated surgically at the Royal Children's Hospital and Mater Children's Hospital in Brisbane over the period from 1991 to 1999. Clinical history, surgical details and pathological investigations were reviewed in each case. Microbiological investigation of necrotic ulcers included standard aerobic and anaerobic culture.

RESULT

Nocardia and Staphylococcus were cultured in two cases, but no positive bites were witnessed and no spiders were identified by either the children or their parents. All cases were treated with silver sulphadiazine creme. Two of the infants required general anaesthesia, excision debridement and split skin grafting. The White-tailed spider, Lampona cylindrata, does not occur in Queensland, but Lampona murina does; neither species has necrotizing components in its venom. Circumstantial evidence is consistent with this syndrome being due to invertebrate envenomation, possibly following arachnid bites.

CONCLUSION

In our experience there is insufficient evidence to impute a specific genus as the cause, at this stage of scientific knowledge. If the offending creature is a spider, we calculate that the syndrome of necrotizing dermatitis occurs in less than 1 in 5000 spider bites.

Forensic pathological aspects of postmortem imaging of gunshot injury to the head: documentation and biometric data

To determine the value of imaging procedures such as computer tomography (CT) and magnetic resonance imaging (MRI) of the head in providing additional information of forensic relevance, we examined 17 cadavers of human victims of gunshot wounds to the head. Three of the victims briefly survived the gunshot wound. The weapons involved were all guns with low muzzle energy (<550 J), i.e., handguns and low-velocity rifles. In the majority of cases ( n=15) a penetrating wound to the head was found, only two cases showed the bullet lodged in the brain. In some cases, imaging of the skull and brain was performed prior to autopsy; in others imaging took place after autopsy on the isolated, formalin-fixed brain. The imaging findings were correlated with the criminological data and the results of macroscopic and microscopic examination of the brain. The findings on the bony structures of the head provided imaging criteria for differentiation between entrance and exit of the gunshot wounds, which corresponded to the forensic pathological findings at autopsy. CT scans and MRI of the cerebral parenchyma revealed lanes of opaque bone and missile fragments along the course of the missile, which allowed recognition of the missile track in 3D reconstruction. Biometric reconstruction allowed easy determination of the angle of the missile track in all three planes. Examination of the parenchymal structures and imaging of the isolated, formalin-fixed brain enabled tracking of the missile path directly along the zone of destruction as well as demonstration of secondary changes such as air bubbles along the bullet course, hemorrhage and edema. The significance of a translucent zone surrounding the missile track in several cases remains unclear; it probably represents tissue destruction secondary to temporary cavitation. The imaging procedures described here allowed excellent documentation of in situ conditions, while the storing of data enabled biometric reconstruction for determination of the angle of trajectory, of entrance and exit wounds, and the extent of tissue damage along the missile track and, possibly, in the zone of temporary cavitation.

Differential cerebellar activation related to perceived pain intensity during noxious thermal stimulation in humans: a functional magnetic resonance imaging study

Little is known about the cerebellar involvement in pain processing in spite of the fact that the cerebellum probably plays a crucial role in pain-related behavior. Using functional magnetic resonance imaging we examined the differential cerebellar activation in 18 healthy subjects in relation to their perceived pain-intensity of noxious and non-noxious thermal stimuli. In contrast to non-noxious (40 degrees C) stimuli, noxious (48.5 degrees C) stimuli revealed activation in the deep cerebellar nuclei, anterior vermis and bilaterally in the cerebellar hemispheric lobule VI. With the same noxious stimulus (48.5 degrees C) there was differential cerebellar activation depending on the perceived pain intensity: high pain intensity ratings were associated with activation in ipsilateral hemispheric lobule III-VI, deep cerebellar nuclei and in the anterior vermis (lobule III). This differential cerebellar activation pattern probably reflects not only somatosensory processing but also perceived pain intensity that may be important for cerebellar modulation of nociceptive circuits.

Disappearance of central thalamic pain syndrome after contralateral parietal lobe lesion: implications for therapeutic brain stimulation

At present there is hardly any appropriate therapy for central pain syndromes available. We report on a unique case of a central thalamic pain syndrome that did not respond to any therapy but disappeared after an additional contralateral parietal lobe lesion. This example indicates that lesions affecting the bilateral balance of thalamo-parietal circuits may lead to pain relief in patients with central pain syndrome, which probably constitutes a bilateral disorder of functional plasticity. This should be taken into account in chronic brain stimulation for persistent pain states.

Psychoneuroendocrine disturbances in a patient with a rare granulomatous disease

Erdheim-Chester disease (ECD) and Langerhans' cell histiocytosis (LCH) are rare granulomatosis-like diseases of unknown etiology which are characterized by lipoidgranulomatous infiltrates in various organs. Contrary to LCH, endocrine and cerebral lesions were infrequently observed in ECD. We report on a patient with the clinical diagnosis of ECD displaying endocrine and cerebral manifestations and skeletal, pulmonary and soft tissue involvement. Disturbance of the endocrine system was revealed by enlargement of the pituitary, partial deficiency of growth hormone (GH), hyperprolactinemia and testosterone deficiency. Cerebral involvement included sinus vein thrombosis, pathologic acoustic evoked potentials, persistence of gadolinium enhancement after magnetic resonance imaging and hypomania. These findings emphasize the importance to assess endocrine and cerebral function in patients with rare granulomatous diseases like ECD and multiorgan involvement.

[Contrast-enhanced intracranial 3 D MR angiography (CE-MRA) in assessing arterial stenoses and aneurysms]

PURPOSE

The aim of this study was to evaluate the diagnostic potential of CE-MR angiography in intracranial arterial stenoses and aneurysms.

MATERIAL AND METHODS

Thirteen patients with intracranial arterial stenoses and ten patients with aneurysms, including 6 cases with GDC coil-occluded aneurysms, were examined by both 3 D TOF-MR angiography and CE-MR angiography. In cases of stenoocclusive diseases colour-coded duplex sonography and in cases of aneurysms arterial digital subtraction angiography served as reference method.

RESULTS

Both TOF-MRA and CE-MRA could well depict filiform stenosis. In contrast to TOF-MRA, CE-MRA did not show any false positive stenosis or occlusion in regions of turbulent or slow blood flow. Stenoses of the medial cerebral artery could not be graded sufficiently by CE-MRA. In aneurysms the parent vessel was better shown by TOF-MRA. CE-MRA, however, more sensitively detected reperfusion in GDC coil-occluded aneurysms.

CONCLUSION

Stenoses of small vessels were graded less exactly by CE-MRA than by TOF-MRA due to lower spatial resolution. CE-MRA, however, seems to be superior in regions of turbulent or slow blood flow. CE-MRA also offers advantages in follow-up examinations of coil-occluded aneurysms.

The acute effect of valproate on cerebral energy metabolism in mice

Sodium valproate (VPA) is used in the acute treatment of status epilepticus and mania. We studied the acute effect of VPA on cerebral energy metabolism in awake mice that received VPA 400 mg kg(-1) and [1-(13)C]glucose or [2-(13)C]acetate. At 25 min, (13)C NMR spectroscopy of brain extracts indicated inhibition of the tricarboxylic acid (TCA) cycle, as could be seen from the accumulation of [4-(13)C]glutamate and reduction in [(13)C]aspartate formation. Concomitantly, the level of ATP was reduced by 40%. To identify the enzymatic step at which the TCA cycle was inhibited [U-(14)C]alpha-ketoglutarate was injected intracerebrally. Inhibition of alpha-ketoglutarate dehydrogenase was evident at 25 min, as shown by accumulation of [(14)C]glutamate. At 45 min the inhibition of alpha-ketoglutarate dehydrogenase was reversed, shown by both (13)C- and (14)C-labeling, and the ATP level was normalized. The study shows for the first time that acute administration of VPA causes inhibition of the TCA cycle activity in vivo. The reduction in brain ATP would be expected to reduce neuronal excitability through modulation of sodium channels which may be clinically advantageous in the initial phase of VPA treatment.