Search

Abstract The measurement of ventilation distribution is currently performed using inhaled tracer gases for multiple breath inhalation studies or imaging techniques to quantify spatial gas distribution. Most tracer gases used for these studies have properties different from that of air. The effect of gas density on regional ventilation distribution has not been studied. This study aimed to measure the effect of gas density on regional ventilation distribution. Methods Ventilation distribution was measured in seven rats using electrical impedance tomography (EIT) in supine, prone, left and right lateral positions while being mechanically ventilated with either air, heliox (30% oxygen, 70% helium) or sulfur hexafluoride (20% SF6, 20% oxygen, 60% air). The effect of gas density on regional ventilation distribution was assessed. Results Gas density did not impact on regional ventilation distribution. The non-dependent lung was better ventilated in all four body positions. Gas density had no further impact on regional filling characteristics. The filling characteristics followed an anatomical pattern with the anterior and left lung showing a greater impedance change during the initial phase of the inspiration. Conclusion It was shown that gas density did not impact on convection dependent ventilation distribution in rats measured with EIT.

Abstract Background Hyperpolarised helium MRI (He3 MRI) is a new technique that enables imaging of the air distribution within the lungs. This allows accurate determination of the ventilation distribution in vivo. The technique has the disadvantages of requiring an expensive helium isotope, complex apparatus and moving the patient to a compatible MRI scanner. Electrical impedance tomography (EIT) a non-invasive bedside technique that allows constant monitoring of lung impedance, which is dependent on changes in air space capacity in the lung. We have used He3MRI measurements of ventilation distribution as the gold standard for assessment of EIT. Methods Seven rats were ventilated in supine, prone, left and right lateral position with 70% helium/30% oxygen for EIT measurements and pure helium for He3 MRI. The same ventilator and settings were used for both measurements. Image dimensions, geometric centre and global in homogeneity index were calculated. Results EIT images were smaller and of lower resolution and contained less anatomical detail than those from He3 MRI. However, both methods could measure positional induced changes in lung ventilation, as assessed by the geometric centre. The global in homogeneity index were comparable between the techniques. Conclusion EIT is a suitable technique for monitoring ventilation distribution and inhomgeneity as assessed by comparison with He3 MRI.

Multiple sclerosis (MS) is an autoimmune disease involving demyelination and axonal damage in the central nervous system (CNS). In this study, we investigated pathological changes in the lumbar spinal cord of C57BL/6 mice induced with progressive experimental autoimmune encephalomyelitis (EAE) disease using 9.4‐T magnetic resonance imaging (MRI). Multiparametric MRI measurements including MR spectroscopy, diffusion tensor imaging (DTI) and volumetric analyses were applied to detect metabolic changes in the CNS of EAE mice. Compared with healthy mice, EAE mice showed a significant reduction in N‐acetyl aspartate and increases in choline, glycine, taurine and lactate. DTI revealed a significant reduction in fractional anisotropy and axial diffusivity and an increase in radial diffusivity in the lumbar spinal cord white matter (WM), while in the grey matter (GM), fractional anisotropy increased. High‐resolution structural imaging also revealed lumbar spinal cord WM hypertrophy and GM atrophy. Importantly, these MRI changes were strongly correlated with EAE disease scoring and pathological changes in the lumbar (L2–L6), particularly WM demyelination lesions and aggregation of immune cells (microglia/macrophages and astrocytes) in this region. This study identified changes in MRI biomarker signatures that can be useful for evaluating the efficacy of novel drugs using EAE models in vivo. [ABSTRACT FROM AUTHOR]

Cowin, Gary J., Stuart Crozier, Zoltan H. Endre, I. Anne Leditschke, and Ian M. Brereton. Cortical and medullary betaine-GPC modulated by osmolality independently of oxygen in the intact kidney. Am. J. Physiol. 277 (Renal Physiol. 46): F338-F346, 1999.--Renal osmolyte concentrations are reduced during reflow following ischemia. Osmolyte decreases may follow oxygen depletion or loss of extracellular osmolality in the medulla. Image-guided volume-localized magnetic resonance (MR) microspectroscopy was used to monitor regional osmolytes during hyposmotic shock and hypoxia in the intact rat kidney. Alternate spectra were acquired from 24-[micro]l voxels in cortex and medulla of the isolated perfused kidney. There was a progressive decrease in the combined betaine-glycerophosphorylcholine (GPC) peak intensity of 21% in cortex and 35% in medulla of normoxic kidneys between 60 and 160 min after commencing perfusion. Hypoxia had no significant effect on the betaine-GPC peak intensity in cortex or medulla, despite a dramatic reduction in tubular sodium, potassium, and water reabsorption. The results suggest that cortical and medullary intracellular osmolyte concentrations depend on osmotically regulated channels that are insensitive to oxygen and dissociated from the oxygen-dependent parameters of renal function, the fractional excretion of sodium, the fractional excretion of potassium, and urine-to-plasma inulin concentration ratio. renal osmolytes; volume-localized magnetic resonance spectroscopy; isolated perfused rat kidney; hyposmotic shock

The main aim of this study was to employ high-resolution MRI to investigate the spatiotemporal development of pathological features associated with contusive spinal cord injury (SCI) in mice. Experimental mice were subjected to either sham surgery or moderate contusive SCI. A 16.4-T small-animal MR system was employed for nondestructive imaging of post-mortem, fixed spinal cord specimens at the subacute (7 days) and more chronic (28-35 days) stages post-injury. Routine histological techniques were used for subsequent investigation of the observed neuropathology at the microscopic level. The central core of the lesion appeared as a dark hypo-intense area on MR images at all time points investigated. Small focal hypo-intense spots were also observed spreading through the dorsal funiculi proximal and distal to the site of impact, an area that is known to undergo gliosis and Wallerian degeneration in response to injury. Histological examination revealed these hypo-intense spots to be high in iron content as determined by Prussian blue staining. Quantitative image analysis confirmed the increased presence of iron deposits at all post-injury time points investigated ( p < 0.05). Distant iron deposits were also detectable through live imaging without the use of contrast-enhancing agents, enabling the longitudinal investigation of this pathology in individual animals. Further immunohistochemical evaluation showed that intracellular iron deposits localised to macrophages/microglia, astrocytes and oligodendrocytes in the subacute phase of SCI, but predominantly to glial fibrillary acidic protein-positive, CC-1-positive astrocytes at later stages of recovery. Progressive, widespread intracellular iron accumulation is thus a normal feature of SCI in mice, and high-resolution MRI can be effectively used to detect and monitor these neuropathological changes with time. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Determining the information content of vocal signals and understanding morphological modifications of vocal anatomy are key steps towards revealing the selection pressures acting on a given species' vocal communication system. Here, we used a combination of acoustic and anatomical data to investigate whether male koala bellows provide reliable information on the caller's body size, and to confirm whether male koalas have a permanently descended larynx. Our results indicate that the spectral prominences of male koala bellows are formants (vocal tract resonances), and show that larger males have lower formant spacing. In contrast, no relationship between body size and the fundamental frequency was found. Anatomical investigations revealed that male koalas have a permanently descended larynx: the first example of this in a marsupial. Furthermore, we found a deeply anchored sternothyroid muscle that could allow male koalas to retract their larynx into the thorax. While this would explain the low formant spacing of the exhalation and initial inhalation phases of male bellows, further research will be required to reveal the anatomical basis for the formant spacing of the later inhalation phases, which is predictive of vocal tract lengths of around 50 cm (nearly the length of an adult koala's body). Taken together, these findings show that the formant spacing of male koala bellows has the potential to provide receivers with reliable information on the caller's body size, and reveal that vocal adaptations allowing callers to exaggerate (or maximise) the acoustic impression of their size have evolved independently in marsupials and placental mammals. [ABSTRACT FROM AUTHOR]