Reduced haemodynamic response in the ageing visual cortex measured by absolute fNIRS

The effect of healthy ageing on visual cortical activation is still to be fully explored. This study aimed to elucidate whether the haemodynamic response (HDR) of the visual cortex altered as a result of ageing. Visually normal (healthy) participants were presented with a simple visual stimulus (reversing checkerboard). Full optometric screening was implemented to identify two age groups: younger adults (n = 12, mean age 21) and older adults (n = 13, mean age 71). Frequency-domain Multi-distance (FD-MD) functional Near-Infrared Spectroscopy (fNIRS) was used to measure absolute changes in oxygenated [HbO] and deoxygenated [HbR] haemoglobin concentrations in the occipital cortices. Utilising a slow event-related design, subjects viewed a full field reversing checkerboard with contrast and check size manipulations (15 and 30 minutes of arc, 50% and 100% contrast). Both groups showed the characteristic response of increased [HbO] and decreased [HbR] during stimulus presentation. However, older adults produced a more varied HDR and often had comparable levels of [HbO] and [HbR] during both stimulus presentation and baseline resting state. Younger adults had significantly greater concentrations of both [HbO] and [HbR] in every investigation regardless of the type of stimulus displayed (p<0.05). The average variance associated with this age-related effect for [HbO] was 88% and [HbR] 91%. Passive viewing of a visual stimulus, without any cognitive input, showed a marked age-related decline in the cortical HDR. Moreover, regardless of stimulus parameters such as check size, the HDR was characterised by age. In concurrence with present neuroimaging literature, we conclude that the visual HDR decreases as healthy ageing proceeds

Changes in oxygen partial pressure of brain tissue in an animal model of obstructive apnea

Background: Cognitive impairment is one of the main consequences of obstructive sleep apnea (OSA) and is usually attributed in part to the oxidative stress caused by intermittent hypoxia in cerebral tissues. The presence of oxygen-reactive species in the brain tissue should be produced by the deoxygenation-reoxygenation cycles which occur at tissue level during recurrent apneic events. However, how changes in arterial blood oxygen saturation (SpO2) during repetitive apneas translate into oxygen partial pressure (PtO2) in brain tissue has not been studied. The objective of this study was to assess whether brain tissue is partially protected from intermittently occurring interruption of O2 supply during recurrent swings in arterial SpO2 in an animal model of OSA. Methods: Twenty-four male Sprague-Dawley rats (300-350 g) were used. Sixteen rats were anesthetized and noninvasively subjected to recurrent obstructive apneas: 60 apneas/h, 15 s each, for 1 h. A control group of 8 rats was instrumented but not subjected to obstructive apneas. PtO2 in the cerebral cortex was measured using a fastresponse oxygen microelectrode. SpO2 was measured by pulse oximetry. The time dependence of arterial SpO2 and brain tissue PtO2 was carried out by Friedman repeated measures ANOVA. Results: Arterial SpO2 showed a stable periodic pattern (no significant changes in maximum [95.5 ± 0.5%; m ± SE] and minimum values [83.9 ± 1.3%]). By contrast, brain tissue PtO2 exhibited a different pattern from that of arterial SpO2. The minimum cerebral cortex PtO2 computed during the first apnea (29.6 ± 2.4 mmHg) was significantly lower than baseline PtO2 (39.7 ± 2.9 mmHg; p = 0.011). In contrast to SpO2, the minimum and maximum values of PtO2 gradually increased (p < 0.001) over the course of the 60 min studied. After 60 min, the maximum (51.9 ± 3.9 mmHg) and minimum (43.7 ± 3.8 mmHg) values of PtO2 were significantly greater relative to baseline and the first apnea dip, respectively. Conclusions: These data suggest that the cerebral cortex is partially protected from intermittently occurring interruption of O2 supply induced by obstructive apneas mimicking OSA

Overview of the DESI Legacy Imaging Surveys

The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing–Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image ≈14,000 deg2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorer satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project

Diminished cerebral circulatory autoregulation in obstructive sleep apnea investigated by near-infrared spectroscopy

We applied near-infrared spectroscopy (NIRS) to assess cerebral tissue oxygenation and hemodynamics in obstructive sleep apnea (OSA) sufferers and control volunteers. We designed NIRS sensors and applied measurement schemes that included certain polysomnography parameters, such as arterial hemoglobin oxygen saturation (SaO2), heart rate (HR), and respiratory signal (RS), together with NIRS parameters, such as oxy- ([O2Hb]), deoxy- ([HHb]), total hemoglobin ([tHb]) concentrations, and tissue hemoglobin oxygen saturation (SO2). Twenty-one volunteers (8 females, 13 males, age 22-74 years) participated in the study. Eight were OSA sufferers, while 13 constituted the control group. Measurements were conducted during breath holding exercises and 30-45 minute daytime naps. In comparing OSA subjects with controls during breath holding, a smaller increase or even a decrease in SO2, [O2Hb], and [tHb] and a simultaneous larger increase in [HHb], confirmed insufficiency of the circulatory compensatory mechanism that prevents brain tissue hypoxia. Changes in cerebral oxygenation and hemodynamics due to hypoxia during breath holding showed statistically significant differences (p&lt;0.05) between control and OSA subjects and between non-snorers and OSA subjects (p&lt;0.03 for Δ[O2Hb], Δ[HHb], Δ[tHb], and ΔSO2). NIRS provides the clinician with important, direct insight on the cerebral tissue oxygenation and hemodynamics related to the chronic intermittent hypoxia in OSA for potential identification of individuals at risk for cerebrovascular morbidity. © 2003 WebSciences

Diminished cerebral circulatory autoregulation in obstructive sleep apnea investigated by near-infrared spectroscopy

We applied near-infrared spectroscopy (NIRS) to assess cerebral tissue oxygenation and hemodynamics in obstructive sleep apnea (OSA) sufferers and control volunteers. We designed NIRS sensors and applied measurement schemes that included certain polysomnography parameters, such as arterial hemoglobin oxygen saturation (SaO2), heart rate (HR), and respiratory signal (RS), together with NIRS parameters, such as oxy- ([O2Hb]), deoxy- ([HHb]), total hemoglobin ([tHb]) concentrations, and tissue hemoglobin oxygen saturation (SO2). Twenty-one volunteers (8 females, 13 males, age 22-74 years) participated in the study. Eight were OSA sufferers, while 13 constituted the control group. Measurements were conducted during breath holding exercises and 30-45 minute daytime naps. In comparing OSA subjects with controls during breath holding, a smaller increase or even a decrease in SO2, [O2Hb], and [tHb] and a simultaneous larger increase in [HHb], confirmed insufficiency of the circulatory compensatory mechanism that prevents brain tissue hypoxia. Changes in cerebral oxygenation and hemodynamics due to hypoxia during breath holding showed statistically significant differences (p&lt;0.05) between control and OSA subjects and between non-snorers and OSA subjects (p&lt;0.03 for Δ[O2Hb], Δ[HHb], Δ[tHb], and ΔSO2). NIRS provides the clinician with important, direct insight on the cerebral tissue oxygenation and hemodynamics related to the chronic intermittent hypoxia in OSA for potential identification of individuals at risk for cerebrovascular morbidity. © 2003 WebSciences