Autonomic modulation, spontaneous baroreflex sensitivity and fatigue in young men after COVID-19.

Impaired autonomic modulation and baroreflex sensitivity (BRS) have been reported during and after COVID-19. Both impairments are associated with negative cardiovascular outcomes. If these impairments were to exist undetected in young men after COVID-19, they could lead to negative cardiovascular outcomes. Fatigue is associated with autonomic dysfunction during and after COVID-19. It is unclear if fatigue can be used as an indicator of impaired autonomic modulation and BRS after COVID-19. This study aims to compare parasympathetic modulation, sympathetic modulation, and BRS between young men who had COVID-19 versus controls and to determine if fatigue is associated with impaired autonomic modulation and BRS. Parasympathetic modulation as the high-frequency power of R-R intervals (lnHFR-R), sympathetic modulation as the low-frequency power of systolic blood pressure variability (LFSBP), and BRS as the -index were measured by power spectral density analysis. These variables were compared between 20 young men who had COVID-19 and 24 controls. Independent t-tests and Mann-Whitney U tests indicated no significant difference between the COVID-19 and the control group in: lnHFR-R, P=0.20; LFSBP, P=0.11, and -index, P=0.20. Fatigue was not associated with impaired autonomic modulation or BRS. There is no difference in autonomic modulations or BRS between young men who had COVID-19 compared to controls. Fatigue did not seem to be associated with impaired autonomic modulation or impaired BRS in young men after COVID-19. Findings suggest that young men might not be at increased cardiovascular risk from COVID-19-related dysautonomia and impaired BRS.

Noise factor of a polyenergetic x-ray beam in computed tomography.

The attenuation characteristics of a polyenergetic x-ray beam in computed tomography can be completely specified by two parameters: the spectral factor, which in turn provides an equivalent single energy, and the noise factor, which describes the noise characteristics of the polyenergetic beam relative to its single-energy equivalent. Noise factors of typical spectra have been calculated. It is found that only moderate filtration is required to bring the noise factors near unity, indicating that there is little increase in image noise caused by the use of polyenergetic spectra. By using noise factor as an analytic tool, it is possible to optimise the filtration for the desired adjustment between noise, scan time, and dose.

Optimum energies for dual-energy computed tomography.

By performing a dual-energy scan, separate information can be obtained on the Compton and photoelectric components of attenuation for an unknown material. This procedure has been analysed for the optimum energies, and for the optimum dose distribution between the two scans. It is found that an equal dose at both energies is a good compromise, compared with optimising the dose distribution for either the Compton or photoelectric components individually. For monoenergetic beams, it is found that low energy of 40 keV produces minimum noise when using high-energy beams of 80-100 keV. This is true whether one maintains constant integral dose or constant surface dose. A low energy of 50 keV, which is more nearly attainable in practice, produces almost as good a degree of accuracy. The analysis can be extended to polyenergetic beams by the inclusion of a noise factor. The above results are qualitatively unchanged, although the noise is increased by about 20% with integral dose equivalence and 50% with surface dose equivalence. It is very important to make the spectra as narrow as possible, especially at the low energy, in order to minimise the noise.

Multidimensional edge detection by hypersurface fitting.

One way to define operators for detecting edges in digital images is to fit a surface (plane, quadric,...) to a neighborhood of each image point and take the magnitude of the gradient of the surface as an estimate of the rate of change of gray level in the image at that point. This approach is extended to define edge detectors applicable to multidimensional arrays of data-e.g., three-dimensional arrays obtained by reconstruction from projections-by locally fitting hypersurfaces to the data. The resulting operators, for hypersurfaces of degree 1 or 2, are closely analogous to those in the two-dimensional case. Examples comparing some of these three-dimensional operators with their twodimensional counterparts are given.

Computed tomography profiles of periventricular hypodensity in hydrocephalus and leukoencephalopathy.

Profiles of hypodense periventricular white matter, drawn from the interior of the frontal horns through the surrounding white matter to the peripheral gray matter, were analyzed in 65 patients. Abnormal curves were grouped into four patterns: linear, double-slope, plateau, and bimodal. The first two, found primarily in hydrocephalic patients, appear to be due to transependymal passage of cerebrospinal fluid (CSF). The linear pattern was found more frequently in acute cases and indicates breakdown of the ventricular wall as a barrier. The double-slope pattern probably indicates a persistent or restored barrier effect at the wall, with residual CSF infiltration of the parenchyma. Most of the other patients' curves showed either a plateau pattern or (especially in primary leukoencephalopathy) a bimodal ("bumpy") pattern which is believed to correspond to the nonuniform nature of the pathological process.