Reduced Cerebrovascular Oxygenation in Individuals with Post-Acute COVID-19 Syndrome (PACS) ("long COVID").

There is evidence that hypoxia occurs in the brain of some individuals who contracted the COVID-19 disease. Furthermore, it has been widely reported that about 13% of individuals who contracted the COVID-19 disease report persistent symptoms after the acute infection stage (>2 months post-acute infection). This is termed post-acute COVID-19 syndrome (PACS) or ("long COVID"). In this study, we aimed to determine if hypoxia measured non-invasively with frequency domain near-infrared spectroscopy (fdNIRS) occurs in asymptomatic and symptomatic individuals with post-acute COVID-19 disease. We show that 26% of our symptomatic group, measured on average 9.6 months post-acute COVID-19 disease, were hypoxic and 12% of the asymptomatic group, measured on average 2.5 months post-acute infection, were hypoxic. Our study indicates that fdNIRS measure of hypoxia in the brain may be a useful tool to identify individuals that are likely to respond to treatments targeted at reducing inflammation and improving oxygenation.

AltitudeOmics: exercise-induced supraspinal fatigue is attenuated in healthy humans after acclimatization to high altitude.

AIMS: We asked whether acclimatization to chronic hypoxia (CH) attenuates the level of supraspinal fatigue that is observed after locomotor exercise in acute hypoxia (AH). METHODS: Seven recreationally active participants performed identical bouts of constant-load cycling (131 ± 39 W, 10.1 ± 1.4 min) on three occasions: (i) in normoxia (N, PI O2 , 147.1 mmHg); (ii) in AH (FI O2 , 0.105; PI O2 , 73.8 mmHg); and (iii) after 14 days in CH (5260 m; PI O2 , 75.7 mmHg). Throughout trials, prefrontal-cortex tissue oxygenation and middle cerebral artery blood velocity (MCAV) were assessed using near-infrared-spectroscopy and transcranial Doppler sonography. Pre- and post-exercise twitch responses to femoral nerve stimulation and transcranial magnetic stimulation were obtained to assess neuromuscular and corticospinal function. RESULTS: In AH, prefrontal oxygenation declined at rest (Δ7 ± 5%) and end-exercise (Δ26 ± 13%) (P < 0.01); the degree of deoxygenation in AH was greater than N and CH (P < 0.05). The cerebral O2 delivery index (MCAV × Ca O2 ) was 19 ± 14% lower during the final minute of exercise in AH compared to N (P = 0.013) and 20 ± 12% lower compared to CH (P = 0.040). Maximum voluntary and potentiated twitch force were decreased below baseline after exercise in AH and CH, but not N. Cortical voluntary activation decreased below baseline after exercise in AH (Δ11%, P = 0.014), but not CH (Δ6%, P = 0.174) or N (Δ4%, P = 0.298). A twofold greater increase in motor-evoked potential amplitude was evident after exercise in CH compared to AH and N. CONCLUSION: These data indicate that exacerbated supraspinal fatigue after exercise in AH is attenuated after 14 days of acclimatization to altitude. The reduced development of supraspinal fatigue in CH may have been attributable to increased corticospinal excitability, consequent to an increased cerebral O2 delivery.

Calcium regulation of flagellation in Naegleria gruberi.

The amoeba-to-flagellate transformation of Naegleria gruberi was studied, exploring the role of calcium in control of this pattern of morphogenesis. A direct and an indirect role for calcium are postulated based on experimental results. Direct inhibition in the presence of calcium is caused by ionophore A23187, substances with ionophore-like activity (amphotericin) and the hormone calcitonin, which facilitate calcium uptake into the cytosol. The indirect role is difficult to assess, but is believed to be related to calcium regulatory protein and its control of cyclic nucleotide levels in the cell, based on inhibition by trifluoperazine. Calcium flux was studied by addition of 45Ca2+ to cell cultures, and tracing its movement during the transformation period. Ultrastructural localization of calcium was attempted in amoeboid and flagellate stages, as well as in reverting flagellates. Deposits that might represent calcium were observed under the plasma membrane and, in calcium-induced reversion, in electron-dense spheres seen in the cytoplasm and at sub-membrane locations, suggesting expulsion of excess calcium.