Hyperoxia evokes pericyte-mediated capillary constriction.

Oxygen supplementation is regularly prescribed to patients to treat or prevent hypoxia. However, excess oxygenation can lead to reduced cerebral blood flow (CBF) in healthy subjects and worsen the neurological outcome of critically ill patients. Most studies on the vascular effects of hyperoxia focus on arteries but there is no research on the effects on cerebral capillary pericytes, which are major regulators of CBF. Here, we used bright-field imaging of cerebral capillaries and modeling of CBF to show that hyperoxia (95% superfused O2) led to an increase in intracellular calcium level in pericytes and a significant capillary constriction, sufficient to cause an estimated 25% decrease in CBF. Although hyperoxia is reported to cause vascular smooth muscle cell contraction via generation of reactive oxygen species (ROS), endothelin-1 and 20-HETE, we found that increased cytosolic and mitochondrial ROS levels and endothelin release were not involved in the pericyte-mediated capillary constriction. However, a 20-HETE synthesis blocker greatly reduced the hyperoxia-evoked capillary constriction. Our findings establish pericytes as regulators of CBF in hyperoxia and 20-HETE synthesis as an oxygen sensor in CBF regulation. The results also provide a mechanism by which clinically administered oxygen can lead to a worse neurological outcome.

Side Differences Regarding the Limb Symmetry Index in Healthy Professional Athletes.

Side differences in the limb symmetry index during hop tests have been rarely investigated in uninjured athletes. Unknown differences can result in false interpretation of hop tests and affect return to sport decision. Hypothesis was that un-injured athletes in Judo and Taekwondo have side differences in hop test and that asymmetries can be predicted based on the athletes fighting display. Differences, risk relationships were analyzed using the chi-squared test and the odds ratio. A two-tailed p value of<0.05 was considered statistically significant. 115 athletes from the national teams were included (mean age 18.4 years; range 13-27 years). 93, 97.4 and 98.3% did not have symmetric hop distance for three hop tests. Up to a quarter did not reach a limb symmetry index of>90. Moreover, 57.4% (n=66) reached longer jumping distance with the standing leg. Ignoring such pre-existent side differences in evaluation of hop tests and not knowing which limb was dominant prior the injury, can lead to premature or delayed return to sports in the rehabilitation process. Therefore, it might be helpful to refer to individual jump lengths for each limb in case of injury by using hop tests in pre-season screening in professional athletes in Judo and Taekwondo.