Historically, determination of the critical cerebral perfusion pressure (CPP) was done in animals by a progressive lowering of arterial pressure yielding a nominal critical CPP of 60 mmHg. Subsequently, it was shown that if the CPP was decreased by increasing intracranial pressure (ICP), critical CPP fell to 30 mmHg. This discrepancy was unexplained. We recently provided evidence that the decrease in critical CPP was due to microvascular shunting resulting in maintained cerebral blood flow (CBF) at a lower CPP. We demonstrated by a progressive increase in ICP in rats using two-photon laser scanning microscopy (2PLSM) that the transition from capillary to microvascular shunt flow is a pathological process. We surmise that the loss of CBF autoregulation revealed by decreasing arterial pressure occurs by dilation of normal cerebral blood vessels whereas that which occurs by increasing ICP is due to microvascular shunting. Our observations indicate that the loss of CBF autoregulation we observed in brain injured patients that changes on an hourly or daily basis reflects an important pathophysiological process impacting on outcome that remains to be determined.
Introduction: We describe the case of a 10-year-old girl with an unusually severe and complicated episode of acute septic arthritis due to Streptococcus dysgalactiae, and systematically review the literature describing osteoarticular infections with this organism. Case Presentation: A 10-year-old girl with hereditary sensory and autonomic neuropathy type 5 and chronic (Charcot) arthropathy of the right knee presented with severe swelling and warmth of the right knee associated with 2 days of fever. She was ultimately diagnosed with septic arthritis of the right knee due to S. dysgalactiae. Her subsequent clinical course was abnormally prolonged and complicated, requiring an 8-week hospitalization, 7 arthrotomies and 8 months of total antimicrobial therapy. Conclusions: Group G Streptococci, including S. dysgalactiae, are unusual causes of septic arthritis. Our patients' clinical course was more severe than typically seen with more common osteoarticular pathogens. We conducted a systematic review of the literature on this condition, which demonstrated 7 previously reported cases of septic arthritis due to this pathogen in children, and also review the most current nomenclature and classification scheme for the organism.
Normal blood flow in the brain as a response to pressure fluctuations is commonly referred to as cerebral autoregulation. Linear, nonparametric models of cerebral autoregulation were estimated for 77 human subjects afflicted with brain injury, with mean arterial pressure used as input, and invasively measured regional cerebral blood flow used as output. The data were continuously monitored from the beginning of subject hospital stay. Mean transfer function gain as a function of frequency was calculated for each subject over a limited time window spanning 48 h, starting postsurgery. The mean transfer function gain of the cerebral autoregulation model provided a highly accurate, statistically significant, assessment of patient outcome. Subjects were accurately grouped by outcome, with a high significance ( ) across the entire measurement spectrum (0.005-0.25 Hz). In addition, the frequency band from 0.1 to 0.25 Hz contains particularly low variance in transfer function gain. This spectral region provides a highly statistically significant ( ) assessment of brain injury patient health that is useful for outcome prediction.
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