It is widely assumed that fetal ischemic brain injury during labor derives almost exclusively from severe, systemic hypoxemia with marked neonatal depression and acidemia. Severe asphyxia, however, is one of several c...It is widely assumed that fetal ischemic brain injury during labor derives almost exclusively from severe, systemic hypoxemia with marked neonatal depression and acidemia. Severe asphyxia, however, is one of several causes of perinatal neurological injury and may not be the most common;most neonates diagnosed with hypoxic-ischemic encephalopathy do not have evidence of severe asphyxia. Sepsis, direct brain trauma, and drug or toxin exposure account for some cases, while mechanical forces of labor and delivery that increase fetal intracranial pressure sufficiently to impair brain perfusion may also contribute. Because of bony compliance and mobile suture lines, the fetal skull changes shape and redistributes cerebrospinal fluid during labor according to constraints imposed by contractions, and bony and soft tissue elements of the birth canal as the head descends. These accommodations, including the increase in intracranial pressure, are adaptive and necessary for efficient descent of the head while safeguarding cerebral blood flow. Autonomic reflexes mediated through central receptors normally provide ample protection of the brain from the considerable pressure exerted on the skull. On occasion, those forces, which are transmitted intracranially, may overcome the various adaptive anatomical, cardiovascular, metabolic, and neurological mechanisms that maintain cerebral perfusion and oxygen availability, resulting in ischemic brain injury. Accepting the notion of a potentially adverse impact of fetal head compression suggests that avoidance of excessive uterine activity and of relentless pushing without steady progress in descent may offer protection for the fetal brain during parturition. Excessive head compression should be considered in the differential diagnosis of ischemic encephalopathy.展开更多
Background:It is one of the most infamous quotes in the history of biomedicine:“It is time to close the book on infectious diseases,and declare the war against pestilence won.”Long attributed to the United States Su...Background:It is one of the most infamous quotes in the history of biomedicine:“It is time to close the book on infectious diseases,and declare the war against pestilence won.”Long attributed to the United States Surgeon General,Dr.William H.Stewart(1965-1969),the statement is frequently used as a foil by scientific and lay authors to underscore the ever-increasing problems of antibiotic-resistant and emerging infections.However,the primary source for the quote has never been identified.Methods:We undertook a comprehensive search of multiple databases encompassing medical literature,news articles,and congressional records to attempt to identify sources for the quote.Results:No source of the quote was identified.However,a trail of source documents was identified that clearly serves as the basis for subsequent,incorrect attribution of the quote to Dr.Stewart.In multiple source documents,Dr.Stewart made statements to the opposite effect,clearly recognizing that infectious diseases had not been conquered.The urban legend was created by a combination of lack of primary witnesses to the originating speech,misunderstanding of points made by Dr.Stewart in the speech,and increasing societal concern about emerging and re-emerging infectious diseases.Conclusions:Attribution to Dr.Stewart of a belief that it was time to close the book on infectious diseases is an urban legend;he never made any such statement.Numerous other verifiable sources,however,confirm that other people in academia adopted this belief.Dr.Stewart should no longer be cited in this regard,and should be replaced with verifiable sources.展开更多
文摘It is widely assumed that fetal ischemic brain injury during labor derives almost exclusively from severe, systemic hypoxemia with marked neonatal depression and acidemia. Severe asphyxia, however, is one of several causes of perinatal neurological injury and may not be the most common;most neonates diagnosed with hypoxic-ischemic encephalopathy do not have evidence of severe asphyxia. Sepsis, direct brain trauma, and drug or toxin exposure account for some cases, while mechanical forces of labor and delivery that increase fetal intracranial pressure sufficiently to impair brain perfusion may also contribute. Because of bony compliance and mobile suture lines, the fetal skull changes shape and redistributes cerebrospinal fluid during labor according to constraints imposed by contractions, and bony and soft tissue elements of the birth canal as the head descends. These accommodations, including the increase in intracranial pressure, are adaptive and necessary for efficient descent of the head while safeguarding cerebral blood flow. Autonomic reflexes mediated through central receptors normally provide ample protection of the brain from the considerable pressure exerted on the skull. On occasion, those forces, which are transmitted intracranially, may overcome the various adaptive anatomical, cardiovascular, metabolic, and neurological mechanisms that maintain cerebral perfusion and oxygen availability, resulting in ischemic brain injury. Accepting the notion of a potentially adverse impact of fetal head compression suggests that avoidance of excessive uterine activity and of relentless pushing without steady progress in descent may offer protection for the fetal brain during parturition. Excessive head compression should be considered in the differential diagnosis of ischemic encephalopathy.
文摘Background:It is one of the most infamous quotes in the history of biomedicine:“It is time to close the book on infectious diseases,and declare the war against pestilence won.”Long attributed to the United States Surgeon General,Dr.William H.Stewart(1965-1969),the statement is frequently used as a foil by scientific and lay authors to underscore the ever-increasing problems of antibiotic-resistant and emerging infections.However,the primary source for the quote has never been identified.Methods:We undertook a comprehensive search of multiple databases encompassing medical literature,news articles,and congressional records to attempt to identify sources for the quote.Results:No source of the quote was identified.However,a trail of source documents was identified that clearly serves as the basis for subsequent,incorrect attribution of the quote to Dr.Stewart.In multiple source documents,Dr.Stewart made statements to the opposite effect,clearly recognizing that infectious diseases had not been conquered.The urban legend was created by a combination of lack of primary witnesses to the originating speech,misunderstanding of points made by Dr.Stewart in the speech,and increasing societal concern about emerging and re-emerging infectious diseases.Conclusions:Attribution to Dr.Stewart of a belief that it was time to close the book on infectious diseases is an urban legend;he never made any such statement.Numerous other verifiable sources,however,confirm that other people in academia adopted this belief.Dr.Stewart should no longer be cited in this regard,and should be replaced with verifiable sources.
