There has been controversy for some time as to whether a posttraumatic influx of calcium ions occurs in stretch/nondisruptively injured axons within the central nervous system in both human diffuse axonal injury and a variety of models of such injury. We have used the oxalate/pyroantimonate technique to provide cytochemical evidence in support of such an ionic influx after focal axonal injury to normoxic guinea pig optic nerve axons, a model for human diffuse axonal injury. We present evidence for morphological changes within 15 min of injury where aggregates of pyroantimonate precipitate occur in nodal blebs at nodes of Ranvier, in focal swellings within axonal mitochondria, and at localized sites of separation of myelin lamellae. In parallel with these studies, we have used cytochemical techniques for localization of membrane pump Ca(2+)-ATPase and ecto-Ca-ATPase activity. There is loss of labelling for membrane pump Ca(2+)-ATPase activity on the nodal axolemma, together with loss of ecto-Ca-ATPase from the external aspect of the myelin sheath at sites of focal separation of myelin lamellae. Disruption of myelin lamellae and loss of ecto-Ca-ATPase activity becomes widespread between 1 and 4 h after injury. This is correlated with both infolding and retraction of the axolemma from the internal aspect of the myelin sheath to form periaxonal spaces which are characterized by aggregates of pyroantimonate precipitate, and the development of myelin intrusions into invaginations of the axolemma such that the regular profile of the axon is lost. There is novel labelling of membrane pump Ca(2+)-ATPase on the cytoplasmic aspect of the internodal axolemma between 1 and 4 h after injury. There is loss of an organized axonal cytoskeleton in a proportion of nerve fibres by 4-6 h after injury. We suggest that these changes demonstrate a progressive pathology linked to calcium ion influx after stretch (non-disruptive) axonal injury to optic nerve myelinated fibres. We posit that calcium influx, linked to or correlated with changes in Ca(2+)-ATPase activities, results in dissolution of the axonal cytoskeleton and axotomy between 4 and 6 h after the initial insult to axons.

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Recent work in animal models of human diffuse axonal injury has generated the hypothesis that, rather than there being physical disruption of the axolemma at the time of injury, a pertubation of the membrane occurs, which leads, over time, to a dysfunction of the physiology of the axolemmal. This dysfunction is posited to lead to a disruption of ionic homeostasis within the injured axon, leading to secondary axotomy some hours after the initial insult. We decided to test the hypothesis that membrane pump/ion channel activity or function is compromised and this would be reflected in structural changes within the axolemma and myelin sheath. We used freeze fracture and cytochemical techniques to provide evidence for change in membrane structure and the activity of membrane pumps after nondisruptive axonal injury in the adult guinea pig optic nerve. Within 10 min of injury, structural changes occurred in the distribution and number of intramembranous particles (IMPs) in the internodal axolemma. By 4 h, there was novel labeling for Ca-ATPase membrane pump activity at the same site. There was loss of IMPs from the nodal axolemma extending over several hours after injury. There was loss of both membrane pump Ca-ATPase and p-nitro-phenylphosphatase (p-NPPase) activity of the node. There was loss of ecto-Ca-ATPase activity but increased labeling for p-NPPase activity at sites of dissociation of compacted myelin. Quantitative freeze-fracture demonstrated statistically significant changes in membrane structure. We provide support for the hypothesis that structural and functional changes occur in the axolemma and myelin sheath at nondisruptive axonal injury.

Mitral propagation velocity (Vp) is a simple, reproducible measure of diastolic function during coronary artery bypass graft surgery that correlates with standard Doppler echocardiographic techniques to identify dysfunction in the setting of a rapid heart rate or variable preload. Vp <50 cm/s identifies abnormal diastolic function in this patient population.