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Biomedical subjects

D N White

Publications and source records attributed to D N White.

At least 55 records · Page 3Linked to original sources
PubMed1979

The limitation of pulsatile flow through the aqueduct of Sylvius as a cause of hydrocephalus.

The concept is advanced that hydrocephalus results from limitation in the pulsatile flow of CSF downwards through the aqueduct of Sylvius during systole which is necessary to accommodate for the pulsatile pressure and volume increase that accompanies the propagation of the arterial pulse through the brain. Evidence is given to show that flow through the fixed human aqueduct is disturbed and not laminar. Further, with the pressures availalbe, the aqueduct is only just large enough to pass the quantity of fluid which must be vented extracranially during systole. Should the capacity of this systolic venting mechanism be exceeded, physical strain will cause cellular damage in the periventricular and periaqueductal regions which, if prolonged, will lead to tissue destruction and hydrocephalus. There appear to be two main causes for hydrocephalus resulting from this mechanism. Firstly, structural lesions, restricting the lumina of the CSF-venting pathways, especially the aqueduct, will reduce the volume of CSF that can flow through these pathways during systole. The hydrocephalic process will then be continuous and only limited when tissue destruction reduces the systolic volume expansion of the brain such that it can be accomodated by the restricted CSF venting pathways. Secondly, conditions which may increase the amount of the systolic volume expansion of the brain beyond the capacity of the CSF venting pathways. Raised mean intracranial pressure is the most important of these conditions. In such cases the hydrocephalus will be limited by the duration of the causal process and possibly also by the enlargement of the venting pathways, as a result of tissue destruction. This hypothesis also accounts for hydrocephalus resulting from obliteration of the cortical subarachnoid space, obstruction to the cranial venous drainage, deformities in the region of the foramen magnum and arterial encroachment upon the ventricular system.

Acidosis↗
PubMed1979

Cerebral surveillance during cardiac surgery.

There is at present no ideal method for determining the adequacy of cerebral blood flow during nonpulsatile cardiopulmonary bypass procedures. Clinical evaluation of cerebral function while the patient is under general anesthesia may be misleading and unsuspected cerebral damage could result if perfusion of the cerebrovascular bed is inadequate. Electroencephalography appears to be the only reliable noninvasive means of cerebral surveillance during the critical periods of nonpulsatile perfusion.

Cardiac Surgical Procedures↗
PubMed1978

Monitoring of electroencephalogram during open-heart surgery. A prospective analysis of 118 cases.

The electroencephalogram (EEG) was prospectively analyzed in 118 consecutive open-heart procedures. In 96 patients (81%) the records were normal whereas in 22 patients (19%) the EEG showed slow wave activity and decreased electrical voltage. In 16 of these patients the EEG abnormality was transient or only of mild degree. In 10 of this group of patients the abnormality occurred with the institution of total cardiopulmonary bypass (CPB) and returned to normal within 2 minutes. In four other patients the abnormalities were mild, persisted to the end of the CPB, and then returned to normal; in two patients the EEG abnormalities developed in the last half of CPB and then returned to normal. In the remaining six patients the EEG was grossly abnormal. In one of these patients the abnormality was secondary to a previous stroke. In five patients, however, the EEG alerted the surgeon to an otherwise unsuspected poor cerebral blood flow. A serious neurologic insult was probably prevented by identifying and correcting the mechanical cause.

Adolescent↗
PubMed1978

Arch versus femoral artery perfusion during cardiopulmonary bypass.

Aortic arch perfusion is favored by most cardiac surgeons. Perfusion via the femoral artery is still used sporadically at reoperations for aneurysms of the ascending aorta, or for the institution of partial pump support in very sick patients prior to opening of the chest. Our over-all experience indicates that surgical complications occurred primarily in the group of patients perfused via the femoral artery. On the other hand, serious disturbance in cerebral perfusion, as determined by electroencephalogram (EEG) monitoring, occurred in 7 percent of the patients perfused via the arch and 3 percent of those perfused via the femoral artery, a difference that was not statistically significant. We continue to advocate aortic arch cannulation and EEG monitoring during cardiopulmonary bypass procedures.

Adolescent↗
PubMed1976

Transient variations in the systolic pulsations in amplitude of intracranial echoes: their artifactual origin.

Variations in the amplitude of intracranial echoes that synchronize with systole are caused by movement of the reflecting interfaces. These movements result from propagation of the arterial pulse through the brain and vary with the arterial pulse pressure and the distance through the vascular tree for which the pulse propagates before being completely attenuated; this distance varies with the degree of arteriolar dilatation. The interpretation of such systolic fluctuations in echo amplitudes is subject to a number of limitations, and their recording is also subject to artifactual variations, usually resulting from the relative motion of the signal with respect to a fixed gate. Transient variation in the systolic fluctuations of echo amplitudes, as a result of various stimuli, can be recorded by a fixed gate but not simultaneously by a tracking gate. They would therefore appear to be artifactual and not indicative of regional changes in cerebral blood flow, which in any case would cause motion and amplitude changes in interfaces that were not confined to the region involved.

Biophysical Phenomena↗