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Biomedical subjects

H Yonas

Publications and source records attributed to H Yonas.

At least 145 records · Page 8Linked to original sources
PubMed1986

Operative exposure and management of the petrous and upper cervical internal carotid artery.

The exposure and operative management of the petrous and upper cervical internal carotid artery (ICA) in 29 patients is detailed. Twenty-seven of these patients had extensive cranial base neoplasms (benign or malignant), 1 had an inflammatory cholesteatoma, and 1 had an aneurysm of the upper cervical ICA immediately proximal to the carotid canal. Preoperative studies useful in the evaluation of these patients included computed tomography, magnetic resonance imaging, cerebral and cervical angiography, and a balloon occlusion test of the ICA with evaluation of neurological status and of cerebral blood flow. The exposure of the upper cervical and petrous ICA was useful to obtain proximal control of the cavernous ICA, aided in the operative approach to extensive petroclival, intracavernous, and parapharyngeal neoplasms, and enabled the total resection of 23 of 27 such tumors. A subtemporal and preauricular infratemporal fossa approach was most commonly used for the exposure of the artery. Intraoperative arterial management consisted of exposure and decompression only, dissection from encasing neoplasm, resection of the invaded arterial segment and vein graft reconstruction, or intentional arterial occlusion. Vascular complications included 1 stroke due to delayed arterial occlusion, 1 stroke and death due to infection spreading from the nasopharynx with bilateral ICA rupture, and 1 pseudoaneurysm formation secondary to wound infection necessitating postoperative balloon occlusion of the ICA. Nonvascular complications included facial nerve paralysis in 10 patients (usually temporary), glossopharyngeal and vagal paralysis in 13 patients requiring Teflon injection of the vocal cord in 9, temporary difficulties with mastication in 9 patients, and wound infection in 3. The surgical exposure and management of the upper cervical and petrous ICA may permit a total operative resection of extensive cranial base neoplasms and is also an alternative for the management of vascular lesions involving these segments of the artery. With malignant neoplasms extending from the nasopharynx, postoperative infection remains a problem and may best be resolved by the use of a vascularized rectus abdominis muscle flap to reconstruct defects of the nasopharynx. Bilateral ICA encasement by neoplasms is also a major problem to be solved. The value of such an aggressive approach to the management of malignant neoplasms remains to be proven.

Carcinoma, Squamous Cell↗
PubMed1986

Xenon/CT cerebral blood flow determination following cranial trauma.

Xenon/CT cerebral blood flow (CBF) analysis has been utilized in the evaluation of 35 patients sustaining severe cranial trauma. The patient population included closed head injury, focal hematoma, and the sequelae of trauma including coma, persistent alteration of consciousness, and brain death. Xe/CT CBF analysis has proven helpful in the determination of appropriate degrees of hyperventilation therapy for the head injured patient. The technique is helpful for determining both local and remote changes of CBF as an aid in deciding upon surgical intervention. Severely decreased flows, compatible with brain death, can be demonstrated. The technique shows promise in the evaluation of physiologic changes accompanying therapy for the injured brain.

Adult↗
PubMed1986

Cerebral blood flow measured by xenon-enhanced computed tomography as a guide to management of patients with cerebrovascular disease.

CT scanning performed before and sequentially during the inhalation of stable xenon (32%), coupled with end-tidal xenon measurements, has made possible the routine construction of regional cerebral blood flow (rCBF) maps with resolution that approximates that of the CT scanner. The capability of obtaining quantitative flow maps with direct anatomic correlation is now available with a commercial package of hardware and software adapted to the General Electric 9800 scanner. The ability to distinguish between normal and reduced rCBF in specific vascular territories has proved useful in the management of cerebrovascular disease. Specific clinical dilemmas that have been addressed with rCBF information from xenon-enhanced CT scanning include the following: In the patient with asymptomatic occlusive disease, is normal rCBF preserved? Is there adequate collateral flow? Are cerebrovascular symptoms a result of emboli or chronic regional low flow? In the patient with complex multivessel occlusive disease, which revascularization procedure is indicated first? Did operation improve rCBF? Should a further procedure be added? May a diffusely diseased but patent artery, which is the source of emboli, be sacrificed safely without compromising rCBF? On the basis of experience with 155 patients, the management and understanding of cerebrovascular disease has been aided substantially by the incorporation of rCBF mapping by xenon-enhanced CT scan in the evaluation of these patients.

Aged↗
PubMed1985

Simultaneous measurements of cerebral blood flow by the xenon/CT method and the microsphere method. A comparison.

Simultaneous measurements of cerebral blood flow have been performed in baboons to assess the correlation between the acute and invasive nondiffusible microsphere technique and the noninvasive xenon-enhanced CT method. Blood flows in small tissue volumes (approximately 1 cm3) were directly compared. The results of these studies demonstrate a statistically significant association between the two methods (P less than .001). Similar correlations were obtained by both the Kendall tau (tau) and the Spearman (r) methods. The problems and limitations of such correlations are discussed.

Animals↗
PubMed1985

Central herniation revealed by focal decrease in blood flow without elevation of intracranial pressure: a case report.

Until recently, in standard hospital settings the tissue blood supply could be inferred only from indirect measures such as assessment of the clinical signs and intracranial pressure (ICP) monitoring. This critical parameter can now be imaged directly with stable xenon-enhanced computed tomographic (CT) imaging. The procedure requires only an additional 10 minutes after a standard head study, yet it provides potentially vital information about tissue perfusion. We describe here a patient in whom a frontal lobe hematoma produced a direct mass effect, causing an element of central herniation with relative sparing of lateral and posterior cortical regions. Although the ICP recordings remained unchanged, symptoms of brain stem compression became apparent. Xenon/CT cerebral blood flow (CBF) mapping demonstrated a flow decrease mainly within the left frontal lobe and throughout central ganglionic structures. After removal of the left frontal hematoma, both clinical status and local and central flow improved. Because the xenon/CT method combines direct anatomical information with blood flow information in one examination, it may be a valuable clinical tool in providing a better understanding of pathophysiology in patients with head injuries and other mass lesions.

Adult↗
PubMed1985

Stable xenon CT blood flow mapping for evaluation of patients with extracranial-intracranial bypass surgery.

Xenon computerized tomography (Xe CT) blood flow studies were conducted in 25 patients referred for a possible extracranial-intracranial bypass procedure for occlusive vascular disease in one or more extra- or intracranial vessels. These studies were helpful in selecting eight candidates for surgery. The Xe CT studies were performed at one or two brain levels using a prototype Xe CT system for measurement of cerebral blood flow which was designed in collaboration with the General Electric Co., and adapted for the GE 9800 scanner. In those patients selected to undergo operation, Xe CT demonstrated compromise of flow reserve regionally, globally, and/or in the watershed area. All eight patients who underwent the procedure showed a favorable clinical response postoperatively, and seven had a dramatic increase in flow. The 17 patients whose baseline CT studies showed no reduction of flow with the Xe CT method were not selected for surgery. All 25 patients have remained neurologically stable to date. Case studies of three of the eight patients undergoing bypass surgery are presented. This limited but consistent experience suggests that Xe CT blood flow mapping makes possible the recognition of brain regions in which flow reserves are compromised. This is due to the relatively high degree of spatial resolution that this technique provides and to the fact that mapping can be correlated directly with the anatomy. Used in combination with a careful clinical examination and an accurate medical history, this study method appears to be a useful guide in the selection of patients who are most at risk from hemodynamic instability and those who are most likely to benefit from flow-augmentation surgery.

Aged↗
PubMed1984

Local cerebral blood flow alterations (Xe-CT method) in an accident victim.

Computed tomography was used before and during inhalation of nonradioactive xenon gas to measure and map local cerebral blood flow noninvasively at two PaCO2 levels in a 19-year-old accident victim. The technique demonstrated normal response to elevated PaCO2 with only a regional loss of autoregulation.

Adult↗
PubMed1984

Xenon/CT blood flow mapping of the kidney and liver.

A noninvasive technique for measuring blood flow by xenon-enhanced X-ray transmission CT has been developed and reported quite extensively in recent years. In this method nonradioactive xenon gas is inhaled, and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential CT. Time-dependent xenon concentration within various tissue segments is used to derive local blood flow maps. The method has been amply discussed in relation to assessment of local cerebral blood flow. Its application to other body organs is explored in this paper, in which results from six preliminary blood flow studies in the liver and kidneys of nonhuman primates are reported. Blood flow in renal cortex ranged from 150 to 280 ml/100 cc/min and hepatic tissue perfusion from 80 to 120 ml/100 cc/min. The advantages and limitations of the method in such applications are discussed.

Animals↗
PubMed1984

Mapping cerebral blood flow by xenon-enhanced computed tomography: clinical experience.

Local cerebral blood flow was measured and mapped using xenon-enhanced x-ray transmission computed tomography. Studies involving 4-6 minutes of xenon-oxygen inhalation can be performed routinely in awake and anesthetized patients with acceptable patient tolerance and compliance. Several case studies of patients with acute and chronic ischemic injuries and other cerebral abnormalities are presented to illustrate characterization of flow pattern in normal and abnormal tissue, as well as the relevance of this flow information to clinical patient management.

Aged↗
PubMed1982

In vivo mapping of local cerebral blood flow by xenon-enhanced computed tomography.

A noninvasive technique has been developed to measure and display local cerebral blood flow (LCBF) in vivo. In this procedure, nonradioactive xenon gas is inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computerized tomography. The time-dependent xenon concentrations in various anatomical units in the brain are used to derive both the local partition coefficient and the LCBF. Functional mapping of blood flow with excellent anatomical specificity has been obtained in the baboon brain. The response of LCBF to stimuli such as changes in carbon dioxide concentrations as well as the variability in LCBF in normal and diseased tissue can be easily demonstrated. This method is applicable to the study of human physiology and pathologic blood flow alterations.

Animals↗
PubMed1982

Errors associated with single-scan determinations of regional cerebral blood flow by xenon enhanced CT.

Possible errors in the determination of xenon concentrations in arterial blood, and uncertainties in CT tissue enhancements during inhalation of xenon-oxygen mixtures, are used to assess errors in the determination of regional cerebral blood flow by the in vivo autoradiographic (single-scan) technique. The results of this study indicate that errors associated with the determination of xenon concentrations in arterial blood decrease rapidly as the time of scanning after the initiation of xenon inhalation is increased. Analysis of errors caused by statistical uncertainties in image enhancement indicate that time of scanning is optimal between 1.5 and 2.5 min for determination of fast flow, while errors in slow-flow determinations gradually decrease as the time of scanning increases.

Autoradiography↗
PubMed1982

Extreme pseudo-occlusion of the internal carotid artery.

Angiographic criteria for the identification of patients with angiographic internal carotid artery occlusion but with anatomical patency are presented. The presence of retained contrast material in a caudal atherosclerotic internal carotid artery stump, especially when accompanied by visualization of the internal carotid artery at the base of the skull, suggests that the internal carotid artery may be patent. Two cases of "extreme" pseudo-occlusion are presented, and the indications for extracranial-intracranial bypass and caudal internal carotid artery stump resection are reviewed.

Aged↗
PubMed1981

The controlled delivery of thiopental and delayed cerebral revascularization.

Sodium thiopental was administered to 10 dogs following embolization of the middle cerebral artery. Its effect on the "grace period" for revascularization was investigated by performing embolectomies 6 hours later. We observed a striking reduction in the size of infarction in the animals treated with thiopental at moderate and prolonged dosage levels. The control animals treated with pentobarbital received less protection against ischemia although blood levels were similar to those of the experimental groups during the period of vascular occlusion.

Animals↗
PubMed1981

Xenon enhanced dynamic computed tomography: multilevel cerebral blood flow studies.

Xenon enhanced computed tomography with a fast scanning mode and interscan table incrementation was used to derive local cerebral blood flow in a nonhuman primate 19 days following infarction. The in vivo autoradiographic methodology was used to derive blood flow in normal and diseased tissue at four different brain levels (slices) during a single inhalation study.

Animals↗