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Biomedical subjects

C M Loftus

Publications and source records attributed to C M Loftus.

At least 55 records · Page 3Linked to original sources
PubMed1990

Studies of collateral perfusion to canine middle cerebral artery territory.

Previous studies of intracranial collateral circulation have not distinguished between true "collateral" blood flow (flow to a region that occurs only when a primary artery is occluded) and "overlap" flow (flow to a region that is present under both normal and demand conditions). These experiments had three purposes: 1) to identify tissues that were truly collateral dependent, 2) to determine potential for true collateral flow in the absence of overlap flow, and 3) to determine whether an anatomical basis for overlap flow could be demonstrated. Branches (700-900 microns) of the dog middle cerebral artery (MCA) were perfused with autologous blood. The perfused region, which was the area at risk, was identified by intravenous injection of neutral red dye. Microspheres were used to measure regional cerebral blood flow (rCBF). Overlap flow was determined by perfusion of the artery with microsphere-free blood. True collateral flow (total rCBF minus overlap flow) was determined by analysis of rCBF to the risk area after cessation of vessel perfusion. Most of the risk area had substantial levels of overlap flow (about one-third of base line). In the center of the area at risk, the true collateral-dependent area was identified [mean overlap flow 4 +/- 1 (mean +/- SE) ml.min-1.100 g-1], which had high levels of perfusion from collateral vessels (102 +/- 14) within 30 s of vascular occlusion. Microfil injection into two adjacent MCA branches showed discrete borders between vascular territories, with no overlapping vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Management of cervical spine injuries in patients with ankylosing spondylitis.

Eleven patients with ankylosing spondylitis and traumatic fracture/dislocation of the spine were identified in a retrospective review of all cases of cervical spine injury treated on the neurosurgical service over a 10-year period. Injury was most often secondary to minor trauma or a motor-vehicle accident, and the level of vertebral involvement was most frequently between C-5 and T-1. Neurological symptoms at presentation ranged from neck pain alone to complete loss of function distal to the level of injury. Initial routine treatment consisted of axial traction for realignment with the minimal weight needed to accomplish this, taking into account the flexion deformity. All patients underwent pluridirectional tomography and/or computerized tomography to delineate the exact sites of injury. Three patients died shortly after admission due to pulmonary complications. The remaining eight patients underwent early posterior stabilization and mobilization in a halo or cervicothoracic brace to achieve fusion. Neurological improvement was achieved in six of these eight cases. The experience described here supports the initiation of axial traction as initial therapy for cervical injuries followed by early surgical stabilization in patients with ankylosing spondylitis. The difficulty of maintaining spinal alignment and the devastating pulmonary problems attendant on conservative management may be obviated by early fusion.

Adult↗
PubMed1989

Cerebral autoregulation following prophylactic and delayed experimental STA-MCA bypass.

Cerebral autoregulation is impaired in ischaemic regions. We hypothesized that pre-existing STA-MCA bypass would be superior to delayed revascularization in maintaining ipsilateral rCBF and preserving cerebral autoregulation following experimental stroke. Two series of dogs were tested to evaluate this hypothesis, but which was disproved for the chosen experimental conditions. In the first, eight dogs underwent craniotomy, STA-MCA bypass, and radiolabeled microsphere rCBF determinations. Blood pressure was manipulated with intravenous adenosine and levarterenol. Ischaemic zone rCBF was measured at MAP 60 mm Hg (97.2 ml.min-1.100 g-1) and MAP 140 mm Hg (113.6) (p = NS), in the intact arterial system with the patent bypass in place. An hemispheric ipsilateral ischaemic lesion was then created, and three further microsphere rCBF determinations were made at MAP 60 mm Hg (41.7 ml.min-1.100 g-1), MAP 100 mm Hg (52.6) and MAP 140 mm Hg (58.3). There were no significant differences between these measurements (ANOVA p = NS). In a second series of five animals the bypass was placed and the stroke lesion created first. Ischaemic zone rCBF was then measured at MAP 60 mm Hg (35 ml.min-1 . 100 g-1) and MAP 140 mm Hg (44 ml.min-1 . 100g-1) (p = NS), with the patent bypass in place. The bypass was then clamped for 15 minutes and profound ischaemia confirmed (5 ml.min-1 . 100 g-1, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effects of hypercapnia on cerebral blood flow following prophylactic and delayed experimental superficial temporal artery-middle cerebral artery bypass.

Cerebral blood flow was studied in dogs to ascertain whether preexisting superficial temporal artery-middle cerebral artery bypass could preserve hypercapnic reactivity following acute ischemia and whether postischemic-delayed revascularization would restore hypercapnic reactivity. In six dogs flow was preserved and some degree of hypercapnic response remained following proximal occlusion with a patent bypass. During complete ischemia (bypass occluded) there was no hypercapnic reactivity in the ischemic zone. Significant flow was restored to the ischemic area following bypass reopening, but a cerebral blood flow decrease was seen with subsequent hypercapnia. In the opposite (control) hemisphere hypercapnia always produced significant cerebral blood flow increases. These data support the superiority of prophylactic over delayed superficial temporal artery-middle cerebral artery bypass in appropriate clinical situations.

Animals↗
PubMed1989

EEG changes during carotid occlusion and hypotension in the rat: the effects of nitrous oxide.

It has been suggested that N2O may alter the sensitivity of the brain to ischemia. To test this hypothesis. we examined the effects of N2O on the development of left-right hemispheric asymmetry in the electroencephalogram (EEG) during hemorrhagic hypotension in rats subjected to unilateral carotid occlusion. Rats were anesthetized with halothane/O2/air, and ventilated to normocarbia (PaCO2 approximately 40 mm Hg). Catheters were placed in the femoral artery and vein, and both common carotid arteries (CCA) were exposed. Bilateral fronto-occipital screws were then placed to record left and right hemispheric EEGs, which were processed by computer and stored on disc. Animals were then randomly assigned to one of three treatment groups (n = 8 each): group 1, 0.5 MAC (0.5%) halothane + 0.5 MAC (70%) N2O; group 2, 1 MAC (1.0%) halothane + 70% nitrogen; and group 3, 1 MAC halothane + 70% N2O. After stabilization, the left CCA were occluded. Animals with EEG changes at this point were discarded. Beginning 5 min later, venous blood withdrawal was started at a rate of 0.25 ml/min, while mean arterial blood pressure (MAP) and EEG were continuously recorded. After exsanguination was complete, EEG data (raw and processed) were re-examined by an individual who was unaware of the anesthetics administered to determine the MAP at which any evidence of EEG asymmetry appeared. There were no intergroup differences in weight, PaO2, PaCO2, pHa, blood glucose. hematocrit, or starting (prebleed) MAP. The earliest change in the EEG was typically a decrease in total amplitude over the hemisphere ipsilateral to the carotid occlusion. Adding 70% N2O to a 1 MAC halothane background (group 2 vs. group 3) had no effect on the MAP at which this EEG asymmetry appeared (54 +/- 13 vs. 53 +/- 10 mm Hg). However, this MAP was significantly higher in animals breathing 0.5 MAC halothane + 0.5 MAC N2O (group 1, 78 +/- 17 mm Hg, p = 0.0019 by ANOVA). We conclude that 70% N2O had no direct effects on the MAP at which EEG abnormalities appear (group 2 vs. 3), and that the observed differences are more closely related to the concentration of volatile agent. Whether these differences are related to anesthetic-induced differences in the brain's tolerance to reduced CBF or whether there are differences in cerebral blood flow (CBF) autoregulation are unknown.

Journal Article↗
PubMed1989

A randomized trial of aspirin or heparin in hospitalized patients with recent transient ischemic attacks. A pilot study.

In a randomized pilot study we compared the efficacy of temporary anticoagulation with intravenous heparin sodium to the efficacy of aspirin in preventing cerebral infarction in hospitalized patients with recent (less than 7 days) transient ischemic attacks (TIAs). Fifty-five patients (33 men, 22 women) aged 36-81 (mean 62.7) years met entry criteria and agreed to participate. Symptoms prompting hospitalization were referable to the carotid distribution in 43 patients (34 hemispheric, nine retinal); 12 patients had vertebrobasilar distribution TIAs. Twenty-seven patients received heparin and 28 received aspirin. Patients were treated until surgery or until long-term medical therapy was instituted, 3-9 (mean 5.5) days in the heparin group and 3-15 (mean 5.8) days in the aspirin group. Recurrent TIAs occurred in eight patients given heparin and in seven treated with aspirin. Infarction occurred in one patient in the heparin group and in four patients in the aspirin group (three brain, one retinal infarction). Initial symptoms in these five patients were referable to the carotid distribution in two and to the vertebrobasilar distribution in three. All patients but the one with a retinal infarction had recurrent TIAs prior to stroke. Our pilot study suggests that hospitalized patients with recent TIAs are at high risk for recurrent TIAs (15 of 55, 27%) and brain infarction (five of 55, 9%) and that patients with recent vertebrobasilar distribution TIAs have a marginally significantly higher risk (odds ratio 6.83, 95% confidence interval 0.65-88.66) of infarction than patients with recent carotid distribution TIAs.

Adolescent↗
PubMed1989

Correlation of experimental rCBF determinations in goats with flow measurements from a Doppler-modified carotid artery shunt.

A carotid artery shunt system has been developed that continuously monitors blood flow rates by embedding a Doppler crystal in the shunt wall. The crystal ranges through a "liquid lens" that enables it to be placed without violation of the shunt lumen. Because the crystal is at a fixed angle (45 degrees) to the axis of blood flow and the diameter of the lumen remains constant, a linear relationship exists between flow rates and the Doppler velocity signal. This shunt system was previously tested in vitro using a pulsatile pump and was found to be accurate to within 4.7% of the actual flow rate. In the present study, animal (goat) experiments were performed consisting of simultaneous carotid shunt flow and bilateral rCBF measurements by the radiolabeled microsphere technique to determine in vivo the accuracy of this Doppler modified shunt and to ascertain the ability of shunt flow to increase in the face of acute contralateral carotid occlusion. Data from five animals show that in vivo shunt flow can be recorded to within 13% of control rCBF and that shunt flow increases nearly 50% under conditions of distal demand (contralateral carotid occlusion). This device may prove useful in laboratory studies of carotid shunt dynamics and in clinical practice to quickly detect correctable shunt flow abnormalities.

Animals↗
PubMed1988

Sequential measurement of somatosensory evoked potentials in a canine model of hemispheric ischaemia.

We have previously shown that occlusion of 6 canine intracranial vessels produces profound hemispheric ischaemia and abolishes the ipsilateral SSEP. In the present study, this work was extended to ascertain the differential contributions of 6 intracranial vessels to SSEP function. Five dogs underwent craniotomy, brain retractions, and ipsilateral arterial microdissection, and were prepared for SSEP recordings. Stimulation-recording sequences were performed firstly prior to craniotomy, secondly following craniotomy and microdissection and thirdly following sequential occlusion of each of 6 vessels: (a) anterior cerebral (A2), (b) ethmoidal, (c) ophthalmic, (d) middle cerebral (MCA), (e) posterior communicating (PCoA), and (f) posterior cerebral artery. Individual SSEP amplitudes and latencies were measured and averaged and values for each wave were compared statistically to baseline values and to the immediately preceding value. Two thalamocortical potential components were identified: an early wave (6-10 ms) and a late wave (10-15 ms). No significant amplitude declines between waves occurred with A2, ethmoidal, and ophthalmic occlusions. Following MCA occlusion, amplitude decreased to 49.1% and 34.5% of baseline in the early and late waves respectively; a significant decrease (p less than 0.05) both from baseline and from post-ophthalmic occlusion. Further occlusions (PCoA and posterior cerebral) produced progressive declines in amplitude to a nadir of 12.5% (early) and 2.1% (late) of baseline. Although latency did increase slightly from baseline with each occlusion (5-7% total), no consistent and significant latency changes were identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Combination of aminocaproic acid and nicardipine in treatment of aneurysmal subarachnoid hemorrhage.

Antifibrinolytic drugs reduce the risk of rebleeding during the first 2 weeks after aneurysmal subarachnoid hemorrhage. However, they do not lower overall mortality, largely because of an increased incidence of cerebral ischemia. The usefulness of antifibrinolytic drugs might be increased if a method to prevent or control vasospasm in patients were to be developed. We recently completed late Phase I and Phase II studies of the calcium ion blocking drug nicardipine in 67 patients treated within 1 week of subarachnoid hemorrhage. Of these 67 patients, 42 had delayed operations and were treated concomitantly with the antifibrinolytic drug aminocaproic acid (1.5 g/hr) for an average of 6 days before surgery. The outcome of these 42 patients is the subject of this report. Fifteen of 42 patients were treated with the lower dosage levels of nicardipine (0.4-4.5 mg/m2/hr), and 27 patients were treated at the highest dosage level (6.0 mg/m2/hr). Using the World Federation of Neurological Surgeons scale for subarachnoid hemorrhage, at admission 18 patients were Grade I, 15 were Grade II, 6 were Grade III, and 3 were Grade IV. Five patients (12%) developed clinical signs of deterioration suggestive of cerebral ischemia with concomitant evidence of vasospasm on arteriography. These patients were all treated with hypervolemic hypertensive therapy. Only one patient (2%) developed an infarction from vasospasm. Two patients developed symptomatic hydrocephalus requiring ventriculoperitoneal shunting, and a third patient required a temporary ventriculostomy. The 3-month postoperative outcomes were excellent. Three patients (7%) rebled. Three patients died, two from rebleeding of the aneurysm and one who never regained consciousness from the initial hemorrhage.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Technical note: in vitro evaluation of an in-line Doppler flow-metering system for carotid artery shunts.

Carotid artery shunts are used extensively during carotid artery surgery to maintain cerebral perfusion. Blood flow through such shunts may be compromised by thrombosis, incorrect placement, or inadvertent clamping of the shunt. Currently, however, no direct method exists to detect poor shunt flow that might precipitate cerebral ischemia. A carotid artery shunt system that continuously monitors blood flow rates has been developed. This system utilizes a Doppler crystal embedded in the wall of a silicone elastomer shunt. The crystal ranges through a "liquid lens" that enables it to be placed without violation of the shunt lumen. Because the crystal is at a fixed angle (45 degrees) to the axis of blood flow and the diameter of the lumen remains constant, a linear relationship should exist between flow rates and the Doppler velocity signal. This hypothesis was tested in vitro using a pulsatile pump and both a starch-water solution and whole blood. Doppler velocity meter readings were compared to timed volume collections over a wide range of flow rates. A direct linear relationship between the Doppler flowmeter and timed volume collections existed, and the system was accurate to within 4.7%. This device may be useful in laboratory studies of carotid shunt dynamics and in clinical practice for early detection of correctable shunt flow abnormalities that could lead to cerebral injury.

Carotid Arteries↗
PubMed1988

Carotid endarterectomy in symptomatic elderly patients.

Fifty-three of 203 consecutive carotid endarterectomies (26%) performed on the Neurosurgical Service at the University of Iowa were in patients over 70 years of age (mean age, 73.4). This series included 38 men and 15 women. Thirty-three patients (62%) presented with transient ischemic attacks, and the remaining 38% were functional stroke patients. Medical risk factors in this group included hypertension in 70%, previous myocardial infarction in 26%, angina in 17%, peripheral vascular disease in 23%, and diabetes in 13%. Sixty-four per cent of the patients had been previously treated with antihypertensive drugs, 43% with antiplatelet agents, and 4% with anticoagulants. Noninvasive vascular evaluation was performed in 25 of 53 (47%) patients, and all underwent angiography before operation. There were no angiographic complications. All patients were operated on with full-channel electroencephalographic (EEG) monitoring. Indwelling shunts were required in 6 of 53 (11%) cases. Intraoperative heparin was given and not reversed; the mean dose was 5100 units. The mean clamp time was 48 minutes. Patch grafts, fashioned from common facial or saphenous veins, were used in 2 patients. Eight patients had contralateral carotid occlusions, but only 2 (25%) required indwelling shunt placement based on EEG criteria. There were no perioperative deaths in this series. One patient had a postoperative stroke, and 1 patient had a postoperative nonfatal myocardial infarction. Transient surgical complications included 3 wound hematomas, 1 wound abscess, and 2 self-limited cranial nerve palsies (13%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

Dose-escalation study of intravenous nicardipine in patients with aneurysmal subarachnoid hemorrhage.

A dose-escalation study of the calcium ion entry blocking drug nicardipine was performed using large dose infusions in 67 patients with recent aneurysmal subarachnoid hemorrhage (SAH). A safe, potentially therapeutic dose of the drug was determined. Patients admitted within 7 days of SAH from a documented cerebral aneurysm were entered into the study if no spasm was present on the initial angiogram. Nicardipine was administered as a continuous intravenous infusion throughout the 14-day period after SAH, regardless of the timing of surgery. To determine the safest possible dose, nicardipine was administered at seven dose levels from 0.01 to 0.15 mg/kg/hr. The total daily doses ranged from 27.7 mg to 375.0 mg. A follow-up angiogram was carried out on all 67 patients 7 to 10 days after SAH. Computerized tomography and neurological examinations were used to determine the presence of cerebral infarction. No major adverse effects, unexpected reactions, or permanent sequelae could be attributed to nicardipine. A decline in blood pressure was noted following administration of the drug. This occurred more frequently among patients given the largest dose but did not produce clinical problems or require discontinuation of the drug. Favorable outcomes were noted in 52 patients (78%). Vasospasm was found by arteriography in 31 patients (46%). A dose-related trend was noted: only eight (24%) of 33 patients treated at the highest dose level (approximately 10 mg/hr) developed arteriographic evidence of vasospasm. Symptomatic vasospasm was diagnosed in only two (6%) of 33 patients treated with this dose. Of the 34 patients receiving the lower dose levels, angiographic spasm was observed in 68% and symptomatic vasospasm in 27%. No deaths due to vasospasm occurred. Nicardipine appears to prevent both vasospasm and cerebral ischemia after SAH. A multicenter randomized double-blind trial to test this hypothesis is planned.

Adult↗
PubMed1987

Management of radiation-induced accelerated carotid atherosclerosis.

Patients with long survival following cervical irradiation are at risk for accelerated carotid atherosclerosis. The neurologic presentation in these patients mimics naturally occurring atheromatous disease, but patients often present at younger ages and with less concurrent coronary or systemic vascular disease. Hypercholesterolemia also contributes to this accelerated arteriosclerosis. Angiographic findings in this disorder include disproportionate involvement of the distal common carotid artery and unusually long carotid lesions. Pathologic findings include destruction of the internal elastic lamina and replacement of the normal intima and media with fibrous tissue. This article describes two surgical patients with radiation-induced accelerated carotid atherosclerosis who typify the presentation and characteristics of this disease.

Adult↗
PubMed1987

Technical controversies in carotid artery surgery.

Carotid endarterectomy has become a routine and safe therapeutic strategy in most neurovascular centers. Wide diversity of opinion and considerable debate, however, persists concerning the ideal methods of anesthetic management, cerebral protection, intraoperative monitoring, and arterial repair. We have examined and summarized the current status of these controversies and have identified several new techniques that hold promise for further development.

Anesthesia↗