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Biomedical subjects

G I Thomas

Publications and source records attributed to G I Thomas.

At least 19 recordsLinked to original sources
PubMed1992

Relation between middle cerebral artery blood flow velocity and stump pressure during carotid endarterectomy.

BACKGROUND AND PURPOSE: Many patient monitoring techniques have been used for detecting cerebral hypoperfusion during carotid endarterectomy. We compared middle cerebral artery blood flow velocities with carotid artery stump pressures to evaluate the indications for common carotid artery cross-clamp shunting and the probable hemodynamic causes of cerebrovascular complications. METHODS: Blood flow velocities were monitored with transcranial Doppler ultrasound and carotid stump pressures were measured at the time of common carotid artery cross-clamping during 97 carotid endarterectomy procedures. Stump pressures measured with the gauge zero reference at the common carotid artery level were correlated with the percentage change of velocities. RESULTS: Middle cerebral artery blood flow velocities usually decreased upon common carotid artery cross-clamping, depending on collateral availability and the autoregulation response. The best fit of the data was to an exponential function concave to the pressure axis, with velocity as a percentage of the pre-cross-clamp value reaching zero at 15 mm Hg stump pressure (r = 0.85 and p less than 0.001). CONCLUSIONS: There is a less critical margin of error with percentage middle cerebral artery blood flow velocity decreases than with stump pressure measurements. This relation establishes changes in middle cerebral artery blood flow velocities as a reliable parameter for judging the effects of carotid cross-clamping on cerebral blood flow and providing an excellent indicator as to the necessity for shunting.

Blood Flow Velocity↗
PubMed1990

Detection of middle cerebral artery emboli during carotid endarterectomy using transcranial Doppler ultrasonography.

The purpose of our study was to define the signal characteristics and clinical circumstances associated with emboli detected in the middle cerebral artery using 2-MHz pulsed transcranial Doppler ultrasound in patients undergoing carotid endarterectomy. Signals designating emboli were transients displaying harmonic qualities the signatures of which were clearly different from those of mechanical and electronic artifacts. We reviewed the audio/video tape recordings from 91 patients for signals of air bubble emboli occurring upon release of common carotid artery crossclamps; recordings from 35 patients (38%) demonstrated air bubble emboli. Transients with signatures identical to those of air bubble emboli were also discovered when bubbles in the bloodstream were improbable; we defined these transients as representing formed-element emboli. Such signals were found in recordings from 24 patients (26%), and they occurred before (both spontaneously and upon common carotid artery compression), during, and after surgical dissection. Signals indicating formed-element emboli were associated with intraluminal platelet thrombus, with ulcerations in the carotid artery, and with transient ischemic attacks or stroke. Most postoperative formed-element emboli did not cause symptoms but, when persisting for hours, they were associated with strokes and cerebral infarction. This Doppler ultrasound method of detecting emboli will be useful in the study of stroke mechanisms and as a clinical test to guide the medical and surgical treatment of patients at risk of stroke.

Arterial Occlusive Diseases↗
PubMed1990

Blood flow velocity in the middle cerebral artery during carotid cross-clamping: loss of regulatory response to carbon dioxide partial pressure. A transcranial Doppler intraoperative study.

The CO2 reactivity of blood flow velocity in the Middle Cerebral Artery (MCA) was explored by Doppler ultrasound, in nine patients, at the time of common carotid artery cross-clamping during vascular surgery, in order to detect if a regulatory response apply during operative occlusion of common carotid artery. Transcranial Doppler was used to monitor ipsilateral MCA blood velocity during carotid surgery. MCA velocity, arterial blood pressure and pCO2 (arterial or end-tidal) were measured, during carotid cross clamping, before and after an increase in pCO2 was induced by changing respiratory rate and volumes. No relevant changes in MCA flow velocities were detected in patients with stable arterial blood pressure. In those patients showing an increase in blood pressure during the surgical procedure the MCA velocity increased accordingly. It is suggested that the cross-clamping of common carotid artery is a critical condition in which no regulatory response can be elicited: blood flow velocity tends to parallel the perfusion pressure and also CO2 reactivity is lost.

Aged↗
PubMed1986

Carotid endarterectomy after Doppler ultrasonographic examination without angiography.

We prospectively reviewed our experience with 32 carotid endarterectomies in 30 patients performed without angiography in a 7 year period. Although this represents 6.7 percent of our total experience with carotid endarterectomy in this period, carotid endarterectomy without angiography is increasing and comprises 17 percent of the last 2 years' total. We have adhered to strict criteria for patient selection that identifies circumstances for a safe operative experience in seven broad categories. Evidence is also presented to reduce an overriding concern for intracranial aneurysms and siphon stenosis if either one exists unrecognized. We are hopeful that in the future, the latter will be identified by intracranial Doppler studies currently being performed. Our experience in this small series has been favorable, with intraoperatively measured lesions equal to the preoperative noninvasive predictions. We suggest that Doppler ultrasonography in its current form can be effectively used in place of conventional angiography or digital subtraction angiography in selected patients.

Aged↗
PubMed1984

The St. Jude experience.

This paper covers our experience with the use of the St. Jude prosthetic heart valve from November 1979 through August 1983 in 91 patients operated on for aortic and mitral valve replacement. Nonfatal complications included hemorrhagic sequela due to anticoagulation, with an annual rate of 1 percent (1.4 percent per 100 patient years), thromboembolism with an annual rate of 0.8 percent (0.87 percent per 100 patient years), sternal infection 1 percent, operative cardiovascular accident 1 percent, and pericardial tamponade 1 percent. Operative mortality was 1 percent, early mortality (within 30 days) was 3 percent, and late mortality was 3 percent, with a total overall mortality of 7 percent. Excluding two patients who died from noncardiac causes, the overall mortality was 5 percent. The mortality rate per year was 2 percent. The survival rate 3.8 years postoperatively was 89 percent for mitral valve replacement patients and 93 percent for aortic valve replacement patients, for an overall 38 year survival rate of 92 percent. All patients were anticoagulated with warfarin. There were no instances of valve failure, replacement, or serious hemolysis. Eighty-three percent were active or working with a New York heart functional class I. In our experience, the complication rate with the St. Jude valve is as low or lower than that for any other mechanical prosthetic cardiac valve available in the world today.

Adult↗
PubMed1979

Aortic valve replacement and the senior citizen.

The elderly patient, regardless of age, faces an early demise from progressive cardiac decompensation secondary to aortic valve disease. Aortic valve replacement can be carried out at a reasonable operative risk and extend the longevity to very close to that of normal life expectancy. It is our feeling, based on these results, that patients with significant symptoms secondary to aortic valvular disease, regardless of age and without other major organ problems, should be given the choice of aortic valve replacement to enhance the quality and quantity of their lives.

Age Factors↗