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Biomedical subjects

W M Blackshear

Publications and source records attributed to W M Blackshear.

28 records · Page 2Linked to original sources
PubMed1980

The influence of limb elevation, examination technique, and outflow system design on venous plethysmography.

The effect of limb elevation and the design of the thigh cuff outflow system on venous capacitance and venous outflow, as determined by strain gauge plethysmography, was reviewed in a group of normal limbs without evidence of deep venous thrombosis. We improved the reliability of plethysmography in evaluating venous outflow, particularly in the early period after cuff deflation, by using uniform leg elevation, large diameter outflow tubing, and single rather than simultaneous limb examinations. Based on this experience, an optimum technique of examination emphasizing precise limb elevation, sequential limb examination and proper design of the cuff outflow system was used to evaluate 21 patients with acute venous thrombosis. The results obtained were compared with previously reported results of strain gauge plethysmography in patients with acute venous thrombosis. This technique significantly reduced the incidence of false-positive results.

Extremities↗
PubMed1979

Venous capacitance and outflow in the postoperative patient.

Venous capacitance and outflow were measured in a series of 50 unselected patients undergoing a variety of general surgical procedures. Studies done prior to operation and the morning after demonstrated a fall in capacitance and outflow that was related to the degree of ambulation. Fully ambulatory patients demonstrated no changes. Males under the age of 40 were unchanged regardless of the type of operation or degree of ambulation. It is likely that the observed changes reflected a reduction in arterial flow but alterations in venous tone cannot be ruled out.

Adolescent↗
PubMed1979

A prospective evaluation of oculoplethysmography and carotid phonoangiography.

With oculoplethysmography, conclusions are drawn regarding the state of internal carotid artery disease by measurements based upon pressure and flow in the eye, a location far removed from the site of the disease. Thus, many potential variables including ocular disease, vessel wall properties, intracranial atherosclerosis and collateral flow may affect the results. Although oculoplethysmography was quite accurate in detecting occlusion of the internal carotid artery, the identification of a high grade stenosis was much less precise. Furthermore, it could not distinguish between stenosis and occlusion, making angiography necessary for accurate diagnosis. In this study, oculoplethysmography, either alone or in combination with carotid phonoangiography, was not of sufficient accuracy to recommend its use as part of a noninvasive evaluation of carotid artery occlusive disease.

Angiography↗
PubMed1979

Detection of carotid occlusive disease by ultrasonic imaging and pulsed Doppler spectrum analysis.

Ultrasonic imaging of the cervical carotid arteries by ultrasonic arteriography and duplex scanning combined with pulsed Doppler spectrum analysis were investigated in a series of patients undergoing arteriography. By using the ultrasonic image as a guide for precise placement of the pulsed Doppler sample volume, the characteristics of blood flow at points of interest in the carotid arteries could be determined. Audible analysis of the Doppler signal permitted correct diagnosis of 23 of 26 (88%) high-grade stenoses or occlusions with ultrasonic arteriography and 24 of 26 (92%) with duplex scanning. Spectrum analysis of Doppler signals obtained with the duplex scanner detected all of the 22 high-grade stenoses. Spectral abnormalities of a lesser degree also were detected in 18 of 23 vessels (78%) with atherosclerotic plaques which should not have reduced cerebral blood flow. These techniques permit the accurate detection of and the distinction between high-grade stenoses and occlusion, as well as the identification of many plaques which are not large enough to affect intracranial hemodynamics.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Carotid artery velocity patterns in normal and stenotic vessels.

Duplex scanning provides real time B-mode images of the carotid bifurcation vessels along with a single gate pulsed Doppler flow velocity detector. By using the B-mode output of the duplex system to measure the Doppler angle and spectrum analysis to measure the frequency content of the Doppler signal, instantaneous flow velocity can be calculated. Mean velocity at peak systole was calculated retrospectively in 68 common (CCA) and internal (ICA) carotid arteries of 39 patients who had undergone prior angiography and prospectively in 30 arteries of 15 healthy young controls. The ratio of mean peak ICA velocity to mean peak CCA velocity at systole (VICA/VCCA) was below 0.8 in all 36 normal arteries and above 1.5 in all 21 high-grade stenoses of 60% or greater diameter reduction. Sixty-one percent of 41 vessels with less than 10 to 55% diameter reduction had a velocity ratio between 0.8 and 1.5. Only 10% of all ICA's with any stenotic lesion were incorrectly classified as normal. VICA/VCCA appears to be an accurate indicator of the degree of ICA stenosis.

Adult↗
PubMedDate not supplied

Ultrasonic demonstration of external and internal carotid patency with common carotid occlusion: a preliminary report.

Non-invasive ultrasonic imaging of the carotid bifurcation by duplex scanning and ultrasonic arteriography combined with pulsed Doppler spectrum analysis demonstrated patency of the external and internal carotid arteries distal to a common carotid occlusion in 3 patients. Common carotid occlusion is not invariably associated with thrombosis of the ipsilateral internal carotid artery. Identification of internal carotid patency by the use of ultrasonic techniques will permit surgical treatment in selected cases.

Aged↗
PubMedDate not supplied

Advantages of continuous electroencephalographic monitoring during carotid artery surgery.

One hundred carotid endarterectomies were performed using selective shunting based on continuous electroencephalographic monitoring (CEM) for the detection of cortical ischemia. Changes associated with ischemia were loss of frequency and amplitude. The results of CEM were correlated with carotid stump pressure (CSP) measurements. Only one (4%) of the 25 patients who developed an abnormal EEG had a mean CSP greater than 50 mmHg: however, CEM was positive in only 24 (45%) of the 53 patients with a CSP less than 50 mmHg. Using EEG as a standard, no CSP criterion (50 or 25 mmHg) was sufficiently sensitive and specific to recommend its routine use (50 mmHg--96% and 61% respectively; 25 mmHg--40% and 96% respectively). Operative mortality was 1%. The three intraoperative neurologic deficits (3%), one transient and two permanent, are analyzed with respect to the operative EEG findings. In the 100 endarterectomy patients and three more undergoing carotid exploration or excision of carotid body tumor EEG changes due to anesthetic problems not associated with carotid clamping were often identified. In 48 additional endarterectomies a computerized display and disk storage of six selected EEG leads, each with a reference trace for comparison, has provided information equivalent to that from the full EEG. EEG monitoring is more accurate than CSP measurement for identifying patients who require shunting, safely dispensing with a shunt in many cases which would otherwise be shunted by standard CSP criteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Carotid endarterectomy without angiography.

Three patients with unilateral hemispheric symptoms suggestive of extracranial carotid occlusive disease and one patient with bilateral symptoms who were allergic to radiographic contrast media were studied by pulsed Doppler ultrasonic arteriography and real time spectrum analysis. Four high grade (greater than 50% diameter reduction) internal carotid stenoses and one low grade (less than 50% diameter reduction) stenosis were identified. The noninvasive findings were confirmed at endarterectomy in all five arteries. Pulsed Doppler ultrasonic imaging combined with real time spectrum analysis can accurately quantitate the degree of atherosclerotic stenosis at the carotid bifurcation. Experience with these four patients suggests that these techniques can be used in lieu of angiography to evaluate patients who are unable to undergo standard radiographic examination.

Aged↗