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Biomedical subjects

W M McKinney

Publications and source records attributed to W M McKinney.

At least 19 recordsLinked to original sources
PubMed2000

Caffeine can affect velocity in the middle cerebral artery during hyperventilation, hypoventilation, and thinking: a transcranial Doppler study.

This study examined possible caffeine-mediated changes in blood flow velocity in the middle cerebral artery (VMCA) induced by tests of cerebrovascular responsiveness. Transcranial Doppler (TCD) sonography provided simultaneous bilateral VMCA measures while healthy college students hypoventilated, hyperventilated, and performed cognitive activities (short-term remembering, generating an autobiographical image, solving problems), each in 31-second tests. VMCA measures were obtained from the same persons, in separate testing sessions, when they were noncaffeinated and under two levels of caffeine: a smaller amount (from a cola, 45 mg/12 oz) and a larger amount (from coffee, 117 mg/8 oz). Compared with the no-caffeine control condition, a smaller amount of caffeine had no significant effects on global VMCA, but a larger amount suppressed VMCA by 5.8%. Time-course analyses showed that VMCA (1) followed a triphasic pattern to increase over baselines during hypoventilation regardless of caffeine condition, (2) slowed below baselines during hyperventilation (with the degree of slowing attenuated under caffeine), and (3) increased over baselines during all cognitive activities (ranges 3.8-6.9%). It is concluded that a large amount of caffeine can suppress VMCA, and this possibility should be anticipated when TCD is used to assess cerebral hemovelocity.

Adult↗
PubMed1998

Vagus nerve imaging with ultrasound: anatomic and in vivo validation.

To provide the anatomic basis and demonstrate the reproducibility of ultrasound studies for the identification of the vagus nerve within its course in the carotid sheath in the neck, cadaveric and in vivo imaging studies were conducted. On transverse B-mode images of the neck, there is a centrally hypoechoic and peripherally hyperechoic structure between the common carotid artery and the jugular vein inside the carotid sheath. This structure was also identified in a fresh, nonpreserved cadaver and was marked with a hypodermic needle by means of a transdermal approach. Neck dissection was performed leaving the carotid sheath intact. B-mode imaging yielded detailed anatomic information about the structures in the carotid sheath. Further dissection showed the vagus nerve as the target of the needle. One hundred consecutive transverse carotid scans were reviewed, and the characteristic echo patterns of the vagus nerve were identified in 97 instances. A distinct and reproducible, round, hypoechoic structure was defined adjacent to the common carotid artery and jugular vein as the vagus nerve. On the basis of this study, a new, noninvasive, and highly reproducible method to locate the vagus nerve in the carotid sheath is introduced. This may lead to further clinical application such as presurgical localization or ultrasound-guided needle studies. Stimulation of the vagus nerve has been proposed for seizure therapy. The diagnosis of vagus nerve tumors may be improved.

Humans↗
PubMed1998

Blood flow velocities in three cerebral arteries in the same subjects modulate during thinking.

College students (n = 22) engaged in thinking activities while simultaneous bilateral velocity (V) measures are obtained from their middle, anterior, and posterior cerebral arteries (MCA, ACA, and PCA). The study follows a 3 x 2 x 6 factorial design with repeated measures on artery insonated (MCA, ACA, and PCA), hemisphere (right and left), and six experimental phases, within which an initial 62-second baseline (BL) period is followed by five 31-second thinking tasks (short-term remembering, generating an image, making decisions, and solving language and math problems). VMCA is faster than BL during each thinking task (range, 4.9%-8.5%; p < 0.001), but changes in VACA, VPCA, and all hemispheric differences are not significant. A stronger degree of increase is present for VMCA than (1) both VACA and VPCA during short-duration remembering, making decisions, and working math problems, and (2) VACA, which in turn is stronger than VPCA when generating images and constructing new words. The authors' study shows that transcranial Doppler neuroimaging conveniently provides physiological indices of thinking from three cerebral arteries of the same subjects.

Adolescent↗
PubMed1997

Modulations in cerebral hemodynamics under three response requirements while solving language-based problems: a transcranial Doppler study.

This experiment used transcranial Doppler ultrasound to measure blood flow velocity in the middle, anterior or posterior cerebral artery (MCA, ACA and PCA, respectively) while separate groups of college students (each n = 20) solved anagrams and constructed new words using letters of a target word, each while viewing, speaking or writing the responses. The silent viewing requirement affected global velocities only while constructing words: velocities in both the MCA and ACA were faster than in the PCA. Speaking the solutions during both types of problems yielded faster overall velocities in the MCA than in the PCA. Finally, writing the solutions while constructing words led to faster velocities in the MCA compared to both the ACA and PCA. Time-course patterns to velocity changes from the thinking periods showed elevations in MCA velocity at the beginning and end of the periods, while PCA velocity typically slowed below baseline in the middle of the periods. These data show that the kind of language-based problem-solving task and the specific response requirement arranged to accomplish a task selectively affected velocity in three cerebral arteries.

Adolescent↗
PubMed1995

Ultrasonography for diagnosis and management of carotid artery atherosclerosis. A position paper of the American Society of Neuroimaging.

The importance of identifying patients with carotid artery stenosis has attained greater significance in light of recent treatment trials of the efficacy of medical and surgical treatment of both symptomatic and asymptomatic carotid stenosis. Doppler and B-mode ultrasonography can accurately diagnose and quantify stenosis at the cervical carotid artery bifurcation. The development of duplex color-flow instruments has enhanced the sensitivity and specificity of this examination. Ultrasonography should be employed as an initial examination to identify patients with carotid artery stenosis and determine whether further evaluation or treatment is necessary.

Blood Flow Velocity↗
PubMed1992

Irradiation-induced atherosclerosis: a factor in therapeutic planning.

Early primary head and neck cancers (stages I and II) and occult metastatic neck disease have caused debate regarding the choice between surgery and irradiation. The arguments for each are reviewed with a new consideration: the acceleration and/or induction of carotid atherosclerosis in irradiated patients. We present clinical case reports (n = 9), a retrospective clinical evaluation for the occurrence of carotid atherosclerosis in irradiated head and neck cancer patients (n = 57) and a comparison study of the extent and distribution of atherosclerosis in irradiated (n = 29) and nonirradiated head and neck cancer patients controlled for age, blood pressure, and tobacco use. The results show that carotid atherosclerosis is found in a wider anatomic distribution and to a greater extent in irradiated than in nonirradiated patients. We conclude that carotid atherosclerosis is induced and/or accelerated by neck irradiation. The implications as they relate to choice of treatment, to pretreatment evaluations, and to long-term follow-up are discussed.

Aged↗
PubMed1990

Evaluation of the associations between carotid artery atherosclerosis and coronary artery stenosis. A case-control study.

To evaluate the consistency, strength, and independence of the relation of carotid atherosclerosis to coronary atherosclerosis, we quantified coronary artery disease risk factors and extent of carotid atherosclerosis (B-mode score) in 343 coronary artery disease patients and 167 disease-free control patients. In univariable analyses, there was a strong association between coronary status and extent of carotid artery disease in men and women older than and younger than 50 years (p less than 0.001 for men and women greater than 50 years, p less than 0.001 for women less than or equal to 50 years, p = 0.045 for men less than or equal to 50). The relation remained strong after control for age in men and women older than 50 years and in women younger than 50 (p less than 0.001 for men and women greater than 50 years, p = 0.003 for women less than or equal to 50) but did not persist after control for age in men younger than 50. Logistic models that included coronary disease risk factors, with or without B-mode score, as independent variables and presence or absence of coronary disease as the outcome variable indicated that the extent of carotid atherosclerosis was a strong, statistically significant independent variable in models for men and women older than 50 years of age. Next, we examined the usefulness of B-mode score as an aid in screening for coronary artery disease in men and women older than 50 years. Classification rules, both including and excluding B-mode score, were developed based on logistic regression and, for comparison, recursive partitioning (decision trees). The performance of these rules and the bias of their performance statistics were estimated. The improved classification of the study sample when B-mode score was incorporated in the rule was statistically significant only for men (p = 0.015). However, the addition of B-mode score was found to 1) increase the median discrimination score for both sex groups based on the logistic model, and 2) yield better sensitivities and specificities for rules based on recursive partitioning. Thus B-mode score is strongly, consistently, and independently associated with coronary artery disease in patients older than 50 and is at least as useful as well-known risk factors for identifying patients with coronary artery disease.

Aging↗
PubMed1989

Cigarette smoking cessation and extracranial carotid atherosclerosis.

Using B-mode ultrasonography, cigarette smoking was found to be a strong, independent risk factor for extracranial carotid atherosclerosis in 1692 black and white men and women admitted for diagnostic evaluation of the carotid arteries. We found that the difference in mean plaque thickness was smaller between past smokers and nonsmokers than between current smokers and nonsmokers, suggesting that the rate of progression of carotid atherosclerosis may be slower in people who quit smoking compared with people who continue to smoke.

Adult↗
PubMed1989

Risk factors for site specific extracranial carotid artery plaque distribution as measured by B-mode ultrasound.

The effect of age, sex, diabetes, hypertension, pulse rate and cigarette smoking on extracranial carotid artery plaque thickness evaluated by B-mode ultrasonography was investigated in a cross-sectional study of 698 white men, 730 white women, 77 black men and 76 black women as part of a clinical ultrasound registry. Subjects were between 24 and 98 years of age, with a mean age of 63 years. Arterial locations evaluated were: proximal, mid and distal common carotid; the bifurcation; and the proximal and mid internal and external carotids. In a general linear multivariate analysis with plaque thickness at each site as the outcome variable, cigarette smoking and age were the two most consistent risk factors, and affected plaque thickness at all the investigated sites. Hypertension affected more sites than diabetes, men had more plaques than women, and except for the common carotid, whites had more plaques than blacks. Thus, risk factors were not uniformly associated with atherosclerosis at all sites of the extracranial carotid arteries.

Adult↗
PubMed1989

Correlation of carotid bruits and carotid atherosclerosis detected by B-mode real-time ultrasonography.

The extent of carotid atherosclerosis evaluated by B-mode real-time ultrasound and the presence of bruits established by carotid phonoangiography were determined in 1,107 patients. Unilateral bruit was associated with increased atherosclerosis compared with no bruit (p less than or equal to 0.0001). However, there was no association between laterality of the bruit and the degree of atherosclerosis (p = 0.66). There was marginal evidence that patients with bilateral bruits had more severe atherosclerosis than patients with unilateral bruit (p = 0.046). The relation between bruit and atherosclerosis categorized by B-mode ultrasound was not sufficient to reliably predict the presence or absence of disease in an individual patient, though the presence of a bruit should be viewed as a risk factor for, or an indicator of, increased risk of systemic atherosclerosis.

Auscultation↗
PubMed1989

The origin and distribution of vasa vasorum at the bifurcation of the common carotid artery with atherosclerosis.

The purpose of our study was to determine the origin and relation of vasa vasorum to atherosclerotic plaque at the bifurcation of the common carotid artery. We randomly selected 12 unembalmed adult human cadavers, 40-96 years of age. We prepared luminal casts of the arteries from eight cadavers and cleared the arteries from the remaining four cadavers. A network of vasa vasorum surrounding atherosclerotic plaque was observed in five luminal casts and in two cleared specimens; the vasa vasorum originated from the superior thyroid and ascending pharyngeal arteries. Three of the five luminal casts also demonstrated vasa vasorum arising directly from the internal carotid artery distal to the plaque. An extensive network of vasa vasorum was not observed in specimens from the five cadavers relatively free of gross atherosclerotic plaque. Our findings demonstrate the importance of the external carotid artery in giving rise to the vasa vasorum that supply the areas of atherosclerotic plaque.

Adult↗
PubMed1989

Extracranial carotid atherosclerosis in black and white patients with transient ischemic attacks.

To evaluate the association between extracranial carotid atherosclerosis, race, and transient ischemic attack, we carried out a retrospective hospital chart review and quantified the extent of noninvasively determined extracranial carotid atherosclerosis in 25 black patients greater than 45 years old with transient ischemic attacks. Two sex- and age-matched white patients with transient ischemic attacks were similarly studied for each black patient. Extent of extracranial carotid atherosclerosis (expressed as B-mode score) was similar for blacks and whites. B-mode score was only slightly less in patients with posterior- than in those with anterior-circulation transient ischemic attacks. Fifty-six patients (35 white, 21 black) had unilateral anterior-circulation transient ischemic attacks. Of the 32 patients with more extensive extracranial carotid atherosclerosis ipsilateral to the affected hemisphere, 23 (66% of 35) were white; only nine (43% of 21) were black. In the 35 white patients, the extent of disease in the ipsilateral carotid artery was significantly greater (p less than 0.03) than that in the contralateral carotid artery. When B-mode scores in the left and right carotid arteries were combined for the subgroup of patients with unilateral anterior-circulation transient ischemic attacks, blacks had slightly more atherosclerosis in the extracranial arteries than whites.

Arteriosclerosis↗
PubMed1988

Three-dimensional transcranial Doppler blood flow mapping in patients with cerebrovascular disorders.

We investigated 60 patients with cerebrovascular disorders using a three-dimensional transcranial Doppler blood flow mapping system. A composite display of the circle of Willis is created with computer assistance, allowing accurate vessel identification and optimal data documentation of blood flow velocity and direction in the basal cerebral arteries. The basilar artery was insonated in every patient; the middle cerebral artery and the most distal internal carotid artery were found in 95% of the patients, the anterior cerebral artery in 85%, and the posterior cerebral artery in 84%. Insonation problems occurred predominantly in elderly women. Transcranial Doppler blood flow mapping showed an abnormal result in 23 of 60 patients (38%). An intracranial stenosis with greater than 50% diameter reduction or occlusion was found in 10 of 31 patients (32%) with completed stroke, reversible ischemic neurologic deficit, or transient ischemic attack. Collateral blood flow mechanisms could be demonstrated in patients with extracranial carotid artery occlusions. Intra-arterial cerebral angiography performed in 21 patients confirmed the transcranial Doppler blood flow mapping diagnosis in 19 (90.5%). In one patient an arteriovenous malformation diagnosed by transcranial Doppler blood flow mapping was confirmed by magnetic resonance imaging.

Adolescent↗
PubMed1987

Anatomic and pathophysiologic studies of the human internal jugular valve.

The results of anatomic and hemodynamic studies of the human internal jugular valve, which is the only venous valve between the right atrium of the heart and the brain, have been reported. Tricuspid internal jugular valves were present in two cadaver subjects without any observed compromise in competency. Most valves tested were competent, with the exception of those from one cadaver which were apparently congenitally incompetent. Acquired or congenital internal jugular valve incompetence may impair cerebral venous return, especially when intrathoracic pressure is increased by positive-pressure ventilation. Screening for internal jugular valve incompetence with a Doppler flowmeter before utilizing this type of mechanical ventilation may help prevent the deleterious effects of cerebral venous congestion.

Cadaver↗
PubMed1985

Ultrasonic evaluation of jugular venous valve competence.

Jugular venous valve competence has been studied in the past only by invasive venography. The authors demonstrate that this valve can be noninvasively studied using real-time and pulsed Doppler ultrasound techniques and relate this to possible clinical implications. Visualization of the jugular valve with real-time ultrasound is reported and its competence documented using pulsed Doppler and M-mode techniques. The clinical relevance to the etiology of the respirator brain syndrome is discussed.

Adult↗
PubMed1982

Extracranial carotid artery arteriosclerosis. Diagnosis with continuous-wave Doppler and real-time ultrasound studies.

To determine the predictive accuracy of Doppler and real-time ultrasound studies, continuous-wave Doppler (CWD) and B-mode real-time ultrasound (RTU) studies of the carotid bifurcation were compared in 50 consecutive patients before cervicocranial arteriography. Four categories of CWD results were formed according to the severity of stenosis. Except for mild to moderate stenosis, there was a high degree of agreement (87.5% to 98.1%) between CWD results and arteriographic diagnosis. Of the arteries classified as normal on RTU study, 95.5% were arteriographically normal; of those classified as abnormal, 94.9% were abnormal on arteriography. In 94.7% of the cases in which RTU demonstrated a possible ulcer, the diagnosis was confirmed by arteriography.

Adult↗