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Biomedical subjects

K P Stewart

Publications and source records attributed to K P Stewart.

7 recordsLinked to original sources
PubMed2001

Cardiac cycle-dependent changes in aortic area and distensibility are reduced in older patients with isolated diastolic heart failure and correlate with exercise intolerance.

OBJECTIVES: The goal of this study was to determine if cardiac cycle-dependent changes in proximal thoracic aortic area and distensibility are associated with exercise intolerance in elderly patients with diastolic heart failure (DHF). BACKGROUND: Aortic compliance declines substantially with age. We hypothesized that a reduction in cardiac cycle-dependent changes in thoracic aortic area and distensibility (above that which occurs with aging) could be associated with the exercise intolerance that is prominent in elderly diastolic heart failure patients. METHODS: Thirty subjects (20 healthy individuals [10 < 30 years of age and 10 > 60 years of age] and 10 individuals > the age of 60 years with DHF) underwent a magnetic resonance imaging (MRI) study of the heart and proximal thoracic aorta followed within 48 h by maximal exercise ergometry with expired gas analysis. RESULTS: The patients with DHF had higher resting brachial pulse and systolic blood pressure, left ventricular mass, aortic wall thickness and mean aortic flow velocity, and, compared with healthy older subjects, they had a significant reduction in MRI-assessed cardiac cycle-dependent change in aortic area and distensibility (p < 0.0001) that correlated with diminished peak exercise oxygen consumption (r = 0.79). After controlling for age and gender in a multivariate analysis, thoracic aortic distensibility was a significant predictor of peak exercise oxygen consumption (p < 0.04). CONCLUSIONS: Older patients with isolated DHF have reduced cardiac cycle-dependent changes in proximal thoracic aortic area and distensibility (beyond that which occurs with normal aging), and this correlates with and may contribute to their severe exercise intolerance.

Adult↗
PubMed2000

Carotid Doppler high-intensity transient signals in dilated cardiomyopathy.

BACKGROUND: Thromboembolism is an infrequent but serious complication in dilated cardiomyopathy (DCM), and the role of primary preventive antithrombotic or anticoagulation therapy is undetermined. High-intensity transient signals (HITS) by Doppler ultrasound representing microemboli have been described in various clinical settings associated with increased risk of stroke. This study assessed the feasibility, reproducibility, and prevalence of HITS in patients with DCM. METHODS: Thirty patients with severely reduced left ventricular ejection fraction (< or = 35%, mean 25%) and New York Heart Association class II to III who were not receiving antithrombotic or anticoagulant therapy and 20 age-matched normal subjects were prospectively examined. Patients with atrial fibrillation, significant cardiac valvular heart disease, a history of cerebrovascular disease, and those who otherwise required antithrombotic or anticoagulation therapy were excluded. One-hour pulsed-wave Doppler recordings over the common carotid artery (CCA) were performed on 3 separate days in each subject by a single, experienced, blinded sonographer with a 4-MHz probe (TC-2000, Nicolet/EME) with a specially designed probe holder. Studies were read in a blinded, random fashion by 2 independent, experienced HITS Doppler recording readers. RESULTS: HITS in the CCA were detected in 6 (20%) of 30 patients with DCM and in 3 (15%) of 20 volunteers. This difference was not statistically significant. Intrareader and interreader reproducibility were high (kappa = 0.91 and 0.84, respectively; P <.001), whereas intrasubject reproducibility over the 3 visits was moderate to low (kappa = 0.22). There was no significant difference between HITS characteristics, that is, intensity and duration, in patients versus controls. CONCLUSIONS: The prevalence of CCA HITS in patients with clinically stable heart failure who are not receiving anticoagulation/antithrombotic therapy and are not in atrial fibrillation is low and not significantly different from normal patients. These data suggest that HITS monitoring is not a viable surrogate marker for increased thromboembolic risk in such patients with DCM.

Adult↗
PubMed1999

Fourier-transform optical microsystems.

The design, fabrication, and initial characterization of a miniature single-pass Fourier-transform spectrometer (FTS) that has an optical bench that measures 1 cm x 5 cm x 10 cm is presented. The FTS is predicated on the classic Michelson interferometer design with a moving mirror. Precision translation of the mirror is accomplished by microfabrication of dovetailed bearing surfaces along single-crystal planes in silicon. Although it is miniaturized, the FTS maintains a relatively high spectral resolution, 0.1 cm-1, with adequate optical throughput.

Equipment Design↗
PubMed1989

Mechanism of altered pattern of left ventricular filling with aging in subjects without cardiac disease.

The mechanism whereby aging, in the absence of cardiac disease, may alter the pattern of left ventricular (LV) diastolic filling is unknown. Accordingly, this study was designed to examine the factors that may be in part responsible for aging's effect on the pattern of LV diastolic filling. The LV end-diastolic pressure-volume relation was analyzed in 11 elderly subjects (68 +/- 5 years, mean +/- standard deviation) and 15 normal young adults (31 +/- 7 years) without coronary artery disease, systemic hypertension, LV hypertrophy or abnormality of LV systolic function. After catheterization, the subjects underwent pulsed Doppler analysis of mitral flow. All had normal 2-dimensional echocardiograms without LV or valvular dysfunction. Peak early filling velocity in the elderly subjects was decreased in comparison with that in young adults (61 +/- 14 vs 83 +/- 8 cm/s, p less than 0.001) and the ratio of early and late diastolic filling velocity was reduced (0.81 +/- 0.26 vs 1.88 +/- 0.40, p less than 0.001). The isovolumic relaxation time did not differ between the elderly and young subjects (158 +/- 20 vs 146 +/- 22 ms, difference not significant). In the elderly, LV end-diastolic pressure was increased (15 +/- 7 vs 11 +/- 4 mm Hg, p less than 0.05) despite a smaller end-diastolic volume index (60 +/- 16 vs 74 +/- 18 ml/m2, p less than 0.05), indicating a shift of the passive diastolic pressure-volume relation. It was concluded that early diastolic filling is reduced in normal aged subjects, even in the absence of coronary artery disease and systolic dysfunction. This altered pattern of diastolic filling may result from a shift of the passive LV diastolic pressure-volume relation.

Aged↗