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Biomedical subjects

M E Brickner

Publications and source records attributed to M E Brickner.

27 records · Page 2Linked to original sources
PubMed1992

Exaggerated pressor response to treadmill exercise in chronic cocaine abusers with left ventricular hypertrophy.

BACKGROUND: Chronic cocaine abuse has been associated with a high prevalence of left ventricular hypertrophy (LVH) in normotensive individuals at rest. This study was conducted to determine whether chronic cocaine abusers with LVH would manifest an exaggerated pressor response to treadmill exercise. METHODS AND RESULTS: Forty-nine normotensive chronic cocaine abusers underwent Bruce protocol treadmill exercise testing until they attained 85% maximum predicted heart rate. A peak exercise systolic blood pressure greater than or equal to 210 mm Hg was defined as abnormal. In addition, they underwent two-dimensional echocardiography and had left ventricular mass determined by the area-length method. LVH was defined as left ventricular mass greater than or equal to 105 g/m2 and a posterior wall thickness greater than or equal to 1.2 cm. Age- and race-matched control subjects also underwent echocardiography and exercise testing. Group differences in peak exercise blood pressure in cocaine abusers with LVH, cocaine abusers without LVH, and control subjects were assessed by ANOVA: Groups were similar concerning age, race, heart rate, resting blood pressure, body surface area, and exercise duration. LVH was present in 16 of 49 (33%) cocaine abusers and three of 30 (10%) control subjects (p = 0.02). Of the 16 cocaine abusers with LVH, 10 (63%) had peak exercise blood pressures greater than or equal to 210 mm Hg, and three others had exercise blood pressures of 200 mm Hg. Therefore, peak exercise systolic blood pressure was significantly higher in cocaine abusers with LVH than in all other groups (p = 0.0001). CONCLUSIONS: Chronic cocaine abusers with LVH manifest an exaggerated pressor response to treadmill exercise. These data suggest that chronic cocaine abuse predisposes a subset of individuals to a heightened pressor response to a given sympathetic stimulus such as exercise and that this may contribute to the pathogenesis of LVH in chronic cocaine abusers.

Adult↗
PubMed1991

In vivo thrombus formation on a guidewire during intravascular ultrasound imaging: evidence for inadequate heparinization.

We present a case in which thrombus formation on a guidewire was visualized during intravascular ultrasound imaging despite the administration of 10,000 units of heparin sulfate prior to the procedure. Gross thrombus formation was confirmed upon removal of the guidewire. The activated clotting time was found to be 191 s, suggesting heparin resistance. This report graphically illustrates the potential thrombogenicity associated with intravascular guidewire manipulation during procedures such as intravascular ultrasound imaging and percutaneous transluminal coronary angioplasty. Moreover, this case suggests that adequate heparinization should be routinely verified by measuring the activated clotting time prior to introducing a guidewire into the arterial system.

Adult↗
PubMed1991

Aortic valve morphology influences regurgitant volume in aortic regurgitation: in vitro evaluation.

STUDY OBJECTIVE: According to the Gorlin hydraulic orifice equation, aortic regurgitation volume can be determined by the regurgitant orifice cross sectional area, diastolic filling period, mean pressure gradient between the aorta and left ventricle, and a constant relating the coefficients of contraction (Cc) and velocity (Cv). This study was performed to determine whether variation in aortic valve morphology affects regurgitant flow volume, Cc and Cv. DESIGN: Four aortic valve templates, modelled after circular, rheumatic, degenerative, and bicuspid lesions, were constructed with equal orifice cross sectional areas in two sizes, 0.2 and 0.7 cm2. These valves were studied in vitro in a flow model of aortic regurgitation, wherein aortic pressure was regulated by varying the height of a column of fluid. Flow, pressure, and velocity were measured, and the coefficient Cc and Cv were calculated from standard equations. MEASUREMENTS AND MAIN RESULTS: Regurgitant volume was assessed at diastolic filling periods of 0.5 and 1.0 s and averaged 15% greater for bicuspid and degenerative as compared to circular or rheumatic valve shapes (p = 0.0001). This difference was accentuated at the shorter diastolic filling time and higher pressure gradient, such that bicuspid lesions allowed 29% more regurgitant flow across the 0.2 cm2 orifice at fluid height of 120 cm over 0.5 s. This difference in regurgitant volume between valve shapes was due to an increased Cc for the bicuspid and degenerative valve shapes, suggesting that they are more efficient orifices than rheumatic or circular valve shapes. CONCLUSIONS: Aortic valve morphology influences regurgitant volume in aortic regurgitation. Specifically, degenerative and bicuspid orifice shapes have a higher contraction coefficient and allow more regurgitant flow than rheumatic or circular orifices at a given driving pressure and diastolic filling time.

Aortic Valve↗
PubMed1991

Left ventricular hypertrophy associated with chronic cocaine abuse.

BACKGROUND: This study was performed to determine whether chronic cocaine abuse is associated with left ventricular hypertrophy in humans. METHODS AND RESULTS: A consecutive series of 40 chronic cocaine abusers 23-44 years old who were enrolled in an inpatient drug rehabilitation program were considered for the study. Subjects with elevated resting blood pressure (n = 4) or a history of hypertension (n = 3) were excluded. Technically adequate two-dimensional echocardiograms were obtained in 30 cocaine abusers and 30 age- and race-matched normal control subjects. All subjects were men, and the groups were similar with regard to resting blood pressure, height, weight, and body surface area. All echocardiograms were read in blinded fashion, and left ventricular mass was calculated by the area-length method. Left ventricular cavity dimensions and wall motion were normal in all subjects. Left ventricular mass index was higher in the cocaine group (103 +/- 24 versus 77 +/- 14 g/m2, p = 0.0001). Posterior wall thickness was increased (1.2 cm or more) in 13 cocaine abusers (43%) compared with four controls (p = 0.0099). CONCLUSIONS: Chronic cocaine abuse is associated with increased left ventricular mass index and wall thickness. Left ventricular hypertrophy may provide a substrate facilitating the development of myocardial ischemia and/or arrhythmias in cocaine abusers.

Adult↗
PubMed1990

Aortic valve morphology: an important in vitro determinant of proximal regurgitant jet width by Doppler color flow mapping.

In vitro and in vivo studies suggest that proximal aortic regurgitant jet width on Doppler color flow mapping predicts severity of aortic regurgitation. The influence of aortic valve morphology on proximal regurgitant jet width has not been studied. Despite equal cross-sectional area, differences in aortic valve morphology may influence regurgitant jet width and thus estimates of severity of aortic regurgitation. Aortic valve simulations representing degenerative, rheumatic and bicuspid valves as well as a circle in two cross-sectional areas (0.2 cm2 and 0.7 cm2) were placed in a flow model using two gradients (50 and 100 mm Hg) to produce simulated aortic regurgitant jets. Flow maps were obtained from parasternal and apical positions with color gain, frames per second, low velocity reject and depth held constant. The mean of three regurgitant jet widths for each shape, size and gradient were compared by three factor analysis of variance. Aortic valve morphology significantly affected regurgitant jet width in both parasternal and apical views (p = 0.0001 by analysis of variance) with bicuspid shapes producing regurgitant jet widths significantly different from all other shapes. Valve area also consistently significantly influenced proximal regurgitant jet width (p = 0.0001) in both views. Initial pressure gradient was less important. It is concluded that in an in vitro flow model aortic valve morphology introduces significant variability in the measurement of proximal regurgitant jet widths independent of orifice cross-sectional area. Estimates of severity of aortic regurgitation may therefore be influenced considerably by aortic valve morphology.

Analysis of Variance↗
PubMed1990

Dissociation of end systole from end ejection in patients with long-term mitral regurgitation.

To determine whether left ventricular (LV) end systole and end ejection uncouple in patients with long-term mitral regurgitation, 59 patients (22 control patients with atypical chest pain, 21 patients with aortic regurgitation, and 16 patients with mitral regurgitation) were studied with micromanometer LV catheters and radionuclide angiograms. End systole was defined as the time of occurrence (Tmax) of the maximum time-varying elastance (Emax), and end ejection was defined as the time of occurrence of minimum ventricular volume (minV) and zero systolic flow as approximated by the aortic dicrotic notch (Aodi). The temporal relation between end systole and end ejection in the control patients was Tmax (331 +/- 42 [SD] msec), minV (336 +/- 36 msec), and then, zero systolic flow (355 +/- 23 msec). This temporal relation was maintained in the patients with aortic regurgitation. In contrast, in the patients with mitral regurgitation, the temporal relation was Tmax (266 +/- 49 msec), zero systolic flow (310 +/- 37 msec, p less than 0.01 vs. Tmax), and then, minV (355 +/- 37 msec, p less than 0.001 vs. Tmax and p less than 0.01 vs. Aodi). Additionally, the average Tmax occurred earlier in the patients with mitral regurgitation than in the control patients and patients with aortic regurgitation (p less than 0.01, for both), whereas the average time to minimum ventricular volume was similar in all three patient groups. Moreover, the average time to zero systolic flow also occurred earlier in the patients with mitral regurgitation than in the control patients (p less than 0.01) and patients with aortic regurgitation (p less than 0.05). Because of the dissociation of end systole from minimum ventricular volume in the patients with mitral regurgitation, the end-ejection pressure-volume relations calculated at minimum ventricular volume did not correlate (r = -0.09), whereas those calculated at zero systolic flow did correlate (r = 0.88) with the Emax slope values. We conclude that end ejection, defined as minimum ventricular volume, dissociates from end systole in patients with mitral regurgitation because of the shortened time to LV end systole in association with preservation of the time to LV end ejection due to the low impedance to ejection presented by the left atrium. Therefore, pressure-volume relations calculated at minimum ventricular volume might not be useful for assessing LV chamber performance in some patients with mitral regurgitation.

Chronic Disease↗
PubMedDate not supplied

Measurement of coronary flow using high-frequency intravascular ultrasound imaging and pulsed Doppler velocimetry: in vitro feasibility studies.

The recent development of intravascular ultrasound imaging offers the potential to measure blood flow as the product of vessel cross-sectional area and mean velocity derived from pulsed Doppler velocimetry. To determine the feasibility of this approach for measuring coronary artery flow, we constructed a flow model of the coronary circulation that allowed flow to be varied by adjusting downstream resistance and aortic driving pressure. Assessment of intracoronary flow velocity was accomplished using a commercially available end-mounted pulsed Doppler catheter. Cross-sectional area of the coronary artery was measured using a 20 MHz mechanical imaging transducer mounted on a 4.8 F catheter. The product of mean velocity and cross-sectional area was compared with coronary flow measured by timed collection in a graduated cylinder by linear regression analysis. Excellent correlations were obtained between coronary flow calculated by the ultrasound method and measured coronary flow at both ostial (r = 0.99, standard error of the estimate [SEE] = 13.9 ml/min) and distal (r = 0.98, SEE = 23.0 ml/min) vessel locations under steady flow conditions. During pulsatile flow, calculated and measured coronary flow also correlated well for ostial (r = 0.98, SEE = 12.7 ml/min) and downstream (r = 0.99, SEE = 9.3 ml/min) locations. That the SEE was lower for pulsatile as compared with steady flow may be explained by the blunting of the flow profile across the vessel lumen by the acceleration phase of pulsatile flow. These data establish the feasibility of measuring coronary artery blood flow using intravascular ultrasound imaging and pulsed Doppler techniques.

Coronary Circulation↗