Biomedical subjects

S Marakas

Publications and source records attributed to S Marakas.

4 recordsLinked to original sources

PubMed1997

Unfavorable effect of smoking on the elastic properties of the human aorta.

BACKGROUND: Smoking is a major risk factor for cardiovascular morbidity and mortality. Because previous studies have shown that smoking affects vasomotor response, we hypothesized that smoking may also acutely alter aortic elastic properties. METHODS AND RESULTS: We studied 40 male current and long-term smokers who underwent diagnostic cardiac catheterization for chest-pain evaluation. Twenty subjects (age, 48 +/- 2 years, mean +/- SEM) were randomly assigned to smoking and 20 (age, 47 +/- 2 years) to sham smoking studies. Aortic elastic properties were studied with the determination of the aortic pressure-diameter relation before smoking, every minute for the first 5 minutes after the initiation of smoking or sham smoking, and every 5 minutes for the following 15 minutes. Instantaneous diameter of the thoracic aorta was measured with a special ultrasonic dimension catheter developed in our laboratory and previously validated. Instantaneous aortic pressure was measured at the same site as was diameter with a Millar micromanometer. Smoking was associated with significant changes in the aortic pressure-diameter relation that denote deterioration of the elastic properties and were maintained during the whole study period: the slope of the pressure-diameter loop became steeper (baseline, 35.43 +/- 1.38; minute 1, 45.26 +/- 1.65; peak at minute 10, 46.36 +/- 1.69 mm Hg/mm; P < .001) and aortic distensibility decreased (baseline, 2.08 +/- 0.12; minute 1, 1.60 +/- 0.08; nadir at minute 5, 1.54 +/- 0.07 x 10(-6) cm2.dyne-1; P < .001). In contrast, no changes in aortic elasticity indexes were observed with sham smoking. CONCLUSIONS: Smoking is associated with an acute deterioration of aortic elastic properties. This effect of smoking may contribute to the unfavorable consequences of smoking on the cardiovascular system.

Aorta, Thoracic↗

PubMed1995

Pressure-diameter relation of the human aorta. A new method of determination by the application of a special ultrasonic dimension catheter.

BACKGROUND: Pressure-diameter relation of the aorta provides important information about the elastic properties of the vessel. However, owing to methodological limitations, data regarding this relation are limited in conscious humans. In the present study, we assessed a new method for the direct estimation of the elastic properties of the aorta in conscious humans by simultaneous acquisition of instantaneous aortic pressure and diameter. METHODS AND RESULTS: With this method, instantaneous diameter of the thoracic aorta was acquired by a newly designed intravascular catheter developed in our institution that incorporates an ultrasonic displacement meter at its distal end. Instantaneous aortic pressure was acquired simultaneously at the same aortic level with a catheter-tip micromanometer. Aortic pressure-diameter loops were derived from computer analysis of data. After in vitro and animal testing, elastic properties of the aorta were investigated in coronary artery disease (CAD) patients (n = 15) and compared with those of control subjects (n = 10). Aortic distensibility was less in the CAD group than in the control group (1.73 +/- 0.33 versus 3.95 +/- 1.09 x 10(-6) x cm2 x dyne-1, P < .001). Compared with control subjects, the mean value of the slope of the pressure-diameter loops was significantly greater in the CAD group (38.89 +/- 8.75 versus 19.62 +/- 5.46 mm Hg.mm-1, P < .001), whereas the mean value of the intercept was lower in this latter group of patients (-785.60 +/- 177.55 versus -313.43 +/- 126.41 mm Hg, P < .001). An excellent correlation was found between the slope of pressure-diameter loop and age in the group of control subjects (r = .827). Ninety-three percent of the patients with CAD had values above the upper 95% confidence limits of the control subjects (P < .001). In a third group of patients (n = 16) in whom assessment of pulse wave velocity was also included in the study of the elastic properties of the aorta, pulse wave velocity had a strong inverse correlation with aortic distensibility (r = -.95) and a strong positive correlation with the slope of the pressure-diameter loop (r = .97). CONCLUSIONS: This new method of determination of pressure-diameter of the aorta enables an accurate and reliable evaluation of the elastic properties of the aorta in conscious humans and may be useful for a profound study of human aorta mechanics.

Animals↗

PubMed1995

A generic environment for linear and nonlinear ECG processing.

Every aspect of cardiac function such as contractibility, depolarization and repolarization of cardiac cells, firing rate of pacemaker cells, is under a complex neurohumoral regulation. Especially the autonomic neuron system through the interplay of its two opposing components, sympathetic and parasympathetic (vagal), is controlling cardiac function on a beat to beat basis. Moreover, the interaction of sympathetic and parasympathetic systems is a non-linear function, with sympathetic tone modulating the response of vagal activation. It has been shown that the power of frequency components and especially the ratio of low to high frequency power spectra of heart rate variability are reliable indicators of sympathovagal balance (A. Malliani et al. 1991. Cardiovascular Neural regulation explored in the frequency domain. Circulation, 84 (2) 482-484. The most known algorithms of linear and non-linear signal processing have been applied to the ECG data recorded from healthy and high risk individuals. These methods together with the study and analysis of QRS frequency spectrum will lead to very useful conclusions with diagnostic and prognostic information. In this paper we will briefly describe the mathematical aspect of these algorithms presenting their results for normal and pathological ECG signals.

Adult↗

PubMed1993

Plasma atrial natriuretic factor in uncomplicated acute myocardial infarction.

Plasma atrial natriuretic factor (ANF) levels were measured in 29 patients who had normal atrial hemodynamics on days 4 and 8 after an uncomplicated acute myocardial infarction (AMI). All patients had increased ANF levels on day 4. On day 8 of the ANF levels had declined significantly to normal values in 14 patients with enzymatically smaller AMI and higher ejection fractions (> or = 40%), while they remained elevated in 16 patients with larger AMI and lower ejection fractions (< 40%). The study data are compatible with increased secretion of ANF by the more extensively damaged left ventricles in AMI.

Adult↗