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Biomedical subjects

N Kolev

Publications and source records attributed to N Kolev.

At least 37 records · Page 2Linked to original sources
PubMed1994

Influence of positive end-expiratory pressure on right and left ventricular performance assessed by Doppler two-dimensional echocardiography.

The advent of modern Doppler two-dimensional ultrasound technology has overcome the need of invasive measurements of several important cardiac parameters. It allows estimation of preload, contractility, and afterload. Positive end-expiratory pressure (PEEP) is associated with a reduction in cardiac output. The responsible mechanisms are controversial. To evaluate the cardiovascular responses to PEEP, we employed different Doppler hemodynamic indices for the first time, combined with conventional two-dimensional echocardiography. Twenty-one healthy, young, and unsedated volunteers were admitted to the study. Under spontaneous respiration, PEEP level was increased stepwise (0, 5, 7.5, 10, 12.5 cm H2O). At each PEEP level, the following right and left ventricular parameters were assessed with Doppler two-dimensional echocardiography: two-dimensional variables: end-diastolic volume indices (EDVI), ejection fraction (EF), and left ventricular afterload-LaPlace relation (combined with cuff systolic pressure); Doppler variables: cardiac index (CI) (combined with two-dimensional measure of valve area), maximum velocity (Vmax), time velocity integral (TVI), acceleration time (AT), deceleration time (DT), deceleration rate (DR), ratio of early to atrial peak (E/A), ratio of isovolumic contraction time to ejection time (IVCT/ET), and maximum blood acceleration (dv/dt) in aorta and main pulmonary artery. Increasing PEEP resulted in a proportional decrease in biventricular EDVI. Moreover, PEEP application is also causing a drop of CI, which is determined from a decrease in Vmax and TVI, while EF, IVCT/ET, dv/dt, Doppler trans-atrioventricular parameters, and afterload stay in normal ranges. Employing Doppler hemodynamic indices for the first time in this study setting clearly supports data that the drop in EDVI and CI during PEEP is caused by reduction in ventricular filling due to decreased venous return. Using the Doppler parameters IVCT/ET and dv/dt, changes in myocardial contractility, as well as changes in afterload (LaPlace relation) can be ruled out.

Adult↗
PubMed1990

[Doppler transmitral blood flow--a new method for assessing myocardial ischemia].

A new method for interpretation of Doppler transmitral flow is presented. The peak of the early diastole is divided into two time intervals and the velocity of the rising and falling of this peak is determined. The method was applied in 31 patients with ischemic heart disease proved by coronarography and 30 healthy persons before and after bicycle ergometry [correction of veloergometric] load. Statistically significant changes of the parameters studied were found. These changes were compared with parallel changes in the electrocardiogram (12 standard leads). This led to the conclusion that Doppler transmitral flow is a more sensitive method for the diagnosis of myocardial ischemia than the electrocardiogram.

Adult↗
PubMed1989

[M-echocardiographic determination of left-ventricular diastolic noncompliance, diastolic wall stress and the rate of relaxation of the circumferential muscle fibers].

New noninvasive contemporary indices for assessment of left ventricular diastolic function are presented. They can be obtained by the simultaneous recording of the M-echocardiographic left ventricular dimensions and the apexcardiogram. These indices are: left ventricular diastolic compliance, left ventricular wall stress and the velocity of the circumferential fibre shortening. These indices are statistically significantly changed to a greater extent in hypertrophic cardiomyopathies and to a lesser extent in ischemic heart disease and arterial hypertension and after nifedipin treatment they improve considerably. The left ventricular diastolic wall stress was studied in both types of left ventricular load: by volumetric load a twofold increased stress of the wall was registered while by tension load the stress of the wall was almost normal.

Adult↗
PubMed1986

Doppler two-dimensional echocardiographic determinations of right ventricular output and diastolic filling.

Two methods of measuring right ventricular cardiac output with pulsed Doppler two-dimensional echocardiography were developed in 29 patients who underwent cardiac catheterization and angiography. Using tricuspid inflow and main pulmonary artery outflow methods we determined cardiac output, and good correlations were observed between thermodilution and Doppler measurements (r = 0.93 and 0.89, respectively). Results by the two methods correlated closely in patients without regurgitant lesions. In patients with tricuspid regurgitation, right ventricular inflow was always greater than right ventricular outflow volume while the reverse was true in those with pulmonary insufficiency. Furthermore, we investigated the right ventricular peak filling rate as the Doppler peak diastolic velocity X cross-sectional area of the tricuspid annulus and half filling right ventricular fraction derived from the time velocity integral of the Doppler-determined velocity curve. For the tricuspid valve morphologically, the Doppler-derived velocity profile in diastole resembled the first derivative of the angiographic right ventricular volume curve. A significant correlation was observed between the Doppler echocardiographic and angiographic peak filling rate (r = 0.84). The results of the present study validate the use of Doppler two-dimensional quantitative measurements of the right ventricular output, regurgitant fraction and indexes of diastolic function.

Adolescent↗
PubMed1984

Combined echo-apexcardiographic assessment of left ventricular function in cardiomyopathy.

Eleven patients with hypertrophic obstructive cardiomyopathy (HOCM) and 9 patients with congestive cardiomyopathy (COCM) were studied to determine the usefulness of mean normalized velocity of circumferential fiber shortening (VCFS), mean normalized velocity of circumferential fiber lengthening (VCFL) and left ventricular diastolic distensibility obtained noninvasively from combined recordings of simultaneously calibrated left apex cardiogram and M-mode echogram. Twenty-two normal subjects were similarly investigated and served as a control. In HOCM VCFS were increased (1.83 +/- 0.2 s-1 versus 1.22 +/- 0.1 s-1 for controls, p less than 0.02) and both VCFL and diastolic distensibility were decreased (VCFL: 0.50 +/- 0.1 s-1 versus 1.32 s-1 in controls, p less than 0.001; diastolic distensibility: 0.03 +/- 0.004 cm/mmHg-1 compared with 0.18 +/- 0.003 cm/mmHg-1 for controls, p less than 0.001). In COCM all investigated indexes were diminished (VCFS: 0.49 +/- 0.1 s-1 versus 1.22 +/- 0.1 s-1 for controls, p less than 0.001; VCFL: 0.70 +/- 0.1 s-1 versus 1.32 +/- 0.1 s-1 in controls, p less than 0.01 and diastolic distensibility: 0.05 +/- 0.003 cm/mmHg-1 compared with 0.18 +/- 0.003 cm/mmHg-1 for controls, p less than 0.01). The echo-apexcardiographic indexes were significantly correlated with many analogous invasive indexes. It is concluded that the value of both M-mode echocardiography and calibrated apex cardiography is enchanced by a combination of the two methods which opens the possibility of a fresh approach to the noninvasive study of cardiac performance in cardiomyopathy.

Adult↗
PubMed1981

Assessment of left ventricular contraction and relaxation by systolic and diastolic time intervals measured from the first derivative of apexcardiogram in cardiomyopathy.

To determine the usefulness of the time intervals obtained from the first derivative of apexcardiogram (dA/dt) in assessing contraction and relaxation in cardiomyopathy, 11 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 9 patients with congestive cardiomyopathy (COCM) with hemodynamically and angiographically documented diagnosis were studied. As a control group 50 normal subjects were used. Since contraction and relaxation is dependent on preload and afterload, the time interval from R wave of electrocardiogram to the positive peak of dA/dt (R to dA/dt) and 2 relaxation parameters derived from negative peak dA/dt, early relaxation index (ERI) and total relaxation index (TRI) were investigated. In HOCM the R to dA/dt were shortened (55 +/- 13 msec versus 76 +/- 14 msec in controls, P less than 0.01) and both ERI and TRI were augmented (ERI: 12.5 +/- 9 versus 4.3 +/- 5 in controls, p less than 0.001; TRI: 147 +/- 29 versus 70 +/- 18 in controls, p less than 0.02). In COCM the R to dA/dt were elongated (124 +/- 14 msec versus 76 +/- 14 msec in controls, P less than 09.001) and both ERI and TRI were decreased (ERI: 2.1 +/- 4 versus 4.3 +/- 5 in controls, p less than 0.005; TRI: 41 +/- 17 versus 70 +/- 18 in controls, p less than 0.002)., Significant correlation between these indices and some internal parameters of myocardial performance were observed. These findings indicate that systolic and diastolic time intervals measured from the first derivative of apexcardiogram may be used as a reliable indices for evaluation of contraction and relaxation independently of preload and afterload.

Adult↗
PubMed1980

[1st derivatives of the apex cardiogram and carotid sphygmogram and their clinical use in aortic valve defects and hypertrophic subaortic stenosis].

Twenty seven patients with valvular aortic stenosis were examined as well 26 patients with hypertrophic subaortic stenosis and 48 subjects with sound hearts, to whom a record was made, consisting of electrocardiogram, phonocardiogram, carotis -- sphigmogram, first derivative of carotis-sphigmogram (dC/dt), apexcardiogram and first derivative of apexcardiogram (dA/dt). Slope index of carotis-sphigmogram was calculated on the base of dC/dt as well as the maximum rate of pressure elevation in carotid artery (max dC/dt), whereas on the base of dA/dt the slope index of apexcardiogram and the interval R--dA/dt were determined. In patients with valvular aortic stenosis dC/dt shows a statistically significance of diminution of the slope index of carotissphigmogram, reduction of max dC/dt and notched descendent arm of the positive peak from dC/dt. In the patients with hypertrophic subaortic stenosis an increased slope index of apexcardiogram was established and a shortening of R--dA/dt interval. It was concluded that dA/dt and dC/dt could give new additional data for the diagnosis and evaluation of the hemodynamics in valvular aortic defects and hypertrophic subaortic stenosis.

Adolescent↗
PubMed1979

[Biomechanical studies of rabbit tendons after repeated injections of corticosteroids].

The purpose of investigation was to determine and compare the mechanical properties of rabbit tendons, injected with celestone as well as noninjected. The authors accepted the dynamic module during cyclic loading and the damaging tension reduced to an unit of body weight of the rabbit. As a result of the experimental biochemical studies they found that tendons, injected with corticosteroids, presented reduced strength and increased deformity in comparison with the noninjected tendons. Histologic examinations, performed additionaly, revealed that the functional properties of the tendons, injected with corticosteroids, were altered before the occurrence of structural changes in the tendinous tissue.

Achilles Tendon↗
PubMed1979

[Phase analysis of the normal and postectopic left ventricular contractions in nonejection click-telesystolic apical murmur syndrome].

ECG, PCG, CSG and ACG were synchronously recorded in 25 patient with non-expulsion click syndrome -- telesystolic murmur as well as in 62 cardiac healthy subjects. With the investigation of the systolic and diastolic intervals, a prolongation of the transformation period was established (Q--1 = 72 +/- 12 msec) and a shortening of the isovolumetric relaxation (A2--0 = 63 +/- 10 msec). The ratio PPE/LVET (period prior to expulsion/left venticular expulsion time) is normal in patients with nonexpulsion click -- telesystolic apical murmur but the comparison of PPE/LVET with a normal contraction with that of the first post extrasystolic contraction shows a statistically significant shortening. The ratio PPE/LVET in prolapse of the mitral valve prior to extrasystole is 0.39 +/- 0.02, and during the first contraction with intensified stroke after a compensatory pause is 0.31 +/- 0.03 (p less than 0.02). The possibility for explanation of the changes in phase analysis are discussed and a conclusion is drawn that they reflect the existence of deviation in the left ventricular mechanics and hemodynamics in case of mitral valve prolapse.

Adolescent↗
PubMed1978

Apex-carotis diagram as related to systolic and diastolic time intervals in myocardial infarction.

Simultaneous recordings of the electrocardiogram, phonocardiogram carotid pulse tracing and left apex cardiogram were obtained in 32 patients with myocardial infarction and 62 normal subjects. This allowed to measure systolic and diastolic time intervals and to construct the apex-carotis diagram (ACD), a new mechanocardiographic method which integrates the carotid pulse tracing and the apexcardiogram in an orthogonal coordinate system. In myocardial infarction, the ACD showed a decrease of the field of ventricular filling, a decrease of the field of ventricular ejection and an increase of the diastolic subsegment. A. The measurement of time intervals showed statistically significant information in those which were directly related to the deformation of the ACD in patients with myocardial infarction.

Adult↗
PubMed1978

[Clinical use of the apex carotid diagram in mitral stenosis].

Apex-carotid diagram (ACD) is a new mechanic-cardiographic method, consisting in integration of carotis-sphygmogram and apex-cardiogram in one diagram. In the present work, 121 patients with mitral stenosis were examined. ACD in mitral stenosis is characterized by an extension of the field of ventricle filling (p less than 0.05) and diminished angle alpha' (p less than 0.001). A reliable correlation was established between the values of angle alpha' and the mean pressure in the left ventricle r = -0.88, p less than 0.001 with a standard deviation of +/- mm Hg.

Adolescent↗