Duration of phases of left ventricular systole using indirect methods. I. Normal subjects

A mathematical model that integrates cardiac electrophysiology, mechanics, and fluid dynamics: Application to the human left heart

We propose a mathematical and numerical model for the simulation of the heart function that couples cardiac electrophysiology, active and passive mechanics and hemodynamics, and includes reduced models for cardiac valves and the circulatory system. Our model accounts for the major feedback effects among the different processes that characterize the heart function, including electro-mechanical and mechano-electrical feedback as well as force-strain and force-velocity relationships. Moreover, it provides a three-dimensional representation of both the cardiac muscle and the hemodynamics, coupled in a fluid-structure interaction (FSI) model. By leveraging the multiphysics nature of the problem, we discretize it in time with a segregated electrophysiology-force generation-FSI approach, allowing for efficiency and flexibility in the numerical solution. We employ a monolithic approach for the numerical discretization of the FSI problem. We use finite elements for the spatial discretization of partial differential equations. We carry out a numerical simulation on a realistic human left heart model, obtaining results that are qualitatively and quantitatively in agreement with physiological ranges and medical images.

Resolution and Speckle Reduction in Cardiac Imaging

Cardiac imaging depends on clear visualization of several different structural and functional components to determine left ventricular and overall cardiac health. Ultrasound imaging is confounded by the characteristic speckle texture resulting from subwavelength scatterers in tissues, which is similar to a multiplicative noise on underlying tissue structure. Reduction of this texture can be achieved through physical means, such as spatial or frequency compounding, or through adaptive image processing. Techniques in both categories require a tradeoff of resolution for speckle texture reduction, which together contribute to overall image quality and diagnostic value. We evaluate this tradeoff for cardiac imaging tasks using spatial compounding as an exemplary speckle reduction method. Spatial compounding averages the decorrelated speckle patterns formed by views of a target from multiple subaperture positions to reduce the texture at the expense of active aperture size (and, in turn, lateral resolution). We demonstrate the use of a novel synthetic aperture focusing technique to decompose harmonic backscattered data from focused beams to their aperture-domain spatial frequency components to enable combined transmit and receive compounding. This tool allows the evaluation of matched data sets from a single acquisition over a wide range of spatial compounding conditions. We quantified the tradeoff between resolution and texture reduction in an imaging phantom and demonstrated improved lesion detectability with increasing levels of spatial compounding. We performed a cardiac ultrasound on 25 subjects to evaluate the degree of compounding useful for diagnostic imaging. Of these, 18 subjects were included in both qualitative and quantitative analysis. We found that compounding improved detectability of the endocardial border according to the generalized contrast-to-noise ratio in all cases, and more aggressive compounding made further improvements in ten out of 18 cases. Three expert reviewers evaluated the images for their usefulness in several diagnostic tasks and ranked four compounding conditions ("none," "low," "medium," and "high"). Contrary to the quantitative metrics that suggested the use of high levels of compounding, the reviewers determined that "low" was usually preferred (77.9%), while "none" or "medium" was selected in 21.2% of cases. We conclude with a brief discussion of the generalization of these results to other speckle reduction methods using the imaging phantom data.

Normal values of regional left ventricular myocardial thickness, mass and distribution-assessed by 320-detector computed tomography angiography in the Copenhagen General Population Study

Left ventricular (LV) hypertrophy is associated with cardiovascular complications and the geometry is important for prognosis. In some cardiovascular diseases, myocardial hypertrophy or dilation occurs regionally without modifying the global size of the heart. It is therefore relevant to determine regional normal reference values of the left ventricle. The aim of this study was to derive reference values of regional LV myocardial thickness (LVMT) and mass (LVMM) from a healthy study group of the general population using cardiac computed tomography angiography (CCTA). We wanted to introduce LV myocardial distribution (LVMD) as a measure of regional variation of the LVMT. Moreover, we wanted to determine whether these parameters varied between men and women. We studied 568 (181 men; 32%) adults, free of cardiovascular disease and risk factors, who underwent 320-detector CCTA. Mean age was 55 (range 40-84) years. Regional LVMT and LVMM were measured, according to the American Heart Association's 17 segment model, using semi-automatic software. Mean LVMT were 6.6 mm for men and 5.4 mm for women (p < 0.001). The normal LV was thickest in the basal septum (segment 3; men = 8.3 mm; women = 7.2 mm) and thinnest in the mid-ventricular anterior wall (segment 7; men = 5.6 mm; women = 4.5 mm) for both men and women. However, the regional LVMD differed between men and women, with the LV being most heterogenic in women. The normal human LV is morphologically heterogenic, and showed same overall pattern but different regional distribution for men and women. This study introduces LVMD and provides gender specific reference values for regional LVMT, LVMM, and LVMD.

Instrumentation to study myofibril mechanics from static to artificial simulations of cardiac cycle

Many causes of heart muscle diseases and skeletal muscle diseases are inherited and caused by mutations in genes of sarcomere proteins which play either a structural or contractile role in the muscle cell. Tissue samples from human hearts with mutations can be obtained but often samples are only a few milligrams and it is necessary to freeze them for storage and transportation. Myofibrils are the fundamental contractile components of the muscle cell and retain all structural elements and contractile proteins performing in contractile event; moreover viable myofibrils can be obtained from frozen tissue.•

We are describing a versatile technique for measuring the contractility and its Ca²⁺ regulation in single myofibrils. The control of myofibril length, incubation medium and data acquisition is carried out using a digital acquisition board via computer software. Using computer control it is possible not only to measure contractile and mechanical parameters but also simulate complex protocols such as a cardiac cycle to vary length and medium independently.

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This single myofibril force assay is well suited for physiological measurements. The system can be adapted to measure tension amplitude, rates of contraction and relaxation, Ca²⁺ dependence of these parameters in dose-response measurements, length-dependent activation, stretch response, myofibril elasticity and response to simulated cardiac cycle length changes. Our approach provides an all-round quantitative way to measure myofibrils performance and to observe the effect of mutations or posttranslational modifications. The technique has been demonstrated by the study of contraction in heart with hypertrophic or dilated cardiomyopathy mutations in sarcomere proteins.

Defining the optimal systolic phase targets using absolute delay time for reconstructions in dual-source coronary CT angiography

To define the optimal systolic phase for dual-source computed tomography angiography using an absolute reconstruction delay time after the R-R interval based on the coronary artery motion, we analyzed images reconstructed between 200 and 420 miliseconds (ms) after the R wave at 20 ms increments in 21 patients. Based on the American Heart Association coronary segmentation guidelines, the origin of six coronary artery landmarks (RCA, AM1, PDA, LM, OM1, and D2) were selected to calculate the coronary artery motion velocity. The velocity of the given landmark was defined as the quotient of the route and the length of the time interval. The x, y and z-coordinates of the selected landmark were recorded, and were used for the calculation of the 3D route of coronary artery motion by using a specific equation. Differences in velocities were assessed by analysis of variance for repeated measures; Bonferroni post hoc tests were used for multiple pair wise comparisons. 1488 landmarks were measured (6 locations at 12 systolic time points) in 21 patients and were analyzed. The mean values of the minimum velocities were calculated separately for each heart rate group (i.e. <65; 65-80; and >80 bpm). The mean lowest coronary artery velocities in each segment occurred in the middle period of each time interval of the acquired systolic phase i.e. 280-340 ms. No differences were found in the minimal coronary artery velocities between the three HR groups, with the exception of the AM1 branch (p = 0.00495) between <65 and >80 bpm (p = 0.03), and at HRs of 65-80 versus >80 bpm (p = 0.006). During an absolute delay of 200-420 ms after the R-wave, the ideal reconstruction interval varies significantly among coronary artery segments. Decreased velocities occur between 280 to 340 ms. Therefore a narrow range of systolic intervals, rather than a single phase, should be acquired.

The influence of calculation method on estimates of cerebral critical closing pressure

The critical closing pressure (CrCP) of cerebral circulation is normally estimated by extrapolation of instantaneous velocity-pressure curves. Different methods of estimation were analysed to assess their robustness and reproducibility in both static and dynamic applications. In ten healthy subjects (mean ± SD age 37.5 ± 9.2 years) continuous recordings of arterial blood pressure (BP, Finapres) and bilateral cerebral blood flow velocity (transcranial Doppler ultrasound, middle cerebral arteries) were obtained at rest. Each session consisted of three separate 5 min recordings. A total of four recording sessions for each subject took place over a 2 week period. A total of 117 recordings contained 34 014 cardiac cycles. For each cardiac cycle, CrCP and resistance-area product (RAP) were estimated using linear regression (LR), principal component analysis (PCA), first harmonic fitting (H1), 2-point systolic/diastolic values (2Ps) and 2-point mean/diastolic values (2Pm). LR and PCA were also applied using only the diastolic phase (LRd, PCAd). The mean values of CrCP and RAP for the entire 5 min recording ('static' condition) were not significantly different for LRd, PCAd, H1 and 2Pm, as opposed to the other methods. The same four methods provided the best results regarding the absence of negative values of CrCP and the coefficient of variation (CV) of the intra-subject standard error of the mean (SEM). On the other hand, 'dynamic' applications, such as the transfer function between mean BP and RAP (coherence and RAP step response) led to a different ranking of methods, but without significant differences in CV SEM coherence. For the CV of the RAP step response though, LRd and PCAd performed badly. These results suggest that H1 or 2Pm perform better than LR analysis and should be used for the estimation of CrCP and RAP for both static and dynamic applications.

Systolic time intervals in acute myocardial infarction

Systolic time intervals (STI) have been measured in 50 individuals without heart disease. Electromechanical systole (QS2), left ventricular ejection time (LVET) and preejection period (PEP), but not PEP/LVET, were correlated to heart rate (HR). Regression equations were made and used when correcting STI for HR in two groups of patients: a) 51 patients with acute myocardial infarction (AMI) b) 22 patients with chest pains, but no AMI. STI was measured on the first 4 days, on the 7th day, on the day of discharge and at a control about 60 days later. In the AMI group there was a reduction in left ventricular performance from the 1st to the 4th day, and the difference in shortening of LVET was significant (p less than 0.001), while PEP and PEP/LVET increased from the 1st to the 3rd day (p less than 0.001). Between the AMI and the control groups there were significant differences (p less than 0.001) in LVET and PEP/LVET on the 3rd, 4th and 7th day, and in PEP on the 3rd and 4th day. STI was not found to separate clinical groups with heart failure of different severity. The survivors had a lower (p less than 0.05) PEP/LVET on the 1st day than those who died. The various localization of the infarction made no difference in STI. LVET was found to be strongly correlated (p less than 0.001) to the hydroxybutyric dehydrogenase values.

Validation of a simple method of assessing cardiac preejection period: a potential index of sympathetic nervous system activity

Traditional noninvasive assessment of sympathetic nervous system (SNS) activity in cardiovascular functioning has been confounded by concurrent parasympathetic influences. Analyses of specific intervals of the cardiac cycle have indicated that the systolic preejection period (PEP) may serve as a reliable index of SNS activity independent of parasympathetic inhibition. In the present study, PEP values derived from a technique employing peripheral pulse wave tracings were compared to values obtained from simultaneous impedance cardiograph recordings. Recordings were made on 15 male subjects who were instructed to rest quietly sitting in an upright position. Results indicated that values obtained from both methods were highly correlated and not significantly different when measurement adjustments on total systole were taken into account. These findings support the validity of the fingertip peripheral-pulse method in obtaining measures of systolic time intervals under resting conditions.

The therapeutic implications of diastolic time changes in systemic hypertension

Twenty-five patients with chronic systemic hypertension were studied. Systolic time intervals and diastolic time were determined at baseline and after 12 weeks of therapy with nadolol, with or without bendroflumethiazide (treatment phase I), then after 12 weeks of therapy with hydralazine, bendroflumethiazide, or both (treatment phase II). Systolic, diastolic, and mean blood pressures were equally controlled after either treatment regimen. Heart rate was significantly slower after treatment phase I compared to baseline or after treatment phase II (p less than 0.001). Systolic time per minute was significantly shorter and diastolic time per beat and per minute were significantly longer after treatment phase I compared to baseline or after treatment phase II (p less than 0.001). Double and triple products decreased after either mode of therapy; however, these parameters were significantly lower after treatment phase I compared to treatment phase II (p less than 0.01). These changes in systolic and diastolic time and double and triple products may be of clinical significance during therapy of chronic systemic hypertension and may help explain the regression of left ventricular hypertrophy in patients with hypertension treated with sympathetic blocking agents.

Systolic time intervals reconsidered. Reevaluation of the preejection period: absence of relation to heart rate

Within limits, systolic time intervals are reliable reflectors of cardiac status and responses to physiologic and pharmacologic challenges, with various functional correlates. That heart rate (HR) is an important determinant of the duration of systole is well accepted, owing to its effect on left ventricular ejection time (LVET). An independent rate effect on preejection period (PEP) is disputed. Some studies in pooled normal subjects at rest showed some degree of HR-PEP covariance, leading to widespread rate correction in practical use. However, although right atrial pacing showed the expected HR-LVET relation, it consistently failed to show an HR-PEP relation. Systolic time intervals were examined from echocardiograms of a deliberately heterogeneous group comprising 50 consecutively appearing persons with sinus rhythm. There was no HR-PEP covariance (r = 0.23; p = not significant). However, our subjects were otherwise comparable to those of other investigators, in that all other relations in these subjects were as expected from studies in both pooled and paced subjects: HR with LVET (r = -0.74; p less than 0.001), PEP/LVET with ejection fraction (r = -0.85; p less than 0.001), and PEP/LVET with velocity of circumferential fiber shortening (r = -0.65, p less than 0.001). Thus, HR correction of PEP is inappropriate. All other relations are substantiated in routinely encountered, unselected subjects.

High-fidelity, infinite time constant calibrated pressure apexcardiogram and its correlation with high-fidelity left ventricular pressure

Images

Serial measurements of systolic time intervals: effects of propranolol alone and combined with other agents in hypertensive patients

Systolic time intervals (STI) were recorded serially before and during 1 year of treatment in 367 hypertensive men. The patients were randomly assigned, double-blind, to one of the following regimens: propranolol alone (P), propranolol plus hydrochlorothiazide (P + T), propranolol plus hydralazine (P + H), propranolol plus hydrochlorothiazide plus hydralazine (P + T + H), or reserpine plus hydrochlorothiazide (R + T). Systolic time intervals were calculated by a computer pattern-recognition and measurement program. Diastolic blood pressure and heart rate (HR) decreased with each treatment regimen. The preejection period (PEP) was prolonged following P alone. The left ventricular ejection time (LVET), after correction for HR, was shortened with P + T and R + T and prolonged after P + H. The PEP/LVET was reduced with P + H. The prolongation of PEP during long-term administration of P is comparable with previous studies of its acute effects and suggests a moderate decrease in left ventricular performance. Calculation of STI also appears to be a useful method for showing the effects of adding other antihypertensive agents.

Haemodynamic effects of a new beta 1-receptor agonist in acute myocardial infarction. A useful antidote to unwanted cardiac effects of beta-blocking agents

The haemodynamic effects of a new beta 1-receptor agonist, 1-(4 hydroxyphenoxy) 3-isopropylamino-2-propanol, were studied in 25 patients after acute myocardial infarction using non-invasive methods. The drug caused an increase in systolic blood pressure and pulse pressure, without change in diastolic blood pressure, and a slight increase in heart rate and reduction in the pre-ejection period. These changes were greater in patients without a history of left heart failure. It is suggested that this cardioselective drug possesses positive inotropic activity but only slight positive chronotropic activity. The substance has been further investigated as a possible antidote to unwanted cardiac side effects of the cardioselective beta-blocker, metoprolol. The changes in the cardiovascular dynamics caused by metoprolol in patients with acute myocardial infarction were promptly reversed by this new beta 1-agonist. With its positive inotropic properties and its efficacy in reversing the effects of a cardioselective beta-blocker, the drug is a potentially useful pharmacological agent to support an acutely depressed myocardium in patients on beta-blocking agents.

Effects of precurarization on the heart measured by systolic time intervals

The effects of precurarization, with or without prior atropine medication, on heart rate, systolic time intervals (preejection period (PEP) and left ventricular ejection time (LVET)) and derivatives from these were studied in 80 healthy patients before minor surgery. Atropine (0.5-0.7 mg i.v.) exerted a vagolytic action with no changes in systolic time intervals. D-tubocurarine (0.5 mg/kg b.w.) did not affect heart rate or systolic time intervals. Both gallamine (0.3 mg/kg b.w.) and pancuronium (0.015 mg/kg b.w.) increased heart rate due to the inherent vagolytic effect. Furthermore, a short-lasting decrease in PEP and an increase in LVET were demonstrated. Consequently, a fall in PEP/LVET and a rise in 1/PEP2 were induced, indicating an increase in cardiac pump performance. These changes were blocked by prior atropine medication, a result which is not easily explainable. Possible clinical implications are discussed.

A study of systolic time intervals during uninterrupted exercise

A method has been developed for obtaining measurements of the systolic time intervals during uninterrupted graded exercise in the upright position on a bicycle ergometer. The method has been applied to 112 subjects divided into 4 groups: two of normal subjects below and above the age of 40, respectively (mean ages 30 and 48 years), and two of patients (mean ages for each about 50 years), both with coronary insufficiency, but one without and the other with abnormality of left ventricular function as shown by ventriculography. The measurements obtained yield linear relations between total electromechanical systole (QS2) and heart rate, between pre-ejection period (PEP) and RR interval for each subject. The average standard deviation about the regression is less than 6 ms for all three regression lines; the average correlation coefficient is greater than 0-93. The younger group of normal subjects have a significantly shorter PEP compared to the older group. Indices have been derived which separate the patient groups from each other and from the normal subjects. Using these indices 86 per cent of all the subjects were correctly classified according to the group to which they belonged. It is concluded that measurements of STI during uninterrupted exercise offer valuable information in the assessment of cardiac patients.

Influence of heart rate increase on uncorrected pre-ejection period/left ventricular ejection time (PEP/LVET) ratio in normal individuals

In 26 normal volunteers, increase in heart rate from mean 73-94 +/- 1-97 to 103-61 +/- 2-72/min, by either intravenous atropine administration or rapid right atrial pacing, produced definite changes in the uncorrected systolic time intervals. As expected, total electromechanical systole (QS2) and left ventricular ejection time (LVET) were shortened, while the pre-ejection period (PEP) was unaffected. There was a consistent and significant increase of the PEP/LVET ratio (P less than 0-001). It is postulated that when this ratio is taken to express left ventricular contractility, it should probably be corrected for heart rate. Appropriate regression equations for such a correction were calculated (PEP/LVET=0-249 + 0-0168 HR).

Relationship between duration of systolic upstroke of apexcardiogram and internal indexes of myocardial function in man

In 11 patients with nonobstructive cardiomyopathy and coronary heart disease and decreased myocardial function of the left ventricle, as well as in nine patients without left heart valvular or myocardial disease, left apexcardiograms were recorded during diagnostic heart catheterization, wherein micromanometers were used; ACG's were registered additionally in 54 healthy volunteers in order to establish the normal range of apexcardiographic parameters. In all cases the apex tracings were recorded by means of a pulse transducer with infinite time constant. The most important finding of this study was the close correlation between the duration of the systolic upstroke (SUT) of the apex tracing and some accepted isovolumic indexes of left heart function (isovolumic contraction time, time interval from the onset to peak of the first derivative of left ventricular pressure, maximal value of the first derivative of left ventricular pressure, and the peak measured velocity of shortening of the contractile elements). Further, the mean value of SUT in patients with impaired left myocardial function was significantly prolonged, compared to the control subjects; an overlap was apparent due to the fact that some of these patients showed a normal left myocardial performance at rest, having an abnormal response only to exercise tests. The apexcardiographic SUT can practically always be measured when the first derivative of apex tracing is simultaneously recorded. It showed itself to be only slightly influenced by the resting heart rate. The mentioned relationship of the systolic upstroke time of the ACG to internal isovolumic indexes of myocardial function makes this noninvasive measurable parameter an additional excellent tool for the evaluation of the left myocardial state, thus supporting a new aspect of the value of quantitative apexcardiography.

Ejection time--heart rate relationship during exercise

The slope of the regression equation for left ventricular ejection time (LVET) vs heart rate (HR) is the appropriate factor for correcting LVET for HR. Because the regression relationship varies under different conditions, we determined the LVET-HR equations for subjects (1) seated at rest on a bicycle ergometer, and (2) during uninterrupted bicycle exercise. In 18 normally active male volunteers, ages 22-37, HR and LVET were measured under the two conditions and the regression relationship for LVET on HR determined for each. Regression equations are as follows: (1) LVET = 379-1.8 HR +/- 11.0 for subjects seated at rest on a bicycle ergometer, and (2) LVET = 371-1.2 HR +/- 13.9 for subjects performing upright bicycle exercise. The slope factors (1.8 and 1.2) differed significantly (p less than 0.01). The data indicate that considerable error can result from arbitrarily applying to exercising or resting subjects a correction factor which does not fit the conditions of the data to be corrected.

Time relation between apex cardiogram and left ventricular events using simultaneous high-fidelity tracings in man

In 10 patients without left heart valvular disease and having normal function of the left ventricle, the left ventricular apex cardiogram with its first derivative (dA/dt), left ventricular pressure with its first derivative (dP/dt), aortic pressure, electrocardiogram, and phonocardiogram were reocrded simultaneously during cardiac catheterization. The apex cardiographic tracings were obtained by means of a transducer with infinite time constant and very high resonant frequency and the LV and aortic pressures with catheter tip-manometers. The onset of the systolic rise of apex cardiographic and LV pressures were found to occur almost simultaneously with the upstroke of LV pressure, preceding that of the apex cardiogram by only 2 +/- 4 ms (mean +/- 1 SD). The summit of the systolic upstroke of the apex cardiogram (called E-point) occurred 37 +/- 9 ms after opening of the aortic valve and 41 +/- 9 ms after peak dP/dt. The peak of dA/dt preceded peak dP/dt by 10 +/- 4 ms. The protodiastolic nadir of the apex cardiogram (called-O-point) occurred slightly earlier (19 +/- 16 ms) than the nadir of the LV pressure curve, with considerable variation. In conclusion, this study using external and internal transducers with similar characteristics gives a new definition of the time relation between the externally recorded apex cardiogram and the haemodynamic events within the left heart in human subjects with normal left ventricular function.

Value of systolic time intervals in assessing severity of congenital aortic stenosis in children

Simultaneous recordings have been made of electrocardiogram, phonocardiogram, carotid pulse tracing, left ventricular pressure, and aortic pressure in 27 children with aortic valve stenosis and 3 children with membranous subaortic stenosis. Peak systolic pressure difference ranged from 10 to 110 mmHg (1.3 to 14.6 kPa). None of the patients had congestive heart failure and cardiac output was in the normal range in all. Total electromechanical systole, left ventricular ejection time, and pre-ejection time were corrected for heart rate, age, and sex. Mild stenosis (peak systolic pressure difference less than or equal to 50 mmHg (6.7 kPa)) was present in 18, severe stenosis (peak systolic pressure difference greater than 50 mmHg) in 12 patients. The externally measured pre-ejection time and ejection time proved to be nearly equal to the corresponding intervals measured internally; from these data it is concluded that pre-ejection time and ejection time in children with aortic stenosis can be measured reliably by non-invasive methods. Mean values for corrected total electromechanical systole and ejection time were prolonged, but the corrected pre-ejection time did not differ from the normal value. When corrected time intervals were plotted against severity of the aortic stenosis as expressed by the peak systolic pressure difference or the aortic valve orifice index, a wide scatter was found. It is concluded that a normal ejection time is strong evidence against a peak systolic pressure difference of more than 50 mmHg (6.7 kPa) or an aortic valve orifice index less than 0.70 cm2 per m2 BSA. A prolonged ejection time, however, may occur in mild as well as in severe stenosis. Total electromechanical systole and pre-ejection time have no value in predicting the severity of aortic stenosis in children.

Effects of age on responses to isometric exercise. Isometric handgrip in noninvasive screening for cardiovascular disease

Isometric handgrip (IHG) imposes an acutely increased afterload on the left ventricle. Utilizing systolic time intervals, we studied various responses to IHG, measured as changes from resting values with near-maximum IHG, in old normal (ON) subjects, young normal (YN) subjects, and old patients with hypertensive heart disease (HHD) and patients with coronary artery disease (CAD). There were no differences in responses to IHG between ON and patients with HHD or patients with CAD. However, there were clear differences between the responses of ON and YN subjects. Increase in heart rate (HR) was much more prominent in YN (ON vs. YN = +11.6 +/- 2.6 vs. +15.6 +/- 5.7 beats per minute p less than 0.001). Pre-ejection period (PEP) end isovolumic contraction time (IVCT) increased in ON but decreased in YN (PEP + 6.2 +/- 1.7 vs. -11.0 +/- 3.7 msec., p less than 0.001; IVCT +8.1 +/- 2.2 vs. -13.8 +/- 3.4 msec., p less than 0.001. Shortening of LVET was much more marked in YN (-6.5 +/- 4.1 VS. -63.3 +/- 9.9 msec. p less than 0.001), but this was entirely due to the HR differences since there was no difference in ejection time index (+ 5.1 +/- 3.4 vs. -0.4 +/- 7.3 msec. p greater than 0.5). IHG produced no significant differences between ON and YN in the timing of the "mitral" component of the first heart sound (q-Im), in the ratio PEP/LVET, or in pulse transmission time (PTT). By contrast, resting control PTT was markedly short in ON, especially those with CAD. Resting PTT in ON was 27.1 +/- 2.6 msec.; in YN 43.7 +/- 1.4 msec.; in CAD patients 20.7 +/- 1.3 msec. We conclude that even near-maximal IHG does not seem to be an adequate noninvasive screening test for cardiovascular disease in that age alone seems to have the most significant influence on the responses.

Evaluation of impedance cardiography as a non-invasive means of measuring systolic time intervals and cardiac output

Impedance cardiography was used for non-invasive determinations of systolic time intervals (STI) and cardiac output. The results were compared with simultaneously obtained invasive measurements of STI from central aortic pressure curves and of cardiac output using the dye-dilution technique. The study was performed on eight dogs during increasing halothane concentration. A close correlation was found between non-invasively and invasively measured left ventricular ejection time = LVET (r = 0.986) and pre-ejection period - PEP (r - 0.948). Measurements of cardiac output derived from changes in thoracic impedance were determined 1) using a fixed value of p (p - the resistivity of blood) and 2) using an individual value of p based on the actual hematocrits. When compared to cardiac outputs obtained by dye-dilution the correlation coefficients were r = 0.806 and r = 0.816, respectively. Impedance cardiography is a useful method of evaluating changes in cardiac output. The method permits simultaneous observations of changes in STI and cardiac output as an index of cardiac function.

Cardiac function during halothane anf fluroxene anesthesia expressed by systolic time intervals

A non-invasive method of measuring the systolic time intervals (STI) during anesthesia is described. Using the ratio between the pre-ejection period and the left ventricular ejection time (PEP/LVET-ratio) as an expression of cardiac function, it is shown in 39 patients that thiopentone exerted a marked depression on the heart (increase in PEP/LVET-ratio). This depression was further aggravated by halothane, while fluroxene caused an improvement of PEP/LVET-ratio. In the immediate post-anesthetic period PEP/LVET-ratio almost reached control value after discontinuation of fluroxene in contrast to halothane, where an increased PEP/LVET-ratio (25%) still persisted. The changes were mainly due to a prolongation of PEP without any specific change in LVET. During the study, PEP/LVET-ratio showed a close correlation to the reciprocal value of the square of the pre-ejection period (1/PEP-2). STI form 27 volunteers were measured and compared to the values from the patients before anesthesia was induced. PEP and PEP/LVET-ratio were significantly shorter in the patient group.

Effects of posture on exercise performance. Measurement by systolic time intervals

Because posture significantly influences cardiac performance, the effects of moderate supine and upright ergometer exercise were compared on the basis of proportional (+37%) rate increments over resting control. Supine exercise produced significant decreases in left ventricular ejection time (LVET), pre-ejection period (PEP), and isovolumic contraction time (IVCT). Ejection time index (ETI) and "corrected ejection time" (LVETc) did not change significantly. Upright exercise produced greater decreases in PEP and LVET, but despite the rate increase there was no change in LVET, which resulted in sharp increases in ETI and LVETc. The discordant directional effects on LVET and its rate-correcting indices between the two postures were consistent with hemodynamic studies demonstrating lack of stroke volume change during supine exercise and increased stroke volume over control during light to moderate upright exercise. Concordant effects on PEP and IVCT are consistent with the inotropic effect of exercise in both postures with an additional Frank-Starling effect postulated during upright exercise.