Dynamic cardiac compression improves contractile efficiency of the heart

The effect of dynamic cardiac compression on left ventricular contractile efficiency was assessed in terms of the pressure-volume relationship and myocardial oxygen consumption. In 11 excised cross-circulated dog hearts, the ventricle was directly compressed during systole (dynamic cardiac compression). Measurements for pressure-volume area (a measure of total mechanical energy), external work, and myocardial oxygen consumption were done before and during dynamic cardiac compression. Dynamic cardiac compression increased pressure-volume area by 28% +/- 17% (mean plus or minus the standard deviation) and external work by 24% +/- 20% (p = 0.0000185 and 0.0000212, respectively) at given end-diastolic and stroke volumes without affecting myocardial oxygen consumption. As a result, the oxygen cost of pressure-volume area, that is, the slope of the myocardial oxygen consumption-pressure-volume area relationship, significantly decreased by 16% +/- 13% (p = 0.0000135) whereas the pressure-volume area-independent myocardial oxygen consumption was unchanged. Then, contractile efficiency, that is, the reciprocal of the slope of the myocardial oxygen consumption-pressure-volume area relationship in joules significantly improved from 45% +/- 8% to 53% +/- 13% (p = 0.0000437). When the native myocardial oxygen consumption-pressure-volume area relationship was assessed by subtracting the dynamic cardiac compression pressure applied to the heart, the slope of the myocardial oxygen comsumption-pressure-volume area relationship returned to the control level. This indicates that the contractile efficiency of the native heart was not affected by dynamic cardiac compression. We conclude that dynamic cardiac compression enhances left ventricular pump function by improving the contractile efficiency of the overall heart leaving the energetics of the native heart unchanged.     

Myocardial tactile stiffness: a variable of regional myocardial function

OBJECTIVES: We developed a new sensor system for in situ measurement of myocardial tactile stiffness-stiffness in a direction perpendicular to the wall-and validated its use for providing a reasonable estimation of regional myocardial function. BACKGROUND: Numerous attempts have been made to directly assess regional myocardial function. The complexity and highly invasive nature of the measuring devices have hampered their in situ application. METHODS: In open chest mongrel dogs, myocardial tactile stiffness, ventricular pressure and ventricular volume were monitored. Under the preload reduction, these variables were measured to determine the relation between the end-systolic pressure-volume relation (ESPVR) and the end-systolic tactile stiffness-volume relation (ESSVR). The changes in myocardial tactile stiffness were monitored in the regional ischemic myocardial model and infarcted model to evaluate their usefulness as indexes of regional myocardial function. RESULTS: Myocardial tactile stiffness changed cyclically and followed a time course similar to left ventricular pressure. When preload was altered, the ESSVR was as linear as the ESPVR. The slope of the ESSVR and that of the ESPVR showed a strong correlation over a wide range of contractility. These results suggest that myocardial tactile stiffness can be a good index of regional wall stress or fiber stress. End-systolic myocardial tactile stiffness of ischemic and infarcted regions decreased significantly, with a concomitant increase in end-diastolic stiffness compared with that of intact myocardium. CONCLUSIONS: Using our tactile sensor system, regional myocardial tactile stiffness of a beating heart was measured with reasonable temporal resolution. We consider myocardial tactile stiffness to be a useful index of regional myocardial function.     

Regional myocardial perfusion and mechanics: a model-based method of analysis

A new parametric model-based method has been developed that allows epicardial strain distributions to be computed on the left ventricular free wall in normal and ischemic myocardium and integrated with the regional distributions of anatomic and physiological measurements so that underlying relationships can be explored. An array of radiopaque markers was sewn on the anterior wall of the left ventricle (LV) in three anesthetized open-chest canines, and their positions were recorded using biplane video fluoroscopy before and 2 min after occlusion of the left anterior descending coronary artery. The three-dimensional (3D) anatomy of the LV and epicardial fiber angles were measured post-mortem using a 3D probe. A prolate spheroidal finite element model was fitted to the epicardial surface points (with <0.2 mm accuracy) and fiber angles (<5 degrees error). Regional myocardial blood flows (MBFs) were measured using fluorescent microspheres and fitted into the model (<0.3 ml min(-1) g(-1) error). Epicardial fiber and cross-fiber strain distributions were computed by allowing the model to deform from end-diastole to end-systole according to the recorded motion of the surface markers. Systolic fiber strain varied from -0.05 to 0.01 within the region of the markers during baseline, and regional MBF varied from 1.5 to 2.0 ml min(-1) g(-1). During 2 min ischemia, regional MBF was less than 0.3 ml min(-1) g(-1) in the ischemic region and 1.0 ml min(-1) g(-1) in the nonischemic region, and fiber strain ranged from 0.05 in the central ischemic zone to -0.025 in the remote nonischemic tissue. This analysis revealed a zone of impaired fiber shortening extending into the normally perfused myocardium that was significantly wider at the base than the apex. A validation analysis showed that a regularizing function can be optimized to minimize both fitting errors and numerical oscillations in the computed strain fields.     

Homogenization modeling for the mechanics of perfused myocardium

Altered coronary perfusion can change the apparent diastolic stiffness of ventricular myocardium--the 'garden hose' effect. Our recent findings showed that myocardial strains are reduced during ventricular filling, primarily along the directions transverse to the coronary microvessels. In this article, we review hypotheses and theoretical models regarding the role that regional wall stress plays in the mechanical interaction between myocardium and coronary circulation. Various mechanisms have been used to explain the effects of the tissue stress on coronary flow, as well as the effect of coronary dynamics on myocardial mechanics. Many models of coronary pressure-flow relations using lumped parameter circuit analogs. Poroelasticity and swelling theories have been used to model the mechanics of perfused muscle. Here, we describe a new mathematical model of the mechanics of perfused myocardium derived using homogenization theory. In this model, perfused myocardium is treated as a nonlinear anisotropic elastic solid embedded with cylindrical vessels of known distensibility. The solid compartment is incompressible but the vascular compartment may change volume according to a simple relation between vessel diameter and perfusion pressure. The work done by the perfusion pressure in changing vascular volume contributes to the macroscopic strain energy and hence affects the stress and stiffness of the composite. Conversely, the stress in the tissue affects microvessel diameter and volume, since tractions transverse to the vessel axis oppose the internal blood pressure. Finite element simulations of passive filling show good agreement of model with experimental results.     

Stress echocardiography in myocardial infarct

For patients with recent myocardial infarction, the main determinants of prognosis are: extent of transmural necrosis, state of the infarct-related artery and the presence and extent of myocardium at risk. The basic principle underlying the use of stress echocardiography states that myocardial ischaemia produces abnormalities of regional wall motion which are by themselves early, sensitive and specific markers of decreased perfusion. Dobutamine infusion allows for evaluation of myocardial contractile reserve by increasing inotropism. In low doses it gives us information on regional viability. In high doses, wall motion under increased oxygen demand, it becomes dependent on the ability of the coronary arteries to increase blood flow. Dipyridamole induces coronary vasodilation. In low doses it produces an increase in the blood flow. In high doses the steal effect deviates blood from the regions dependent on stenosed arteries. Ischaemia and regional wall motion abnormalities ensue. A negative stress echocardiogram, either under dobutamine or dipyridamole, has an excellent negative predictive value while a positive stress echocardiogram is predictive of an increased rate of events in the follow-up.     

Acute changes in preload, afterload, and systolic function after superior cavopulmonary connection

BACKGROUND: Superior cavopulmonary connection reduces the volume work of the single ventricle. METHODS: To determine the effects of superior cavopulmonary connection on preload, wall stress (or afterload), and systolic ventricular function, we studied 9 patients before and after operation, and at hospital discharge. Using echocardiography, preload was estimated by the ventricular end-diastolic area, and wall stress was calculated at end-systole and peak-systole. Ventricular function was represented by rate-corrected velocity of circumferential fiber shortening and fractional area change divided by rate-corrected ejection time. RESULTS: End-diastolic area and wall stress decreased postoperatively. Ventricular wall thickness increased with a concomitant decrease in cavity area. There was no change in mean blood pressure or heart rate or in rate-corrected velocity of circumferential fiber shortening or fractional area change divided by rate-corrected ejection time. These findings persisted at hospital discharge. CONCLUSIONS: In single ventricles, superior cavopulmonary correction results in an immediate decrease in preload and afterload. The decrease in afterload results primarily from alterations in ventricular geometry. Although no improvement in systolic function was noted, diminished work related to the reduction in loading conditions may have beneficial long-term effects on preserving myocardial performance.     

Classical conditioning, differential conditioning, and second-order conditioning of the Aplysia gill-withdrawal reflex in a simplified mantle organ preparation

OBJECTIVE: The sensitive relationship between regional myocardial perfusion and local systolic deformation during acute myocardial ischemia is not independent of the transmural location or segment orientation. The aim of this study was to determine the effects of fiber orientation and transmural location on the relationships between regional myocardial flow and three-dimensional systolic wall strain during graded coronary artery occlusions. METHODS: Transmural distributions of three-dimensional strain (by biplane radiography of implanted radiopaque markers) and myocardial blood flows (using fluorescent microspheres) were measured in the ischemic region during graded left anterior descending (LAD) coronary artery occlusions in 12 anesthetized dogs. RESULTS: Occlusion of the coronary artery did not significantly alter mean heart rate or end-systolic pressure. As flow decreased during graded occlusions, ischemia significantly changed systolic circumferential, longitudinal, radial, fiber and cross-fiber strains (p < 0.004). There was a significant effect of transmural position on circumferential, cross-fiber and radial strains, but not on fiber or longitudinal strains. Ischemia significantly altered all normal strains: circumferential, longitudinal, fiber, cross-fiber and radial. There was a strong interaction effect between transmural location and blood flow for circumferential, cross-fiber and radial strains, but not fiber or longitudinal strains. CONCLUSION: During non-transmural ischemia, there is evidence of strong transmural tethering in the cross-fiber direction, whereas the fiber-strain flow relation is independent of transmural position. Thus, whether the relationship between local myocardial bloodflow and systolic strain during acute ischemia is dependent on transmural location, depends on segment orientation.     

Effect of MCI-154, a cardiotonic agent, on regional contractile function and myocardial oxygen consumption in the presence and absence of coronary artery stenosis in dogs

The effects of MCI-154 (6-[4-(4'-pyridyl)aminophenyl]-4,5-dihydro-3(2H)- pyridazinone hydrochloride.3H2O), a cardiotonic agent with calcium sensitizing actions, on regional contractile function and myocardial oxygen consumption (MVO2) were studied in the dog hearts with and without partial occlusion of the left anterior descending coronary artery and compared with those of dobutamine. Segment shortening by sonomicrometry, regional myocardial blood flow by microspheres and the oxygen content of coronary venous blood drawn from the ischemic left anterior descending coronary artery area were simultaneously measured. The ischemic zone segment shortening and left ventricular (LV) dP/dtmax were decreased after partial occlusion. The infusion of MCI-154 starting 20 min after ischemia improved the depressed segment shortening and LV dP/dtmax without increasing the ischemic zone MVO2 and regional myocardial blood flow. In the nonischemic hearts, MCI-154 did not increase MVO2 and coronary blood flow despite the augmentation of myocardial contractility. MCI-154 decreased LV end-diastolic pressure and systemic blood pressure. On the other hand, dobutamine failed to increase the ischemic zone segment shortening, but the drug increased MVO2, coronary blood flow and LV dP/dtmax in both ischemic and nonischemic hearts. These results indicate that MCI-154 alleviates the ischemic contractile failure without increasing myocardial oxygen demand. Thus, MCI-154 may be useful in the management of heart failure with reduced coronary reserve.     

Left ventricular contractile performance, ventriculoarterial coupling, and left ventricular efficiency in hypertensive patients with left ventricular hypertrophy

Contractile performance of hypertrophied left ventricle may be depressed in arterial hypertension. Ventriculoarterial coupling is impaired when myocardial contractile performance is reduced and when afterload is increased. The left ventricular contractile performance and the ventriculoarterial coupling were evaluated in 30 hypertensive patients with moderate left ventricular hypertrophy and 20 control subjects. Left ventricular angiography coupled with the simultaneous recording of pressures with a micromanometer were used to determine end-systolic stress/volume index, the slope of end-systolic pressure-volume relationship, ie, end-systolic elastance, effective arterial elastance, external work, and pressure-volume area. In hypertensive patients, left ventricular contractile performance, as assessed by end-systolic elastance/ 100 g myocardial mass, was depressed (4.35 +/- 1.13 v 5.21 +/- 1.89 mm Hg/mL/100 g in control subjects P < .02), when end-systolic stress-to-volume ratio was comparable in the two groups (3.85 +/- 0.99 g/cm2/mL in hypertensive patients versus 3.51 +/- 0.77 g/cm2/mL in control subjects). Ventriculoarterial coupling, evaluated through effective arterial elastance/end-systolic elastance ratio, was slightly higher in hypertensive patients (0.53 +/- 0.08 v 0.48 +/- 0.09 mm Hg/mL in control subjects, P < .05), and work efficiency (external work/pressure-volume area) was similar in the two groups (0.78 +/- 0.04 mm Hg/mL in hypertensive patients versus 0.80 +/- 0.03 mm Hg/mL in control subjects). This study shows that despite a slight depression of left ventricular contractile performance, work efficiency is preserved and ventriculoarterial coupling is almost normal in hypertensive patients with left ventricular hypertrophy. Thus, it appears that left ventricular hypertrophy might be a useful means of preserving the match between left ventricle and arterial receptor with minimal energy cost.     

Quantitative two-dimensional echocardiographic assessment of regional wall motion during transient ischemia and reperfusion in the rat

Nonlethal myocardial ischemia produces profound and long-lasting effects on regional ventricular function and metabolism (myocardial stunning) and protects against myocardial infarction from subsequent prolonged ischemia (ischemic preconditioning). Two-dimensional echocardiography (2DE) is an essential tool for quantitative analysis of regional and global left ventricular (LV) function during myocardial ischemia and reperfusion and the study of these phenomena. However, the inability to perform 2DE in the open-chest rat heart has seriously limited the use of this model. To investigate the effect of transient coronary occlusion on segmental wall motion and LV geometry, we employed a 20 MHz intravascular ultrasound catheter placed on the epicardial surface of the rat heart (n = 15) to yield 2DE images suitable for quantitative analysis. Three 2-minute left coronary occlusions were made, separated by 5 minutes of reperfusion, with imaging during occlusion and at 5 and 60 minutes of reperfusion. Ischemic and nonischemic wall thicknesses, LV cross-sectional area, estimated LV volume, and the fractional changes of these parameters were measured. In eight animals these values were also compared with necropsy measurements of wall thickness, LV cross-sectional area, and volume. LV and right ventricular structures were well visualized in short-axis cross-sectional images in all animals, and images suitable for quantitative analysis were obtained in 92% of the periods. Coronary occlusion caused immediate, marked LV cavitary expansion, which rapidly returned to normal by 5 minutes of reperfusion. Active systolic thickening of the anterior wall at baseline (47% +/- 3%) became passive thinning during occlusion (-6% +/- 2%) and recovered partially, to 30% +/- 3% at 5 minutes of reperfusion and 42% +/- 4% at 60 minutes (p < 0.0005 at 5 minutes of reperfusion vs baseline; p not significant at 60 minutes). Recovery of thickening after 5 minutes of reperfusion was not different after the first versus third occlusion (23% +/- 4% vs 30% +/- 3%; p = 0.19). Measurements made by 2DE correlated well with those made by necropsy, although wall thickness was slightly thicker by 2DE. We conclude that epicardial echocardiography with an intravascular ultrasound catheter provides quantifiable 2DE images in this model and yields accurate information on segmental wall thickening and ventricular geometry not available by other techniques. Left coronary occlusion in the rat is associated with marked global and segmental LV expansion, which rapidly reverses with reperfusion. Postischemic regional wall motion abnormalities are present after coronary occlusion as brief as 2 minutes and can be measured accurately. The effect of multiple brief occlusions is not cumulative.(ABSTRACT TRUNCATED AT 400 WORDS)     

X46级管线钢热连轧过程中温度场及平均流变应力的预测

采用有限元计算模型和实测轧件温度以及精轧各道次的轧制压力值，对不同边界条件下的传热系数和塑性功转热率进行了优化计算，得到了轧件断面温度场。在此基础上考虑了再结晶等因素，建立了计算精轧过程中应力一应变曲线的流变应力模型，并利用该模型对X46级管线钢精轧各道次的流变应力进行了预测。结果表明：该模型的计算结果与用Sims法计算的结果吻合较好，能真实反映工业生产的实际情况。     

Inhaled nitric oxide is not a myocardial depressant in a porcine model of heart failure

BACKGROUND: Inhaled nitric oxide has been shown to be a potent and selective pulmonary vasodilator. Reports of increases in left ventricular end-diastolic pressure and episodes of pulmonary edema during the clinical use of inhaled nitric oxide in patients with preexisting left ventricular dysfunction have raised concerns that this agent may have myocardial depressant effects. We therefore undertook a study of the effects of inhaled nitric oxide on myocardial contractility in a porcine model of ventricular failure and pulmonary hypertension. METHODS: After inducing heart failure in 10 pigs by rapid ventricular pacing, hemodynamic measurements and pressure-volume diagrams (by the conductance method) were obtained in six animals at baseline and during administration of inhaled nitric oxide at concentrations of 20 and 40 ppm. Myocardial contractile state was assessed by the end-systolic pressure-volume relationship and preload-recruitable stroke work, whereas diastolic function was measured in terms of the end-diastolic pressure-volume relationship and the pressure decay time constant T. RESULTS: Baseline hemodynamics reflected heart failure and pulmonary hypertension, and inhaled nitric oxide induced significant reductions in mean pulmonary artery pressure and pulmonary vascular resistance. Although left ventricular end-diastolic pressure increased during administration of inhaled nitric oxide, no changes were observed in measures of systolic or diastolic function. CONCLUSIONS: Inhaled nitric oxide reduced pulmonary vascular resistance but did not alter myocardial contractility or diastolic function. Increases in left ventricular end-diastolic pressure during inhaled nitric oxide therapy are therefore not due to myocardial depression and may be related to increases in volume delivery to the left side of the heart resulting from reduced pulmonary vascular resistance.     

Effects of sotalol and vagal stimulation on ischemic myocardial blood flow distribution in the canine heart

The purpose of the present study was to compare the effect of equivalent decreases in heart rate produced by sotalol and bilateral vagal stimulation on regional myocardial blood flow and coronary perfusion pressure distal to a severe stenosis of the left circumflex coronary artery in anesthetized dogs. Tissue blood flow was measured with radioactive microspheres (15 mu). Vagal stimulation or beta adrenergic blockade produced by sotalol (1.0 mg/kg i.v.) reduced heart rate approximately 35 beats/min. This decrease in rate was accompanied by nearly equivalent increases (P less than 0.05) in diastolic perfusion time and subendocardial blood flow and in the ischemic region. Both interventions also significantly increased the oxygen supply-demand balance (distal diastolic pressure time index divided by the tension time index) in the ischemic region. These values returned to control after cessation of vagal stimulation or during atrial pacing to predrug heart rate. Coronary perfusion pressure distal to the stenosis increased significantly only in the sotalol-treated group. These results suggest that a decrease in heart rate and increase in diastolic perfusion time are important factors in the favorable redistribution of ischemic myocardial blood flow and increase in the oxygen supply-demand balance observed after beta adrenergic blockade with sotalol or after vagal stimulation. Whether these beneficial actions are solely due to the prolonged diastolic perfusion period or to reduced oxygen demand and a return to autoregulation in the ischemic area cannot be determined with certainty.     

Noninvasive quantification of regional myocardial metabolic rate for oxygen by use of 15O2 inhalation and positron emission tomography. Theory, error analysis, and application in humans

BACKGROUND: A method has been developed to measure the regional myocardial metabolic rate of oxygen consumption (rMMRO2) and oxygen extraction fraction (rOEF) quantitatively and noninvasively in humans by use of 15O2 inhalation and positron emission tomography. This article describes the theory, an error analysis of the technique, and procedures of the method used in a human feasibility study. METHODS AND RESULTS: Inhaled 15O2 is transported to peripheral tissues, where it is converted to 15O-labeled water of metabolism, which exchanges with the relatively large extravascular tissue space. Quantification of this buildup of radioactivity allows the calculation of rMMRO2 and rOEF. However, a correction for the spillover of the pulmonary gas radioactivity signal into myocardial regions is required and has been made by use of a gas volume distribution estimated from the transmission scan. This was validated by comparative measurements using the inert gas [11C]CH4 in four greyhounds. Spillover of the cardiac chamber radioactivity has been corrected for with an inhaled [13O]CO (blood volume) scan. The underestimation of myocardial radioactivity due to wall motion and thickness has been corrected for by use of values of tissue fraction obtained from the flow measurement [15OKCO2 scan). Values of rOEF were similar (within 4%) whether obtained from gas volume measurements determined from the transmission or [11C]CH4 scan data. 15O2 scan information from six healthy volunteers showed a clear distribution of myocardial radioactivity after the vascular and pulmonary gas 15O background was subtracted. Subsequent compartmental analysis resulted in values for rOEF and rMMRO2 of 0.60 +/- 0.11 and 0.10 +/- 0.03 mL.min-1.g-1 in the human myocardium at rest. CONCLUSIONS: The results of this study are in good agreement with established values. This is the first known approach to allow the direct quantitative determination of rOEF and oxygen metabolism to be made noninvasively on a regional basis.     

残氧量模型的修正方法在比例控制型烧嘴上的应用

针对首钢京唐公司某退火炉残氧量设定值与实测值偏差过大问题,提出一种针对燃烧控制系统残氧量模型的修正方法。通过测量烧嘴出口处烟气中的残氧量,得出燃烧控制系统空燃比实测值与设定值的偏差,从而计算出助燃空气流量修正值,并依此对残氧量模型进行修正。残氧量模型修正方法应用后,该退火炉残氧量设定值与实测值的平均偏差由3.37%降至0.15%,且各加热控制区残氧量偏差均小于1%,解决了因残氧量设定值与实测值偏差过大而导致残氧量模型无法应用于实际生产现场的难题。     

An experimental technique for estimating regional myocardial segment work in vivo

We determined the capabilities and limitations of an experimental approach to measure segment work (force x distance) of myocardial regions in the in vivo beating heart. In 18 open-chest anesthetized dogs, segment length was measured using ultrasonic dimension transducers, and developed force was measured with miniature force transducers. Work was defined as the integrated multiples of instantaneous force and shortening during a single (averaged) beat, corresponding to the area under the length-force loop. Changes in work over a range of 9.78 x 10(-4) to 2.93 x 10(-2) J/g/min were produced by vena caval constriction, aortic constriction, atrial pacing, and isoproterenol (0.5 and 1.0 micrograms/kg/min). Work was measured in both major and minor axes. In 60% of the animals, work in the minor axis was 9.2-fold greater than in the major axis. In the others, all interventions changed regional work to the same extent in both axes (r = 0.802; p < 0.05). Work changes were also compared between the base, anterior, and posterior walls. The response was directionally similar in all regions, ranging from -79 +/- 1% during caval occlusion to 278 +/- 98% during isoproterenol. The effective size of the measured muscle mass was limited to the transducer area because the amplitude and pattern of both force development and segment shortening were not changed until deep myocardial cuts were as close as 2 mm from the measuring area. We conclude that work measurement in the minor axis is quantitatively representative of fiber work in that region.     

Left ventricular ORS widening decreases Emax without lowering VO2-PVA relation in dog hearts

We observed a few rare spontaneous cases of a suddenly widened QRS wave of left ventricular ECG associated with a simultaneous decrease in left ventricular (LV) contractility (Emax, end-systolic pressure-volume ratio) in excised cross-circulated dog heart experiments. The decreased Emax was not associated with a descent of the relation between cardiac oxygen consumption (VO2) and LV systolic pressure-volume area (PVA, a measure of total ventricular mechanical energy). This result is intriguing because ventricular VO2-PVA relation generally changes its elevation in proportion to Emax under various inotropic interventions. We suspected the unusual observation to reflect no change in myocardial contractility despite ventricular asynchrony augmented by an intraventricular conduction defect.     

Localization of heparin binding activity in recombinant laminin G domain

BACKGROUND: Smoking regulations at the workplace have been found to be acceptable and effective in many studies conducted in the United States. There is limited knowledge, however, on acceptance and effects of smoking regulations in European countries, particularly among blue collar employees. METHODS: We conducted a survey on smoking behaviour and attitude toward smoking regulations and passive smoking in a South German metal company. A self-administered questionnaire was mailed to 1,500 predominantly blue collar employees of whom 974 participated in the study (response rate 64.9%). RESULTS: About 30% of the employees were not allowed to smoke at their immediate work area. Among them, about 95% of both smokers and nonsmokers agreed with this smoking policy. More than 60% of nonsmoking blue collar workers were bothered by passive smoking at work whether or not smoking was allowed at their immediate work area. In contrast, the proportion of nonsmoking white collar employees who were bothered by passive smoking varied from 52% if smoking was allowed at their immediate work area to 18% if smoking was not allowed. Prevalence of active smoking and average amount of smoking among active smokers were considerably lower among employees who were not allowed to smoke at work than among other employees. These differences were partly due to confounding by occupation, however, which was strongly related to both smoking habits and smoking policy. CONCLUSIONS: Our results, which confirm and extend previous findings, give further support to the acceptability and potential effectiveness of smoking regulations at the workplace. Particular efforts should be devoted to limit both active and passive smoking among blue collar employees.     

Effect of exercise on left ventricular mechanical efficiency in conscious dogs

BACKGROUND: We studied the effect of exercise (7.2 to 8.0 km/h) on the efficiency of the conversion of metabolic energy to external work or stroke work (SW) by the left ventricle (LV). METHODS AND RESULTS: Energy use was calculated from LV myocardial oxygen consumption per beat (MVO2). LV volume was calculated from orthogonal dimensions and coronary flow measured with ultrasonic flow probes. The total mechanical energy of the LV was calculated as the pressure-volume area (PVA). At rest, the MVO2-PVA point fell on the MVO2-PVA relation determined by steady-state changes in arterial pressure produced by graded infusions of phenylephrine. Exercise increased the slope (Ees) of LV end-systolic pressure-volume (PV) relation by 29%. During exercise, the MVO2-PVA point shifted to the right only slightly above the control MVO2-PVA relation by 0.007 +/- 0.005 mL O2.beat-1.100 g LV-1. Despite the increase in ventricular contractility with exercise, the PVA/MVO2 ratio was unchanged because of the marked increase in PVA. During exercise, the transmission of total mechanical energy to external work (SW/PVA) increased from 65 +/- 5% to 72 +/- 4% (P < .01) as the ratio of the arterial end-systolic elastance to Ees decreased from 1.1 +/- 0.2 to 0.8 +/- 0.1 (P < .05). Thus, LV mechanical efficiency (SW/MVO2 = SW/PVA.PVA/MVO2) improved from 12.9 +/- 1.5% to 14.3 +/- 1.1% (P < .05) during exercise. CONCLUSIONS: Exercise increases the efficiency of conversion of metabolic energy to external work by the LV due to alteration in LV arterial coupling resulting in increased production of mechanical energy and enhanced transmission of mechanical energy to external work, which more than offsets any increased metabolic cost of the enhanced contractility.     

Real-time strain rate imaging of the left ventricle by ultrasound

The regional function of the left ventricle can be visualized in real-time using the new strain rate imaging method. Deformation or strain of a tissue segment occurs over time during the cardiac cycle. The rate of this deformation, the strain rate, is equivalent to the velocity gradient, and can be estimated using the tissue Doppler technique. We present the strain rate as color-coded 2-dimensional cine-loops and color M-modes showing the strain rate component along the ultrasound beam axis. We tested the method in 6 healthy subjects and 6 patients with myocardial infarction. In the healthy hearts, a spatially homogeneous distribution of the strain rate was found. In the infarcted hearts, all the infarcted areas in this study showed up as hypokinetic or akinetic, demonstrating that this method may be used for imaging of regional dysfunction. Shortcomings of the method are discussed, as are some possible future applications of the method.