Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study.

Maximal heart rate (HRmax ) declines substantially with age, but the magnitude and possible modifying effect of gender, body composition, and physical activity are not fully established. The present study examined the relationship between HRmax and age in 3320 healthy men and women within a wide age range using data from the HUNT Fitness Study (2007-2008). Subjects were included if a maximal effort could be verified during a maximal exercise test. General linear modeling was used to determine the effect of age on HRmax . Subsequently, the effects of gender, body mass index (BMI), physical activity status, and maximal oxygen uptake were examined. Mean predicted HRmax by three former prediction formulas were compared with measured HRmax within 10-year age groups. HRmax was univariately explained by the formula 211 - 0.64·age (SEE, 10.8), and we found no evidence of interaction with gender, physical activity, VO2max level, or BMI groups. There were only minor age-adjusted differences in HRmax between these groups. Previously suggested prediction equations underestimated measured HRmax in subjects older than 30 years. HRmax predicted by age alone may be practically convenient for various groups, although a standard error of 10.8 beats/min must be taken into account. HRmax in healthy, older subjects and women were higher than previously reported.

Interval and strength training in CAD patients.

This study sought to study the effect of high intensity aerobic interval endurance training on peak stroke volume and maximal strength training on mechanical efficiency in coronary artery disease (CAD) patients. 8 CAD patients (age 61.4 ± 3.7 years) trained 30 interval training sessions with 4 × 4 min intervals at 85-95% of peak heart rate while 10 CAD patients (age 66.5 ± 5.5 years) trained 24 sessions of maximal horizontal leg press. In the interval training group peak stroke volume increased significantly by 23% from 94.1 ± 23.0 mL · beat (-1) to 115.8 ± 22.4 mL · beat (-1) (p<0.05). Peak oxygen uptake increased significantly by 17% from 27.2 ± 4.5 mL · kg (-1) · min (-1) to 31.8 ± 5.0 mL · kg (-1) min (-1) (p<0.05) in the same group. In contrast, there was no such exercise training-induced change in peak stroke volume or peak oxygen uptake in the maximal strength training group, despite a 35% improvement in sub maximal walking performance.

Maximal strength training restores walking mechanical efficiency in heart patients.

The purpose of this study was to investigate whether maximal strength leg press training improves walking mechanical efficiency in coronary artery disease patients. Ten coronary artery disease patients trained 24 sessions of horizontal leg press. Each training session consisted of 4 sets with 4 repetitions of maximal mobilization of concentric force to exhaustion. Seven healthy age matched subjects served as time controls. Maximal strength training improved walking mechanical efficiency (i.e. the oxygen cost to generate a given work load) by 35% (p=0.007) in coronary artery disease patients (from 18+/-4% at pre test to 25+/-6% at post test), and restored walking efficiency to the level of the healthy age matched controls ( approximately 25%). Strength training further improved one repetition maximum from 138+/-24 to 198+/-24 kg (44%) (p=0.000) and rate of force development by 85% (p=0.001), with no change in the control group. Maximal strength leg press training restores walking mechanical efficiency and significantly improves one repetition maximum and rate of force development in coronary artery disease patients after 24 training sessions each lasting only 20 min.

Left ventricular mechanics during exercise: a Doppler and tissue Doppler study.

AIMS: To study left ventricular mechanics of exercise with Doppler and tissue Doppler. METHODS AND RESULTS: Twenty-one males (mean age, 26; height, 184 cm; weight, 84 kg), exercised on a bicycle, with increasing workload, with oxygen uptake, Doppler flow and tissue Doppler recordings during exercise. There was correlation between peak systolic LVOT flow and annulus velocity; R=0.72, (p<0.001) and between peak mitral E flow and annulus E(a) velocity; R=0.68(p<0.001). Finally there was correlation between peak LVOT and mitral flow velocity; R=0.83(p<0.001) and peak systolic and early diastolic annulus velocity R=0.69(p<0.001). All intervals of the heart cycle decreased with RR-interval. There was a linear relation between diastolic filling and RR-interval, while ejection period was less increased with RR-intervals above 600 ms, and thus not a linear relationship. There was no change in E/E(a) ratio during exercise. CONCLUSIONS: Mechanism for increased filling as well as ejection during exercise seems to be increased contraction and relaxation velocity, with no evidence of Frank-Starling mechanism. Bazett's formula gives a better heart rate correction of LVET at high heart rates than Weissler's.

High frame rate strain rate imaging of the interventricular septum in healthy subjects.

OBJECTIVE: In the present study the feasibility was assessed of a new strain rate imaging method with a very high frame rate of around 300 frames per second. METHODS: Digital radio-frequency (RF) data were obtained in nine healthy subjects using a sector of 20-30 degrees in an apical four chamber view. The RF data were analysed using a dedicated software package that displays strain rate images and profiles and calculates strain rate values. With the new method, it is possible to study events and spatial-temporal differences in the heart cycle with duration down to 3.5-3 ms, including the pre-ejection period and the isovolumic relaxation period. Since the interventricular septum (IVS) is of crucial importance for the left and right ventricular function, we assessed changes through the heart cycle of the strain rate in the IVS. RESULTS: Mean peak systolic strain rate in the healthy subjects was -1.65+/-0.13 s(-1). Mean peak diastolic strain rate during early filling was 3.14+/-0.50 s(-1) and during atrial systole 0.99+/-0.09 s(-1). We found individual differences in the strain rate patterns, but in all subjects, the ventricular contraction started simultaneously in all parts of the septum. After the ejection period, the elongation started before aortic valve closure, in the midinferior septum and propagated towards the apex. CONCLUSION: High frame rate strain rate imaging makes it possible to study rapid deformation patterns in the heart walls.

Impact of coronary artery disease on left ventricular systolic function and geometry in hypertensive patients with left ventricular hypertrophy (the LIFE study).

Hypertensive patients with left ventricular (LV) hypertrophy have a higher incidence of cardiovascular events than those without it. We hypothesized that a close relation exists between clinical evidence of coronary artery disease (CAD) and alterations in LV structure and function that contribute to their higher risk. Echocardiograms were recorded in 963 hypertensive patients (mean age 66 +/- 7 years, 41% women) with electrocardiographic LV hypertrophy, and divided into 149 with and 814 without clinical (prior myocardial infarction or angina pectoris) or electrocardiographic (Minnesota codes 1.1, 1.2) evidence of CAD. Patients with CAD had larger LV internal dimensions (5.5 +/- 0.6 vs 5.2 +/- 0.5 cm), increased LV mass (136 +/- 31 vs 122 +/- 24 g/m(2), and 62.4 +/- 19.4 vs 55.5 +/- 12.1 g/m(2.7)), lower ejection fraction (58 +/- 10% vs 62 +/- 8%), higher circumferential end-systolic wall stress (cESS) (198 +/- 59 vs 181 +/- 47 kdynes/cm(2), all p <0.001), and higher total peripheral resistances (2,088 +/- 628 vs 1,963 +/- 553 dynes x s x m(2)/cm(3), p = 0.02). Although eccentric LV hypertrophy predominated, the CAD group had a greater prevalence of this geometric pattern than the non-CAD group (56% vs 47%, p <0.02). An index of myocardial oxygen demand per beat--the LV mass x cESS x ejection time--was 20% higher in patients with CAD. In conclusion, clinical evidence of CAD in hypertensive patients with electrocardiographic evidence of LV hypertrophy identifies subjects with structural and functional abnormalities at high risk for cardiovascular events. LV mass. cESS. ejection time, a noninvasive index that parallels myocardial oxygen demand per beat, is especially high in hypertensive patients with CAD.

Atrioventricular plane displacement in female endurance athletes.

INTRODUCTION: A novel hypothesis for increased ventricular pumping describes the heart as a displacement pump, in which atrioventricular plane displacement (AVPD) is an important mechanism. The hypothesis predicts that AVPD increases at high heart rates. The aim of the present study was to determine whether AVPD increases during exercise at high heart rates. A secondary aim was to study the left ventricular function and dimensions in endurance-trained young female athletes. METHODS: Eight female cross-country skiers (18.5 +/- 0.9 yr, 169.3 +/- 2.9 cm, 55.7 +/- 4.2 kg, and 64.8 +/- 3.7 mL x kg(-1) x min(-1) in maximal oxygen uptake) were compared with seven sedentary female controls (18.0 +/- 0.6 yr, 175.0 +/- 2.5 cm, 71.1 +/- 4.1 kg, and 42.8 +/- 3.0 mL x kg(-1) x min(-1) in maximal oxygen uptake). Cardiac anatomy and function were assessed by echocardiography. RESULTS: Whereas left ventricular ejection fraction (LVEF) increased in both groups, AVPD fell significantly during exercise. AVPD did not correlate with LVEF, and there were no differences in AVPD between groups either at rest or during exercise. Cardiac output index (mL x lean body mass(-0.67)) and stroke volume index (mL x lean body mass(-1)) were higher in the trained group. The trained group had a larger left ventricular mass, and left ventricular internal dimensions, scaled to lean body mass. CONCLUSIONS: This first study to examine AVPD at rest and during exercise in endurance-trained athletes did not indicate that AVPD is an important mechanism of increased cardiac pumping during exercise. Endurance-trained female athletes have larger left ventricular dimensions and increased function as compared with sedentary subjects.

Regional expression of endothelin-1, ANP, IGF-1, and LV wall stress in the infarcted rat heart.

We hypothesized that myocardial infarction induces regional and temporal differences in endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and insulin-like growth factor-1 (IGF-1) gene expression that correlate with left ventricular (LV) wall stress. Echocardiography and LV pressure measurements were performed in coronary artery-ligated or sham-operated rats. Gene expression was measured by competitive RT-PCR in the infarct, border zone, and remote area and in regionally isolated cardiomyocytes. ET-1 and IGF-1 expression was highest in the infarcted myocardium, whereas ANP expression was highest in noninfarcted myocardium. For all genes, remote area expression was highest after 7 days. At 42 days, ANP maintained maximum expression, ET-1 decreased to 50% of peak levels, and IGF-1 was normalized. Cardiomyocyte expression followed the same pattern as in the myocardium except for a markedly lower IGF-1 expression. Diastolic wall stress was the best hemodynamic variable to predict ET-1 and ANP expression in the remote area. We conclude that ET-1, ANP, and IGF-1 are expressed in different patterns in the infarcted heart in relation to time, functional regions, cellular distribution, and mechanical load.

Strain rate imaging in normal and reduced diastolic function: comparison with pulsed Doppler tissue imaging of the mitral annulus.

OBJECTIVES: The pixel velocity values obtained by color Doppler tissue imaging (DTI) can be processed to velocity gradients as a measure of longitudinal strain rate with a technique termed strain rate imaging (SRI). Color mapping of strain rate does show the spatial-temporal relations of the diastolic phases. The phases of early filling and late filling during atrial systole can be seen to consist of a stretch wave in the myocardium, propagating from the base to the apex. Diastolic function is characterized by both peak strain rate and propagation velocity of this wave. The goals of this study were to establish normal values for these measurements and to study the changes with minimal diastolic dysfunction. METHODS: Twenty-eight healthy control subjects and 26 patients with hypertension and normal systolic function were studied. The patients had normal blood pressure on treatment, normal ejection fraction, minimal hypertrophy, and moderately prolonged deceleration and isovolumic relaxation times. Real-time SRI color cineloops, ordinary echocardiography and Doppler recordings, and pulsed wave DTI from the mitral ring were acquired and processed. RESULTS: Patients showed a reduction of systolic and early diastolic tissue velocities and strain rates and no significant increase in late diastolic tissue velocity and strain rate. Propagation velocity of diastolic strain during both early and late filling phases was reduced in the patients. The combination of changes in peak strain rate and propagation velocity of strain rate corresponded with changes in DTI. CONCLUSION: Diastolic deformation of the ventricle can be shown as a complex series of events, with temporal sequences in the ventricle. The peak strain rate and the propagation velocities of strain rate can describe the two main diastolic events: early and late filling. In reduced diastolic function, both are reduced during early filling. The velocities of the mitral ring are the result of this combination. This adds information about the physiology and pathophysiology of diastole.

Strain rate imaging by ultrasonography in the diagnosis of coronary artery disease.

Regional strain rate in the left ventricle can be assessed in real time and color mapped. The method is termed strain rate imaging (SRI), and findings correspond well with 2-dimensional echocardiography. This study addresses SRI as a method for localizing coronary lesions, compared with standard echocardiography. Twenty patients with acute myocardial infarction who underwent coronary angiography for clinical reasons were examined with SRI and standard echocardiography. Wall motion was graded by SRI color and separately by wall thickening. Strain rate imaging and 2-dimensional echocardiography results agreed well. An infarct-related artery was identified from angiograms combined with electrocardiograms. Both methods identified an infarct-related artery in 19 possible cases and had equal sensitivity and specificity for wall segments affected by lesion. Combining the information from both methods did not change accuracy. The study validates SRI as a method for assessing regional wall function in coronary artery disease. The advantages of SRI are discussed and measurements of strain rates are given.

Semiautomatic contour detection in ultrasound M-mode images.

We have developed a method for semiautomatic contour detection in M-mode images. The method combines tissue Doppler and grey-scale data. It was used to detect: 1. the left endocardium of the septum, the endocardium and epicardium of the posterior wall in 16 left ventricular short-axis M-modes, and 2. the mitral ring in 38 anatomical M-modes extracted pair-wise in 19 apical four-chamber cine-loops (healthy subjects). We validated the results by comparing the computer-generated contours with contours manually outlined by four echocardiographers. For all boundaries, the average distance between the computer-generated contours and the manual outlines was smaller than the average distance between the manual outlines. We also calculated left ventricular wall thickness and diameter at end-diastole and end-systole and lateral and septal mitral ring excursions, and found, on average, clinically negligible differences between the computer-generated indices and the same indices based on manual outlines (0.8-1.8 mm). The results were also within published normal values. In conclusion, this initial study showed that it was feasible in a robust and efficient manner to detect continuous wall boundaries in M-mode images so that tracings of left ventricular wall thickness, diameter and long axis could be derived.

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.