Influence of 12 weeks of jogging on magnetic resonance-determined left ventricular characteristics in previously sedentary subjects free of cardiovascular disease

Quantification of Myocardial Blood Flow by Machine Learning Analysis of Modified Dual Bolus MRI Examination

Contrast-enhanced magnetic resonance imaging (MRI) is a promising method for estimating myocardial blood flow (MBF). However, it is often affected by noise from imaging artefacts, such as dark rim artefact obscuring relevant features. Machine learning enables extracting important features from such noisy data and is increasingly applied in areas where traditional approaches are limited. In this study, we investigate the capacity of machine learning, particularly support vector machines (SVM) and random forests (RF), for estimating MBF from tissue impulse response signal in an animal model. Domestic pigs (n = 5) were subjected to contrast enhanced first pass MRI (MRI-FP) and the impulse response at different regions of the myocardium (n = 24/pig) were evaluated at rest (n = 120) and stress (n = 96). Reference MBF was then measured using positron emission tomography (PET). Since the impulse response may include artefacts, classification models based on SVM and RF were developed to discriminate noisy signal. In addition, regression models based on SVM, RF and linear regression (for comparison) were developed for estimating MBF from the impulse response at rest and stress. The classification and regression models were trained on data from 4 pigs (n = 168) and tested on 1 pig (n = 48). Models based on SVM and RF outperformed linear regression, with higher correlation (R_SVM² = 0.81, R_RF² = 0.74, R_{linear_regression}² = 0.60; ρ_SVM = 0.76, ρ_RF = 0.76, ρ_{linear_regression} = 0.71) and lower error (RMSE_SVM = 0.67 mL/g/min, RMSE_RF = 0.77 mL/g/min, RMSE_{linear_regression} = 0.96 mL/g/min) for predicting MBF from MRI impulse response signal. Classifier based on SVM was optimal for detecting impulse response signals with artefacts (accuracy = 92%). Modified dual bolus MRI signal, combined with machine learning, has potential for accurately estimating MBF at rest and stress states, even from signals with dark rim artefacts. This could provide a protocol for reliable and easy estimation of MBF, although further research is needed to clinically validate the approach.

Physical activity measured by accelerometry and its associations with cardiac structure and vascular function in young and middle-aged adults

BACKGROUND

Physical activity is associated with several health benefits, including lower cardiovascular disease risk. The independent influence of physical activity on cardiac and vascular function in the community, however, has been sparsely investigated.

MEASURES AND RESULTS

We related objective measures of moderate- to vigorous-intensity physical activity (MVPA, assessed by accelerometry) to cardiac and vascular indices in 2376 participants of the Framingham Heart Study third generation cohort (54% women, mean age 47 years). Using multivariable regression models, we related MVPA to the following echocardiographic and vascular measures: left ventricular mass, left atrial and aortic root sizes, carotid-femoral pulse wave velocity, augmentation index, and forward pressure wave. Men and women engaged in MVPA 29.9±21.4 and 25.5±19.4 min/day, respectively. Higher values of MVPA (per 10-minute increment) were associated with lower carotid-femoral pulse wave velocity (estimate -0.53 ms/m; P=0.006) and lower forward pressure wave (estimate -0.23 mm Hg; P=0.03) but were not associated with augmentation index (estimate 0.13%; P=0.25). MVPA was associated positively with log(e) left ventricular mass (estimate 0.006 log(e) [g/m(2)]; P=0.0003), left ventricular wall thickness (estimate 0.07 mm; P=0.0001), and left atrial dimension (estimate 0.10 mm; P=0.01). MVPA also tended to be positively associated with aortic root dimension (estimate 0.05 mm; P=0.052). Associations of MVPA with cardiovascular measures were similar, in general, for bouts lasting <10 versus ≥10 minutes.

CONCLUSIONS

In our community-based sample, greater physical activity was associated with lower vascular stiffness but with higher echocardiographic left ventricular mass and left atrial size. These findings suggest complex relations of usual levels of physical activity and cardiovascular remodeling.

Effects of a low-volume aerobic-type interval exercise on VO2max and cardiac mass

PURPOSE

The aim of this study was to compare the effects of time-efficient, low-volume interval exercises on cardiorespiratory capacity and left ventricular (LV) mass with traditional continuous exercise in sedentary adults.

METHODS

Forty-two healthy but sedentary male subjects (age 26.5 ± 6.2 yr) participated in an 8-wk, five times per week, supervised exercise intervention. They were randomly assigned to one of three exercise protocols: sprint interval training (SIT, 5 min, 100 kcal), high-intensity interval aerobic training (HIAT, 13 min, 180 kcal), and continuous aerobic training (CAT, 40 min, 360 kcal). Cardiorespiratory capacity (V˙O2max) and LV mass (3T-MRI) were measured preintervention and postintervention.

RESULTS

We observed significant (P < 0.01) increases in V˙O2max in all three groups, and the effect of the HIAT was the greatest of the three (SIT, 16.7% ± 11.6%; HIAT, 22.5% ± 12.2%; CAT, 10.0% ± 8.9%; P = 0.01). There were significant changes in LV mass, stroke volume (SV), and resting HR in both the SIT (LV mass, 6.5% ± 8.3%; SV, 5.3% ± 8.3%; HR, -7.3% ± 11.1%; all P < 0.05) and HIAT (LV mass, 8.0% ± 8.3%; SV, 12.1% ± 9.8%; HR, -12.7% ± 12.2%; all P < 0.01) but not in the CAT (LV mass, 2.5% ± 10.1%; SV, 3.6% ± 6.6%; HR, -2.2% ± 13.3%; all P > 0.05).

CONCLUSIONS

Our study revealed that V˙O2max improvement with the HIAT was greater than with the CAT despite the HIAT being performed with a far lower volume and in far less time than the CAT. This suggests that the HIAT has potential as a time-efficient training mode to improve V˙O2max in sedentary adults.

Sex differences in ventricular-vascular coupling following endurance training

Introduction

Ventricular and vascular coupling is defined as the ratio of arterial elastance (Ea) to ventricular elastance (Elv) and describes the interaction between the heart and arterial system. There are sex differences in both arterial and ventricular function in response to both acute exercise and aerobic exercise training.

Purpose

To examine the effects of aerobic exercise training on elastances and the coupling ratio in young adult men and women. We hypothesized a reduction in the coupling ratio in both sexes due to a decrease in Ea that would be more pronounced in men and an increase in Elv that would be larger in women.

Methods

Fifty-three healthy, young adults completed the study. Central pulse wave velocity and heart volumes were measured before and after an 8-week aerobic training intervention. Elastances were calculated as Ea = end-systolic pressure/stroke volume and Elv = end-systolic pressure/end-systolic volume and indexed to body surface area.

Results

After the intervention, women augmented indexed and un-indexed Elv from 2.09 ± 0.61 to 2.52 ± 0.80 mmHg/ml, p < 0.05, and reduced the coupling ratio from 0.72 ± 18 to 0.62 ± 15, p < 0.05, while men maintained their pre-training ratio (from 0.66 ± 0.20 to 0.74 ± 0.21, p > 0.05). Women also reduced end-systolic pressure (from 91 ± 10 to 87 ± 10 mmHg), and both groups reduced central pulse wave velocity (from 6.0 ± 1.0 to 5.6 ± 0.6 m/s, p < 0.05).

Conclusion

We conclude that after 8 weeks of aerobic training, only women reduced their coupling ratio due to an increase in Elv. This suggests that aerobic exercise training elicits sex-dependent changes in the coupling ratio in young, healthy individuals.

Improved ejection fraction after exercise training in obesity is accompanied by reduced cardiac lipid content

CONTEXT

Skeletal muscle and cardiac lipid accumulation are associated with diminished insulin sensitivity and cardiac function, respectively. In skeletal muscle, physical activity paradoxically increases fat accumulation, despite improvement in insulin sensitivity. Whether cardiac muscle responds similarly remains unknown.

OBJECTIVE

The objective of the study was to investigate cardiac lipid content and cardiac function after a 12-wk training program.

DESIGN

This was an intervention study with pre/postmeasurements.

SETTING

The study was conducted at Maastricht University Medical Center.

PARTICIPANTS

Participants included 14 healthy, male overweight/obese subjects (age 58.4 +/- 0.9 yr, body mass index 29.9 +/- 0.01 kg/m(2)).

INTERVENTION

Intervention included a supervised 12-wk training program with three sessions per week (endurance and strength training).

MAIN OUTCOME MEASURES

Maximal whole-body oxygen uptake, fasting plasma parameters, systolic function (by CINE-magnetic resonance imaging), and cardiac lipid content (by proton magnetic resonance spectroscopy) were measured.

RESULTS

Maximal whole-body oxygen uptake increased (from 2559 +/- 131 to 2702 +/- 124 ml/min after training, P = 0.05). Plasma concentrations of glucose decreased (from 6.3 +/- 0.2 to 5.7 +/- 0.2 mmol/liter, P < 0.001); plasma triacylglycerols and (free) fatty acids did not change. Also, body weight (from 94.2 +/- 3.6 to 92.9 +/- 3.6 kg, P = 0.10) and fat percentage (from 33.6 +/- 1.7 to 32.5 +/- 2.0%, P = 0.14) was unchanged. Left ventricular ejection fraction improved (from 52.2 +/- 1.3 to 54.2 +/- 1.2%, P = 0.02), and cardiac lipid content in the septum was decreased after training (0.99 +/- 0.15 to 0.54 +/- 0.04%, P = 0.02).

CONCLUSIONS

Twelve weeks of endurance/strength training significantly reduced cardiac lipid content in overweight subjects and was paralleled by improved ejection fraction. This is in line with a lipotoxic action of (excess) cardiac lipids on cardiac function, although a causal relationship cannot be derived from this study. Further research is needed to clarify the clinical relevance of cardiac lipid content in the etiology of cardiovascular complications.