Functional and structural changes in aorta of mice divergently selected for basal metabolic rate

Cardiovascular diseases (CVD) are one of the most common causes of mortality likely genetically linked to the variation in basal metabolic rate (BMR). A robust test of the significance of such association may be provided by artificial selection experiments on animals selected for diversification of BMR. Here we asked whether genetically determined differences in BMR correlate with anatomical shift in endothelium structure and if so, the relaxation and contraction responses of the aorta in mice from two lines of Swiss-Webster laboratory mice (Mus musculus) divergently selected for high or low BMR (HBMR and LBMR lines, respectively). Functional and structural study of aorta showed that a selection for divergent BMR resulted in the between-line difference in diastolic aortic capacity. The relaxation was stronger in aorta of the HBMR mice, which may stem from greater flexibility of aorta mediated by higher activity of Ca²⁺-activated K⁺ channels. Structural examination also indicated that HBMR mice had significantly thicker aorta's middle layer compared to LBMR animals. Such changes may promote arterial stiffness predisposing to cardiovascular diseases. BMR-related differences in the structure and relaxation ability of aortas in studied animals may be reminiscent of potential risk factors in the development of CVD in humans.

Intrafamilial aggregation and heritability of tissue Doppler indexes of left ventricular diastolic function in a group of African descent

Although several indexes of left ventricular (LV) diastolic function show heritability, the genetic influence on the tissue Doppler index, E/e' (early transmitral velocity/velocity of myocardial tissue lengthening), an index of LV filling pressures in those of black African descent is currently unknown. Furthermore, whether any genetic influences on E/e' are through an impact of LV remodeling or aortic function is unknown. Intrafamilial aggregation and heritability (SAGE software) of E/e' (echocardiography) were assessed in 129 nuclear families (29 spouse pairs, 216 parent-child pairs, and 113 sibling-sibling pairs) from an urban developing community of black Africans, independent of LV mass index (LVMI), LV relative wall thickness (RWT), central aortic systolic pressure (SBPc), and backward wave pressures (Pb) (applanation tonometry, SphygmoCor software). Independent of confounders including LVMI and RWT, E/e' was correlated in parent-child (r = 0.23; P < .001) and sibling-sibling (r = 0.29; P < .005), but not in spouse (r = 0.13; P = .51) pairs. The relationships between parent-child (r = 0.22; P < .001) and sibling-sibling (r = 0.29; P < .005) pairs persisted with adjustments for SBPc. The relationships between parent-child (r = 0.22; P < .001) and sibling-sibling (r = 0.26; P < .01) pairs also persisted with adjustments for Pb. Independent of confounders including LVMI and RWT, E/e' showed significant heritability (h(2) ± standard error of the mean [SEM] = 0.51 ± 0.11; P < .0001) which similarly persisted with adjustments for SBPc (h(2) ± SEM = 0.50 ± 0.11; P < .0001) and Pb (h(2) ± SEM = 0.49 ± 0.11; P < .0001). In conclusion, in a group of African ancestry, independent of LV remodeling and aortic function, E/e' shows significant intrafamilial aggregation and robust heritability. Hence, genetic factors may play an important role in determining moderate-to-severe LV diastolic dysfunction independent of cardiac remodeling or aortic function in groups of black African ancestry.

The cardiac blood supply-workload balance in children

It is well known that the reflected pressure wave in small children returns earlier than that in adolescent. The reason of early return of the reflected pressure wave in infancy is their height. The short distance between heart and reflection point makes the reflected pressure wave returning to the heart earlier. In adult, the early return (during systole) of the reflected pressure wave means disadvantage to cardiac blood supply-workload balance. The purpose of this study was to clarify whether the early return of the reflected pressure wave in small children impairs the cardiac blood supply-workload balance. This study enrolled 37 small left-to-right shunt patients with normal aortic circulation below 15 years of age. The aortic pressure waveform was recorded using a pressure sensor mounted catheter, and augmentation index and subendocardial viability ratio were calculated. The age of patients was 6.1 ± 3.2 years. The augmentation index was 8.7 ± 14.3 % and the index had a negative correlation with patients' age (r = -0.6243, p < 0.0001). The subendocardial viability ratio, which means the cardiac blood supply-workload balance, was 0.92 ± 0.14 and the index had a positive relationship with patients' age (r = 0.6435, p < 0.0001). The cardiac blood supply-workload balance gradually improves from infancy to young adulthood. One of the causes of the unfavorable cardiac blood supply-workload balance in infancy would be the accelerated aortic pressure wave reflection due to their short height.

Comprehensive assessment of biventricular function and aortic stiffness in athletes with different forms of training by three-dimensional echocardiography and strain imaging

AIMS

Previous studies have shown distinct models of cardiac adaptations to the training in master athletes and different effects of endurance and strength-training on cardiovascular function. We attempted to assess left-ventricular (LV) function, aortic (Ao) function, and right-ventricular (RV) function in athletes with different forms of training by using three-dimensional (3D) echocardiography, tissue Doppler imaging (TDI) and speckle-tracking imaging (STI).

METHODS AND RESULTS

We examined 35 male marathon runners (endurance-trained athletes, ETA), 35 powerlifting athletes (strength-trained athletes, STA), 35 martial arts athletes (mixed-trained athletes, MTA), and 35 sedentary untrained healthy men (controls, CTR). Two-dimensional and three-dimensional echocardiography were performed for the assessment of LV and RV systolic/diastolic function. LV and RV longitudinal strain (LS) and LV torsion (LVtor) were determined using STI (EchoPAC BT11, GE-Ultrasound). Maximum velocity of systolic wall expansion peaks (AoSvel) was determined using TDI. ETA experienced LV eccentric hypertrophy with increased 3D LV end-diastolic volume and mass and significant increase in peak systolic apical rotation and LVtor. In all groups of athletes, RV-LS was reduced at rest and improved after exercise. AoSvel was significantly increased in ETA and MTA and significantly decreased in STA compared with CTR. There were good correlations between LV remodelling and aortic stiffness values. Multivariate analysis showed aortic wall velocities to be independently related to LV mass index.

CONCLUSION

In strength-trained, endurance-trained, and mixed-trained athletes, ventricular and vascular response assessed by 3DE, TDI, and STI underlies different adaptations of LV, RV, and aortic indexes.