Discussion
The present study assessed peak EL in three major phases of the cardiac cycle in elderly patients with hypertension. The results obtained showed that age and LVMI did not correlate with peak EL in these patients and that the indices of transmitral flow and LVOT parameters were associated with ED-EL, LD-EL, and Sys-EL.
Three peaks were observed in EL in the LV cavity of elderly outpatients in the present study, which is consistent with previous findings (12) (13) (14) (17). In the present study, ED-EL and LD-EL were higher than Sys-EL, while LD-EL was higher than ED-EL. These results were in contrast to the findings obtained from children and young healthy volunteers, showing that ED-EL was more likely to be higher than LD-EL (12) (13).
In the present study, a direct correlation was not observed between EL and age; however, EL correlated with the parameters of diastolic function. Diastolic function in the LV decreases with age (1). Aging is associated with cardiovascular stiffness and structural changes due to cardiomyopathy, ischemia, or ventricular dysfunction, resulting in LV diastolic dysfunction. Diastolic function in the LV involves relaxation and compliance. Regarding echocardiographic parameters, reduced LV relaxation generally decreases the E/A ratio and e’, leading to an impaired relaxation pattern (9). The JAMP (The Japanese Normal Values for Echocardiographic Measurements Project) study previously reported normal values for echocardiographic parameters in a healthy Japanese population and showed that the age at which E wave and A wave heights are reversed in a healthy population is approximately 60 years old (18). Patients in the present study were older than 60 years (between 66 and 97 years), and all had hypertension; therefore, LV diastolic dysfunction of varying severities was more prevalent in this group than in children and a young healthy population. The differences observed in EL patterns between the elderly patients in the present study and children or a young healthy population in previous studies were attributed to LV diastolic dysfunction.
In the present study, a higher E wave velocity positively correlated with higher ED-EL. Due to the age of this study group, very few patients had normal diastolic function. Therefore, the higher E wave velocity in this study reflected the severity of LV diastolic dysfunction, resulting in higher ED-EL. Wang et al. previously examined LV diastolic dysfunction and EL in chronic kidney diseases patients with preserved LVEF (LVEF>50%) and sinus rhythm based on blood fluid dynamics using VFM (7). The findings obtained revealed that ED-EL and LD-EL were higher in patients with grade II or III diastolic dysfunction than in those with grade Ⅰ, and were also higher in patients with grade I diastolic dysfunction than in the control group. The majority of patients in the present study had grade Ⅰ or II diastolic dysfunction, and the peak diastolic EL pattern observed was similar to that reported previously. Therefore, this suggested that LV diastolic dysfunction caused by aging and hypertension increased ED-EL and LD-EL in the LV cavity.
The proportion of patients with HF and preserved EF (HFpEF) is high in the elderly (16) (14, 19). HFpEF often necessitates the evaluation of LV diastolic function. Diastolic dysfunction is assessed by combining various measurements obtained from echocardiography (9); however, this method is complex. The present results and previous findings indicated a relationship between EL in LV and LV diastolic function (14) (20). Therefore, the evaluation of LV EL in each phase, which is simpler than existing methods, has potential as a useful and comprehensive parameter for assessing diastolic function.
Sys-EL correlated with peak velocity in LVOT and the E/A ratio. Peak velocity in LVOT showed a positive correlation. Based on patient backgrounds and exclusion criteria, the patient population examined in the present study had relatively stable cardiac function and none had more than moderate valvular diseases. Therefore, it is considered that morphological changes in LVOT, such as sigmoid septum or hypertensive hypertrophy, which are often observed in elderly patients, affected LVOT parameters. These morphological factors need to be considered in future research. The E/A ratio negatively correlated with Sys-EL. The E/A ratio is a comprehensive index of LV diastolic function and is used to evaluate left ventricular relaxation ability, LV filling pressure, and atrial function (9) (21). In elderly patients, a higher E/A ratio reflects more severe diastolic dysfunction of LV and often accompanies LV systolic dysfunction. Therefore, a higher E/A ratio is associated with lower Sys-EL. The results obtained on the E/A ratio in the present study suggested that diastolic function affected not only diastolic, but also systolic blood flow. Previous studies reported that the incidence of isolated diastolic HF was low and many patients with diastolic HF exhibited subclinical systolic function (22) ((23), which was consistent with the present results on the E/A ratio in Sys.
LVOT TVI and flow velocity positively correlated with ED-EL and LD-EL (Figure 2), suggesting that LVOT blood flow affected LV diastolic function. Blood is viscous and generates frictional heat due to its viscosity at sites at which turbulent flow and vortexes occur. The energy of this frictional heat is called EL in blood flow. EL increases at sites at which large vortexes occur locally and is smaller at those with laminar flow (7) (8) (20). In the present study, LVOT parameters related to vector positively correlated with EL in the LV during ED, LD, and Sys. The morphology of the LVOT affects the formation of LV blood flow. Therefore, the morphology of the LVOT might be associated to intraventricular vector change, not only during Sys, but also ED and LD. Previous studies investigated vortexes in the LV cavity and their contribution to EL (14, 20) (24). The present study did not assess the formation of vortexes. The LVOT diameter did not correlate with EL in this study. Therefore, other factors affecting the morphology of LVOT, such as the angle between LVOT and LV inflow or sigmoid septum, may contribute to EL. In future studies, it is necessary to investigate the effects of these left ventricular outflow tract morphology-related factors on left ventricular blood flow and vortex formation.