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.