Sex differences in left ventricular stroke work and cardiac power output per unit myocardium relate to blood pressure in apparently healthy adults

Abstract

Background: Left ventricular stroke work per unit myocardium (LVSWM) and cardiac power output per unit myocardium (CPOM) are important measures of myocardial workload. The sex differences in the myocardial workload and its correlation with blood pressure remain largely unclear.

Objectives: The purpose of this study is to investigate the sex differences in LVSWM and CPOM, and to relate them to blood pressure in a cohort of apparently healthy adults.

Methods: The LVSWM and CPOM were estimated in 596 age- and heart rate-matched apparently healthy adults (298 men) using transthoracic echocardiography combined with cuff-measured brachial blood pressure. The data were compared between sexes, and the sex differences in LVSWM and CPOM were related to blood pressure.

Results: After adjustment for the blood pressure, the LVSWM and CPOM were higher in women than in men [75.0 (73.7-76.4) vs 64.9 (63.5-66.2) cJ/100g for LVSWM, and 912.4 (894.1-930.6) vs 780.2 (762.0-798.5) milliwatt/100g for CPOM, respectively; all P<0.001]. After adjustment for the LVSWM and CPOM, the mean systolic and diastolic blood pressure were 7.4 mm Hg and 5.2 mm Hg higher in men than in women, respectively (all P<0.001).

Conclusions: For any given blood pressure, the workload per unit myocardium is higher in apparently healthy women than in their male counterparts. A sex-specific definition of normal blood pressure with a relatively lower threshold for women can minimize the sex differences in the myocardial workload, which might reduce the potentially comparatively higher risk of heart failure in women.

Fig 1. Sex difference in LV external work in 596 apparently healthy adults (298 men).

The LVSW and CPO, which represent the overall LV function, are higher in men than in women (Fig A and B). The LVSWM and CPOM, which represent the workload per unit LVM, are higher in women than in men (Fig C and D). Nonstandard abbreviations and acronyms as in Table 1.

Fig 2. Linear correlation and regression between the LVSWM and Ó_ƒ—peak, and between CPOM and Ó_ƒ—peak in 596 apparently healthy adults (298 men).

Very strong correlation exists between the LVSWM and the Ó_ƒ—peak (A), and a strong correlation exists between the CPOM and the Ó_ƒ—peak (B). The natural logarithm of LVSWM, CPOM, and the Ó_ƒ—peak are normally distributed data. C and D show that both the LVSWM and the CPOM increase with Ó_ƒ—peak (ln LVSWM = -3.233 + 1.223 × ln Ó_ƒ—peak; and -1.007 + 1.266 × ln Ó_ƒ—peak). These figures indicate that the higher the LV myocardial afterload is, the more work has to be done by per unit myocardium. Abbreviations as Table 1.