Sex and the cardiovascular system: the intriguing tale of how women and men regulate cardiovascular function differently

Abstract

The ability to recognize and appreciate from a reproductive standpoint that males and females possess different attributes has been long standing. Only more recently have we begun to look more deeply into both the similarities and differences between men and women, as well as between boys and girls, with respect to the structure and function of other organ systems. This article focuses on the cardiovascular system, with examples of sex differences in the control of coronary function, blood pressure, and volume. Recognizing the differences between the sexes with respect to cardiovascular function facilitates understanding of the mechanisms whereby homeostasis can be achieved using different contributions or components of the living system. Furthermore, recognition of the differences as well as the similarities permits the design of appropriate diagnostic instruments, recognition of sex-specific pathophysiology, and implementation of appropriate treatment of cardiovascular disease in men and women.

Fig. 1.

Sampling a subset of a population may represent only a portion of the population. Many of the data on healthy humans came from studies of Caucasians men of 18–22 yr of age that were part of the military, athletes, or European medical students. Depending on the variable measured, the degree of overlap between females (F) and males (M) could range from negligible to complete, and, a priori, it cannot be predicted whether they accurately reflect the responses of both sexes, even of the same age and race.

Fig. 2.

Total plasma protein and plasma albumin concentrations for males and females at 4 ages. Data are redrawn from Ciba-Giegy data tables (20a) (A). In B, the data shown in A were used to construct a plot of the net plasma oncotic pressures for the same groups. Dashed lines represent the “normal” values for humans (20a).

Fig. 3.

Is the Starling balance the same for males and females? In normal males and females, yes, the Starling balance is maintained; apparently, in females, the lower oncotic pressure (Δπ) is offset by the lower capillary hydrostatic pressure (P_cap) relative to that of healthy normal males.

Fig. 4.

In hypertension, the P_cap of females, while raised, is still less than that of males, as is Δπ. Without any changes in the system [e.g., hydraulic conductivity (L_p) and surface area (S) remain as in health], the forces favor fluid movement into the tissues of males relative to females (A). While Δπ remains, there is a reduction in the total number of skeletal muscle microvessels in hypertensive males, resulting in a reduction in S in the face of a rise in P_cap, bringing the Starling forces back into balance in males and females (B).