Pathophysiology
Cardiac output and peripheral resistance are the two determinants of arterial pressure. and so blood pressure is normally dependent on the balance between cardiac output and peripheral resistance. Cardiac output is determined by stroke volume and heart rate; stroke volume is related to myocardial contractility and to the size of the vascular compartment. Peripheral resistance is determined by functional and anatomic changes in small arteries and arterioles. The pathophysiology of essential hypertension is an area of research, and until now remains not well understood, but many theories have been proposed to explain this.
What is known is that cardiac output is raised early in the disease course, with total peripheral resistance (TPR) normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:
- An overactive Renin-angiotensin system leads to vasoconstriction and retention of sodium and water. The increase in blood volume leads to hypertension.
- An overactive sympathetic nervous system, leading to increased stress responses.
It is also known that hypertension is highly heritable and polygenic (caused by more than one gene) and a few candidate genes have been postulated in the etiology of this condition.
Read more about this topic: Essential Hypertension