Some patients suffer from high ventricular pressure. This causes fluid to build up outside the blood capillaries. Explain why? How does widening the blood vessels using drugs reduce blood pressure?

Blood pressure is the result of the force exerted by the blood against the arteries through which it flows.This is determined by various factors including the compliance of blood vessels, the presence of atherosclerotic disease, fluid status and cardiac function. A common medical condition resulting in high pressure within blood vessels is heart failure where there is a reduction in cardiac output predominately due to reduced stroke volume as the heart muscle is damaged. This relates to the equation: CO = HR x SVIn situations such as when there is a higher ventricular blood pressure and hence, high capillary pressures (as these are the downstream vessels), there is an increase in hydrostatic pressure. This is the pressure exerted by the blood. The distribution of fluid in the body is controlled by the balance between this hydrostatic pressure and oncotic pressure, which is the pulling effect of proteins within the blood. As hydrostatic pressure increases, there comes a point where this pressure is greater than the oncotic pressure and an imbalance is created. Fluid is forced/filtered outside the blood capillaries leading to increased extracellular fluid and classical signs and symptoms of right heart failure, like pulmonary oedema (fluid in the lungs), and peripheral oedema (fluid in the legs, small of back). This fluid is now extracellular and as such, cannot be drained by the lymphatic system so will continue to build up as long as there are unequal pressures.Some drugs that we can give patients help to reduce these problems. By widening blood vessels, e.g. using nitrates, the pressure within these vessels falls. This can help the heart and reduce blood pressure indirectly by reducing strain (less venous return, and hence reduced stroke volume), but can also directly reduce blood pressure by reducing the hydrostatic pressure exerted by the fluid (less resistance in blood vessels). As this pressure is reduced the equilibrium with oncotic pressure can be reached and hence the fluid shift does not occur and the signs and symptoms related to tissue fluid build up can be reduced.This is how I would want the answer to be explained - in my experience, I achieved better results by using a bullet point approach where I checked past papers and learnt the relevant points for each question. By answering in this way, it makes each separate point clear, and reminds you (and the examiner!) to include all the necessary information.