Heart Disease and Nutrition

Define coronary heart disease (CHD)

Coronary heart disease (CHD), also known as coronary artery disease, is a disease in which the coronary arteries supplying the heart are unable to provide it with enough blood.

Discuss the importance of CBF & myocardial O2 demand

The heart is a very oxygen-hungry organ. Every minute, it consumes more oxygen than any other organ of the body. The heart is also extremely efficient at extracting oxygen from the blood (removes around 75% of oxygen from the blood passing through), so during times of increased oxygen demand, there isn't a lot of leeway for the heart to remove more oxygen from the blood. Instead, coronary blood flow (CBF) is most important for maintaining oxygen delivery during times of need, such as during exercise.

Coronary blood flow is greatest during diastole (relaxation of the heart), as during systole (contraction) the blood vessels are squeezed. In fact, at the end of isovolumetric contraction, there might even be some backflow from the coronary arteries to the aorta. Another factor affecting CBF is perfusion pressure: the greater the perfusion pressure, the greater the blood flow.

Explain the causes & risk factors for CHD

Causes

The main causes of CHD are vascular spasm, atherosclerosis, and other complications such as thromboses (clots).

Vascular spasm refers to transient vasoconstriction. Common triggers include cold, physical exertion and anxiety, and can occur in both healthy and CHD patients. Vascular spasm is reversible and rarely causes long-term damage. Vascular spasm can be caused by α-vasoconstrictors (e.g. noradrenaline), but in some cases it might be caused by a heightened vasoconstrictor response to acetylcholine, or by deficient basal release of nitric oxide.

Atherosclerosis refers to the formation of a plaque, which is made up of cholesterol, calcium and white blood cells. It is initiated by inflammatory processes. Macrophages can digest LDL, forming foam cells, which can eventually rupture to form fatty streaks. There are two main types of plaques: stable plaques, which consist of mainly smooth muscle and extracellular matrix, and unstable plaques, which consist of mainly macrophages and foam cells. Atherosclerosis can cause partial or complete blockages of the coronary arteries. The amount of damage caused depends on the size and location of the blood vessel.

When atherosclerotic plaques form, they may not be noticed immediately. That is because we have collateral vessels that can grow rapidly when there is a blockage. Symptoms may only occur once the collateral vessels are also blocked. Therefore, CHD is often known as a "silent killer."

Thromboses are caused by blood platelets sticking to collagen. This may be related to atherosclerosis: collagen may be exposed when plaque breaks through a weakened endothelial lining. Thromboses can also block arteries and cause damage.

Risk factors

Risk factors can be broken down into uncontrollable and controllable risk factors. Uncontrollable factors are things that you can't do much about, such as age (risk increases with age), sex (pre-menopausal females are less likely to get CHD as oestrogen has a protective effect) and heredity (certain conditions, such as familial hypercholesterolaemia, can increase your risk). Controllable factors are things that you can control to some extent, such as blood pressure, high blood cholesterol, smoking, obesity, physical activity, and so on.

There are several ways in which hypertension can lead to CHD. Hypertension induces endothelial dysfunction, exacerbating atherosclerosis. It may also lead to left ventricular hypertrophy, as the ventricles need to grow larger to pump against the greater pressure. The problem with this is that the larger muscle needs more blood. Hypertension is also associated with other metabolic disorders such as insulin resistance, which may contribute to CHD risk.

Hyperglycaemia, such as in diabetes, can raise CHD risk in several ways. Hyperglycaemia can lead to glycosylation of proteins in the arterial wall, which in turn can lead to atherosclerosis. Hyperglycemia can also increase the formation of reactive oxygen species, also leading to atherosclerosis.

Smoking is not only bad for your lungs, but is also bad for your heart. Smoking lowers HDL levels and increases circulating fibrinogen, increasing risk of atherosclerosis. Nicotine can cause vasoconstriction, and carbon monoxide reduces the oxygen carrying capacity of the blood.

Discuss prevention & treatment of CVD

The main preventative strategies for CVD are eating a healthy diet and exercising. Treatments involve lifestyle changes, medication (mainly nitroglycerin, a potent vasodilator) and, in more extreme cases, bypass surgery.

Describe the Mediterranean diet

The Mediterranean diet is often touted as a healthy diet for CHD prevention. It is characterised by lots of fruit, vegetables, grains, and so on, more fish, poultry and dairy than red meat, and olive oil as the main source of fat. Olive oil has very high levels of monounsaturated fats, particularly oleic acid, which may have a protective effect against CHD. Olive oil also contains phenols, which inhibit the production of reactive oxygen species.