The cardiac cycle involves systole and diastole and is carried out automatically through the nodal tissues of the heart. Our body has the ability to increase or decrease the cardiac output when required. This is because nodal tissues, which induce cardiac activity, are controlled by the medulla oblongata of the brain through sympathetic and parasympathetic nerves.
The cardiac output can be measured using an electro-cardiograph. This recording is called an electrocardiogram or ECG. It provides information on the rate of heartbeat and the size and position of the chambers of the heart.
In a standard ECG, the ‘P’ wave corresponds to the contraction of the atria, that is, atrial systole. It is followed by the ‘QRS’ wave which corresponds to the contraction of the ventricles, that is, the ventricular systole. The final ‘T’ wave corresponds to the relaxation of the ventricles to the normal state. The number of QRS complexes is equal to the number of heartbeats. Hence, any deviation from the standard ECG signals a problem relating to the heart.
Blood pressure or BP is the pressure exerted by the blood on the walls of the blood vessels, when the heart pumps the blood and is measured using a sphygmomanometer. The heart undergoes alternate systole and diastole and hence BP is measured as systolic pressure and diastolic pressure. A healthy individual has a systolic and diastolic pressure of 120 over 80 mmHg. When BP is 100 over 50 or less, it is called low blood pressure or hypotension. Similarly, when BP is 140 over 90 or more, it is called high blood pressure or hypertension.
Thus, any drastic change from normal blood pressure leads to coronary artery disease or CAD. Calcium, fats and cholesterol accumulate together and form plaque in the coronary artery, thereby affecting the coronary circulation of the heart. This accumulation of plaque is called atherosclerosis. Some of the symptoms of CAD include angina, heart attack, cardiac arrest or heart failure.