X. EXERCISE STRESS TEST
Graded exercise testing introduced by Robert Bruce five decades ago remains an important diagnostic test for coronary artery disease. When coronary arteries become obstructed by atheromatous plaques, the supply of blood to the heart muscle becomes deficient and the muscle shows signs of ischemia that can be detected by the ECG. Ischemia is defined as a temporary lack of blood and oxygen to an area of cells for example the heart muscle, usually due to severe obstruction of the artery supplying blood to this area of muscle. Thus, the term ischemic heart disease is often used by physicians as it is the manifestation of coronary artery disease.
A stress test involves walking on the treadmill or cycling while your ECG is continuously recorded. The ECG terminals are taped onto your chest. Walking on the tread¬mill is easier if you wear running shoes or other comfor¬table flat shoes. The treadmill speed and its inclination are programmed to increase every three minutes so that you walk faster up a grade and are jogging by the 10th minute. Healthy individuals are exercised to 90% of their maximal heart rate. The test is discontinued if chest or leg pain, fatigue, or shortness of breath develops or if the ECG shows insufficient oxygen to the heart muscle. The blood pressure is taken every three minutes, and the systolic blood pressure usually rises by 20–40 mmHg. A 40-year-old who is physically fit with good cardiopulmonary condition can usually exercise for 10–12 minutes, reaching a heart rate of 160–180 beats per minute without having undue shortness of breath. The test is completed by about 2 minutes of slow walking to cool down before the treadmill is turned off.