Chapter 20 Clinical Exercise Physiology
Uses of Clinical Exercise Testing • Diagnose the presence and severity of disease • Establish the functional capacity of an individual • Evaluate medical therapy Exercise testing is used in a variety of clinical settings that are summarized in Table 16.1. The importance of exercise in the prevention, diagnosis,and rehabilitation of the most common and deadly diseases of today’s society can not be overemphasized.
Contraindications of Clinical Exercise Testing Due to the potential for exercise to pose a too greater risk to life or injury in individuals with disease or specific symptoms of disease or ill health, guidelines exist for when to not conduct an exercise test. Some of the contraindications to exercise testing include: • Recent MI • Third-degree AVblock • Severe aortic stenosis • Acite infection • Unstable angina • Acute congestive heart failure • Aneurysm • Significant emotional distress
R T P T Knowledge of electrocardiography (ECG) is essential in clinical exercise physiology. The 12-lead ECG is a vital component of the evaluation of heart function during the exercise test. P Q S P-R Q-T Atrial depoplarization Ventricular depolarization
Interpretation of the 12-Lead Electrocardiogram You should use a consistent approach every time you evaluate any ECG. Rate Rhythm Axis Tachycardia - HR > 100 b/min Bradycardia - HR < 60 b/min Arrhythmias - abnormal or inconsistent cardiac rhythms Axis - refers to the direction of depolarization of the mean QRS vector (0 - +90)
-90° The hexaxial arrangement of the limb leads -150° -30° aVR aVL I 0° 180° +120° III II +60° aVF +90°
ST-Segment Depression The hallmark of myocardial ischemia. Caused by the reduction in arterial blood supply to region(s) of the myocardium, which in turn alters the myocardial membrane potential, causing the ST segment depression. Downsloping Horizontal Upsloping Myocardial Infarction - myocardial cell death resulting from excess ischemia. The ability to detect myocardial ischemia on the ECG is increased by the inclusion of the precordial leads.
The Mason-Likar system for 12-lead ECG evaluation Limb-lead electrodes Precordial-lead electrodes
Some Common Clinical Exercise Test Protocols Bruce Naughton-Balke Balke The Bruce protocol
systolic mean diastolic
Predictive Value of Clinical Exercise Testing How accurately an exercise test correctly identifies an individual with coronary artery disease. The predictive value is estimated using Baye’s Theorum in the calculation of test sensitivity and specificity. Sensitivity - % of individuals who are tested that will have an abnormal test (~71%). Thus, there is a 29% likelihood for a false negative test. Specificity - % of individuals who are tested that will have a normal test (~73%). Thus, there is a 27% likelihood for a false positive test. Note: a positive test is one that detects disease when it is present