Exercise Physiology Section 7 PDF

Section 7 Cardiovascular & Autonomic response to Exercise&  Some Abnormal ECG Recordings 1. Sinus Tachycardia Elevated heart rate of impulses greater than 100 beats/min in an average adult. Causes: Physiological: exercise and stress. Pathological: fever and hyperthyroidism. Symptom...

Section 7 Cardiovascular & Autonomic response to Exercise&  Some Abnormal ECG Recordings 1. Sinus Tachycardia Elevated heart rate of impulses greater than 100 beats/min in an average adult. Causes: Physiological: exercise and stress. Pathological: fever and hyperthyroidism. Symptoms: Sinus tachycardia is often asymptomatic unless very rapid it may cause Heart palpitations , a racing, uncomfortable heartbeat or a sensation of "flopping" in the chest. Treatment:*Treatment of the cause. * Beta blockers are useful if the cause is sympathetic over activity.  2. Sinus Bradycardia Bradycardia can be a serious problem if the heart doesn't pump enough oxygen-rich blood to the body, brain and other organs might not get enough oxygen, possibly causing these Symptoms: *Near-fainting or fainting (syncope) *Fatigue *Chest pains *Easily tiring during physical activity  Causes of sinus bradycardia: 1-Vagal stimulation 2-Acetylcholine 3-Digitalis 4-Beta blocker When a slow heart rate is physiologically normal? 5-Well- trained athletes.  Effect of exercise on ECG: Cause: altered action potential duration, conduction velocity, and contractile velocity associated with the increase in heart rate during exercise. A -Heart rate increases linearly with exercise intensity up to maximum heart rate Failure of heart rate to rise or an abnormally slow increase during exercise (chronotropic incompetence) may indicate; -Electrical conduction pathway disease. -It may be drug induced by beta-blockers or calcium channel antagonists. B- RR interval: decreases C-QRS complex: minimal shortening D- QT interval experiences a rate-related shortening. N.B.Sometimes ECG abnormalities seen only during exercise. It is called a “stress test" or a “treadmill test" The autonomic nervous system regulates important functions of the body as blood pressure (BP), heart rate, thermoregulation and respiration. Autonomic function tests during exercise: These tests measure how the various systems in the body controlled by the autonomic nervous system respond to stimulation. They include: i- Heart rate variation during respiration ii- Heart rate variation during postural change iii- Heart rate response to valsalva manouver  i- Heart rate variation during respiration HR increases during inspiration and decreases during expiration Theses changes is called respiratory sinus arrhythmia. Respiratory sinus arrhythmia: cyclic variation in heart rate with respitation. - Heart rate increases during inspiration and decreases during expiration - It is a physiological phenomenon known as cardio-respiratory coupling results in modulation of sinus rhythm by breathing. - It occurs during rest and persist during exercise due to increase in ventilation. - Value :At rest it improves the efficiency of pulmonary gas exchange via efficient ventilation/perfusion matching. During exercise it increased due to increase ventilation. **Is detected by recording HR by using ECG while the subject is breathing deeply **The R-R interval on an ECG is shortened during inspiration and prolonged during expiration. Explanation of Sinus arrhythmia **HR increases during inspiration due to decreased cardiac vagal activity **HR decreases during expiration due to increased vagal activity **So, It is considered an index of cardiac vagal function. Procedure: 1- Connect ECG electrodes for recoding lead II 2- Ask the subject to breath deeply at a rate six breaths per minute for 3 cycles (allowing 5 seconds each for inspiration and expiration) 3- Record maximum and minimum heart rate with each respiratory cycle 4- Average the 3 differences: - Normal: > or equal 15 beats /min - Borderline: = 11-14 beats/min - Abnormal: < or equal 10 beats /min