THE CARDIOVASCULAR SYSTEM

Transcription

1 THE CARDIOVASCULAR SYSTEM AND RESPONSES TO EXERCISE Mr. S. Kelly PSK 4U North Grenville DHS THE HEART: A REVIEW Cardiac muscle = myocardium Heart divided into two sides, 4 chambers (L & R) RS: pulmonary circulation (pumping deoxygenated blood to lungs) LS: systemic circulation (pumping oxygenated blood to the rest of the body) 1

2 THE ECG Electrocardiogram: graphic representation of electrical activity associated with heart contraction We can review this if necessary Note: electrical stimulation of heart VERY similar to electrical stimulation/contraction of skeletal muscles How does it look during exercise? FOCUS ON THE QRS WAVE The DURATION of the QRS wave is shorter in children and in tachycardia (elevated HR, accepted in adults as HR>100 BPM which often happens during exercise) An increase in AMPLITUDE of the QRS wave indicates cardiac hypertrophy (more on the significance of this to follow) Simply put, HR increases during exercise, so frequency and amplitude of the wave increase but not by the same amount. 2

3 CONCEPT HIGHLIGHT: VENOUS RETURN Generally: the return of blood to the heart. Four specific components to venous return (work simultaneously) Skeletal muscle pump Blood massaged back to heart by contraction of skeletal muscles (compression of veins) One-way valves in veins ensure proper direction of flow Thoracic pump (breathing) Pressure difference between thoracic cavity (low) and abdominal cavity (high) with each breath taken VENOUS RETURN CONT D Pressure difference in chest veins vs. abdominal veins also exists, one way valves ensure travel of blood from area of high pressure to low pressure Venoconstriction The nervous system stimulates constriction of veins during times of elevated cardiac output (ex: exercise) Nervous Stimulation of the heart (increase in blood flow throughout the body Key Question: Why is venous return so important during exercise? A: most important factor in regulating SV (later ) 3

4 CONCEPT HIGHLIGHT: BLOOD PRESSURE Cardiac Cycle: events of one heart beat 1. Dyastole: relaxation phase, heart filling 2. Systole: contraction phase, heart emptying Systolic pressure (numerator) is measured in arteries during contraction Dyastolic pressure (denominator) is measured in arteries during relaxation Common normal blood pressure: 120/80 (mmhg) Why is this important? How does it affect exercise? BLOOD PRESSURE AND EXERCISE Generally: Systolic pressure increases during exercise due largely to increased cardiac output Arteries expand during exercise (vasodilation) As a result, diastolic pressure may decrease a few points but often remains constant. As a result, blood pressure during and just after exercise is elevated, but (similar to HR) returns to resting levels after recovery/cool down BP and HR return to normal at similar rates. Failure for this to happen at similar rates (or at all) indicates potentially serious issues 4

5 DEFINITIONS AND CONCEPTS Cardiac Output (Q): volume of blood pumped out of the left ventricle in 1 min (L/min) Stroke Volume: amount of blood ejected from left ventricle in 1 beat (ml) LVESV: left ventricular end-systolic volume is the amount of blood remaining in the left ventricle after contraction LVEDV: left ventricular end-diastolic volume is the amount of blood in the left ventricle after the contraction of the left atrium 5

6 STROKE VOLUME SV(mL) = LVEDV (ml) LVESV (ml) There are 3 (but really 4) regulating factors for stroke volume 1. LVEDV 2. Aortic blood pressure 3. Strength (intensity) of ventricular contraction 4. Venous return (amount of blood returned to the heart) Stroke volume changes when any of these factors change (they ALL tend to change with exercise) Also changes with preload and afterload placed on LV (higher afterload = lower SV) 6

7 THE FRANK-STARLING LAW (GENERALLY) The ability of the heart to stretch and increase force of contractions in response to exercise Specifically: Left ventricle has the capacity to stretch, which accommodates increases in LVEDV When the ventricle stretches, more forceful ventricular contractions are the result More forceful ventricular contractions (cardiac muscle) mean that more blood is ejected BUT: the ventricle will only stretch so much after which point SV actually decreases Why is this important in terms of exercise? HEART RATE BASICS Measured in beats per minute Q (L/min) = SV (ml) x HR (beats/min) During exercise, Q can increase 15-20L/min Result of increased SV and HR Prolonged exercise results in fluid loss, therefore decrease in SV Q is maintained by a gradual increase in HR This is called cardiovascular drift Key concept: why are cardiovascular drift and hydration so important during exercise? 7

8 EXERCISE VS. REST CONCEPT HIGHLIGHT: HYPERTROPHIC CARDIOMYOPATHY Genetic condition involving abnormal thickening (hypertrophy) of the myocardium Most common cause of sudden death in athletes More serious in younger athletes One part of myocardium is often thicker than in the rest of the heart (asymmentric) Two mechanisms: 1. Thicker myocardium makes heart work harder to pump same amount of blood 2. Erratic configuration of myocardium cells causes fatal arrhythmia 8

9 PROBLEMS AND HCM VS. TRAINING Training: enlargement of heart chambers HCM: enlargement of heart walls Problem: varying causes of HCM so difficult to identify high-risk population Problem: grey area wherein chambers and walls enlarge slightly thereby confusing source of enlargement (in athletes) Recognize symptoms (see next slide) Solution (so far): decondition the athlete (no training) over several months Measure heart size; if heart has shrunk, enlargement was the result of training, not HCM SYMPTOMS AND PROBLEMS Symptoms Chest pain Dizziness Fainting Hypertension Palpitations Shortness of breath Undue or early fatigue Shortness of breath when lying down Problems Symptoms lead to misdiagnosis of athsma Some symptoms similar to those of intense training Lack of screening for HCM (in Italy all athletes are screened, HCM deaths nearly nonexistent). 9

10 TESTS FOR HCM Echocardiogram (thickened walls show up on echo) Blood tests Electrocardiogram Chest x-ray Stress test MRI Cardiac catheterization SOLUTIONS Cardiac screening ex: 2008 Maryland HS T&F Championships Doctors from Johns Hopkins Hospital provide free screening to 1000 athletes Implanted cardioverter-defibrillator Matchbox-sized device surgically implanted in chest to shock arrhythmic heart back to homeostatic rhythm Septal Myectomy: outflow valve from ventricle to aorta is widened surgically when meds don t work 10

11 SOLUTIONS CONT D Fluid/sodium restrictions: usually when heart failure symptoms present, usually alcohol restrictions Exercise: usually restricted to non-competitive aerobic activity, high-intensity, contact, and heavy resistance training are limited Follow up visits, preventing infections such as bacterial endocarditis (practicing good oral hygiene, regular medical appts 11