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HEART BEATS, BLOOD PRESSURE, HEART RATE SB1 3C: DECEMBER 2012 ELECTRICITY AND THE HEART: WHY DO YOU SHOCK A PERSON TO GET THEIR HEART BEATING AGAIN? The heart generates its own electrical impulse The cardiac electrical signal controls: the number of electrical impulses (heart rate) It triggers the heart muscle to contract in the correct sequence as it spreads across the heart MEASURING HEART BEATS: Electrical activity of the heart is measured using an electrocardiograph: Instrument that detects electrical activity of the heart Electrocardiograph produces electrocardiogram (ECG or EKG) Graphical record of heart rate and rhythm AED AED (automated external defibrillator) Machine that delivers electric shock to the heart to restart the heart Used when: heart contractions are not coordinated and muscles are quivering not contracting (ventricular fibrillation) Heart rate is abnormal (cardiac arrhythmia) Heart rate is too fast (ventricular tachycardia) Improves survival rates by up to 30% if delivered in the first few minutes. With each passing minute, the probability of survival declines by 7 to 10% HEART RATE: Number of heart beats per unit time Expressed as beats per minute (bpm) Changes during rest, activity, exercise Detected by taking pulse: Radial artery (wrist) Carotid artery (neck) What is your pulse? Average healthy adult – 60-80bpm at rest Lance Armstrong – 32bpm at rest HEART SOUNDS: Lubb-dubb heart sounds are caused by closing of heart valves Valves of the heart close when heart contracts to prevent blood from flowing back into the ventricles Steps: http://www.youtube.com/watch?v=qYBtchCqPao 1. 2. 3. Atria relax, fill with blood – diastole Atria pushes blood into ventricle Ventricles contract, pushing blood into arteries – systole Increased pressure during systole causes AV valves to close – lubb sound Ventricles relax, pressure decreases, causes Semilunar valves to close – dubb sound BLOOD PRESSURE: The force of the blood on the walls of the arteries Measured using a sphygmomanmeter Cuff with air pocket is wrapped around arm Air pocket is inflated Cuts off blood flow to the arteries in the arm Stethoscope listens to blood entering the arm as the air is gradually released The pressure that you first hear the sound at is called the systolic blood pressure The cuff is deflated until you can’t hear the sound anymore, at this pressure it is diastolic pressure BLOOD PRESSURE: Normal systolic blood pressure for young people: Normal diastolic BP for young people: 80mm Hg Therefore, BP would be recorded as: 120mm Hg 120/80 or 120 over 80 Now you try: Lab: measuring heart rate and blood pressure