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Cardiac Cycle Setting the Tempo Cardiac Cycle – Overview • Events of each heartbeat – Highly coordinated so that both atria contract together and then both ventricles contract together • Systole – contraction of heart muscle • Diastole – relaxation of heart muscle Overview cont’d • Time for each cycle is influenced by autonomic nerves. • Two regulatory nervous systems – Sympathetic nervous system • Forms a division of the autonomic nervous system • Prepares the body for stress increases heart rate. – Parasympathetic nervous systems • Returns the body to normal resting state following stress Cardiac Cycle cont’d • Cardiac muscles are able to contract without being stimulated by external nerves. – Called myogenic muscle – allows your heart to beat without a continual reminder – Also able to recover quickly, the only rest they get is small time between beats. • Normal heart rate at rest is about 60-80 beats per minute Stages of the Cardiac Cycle • Fig 12.5 12-5 Heart Beat - Sounds • Caused by the closing of the heart valves – Lubb – AV valves close – Dubb – Semi lunar valves close • Heart murmurs are caused by an incomplete seal on a valve – Blood leaks past the closed valve, or flows backwards in the heart. – causes a whoosing, or gurgling sound Heart Beat - Intrinsic Control • Heart has its own intrinsic conduction system • Autorhymicity-unlike skeletal muscle, cardiac muscle can contract without neural stimulation • The autonomic nervous system does has inputs to the heart and normally regulates rate • Nodal tissue-2 areas in the heart • Has both muscular and nervous characteristics • Can generate action potentials to cause contraction • SA node and AV node 12-7 Heart Beat – The Pacemaker • Sinoatrial Node (SA) – A bundle of specialized nerves and muscles – located where the vena cava enter the right atrium. (#1) – Sends a signal over the two atria • Atrioventricular node (AV). – Located the lower part of the right atrium close to the tricuspid valve (#2) – picks up electrical impulses Heart Beat – The Pacemaker • AV Node sends nerve impulses via the Purkinje Fibres (#4) – two large nerve fibres – run through the septum, • Each nerve impulse triggers cardiac contraction – Atria contract first, followed by ventricles. Heart Beat • Tachycardia – Fast heart beat – heart rate exceeds 100 beats per min – can result from exercise or from the consumption of such drugs as caffeine or nicotine. • Bradycardia – Slow heart beat – Heart beat lower than 60 bpm – Can result from degeneration of the muscle (age), disease Mapping the Heart Beat • Electrocardiogram (ECG or EKG) – test that measures the electrical activity of the heart. – Traces how long the electrical wave takes to pass through your heart – Printed on paper covered with a grid of squares each represents 0.04 seconds. • 25 squares = 1 second • ECG’s printouts are usually is 6 seconds; a "six second strip." • Changes in electrical current reveal normal or abnormal events of the cardiac cycle. • Determines if – activity is normal, fast or irregular. – heart is enlarged or overworked. Interpreting ECG • P wave – first little hump – atria receives signal and contracts • QRS complex – Ventricles receive signal and contract – May just be an RS… this is still normal • R wave is the first wave ABOVE the midline • T wave – Recovery of the heart Normal Rhythm Bradycardia Tachycardia Abnormal Rhythym V-Tach (NO QRS) Blood Pressure Blood Pressure • A measure of the pressure or force of blood against the walls of your arteries • Systolic – the pressure when your heart contracts and pushes blood out – Highest pressure • Diastolic – the lowest pressure when the heart relaxes between beats • Normal blood pressure is below 120/80 mm Hg. – High blood pressure is consistently more than 140/90 mm Hg Our Heart the Pump The ventricles relax • Backflow prevented by closing of aortic and pulmonary valves Ventricles contract • Forces the AV valves shut, pushes blood into the arteries. Atria relax • causes them to fill with blood Atrial walls contract • Forces the AV valves open, and blood flows into the ventricles filling them up Sphygmomanometer • Measures blood pressure indirectly – Measures the pressure exerted by blood in the brachial artery • Blood flowing through the brachial artery makes no noise – A stethoscope is placed below the cuff to listen for the blood • The cuff is placed around your arm and brachial artery. – Air is pumped into the cuff until circulation is restricted. Sphygmomanometer • Pressure is slowly lowered until the blood is able to flow past, this is the systolic pressure – Doctors will hear this blood rushing through as a beat • Pressure continues to be lowered until the noise disappears – This is the diastolic pressure – Blood no longer needs to force the artery open to pass through. Blood Pressure Clip Factors affecting Blood Pressure • Cardiac output – The volume of blood pumped from the heart each minute – Increased output will increase blood pressure. • Raising your heart rate increases output! Factors affecting Blood Pressure • Arteriolar resistance – Diameter of the arterioles is regulated by muscles in their walls • Arteriolar Constriction reduces blood flow, causing higher blood pressure. • Arteriolar dilation, opens vessels increases blood flow and decreases blood pressure High Blood Pressure Factors • High Blood Volume – High Salt levels cause excess water in our blood increasing our blood volume • Increased Cardiac Output – Tachycardia – Overactive Sympathetic Nervous System • Arteriolar Constrictors – Caffeine and Nicotine – Cold – Blockages in the arteries • Caused by artheriosclerosis Low Blood Pressure Factors • Low Blood Volume – Dehydration – Starvation (anorexia) – Bleeding • Decreased Cardiac Output – Bradycardia – Insufficient stroke volume – Valve problems • Arteriolar Dilation – Heat – Brain injury • Arteriolar walls stop contracting