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 Divided into two phases: 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 affect the cardiac cycle: Sympathetic 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 Atria contract. Ventricles contract. Heart relaxes and fills.

Stages of the Cardiac Cycle 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 Ventricles contract Forces the AV valves shut, pushes blood into the arteries. The ventricles relax Backflow prevented by closing of aortic and pulmonary valves Diastole Systole

Heart Beat - Sounds Caused by the closing of the heart valves Lubb – AV (atrioventricular) 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 system to conduct signals that trigger muscle contractions. Autorhythmic - cardiac muscle can contract without stimulation from the nerves. The autonomic nervous system does have inputs to the heart and normally regulates heart rate. Nodal tissue - 2 areas in the heart Has both muscular and nervous characteristics Can generate action potentials to cause contraction Sinoatrial (SA) node and atrioventricular (AV) node

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) (#2). Located in the lower part of the right atrium close to the tricuspid valve 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 Bradycardia 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), and disease.

Blood Pressure

Blood Pressure A measure of the pressure or force of blood against the walls of your arteries Systolic pressure the pressure when your heart contracts and pushes blood out Highest pressure Diastolic pressure 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

Factors affecting Blood Pressure Cardiac output This is 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 This is how much the arterioles resist the flow of blood. Diameter of the arterioles is regulated by muscles in their walls Arteriolar Constriction reduces blood flow, causing higher blood pressure. Arteriolar dilation opens vessels and increases blood flow, decreasing 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 arteriosclerosis

Low Blood Pressure Factors Low Blood Volume Dehydration Starvation (anorexia) Bleeding Decreased Cardiac Output Bradycardia Insufficient volume of blood being pumped Valve problems Arteriolar Dilation Heat Brain injury Arteriolar walls stop contracting

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 QRS complex T 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)