Cardiac Control During Exercise

Functions of the Cardiovascular System The cardiovascular system serves a number of important functions, the major cardiovascular functions fall into five categories: 1. Delivery 2. Removal 3. Transport 4. Maintenance 5. Prevention

Functions of the Cardiovascular System Delivers O2 and nutrients to every cell in the body Removes CO2 and waste from every cell in the body Transports hormones from glands to their target receptors Maintains body temperature and pH levels Prevents infection

Structure and Function of the Cardiovascular System Any system of circulation requires three components: 1. Pump (Heart) 2. A system of channels (the blood vessels) 3. A fluid medium (the blood)

Structure and Function of the Cardiovascular System Heart Two Atria (receivers) Two Ventricles (senders) Path of Blood (Cell to Heart) **Deoxygenated Blood ** Capillaries Venules Veins Superior or Inferior Vena Cava

Structure and Function of the Cardiovascular System Path of Blood (At the Heart) ** Deoxygenated Blood ** Right Atrium Right Ventricle Pulmonary Arteries *Lungs--> Receives Oxygen ** Oxygenated Blood ** Pulmonary Veins Left Atrium Left Ventricle Path of Blood (Heart to Cell) ** Oxygenated Blood ** Aorta Arteries Arterioles Capillaries

The Cardiac Conduction System The heart has the ability to generate its own electrical signal called autoconduction. The heart contracts rhythmically without neural stimulation The four of the components of the cardiac conduction system are: 1. Sinoatrial (SA) node 2. Atrioventricular (AV) node 3. Atrioventicular (AV) bundle 4. Purkinje fibers

The Cardiac Conduction System The impulse for the heart to contract is initiated from the SA node (The Pace Maker) The electrical impulse spreads to the AV node As the electrical impulse spreads through the Atria they are signalled to contract The AV node conducts the impulse fron the atria to the ventricles The impulse then enters the AV bundle and then the Purkinje fibers

Extrinsic Control of the Heart Activity Although the heart initiates its own electrical stimulus (intrinsic control), it can be altered Three Extrinsic systems that can affect the heart are: 1. The parasympathetic nervous system 2. The sympathetic nervous system 3. The endocrine system (hormones)

Extrinsic Control of the Heart Activity The Parasympathetic Nervous System It slows down impulse conduction thus, decreases heart rate The Sympathetic Nervous System It stimulates the impulse thus, increasing heart rate The Endocrine System Norepinephrine and Epinephrine (Cateholamines) Stimulate the heart, increasing its rate

Vascular System Vessels that transport blood from the heart to the tissues and back: Arteries Arterioles Capillaries Venules Veins

Vascular System Arteries & Arterioles Capillaries Veins Carries blood AWAY from the heart Carries oxygenated blood The largest largest, most muscular & most elastic Capillaries Narrowest vessels , one cell thick All exchange between blood and tissue occurs at the capillaries Veins Carries blood TOWARDS the heart Carries deoxygenated blood Contain valves to prevent back flow of blood

Vascular System Return of Blood to the Heart Most of the time we are in an upright position, the cardiovascular system requires assistance to overcome the force of gravity when returning blood for the lower parts of the body. The three basic mechanism are: 1. Breathing 2. The Muscle Pump 3. Valves

Vascular System 1. Breathing 2. The Muscle Pump 3. Valves Each time you inhale or exhale, pressure changes in the abdominal and thoracic cavities assist blood return to the heart 2. The Muscle Pump When skeletal muscle contract the vein in the immediate vicinity are compressed and blood is pushed upward towards the heart 3. Valves Inside the veins Allow the blood to flow in ONE direction, thus preventing back flow and pooling of blood

The Blood The volume of blood in the body varies considerably with individual size and state of training Larger the size and the highier the level of endurance training the highier the amount of blood ~ Without training 5-6 L in men and 4-5 L in women

Composition of Blood 55 - 60 % of the total blood volume is Plasma 90% of Plasma is H2O 40 - 45 % of total blood volume are Red Blood Cells (RBC), White Blood Cells (WBC) or Platelets

The Blood Red Blood Cells White Blood Cells Platelets RBC transport oxygen primarily bound to their hemoglobin Each RBC contains ~ 250 million hemoglobin, each able to bind to 4 O2 molecules, so each RBC can bind up to a billion molecules of O2 White Blood Cells WBC protect the body from disease organism invasion Adults have ~ 7, 000 WBC per cubic mm of blood Platelets Are not really cells, but rather cell fragments Required for blood coagulation (clotting), which prevents excessive blood loss

Cardiovascular Response to Exercise All changes to the cardiovascular system have a similar goal: To allow the system to meet the increased demands placed upon it by carrying out its functions with maximum efficiency We will look at the changes of the following components of the cardiovascular system: Heart Rate Stroke Volume Cardiac Output

Heart Rate Heart rate reflects the amount of work the heart must do to meet the increased demands of the body when engaged in activity Must compare at Rest vs. Exercise Maximum Heart Rate - the highest heart rate value you achieve in ALL OUT effort to the point of exhaustion HR max = 220 - Age

Heart Rate Resting Heart Rate Heart Rate during PA Avg 60 - 80 bpm can be as high as +100bpm to as low as 28-40 bpm Your rest heart rate dereases with age but increases with temperature or altitude Pre exercise heart rate are NOT good indicators of RHR Heart Rate during PA When you begin your HR increases rapidly in proportion with the intensity of the PA When the rate of work is held constant at submaximal levels, HR reaches a plateau This plateau is the steady state heart rate

Measuring your Heart Rate

Stroke Volume Stroke Volume is determined by: Stroke Volume is the volume of blood pumped per contraction Stroke Volume is determined by: 1. The volume of venous blood returned to the heart 2. The capacity to enlarge the ventricle 3. Ventricle contractility 4. Aortic or Pulmonary Artery pressure (the pressure which the ventricle must contract against) The first two have to do with the filling capacity of the ventricles The second two have to do with the ability to empty the ventricles

Stroke Volume SV = EDV - ESV Stroke volume increases with increasing rates of work, but only up to exercise intensities between 40-60% of maximal capacity End-Diastolic Volume (EDV) - the volume of the ventricle when filled End-Systolic Volume (ESV) - the volume of the blood remaining in the ventricle SV = EDV - ESV

Explanations of SV Increase Frank-Starling Mechanism A larger volume of blood enters the chamber when your ventricle fills up, thus the ventricle walls will stretch more. In order to eject the greater amount of blood, your ventricle must react to this increased stretching by contracting more strongly. There is also an increase in the muscular strength of the ventricle through exercise, thus increasing the contractile strength of the ventricle

Cardiac Output Cardiac Output is the total volume of blood pumped by the ventricle per minute or simply the product of heart rate (HR) and stroke volume (SV) CO = HR x SV Thus any changes in HR or SV will have an impact on the other component.

Cardiac Output 1. You rise from a reclining position to a sitting position, to standing. 2. You start to walk, than jog and finally run? How does your heart respond?

Cardiac Output 1. If your HR in the reclining position is 50 bpm it will increase to about 55 bpm and to about 60 pbm. When your body shifts from reclining to a standing position your SV drops immediately, due to gravity pulling the blood down and decreasing the amount of blood to the heart. Thus, the increase in HR when changing to an upright position is to maintain the Cardiac Output because CO = SV x HR

Cardiac Output #2 As you begin your activity, your HR increases from about 60 bpm to 90 bpm, with a jog it goes to 140 bpm and can reach 180 bpm with a run. The increase in HR maintains your CO when changing positions However, your SV and your HR both increase during activity thus, increasing your cardiac output

Cardiac Output During exercise, cardiac output increases primarily tomatch the need for increased oxygen supply to the working muscles!!!