Cardiovascular IV
Cardiovascular System IV: Blood Flow and Pressure
Lecture Plan
Main Questions:
How do you control cardiac output?
What is the equation for cardiac output (CO)?
How do you regulate your blood flow?
Factors affecting blood flow include vessel size and blood thickness.How do you regulate your blood pressure?
Factors that regulate blood pressure include cardiac output and blood vessel resistance.Measuring blood pressure and understanding its importance in heart health.
Endurance Athletes Characteristics
Endurance athletes often have:
Bigger hearts with thicker walls that help pump blood more effectively.
Stronger hearts that can contract better, allowing for a higher stroke volume.
Lower resting heart rates, which means they can pump more blood with each beat, so they don't need to beat as often.
All of the above (Make a guess!)
Cardiac Output (CO)
Definition: Cardiac Output (CO) is the total amount of blood that each ventricle of the heart pumps out every minute. This measure shows how effectively the heart is working.
Formula:
Typical stroke volume is around 75 mL/beat (the volume of blood ejected with each heartbeat).
Typical CO is about 5,500 mL/min, or approximately 5.5 liters/min.
Heart Rate (HR): This is the number of times the heart beats in one minute.
Stroke Volume (SV): This is the amount of blood pumped by each ventricle per heartbeat, usually about 70 mL per beat but can be higher during exercise.
Reference to Video: "Cardiac Output" provides useful visual explanations about measuring and interpreting cardiac output.
Cardiac Output and Endurance Athletes
When we talk about endurance athletes:
They train their hearts a lot, resulting in bigger and stronger hearts.
These improvements allow for a higher stroke volume, which means they can maintain the same cardiac output with a lower heart rate, which is why they can perform better during long activities.
Factors Affecting Heart Rate
Brain: The area of the brain (medulla) controls heart rate by sending signals to the heart.
Neurotransmitters/Hormones:
Norepinephrine (NE): Increases heart rate and contractility.
Epinephrine: Released in stress situations, increases both heart rate and force of heart contractions.
Acetylcholine (ACh): Slows heart rate when activated by the body’s rest and digest response.
Heart Mechanism: The Sinoatrial (SA) Node is the natural pacemaker of the heart, controlling how fast the heart beats. Factors like exercise can stimulate this process to speed up the heart rate.
Heart Volumes
End-Diastolic Volume (EDV): The total volume of blood in the ventricle at the end of filling before the heart contracts, important for determining how much blood can be pumped out.
End-Systolic Volume (ESV): The volume of blood left in the ventricle after the heart has pumped out blood.
Stroke Volume (SV): Calculated by the difference between EDV and ESV:
Factors that Influence Stroke Volume
Venous Return: This is the amount of blood returning to the heart through veins, affecting EDV significantly.
Depends on: Amount of blood volume and the pressure in the veins.
Helped by:
Sympathetic nerves help blood vessels contract to push blood back to the heart.
Skeletal muscle pumps that help squeeze veins during movement.
Pressure drop while inhaling, which helps draw blood back to the heart.
Respiratory Pump:As the diaphragm contracts during inhalation, the intrathoracic pressure decreases, facilitating venous return from the abdomen and lower limbs to the heart. This process is crucial for maintaining venous blood flow, particularly during physical activity when muscle contractions and respiratory movements work in tandem to enhance circulation.
Control Mechanisms of Stroke Volume
Extrinsic Control: The strength of heart contractions can be increased by the sympathetic nervous system and hormones like epinephrine during times of stress or exercise.
Intrinsic Control: Related to how well the heart muscles can contract based on how much they are stretched at the start of a contraction:
The Frank-Starling Law of the Heart states that the more blood present in the ventricle before contraction, the stronger the heart will contract to pump it out.
Preload and Afterload
Preload: This refers to how much the heart is filled with blood before it contracts. The greater the filling (EDV), the stronger the contraction, which increases stroke volume.
Afterload: This is the pressure the heart has to work against to pump blood out into the arteries. Higher afterload means the heart has to work harder, which can leave more blood in the ventricle after contraction.( blood that sit in arterties = arterial blood pressure)
PV-loop describes press and volume of cardiac cycle over one complete heartbeat, illustrating the relationships between preload, afterload, stroke volume, and cardiac output. 2) passive ventricular filling occurs volume increases considerably and pressure increases slightly as blood enters. 3) atrial contraction completes filing. end diastolic volume is reached
Summary of Cardiac Output Control
Cardiac output is controlled by both heart rate and stroke volume, influenced by many factors such as hormones and nervous system activity.
Blood Flow Regulation
Key Factors: Blood flow is influenced primarily by pressure differences and resistance in the blood vessels.
Extrinsic vs. Intrinsic Factors: Extrinsic factors come from outside the blood vessels, like signals from the nervous system, whereas intrinsic factors are based on the needs of the organs themselves.
Pressure Dynamics
Blood naturally flows from areas of high pressure to areas of low pressure, similar to how air flows.
Normal blood pressure in arteries typically ranges around 80 to 120 mmHg, where higher values indicate stronger pressure during heart contractions.
Resistance in Blood Flow
Definition: Resistance is the force that opposes blood flow due to friction between blood and the walls of blood vessels.
Higher blood viscosity (thicker blood) increases resistance.
Factors that increase resistance include reducing the size of the blood vessels (vasoconstriction), which makes the heart work harder.
Vasoconstriction:the narrowing of blood vessels, which leads to increased resistance and elevated blood pressure as the volume of blood must push through a smaller diameter. This process can be influenced by various factors such as stress, hormones, and temperature, ultimately affecting overall cardiovascular health.
Blood Flow in Different Situations
Fight or Flight Reaction: In stressful situations, blood is redirected away from the digestive system to muscles and vital organs, allowing for a quick response to danger.
Extrinsic Factors Affecting Blood Flow
Sympathetic Nervous System: Releases epinephrine, which causes blood vessels in non-essential areas like the digestive system to constrict, while causing dilation (widening) in blood vessels serving muscles, increasing blood flow there.
Parasympathetic Nervous System: Acetylcholine can cause blood vessels in the digestive muscles to widen, allowing for more blood flow during rest.
Intrinsic Autoregulation Mechanism
Certain organs like the brain and kidneys can adjust their own blood flow based on their needs, regardless of overall body blood pressure, often triggered by chemical signals from the organs themselves.
-Autoregulation = vasodialation
-only brain and kidney can do this effectively, allowing them to maintain consistent function even during systemic fluctuations.
Regional Blood Flow Distribution
Different body parts need different amounts of blood depending on what they're doing:
The brain, skeletal muscles, heart, and skin have varying health needs, with blood flow adjusting to meet those requirements, particularly during different activities.
Blood Flow to Heart
Coronary Arteries supply blood directly to the heart muscle, ensuring it gets enough oxygen.
Trained athletes often have more coronary arteries, which assists in their higher performance and better heart health.
Blockages can be treated by procedures like balloon angioplasty or stent placement.
Blood Flow to Skeletal Muscles
During exercise, about 80% of blood is directed to skeletal muscles (through vasodilation), allowing them to work efficiently.
When at rest, only about 15% of blood is supplied to muscles, balancing supply based on activity levels.
Blood Flow to Brain
Increased activity in certain brain areas requires more blood, leading to localized widening of blood vessels (vasodilation) there to ensure adequate oxygen supply.
Blood Flow to Skin
Blood flow to the skin helps regulate body temperature; this is especially important when dealing with temperature changes from outside.
Normal blood temperature is around 38ºC (100.4ºF), and changes in blood vessel size can make the skin appear red or pale.
Summary of Blood Flow Regulation
Various factors influence how much blood flows to different body parts, including resistance and regulation by the nervous system.
Blood Pressure Overview
Definition: Blood pressure is the force that blood exerts on the walls of blood vessels, crucial for circulation and vascular health.
Regulation: Blood pressure is influenced by cardiac output, the amount of blood in circulation, and the resistance in the blood vessels.
Blood Pressure Regulation Mechanisms
An increase in the amount of blood pumped by the heart can lead to higher blood pressure, as can higher blood volumes due to fluid intake, emphasizing the interconnectedness of these factors in maintaining stable blood pressure.
-2 factors that affect BP is Cardiac output ,diameter of blood vessels, distance
Additionally, the elasticity of the blood vessel walls plays a crucial role; as arteries lose elasticity with age or disease, they can contribute to elevated blood pressure.
Effects of BP :
1. VOLUME: Increased blood volume can lead to higher blood pressure as the heart must work harder to pump the excess fluid throughout the body.
2.POSITION : Proper positioning of the body can influence blood pressure; for example, lying down often results in lower pressure readings compared to standing or sitting, due to changes in venous return and cardiac output.
3. ACTIVITY: Increased physical activity can influence blood pressure significantly; regular exercise helps to strengthen the heart, allowing it to pump more efficiently and potentially lowering resting blood pressure.
4. COLD TEMP( VASOCONSTRICTION): exposure to cold temperatures can lead to vasoconstriction, which increases blood pressure as blood vessels narrow, thereby raising resistance to blood flow. This physiological response can be particularly evident in colder climates or during winter months.
5. RESPIRATORY PUMP: the respiratory pump works by creating pressure changes in the thoracic cavity during breathing. When we inhale, the diaphragm contracts and moves downward, decreasing pressure within the thoracic cavity and allowing blood to flow more easily from the veins back to the heart. This can help to enhance venous return and, subsequently, improve cardiac output and regulate blood pressure.
Clinical Case Scenario with Mark
Mark's case illustrates how dehydration can lower blood volume, thereby dropping blood pressure and demonstrating the body's physiological responses to maintain stability.
Regulation through Constriction
Constriction of blood vessels can raise resistance to blood flow, resulting in increased blood pressure as the heart works harder during such conditions.
Clinical Application of Hypertension Treatment
Mark was prescribed lisinopril, a type of medication that helps lower blood pressure by blocking a hormone (Angiotensin II) that normally causes blood vessels to constrict, promoting relaxation and better blood flow.
Pressure Gradients in Vessels
As blood moves away from the heart (the aorta), the pressure decreases, showing how the circulatory system delivers blood while working against gravity and distance to reach all body parts.
Mid arteries branching out from the aorta experience a significant drop in pressure, yet they are designed to maintain sufficient pressure to ensure that blood efficiently reaches the capillary beds.
Capillaries are increase surface area for decrease pressure , allowing for efficient gas and nutrient exchange with surrounding tissues. This decrease in pressure within the capillary beds is essential for promoting the diffusion of oxygen and nutrients, as well as the removal of waste products, which is facilitated by the thin walls of the capillaries that enhance permeability.
Regulation by Baroreceptor Reflex
Baroreceptor Function: These are stretch receptors in the arteries that detect blood pressure changes and trigger automatic responses to adjust blood flow, like widening or narrowing blood vessels based on current pressure levels.
vasomotor center: Located in the medulla oblongata, the vasomotor center regulates vascular tone and is responsible for the constriction and dilation of blood vessels, thereby influencing blood pressure and ensuring adequate blood flow to various organs.
Measurement of Blood Pressure
Arterial blood pressure: pressure in arteries during cardiac cycle in arteries supplied by the aorta
Parameters:
Systolic Pressure: This is the pressure in the arteries during heartbeats (e.g., around 120 mmHg).
Diastolic Pressure: This pressure occurs between heartbeats when the heart is not contracting (e.g., around 80 mmHg).
Measurement Techniques involve listening to blood sounds as blood flows back into the artery with a cuff.
Pulse:This refers to the rhythmic expansion and contraction of the arteries as blood is pumped by the heart, typically measured at the wrist or neck, and averages around 60 to 100 beats per minute in a resting adult.
Mean Arterial Pressure (MAP)
Definition: The average blood pressure in a person’s arteries during one complete heartbeat cycle, important for assessing organ health and blood flow; typically around 93 mmHg.
Abnormal Cardiovascular Function
Hypertension: This is consistently high blood pressure (greater than 140/90 mmHg) and can lead to severe health problems like strokes and heart attacks.
Risk factors include age, being overweight, consuming too much salt, and family history.
Treatments usually involve lifestyle changes and medication to help manage these levels.
Circulatory Shock: This is a serious condition where not enough blood flows to the organs, potentially leading to organ failure.
hypovolemic shock: A type of circulatory shock that occurs due to a significant loss of blood volume, often resulting from severe bleeding or dehydration.
septic shock: A type of circulatory shock caused by severe infections that lead to systemic inflammation and a significant drop in blood pressure.
Congestive Heart Failure: This occurs when the heart can't pump enough blood to meet the body's needs, causing symptoms like shortness of breath and swelling from fluid build-up.