Physiology Lecture #6- Cardiovascular response to exercise

What are the major functions of the cardiovascular system?

• delivery of O2

• removal of CO2

• transport of hormones

• thermoregulation

• maintenance of acid-base balance

• immune function

What are the 2 divisions of the CV system?

Pulmonary circuit and Systemic circuit

Pulmonary circuit

• right side of heart

• pulmonary arteries, veins, & capillary beds

Systemic circuit

• left side of the heart

• arteries, veins, & capillary beds

• O2 to the rest of the body

What are the 4 chambers of the heart?

Right atrium

Right ventricle

Left atrium

Left ventricle

Right atrium

Receives blood from superior and inferior vena cava

Right ventricle

receives blood from right atrium

Left atrium

receives blood from pulmonary veins (from the lungs)

Left ventricle

receives blood from left atrium, delivers blood to the systemic circuit via the aorta

• more force

What are the 4 valves of the heart and what is their purpose?

Tricuspid valve

Pulmonary valve

Mitral valve

Aortic valve

Stop back flow of blood

Tricuspid valve (right A-V valve)

Between right atrium and right ventricle

Pulmonary valve (semilunar valve)

Between right ventricle and pulmonary trunk

Bicuspid/mitral valve (left A-V valve)

Between left atrium and left ventricle

Aortic Valve (semilunar valve)

Between left ventricle and aorta

What are the 3 layers of the heart wall?

1. endocardium

2. myocardium

3. epicardium

Characteristics of skeletal muscle

Appearance: long, unbranched, multinucleated

Type of activity: contracts as needed to produce precise movement

Fiber type: Type I, IIa, IIx

Contraction Type: voluntary

Activation Type: Motor units control group of fibers

Characteristics of Cardiac Muscle

Appearance: shorter, branches connected by intercalated discs, single nucleus

Type of Activity: Continuous rhythmic contractions

Fiber type: striated with one fiber type, similar to type I fibers with multiple mitochondria & large capillary density

Contraction type: involuntary

Activation type: No motor units, contracts as one unit with gap junctions

Why doesn’t the heart get sore?

• more you fill it, more forceful contraction

• but you can’t eccentrically train it muscles which causes soreness

• increased volume of movement doesn’t put that much increased demand on the heart to make it get sore

Coronary circulation

The system of blood vessels that supplies oxygen-rich blood to the heart muscle itself

Includes:

• Left and Right coronary arteries

• marginal artery

• circumflex artery

• left anterior descending/interventricular artery

• Posterior interventricular artery

path of blood through the heart

When is systole on an ECG?

QRS complex and ST segment

When is diastole on an ECG?

T Wave and PR interval

What happens in diastole?

• pressure in ventricles is low

• filling with blood from atria

• A-V valves open

What happens in systole?

• pressure in ventricles rise

• blood ejected into pulmonary and systemic circulation

• semilunar valves open

What makes the Lub and Dub heart sounds?

First: closing of A-V valves

Second: closing of aortic and pulmonary valves

What makes up the intrinsic conduction system of the heart?

1. Sinoatrial Node

2. Atrioventricular node

3. AV bundle (bundle of his)

4. R/L bundle branches

5. Purkinje fibers

Extrinsic control of heart activity: parasympathetic nervous system

• reaches heart via vagus nerve

• carries impulses to SA, AV nodes

  • releases Ach, hyperpolarizes cells

  • decreases HR & force of contraction

• Decrease HR below intrinsic HR

  • intrinsic HR = 100 beats/min

  • normal resting HR = 60-100 beats/min

  • elite endurance athlete have 35 beats/min

Extrinsic control of heart activity: Sympathetic nervous system

• opposite effect of parasympathetic

• carries impulses to SA, AV nodes

  • releases norepinephrine, facilitates depolarization

  • increase HR, force of contraction

  • endocrine system can exert similar effect

• Increases HR above intrinsic HR

  • determines HR during physical, emotional stress

  • sympathetic stimulation can increase HR to max of 250 bpm

What are the 3 basic phases of an ECG?

P wave: atrial depolarization

QRS complex: ventricular depolarization

T-Wave: ventricular repolarization

Systole

Contraction phase, chambers expel blood (QRS to T-wave)

Diastole

Relaxation phase, chambers fill with blood (T-wave to QRS

How much blood is ejected from ventricles/beat?

~2/3 of blood is ejected from ventricle/beat

Heart rate

beats per minute

stroke volume

volume of blood pumped per contraction

SV= EDV-ESV

cardiac output

total volume of blood pumped by the ventricle per minute

Q=HRxSV

End-diastolic volume

volume of blood in ventricle just before contraction

End-systolic volume

volume of blood in ventricle just after contraction (what’s left over)

Cardiac output (CO)

Blood pumped by the heart per minute (L/min)

CO= HRxSV

Male= 5.0 L/min

Female= 4.0 L/min

what are the 4 factors to determine SV?

1. volume of venous blood returned to the heart (EDV, preload)

2. ventricular distensibility

3. ventricular contractility

4. aortic pressure (afterload)

Male and female stroke volume

Male= 70mL

Female= 50mL

Regulation of stroke volume

1. volume returned to the heart

• end diastolic volume ‘preload’

• volume of blood in ventricles at the end of diastole

• primarily influenced by venous return

2. ventricular distensibility

• frank-starling mechanism

3. Strength of ventricular contraction

4. Aortic Pressure

• pressure the heart must pump against to eject blood

• impedes ejection of blood from the left ventricle

Frank-Starling Mechanism

• the force of contraction of cardiac muscle is proportional to its initial resting length

• SV= EDV-ESV

Ejection Fraction

• proportion of blood pumped out of the left ventricle with each beat

• averages 60% at rest

• clinical relevance- systolic heart failure

Systolic blood pressure

• highest pressure within the vascular system

• generated during cardiac contraction

Diastolic blood pressure

• lowest pressure within the vascular system

• when the heart is relaxed

• indication of peripheral resistance

Blood pressure measurement

1. locate brachial artery

2. place cuff on upper arm

3. place stethoscope over brachial a. just below antecubital space

4. inflate cuff to between 180-200mg

5. gradually release pressure

6. note pressure when you hear first beat

7. note pressure when you hear the sound disappear

Blood pressure chart

Venous return

• deoxygenated blood returned to the heart via the superior and inferior vena cava

• valves prevent backflow of blood

• low pressure system

• venous pooling- clinical implications

Factors influencing venous return

• valves in the veins

• vasocontriction

• muscle pump action

Artery characteristics

• thick strong wall

• high pressure

• endothelial lining

• smooth muscle

• outer layer of connective tissue

Vein characteristics

• thinner wall than artery

• low pressure

• endothelial lining

• smooth muscle

• large lumen

• also have valves

Pressure gradient

• Blood flow: high pressure → low pressure

• 100 mmHg

Resistance to blood flow equation

What can effect blood flow?

• blood viscosity

• vessel length

• vessel radius

Blood flow equation

Blood flow= change in pressure/ resistance

Vasoconstriction

radius of the vessel decreases, decreasing blood flow

Vasodilation

radius of the vessel increases, increasing blood flow

Estimated HRmax

HRmax= 220-age in years

HRmax= 208-(0.7x age in years)

HR and Exercise

HR increases in direct proportion to increase in exercise intensity

Steady-State Heart Rate

1. Constant workload: HR increases rapidly until it reaches a plateau (steady state)

2. Increase in workload: HR increases to new steady-state value in 2-3 minutes

3. With exercise training: decreased steady-state heart rate for given submaximal workload

Stroke volume and acute exercise

1. SV increases directly with increasing work rate

2. untrained: SV plateaus at ~40-60% of VO2 max

3. trained individuals: can increase max SV at higher intensity levels

Increased preload, decreased afterload, increased contractility

Increased preload leads to…

Increased…

• plasma volume

• venous return

• ventricular volume

Decreased afterload leads to…

• decreased arterial constriction

• increased max muscle blood flow

Increased stroke volume during exercise

1. Frank-starling mechanism: enhanced cardiac filling during diastole (preload)

2. Decreased total peripheral resistance: (afterload) due to increased vasodilation

3. Neurohormonal Influence: increased ventricular contractility due to increased sympathetic stimulation

Stroke volume with endurance training

Increases…

• SV at rest

• SV at a given submax work level

• SV at max exercise intensity

trained individual: If heart rate decreases and stroke volume increases, what is the net effect of CO? (CO=HRxSV)

stays the same

During max exercise…

significant increase in CO secondary to increased max SV

Response to acute exercise

Increased HR, SV, CO

Response to endurance training

• decreased HR at rest

• decreased HR w/ given submax work rate

• faster recovery HR

• increased SV at rest

• increased SV with given submax work rate

• CO at rest and w/ given submax exercise work rate → little change

Heart size and endurance training

• increases size of left ventricle as a result of ventricular filling

• increases thickness of left ventricle wall

• more forceful contraction

Blood pressure and acute exercise

• increases systolic BP in proportion to exercise intensity

• no significant change to diastolic BP during acute dynamic exercise; may decrease

BP response and endurance training

• decreased systolic BP at rest & for a given submax exercise work rate

• decreased diastolic BP at rest & for a given submax exercise work rate

Blood flow and acute exercise

Increased:

• muscle blood flow

• skin blood flow

Decreased:

• kidney blood flow

• splanchnic blood flow (liver, stomach, intestines)

What is the major contributor to redistribution of blood flow?

sympathetic nervous system