Cardiovascular System Responses to Exercise - Q and BP

CO and Exercise Intensity

• CO output increase when HR and SV increase

• trained individuals achieve a higher maximal CO

• elite athletes - CO increases the most

CO @ Rest - Trained Athletes

• HR is higher in untrained athletes than trained athletes

• SV is higher in trained athletes than untrained athletes

CO @ Max Exercise

• HR is the same in trained and untrained (200 bpm)

• SV is higher in trained athletes than untrained athletes

• CO is more in trained athletes

Blood Pressure (BP)

force exerted by blood agianst the arterial wall

• measured in mm Hg

Aorta

stores a portion of blood generating pressure within the system

Blood Pressure Blood Flow

• normal blood vessel → normal BP

• narrow blood vessel → high BP, increase pressure

What Regulates Blood Flow

sphincter constrction and relaxation

Factors Triggering the Relaxation of Precapillary Sphincters to Open More Capillaries

1. drving force of increase local BP

2. local metabolites

Arterial Blood Pressure

expressed as systolic/diastolic

• 120/80 mmHg

Pulse Pressure

PP = systolic BP - diastolic BP

• 120 - 80 = 40

Mean Arterial Pressure (MAP)

average pressure during a cardiac cycle

• can be estimated at rest

MAP Equation

MAP = DBP + 0.33 (SBP - DBP)

• 80 + 0.33 (120-80)

• 80 + 13

• 93 mmHg

MAP Equation Does Not Work During Exercise

based on timing of cardiac cycle

Blood Pressure Regulation - Acutely

• short-term regulation

1. SNS

2. baroreceptors (pressure sensors)

Baroreceptors

• on aorta and carotid artery

• information sent to CVCC

• increase BP → decrease afferent information (decrease CO)

• decrease BP → increase afferent information (increase CO)

BP Regulation - Chronically

• long-term regulation

• via blood volume control in kidneys

• stimulus to either retain (increase BV) or remove (decrease BV)

CO Helps Maintain

BP which drives blood flow

3 Important Components of CV System

1. heart (pump → motor)

2. vascular network (tubing → highways/roads)

3. blood (fluid medium)

Blood Carrying Capacity

• average Hct = 15 g/100 mL

• each g binds 1.34 mL O2

• 15 g x 1.34 g/100 mL

• 20 mL O2 in 100 mL of blood

a-v O2 Difference

• O2 rich blood sent from heart → 20 mL O2 per 100 mL of blood

• O2 depleted blood sent back to heart → 15 mL O2 per 100 mL of blood

a-v O2 Difference at Rest

4-5 mL O2 per 100 mL of blood

a-v O2 Difference During Exercise

12-15 mL O2 per 100 mL of blood

a-v O2 Difference - What Does This Mean?

1. we don’t use much O2 at rest

2. we have a large capacity to increase a-v O2 difference

Fick Principle - VO2 Can be Determined By

amount of blood being pumped from the heart and the amount of O2 being extracted from the lungs

Fick Principle Equation

VO2 = Q x (a-v O2 diff)

Why is Fick Principle Important

• Q is blood pumped out of the heart

• a-v O2 difference is the amount of O2 extracted at the muscle

a-v O2 Units Should Be In

mL O2 per L

Blood Flow

pressure/resistance

Factors Affecting Blood Flow

1. viscosity

2. length

3. radius

Hemodynamics

• vessel length remains constant

• blood viscosity varies only slightly

• vessel radius affect blood flow the most

Vasoconstriction and Vasodilation

provide the crucial mechanism to regulate regional blood flow

Totoal Amount of BV

does not change

• 4-5 L

How Does More O2 Rich Blood Get to Active Tissues

1. pump blood → more blood

2. re-direct blood from inactive to active

Inactive Tissues

has less O2 needs

Active Tissues

would need more O2

Vasoconstriction

occurs of vasculature to inactive tissue

Vasodilation

occurs to vasculature to active tissues

Q Distribution

• most tissues decrease at expsenses of skeletal muscle

• heart receives increase

• brain recieves increase

Q Redistribution at Rest

• skeletal muscles: 20%

• brain: 14%

• heart: 4%

Q Redistribution at Exercise

• skeletal muscles: 84%

• brain: 4%

• heart: 4%

How Does Re-Distribution Work

arterioles control flow to these beds

• arterioles influenced by: autoregulation and extrinsic neural control

Effect of Exercise on BF

blood flow couples to metabolic demands

Exercise “Opens” Capillaries

not many open @ rest

• increase total muscle BF

• increase CSA for gas exchange

• change in velocity (allows exchange)