Exercise Physiology Exam 2: Chapter 11

What does Q represent, and what is it equal to?

Q = cardiac output = HR x SV

how much blood moves

What is CaO2?

arterial oxygen content, the total amount of O2 carried in a given volume of arterial blood (bound to hemoglobin and dissolved in plasma)

what is a-VO2 diff?

arterial venous oxygen difference

the difference in the amount of blood between arterial blood and venous blood

how much oxygen your working muscles and tissues extract from the bloodstream

over a minute, which ventricle pumps more blood?

they pump the same amount

the left ventricle is larger because it pumps blood further but its still the same volume of blood (left = systemic)

arteries vs. veins function

arteries carry blood away from the heart, veins return it

components of the pulmonary circuit

right ventricle, lungs, left atrium

components of the systemic circuit

left ventricle, body, right atrium

Path of blood

1. enters through the superior or inferior vena cava

2. into the right atrium- through the tricuspid valve

3. right ventricle- pulmonary semilunar valve - pulmonary arteries- lungs (pulmonary capillaries) -pulmonary veins (right and left)

4. left atrium - bicuspid valve

5. left ventricle - aortic semilunar valve - aorta -arteries -systemic capillaries - veins

6. superior/inferior vena cava

What is VO2 max equal to?

VO2max = cardiac output x stroke volume

How does the heart contract as one unit?

Excitation passes cell to cell through gap junctions, so the atria contract as one unit, and the ventricles as another: two syncytia create a functional syncytium

cardiac and skeletal muscles are both striated (use actin and myosin), adjacent cells are joined end to end by intercalated discs. Discs carry gap junctions, which pass electrical activity cell to cell

A donor heart with every nerve cut in a supportive environment. What does it do?

It beats faster than resting HR

because resting HR sits below the SA node’s intrinsic rate because vagal tone predominates at rest, if you remove those nerves, the heart speeds up

resting HR of 75 is a break, not an engine speed

pacemaker cells depolarize spontaneously and the fastest sets the rate

SA node is the fastest in the right atrium, AV node is about 40 to 60 per minute, and takes over if the SA node fails

vagal tone holds resting rate at about 75, below the intrinsic rate

a resting rate of 40 does not itself tell you an athelete has a failing SA node

What does the P wave represent?

depolarization and contraction of atria

What does the QRS complex represent?

the ventricles depolarize, and then contract

What does the T wave reprsent

the ventricles repolarize and then relax

atrial repolarization is buried under the QRS and can surface in exercise

The whole conduction system has fired before the QRS appears

the U wave is inconsistent, and commoner in slower cycles

from rest to hard exercise: the beat goes from 0.8s (75bpm) to 0.33s (180bpm). What happens to filling time?

filling time falls much further to about a quarter of what it once was.

What is the first thing to be shortened when you speed up the heart?

filling time is shortened because diastole is shortened more than systole is

Label the parts of the heart

1. superior vena cava

2. right pulmonary veins

3. tricuspid valve

4. right ventricle

5. inferior vena cava

6. aorta

7. left pulmonary artery

8. left pulmonary veins

9. bicuspid valve

10. left ventricle

How to read an ECG strip

determine HR

determine whether the rhythm is regular

identify P wave, QRS complex, and T wave

regular rhythm: HR = 60/( R -R interval in seconds)

The cardiac cycle

ventricular filling and ejection

diastole: ventricles relax and fill

systole: the ventricles contract and eject blood

pressure opens valves and valves set volumes

What is the effect of speeding up HR on cardiac cycle?

cuts filling time first because it shortens diastole more than systole

for EDV to hold up, filling rate must rise to compensate

End diastolic volume

the volume in the ventricle at the END of diastole, about 130 mL

End systolic volume

the volume left at the end of systole, about 60mL

Stroke volume

EDV - ESV about 70mL

ejection fraction

SV/EDV, the fraction of what was there that left

Cardiac Output

Q = HR x SV about 5L/min at rest, near the whole blood volume every minute

What three things set SV

Preload, contractility, afterload

only preload and contractility explain stroke volume differences between people

What is preload?

volume of blood returned to the heart (represented by EDV)

stretch is the mechanism, not the definition - increases stroke volume

raised by venous return

what is Contractility?

the force of contraction at a given fill

set by sympathetic nerves and catecholamines

acts independently of filling volume

what is afterload?

the resistance the ventricle ejects against

set mainly by aortic pressure

does not explain differences in SV

what is the Frank Starling mechanism

greater ventricular filling increases cardiac muscle stretch, which increases contraction force and stroke volume

only increases up to a point

How do your leg muscles act as a pump?

contraction of leg muscles compresses veins, and empties them toward the herat because they have one way valves

becomes important when standing because gravity promotes blood pooling in the legs

if you reduce a vessels radius to 1/2, what happens to flow through it?

it falls to 1/16

Poiseuille’s law

R = 1/r^4

Resistance is equal to 1/radius^4

Lining of blood vessels

3 layers- adventitia, tunica media, tunica intima

media- smooth muscle, sets diameter

intima- once cell layer - endothelium

capillaries are endothelium only

endothelium moves materials out and prevents clots, releases factors that dilate and constrict the media

Where is blood velocity the slowest?

in the capillaries

as total cross-sectional area increases, average blood velocity decreases

slow capillary flow facilitates gas and nutrient exchange

What is hematocrit

the fraction of blood volume occupied by red blood cells

men: 43-48%

women: 38-45%

red blood cells carry oxygen through Hb

Plasma

55% of blood, and 90% of it is water

Why does blood volume matter?

it influences venous return, ventricular filling, and stroke volume

How do you calculate pulse pressure

SBP - DBP

represents the force you heart generates with each contraction

at rest DBP is one third of pulse pressure

Mean arterial pressure

MAP = DBP + 1/3 (Pulse pressure)

cardiac output equation in terms of Resistance to flow

Q = MAP / TPR so MAP = Q x TPR

flow = pressure/resistance

total peripheral resistance

opposes flow, mostly friction on vessel walls

Three cardio centers in the medulla

Cardioaccelerator: sympathetic nerves, raises rate and force

cardioinhibitor, the vagal nucleus: vagus nerve (PNS), lowers HR and force

vasomotor: arterial smooth muscle, SYMPATHETIC only, vasodilates or constricts

parasympathetic has little direct control over systemic arterioles

Sympathetic nervous system on cardiovascular system

heart: raises rate and force

vessels: constricts most arterioles

skin is the one exception

also drives the adrenal medulla

Parasympathetic nervous system on cardiovascular system

Heart: lowers rate and force via vagus nerve

vessels: essentially none

opposite of sympathetic only for the heart

dilation comes from sympathetic withdrawl

baroreflex

detect arterial stretch in the carotid sinus and aortic arch

when blood pressure increases:

baroreceptor firing increases, medulla recieves the signal, PNS activity increases, SNS decreases, HR and vascular resistance decrease

during exercise, the baroreflex resets to regulate pressure around a higher operating point

How does sympathetic drive raise SV without more filling?

Frank-Starling: more EDV, more SV

contractility: more force at the SAME end-diastolic volume

sympathetic nerves and circulating catecholamines raise contractility

in exercise both levers pull at once

Neural vs. Hormonal control

Neural control acts in seconds

hormonal control operates over longer periods of times

• epi and norepi do what nerves do but slower

• aldosterone: retain sodium, and water follows

• ADH: retain water, and constrict vessels

more volume = more venous return, so more stroke volume

Heart rate variability

varies from person to person

variation in the time intervals between normal heartbeats - never like a perfect metronome —> index of autonomic balance

low variability predicts cardiovascular events and death in the general population- means its too much like metronome and not adapting to changing stimulus

Why is cardiac output almost never measured directly

It would require an arterial and mixed venous blood sample

Q = VO2/a-vO2diff

Doppler echoL SV from aortic area x velocity - doesn’t require steady state, so it works at maximal exercise but very expensive and hard to do during exercise

Everyday: measure HR and SV then Q = HR x SV

Why is VO2 max a cardiovascular measurment?

O2 delivery is limited by the cardiovascular system, so the highest O2 uptake a person can reach is a measure of cardiovascular capacity

What field tests estimate VO2max

one mile run or walk

20 meter shuttle run PACER

rockport walking test

walking tests suit older, heavier, or sedentary individuals

even an estimate improves health-risk classification

blood pressure at rest vs exercise

at rest: DBP2 (fifth Korotkoff sound) - sound disappears through stethescope

exercise: DBP1 (fourth korotkoff sound) - sound is muffled - recommended for children, adults exercising and if DBP2 is lower than 40

Why does the heart recieve most of its blood during diastole?

the myocardium contract forcefully during systole, so coronary blood vessels are compressed- especially those supplying the LV

Why can’t the myoxardium increase its O2 extraction during exercise?

the heart already extracts 60-70% of delivered O2 at rest, so there is little room for increase a-vO2 lever is unavailable

meet greater O2 demand by increasing coronary blood flow - the lever

harder contraction forces more in

Rate pressure product

Rate pressure product (RPP) estimates myocardial O2 use - dynamic and static

RPP = HR x SBP

ST depression

occurs when myocardial O2 demand exceeds supply

not enough O2 causes ischemia, which changes ventricular repolarization - downward displacement of ST on ECG

demand rises with HR and SBP so with RPP