Exercise Physiology Exam #4

purposes of the cardiorespiratory system

• transport O₂ and nutrients to tissues

• removal of CO₂ wastes from tissues

• regulation of body temperature

two major adjustments of blood flow during exercise

1. increased cardiac output

2. redistribution of blood flow

path of blood

vena cavae —> right atrium —> right AV (tricuspid) valve —> right ventricle —> pulmonary valve —> pulmonary arteries —> lungs —> pulmonary veins —> left atrium —> left AV (bicuspid) valve —> left ventricle —> aortic valve —> aorta —> systemic circulation

chordae tendinae

fibrous cords that anchor the AV valve to the ventricle walls and keep them from flipping backwards when the ventricle contracts

heart

organ that creates pressure to pump blood

• does not create flow, creates PRESSURE

pulmonary circuit

• right side of the heart

• pumps deoxygenated blood to the lungs via pulmonary arteries

• returns oxygenated blood to the left side of the heart via pulmonary veins

systemic circuit

• left side of the heart

• pumps oxygenated blood to the whole body via arteries

• returns deoxygenated blood to the right side of the heart via veins

order of heart mechanisms

AV valves open —> ventricles fill passively —> atrial contraction (or kick) —> ventricular contraction —> aortic/pulmonary valves open —> ejection through the pulmonary artery/aorta

• electrical event —> mechanical event —> pressure change —> volume change

myocardial infarction

when a part of the heart’s wall dies

myocardial ischemia

when a part of the heart’s wall is not getting enough oxygen due to lack of blood flow and could lead to a myocardial infarction

endocardium

innermost layer of the heart

-it’s made up of simple squamous cells and it’s what lines the atria and ventricles

myocardium

thick, middle later of the heart made up of cardiac myocytes

-blood vessels are found here

pericardium

outermost layer of the heart and it has 3 layers of its own

-the middle layer is the pericardial cavity and it contains fluid that allows for friction-free beating of the heart

-outermost layer is fibrous, fatty, and is strongly attached to the great vessels, sternum and diaphragm

cardiac muscle (myocardium)

type of muscle that only has one fiber type and it similar to type I muscle fibers

• has high capillary density

• high number of mitochondria

• striated

• only one nucleus per cell

• small, short, branched

• continuous, involuntary rhythmic contractions

• calcium-induced calcium release with calcium coming from sarcoplasmic reticulum and from outside the cell

• no satellite cells present

ventricular systole

contraction phase

• ejection of blood in pulmonary and systemic circulation (~2/3 blood is ejected from ventricles per beat)

• pressure in ventricles rises

• semilunar valves open when ventricular P > aortic P

• is shorter during exercise

ventricular diastole

relaxation phase

• filling with blood from atria

• pressure in ventricles is low

• AV valves open when ventricular P < atrial P

• takes longer than systole when you’re at rest

• is shorter during exercise

average aortic bp

120/80 mmHg

• pressure the heart must pump against to eject blood

• “afterload”

heart sounds

• “lub” sound: closing of AV valves

• “dub” sound: closing of aortic and pulmonary semilunar valves

isovolumetric relaxation

occurs in early diastole and all gates are closed here

stroke volume

the amount of blood ejected from the ventricle

• SV=EDV-ESV

• SV=CO/HR

end-diastolic volume (EDV)

volume of blood left at the end of ventricular filling

• preload

end-systolic volume (ESV)

volume of blood left in the ventricle after contraction

atrial kick

the atrial contraction that gives ventricular filling an extra boost

c wave

the bump that follows the atrial kick in the Wigger’s diagram

• is due to the AV valves bulging into the atria

v wave

the final point before the AV valve opens again and the ventricles begin to fill in the Wigger’s diagram

• aortic valve shutting causes this bump in the aortic pressure line

cardiac output

the amount of blood your heart pumps per minute

• CO = HR * SV

P wave

part on an ECG that denotes when the blood moves from the atria into the ventricles (so it’s part of diastole)

• lasts 0.8 seconds

• represents the depolarization of the atria

QRS complex

part of the ECG that…

• represents ventricular depolarization

• causes ventricular contraction

• leads to AV valve shutting

• leads to aortic valve opening

• transitions into phase 2 (isovolumetric contraction, then ejection)

• typically 0.06 to 0.1 seconds

• polarization, depolarization, to even stronger repolarization

T wave

part of the ECG that denotes when blood moves from vena cavae to atria

• early diastole

• ventricular repolarization

• potassium is leaving the cells here

pulse pressure

difference between systolic and diastolic pressure and it’s the amount of pressure the heart is generating with each beat

• PP=SBP- DBP

mean arterial pressure (MAP)

average pressure in the arteries

determinants of MAP

• cardiac output

• total vascular resistance

chronotropy

the effect that change’s the heart’s rate of contraction, influencing how quickly the SA node fires and thus how many beats occur per minute

preload

end diastolic pressure and degree of stretch of cardiac muscle cells before they contract

• increased in hypervolemia, regurgitation of cardiac valves, heart failure

afterload

resistance left ventricle must overcome to circulate blood

• increased in hypertension and vasoconstriction

• when it increases, it increases cardiac workload

• hypertension increases afterload, which results in increased ESV and reduced stroke volume

Frank-Starling law

fundamental principle that the heart pumps harder when it’s filled with more blood

• cause cardiac muscle exhibits a length-tension relationship

• stroke volume increases when there is an increase in venous return

what increases venous return

• venoconstriction via SNS

• skeletal muscle pump

• respiratory pump (changes in thoracic pressure pull blood toward heart)

cardiac output is increased by

• increase in heart rate (increase in sympathetic adrenergic activity and decrease in parasympathetic activity)

• increase in stroke volume (increase in central venous pressure, increase in inotropy, increase in lusitropy)

MAP and PP increased by

• CO increases more than SVR decreases

• Increase in stroke volume increases PP

CVP maintained by

• venous constriction (increase in sympathetic adrenergic activity)

• muscle pump activity

• abdominothoracic pump

SVR decreased by

• metabolic vasodilation in active muscle and heart

• skin vasodilation

preload increased by

• increase in EDV

• increase in plasma volume

afterload decreased by

decrease in the arteriolar constriction in muscles, increasing maximal muscle blood flow with no change in mean arterial blood pressure

• so ventricle ends up working less hard

maximal stroke volume increased by

• increase in preload

• increase in contractility

• decrease in afterload

phase 1

ventricular filling (mid-to-late diastole)

• accompanied by atrial contraction

phase 2a

isovolumetric contraction phase

• start of ventricular systole

phase 2b

ventricular ejection phase

• pressure in the LV exceeds pressure in the LA and aorta

• begins with aortic valve opening

• blood flows from the LV into the aorta

• volume in the LV decreases

phase 3

isovolumetric relaxation

• early diastole

what decreases BP to its set point

• decrease in SNS activity

• systemic vasodilation

physiological determinants of MAP

MAP = CO(SVR)

clinical determinants of MAP

MAP = DBP + 1/3(SBP-DBP)

respiratory pump

increased volume during inhalation decreases pressure in the thoracic cavity, pulling blood back to the heart

• this increases venous return, which increases stroke volume

what increases stroke volume during exercise

• increased contractility (increases ejection power, so more blood is pumped out)

• increased skeletal muscle contractions (increases venous return/preload)

• increased breathing rate (respiratory pump mechanism increases venous return)

• increased venoconstriction

how afterload is affected by exercise

there ends up being an increase in this in the left ventricle because more pressure is needed to pump the increased preload into the aorta

positive inotropic agents

• increased calcium influx due to increased sympathetic stimulation

• hormones like thyroxine, glucagon, and epinephrine

negative inotropic agents

• acidosis

• increased extracellular potassium

• calcium channel blockers

central command

initial signal to “drive” cardiovascular system comes from higher brain centers

• due to centrally generated motor signals

• in regards to BP central control

exercise pressor reflex

neural feedback system that increases heart rate, blood pressure, and breathing during physical activity

• involved muscle chemoreceptors and muscle proprioceptors

metaboreflex

¤Chemicals released from contraction stimulate chemoreceptors

¤Stimulation of chemoreceptors send afferent information to the medullary CV centers via group IV afferent nerves.

¤This causes a “shift” in MAP control: baroreflex resetting

mechanoreflex

¤Mechanical deformation (movement) from contracting/moving limbs stimulate mechanoreceptors

¤Stimulation of mechanoreceptors send afferent information to the medullary CV centers via group III afferent nerves

¤This causes a “shift” in MAP control: baroreflex resetting

relationship between resistance and vessel radius

• halving the radius of a blood vessel increases the resistance 16 fold

• doubling the radius of a blood vessel decreases the resistance 16 fold

what produces minimum SVR during exercise

• exercising on a hot day

• exercising the whole body

• exercising at a high intensity

aerobically trained heart

• left ventricle is larger primarily due to eccentric hypertrophy

• LV can fill more and contract more efficiently

• stroke volume is increased

eccentric hypertrophy

when more sarcomeres are added in series to the heart wall due to volume overload that occurs during aerobic training

changing of MAP at onset of exercise

1. central command

2. mechanical

3. metabolic (things like calcium)

4. autonomic (SNS)

5. humoral (hormones)