Physiology II- Blood Pressure and Cardiac Cycle

in healthy person, SV should be?

> 60ml

• Systolic

relating to phase of heartbeat when the heart muscles contracts and pumps blood from the chambers into the arteries

• Diastolic

relating to the phase of the heartbeat when the heart muscle relax and allows the chambers of the heart to fill with blood

blood pressure measurement by?

• Auscultation- mercury sphygmomanometer + stethoscope OR mechanical manometer + stethoscope • Oscillometry

ejection fraction in healthy person?

55%-75% -IMPORTANT MEASUREMENT OF CARDIAC EFFICIENCY -EF used clinically to assess cardiac status in patients with heart failure

which is longer in seconds, atria systole or atria diastole?

diastole

Preload

the vol of blood that the ventricle has available to pump

REGULATION OF CARDIAC OUTPUT 2. parasympathetic nervous system

- controls SA node and AV node. - releases Acetylcholine (Ach). - decreases heart rate (negative chronotropic). - prolongs delay at AV node. - has little effect on contractility.

REGULATION OF CARDIAC OUTPUT 1. sympathetic nervous system

- controls all components of the heart. - release Norepinephrine (NE). - increases heart rate (positive chronotropic) and contractility (positive inotropic).

What is the annulus fibrosus?

-4 cardiac chambers built upon ring of fibrous fatty tissue located at the atrio-ventricular junction called ANULUS FIBROSIS; -electrically insulates the atria from the ventricles

anatomically heart consists of? ENDOCARDIUM MYOCARDIUM EPICARDIUM PERICARDIUM

-ENDOCARDIUM; composed of epithelial cells -MYOCARDIUM; composed of specialised muscle cells called myocytes -EPICARDIUM; composed of a thin layer of mesothelial cells and connective tissue -PERICARDIUM; fibrous sac encloses heart

how does the action potential change depending on which cell along the journey it takes?

-SA node broad peak + slow depolarisation - ventricular myotcytes; -very fast and sudden depolarisation; -then plateau phase then depolarisation

reasons for refractory period

-another AP cant be stimulated

PHASES OF CARDIAC CYCLE

1. Atrial contraction 2. Isovolumetric ventricular contraction 3. Rapid ventricular ejection 4. Isovolumetric ventricular relaxation 5. Rapid ventricular filling

NERVOUS SYSTEM REGULATION OF HEART RATE role of: 1. input from cardiovascular center 2. signals to medulla oblongata 3. output to heart via cardiac accelerator nerves (sympathetic) or Vagus (X) nerves (parasympathetic)

1. Input from cardiovascular center FROM HUGHER BRAIN CENTRES: -cerebal cortex, limbic system, hypothalamus FROM SENSORY RECEPTORS -proprioreceptors; monitor movements -chemoreceptors; monitor blood chem -baroreceptors; monitor BP 2. to medulla oblongata 3. OUTPUT TO HEART CARDIAC ACCELERATOR NERVES (SYMPATHETIC) -INC rate of spontaneous depolarisation in SA node (+ AV node) -inc HR -INC contractility of atria + ventricles -inc stoke vol VAGUS NERVE (X) (parasympathetic) -dec rate of spontaneous depolarisation in SA node (+ AV node) dec HR

normal BP

120/80

pre-hypertension BP

120/80- 140/90

hypertension BP

140/90 and higher

does the left ventricle empty completely during systole?

NO

PHASES OF CARDIAC CYCLE 4. ISOVOLUMETRIC VENTRICULAR RELAXATION

OVERVIEW -Isovolumetric Ventricular Relaxation is characterized by the end of active tension in the ventricular myocardium and thus relaxation of the ventricular muscle -However, because the ventricular pressure remains above that of the atria, no filling of the ventricles can occur and thus their volume remains constant during this phase EVENTS 1.Valves: This phase begins with snapping shut of aortic valve and pulmonic valves and ends with opening of the AV valves. All valves are shut during this phase and no blood enters or exits the ventricles 2.ECG: No wave forms occur during this phase and the heart is fully repolarized 3.Ventricular Volume: Ventricular volume does not change as no blood enters or exits ventricles 4. Ventricular Pressure: Rapidly falls as ventricle relaxes 5. Aortic Pressure: The beginning of this phase is characterized by a small blip in the Aortic Pressure curve, termed the "Dicrotic Notch" which occurs due to snapping shut of the aortic valve. Following this event the aortic pressure slowly declines as blood moves into the circulation 6.Atrial Pressure: The atrial pressure continues to rise as venous return fills these chambers 7. Heart Sounds: Snapping shut of aortic valve and pulmonic valves at beginning of this phase results in the S2 heart sound

PHASES OF CARDIAC CYCLE 5. VENTRICULAR FILLING

OVERVIEW -Ventricular Filling occurs when the intraventricular pressure falls below that in the atria, allowing the AV valves to open and atrial blood to enter -Entry of blood into the ventricles is not linear and the majority occurs during the first part of this phase -The length of the ventricular filling phase is the most variable in all the cardiac cycle -When the heart rate is high, this phase is shortened whereas at low heart rates, this phase is lengthened EVENTS 1. Valves: Opening of the tricuspid valve and mitral valves allows entry of atrial blood into the ventricles 2. ECG: The heart is electrophysiologically quiet during this phase; however, the P wave occurs at the end of this phase and represents a wave of atrial depolarization which initiates the subsequent Atrial Systole 3. Ventricular Volume: Ventricular Volume increases rapidly during the initial parts of this phase as blood rushes in from the atria. However, as the ventricles approach their VEDV, the rate of blood entry slowly tables off 4. Ventricular Pressure: Ventricular pressure is slightly lower than the atrial pressure during this phase allowing entry of blood 5. Aortic Pressure: Continues to decline as blood runs out into circulation 6. Atrial Pressure: Atrial pressure is slightly higher than ventricular pressure during this phase allowing movement of blood from atria to ventricles. Because the building atrial pressure in the previous phase is suddenly released as the AV valves open, this is observed as the "V Wave" 7. Heart Sounds: No heart sounds are normally heard in adults but in children the rapid movement of blood between atria and ventricles can cause an S3

PHASES OF CARDIAC CYCLE 2. ISOVOLUMETRIC VENTRICULAR CONTRACTIO N

OVERVIEW -Isovolumetric Ventricular Contraction is characterized by contraction of ventricles prior to opening of the semilunar valves (i.e. aortic valve or pulmonic valves) -Although ventricular tension and pressure are generated during this phase, they are not sufficient to overcome the pressure within the aorta and pulmonary artery -Consequently, the pressures within the ventricles increase whilst their volume remains constant (i.e. isovolumetric contraction) EVENTS 1. Valves: This phase begins with the snapping shut of the atrioventricular valves. Consequently, during this phase all valves are closed 2. ECG: This phase immediately follows the QRS complex which represents the rapid spread of depolarization throughout the ventricles 3. Ventricular Volume: Remains constant at the VEDV as no ejection of blood occurs during this phase 4.Ventricular Pressure: Rapidly rises as ventricles contract 5. Aortic Pressure: Reaches its lowest point at the end of this phase as blood continues to flow out into the circulation 6. Atrial Pressure: The increase in atrial pressure observed in this phase is termed the "C Wave" and represents the bulging of the atrioventricular valves into the atria as the ventricles contract 7. Heart Sounds: The snapping shut of the semilunar Valve results in the S1 heart sound

PHASES OF CARDIAC CYCLE 3. VENTRICULAR EJECTION

OVERVIEW o Ventricular Ejection occurs when the pressure within the ventricles overcomes that in the aorta and the pulmonary artery o With the opening of the aortic valve and pulmonic valve, blood effluxes from the ventricles and into the vasculature o Nearly 70% of the blood ejects in the first third of ventricular ejection and represents a period of "Rapid Ventricular Ejection" whereas the final 30% of blood ejects in the remainder of the time, representing a period of "Slow Ventricular Ejection" EVENTS 1. Valves: This phase begins with the opening of the aortic valve and pulmonic valve and ends with these same valves closing 2.ECG: The T wave occurs during the latter half of this phase and represents the repolarization of ventricular muscle 3. Ventricular Volume: Most of the ventricular volume is emptied during the first third of this phase (i.e. Raid Ventricular Ejection) while the remainder is ejected during the final two-thirds of the phase (i.e. Slow Ventricular Ejection), ultimately reaching the VESV 4. Ventricular Pressure: Ventricular pressure rises fairly rapidly, peaks roughly half way through this phase, and then begins to fall as ventricular ejection ends 5. Aortic Pressure: Because the Aortic Valve is open during this phase, the aortic pressure matches the ventricular pressure 6. Atrial Pressure: Falls initially during this phase as inward bulging of the atrioventricular valves relaxes but then slowly builds as the atria begin filling with the venous return 7. Heart Sounds: There are no heart sounds during this phase

PHASES OF CARDIAC CYCLE 1. ATRIAL CONTRACTION

OVERVIEW: -Atrial Eeection is the phase in which the left ventricle is filled with blood from the atria -The majority of filling occurs during the initial portion of this phase while the atria are completely at rest -In the final portion of the phase, termed "Atrial Systole", the atria contract and push roughly 25% of final Ventricular End Diastolic Volume (VEDV) into the ventricles EVENTS 1. Valves: Atrioventricular Valves (i.e. tricuspid valve and mitral valve) are open, allowing blood to enter ventricle from atria. This phase ends with Atrioventricular Valve closure 2.ECG: This phase immediately follows the P Wave which represents the spread of depolarization across the atria. Consequently, this phase occurs during the PR interval 3.Ventricular Volume: Increases from the Ventricular End Systolic Volume (VESV) to the Ventricular End Diastolic Volume (VEDV). Again, atrial contraction accounts for roughly 25% of the final VEDV 4.Ventricular Pressure: Slightly increases due to injection of blood from atria but then decreases due to closing of AV Valves 5. Aortic Pressure: Continues decline as blood runs out into circulation 6.Atrial Pressure: During the latter part of this phase, atrial systole causes a transient increase in atrial pressure which is termed the "A Wave" 7. Heart Sound: In individuals with left ventricular hypertrophy injection of atrial blood into the thickened ventricles will manifest as the S4 heart sound which is not audible in normal individuals

ECG describe waves meaning?

P wave- atria depolarise QRS complex/ r wave- ventricles depolarise T wave- ventricles repolarise

heart rhythm determined by?

PACEMAKER CELLS IN THE SINO-ATRIAL (SA) NODE; DEPOLARISE SPONTANEOUSLY

IN RESTING STATE; THIS MEANS CARDIAC MUSCLE CELLS ARE?

POLARISED; -means an electrical difference exists between neg charged inside and POS charged outside of cell membrane

NON PACEMAKER ACTION POTENTIALS

Phase 0 -depolarisation (Na+ channels open FAST) 1 -EARLY repolarisation (Na+ channels close + some K+ leave) 2 -PLATEAU -Ca2+ influx; SLOW 3. repolarisation (K+ OUT) 4. resting (restoration of normal iconic balance by pumps)

stroke volume equation involving end diastolic volume and end systolic volume?

Stroke volume= end diastolic volume- end systolic volume

stroke volume

The amount of blood ejected from the heart in one contraction -vol per beat

cardiac cycle is?

The series of events that occur from the beginning of one heartbeat to the beginning of the next; 1 heart beat

is ventricle systole and ventricle diastole same length of time in seconds?

YES

Stroke volume

amount of blood transferred from LV to arterial system during SYSTOLE SV= approx 80-90ml

irregular rhythm?

arrhythmia

afterload

arterial pressure against which the muscle will contract

why BP inc with age?

as get older blood vessels start to narrow so higher BP generally

• Mean arterial pressure

average blood pressure in an individual during a single cardiac cycle

lowest pressure in aorta called?

diastolic pressure • As the left ventricle is relaxing and refilling, the pressure in the aorta falls The lowest pressure in the aorta, which occurs just before the ventricle ejects blood into the aorta, is termed the diastolic pressure (Pdiastolic).

resting potential

electrical charge across the cell membrane of a resting neuron

heart beat HEART BEAT TRIGGERED BY?

electrical system within heart wall called pacemaker conduction system (AVN, SAN)

Function of annulus fibrosus

electrically insulates the atria from the ventricles

jugular venous pressure

indirectly observed pressure over the venous system via visualization of the internal jugular vein. • JVP provides an indirect measure of central venous pressure (CVP) • The internal jugular vein connects to the right atrium without any intervening valves-thus acting as a column for the blood in the right atrium • Patient placed at 45o angle

AUTONOMIC CONTROL OF SAN SAN contains autorhythmic fibres that do what?

initiate AP • Nerve impulses from the autonomic nervous system (ANS) and hormones (e.g. adrenaline) modify the timing and strength of each heartbeat, but they do not establish the fundamental rhythm.

heart beat pacemaker job?

initiates electrical discharge; conducted from one muscle fibre to the next

cardiac cycle opening + closing of heart valves is?

passive + actuated by differential pressures of chambers which valve straddles

Mean arterial pressure equation

mean arterial pressure= diastolic pressure + 1/3 pulse pressure

blood pressure

measurement of the force against the walls of the arteries as the heart pumps blood throughout the body

ejection fraction

measurement of the volume percentage of left ventricular contents ejected with each contraction EF= SV/ EDV

blood pressure measured in?

mmHg

CARDIAC ELECTRICAL ACTIVITY DUE TO?

movement of ions (charged particles such as Na, K, Ca) across cell membrane

why can changes in right atrial pressure be indirectly observed as changes in JUGULAR VENOUS PRESSURE (JVP)?

no valves between right atrium and vena cava

heart rate

number of beats per minute

cardiac cycle DIASTOLE

occurs when ventricles relaxed; ISOMETRIC VENTRICULAR RELAXATION, VENTRICULAR FOLLING + ATRIAL EJECTION

DESCRIBE SA NODE ACTION POTENTIALS

phase 4 -gradual rise in membrane potential -K+ out dec -inc in inward current; Na+ and Ca2+ 0 -LARGE Ca2+ influx once threshold reached 2 -Ca2+ channels start to close 3 K+ flowing out repolarises cell

mean arterial pressure

pressure forcing blood into tissues, averaged over cardiac cycle As blood is pumped out of the left ventricle into the aorta and distributing arteries, pressure is generated. -MAPPED BY OHMS LAW

refractory periods in non-pacemaker cells why refractory period of cardiac muscle longer than that of skeletal muscle?

prevents tetanus from occurring and ensures that each contraction is followed by enough time to allow the heart chamber to refill with blood before the next contraction.

systemic vascular resistance

resistance to blood flow out of the left ventricle created by the systemic circulatory system

normal rhythm called?

sinus rhythm

refractory period

the time following an action potential during which a new action potential cannot be initiated

maximal aortic pressure following ejection called?

systolic pressure • As blood is pumped out of the left ventricle into the aorta and distributing arteries, pressure is generated.

AUTONOMIC CONTROL OF SAN called when Heart beat 1. >100bpm? 2. <50bpm

tachycardia bradycardia • SYMPATHETIC ACTIVITY RELEASES NORADRENALINE; INC SLOPE OF PHASE 4 + DEC TIME TO REACH THRESHOLD • PARASYMPATHETIC ACTIVITY RELEASES ACETYLCHOLINE; DEC SLOPE OF PHASE 4 + EXTENDS TIME TO REACH THRESHOLD

contractility

the force that the muscle can create at the given length

• Blood pressure

the pressure of the blood in the circulatory system; often measured for diagnosis as it is closely related to force and rate of the heartbeat and the diameter and elasticity of arterial walls

End diastolic vol

total vol of blood in ventricle at end of DIASTOLE DEPENDENT ON PRELOAD EDV= approx 140ml

AUTONOMIC CONTROL OF SAN what nerve innervates SA node?

vagus nerve; reduce rate to 60-80bpm -SAN before this contains autorhythmic fibres that initiate an action potential (100-110 per minute)

CARDIAC OUTPUT

volume of blood pumped each minute -expressed by the following equation • To increase cardiac output (CO), need to increase Stoke Volume (SV) or increase HR (HR) or inc BOTH

End systolic vol

volume of blood remaining in ventricle at end of systole DEPENDENT ON AFTERLOAD ESV= approx 50ml

characteristics of cardiac conduction cells AUTOMATICITY EXCITABILITY CONDUCTIVITY

• Automaticity- ability to initiate electrical impulse • Excitability- ability to respond to an electrical impulse • Conductivity- ability to transmit an electrical impulse from one cell to another

heart beat describe each myocyte

• Each myocyte- contains many MYOFIBRIL units; each myofibril composed of numerous basic contractile units called sarcomeres • Sarcomeres; resting length approx 2 um; COMPOSED OF INTERDIGITATING FILAMENTS 1. Thick myosin filament 2. Thin actin filament • Adjacent myocytes attached end-to-end in stepped face, the intercalated disc: -gap junction transmits electrical current between myocytes -desmosomes provide mechanical strength

ECG

• Graphic record of electric currents that are generated by the heart muscles • Electrical impulses are picked up by the surface electrode which are placed at various points on the body and connect the ECG machine to the body • Electrocardiogram (ECG or EKG) is measured from 12 electrodes placed on the surface of the chest. • ECG is a vector measurement (magnitude of depolarisation and direction). • Changes in the ECG are used to diagnose heart arrhythmias

CONDUCTION OF IMPULSE IN HEART SEQUENCE?

• IMPULSE IN HEART SEQUENCE 1. SA node 2. atrium 3. AV node 4. Purkinje fibre 5. ventricle

nervous system job in heart beat?

• Nervous system reg rate of heart beat; DOES NOT GENERATE SIGNALS THAT CAUSE HEART TO BEAT -HEART WILL CARRY ON BEATING WITHOUT AUTONOMIC NERVOUS SYSTEM INPUT

Ohm's Law

• OHMS LAW - Mean arterial pressure (MAP)= CO x SVR CO- cardiac output SVR- systemic vascular resistance

stoke volume determined by 3 factors?

• Preload- the vol of blood that the ventricle has available to pump • Contractility- the force that the muscle can create at the given length • Afterload- arterial pressure against which the muscle will contract -These factors establish the volume of blood pumped with each heart beat

heart beat describe sarcomeres

• Sarcomeres; resting length approx 2 um; COMPOSED OF INTERDIGITATING FILAMENTS 1. Thick myosin filament 2. Thin actin filament • Adjacent myocytes attached end-to-end in stepped face, the intercalated disc: -gap junction transmits electrical current between myocytes -desmosomes provide mechanical strength

REFRACTORY PERIODS IN NON-PACEMAKER CELLS ABSOLUTE REFRACTORY PERIODS AND EFFECTIVE REFRACTORY PERIOD

• Stimulus arriving at adjacent myocyte will not excite adjacent myocyte as still in absolute refractory period • IN EFFECTIVE REFRACTORY PERIOD, SHOULD STIMULUS ARRIVE- SIGNAL WOULD BE PROPAGATED -After ARP but before ERP; non-propagated response -After ERP- propagated AP

cardiac cycle SYSTOLE

• Systole- occurs when the ventricles producing active tension; includes ISOMETRIC VENTRICULAR CONTRACTION + VENTRICULAR EJECTION phases