EXSS1010 Lecture Notes - Lecture 3: Systolic Geometry, Qrs Complex, Cardiac Output
30 May 2018
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EXSS1010 - CARDIOVASCULAR REGULATION
LECTURE OBJECTIVES:
1. Describe the intrinsic mechanisms that regulate heart rate
2. List the methods used to analyse the cardiac cycle
3. Describe the extrinsic mechanisms that regulate heart rate
4. Discuss how blood flow changes during exercise
5. Understand the intrinsic and extrinsic factors that influence blood flow
THE CV SYSTEM
• Three major circulatory elements
o 1. A pump (heart)
o 2. Channels or tubes (blood vessels)
o 3. A fluid medium (blood)
• Heart is a four-chambered organ generates pressure to drive blood through vessels
• Muscular organ - myocardium
• Blood flow must meet metabolic demands
• What regulates the heart?
CARDIOVASCULAR REGULATION
• The cardiovascular system is regulated by intrinsic vs extrinsic factors
• Work synergistically to influence cardiovascular function
o Heart rate
o Blood pressure
o Blood flow
• Cardiac muscle tissue innovated by electrical impulses
• Generated intrinsically but influenced by neural factors outside the heart (extrinsic)
INTRINSIC CONTROL OF THE HEART
• Spontaneous rhythmicity: special heart cells generate and spread electrical signal
o Sinoatrial (SA) node
o Atrioventricular (AV) node
o AV bundle (bundle of His)
o Purkinje fibers
• Electrical signal spreads via gap junctions
o Intrinsic heart rate (HR): 100 beats/min
o Observed in heart transplant patients (no neural innervation)
o https://www.youtube.com/watch?v=hllPRNSJwDA
• SA node: initiates contraction signal
o Pacemaker cells in upper posterior RA wall
o Signal spreads from SA node via RA/LA to AV node
o Stimulates RA, LA contraction
• AV node: delays, relays signal to ventricles
o In RA wall near center of heart
o Delay allows RA, LA to contract before RV, LV
o Relays signal to AV bundle after delay
• AV bundle: relays signal to RV, LV
o Travels along interventricular septum
o Divides into right and left bundle branches
o Sends signal toward apex of heart
• Purkinje fibers: send signal into RV, LV
find more resources at oneclass.com
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o Terminal branches of right and left bundle branches
o Spread throughout entire ventricle wall
o Stimulate RV, LV contraction
ELECTROCARDIOGRAM
• The ECG reflects electrical activity across the heart during a cardiac cycle
• Diastole
o Relaxation/filling phase
o 62% of cycle duration
• Systole
o Contraction/emptyingphase
o 38% of cycle duration
• Monitor the heart during different physical activities and exercise stress testing
CONSIDERATIONS FOR ECG
• Type of ECG
o Number of leads
• Electrode placement
o Can lead to noise
• Skin preparation
o Reduces etraeous electrical oise
o Abrade the skin
o Alcohol wipes remove surface epidermis and oil
12 LEAD ECG
• Gold standard for exercise stress testing
• 10 electrodes for 12 leads (views) of the heart
• Limb electrodes can be modified for exercise
o Clavicle & hips vs wrist and ankle
THREE LEAD ECG
• Less diagnostic value than 12 lead
• Useful in functional exercise testing & continuous monitoring
• 3 electrodes allow 3 leads (views)
• Variations in electrode placements exist
ECG WAVES
• P ae: Atrial depolarizatio → atria cotract
• QRS complex: Ventricular depolarization → etricles cotract
• QRS complex obscures atrial repolarization
• T ae: Vetricular repolarizatio → etricles rela
EXTRNSIC REGULATION OF THE HEART
THE AUTONOMIC NERVOUS SYSTEM
• Cardiovascular system is external regulated by autonomic nervous system
o Direct innovation
o Indirect via circulating hormones
o Involuntary
• Sympathetic: fit or flight
o Prepare for physical activity
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The cv system: three major circulatory elements, 1. Spontaneous rhythmicity: special heart cells generate and spread electrical signal: sinoatrial (sa) node, atrioventricular (av) node, av bundle (bundle of his, purkinje fibers, electrical signal spreads via gap junctions. Intrinsic heart rate (hr): 100 beats/min: observed in heart transplant patients (no neural innervation, https://www. youtube. com/watch?v=hllprnsjwda. Sa node: initiates contraction signal: pacemaker cells in upper posterior ra wall, signal spreads from sa node via ra/la to av node, stimulates ra, la contraction, av node: delays, relays signal to ventricles. Electrocardiogram: the ecg reflects electrical activity across the heart during a cardiac cycle, diastole, relaxation/filling phase, 62% of cycle duration. Systole: contraction/emptyingphase, 38% of cycle duration, monitor the heart during different physical activities and exercise stress testing. Considerations for ecg: type of ecg, number of leads, electrode placement, can lead to noise. Skin preparation: reduces e(cid:454)tra(cid:374)eous electrical (cid:862)(cid:374)oise(cid:863, abrade the skin, alcohol wipes remove surface epidermis and oil.
