Cardiovascular Physiology Quiz

Cardiovascular Physiology & Pharmacology (2)

• Course title: Cardiovascular Physiology & Pharmacology (2)
• Lecturer: Dr Stella Koutsikou
• Module code: MSOP1003
• Office location: Anson 307
• Email address: [email protected]

Intrinsic Electrical Conduction System

• Heart Rate (HR): Number of times the heart beats per minute (bpm)
• HR is set by the sinoatrial (SA) node
• HR is regulated by the autonomic nervous system
• SA Node: Autorhythmic pacemaker of the heart
• Intrinsic rate of the SA node: 100-110 bpm
• Parasympathetic Nervous System: Control
• Average resting HR: 70 bpm
• Sympathetic Nervous System: Increases HR

Learning Objectives

• Describe heart's mechanical events during systole and diastole
• Understand cardiac output and factors affecting it
• Align intrinsic excitability with myocardium contraction
• Define blood pressure (BP) and factors affecting it
• Understand normal control of BP
• Pharmacology related to heart contractility and blood pressure control

The Cardiac Cycle

• The orderly process of cardiac cell depolarization triggering atrial and ventricular contractions and relaxations
• Diastole: Relaxation of cardiac muscle
• Systole: Contraction of cardiac muscle
• Depolarization of cardiac myocytes leads to contraction of cardiac muscle
• The cardiac cycle repeats with every heartbeat

The Cardiac Cycle: Phases

• The cardiac cycle is split into two major phases related to ventricular relaxation and contraction. Different points of the cycle are marked by the presence of various waves on the ECG.
• Systole: Period of ventricular contraction and blood ejection (0.3 seconds)
• Diastole: Ventricular relaxation and blood filling (0.5 seconds)
• The typical heart rate = 72 bpm and the cycle takes ~0.8s

Blood Pressure

• Blood flows from higher to lower pressure
• Systole (contraction) increases pressure
• Diastole (relaxation) reduces pressure
• Valves open/close depending on pressure gradients
• Semilunar valves open during systole when ventricular pressure higher than aortic pressure; AV values open during diastole
• Measuring arterial blood pressure: pressure on artery walls in mmHg
• Systolic pressure: Pressure when ventricles contract (higher number)
• Diastolic pressure: Pressure when ventricles relax (lower number)

Mechanical Events During Cardiac Cycle

• Detailed graphic representations showing atrial and ventricular pressure and volume changes over the cardiac cycle.
• ECG (electrocardiogram) and phonocardiogram (sounds) activity aligned with pressure/volume changes.
• Show different phases of the cycle: atrial depolarization and contraction, AV valve closure, isovolumetric contraction, ventricular ejection, etc.

Cardiac Output

• CO = HR x SV
• CO = Cardiac Output (liters/minute)
• HR = Heart Rate (beats/minute)
• SV = Stroke Volume (liters/heartbeat)

Factors Affecting HR, CO & BP

• Vagus nerve (parasympathetic), Acetylcholine affects heart,innervates the atria, SA node and AV node.
• Sympathetic nerves (sympathetic), Norepinephrine (NE), Beta-1 (β1) receptors, innervates atria, SA node and AV node.
• Factors affecting SV: preload, afterload
• Preload: degree of myocardium stretch before contraction determined by venous return (end diastolic volume).
• Afterload: peripheral resistance contracting ventricular muscle needs to work against.
• High preload = high SV ; High afterload = low SV

Beta Blockers

• Beta blockers (e.g., Bisoprolol) reduce Ca2+ entering pacemaker cells during phase 4 and reduce conduction velocity, reducing HR and thus CO.

ANS Regulation of Heart Rate

• Autonomic nervous system regulates CO and BP.
• Baroreceptor reflex is essential for maintaining stable BP
• BP=CO x PVR (Peripheral vascular resistance)