Basic Cardiovascular Physiology

1. Blood Pressure:

• Mean Arterial Pressure (MAP): The average blood pressure generated during a cardiac cycle.

• MAP Calculation: MAP = Diastolic pressure + (Systolic pressure – Diastolic pressure)/3

• Age-related changes: MAP is lowest in children and higher in elderly people.

• Role: Force that propels blood through the circulatory system, reflecting the heart’s ability to function.

• Which phase of the cardiac cycle lasts the longest?

• Complete diastole takes up 65% of the cardiac cycle.

• Cardiac Cycle:

• Cardiac cycle lasts for 0.8 seconds:

• Atrial systole: Atrial contraction, pushing blood from atria to ventricles through the atrioventricular valves (approximately 35% of blood volume is opened). Duration: 0.1 seconds.

• Ventricular systole:

• Isovolumetric contraction: 0.05 seconds, atrioventricular valves close.

• Ejection: 0.25 seconds, aortic and pulmonary valves open, blood is pumped out to arteries. Includes rapid ejection phase (0.09 seconds) and slow ejection phase (0.16 seconds).

• Complete diastole: 0.4 seconds, ventricles relax, blood pressure gradually decreases. Aortic and pulmonary valves close when ventricular pressure is lower than arterial pressure. Isovolumetric relaxation phase because no valve is open. Atrioventricular valves reopen when ventricular pressure is lower than atrial pressure.

• Sinus rhythm: 70-80 beats per minute.

• What force drives blood flow in arteries?

• Ventricular contraction during ventricular systole.

2. Physiological Properties of Arteries:

• Arteries have 2 physiological properties:

• Elasticity: Helps regulate blood flow.

• Constriction: Helps regulate blood pressure.

3. Phases in the Cardiac Cycle:

• Duration of atrial systole: 0.1 seconds.

• Duration of isovolumetric contraction: 0.05 seconds.

• Duration of ventricular ejection: 0.25 seconds.

4. Heart Valves:

• Atrioventricular valves:

• Left side: Mitral valve.

• Right side: Tricuspid valve.

• Function: Open to allow blood flow from atria to ventricles, close to prevent backflow from ventricles to atria.

5. Arteriovenous Malformation:

• Definition: An abnormal connection between an artery and a vein.

• Causes: Congenital or due to injury.

6. Electrocardiogram (ECG):

• Role: Monitor the heart’s activity, rate, and rhythm.

• Signs of premature ventricular contractions: …

7. Capillary Pressure:

• Capillary pressure (arteriolar end):

• Hydrostatic pressure: 30 mmHg.

• Colloid osmotic pressure: 8 mmHg.

• Interstitial fluid pressure: -3 mmHg.

• Plasma colloid osmotic pressure: 28 mmHg.

• Net filtration pressure: 13 mmHg (force that pushes fluid from arterioles into interstitial spaces).

• Capillary pressure (venular end):

• Plasma colloid osmotic pressure: 28 mmHg.

• Hydrostatic capillary pressure: 10 mmHg.

• Interstitial fluid colloid osmotic pressure: 8 mmHg.

• Interstitial fluid pressure: -3 mmHg.

• Net reabsorption pressure: 7 mmHg (force that draws fluid from interstitial spaces into venules).

8. Cardiac Conduction System:

• Sinoatrial (SA) Node:

• Location: Right atrium, where the superior vena cava enters the heart.

• Frequency: 70-80 beats per minute.

• Controlled by the sympathetic and parasympathetic nervous systems.

• Atrioventricular (AV) Node:

• Location: Interatrial septum, near the SA node.

• Frequency: 40-60 beats per minute.

• Controlled by the sympathetic and parasympathetic nervous systems.

• Bundle of His:

• Transmits impulses from atria to ventricles.

• Divides into left and right branches.

• Frequency: 30-40 beats per minute.

• Controlled by the sympathetic nervous system.

• Purkinje fibers:

• Transmit impulses to the ventricles.

• Frequency: 15-40 beats per minute.

9. Cardiac Parameters:

• Stroke volume: 60-70 ml.

• Cardiac output: Amount of blood the heart pumps into arteries per minute.

• Formula: Q = Qs x f

• Qs: Stroke volume.

• f: Heart rate in beats per minute.

• Heart sounds:

• S1: First heart sound, low-pitched and long, heard at the apex of the heart. Produced by closure of the atrioventricular valves, as ventricles contract and pump blood into arteries.

• S2: Second heart sound, high-pitched and short, heard at the aortic and pulmonary valve areas. Produced by closure of the aortic and pulmonary valves, marking the beginning of ventricular relaxation.

10. Concepts:

• Cardiac arrest: After 4 minutes, the brain will suffer irreversible damage.

• Systemic circulation: Oxygen-rich blood travels from the left ventricle -> arteries -> organs for metabolic exchange -> veins -> right ventricle.

• Pulmonary circulation: Carbon dioxide-rich blood travels from the right ventricle -> pulmonary arteries -> gas exchange in the lungs -> pulmonary veins -> left ventricle.

• Capillaries: Also known as microcirculation.

• Main driving force of circulation: The heart.

• Aorta: Artery with a valve, carrying oxygen-rich blood.

• Pulmonary artery: Artery with a valve, carrying carbon dioxide-rich blood.

• Aneurysm: Bulging or dilation of an artery wall.

• Pseudoaneurysm: A pulsatile collection of blood around an artery, not a dilation of the artery wall itself.

11. Electrocardiogram (ECG) Leads:

• Bipolar limb leads:

• DI: Right arm (-) – Left arm (+).

• DII: Right arm (-) – Left leg (+).

• DIII: Left arm (-) – Left leg (+).

• Unipolar limb leads:

• aVR: Right arm (+).

• aVL: Left arm (+).

• aVF: Left leg (+).

Note: This article provides basic information on cardiovascular physiology. For a deeper understanding of the subject, consult specialized literature.