Hemodynamics

Question 1

Can you describe the pathway of blood flow through the heart, starting from the vena cava and ending at the aorta?

Answer 1

Vena Cava: Blood from the body returns to the heart through the superior and inferior vena cava. This blood is deoxygenated and enters the right atrium.

Right Atrium: The right atrium receives deoxygenated blood and pumps it through the tricuspid valve into the right ventricle.

Right Ventricle: The right ventricle contracts and pumps the deoxygenated blood through the pulmonary valve into the pulmonary artery.

Pulmonary Artery: The pulmonary artery carries the deoxygenated blood to the lungs, where it is oxygenated.

Lungs: In the lungs, blood picks up oxygen and releases carbon dioxide.

Pulmonary Veins: Oxygenated blood returns from the lungs to the heart via the pulmonary veins, entering the left atrium.

Left Atrium: The left atrium pumps oxygenated blood through the mitral valve into the left ventricle.

Left Ventricle: The left ventricle contracts and pumps the oxygen-rich blood through the aortic valve into the aorta, which distributes it throughout the body.

Question 2

What is the function of the coronary sinus in the heart?

Answer 2

The coronary sinus is a large vein located on the posterior surface of the heart that collects deoxygenated blood from the heart’s coronary veins. Its primary function is to drain blood from the myocardium (heart muscle) and return it to the right atrium of the heart. The coronary sinus plays a crucial role in the heart’s venous circulation by ensuring that deoxygenated blood from the heart’s own tissues is returned to the heart for re-oxygenation through the lungs.

Question 3

What is the function of arteries in the circulatory system?

Answer 3

Arteries are blood vessels that carry oxygenated blood away from the heart to the body’s tissues and organs. They have thick, muscular walls to withstand the high pressure of blood being pumped by the heart. The main artery, the aorta, branches into smaller arteries that progressively divide into arterioles as they get further from the heart.

Question 4

What is the function of arterioles in the circulatory system?

Answer 4

Arterioles are small branches of arteries that regulate blood flow into the capillaries. They have muscular walls that allow them to constrict or dilate, thereby controlling the amount of blood that flows into specific tissues. By adjusting their diameter, arterioles help regulate blood pressure and distribution of blood, particularly in response to the body’s changing needs.

Question 5

What is the function of veins in the circulatory system?

Answer 5

Veins are blood vessels that carry deoxygenated blood back to the heart from the body’s tissues. They have thinner walls compared to arteries, as the blood pressure in veins is much lower. To ensure that blood moves efficiently toward the heart, veins contain one-way valves that prevent blood from flowing backward due to gravity, especially in the lower extremities.

Question 6

What is the function of venules in the circulatory system?

Answer 6

Venules are small blood vessels that collect deoxygenated blood from the capillaries and drain it into larger veins. They play a crucial role in returning blood from the tissues back to the veins. Venules have thinner walls than veins and help transport blood from the capillaries, where nutrient and gas exchange occurred, into the larger veins that will eventually return the blood to the heart.

Question 7

What is the function of capillaries in the circulatory system?

Answer 7

Capillaries are the smallest blood vessels and the site of gas, nutrient, and waste exchange between the blood and the body’s tissues. Their walls are very thin (only one cell thick), allowing oxygen, nutrients, carbon dioxide, and waste products to pass through via diffusion. Capillaries form networks (capillary beds) that deliver oxygen and nutrients to tissues and remove waste products like carbon dioxide.

Question 8

What is the formula for oxygen delivery (DO2) and how is it broken down?

Answer 8

The formula for oxygen delivery (DO2) is:

DO2=CO×CaO2×10

CO = Cardiac Output (amount of blood the heart pumps per minute)

CaO2 = Arterial Oxygen Content (amount of oxygen in the blood)

10 = Conversion factor to match units of cardiac output (L/min) and oxygen content (mL O2/dL of blood).

Question 9

What is cardiac output (CO), and how do you calculate it?

Answer 9

Cardiac output (CO) is the volume of blood the heart pumps per minute. It is a critical measure of the heart’s efficiency in circulating blood and oxygen throughout the body.

The formula for cardiac output (CO) is:

CO=SV×HR

SV = Stroke Volume (the amount of blood pumped by the heart with each beat)

HR = Heart Rate (beats per minute)

Cardiac output is typically measured in L/min.

The normal range for CO is equal to 4-8 liters per min

Question 10

What is stroke volume (SV), and how do you calculate it?

Answer 10

Stroke volume (SV) is the amount of blood pumped by the heart’s left ventricle with each heartbeat.

The formula for stroke volume (SV) is:

SV=EDV−ESV or SV= Preload + Contractility + afterload

EDV = End-Diastolic Volume (the total amount of blood in the ventricle at the end of diastole)

ESV = End-Systolic Volume (the amount of blood remaining in the ventricle after systole)

SV is typically measured in milliliters per beat (mL/beat).

The normal range for SV is equal to 60-120 milliliters per beat

Question 11

What is afterload?

Answer 11

(Resistance) Afterload refers to the resistance the heart must overcome to eject blood during systole (contraction). It is mainly determined by the systemic vascular resistance (SVR) and the condition of the aortic valve. Higher afterload means more pressure is required to pump blood, which can decrease stroke volume and increase cardiac workload. Conditions such as hypertension or aortic stenosis increase afterload.

Question 12

What is contractility?

Answer 12

Contractility is the intrinsic ability of the heart muscle to contract. It reflects the heart’s ability to pump blood, independent of preload and afterload. Increased contractility increases stroke volume and cardiac output, while decreased contractility (such as in heart failure) can decrease both. It is influenced by factors like sympathetic nervous system activation and the availability of calcium for muscle contraction.

Question 13

What is preload?

Answer 13

(Filling Pressure) Preload is the amount of stretch in the heart’s ventricles at the end of diastole (just before contraction). It is largely determined by the venous return to the heart and the end-diastolic volume (EDV). The greater the venous return, the greater the preload, which in turn can increase stroke volume (according to Starling’s Law).

Factors determining preload:
Blood Volume
Fluid Volume Distribution
Atrial Contraction

Question 14

What is the cardiac index (CI), and how do you calculate it?

Answer 14

Cardiac index (CI) is a measure of cardiac output that is normalized for body surface area (BSA), allowing for comparison across individuals of different sizes.

The formula for cardiac index (CI) is:

CI= BSA/CO
​
CO = Cardiac output (L/min)

BSA = Body surface area (m²)

The normal range for cardiac index is approximately 2.5 to 4.0 L/min/m².

Question 15

What is hemoglobin (Hgb), and what is its role in oxygen transport?

Answer 15

Hemoglobin (Hgb) is a protein found in red blood cells that binds to oxygen in the lungs and carries it to tissues throughout the body. It also helps carry carbon dioxide from tissues back to the lungs. Hemoglobin has a strong affinity for oxygen, and its ability to bind oxygen depends on factors like pH, temperature, and carbon dioxide levels.

Question 16

How do you calculate the concentration of oxygen in arterial blood (CaO2)?

Answer 16

The concentration of oxygen in arterial blood (CaO2) is the amount of oxygen carried by hemoglobin and dissolved in plasma. The formula is:

CaO2=(1.34×Hgb×SaO2)+(0.003×PaO2)

1.34 = amount of oxygen each gram of hemoglobin can carry (in mL O2/g Hgb)

Hgb = Hemoglobin concentration (g/dL)

SaO2 = Arterial oxygen saturation (%)

PaO2 = Partial pressure of oxygen in arterial blood (mmHg)

The first term represents oxygen bound to hemoglobin, while the second term represents the small amount of oxygen dissolved in plasma.

Question 17

What is PaO2, and what does it represent?

Answer 17

PaO2 is the partial pressure of oxygen in arterial blood. It is a measure of the amount of oxygen dissolved in the blood and is typically used to assess the oxygenation status of a patient. PaO2 is measured in mmHg and is an important component of the arterial blood gas (ABG) test. The normal range for PaO2 is generally 75–100 mmHg. Values outside this range can indicate hypoxemia (low oxygen levels) or hyperoxia (high oxygen levels).

Question 18

What is tachycardia, what are contributing factors?

Answer 18

Tachycardia is a HR that is greater than or equal to 100 beats per minute.

Tachycardia: decreased SV = increased HR

Common causes of tachycardia include hypovolemia, hypotension, sympathetic nervous system, Infection, & exercise.

A HR greater than 180 b/min results in a decreased cardiac output (120 b/min for a diseased heart).

Question 19

What is bradycardia, what are contributing factors?

Answer 19

bradycardia is a HR that is less than or equal to 60 beats per minute.

Bradycardia: Increased SV = Decreased HR

Common causes of bradycardia include athletes, arrythmias, heart blocks, previous myocardial infarctions, medications (Beta-blockers & calcium channel gate blockers).

Question 20

What is End-Diastolic Volume (EDV), and what does it represent?

Answer 20

End-Diastolic Volume (EDV) is the volume of blood in the left ventricle at the end of diastole, just before the heart contracts. It reflects the amount of blood the ventricle has filled with during relaxation.

It is influenced by venous return, filling time, and ventricular compliance.

A normal EDV is approximately 120–130 mL in a healthy adult.

EDV contributes directly to preload and affects stroke volume via the Frank-Starling mechanism.

Question 21

What is End-Systolic Volume (ESV), and what does it represent?

Answer 21

End-Systolic Volume (ESV) is the volume of blood remaining in the left ventricle at the end of systole, after the heart has contracted and ejected blood into the aorta.

It reflects how effectively the heart emptied during contraction.

Normal ESV is approximately 50–60 mL in a healthy adult.

ESV is affected by afterload, contractility, and ventricular size.

A lower ESV indicates stronger contractility, while a higher ESV may suggest impaired ejection, as seen in heart failure.

Question 22

What can increase and decrease contractility?

Answer 22

Increased Contractility = Increased Stroke Volume

Causes Increased O2 demand, sympathetic nervous system, & exercise.

Decreased Contractility = Decreased Stroke Volume

Decreased O2 demand, history of myocardial infraction, heart surgery, hypocalcemia, hypoxia, hypercapnia, hyperkalemia, & metabolic acidosis.

Question 23

What is the difference between systole and diastole in the cardiac cycle?

Answer 23

Systole is the phase of the cardiac cycle when the heart contracts to pump blood out of the ventricles.

Ventricular pressure increases, forcing the aortic and pulmonary valves open.

Blood is ejected into the aorta and pulmonary artery.

This phase corresponds to the “lub” (S1) sound from closure of the AV valves (mitral and tricuspid).

Diastole is the phase when the heart relaxes and the ventricles fill with blood.

The aortic and pulmonary valves close, and the AV valves open, allowing blood to flow from the atria to the ventricles.

Diastole allows for coronary artery perfusion and accounts for most of the cardiac cycle duration.

The “dub” (S2) sound corresponds to closure of the aortic and pulmonary valves.

Question 24

What is blood pressure and how can you calculate it?

Answer 24

Blood pressure is the force exerted by circulating blood on the walls of blood vessels, especially arteries. It reflects the pressure generated by the heart during systole and diastole.

Blood pressure can be calculated with the formula: CO (Cardiac Output) x SVR (Systemic Vascular Resistance)

Question 25

What is MAP (Mean Arterial Pressure), what is the normal level, and how can we calculate it?

Answer 25

The average arterial pressure during a full cardiac cycle; essential for organ perfusion. 70–100 mmHg; ≥65 mmHg is typically needed for adequate organ perfusion. MAP = (SBP + 2 × DBP) ÷ 3

Question 26

What is pulse pressure, what is the normal range for pulse pressure, and how can we calculate it?

Answer 26

The difference between systolic and diastolic pressure; shows the force of each heartbeat. Pulse Pressure = SBP – DBP 30–40 mmHg

Question 27

What is Central Venous Pressure (CVP), what is its normal range, and what factors increase or decrease it?

Answer 27

Central Venous Pressure (CVP) is the pressure within the thoracic vena cava near the right atrium, reflecting right ventricular preload (volume status and venous return). Normal range: 2–10 mmHg Increased CVP: Fluid overload, right heart failure, pulmonary hypertension, cardiac tamponade, tension pneumothorax Decreased CVP: Hypovolemia, hemorrhage, dehydration, vasodilation (e.g., from sepsis)

Question 28

What is an arterial line and what is the significance of the dicrotic notch?

Answer 28

An arterial line (A-line) is a thin catheter inserted into an artery (commonly the radial or femoral artery) used for continuous blood pressure monitoring and frequent blood sampling (especially ABGs). The dicrotic notch is a small downward deflection in the arterial waveform that represents aortic valve closure. It marks the transition between systole and diastole and is a key indicator of waveform accuracy.

Question 29

What is FloTrac and what does it measure?

Answer 29

FloTrac is a hemodynamic monitoring system that connects to an arterial line and uses pulse contour analysis to estimate stroke volume (SV), cardiac output (CO), and stroke volume variation (SVV) — without needing a pulmonary artery catheter. It continuously analyzes the arterial waveform to provide real-time data. Useful in managing fluid responsiveness and cardiac performance, especially in critically ill or surgical patients. Less invasive than traditional methods like a Swan-Ganz catheter. Causes of inaccuracy include: Irregular heart rhythms (e.g., atrial fibrillation) Severe vasodilation (e.g., in septic shock) Aortic regurgitation Low arterial waveform quality (e.g., dampened waveform from improper A-line setup) Rapidly changing vascular tone Extremely low or high SVR FloTrac works best in patients who are sedated, mechanically ventilated, and in sinus rhythm.

Question 30

What is a Swan-Ganz (PA) catheter, what can it do, and what information does it provide?

Answer 30

A Swan-Ganz (pulmonary artery) catheter is a specialized catheter inserted into a central vein, threaded into the right heart, and into the pulmonary artery. It provides direct measurements of pulmonary artery pressure (PAP), pulmonary capillary wedge pressure (PCWP), and cardiac output (CO). It can also measure right atrial pressure (RAP) and mixed venous oxygen saturation (SvO2). It helps assess right and left heart function, fluid status, and pulmonary pressures. Useful for patients in shock, heart failure, and severe pulmonary issues.

Question 31

What is pulmonary artery pressure (PAP) and what is its normal measurement?

Answer 31

Pulmonary artery pressure (PAP) measures the pressure in the pulmonary artery, reflecting right ventricular function and pulmonary circulation status. Normal PAP: Systolic PAP (PAPs): 15-30 mmHg Diastolic PAP (PADP): 4-12 mmHg Mean PAP (MPAP): 10-20 mmHg Increased PAP can indicate pulmonary hypertension, left heart failure, or acute respiratory distress syndrome (ARDS).

Question 32

What is pulmonary capillary wedge pressure (PCWP) and what is its normal measurement?

Answer 32

Pulmonary capillary wedge pressure (PCWP) is an indirect measurement of left atrial pressure, reflecting left heart preload and filling pressures. Normal PCWP: 4-12 mmHg Elevated PCWP suggests left heart dysfunction, fluid overload, or mitral valve issues. PCWP is measured using the Swan-Ganz catheter by inflating the balloon at the catheter tip to "wedge" it in a small pulmonary artery branch.

Question 33

How do you treat non-compensatory tachycardia, and what are the types of stable and unstable tachycardia?

Answer 33

Non-compensatory tachycardia (such as supraventricular tachycardia (SVT)) is treated by addressing the underlying rhythm and its stability. Types of tachycardia: Stable: Regular rhythm, no signs of shock or hemodynamic compromise. Unstable: Rapid heart rate causing significant symptoms (hypotension, altered mental status, chest pain, shortness of breath). Treatment for stable tachycardia: Vagal maneuvers (e.g., Valsalva maneuver) Adenosine (for SVT or narrow-complex tachycardia) Beta-blockers or calcium channel blockers (e.g., diltiazem, metoprolol) Treatment for unstable tachycardia: Synchronized cardioversion (for unstable SVT or narrow complex tachycardia) Defibrillation may be required for wide-complex tachycardias (e.g., ventricular fibrillation (VF) or pulseless VTAC).

Question 34

How do you treat ventricular tachycardia (VTAC) in stable and unstable patients?

Answer 34

VTAC treatment depends on whether the patient is stable or unstable. Stable VTAC: Antiarrhythmic medications: Amiodarone (300 mg IV bolus, followed by 1 mg/min for 6 hours, then 0.5 mg/min) Lidocaine (1-1.5 mg/kg IV bolus, followed by infusion) Electrolyte correction (e.g., magnesium, potassium) Cardiology consultation for potential ICD (implantable cardioverter-defibrillator) implantation if recurrent. Unstable VTAC: Synchronized cardioversion: Start with 100 J and increase if needed. If patient is pulseless (i.e., pulseless VTAC or VF), proceed with defibrillation and CPR.

Question 35

How do you treat bradycardia in stable and unstable patients?

Answer 35

Bradycardia treatment depends on whether the patient is stable or unstable. Stable Bradycardia: Monitor closely (vital signs, ECG) Atropine (0.5 mg IV, may repeat every 3-5 minutes up to 3 mg) Consider transcutaneous pacing if symptoms persist or atropine is ineffective. Unstable Bradycardia: Transcutaneous pacing (first-line for unstable bradycardia if atropine is ineffective) If pacing unavailable or ineffective, consider dopamine (2-10 mcg/kg/min IV) or epinephrine (2-10 mcg/min IV) infusion. Consider temporary transvenous pacing if symptoms remain unresolved.

Question 36

What is transvenous pacing and when is it used?

Answer 36

ransvenous pacing is a temporary form of cardiac pacing where a pacing catheter is inserted through a central vein (like the internal jugular, subclavian, or femoral vein) and advanced into the right ventricle to deliver electrical impulses directly to the heart. Used for: Symptomatic bradycardia unresponsive to atropine or transcutaneous pacing High-degree AV blocks (e.g., Mobitz II or 3rd-degree block) Bridge to permanent pacemaker placement Overdrive pacing in certain tachyarrhythmias (rare) Requires continuous ECG monitoring and is typically performed in an ICU or critical care setting.

Question 37

What is myocardial contractility, and how do you treat high and low contractility?

Answer 37

Myocardial contractility refers to the strength of the heart's contraction, independent of preload and afterload. Low Contractility (e.g., heart failure, cardiogenic shock): Treatment includes: Inotropes to increase contractility: Dobutamine Dopamine (moderate doses) Milrinone Optimize preload and afterload (fluids, vasodilators, or diuretics as appropriate) Correct underlying causes (e.g., ischemia, electrolyte imbalances) High Contractility (rare but may occur in states like sepsis or stimulant use): Treatment includes: Beta-blockers (e.g., metoprolol, esmolol) to reduce cardiac workload Calcium channel blockers (e.g., diltiazem) in some cases Treat the underlying cause (e.g., sepsis, pain, anxiety, drug toxicity) VAD or Impella used for support

Question 38

What is an Impella device and what does it do?

Answer 38

The Impella is a percutaneous ventricular assist device (VAD) used to support heart function in patients with severe cardiac compromise. It is inserted via a large artery (commonly the femoral artery) and advanced into the left ventricle. The device actively pulls blood from the LV and pumps it into the aorta, decreasing LV workload and improving cardiac output. Used for: Cardiogenic shock High-risk PCI (percutaneous coronary intervention) Bridge to recovery or more advanced mechanical support Benefits: Offloads the left ventricle Improves perfusion to vital organs Reduces myocardial oxygen demand Requires close monitoring in ICU due to risks like bleeding, hemolysis, limb ischemia, or device malfunction.

Question 39

How do you treat high and low preload?

Answer 39

Low Preload (e.g., hypovolemia, dehydration, hemorrhage): Give IV fluids (crystalloids or blood products) Consider vasopressors (if hypotensive and fluids are not enough) Treat underlying cause (e.g., bleeding, dehydration) High Preload (e.g., fluid overload, heart failure): Diuretics (e.g., furosemide) Vasodilators (e.g., nitroglycerin, morphine) Dialysis (in renal failure or severe overload) Positioning: elevate head of bed to reduce venous return

Question 40

How do you treat high and low afterload?

Answer 40

Low Afterload (SVR Less than 800) (e.g., distributive shock like sepsis): Vasopressors to increase systemic vascular resistance (SVR): Norepinephrine (Levophed) Phenylephrine Vasopressin Treat the underlying cause (e.g., antibiotics for sepsis) High Afterload (SVR Greater than 1200) (e.g., hypertension, aortic stenosis): Vasodilators to reduce SVR: Nitroprusside, nicardipine, nitroglycerin Antihypertensives: ACE inhibitors, beta-blockers Inotropes may be used if cardiac output is poor (e.g., milrinone) Treat the cause (e.g., manage HTN, relieve valve obstruction)

Question 41

What is an IABP (Intra-Aortic Balloon Pump) and how does it work?

Answer 41

An IABP is a mechanical circulatory support device used to assist the heart in pumping blood and improving coronary perfusion. How it works: Inserted via the femoral artery and positioned in the descending thoracic aorta, just below the left subclavian artery. The balloon inflates during diastole, increasing coronary artery perfusion. The balloon deflates just before systole, creating a vacuum effect that reduces afterload and myocardial oxygen demand. Indications: Cardiogenic shock Acute MI with complications Bridge to more definitive therapy (e.g., transplant, Impella, ECMO) Unstable angina not responsive to medication Contraindications: Aortic dissection Severe aortic regurgitation End-stage peripheral vascular disease Requires close monitoring in ICU with arterial line and waveform analysis.