Pump mechanics · Cardio & Respiratory
Cardiac Cycle & Hemodynamics MCQ
Diastole vs systole, EDV/ESV/SV/CO/EF formulas, preload-afterload-contractility, S1–S4 heart sounds, and what changes in heart failure. 25 MCQs and 9 INBDE patient cases.
25 practice MCQsQuick-reference tableMnemonics + clinical pearlsFull distractor explanations
High-yield review
Concept summary and clinical relevance.
Quick-reference structure first, then detailed coverage. Mnemonics in amber, clinical pearls in blue.
Cardiac physiology shows up on the INBDE both as straight equations (CO = HR × SV) and as clinical reasoning (low EF, S3 gallop, vasovagal syncope in the dental chair). Lock the formulas, the heart sounds, and the preload/afterload/contractility framework: most of the module unfolds from there.
Hemodynamic measures: definitions and formulas
| Measure | Definition | Formula / value |
|---|---|---|
| EDV (end-diastolic volume) | Maximum filling volume before contraction | ~120 mL |
| ESV (end-systolic volume) | Volume left after ejection | ~50 mL |
| SV (stroke volume) | Blood ejected per beat | EDV − ESV (~70 mL) |
| CO (cardiac output) | Total blood pumped per minute | HR × SV (~5 L/min at rest) |
| EF (ejection fraction) | Fraction of EDV ejected | SV ÷ EDV (normal > 55%) |
Preload, afterload, contractility: what changes them
| Variable | Driven by | Effect on SV |
|---|---|---|
| Preload | Venous return / EDV | ↑ preload → ↑ SV (Frank–Starling) |
| Afterload | Arterial resistance (BP) | ↑ afterload → ↓ SV |
| Contractility | Sympathetic tone, catecholamines | ↑ contractility → ↑ SV, ↓ ESV |
| Heart rate (very high) | Tachycardia > 180 bpm | Reduces filling time → ↓ SV → ↓ CO |
Heart sounds: what they mean
| Sound | Cause | Clinical meaning |
|---|---|---|
| S1 | AV valves close (mitral + tricuspid) | Marks start of systole |
| S2 | Semilunar valves close (aortic + pulmonic) | Marks start of diastole |
| S3 | Rapid ventricular filling | Normal in youth/athletes; pathologic in adults → heart failure / volume overload |
| S4 | Atrial contraction into stiff ventricle | Pathologic → HTN, LV hypertrophy, ischemia |
Clinical pearl, Why this matters in the dental chair
A patient with EF of 30% has reduced cardiac output and limited reserve: long appointments, supine positioning, or epinephrine in local anesthetic can tip them into trouble. An audible S3 in an adult is a red flag for failure; an S4 suggests stiff (hypertensive or hypertrophic) heart. Vasovagal syncope is the most common dental cardiac event and is fundamentally a preload problem (parasympathetic surge → ↓ venous return → ↓ CO).
Clinical pearl, PV loop in 30 seconds
Width of the loop = stroke volume. Increased preload shifts the loop to the right and widens it (more SV). Increased afterload makes the loop taller and narrower (less SV). Increased contractility shifts the upper-left corner up and to the left (lower ESV, more SV). The board questions reduce to which of these three is changing.
Mnemonic, Core formulas
“EDV − ESV = SV. CO = HR × SV. EF = SV ÷ EDV.” Three equations cover most cardiac calculation questions.
Mnemonic, Heart sounds
“S1 = Start of Systole. S2 = Start of Diastole. S3 = CHF. S4 = Stiff.”
Mnemonic, Determinants of stroke volume
“Preload = Push in. Afterload = Push against. Contractility = Punch.” More push in or harder punch → more SV. More push against → less SV.
Phases of the cardiac cycle
- Diastole (filling): AV valves open; ventricles fill passively, then atrial contraction adds the final 10–20% (the “atrial kick”). Ends at EDV.
- Isovolumetric contraction: AV valves close (S1), all valves shut, pressure rises sharply.
- Ejection: aortic and pulmonic valves open, blood leaves the ventricle.
- Isovolumetric relaxation: semilunar valves close (S2), all valves shut until diastolic filling begins again.
Hemodynamic regulation
- Preload: determined by venous return / EDV. Frank–Starling: more stretch → stronger contraction → ↑ SV.
- Afterload: arterial resistance the heart must pump against. Higher BP → ↓ SV.
- Contractility: increased by sympathetic tone, β1 stimulation, and circulating catecholamines.
- Heart rate: ↑ HR usually ↑ CO, but HR > 180 bpm reduces filling time and can drop CO.
Clinical syndromes
- Systolic heart failure (HFrEF, EF < 40%): reduced contractility, ↑ EDV, ↓ EF.
- Diastolic heart failure (HFpEF, EF preserved): stiff ventricle, poor filling.
- Left-sided HF: pulmonary congestion, orthopnea, dyspnea: patient may struggle when supine in the chair.
- Right-sided HF: jugular venous distension, peripheral edema, hepatomegaly.
- Vasovagal syncope: parasympathetic surge → bradycardia + ↓ preload → fainting (most common dental cardiac event).
Core Recall Check
25 board-style MCQs.
Active recall is the highest-yield study method. Pick an answer, check it, and read why every distractor is wrong.
0 of 25 answered · 0 correct
Keys: A-E or 1-5, Enter to check
- Question 1EasyDuring which phase of the cardiac cycle do the ventricles fill with blood?
- Question 2EasyWhich valves close at the start of ventricular systole, producing the S1 heart sound?
- Question 3EasyStroke volume is calculated as:
- Question 4EasyCardiac output (CO) is defined as:
- Question 5EasyA normal ejection fraction is typically:
- Question 6ModerateIncreasing preload (end-diastolic volume) generally:
- Question 7ModerateIncreased afterload (arterial resistance) has which effect on stroke volume?
- Question 8ModerateIf heart rate rises too high (e.g., > 180 bpm), cardiac output may fall due to:
- Question 9EasyThe first heart sound (S1) corresponds to:
- Question 10ModerateA fourth heart sound (S4) usually indicates:
- Question 11ModerateWhich heart sound is most closely linked to heart failure in adults?
- Question 12EasyThe second heart sound (S2) is produced by:
- Question 13ModerateDuring isovolumetric contraction, the heart valves are:
- Question 14ModerateThe aortic valve opens and ejection begins when:
- Question 15ModerateThe Frank-Starling relationship describes stroke volume increasing with greater:
- Question 16ModerateContractility is most increased by:
- Question 17ModerateIf end-diastolic volume is 120 mL and end-systolic volume is 60 mL, the ejection fraction is:
- Question 18EasyPulse pressure is defined as:
- Question 19ModerateMean arterial pressure is best approximated by:
- Question 20ModerateBlood flow to the left ventricular myocardium occurs mainly during:
- Question 21HardThe atrial contribution to ventricular filling (the atrial kick) becomes most important when:
- Question 22ModerateA third heart sound (S3) is produced by:
- Question 23ModerateIncreased contractility most directly lowers which value?
- Question 24ModerateWhich set of findings most suggests right-sided heart failure?
- Question 25ModerateVasovagal syncope lowers cardiac output mainly by:
Clinical Reasoning Cases
INBDE patient cases.
9 ADA INBDE-format patient cases on cardiac cycle. Each case is a shared patient box plus linked questions with full distractor explanations.
INBDE Patient Cases
Cardiac Cycle INBDE Patient Cases →
9 patient cases · 45 linked questions
Open cases →
Author
Dr. Isaac Sun, DDS
Founder, KYT Dental Services. These MCQs are reviewed by a practicing clinician and offered as an educational reference for dental students.
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