Cardiac Cycle & Hemodynamics: INBDE Review
Diastole vs systole, EDV/ESV/SV/CO/EF formulas, preload-afterload-contractility, S1–S4 heart sounds, and what changes in heart failure. 11 board-style MCQs.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. 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 chapter unfolds from there.
| 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%) |
| 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 |
| 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 |
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).
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong, that's where the learning compounds.
The MCQs above are Core Recall, testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- 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?
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.