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.