Canonical Question
Mycocardial O2
Master answer
Myocardial O2 Supply
RIGHT VENTRICLE
LEFT VENTRICLE
- Supply:
- Right coronary artery and its branches
- conus artery supplies the infundibulum
- acute marginal arteries supply the anterior free wall
- posterior descending artery via septal branches supply the posterior 1/3 IV septum (PDA arises from RCA in Right dominant circulation and LCx in Left dominant circulation
- the other 2/3 of the IV septum is supplied by septal branches of the left anterior descending artery
- Supply: Left Main Coronary
- LAD (supplies the free wall and most of the papillary muscles)
- Diagonals
- Septal perforators
- LCx: inferolateral LV wall
- Obtuse Marginal branches
- LAD (supplies the free wall and most of the papillary muscles)
- RV Coronary blood flow
- RV pressures are low during both systole and diastole.
- flow during both systole and diastole
- LV Coronary blood flow
- The pressure inside the left ventricle is slightly higher than in the aorta during systole.
- Flow predominantly during diastole.
- Subendocardial flow ceases during systole.
Myocardial O2 Demand
Determinants of myocardial O₂ demand:
- MVO₂ (ie extraction)
- High at rest (55-65%) cf. body average of 25%
- Extraction ratio can only rise by factor of < 2 to 90%
- AV Δ O₂ = 11 mL/dL
- Coronary venous O₂ content = 5 mL/dL
- Normally consumption 21 to 27 mls of O2/min.
- Determined by
- Wall tension.
- preload (EDV/EDP) and afterload (SVR)
- Contractility.
- Heart rate.
- ↑HR → ↓ supply
- ↑HR → ↑ demand (as ↑ MRO2)
- Wall tension.
RIGHT VENTRICLE
LEFT VENTRICLE
| Pumps against less resistance (PVR) → less systolic pressure → less O2 demand may be compromised during acute or chronic increases in right ventricle afterload resulting from pulmonary arterial hypertension | Pumps against higher afterload, thus more demand |
| ability to downregulate its metabolic demand during coronary hypoperfusion and thereby maintain contractile function and energy stores | |
| Activation of SNS causes relatively small changes in O2 demand | Activation of SNS causes more pronounced increase in O2 demand |
Exam appearances
| Exam | Exact wording | Relationship | Success |
|---|---|---|---|
| 2016B Q07 | Compare and contrast the supply and demand of oxygen for the right and left ventricle. | historical_member | — |