Physiology
Cardiovascular Physiology
Cardiovascular physiology for MBBS and NEET-PG: cardiac output, Frank-Starling law, cardiac cycle, heart sounds, JVP and blood pressure regulation, mapped to NMC codes PY5.
MedNext Academy | 3 min read
Cardiovascular Physiology
Cardiovascular physiology for MBBS and NEET-PG: cardiac output, Frank-Starling law, cardiac cycle, heart sounds, JVP and blood pressure regulation, mapped to NMC codes PY5.
Cardiovascular physiology is the mechanistic backbone of cardiology. It covers the cardiac cycle, the determinants of cardiac output, the cardiac action potential and pacemaker activity, the heart sounds and venous pulse, and the reflexes that regulate blood pressure.
High-yield: Cardiovascular Physiology
- Cardiac output equals heart rate times stroke volume and is about 5 litres per minute at rest.
- Stroke volume is set by preload, afterload and contractility.
- The Frank-Starling law states that a greater venous return, or preload, increases stroke volume up to a point.
- Ejection fraction is stroke volume divided by end-diastolic volume; normal is about 55 to 70%.
- The first heart sound is closure of the mitral and tricuspid valves; the second is closure of the aortic and pulmonary valves.
- The a wave of the jugular venous pulse is atrial contraction; a cannon a wave occurs in complete heart block.
- The plateau of the ventricular action potential is due to calcium entry through L-type channels.
- The SA node is the pacemaker because it has the fastest rate of phase 4 depolarisation.
- Baroreceptors in the carotid sinus and aortic arch buffer acute changes in blood pressure.
- Mean arterial pressure equals cardiac output times systemic vascular resistance.
- Isovolumetric contraction lies between mitral closure and aortic opening, with no change in ventricular volume.
- Coronary blood flow to the left ventricle occurs mainly during diastole.
- The dicrotic notch on the aortic pressure curve marks aortic valve closure.
- Sympathetic stimulation raises heart rate and contractility, while parasympathetic stimulation slows the heart through the vagus.
Cardiac cycle landmarks
- **S1 / S2:** Mitral and tricuspid closure; aortic and pulmonary closure.
- **JVP a wave:** Atrial contraction. Cannon a wave in complete heart block.
- **Ejection fraction:** Stroke volume over end-diastolic volume. Normal 55 to 70%.
- **MAP:** Cardiac output times systemic vascular resistance.
NMC competencies in this chapter
- **PY5.1:** Properties of cardiac muscle and the cardiac action potential
- **PY5.4:** The cardiac cycle and heart sounds
- **PY5.7:** Cardiac output and its regulation
- **PY5.10:** Arterial blood pressure and its regulation
- **PY5.13:** Regional circulations including coronary blood flow
Frequently Asked Questions
What determines cardiac output?
Cardiac output is heart rate times stroke volume, and stroke volume is set by preload, afterload and contractility.
What causes the first and second heart sounds?
The first sound is closure of the mitral and tricuspid valves at the start of systole, and the second is closure of the aortic and pulmonary valves at the end of systole.
Why does coronary flow happen in diastole?
During systole the contracting left ventricle compresses its own vessels, so most left ventricular coronary flow occurs in diastole when the muscle relaxes.
What is a cannon a wave?
A large a wave in the jugular venous pulse produced when the atrium contracts against a closed tricuspid valve, seen in complete heart block.
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