Almost every cardiovascular question resolves into one of three things: what determines the output of the pump, what determines the return to it, and how the two are held equal beat by beat. This module builds the pump first, because the pressure-volume loop is the object most of the rest is described against; then the circuit and its control; then the applied physiology; and finally the electrical activity that sets the whole thing going.
Orientation
What this module covers, and how to work through it
The organising idea is that the heart and the circulation are a coupled system, not two topics. Stroke volume is set by preload, afterload and contractility; preload is set by venous return; venous return is set by the circulation the heart is pumping into. Any account of cardiac output that stops at the heart has only done half the problem, which is why the pump and the circulation are consecutive lessons that reference each other rather than separate ones.
Two interactive figures carry a large part of the teaching. The pressure-volume loop in lesson 1 is a real time-varying-elastance ventricle coupled to a Windkessel arterial load, so every pathology it draws is the model’s own output rather than a hand-drawn shape; the action potential trace in lesson 4 works the same way. Both are worth driving rather than reading.
Prerequisites for the module as a whole
These carry material this module builds on directly and does not repeat. Work through them first if they are not already secure:
- Cellular physiology — membrane potentials: the resting membrane potential, the Nernst and Goldman-Hodgkin-Katz equations and the generic action potential, which lesson 4 specialises to cardiac tissue.
- Cellular physiology — signalling: G-protein-coupled receptors and calcium as a second messenger, which underlie autonomic modulation of both rate and contractility.
Syllabus
MMed syllabus mapping
| Syllabus area | Lessons | What is covered |
|---|---|---|
| The heart as a pump | Lesson 1 | Pressure, flow and resistance; cardiac muscle and excitation-contraction coupling; the cardiac cycle, heart sounds and valve events; the pressure-volume loop and its response to loading conditions |
| The circulation | Lesson 2 | Cardiac output and venous return as a coupled system; preload, afterload, contractility and compliance; resistance, capacitance and capillary exchange; the coronary circulation; baroreceptor and chemoreceptor control |
| Applied cardiovascular physiology | Lesson 3 | Posture, the Valsalva manoeuvre, exercise and haemorrhagic shock; the cardiovascular effects of anaesthesia and positive-pressure ventilation |
| Cardiac electrical activity | Lesson 4 | Ventricular and nodal action potentials phase by phase, ionic automaticity, autonomic modulation and the effects of antiarrhythmic drugs and electrolyte disturbance |
The pathway
All 4 lessons, in order
Part I
The pump and the circuit
The heart and the circulation as one coupled system. Lesson 1 builds the pressure-volume loop; lesson 2 shows what the loop is pumping into and what returns to it.
- The heart as a pump
Pressure, flow and resistance; cardiac muscle and excitation-contraction coupling; the cardiac cycle and its heart sounds; and the pressure-volume loop, with an interactive ventricle you can load and unload.
- The circulation
Cardiac output and venous return as a coupled system, ventricular function curves, resistance and capacitance, capillary exchange, the coronary circulation, and reflex cardiovascular control.
Part II
Applied and electrical
What the system does under load, and the electrical activity that drives it. Lesson 4 is deliberately last: the action potential is easier to hold once you know what the contraction it triggers has to achieve.
- Applied and anaesthetic cardiovascular physiology
Posture, the Valsalva manoeuvre, exercise and haemorrhage, and what anaesthesia and positive-pressure ventilation do to a circulation you now understand mechanistically.
- Cardiac electrical activity
The ventricular myocyte through phases 0 to 4 and the sinoatrial node's pacemaker potential, with the ionic current behind each phase and what autonomic tone, electrolytes and antiarrhythmics do to the trace.
Objectives
The full objective wording
- The heart as a pumpCardiac cycle, pressure-flow relationships, heart sounds and valve activity, and the pressure-volume loop
- The circulationCardiac output, venous return, blood pressure and determinants of blood flow, with ventricular function curves, preload, afterload, contractility and compliance
- Applied cardiovascularCirculatory effects of posture, age, exercise, ventilation and the Valsalva manoeuvre, and the cardiovascular consequences of anaesthesia
- Cardiac electrical activityVentricular and nodal action potentials, ionic automaticity, autonomic modulation and antiarrhythmic effects