PY5.1-16 | Cardiovascular Physiology — Summary & Reflection

REFLECT

Apply what you've learned to your own body and your future patients:

1. Check your pulse — feel your radial pulse for 15 seconds and multiply by 4. Is your resting HR between 60-100? Your SA node is setting this rate, and your vagus nerve is keeping it in check.

1. Check your BP — if you have access to a sphygmomanometer, measure your BP lying down, then immediately after standing. Is there a drop of >20 mmHg systolic? That's orthostatic hypotension.

1. Listen to heart sounds — with a stethoscope on a colleague's chest at the apex (5th intercostal space, mid-clavicular line), listen for S1 and S2. Which is louder at the apex (S1) and which at the base (S2)?

1. The Breathless Farmer — you'll discuss a PBL case of heart failure in this module. Before you do, think about: if a farmer comes to your PHC with ankle swelling and breathlessness, what questions would you ask and what would you look for on examination?

1. Connect the dots — in Anatomy, you studied the heart's chambers and valves (AN22). Now match each anatomical structure to its physiological function: Why are the ventricular walls thicker than the atrial walls? Why is the left ventricle thicker than the right? Why does the aortic valve have three cusps?

KEY TAKEAWAYS

Key takeaways — your study checklist:

1. Cardiac muscle has 5 unique properties: automaticity, rhythmicity, conductivity, excitability, contractility. The long refractory period (Phase 2 plateau) prevents tetanus.
2. Cardiac cycle has 7 phases. S1 = AV valve closure (start of systole). S2 = semilunar valve closure (end of systole). Both isovolumetric phases have ALL valves closed.
3. Conduction system: SA node -> AV node (0.1s delay) -> Bundle of His -> bundle branches -> Purkinje fibres. ECG: P = atrial depolarization, QRS = ventricular depolarization, T = ventricular repolarization.
4. ECG normals: PR 0.12-0.20 s, QRS < 0.12 s, QT < 0.44 s. ST elevation = MI.
5. Cardiac output = HR x SV (~5 L/min). Regulated by preload (Frank-Starling), afterload, contractility, and HR.
6. BP = CO x TPR. MAP = DBP + 1/3(PP). MAP < 60 = inadequate perfusion.
7. Baroreceptor reflex is the primary short-term BP regulator (carotid sinus CN IX, aortic arch CN X). RAAS is the primary long-term regulator.
8. JVP waves: a (atrial contraction), c (tricuspid bulge), v (atrial filling). x and y descents.
9. Shock = inadequate tissue perfusion. Four types: hypovolaemic, cardiogenic, distributive, obstructive. Compensatory mechanisms may mask early shock.
10. Heart failure = pump failure. Compensatory mechanisms (Frank-Starling, sympathetic, RAAS) are initially helpful but ultimately worsen the disease. Treatment targets these mechanisms.