Understanding the Heart - PE Paper 1

The Heart and Blood Pressure Basics

Blood pressure measures how hard your heart pushes blood around your body. Think of it like water pressure in your pipes - the harder the pump works, the higher the pressure.

During exercise, your blood pressure increases because your muscles need more oxygen and nutrients. Your heart has to work harder to deliver what your body demands.

The cardiac cycle has two main phases: diastole (when your heart fills with blood) and systole (when it squeezes to pump blood out). Pressure changes control when different valves open and close, making sure blood flows in the right direction.

Quick Tip: Normal resting blood pressure is around 120/80 - the first number is systolic pressure, the second is diastolic.

Cardiac Output: The Heart's Performance Measure

Cardiac output (Q) tells you how much blood your heart pumps each minute. It's calculated using a simple formula: Q = HR × SV (heart rate times stroke volume).

Heart rate (HR) is your heartbeats per minute - typically 70-80 bpm at rest. Stroke volume (SV) is how much blood gets pumped out with each heartbeat, usually around 70ml.

When you exercise, your cardiac output increases dramatically. Your heart rate shoots up before you even start moving thanks to adrenaline - your body's way of getting ready for action.

The graph pattern is predictable: HR rises quickly when exercise starts, plateaus during steady activity, then slowly returns to normal during recovery. Your maximum heart rate is roughly 220 minus your age.

Remember: Adrenaline kicks in before exercise even begins, preparing your cardiovascular system for the work ahead.

How Exercise Affects Heart Function

Stroke volume increases during moderate exercise because more blood flows back to your heart, stretching the chamber walls. This stretching allows more blood to be pumped out with each beat.

However, at very high intensities, stroke volume actually decreases. When your heart rate gets extremely high, there isn't enough time between beats for the chambers to fill completely.

The beauty of cardiac output is that even when stroke volume drops, the massive increase in heart rate more than compensates. This ensures working muscles continue getting the oxygen they need.

Without this anticipatory response from adrenaline, there'd be a dangerous lag time where your muscles wouldn't get enough blood flow. Your cardiovascular system is essentially future-proofing itself for the exercise demands ahead.

Key Point: Higher cardiac output means more oxygen delivery and faster CO₂ removal, which delays fatigue and keeps you performing longer.