3.5.8 Interpreting Data on the Cardiovascular System

Key Cardiovascular Parameters:

1. Heart Rate ($HR$):

• Measured in beats per minute ($bpm$).
• Reflects the number of times the heart contracts in one minute.
• Increases during exercise or stress to meet the oxygen demands of tissues.

2. Stroke Volume ($SV$):

• The amount of blood ejected by the heart in one contraction.
• Measured in millilitres ($mL$).
• Stroke volume typically increases with exercise or improved fitness.

3. Cardiac Output ($CO$):

• The total volume of blood pumped by the heart per minute.

• Equation: $\text{Cardiac Output (CO)} = \text{Heart Rate (HR)} \times \text{Stroke Volume (SV)}$

• Measured in litres per minute (L/min).

4. Blood Pressure ($BP$):

• Force exerted by circulating blood on the walls of arteries.
• Recorded as systolic pressure (pressure during heart contraction) over diastolic pressure (pressure during relaxation).
• Example: 120/80 mmHg (normal adult blood pressure).

Key Trends and Patterns:

1. Resting vs. Active State:

• At Rest:
• Lower heart rate and cardiac output.
• Stable blood pressure.
• During Exercise:
• Increased heart rate and stroke volume, leading to higher cardiac output.
• Systolic blood pressure increases to supply more oxygen and nutrients.

2. Impact of Fitness Levels:

• Trained individuals:
• Lower resting heart rate due to increased stroke volume.
• Faster recovery to resting heart rate after exercise.
• Untrained individuals:
• Higher resting heart rate and slower recovery after exercise.

3. Disease States:

• Hypertension (high blood pressure):
• Elevated systolic or diastolic pressure.
• Increases risk of heart disease and stroke.
• Atherosclerosis:
• Narrowing of arteries reduces blood flow and increases blood pressure.

Data Interpretation Skills:

1. Graphs and Tables:

• Recognise patterns in heart rate, blood pressure, or cardiac output during rest, exercise, and recovery.
• Identify anomalies, such as unusually high blood pressure or slow heart rate recovery.

2. Relationships Between Variables:

• Link changes in heart rate or blood pressure to physiological processes (e.g., increased oxygen demand during exercise).
• Use cardiac output equations to calculate missing values.

3. Exam Tip:

• Pay attention to units (e.g., bpm for heart rate, mmHg for blood pressure).
• Ensure calculations are accurate and include the correct units.

Example Question:

Question: A person's heart rate increases from 70 bpm at rest to 140 bpm during exercise. Their stroke volume also increases from 70 mL to 100 mL. Calculate their cardiac output during exercise.

Answer:

$$\text{CO} = \text{HR} \times \text{SV} = 140 \, \text{bpm} \times 100 \, \text{mL} = 14,000 \, \text{mL/min} = :success[14 \, \text{L/min}].$$

Key Terms:

• Heart Rate ($HR$): Number of heartbeats per minute.
• Stroke Volume ($SV$): Volume of blood pumped per contraction.
• Cardiac Output ($CO$): Total volume of blood pumped per minute.
• Blood Pressure ($BP$): Force of blood against artery walls.