Heart Parameters

week 1

Cardiac Output (CO)

The volume of blood the heart pumps out in one minute, measured in litres (L) per minute (min)

Stroke Volume (SV)

The volume of blood ejected by the left ventricle per contraction (beat).
Expressed in millilitres (mLs)

Cardiac Output Formula

CO = HR (heart rate) x SV (stroke volume)

Heart Rate

Number of heart beats per minute (BPM)

Factors Affecting Heart Rate

➢ Sympathetic or Parasympathetic Stimulation
➢ Circulating Blood Volume
➢ Fitness Level, Body Size, Age
➢ Temperature
➢ Body Position

Chronotropy

The ability to change the rate or timing of heart rate.

3 main components of stroke volume

Preload

Afterload

Contractillity

Preload

The maximum stretching of cardiac muscle cells (myocytes) at the end of diastole (ventricular filling) just before contraction

Factors Affecting Preload

➢ Circulating Blood Volume
➢ Venous Tone
➢ Ventricular Compliance
➢ Atrial Contraction
➢ Heart Rate

Afterload

The force or resistance that the heart's ventricles must overcome to eject blood into the arteries during contraction.

Factors Affecting Afterload

➢ Vascular Resistance
➢ Ventricular Pressure
➢ Valve Stenosis

Consequences of High Afterload

➢ Reduced Stroke Volume
➢ Increased Workload
➢ Ventricular Hypertrophy

Contractility

The ability of cardiac muscle tissue to shorten forcefully and generate tension or work

Factors Affecting Contractility

➢ Sympathetic or Parasympathetic Stimulation
➢ Heart Rate
➢ Changes in pH, Electrolyte Levels, Disease States

Inotropy

The force of cardiac contractility

• Positive inotropy → Increases myocardial contractility

• Negative inotropy → Decreases myocardial contractility