BSCI202 LAB PRACTICAL 2

Human Cardiovascular Physiology

• cardiac cycle: the cycle of contraction and relaxation of both atria and ventricles

• systole: contraction of the atria (atrial systole) or the ventricles (ventricular systole)

  • blood is being pumped out of a chamber during systole

• diastole: relaxation of the atria (atrial diastole) or the ventricle (ventricular diastole)

  • Blood is filling a chamber during diastole

Phases of Cardiac Cycle

Atrial diastole

• blood delivered into atria via veins

• 80% of blood flows passively into the ventricles (also in diastole)

Atrial systole

• Last 20% of blood left in atria delivered to the ventricles by atrial systole

Ventricular systole

• Begins shortly after atrial systole

• Ventricular contraction begins, pressure rises, closing the AV valves

• Ejection phase – as pressure begins to rise in the ventricles, blood is pumped into the great arteries

Ventricular diastole

• Cycle repeats

Dicrotic notch → where SL valve closes and pressure of ventricles continues to fall back down

Cardiac Cycle through Heart

Auscultation of Heart Sounds

A stethoscope is used to auscultate heart sounds

• 1st heart sound: lub – closure of the AV valves

• 2nd heart sound: dub – closure of the SL valves

• Heart murmur: an abnormal heart sound

  • Indicates a defect in one of the valves

Pulse

• Pulse: surges of pressure in arteries (as heart pushes blood out during the cardiac cycle)

  • Equivalent to the heart rate

• Heart rate: number of beats per minute (bpm)

  • Normal range for resting heart rate: 60-100 bpm

  • Average resting heart rate: 70-76 bpm

• Average heart beat lasts 0.8 seconds

• How to calculate heart rate from heart beat length

  • 60 seconds / Heart Beat Duration = HR

  • Average heart rate: 60 seconds / 0.8 seconds = 75 bpm

Blood Pressure

• blood pressure: pressure exerted against walls of the arteries

• typically, blood pressure is reported as combination of two values: systolic and diastolic blood pressure

• systolic blood pressure (SBP): pressure exerted against the walls of the arteries during ventricular systole

• diastolic blood pressure (DBP): pressure exerted against the arterial wall during ventricular diastole

• measured using a sphygmomanometer - an inflatable cuff connected to a pressure gauge

  • Units: measured in mmHg

  • Expressed as SBP over DBP

  • Normal Blood Pressure: less than 120/80 mmHg

Measuring Blood Pressure

How to measure systolic and diastolic blood pressure

1. Place blood pressure cuff on upper left arm

2. Place stethoscope on the brachial artery

3. Inflate pressure in cuff until circulation is cut off

   • Do not inflate higher than 160mmHg

4. Use valve to slowly release pressure by̴ 2mmHg/second

5. The first sound heard in the stethoscope (crackling or knocking sound) = pressure reading at this time is the systolic pressure

   • This is called the sounds of Korotkoff

6. When that sound disappears = pressure reading at this time is the diastolic pressure

Calculating Overall Blood Pressure

• Total peripheral resistance (TPR) – the amount of force exerted on circulating blood by the vasculature

• Stroke volume (SV) – the amount of blood pumped by the left ventricle during one contraction

  • Average SV is 70ml

• Cardiac output (CO) – the amount of blood pumped by the heart in one minute

  • 𝐶𝑂 = 𝑆𝑉×𝐻𝑅

  • 𝐵𝑃 = 𝐶𝑂×𝑇𝑃𝑅

    • calculated value is different than the SBP/DBP values that would normally be measured by a medical professional

Calculating Other Pressures

• Pulse pressure is the difference between systolic and diastolic blood pressure

  • 𝑃𝑢𝑙𝑠𝑒 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝑆𝐵𝑃 − 𝐷𝐵𝑃

• Mean arterial pressure (MAP) is the average pressure in a patient’s arteries during one cardiac cycle

  • Represents the force generated by the heart during contraction

  • Considered a better indicator of perfusion to vital organs than SBP

  • 𝑀𝐴𝑃 = 𝐷𝐵𝑃 + (pulse pressure/3)

    • 2/3 of time spent in diastolic state, while only 1/3 time spent in systolic state during cardiac cycle