Chapter 33A: Human Cardiovascular Physiology: Blood Pressure and Pulse Determinations

The cardiac cycle includes all the events related to the flow of blood through the heart during one complete heartbeat.

Heart Valves

During the cardiac cycle, heart valves open and close in response to differences in blood pressure on their two sides.

The Heart Valves:

  • Pulmonary semilunar valve
  • Aortic Semilunar Valve
  • Left AV valve or Bicuspid valve or Mitral valve
  • Right AV valve or Tricuspid valve
2 mail phases:
  • SystoleContraction
  • Diastole - Relaxation

Overview of Cardiac Cycle

Phases of the Cardiac Cyce

  • 1 – Ventricular filling and atrial contraction
  • 2a – Isovolumetric contraction phase
  • 2b – Ventricular ejection phase
  • 3 – Isovolumetric relaxation and ventricular filling
      1. Ventricular Filling - Occurs during mid to late diastole.
      • Ventricular Filling: Passive: occurs during mid to late diastole, when the heart chambers are relaxed. Blood flows passively into the atria, through open AV valves, and into the ventricles, where the pressure is lower.
      • Ventricular Filling: Atrial Contraction: Atria contract, forcing the remaining blood into the ventricles. Blood flows through both sides of the heart at the same time.
      2. Ventricular Systole - Includes isovolumetric contraction and ventricular ejection.
      • Isovolumetric contraction: Ventricles contract and intraventricular pressure rises, closing the AV valves. Briefly, ventricles are completely closed chambers.
      • Ventricular ejection: Rising ventricular pressure forces semilunar valves open. Blood is ejected from the heart into the aorta and pulmonary trunk
      • Dicrotic notch represents the interruption of smooth flow due to the brief backflow of blood that closes the aortic semilunar valve when the ventricles relax.
      3. Isovolumetric Relaxation - Occurs during early diastole.
      • Isovolumetric Relaxation: Ventricles relax and ventricular pressure drops. Blood backflows, closing semilunar valves. Ventricles are totally closed off again.
      • Atrial Filling: Meanwhile, the atria have been filling with blood. When atrial pressure exceeds ventricular pressure, AV valves open and ventricular filling, phase 1 begins again.

Heart Sounds (lub-dup)

  • S1 - 1st sound (lub) – closing of the AV valves. Louder and longer than the second sound. Beginning of ventricular systole
  • S2 - 2nd sound (dup) – closing of the semilunar valves. Short, sharp sound. End of ventricular systole.
    • Murmur - an abnormal sound of the heart; sometimes a sign of abnormal function of the heart valves

The Pulse

  • Pulse – alternating surges in arterial blood pressure due to ventricular systole and diastole. Normally, the pulse rate equals the heart rate and averages 70-76 beats per minute while at rest. Normally, the pulse rate equals the heart rate and averages 70-76 beats per minute while at rest, however this number will wary based on age and the level physical fitness.
    • Pulse pressure – is the difference between the systolic and diastolic pressures. Indicates the amount of blood forced out of the heart during systole.
    • Pulse Pressure = Systolic Pressure - Diastolic Pressure
    • Pulse deficit – is the difference between the apical and radial pulse often associated with atrial fibrillation. Your pulse is taken by touching one of several "pulse points" located on your body. These spots are areas where the arteries are near to the surface of the skin that the movement of blood through them can be felt. You can actually feel arteries expand and contract, since the artery keeps pace with the heart.
      • Common carotid pulse – anterior neck.
      • Facial pulse – anterior to angle of mandible.
      • Superficial temporal pulse – anterior to tragus of ear.
      • Axillary pulse – within axilla.
      • Apical pulse – not taken over an artery. Instead, it is taken over the the apex of the heart itself.
      • Brachial pulse – medial arm, between biceps and triceps.
      • Radial pulse – anterior, lateral wrist.
      • Femoral pulse – inguinal region.
      • Popliteal pulse – posterior knee.
      • Posterior tibial pulse – ankle.
      • Dorsalis pedis pulse – dorsal surface (top) of foot.

Blood Pressure

Blood pressure is an important indicator of cardiovascular health. It is influenced by the contractile activities of the heart and conditions and activities of the blood vessels.

Blood Pressure Defined:

  • The pumping action of the heart generates blood flow.
  • Blood Pressure is the force that blood exerts against blood vessel walls.
  • Blood pressure results when that flow is met by resistance from vessel walls.
  • Blood pressure is expressed in millimeters of mercury (mm Hg). For example a blood pressure of 120 mm Hg is equivalent to a pressure exerted by a column of mercury 120 mm high.
  • The blood pressure is determined by the rate of blood flow produced by the heart (cardiac output – the amount of blood pumped by each ventricle in 1 minute), and the resistance of the blood vessels to blood flow (Peripheral resistance).
    • Laminar Flow: Blood flows faster in the center of a vessel than near the sides, because the blood near the sides is hitting the walls of the vessels. This is called laminar flow and it is due to the friction (resistance) between the blood and the vessel walls. The greater the resistance, the slower the blood flow.
    • Systolic Pressure is the maximum pressure exerted by the blood against the artery walls. It is the result of ventricular systole or contraction. It is normally about 120 mm Hg.
    • Diastolic Pressure is the lowest pressure in the artery. It's a result of ventricular diastole (relaxation) and is usually around 80 mm Hg.
  • Mean Arterial Pressure (MAP)
    • A term used in medicine to describe a notional average blood pressure in an individual.
    • It is defined as the average arterial pressure during a single cardiac cycle.
    • Mean Arterial Pressure (MAP) = Diastolic Pressure + 1/3 Pulse Pressure
    • MAP is closer to the diastolic pressure than systolic pressure because the heart stays longer in diastole.

How blood pressure is measured

  • Korotkoff Sounds are the sounds heard through the stethoscope (acoustic medical device) over an artery when blood pressure is determined by the auscultatory method with sphygmomanometer (blood pressure measuring device)

    • As the pressure cuff deflates, first clear sound indicates systolic pressure; the last clear sound indicates diastolic pressure. When sounds cease to be heard the cuff has deflated past the diastolic pressure.
    • It is generally accepted that there are five phases of Korotkoff sounds. Each phase is characterised by the volume and quality of sound heard. The figure below illustrates these phases.
    • In this example, the systolic and diastolic pressures are 120mmHg and 80mmHg respectively.

      • Korotkoff I - is a sharp thud (systolic point) results by the closing shut of the artery walls that.
      • Korotkoff II - is a loud blowing sound caused by the swirling currents in the blood as the flow through the artery increases.
      • Korotkoff III - is a soft thud due to the increased flow of blood pounding against the artery walls.
      • Korotkoff - IV - is a soft blowing sound (diastolic point). The blood flow is becoming less turbulent.
      • Korotkoff V - is silence. The blood flow has returned to normal and is now laminar. The pressure cuff is deflated entirely and removed.

WHO Blood Pressure Classifications

  • Standards for assessment of high or low blood pressure have been established by the World Health Organization (WHO) as shown on the following chart:

Effects of stress on blood pressure and heart rate

  • Stress like exercise and poor posture, as well as emotional state and feeling pain has profound effects on blood pressure and pulse.
  • The endurance to physical stress is measured in form of the index of physical fitness which represents your overall cardiovascular health.
  • Formula: (exercise duration in seconds X 100)/ (2 X sum of the three pulse counts in recovery)
  • This formula can be put to a test by a simple step test.
  • Cardiovascular reactivity can be assessed by noxious sensory stimulus – thermal or pain stimulus
  • Cold presser test – subjects hand is immersed in cold water and index of response is recorded (changes is systolic and diastolic pressures)
  • Subjects are classified as hyporeactors (drop or rise range of 0-22 Hg) and hyperreactors (rise of 23 Hg or more)