Cardiac Cycle and Blood Pressure

Cardiac Cycle and Blood Pressure

• With each contraction, the left ventricle (LV) ejects a volume of blood into the aorta, which then perfuses the arterial tree.
• The ensuing pressure wave generates the arterial pulse, but a palpable delay between ventricular contraction and peripheral pulses makes them unsuitable for timing events in the cardiac cycle.
• Blood pressure in the arterial system varies during the cardiac cycle, peaking in systole and falling to its lowest trough in diastole.
• The levels measured with the blood pressure cuff, or sphygmomanometer, are the peak (systolic) and lowest (diastolic) pressures.
• The difference between systolic and diastolic pressures is known as the pulse pressure.

Factors Affecting Blood Pressure

• Left ventricular stroke volume affects blood pressure.
• Distensibility of the aorta and the large arteries influences blood pressure.
• Peripheral vascular resistance, particularly at the arteriolar level, impacts blood pressure.
• Volume of blood in the arterial system also affects blood pressure.
• Changes in any of these four factors alter systolic pressure, diastolic pressure, or both.

Blood Pressure Fluctuations

• Blood pressure levels fluctuate significantly throughout a 24-hour period.
• Factors contributing to blood pressure fluctuations include:
  • Physical activity
  • Emotional state
  • Pain
  • Noise
  • Environmental temperature
  • Use of coffee, tobacco, and other drugs
  • Time of day

Jugular Venous Pressure (JVP) and Cardiac Function

• JVP reflects right atrial pressure, which equals central venous pressure and right ventricular end-diastolic pressure.
• JVP is best estimated from the right internal jugular vein, which has the most direct channel into the right atrium.

Jugular Venous Pulsations

• Changing pressures in the right atrium during diastole and systole produce oscillations of filling and emptying in the jugular veins.
• Atrial contraction produces an a wave in the jugular veins just before S1 and systole.
• The x descent occurs during continued atrial relaxation.
• The v wave occurs as right atrial pressure begins to rise with inflow from the vena cava during right ventricular systole.
• The y descent occurs as blood passively empties from the right atrium into the RV during early and middiastole.

Simplified Way to Remember the Three Peaks

• a wave: atrial contraction
• c wave: carotid transmission (or closure of the tricuspid valve)
• v wave: venous filling

Abnormal JVP Patterns

• Abnormally prominent cannon a waves: increased resistance to right atrial contraction, tricuspid stenosis, severe AV block, supraventricular tachycardia, junctional tachycardia, pulmonary hypertension, and pulmonic stenosis.
• Absent a waves: atrial fibrillation.
• Increased v waves: tricuspid regurgitation, atrial septal defects, and constrictive pericarditis.

Effects of Aging on Cardiovascular System

• Aging affects the location of the apical impulse, making it harder to find in older adults due to the deepening of the chest in its anteroposterior (AP) diameter.
• The pitch of heart sounds and murmurs changes with age.
• Arterial stiffness increases with age.
• Blood pressure is affected by aging.

Heart Murmurs and Age

• Almost everyone has a heart murmur at some point in their life.
• Most murmurs are normal variants and occur without other evidence of cardiovascular abnormality.
• Murmurs vary with age, and understanding their patterns helps distinguish normal from abnormal.
• Murmurs can originate in large blood vessels as well as in the heart.

Age-Related Murmurs

• The jugular venous hum is common in children and may still be heard through young adulthood.
• The cervical systolic murmur, or bruit, may be innocent in children but suspicious for atherosclerotic disease in adults.