Lecture Notes: Systemic Blood Pressure

Introduction to Blood Pressure

• Focus on systemic blood pressure (blood flow from heart to tissues).
• Blood flow generated by heart's pumping action.
• Pressure occurs when blood flow is opposed by resistance.
• Higher resistance = higher pressure.

Systemic Pressure Overview

• Highest pressure in the aorta; declines as it travels through the body.
• Steepest pressure drop in arterioles due to greatest resistance.
• Highest pressures in arteries, lowest in veins.

Arterial Blood Pressure Influences

• Elasticity of Arteries: Close to the heart, elasticity affects pressure.
• Blood Volume: Amount of blood forced into arteries.
  • Related to stroke volume (blood pumped from ventricles).

Blood Pressure Phases

• Pulsatile Nature: Blood pressure fluctuates with heartbeat.
  • Systolic Pressure: During ventricular contraction (average 120 mmHg).
  • Diastolic Pressure: During ventricular relaxation (average 70-80 mmHg).
• Pulse Pressure: Difference between systolic and diastolic pressures.
  • Example: 120 over 80 results in a pulse pressure of 40 mmHg.

Pulse and Blood Pressure Calculation

• Pulse: Throbbing due to pulse pressure difference.
• Mean Arterial Pressure (MAP): Drives blood into tissues.
  • Calculation: Diastolic pressure + 1/3 of pulse pressure.
  • Example: For 120/80 BP, MAP = 80 + (1/3 * 40) = 93 mmHg.*

Vital Signs and Pulse Points

• Vital Signs: Pulse, blood pressure, respiratory rate, body temperature.
• Pulse Points: Areas to feel pulse, e.g., radial pulse at the wrist.
• Pressure Points: Used to stop bleeding by applying pressure.

Measuring Blood Pressure

• Indirectly measured using sphygmomanometer.
• Systolic pressure: First sound heard; diastolic: when sounds disappear.
• Capillary blood pressure: Lower than arterial, ranges from 35 to 17 mmHg.

Venous Blood Pressure

• Low and steady due to distance from the heart.
• Gradient about 15 mmHg.

Venous Return Mechanisms

• Muscular Pump: Skeletal muscle contractions push blood towards heart.
  • Veins have valves to prevent backflow.
• Respiratory Pump: Pressure changes during breathing assist blood flow.
• Sympathetic Venoconstriction: Smooth muscles constrict veins, aiding blood return.

Summary

• Venous return increases stroke volume and cardiac output.
• Understanding systemic blood pressure involves mechanical and physiological components like resistance, elasticity, and pressure changes.