Applied Cardiovascular Physiology Lecture Notes

Introduction

• Presenter: Arnie on Counter10 Podcast
• Topic: Applied Cardiovascular Physiology
• Series: Second last topic in cardiovascular series; final topic is measurement.
• Structure: Divided into two parts; today covers learning objectives, second part will cover SAQs.
• Upcoming: Live practice Viber demonstration and special guest episodes.

Learning Objectives

Pneumoperitoneum

• Definition: Gas (CO2) insufflation into the peritoneal cavity during laparoscopic surgery.
• Physiological Effects
  • Increase in intra-abdominal pressure causes:
    • Cardiovascular: Auto-transfusion of blood, transient increase in venous return and cardiac output, followed by decreased venous return with increased sympathetic activity to maintain cardiac output.
    • Respiratory: Decrease in FRC, respiratory compliance, and VQ mismatching leading to hypoxemia and hypercarbia.
    • GI: Predisposition to gastric regurgitation; mechanical compression affecting blood flow and risking ischemia.
    • Renal: Decrease in renal function, GFR, and urine output due to increased sympathetic activity.
    • Neurological: Slight increase in ICP due to decreased cerebral venous drainage.
  • CO2 Absorption: Leads to increased sympathetic activity, tachycardia, vasoconstriction, and biochemical changes.

Patient Positions and Anesthesia

• Positions: Supine, Trendelenburg, Reverse Trendelenburg, Lateral, Lithotomy, Prone.
  • Physiological changes affected by hydrostatic pressure and gravity.
  • Trendelenburg: Initial increase in cardiac output due to auto-transfusion; effects normalize after 10-15 minutes.
  • Reverse Trendelenburg: Decrease in blood pressure and cerebral perfusion pressure.
• Impact of Anesthesia
  • General Anesthetic: Blunts baroreceptor reflex, decreases cardiac output, increases vasodilation.
  • Neuroaxial Anesthetic: Depends on level of blockade; can significantly affect cardiovascular responses.

Cardiovascular Response to Various Conditions

• Exercise
  • Increase in heart rate more than stroke volume.
  • Key terms: VO2 max (aerobic capacity), anaerobic threshold (when O2 supply can't meet demand).
  • Isotonic vs Isometric Exercise: Different effects on systemic vascular resistance and afterload.
• Valsalva Maneuver
  • Four phases involving changes in blood pressure and heart rate due to altered intrathoracic pressure.
  • Clinical Utility: Assesses autonomic function, terminates SVTs, checks for surgical bleeding.
• Positive Pressure Ventilation and PEEP
  • PPV: Alters preload and afterload; effects on right and left heart differ between inspiration and expiration.
  • PEEP: Prolonged positive pressure can affect cardiac output; used in conditions like APO.

Cardiovascular Changes with Aging

• Cardiac Changes
  • Conduction: Decreased pacemaker cells, increased arrhythmia risk.
  • Structural: Increased collagen, myocyte size; decreased compliance.
  • Functional: Greater reliance on atrial kick; less change in heart rate.
• Vascular Changes
  • Decreased elasticity and compliance; increased systemic vascular resistance.
• Autonomic Changes
  • Decreased beta-receptor responsiveness and baroreceptor sensitivity.

Cardiovascular Changes with Obesity

• Cardiac Changes
  • Conduction and Structural: Fatty infiltration, left ventricular hypertrophy.
  • Functional: Increased cardiac output mainly due to increased stroke volume.
• Vascular Changes
  • Hypervolemia, polycythemia, increased atherosclerosis.
• Autonomic Changes: No major changes.
• Pathogenesis: Adipokines like Leptin, Angiotensinogen affect vascular tone and cardiac structure.

Shock

• Definition: Failure of oxygen delivery due to inadequate perfusion, oxygen saturation, or increased demand.
• Types: Hypovolemic, Cardiogenic, Obstructive, Distributive.
• Stages: Initial, Compensatory, Progressive, Irreversible.
• Compensatory Mechanisms: Baroreceptor reflex, humoral response, blood redistribution.
• Differentiation of Shock Types
  • Hypovolemic: Decreased preload, cool peripheries.
  • Cardiogenic: High preload, cool peripheries.
  • Obstructive: Low preload, cool peripheries.
  • Distributive: Warm peripheries, low SVR.