Venous collapse and the respiratory variability in systemic venous return

Area of Science:

• Cardiovascular Physiology
• Hemodynamics
• Respiratory Mechanics

Background:

• Systemic venous return is crucial for maintaining cardiac output.
• Venous collapse, a phenomenon where great veins narrow, can limit venous return.
• The impact of venous collapse on beat-to-beat respiratory variations in venous return is not well understood.

Purpose of the Study:

• To investigate the effects of venous collapse on respiratory variations in systemic venous return.
• To model venous collapse and its influence on cardiovascular dynamics.

Main Methods:

• A cardiovascular model was adapted to include venous collapse, characterized by increased hemodynamic resistance and vessel compliance.
• Respiration was simulated using varying levels of intrathoracic pressure to create collapsed, transition, and distended states of the abdominal vena cava and jugular vein.
• Venous return volume and abdominal vena caval volume were measured across respiratory cycles.

Main Results:

• Reduced venous return variability was observed in the fully collapsed zone due to increased resistance.
• Significantly increased venous return variability occurred in the transition zone between collapse and distension.
• Low venous return variability was noted in the fully distended zone.
• Increased compliance change during collapse amplified flow variability in the transition zone.

Conclusions:

• Venous collapse enhances respiratory variations in venous return within the transition zone.
• These variations in venous return can contribute to systemic arterial pressure fluctuations.
• The collapsible nature of the great veins may play a role in respiratory variations of systemic arterial pressure.