Pulsatile and nonpulsatile pressure-flow relationships in zone 3 excised rabbit lungs

Area of Science:

• Physiology
• Cardiovascular Research
• Pulmonary Circulation

Background:

• Pulmonary arterial pressure (Ppa) is a critical determinant of cardiovascular function.
• Understanding the impact of flow dynamics, specifically pulsatile versus nonpulsatile flow, on Ppa is essential for comprehending pulmonary circulation.
• Previous research has not fully elucidated these relationships across a wide range of physiological parameters.

Purpose of the Study:

• To compare the effects of pulsatile versus nonpulsatile flow on pulmonary arterial pressure (Ppa)-Q relationships in zone 3 of the lungs.
• To investigate these effects across a wide range of pulse rates, stroke volumes (SV), and flow rates (Q).

Main Methods:

• Utilized excised rabbit left lungs perfused with a specialized solution.
• Generated pulsatile flow using a diaphragm pump and nonpulsatile flow via an arterial reservoir.
• Systematically varied stroke volume (0.5, 1, 2 ml) and flow rate (100-600 ml/min) while measuring Ppa and left atrial pressure.

Main Results:

• No significant differences in Ppa-Q curves were observed between pulsatile and nonpulsatile flow at the lowest stroke volume.
• At higher stroke volumes, pulsatile flow resulted in a greater Ppa compared to nonpulsatile flow for Q > 100 ml/min.
• The slopes of the Ppa-Q curves were steeper under pulsatile flow conditions at the two larger stroke volumes.

Conclusions:

• Pulsatile flow characteristics, particularly at higher stroke volumes, lead to elevated pulmonary arterial pressure compared to nonpulsatile flow.
• Increased turbulence and less ideal velocity profiles, driven by inertial forces, explain the observed Ppa differences.
• These findings have implications for understanding pulmonary hemodynamics under varying physiological conditions.