Lung border sweep upon phrenic stimulation: dynamic fall in pleural liquid pressure.

Area of Science:

• Respiratory Physiology
• Biomechanics

Background:

• Pleural pressure dynamics are crucial for understanding lung function.
• Measuring pleural liquid pressure (Pliq) provides insights into the mechanics of breathing.

Purpose of the Study:

• To quantify pleural liquid pressure (Pliq) changes during phrenic nerve stimulation (PS) in dogs.
• To investigate the viscous losses of pleural liquid during different breathing conditions.

Main Methods:

• Pleural pressure was measured using a capsule in the 9th or 10th intercostal space (ICS) of dogs.
• Measurements were taken during tetanic stimulation of phrenic nerves (PS) and spontaneous breathing (SB).
• The speed and displacement of the lung border were analyzed to estimate dynamic pressure falls.

Main Results:

• A marked negative spike in Pliq occurred when the lung border passed under the capsule.
• During PS, the Pliq spike was greater and longer in the 10th ICS compared to the 9th ICS.
• Dynamic fall in Pliq was significantly higher during PS (12-16 cm H2O) than during SB (4 cm H2O), suggesting substantial viscous losses.

Conclusions:

• Dynamic fall in Pliq during breathing is primarily due to viscous losses in the pleural liquid.
• These viscous losses increase with pleural liquid thinning, lung border speed, and displacement.
• Estimated viscous loss at normal lung volumes is approximately 2 cm H2O per cm displacement at 1 cm/sec speed.