Positive pleural pressure decreases coronary perfusion

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics
• Myocardial Perfusion

Background:

• Positive pressure surrounding the heart (PSH) may affect left ventricular (LV) afterload and coronary perfusion.
• The direct impact of elevated PSH on coronary blood flow and myocardial oxygen supply is not fully understood.

Purpose of the Study:

• To investigate the effects of positive pressure surrounding the heart (PSH) on coronary perfusion in an isolated heart-lung preparation.
• To determine if elevated PSH mechanically impedes coronary blood flow and induces myocardial ischemia.

Main Methods:

• Isolated canine heart-lung preparation with controlled venous return, arterial pressure, and lung volume.
• Progressively increased PSH in 10-mmHg increments (0–60 mmHg) while monitoring left atrial transmural pressure and circumflex coronary artery flow.
• Administered adenosine to assess maximal coronary vasodilation response to PSH.
• Measured aortic-coronary sinus lactate difference to assess myocardial lactate extraction.

Main Results:

• Increased PSH significantly reduced left atrial transmural pressure, initially suggesting decreased LV afterload.
• At PSH levels >30 mmHg, left atrial transmural pressure increased, indicating impaired cardiac function.
• Coronary artery flow significantly decreased with increasing PSH, an effect amplified during maximal vasodilation.
• Elevated PSH to 60 mmHg for 90 seconds resulted in a significant decrease in the aortic-coronary sinus lactate difference, indicating myocardial ischemia.

Conclusions:

• Positive pressure surrounding the heart directly impedes coronary blood flow.
• Elevated PSH can lead to myocardial ischemia and potentially ischemic cardiac dysfunction.
• These findings are particularly relevant for patients with hypotension or coronary artery disease.