Mechanical heart-lung interaction with positive end-expiratory pressure

Area of Science:

• Cardiovascular Physiology
• Respiratory Mechanics

Background:

• Previous studies suggested positive end-expiratory pressure (PEEP) impairs left ventricular (LV) function.
• These effects were attributed to neural, humoral, or mechanical factors, often measured during expiration.

Purpose of the Study:

• To investigate the mechanical effects of PEEP on cardiac function during both inspiration and expiration.
• To differentiate mechanical effects from neural and humoral influences.

Main Methods:

• Open-chest dogs with arrested circulation and cardioplegic perfusion.
• Ventricular pressure measurement using balloons.
• Controlled ventilation, varying PEEP, tidal volume, chest wall compliance, and heart volume.
• Atrial venting to prevent blood volume shifts.

Main Results:

• Isovolumic ventricular pressures increased significantly with PEEP (P < 0.001).
• Heart-lung interactions were significantly greater during inspiration with PEEP (P < 0.001).
• PEEP's effects were modulated by heart volume and respiratory system compliance (P < 0.01).

Conclusions:

• PEEP exerts a mechanical compressive force on the heart via lung expansion.
• This mechanical compression may explain diminished LV function and diastolic compliance.
• Increased inspiratory compressive forces during PEEP may significantly impact hemodynamics.