Extracardiac pressure changes do not alter contractile function of the isolated left ventricle

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics

Background:

• Understanding the factors influencing left ventricular (LV) contractile function is crucial for diagnosing and treating heart conditions.
• Extracardiac pressure, the pressure surrounding the heart, is a potential but understudied factor affecting cardiac performance.

Purpose of the Study:

• To investigate the impact of varying extracardiac pressures on the contractile function of the left ventricle.
• To determine if extracardiac pressure influences key parameters of left ventricular pump function.

Main Methods:

• Utilized isolated, perfused canine hearts within a sealed chamber to control extracardiac pressure.
• Analyzed left ventricular pressure-volume relationships across a range of extracardiac pressures (-60 to 60 mm Hg).
• Assessed parameters such as end-systolic elastance (Ees) and volume axis intercept (Vo) to evaluate pump function.

Main Results:

• No significant alterations in Ees or Vo were observed with changes in extracardiac pressure.
• Developed left ventricular pressure remained constant during both isovolumic and ejecting contractions across all tested extracardiac pressures.
• Pressure-volume loops were consistent regardless of the applied extracardiac pressure when afterload and preload were adjusted accordingly.

Conclusions:

• Transmural pressure, not absolute extracardiac pressure, is the dominant loading factor influencing left ventricular contraction.
• Myocardial contractile function is independent of the absolute level of extracardiac pressure.