Effects of increased afterload on left ventricular function in closed-chest dogs

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics
• Hemodynamics

Background:

• Left ventricular (LV) mechanical response to increased afterload may differ in intact circulation versus isolated LV.
• Secondary hemodynamic changes are difficult to isolate in intact systems.

Purpose of the Study:

• To evaluate the integrated response of the LV in closed-chest dogs to sustained increases in afterload.
• To quantify pressure-volume relationships and energy transfer efficiency under altered afterload.

Main Methods:

• Utilized chronically instrumented closed-chest dogs under autonomic blockade and anesthesia.
• Measured LV pressure and dimensions using manometers and orthogonal gauges.
• Analyzed end-systolic pressure-volume (PES-VES) and stroke work-end-diastolic volume (SW-EDV) relations.
• Quantified pressure-volume area (PVA) and its relation to end-diastolic volume (EDV).

Main Results:

• Balloon inflation in the aorta significantly increased LV end-systolic pressure (PES) and end-diastolic volume (LVEDV).
• The slope of the PES-VES relation was unchanged, but V100 (volume intercept) decreased.
• The pressure-volume area (PVA)-end-diastolic volume (EDV) relation slope increased, indicating greater PVA.
• Energy transfer efficiency (TransPVA) significantly decreased from 52.5% to 42.6%.

Conclusions:

• Sustained increases in afterload in an intact circulatory system lead to significant alterations in LV mechanics.
• Despite increased PVA, the efficiency of converting this potential energy to stroke work is reduced.
• These findings underscore the complex integrated response of the LV within the intact circulation.