Mechanical determinants of transient changes in stroke volume

Area of Science:

• Cardiovascular Physiology
• Cardiac Mechanics
• Hemodynamics

Background:

• Understanding beat-to-beat regulation of stroke volume (SV) is crucial for defining left ventricular (LV) function.
• Sudden changes in hydraulic loading impedance significantly impact cardiac output and ventricular performance.

Purpose of the Study:

• To investigate the transient response of the LV to abrupt alterations in hydraulic loading impedance.
• To identify the key determinants of stroke volume regulation on a beat-to-beat basis.

Main Methods:

• Utilized eight canine isolated heart-lung preparations with controlled LV loading impedance.
• Induced sudden increases in hydraulic resistance at a specific diastolic interval.
• Analyzed transient responses in SV, end-diastolic pressure (EDP), and end-systolic pressure (ESP) using six predictive models.

Main Results:

• Models incorporating preceding beat end-systolic pressure (ESP) and end-diastolic pressure (EDP), along with the current beat's ESP and EDP, were superior predictors of SV.
• The relative influence on SV was ranked: 1) current beat ESP, 2) preceding beat ESP, 3) current beat EDP, 4) preceding beat SV.
• Adding nonlinearities or coronary perfusion pressure effects did not enhance predictive accuracy.

Conclusions:

• Beat-to-beat stroke volume regulation is significantly influenced by the mechanical state of the left ventricle in the preceding cardiac cycle.
• End-systolic pressure of both the ejecting and preceding beats are primary determinants of stroke volume.