Changes of left ventricular diastolic function in exercising dogs without and with ischemia

Area of Science:

• Cardiology
• Physiology
• Biomedical Engineering

Background:

• Left ventricular (LV) diastolic function is crucial for cardiac health.
• Understanding how exercise and ischemia affect diastolic function is important for diagnosing and managing heart conditions.

Purpose of the Study:

• To examine left ventricular (LV) diastolic function during exercise, both with and without regional ischemia.
• To assess the impact of ischemia on LV filling dynamics, relaxation, and pressure-volume relationships.

Main Methods:

• Eight conscious dogs were instrumented with ultrasonic devices to measure LV wall thickness and volume.
• Treadmill exercise was performed, with ischemia induced using a hydraulic occluder.
• LV filling was assessed using peak filling rate (PFR), mean filling rates (mFR1, mFR2), early filling index (PDm), and atrial filling percentage.
• LV relaxation (tau) and wall thinning rates were also evaluated.

Main Results:

• During control exercise, LV diastolic function improved, with enhanced relaxation, increased filling rates (PFR, mFR1, mFR2), and greater early and overall diastolic filling.
• Ischemic exercise led to depressed systolic function, impaired LV relaxation, and reduced filling rates (PFR, mFR1).
• Ischemia caused a significant decrease in early diastolic filling and overall diastolic filling, along with an upward shift of the early diastolic pressure-volume curve.

Conclusions:

• Exercise alone enhances LV diastolic function and filling.
• Regional ischemia during exercise markedly impairs LV diastolic filling due to reduced relaxation, altered pressure-volume dynamics, and impaired systolic function.
• Nonuniformity of wall motion and the absence of compensatory late diastolic filling further contribute to diastolic dysfunction during ischemia.