Effects of spontaneous respiration on canine left ventricular function

Area of Science:

• Physiology
• Cardiovascular System
• Respiratory System

Background:

• Spontaneous inspiration involves changes in intrathoracic pressure.
• The impact of these pressure changes on left ventricular function is not fully understood.

Purpose of the Study:

• To elucidate the mechanism behind the reduction in left ventricular stroke volume during spontaneous inspiration.

Main Methods:

• Left heart transmural pressures were measured using left atrial and left ventricular diastolic pressures relative to esophageal pressure.
• Left ventricular end-systolic and end-diastolic volumes were estimated using ultrasonic crystal transit time measurements.
• Changes in stroke volume were correlated with pleural pressure variations.

Main Results:

• Left ventricular stroke volume decreased during spontaneous inspiration as pleural pressure fell.
• This decrease was primarily due to an increase in end-systolic volume, with minimal change in end-diastolic volume.
• Diastolic left ventricular transmural pressure increased, indicating reduced diastolic compliance, but this was not the main cause of stroke volume reduction.

Conclusions:

• Spontaneous inspiration impedes left ventricular ejection due to altered transmural pressures.
• Reduced left ventricular compliance during inspiration contributes to, but does not primarily cause, the decrease in stroke volume.