Immediate effect of expiratory loading on left ventricular stroke volume

Area of Science:

• Cardiology
• Physiology

Background:

• Limited understanding of immediate effects of positive intrathoracic pressure on cardiac dynamics.
• Extensive research exists on steady-state effects of positive pleural pressure.

Purpose of the Study:

• To investigate the acute effects of positive intrathoracic pressure on cardiac dynamics.
• To determine the mechanisms behind immediate changes in left ventricular stroke volume during loaded expiration.

Main Methods:

• Utilized electrocardiographically gated radionuclide ventriculography.
• Employed a respiratory gating technique in nine healthy subjects.
• Compared quiet breathing with expiration against a 24 cm H2O expiratory threshold load.

Main Results:

• Respiratory loading increased stroke counts by 29.4% (p < .001).
• End-diastolic counts rose by 26.1% (p < .001), indicating increased left ventricular filling.
• End-systolic counts increased by 18.8% (p < .05), but ejection fraction remained unchanged.

Conclusions:

• The immediate increase in left ventricular stroke volume during loaded expiration is primarily due to enhanced ventricular filling.
• Augmentation of left ventricular ejection does not significantly contribute to the acute stroke volume increase.
• Increased pulmonary venous return may result from enhanced left ventricular distensibility secondary to altered right ventricular filling.