What is the effect of inspiration on venous return to the left atrium?

From the Guidelines

During inspiration, venous return to the left atrium decreases due to the increase in intrathoracic pressure, which reduces the gradient for venous return to the heart 1. This decrease in venous return is a result of the mechanical effects of inspiration on the cardiovascular system.

Key Factors Affecting Venous Return

• The decrease in pleural pressure (Ppl) during spontaneous inspiratory efforts increases the gradient for the return of blood to the right ventricle (RV), but the subsequent increase in RV filling is passed to the left ventricle (LV) over the next few beats 1.
• The use of positive airway pressure, such as positive end-expiratory pressure (PEEP), decreases LV afterload but also decreases venous return to the RV and eventually to the LV 1.
• The pressure gradient from the upstream large venous reservoir to the heart is normally only 4–8 mmHg, making it susceptible to changes in Ppl 1.

Clinical Implications

• The decrease in venous return during inspiration can lead to a decrease in cardiac output, particularly in patients with decreased LV function or increased capillary permeability 1.
• The use of PEEP can help to maintain a relatively open lung and improve oxygenation, but it can also increase pulmonary vascular resistance and decrease venous return 1.
• Clinicians should be aware of the potential effects of inspiration on venous return and cardiac output, particularly in patients with underlying cardiovascular or respiratory disease 1.

From the Research

Effect of Inspiration on Venous Return

• The effect of inspiration on venous return to the left atrium is complex and involves multiple factors, including changes in intrathoracic pressure, venous return, and ventricular interdependence 2, 3, 4, 5.
• During inspiration, the decrease in intrathoracic pressure can increase venous return to the right heart, but this does not necessarily translate to an increase in venous return to the left atrium 2, 5.
• The increase in right heart volume during inspiration can lead to a decrease in left ventricular diastolic filling and stroke volume due to ventricular interdependence 3, 5.
• However, the use of inspiratory resistance can enhance venous return and cardiac stroke volume, suggesting that the respiratory pump can be harnessed to increase circulation 6.

Mechanisms of Reduced Venous Return

• Reduced left ventricular diastolic filling during inspiration is thought to be the primary mechanism responsible for decreased stroke volume during inspiration 3, 5.
• Increased left ventricular afterload due to decreased intrathoracic pressure can also impede outflow and decrease stroke volume 5.
• Venous return from the lower body may be an important determinant of pulsus paradoxus, particularly when lung volume increases 3.

Clinical Implications

• The use of inspiratory resistance to enhance venous return and cardiac stroke volume may have clinical applications in the treatment of hypotension, including orthostatic hypotension, hemorrhagic shock, and septic shock 6.
• Understanding the mechanisms of reduced venous return during inspiration can inform the development of new treatments for conditions associated with hypotension and decreased cardiac output 2, 3, 4, 5, 6.