How does the Valsalva maneuver decrease preload?

From the Guidelines

The Valsalva maneuver decreases preload by increasing intrathoracic pressure, which impedes venous return to the heart. When a person performs Valsalva by forcefully exhaling against a closed glottis (as when straining during a bowel movement or heavy lifting), the increased pressure in the chest compresses the great veins and right atrium. This compression creates resistance against blood flowing back to the heart from the peripheral circulation, effectively reducing the volume of blood returning to the heart (preload) 1. The reduced venous return leads to decreased right ventricular filling, which subsequently results in decreased left ventricular filling and stroke volume. This mechanism explains why people may feel lightheaded or even faint during prolonged Valsalva maneuvers, as the reduced preload leads to decreased cardiac output and potentially lower cerebral perfusion.

Key Points

• The Valsalva maneuver is used to terminate supraventricular tachycardias by changing preload and subsequent baroreceptor responses to restore normal heart rhythm 1.
• The maneuver involves forcefully exhaling against a closed glottis, increasing intrathoracic pressure, and compressing the great veins and right atrium 1.
• This compression reduces venous return, leading to decreased right ventricular filling, left ventricular filling, and stroke volume 1.
• Clinically, the Valsalva maneuver is utilized in certain situations, such as terminating supraventricular tachycardias, where changes in preload and baroreceptor responses help restore normal heart rhythm 1.

Clinical Implications

The Valsalva maneuver has significant clinical implications, particularly in the management of supraventricular tachycardias. By understanding the mechanism by which the Valsalva maneuver decreases preload, healthcare providers can effectively utilize this technique to restore normal heart rhythm in patients with supraventricular tachycardias. Additionally, the Valsalva maneuver can be used to diagnose and assess left ventricular diastolic dysfunction in patients with heart failure 1.

From the Research

Mechanism of Preload Decrease

• The Valsalva maneuver decreases preload by increasing intrathoracic pressure, which in turn decreases venous return to the heart 2.
• During the strain, peripheral venous pressures become increased, and systolic and pulse pressures begin to fall while mean arterial pressure remains near or is elevated above control levels 2.
• The decrease in venous return is due to the increased intrathoracic pressure, which compresses the veins and reduces blood flow back to the heart.

Effects on Cardiovascular System

• The Valsalva maneuver also increases total peripheral resistance, which begins after about 7 seconds of strain, producing further increases in afterload 2.
• The heart rate and cardiac contractility are increased to maintain cardiac output in the presence of diminished venous return 2.
• The Valsalva maneuver can be used as a bedside test to estimate filling pressures in patients with heart failure, with studies demonstrating a significant correlation between the cardiovascular response to the Valsalva maneuver and invasively measured ventricular filling pressures 3.

Mathematical Modeling

• Mathematical models of the cardiovascular response to the Valsalva maneuver have been developed to simulate the haemodynamic response to the maneuver, including the effects of baroreflex mechanisms and nonlinear interactions between regulatory mechanisms 4.
• These models can be used to analyze the interactions between the cardiovascular system and autonomic regulatory mechanisms, and to aid in the interpretation of patient responses to the Valsalva maneuver.

Positional Effects

• The position of the patient during the Valsalva maneuver can affect the results, with a 20 degree angle of head-up tilt position reducing the frequency of flat-top responses and improving reflex vasoconstriction and the Valsalva ratio 5.
• The effects of the Valsalva maneuver on hemodynamic response to strength exercises have also been studied, with results suggesting that a brief Valsalva maneuver may actually protect arteries located in the thorax and in the brain by diminishing transmural pressure acting across these vessels 6.