From the Guidelines
Squatting is beneficial for increasing left ventricular output, as it enhances venous return to the heart through the compression of veins in the lower extremities, thereby increasing preload and subsequent stroke volume, as supported by the physiological effects of physical counter-pressure maneuvers described in the 2017 ACC/AHA/HRS guideline 1.
Physiological Mechanism
The physiological mechanism behind the increase in left ventricular output during squatting involves the compression of veins in the lower extremities, which forces blood toward the heart, increasing preload. This increased preload stretches the cardiac muscle fibers, leading to stronger contractions and greater stroke volume, according to the Frank-Starling mechanism. Additionally, squatting increases peripheral vascular resistance by compressing arteries in the legs, raising afterload and blood pressure.
Clinical Implications
The benefits of squatting on left ventricular output can be particularly useful in certain clinical contexts, such as in patients with neurogenic orthostatic hypotension (OH), where physical counter-pressure maneuvers like squatting can help increase blood pressure and improve orthostatic tolerance, as noted in the guideline 1. However, the effectiveness and safety of squatting as a maneuver to improve left ventricular output must be considered on a case-by-case basis, taking into account the individual patient's condition and any potential contraindications.
Evidence Support
The 2017 ACC/AHA/HRS guideline 1 provides evidence supporting the use of physical counter-pressure maneuvers, including squatting, as a beneficial intervention for patients with neurogenic OH, highlighting its potential to increase cardiac output and improve symptoms. While the guideline does not specifically quantify the increase in left ventricular output during squatting, it emphasizes the importance of such maneuvers in managing orthostatic intolerance.
From the Research
Effect of Squatting on Left Ventricular Output
- The effect of squatting on left ventricular (LV) output has been studied in various contexts, including its use as a provocative maneuver to diagnose dynamic left ventricular outflow tract obstruction in hypertrophic cardiomyopathy 2.
- Squatting has been shown to increase cardiac output and arterial blood pressure, accompanied by a decrease in heart rate and forearm vascular resistance, due to augmented venous return from compression of leg veins and activation of cardiopulmonary and arterial baroreflexes 3.
- In healthy individuals, squatting is associated with an increase in stroke volume index and mean arterial pressure, which are sustained throughout squatting, as well as a transient decline in peripheral vascular resistance 3.
- A study on the effect of standing and squatting on echocardiographic left ventricular function found that squatting was accompanied by an increase in LV cavity dimension, a slight decrease in heart rate, and an increase in calculated stroke index and cardiac index 4.
- The increase in cardiac output and blood pressure during squatting is primarily due to augmented venous return and is not altered by cardiac denervation, as demonstrated by similar responses in normal individuals and heart transplant recipients 3.
- The squatting test has been proposed as a therapeutic means to counteract the fall in blood pressure in patients suffering from dizziness due to dysautonomia and orthostatic hypotension or presenting pre-syncope symptoms 5.