From the Research
Squatting increases venous return to the left atrium by compressing the veins in the lower extremities and increasing intra-abdominal pressure, as demonstrated by the most recent study in 2012 1. When a person squats, the mechanical compression of the leg veins forces blood toward the heart, while the increased abdominal pressure pushes blood from the splanchnic circulation into the central venous system. This results in an immediate increase in preload to both the right and left sides of the heart. For the left atrium specifically, this increased venous return first passes through the pulmonary circulation before reaching the left atrium via the pulmonary veins. The augmented venous return leads to increased left atrial filling, which subsequently increases left ventricular end-diastolic volume and stroke volume through the Frank-Starling mechanism.
Key Points
- Squatting increases cardiac output and arterial blood pressure, accompanied by an immediate decrease in heart rate and forearm vascular resistance, as shown in a study from 1995 2.
- The rise in cardiac output and blood pressure is attributed to augmented venous return from compression of leg veins, while the decreases in heart rate and forearm vascular resistance are probably due to activation of cardiopulmonary and arterial baroreflexes.
- The effects of squatting on venous return are transient and return to baseline once the squatting position is released, making it a useful maneuver for temporarily improving cardiac output in certain conditions like hypertrophic cardiomyopathy or tetralogy of Fallot, where increased preload can be beneficial, as discussed in a study from 2011 3.
Physiological Response
The physiological response to squatting is complex and involves multiple mechanisms, including:
- Increased intra-abdominal pressure, which pushes blood from the splanchnic circulation into the central venous system
- Mechanical compression of the leg veins, which forces blood toward the heart
- Activation of cardiopulmonary and arterial baroreflexes, which lead to decreases in heart rate and forearm vascular resistance
- Increased venous return, which leads to increased left atrial filling and subsequently increases left ventricular end-diastolic volume and stroke volume through the Frank-Starling mechanism, as demonstrated by the study in 2012 1.