In patients with hypertrophic obstructive cardiomyopathy, which position typically causes the murmur to increase?

In patients with hypertrophic obstructive cardiomyopathy (HOCM), the murmur is often influenced by changes in preload and afterload. When a patient moves from a standing position, the venous return to the heart decreases, as the blood pools in the lower extremities. This reduction in preload results in less filling of the left ventricle, which can increase the intensity of the outflow tract obstruction caused by hypertrophy of the myocardium.

Therefore, when the patient stands, the murmur typically becomes more pronounced due to the augmented gradient between the left ventricle and the outflow tract. This is in contrast to positions like squatting or sitting, which would generally enhance venous return, reduce the murmur's intensity, and improve the left ventricular filling.

Understanding the mechanics of blood flow and how body positions impact heart function is essential in recognizing why standing amplifies the murmur associated with HOCM.