Part One: Maneuvers and Positions
Preload: In cardiac physiology, preload is the end diastolic pressure that stretches the right or left ventricle of the heart to its greatest geometric dimensions under variable physiologic demand. Generally it is the venous blood that is returning into the right atrium for oxygenation. Preload is affected by venous blood pressure and the rate of venous return. These are affected by venous tone and volume of circulating blood.
Maneuvers that increase preload or Venous return to the heart are: Raising your legs or Squatting.
Maneuvers that decrease preload or venous return to the heart are: Standing or Valsalva maneuver. Standing decreases venous return and ventricular filling. As a result, standing decreases the intensity of all murmurs except Idiopathic Hypertrophic Subaortic Stenosis (IHSS) and mitral valve prolapse.
Squatting increases peripheral resistance and increases ventricular filling. It brings out the murmurs of ventricular septal defect, aortic insufficiency, and mitral insufficiency.
Generally ALL murmurs increase in intensity (They get louder or Worsen) with an increase in Venous return (increased blood volume inside heart) EXCEPT for two cases:
Hypertrophic obstructive Cardiomyopathy (HOCM) and Mitral Valve Prolapse (MVP). The increase in preload will reduce the intensity [Quiet down or Improve] the murmur.
Breathing: All right-sided murmurs increase with inspiration (Carvallo sign). Many left-sided murmurs decrease with inspiration, but they may be very difficult to hear. Therefore, respiratory variation can help differentiate corresponding right-sided from left-sided murmurs; for example, tricuspid regurgitation from mitral regurgitation.
Sitting up and leaning forward accentuates the second heart sound (S2) and increases the aortic insufficiency murmur. The left lateral decubitus position increases murmur of mitral stenosis. Some people feel that the exercise component of moving into the left lateral decubitus position accounts for the increase in the murmur.
Part Two: Afterload
Afterload is the tension or stress developed in the wall of the left ventricle during ejection. In other words, it is the end load against which the heart contracts to eject oxygenated blood to the body. Afterload is readily broken into components; aortic pressure and/or the pressure the must overcome to eject blood.
Afterload maneuvers – will change the artery diameter making it smaller and therefore resistance to forward flow (decreasing the amount of blood that leaves the left ventricle). Therefore, the hand grip maneuver will increase the afterload.
Think about it like this… Hand gripping is like squatting of upper limb but since upper limb unlike the legs has very small amount of blood- this doesn’t affect venous return rather it only effects the afterload by increase in AFTER LOAD since it makes it harder for the forward flow of oxygenated blood. Therefore we can understand that “backward flow” murmurs seen in: Aortic Regurgitation, Mitral regurgitation and Ventral Septal Defects (VSD) will increase the intensity of the murmur.
Consider Murmur groups in FORWARD FLOW AND BACKWARD FLOW MURMURS. Forward flow [Obstruction] murmurs i.e. Aortic Stenosis (AS), Mitral Stenosis (MS), HOCM and MVP with the handgrip maneuver which increases vascular resistance the murmur intensity would logically decrease or improve.
Think about it: A murmur is a pathologic heart sound due to turbulent blood flow. If there is a great pressure difference across a valve the murmur turbulence will increase. Once you start to equalize the pressure on two sides of valve i.e. reduce turbulence via the handgrip maneuver this will reduce the intensity of forward flow murmur.
Amyl nitrite is a potent vasodilator (i.e., it expands blood vessels, resulting in lowering of the blood pressure). Alkyl nitrites function as a source of nitric oxide, which signals for relaxation of the involuntary muscles. Physical effects include decrease in blood pressure, headache, flushing of the face, increased heart rate, dizziness, and relaxation of involuntary muscles, especially the blood vessel walls and the anal sphincter. Mainly Amyl nitrite reduce afterload by vasodilation this causes a decrease in the forward flow pressure, hence blood flows forward more smoothly in Aortic Stenosis (AS), Mitral Stenosis (MS), HOCM and MVP.
Backflow murmurs [AR MR VSD] reduce in intensity as pressure gradient increases across a valve where as forward Flow (AS, MS, HOCM and MVP) obstruction Murmurs INCREASE in Intensity as Pressure gradient across valve increases. High pressure in the left ventricle combined with a very low pressure in aorta will lead to more turbulent flow and increased intensity of murmur.