Update (30/9/2015) : Correction made in the following sections : Manuevers increasing afterload, maneuvers decreasing afterload. Also, the summary table has been updated and corrected. Please review it again if you have already read it before.
It’s an interesting topic and very important too. Unfortunately it’s not given well in most places and given wrong in many books which adds to the confusion. Allow me to simplify this topic and make it easy to understand for you.
Let’s divide maneuvers into two types: 1) Basic, 2) Advanced (This classification is purely made up and has no clinical significance… it’s just to make it easy to remember)
BASIC MANEUVERS These include effect of inspiration and expiration…
1) INSPIRATION: Inspiration increase right-sided heart murmurs
2) EXPIRATION: Expiration increase left-sided heart murmurs
Mechanism: During inspiration, there is more negative intrathoracic pressure which pulls the venous blood from all over body into heart, also Right atrial pressure decreases during inspiration. All this combines to increase venous return (Preload) into Right side of heart. At the same time, during inspiration, as lung are expanding, pulmonary blood volume increases and there is decrease in blood flow from lungs into Left atrium. So basically, preload of Left side of heart decreases during inspiration. This is the reason, Right sided heart sounds and murmurs increase during inspiration and left sided heart sounds and murmurs decrease in intensity. During expiration, as intrathoracic pressure rises, the venous return from body decreases. Also, Right atrial pressure (which is closely associated with intrapleural pressure) increases. All this lead to decreased preload of Right side of heart. At the same time, lung deflation during expiration causes more blood to flow from lungs to Left atrium. This increases the preload of left side of heart. Therefore, during expiration, left sided heart sounds and murmurs increase in intensity while right sided murmurs decrease.
Exception : MVP and HOCM murmurs DO NOT increase on expiration
How to remember: “RILE” Right sided – Inspiration… Left sided – Expiration
ADVANCED MANEUVERS There are four important groups of maneuvers
1) Maneuvers increasing preload e.g. rapid squatting, passive leg raising, reclining position, beta blocker, bradycardia or intravascular volume expansion
2) Maneuvers decreasing preload e.g. second phase of valsalva, standing or hypovolemia
3) Maneuvers increasing afterload e.g. hand grip
4) Maneuvers decreasing afterload e.g. amyl nitrite inhalation
- MANEUVERS WHICH INCREASE PRELOAD e.g. RAPID SQUATTING:
Increase intensity of most murmurs including AS, Decrease intensity of HOCM and MVP murmurs
Mechanism : Increased preload -> more blood in heart to pump through valves -> Louder murmurs including AS In case of HOCM, Increased preload -> Increased LV volume and stretching of LV walls -> increased distance between mitral valve leaflet and inter-ventricular septum -> decreased LV outflow obstruction -> decreased intensity of HOCM murmur In case of MVP, Increased preload -> Increased LV volume and stretching of LV walls -> stretching of lax chordae tendinae holding the mitral valve leaflets -> decrease in prolapse -> decreased intensity and delayed click in MVP
- MANEUVERS WHICH DECREASE PRELOAD e.g. VALSALVA or STANDING:
Decrease intensity of most murmurs including AS, Increase intensity of HOCM and MVP murmurs
Mechanism : vice versa of the mechanism discussed in rapid squatting
(Image Source : http://imindmaps.blogspot.com)
- MANEUVERS WHICH INCREASE AFTERLOAD e.g. HAND GRIP:
Decrease intensity of AS, HOCM & MVP murmur
Mechanism : Handgrip increase TPR which increase afterload. Increase afterload makes it difficult for blood to flow forward from heart into aorta. Therefore, decreased forward flow will lead to decrease in intensity of forward flow murmurs e.g. AS, while it will increase the intensity of regurgitant or backward flow murmurs e.g. MR.
In case of HOCM and MVP, its worth remembering that anything that increase the blood inside Left ventricle will decrease the HOCM and MVP murmurs.
Explanation : In HOCM, the obstruction to outflow is caused by (1) hypertrophic interventricular septum on one side and (2) Systolic anterior motion of Mitral valve leaflet on the other side. Both of them come together and cause sub-aortic (i.e. below the aortic valve) stenosis. When the heart is filled with more blood, they separate away and thus, the obstruction decreases. On the other hand, if heart has less blood, they will come close to each other and will cause more obstruction. How to remember : “HOCM murmur can be squashed with hands”
In MVP, the cause of regurgitation is floppy chordae tendinae holding the mitral valve leaflets. When heart is filled with extra blood, the tendinae become tense leading to less regurgitation. So, anything that will increase the blood inside left ventricle will decrease the MVP murmur.
- MANEUVERS WHICH DECREASE AFTERLOAD e.g. AMYL NITRITE INHALATION:
Increase intensity of AS, HOCM & MVP murmur
Curious case of Amyl nitrite : Amyl nitrite is a vasodilator similar to Nitroglycerin but where Nitroglycerin has major effect on veins (i.e. Venodilator), Amy nitrite has major effect on arteries/arterioles (i.e. Arteriodilator). So, when we give Nitroglycerin to patient, prominent effect is decrease in preload (dependent on veins). But, when Amyl nitrite is given, the major effect is decrease in afterload (dependent on arteries). That is the reason to classify Amyl nitrite in separate category from valsalva or standing (which only decrease preload).
Now, coming on to the effect of Amyl nitrite inhalation, it dilates the large arteries -> decrease total peripheral resistance (TPR) -> decreased afterload -> increased forward flow of blood in left side of heart.
Effect on AS murmur : As the blood flow through aortic valve increases, the murmur increases in intensity.
Effect on HOCM and MVP murmur : As the blood flowing out of heart increases, there is lesser amount of blood inside the heart at any time. As already explained in the previous maneuver, lesser blood inside left ventricle will increase the murmurs of HOCM and MVP due to the reasons already stated.
Exception : Mitral stenosis murmur is not affected by the maneuvers affecting afterload e.g. Hand grip and amyl nitrite inhalation. This is because the maneuvers affecting afterload doesnot affect ventricular filling during diastole.
- Summary :
Hope it helped you… 🙂 Feel free to comment, like and share. (P.S.: The information contained in this post is not comprehensive and only discusses the important aspects of dynamic auscultation important regarding board examinations and USMLE)