What is dynamic auscultation?

Simplest form of dynamic auscultation is checking the effect of inspiration and expiration on the various auscultatory events, which we are taught in the very beginning of our career. Yet dynamic auscultation is a wide term which includes various physical and pharmacological maneuvers to assess the characteristics of heart sounds and murmurs. In the era prior to colour Doppler echocardiography, we had to rely solely on dynamic auscultation for the differential diagnosis of many cardiac conditions. Some of the methods applied are Valsalva maneuver, change of position, exercise, observation of post ectopic beat, compression of both brachial arteries with a blood pressure cuff and pharmacologic maneuvers like inhalation of amyl nitrate.

We know that right sided heart sounds and murmurs increase with inspiration due to the increase in venous return and consequent increase in flow through the right sided chambers. The only right sided event which is better heard in expiration is the phasic ejection click of valvar pulmonary stenosis. As the doming pulmonary valve is already partially domed at the end of diastole in inspiration, the opening movement is less in inspiration. In expiration, lower filling pressure of the right ventricle keeps the pulmonary valve less domed at the end of diastole so that the abrupt opening in systole causes a louder ejection click. Phasic changes of Korotkoff sounds during blood pressure measurement in inspiration and expiration is helpful in documenting the level of pulsus paradoxus.

Most cardiac murmurs decrease in length and intensity during a Valsalva maneuver. The classical exceptions are the murmur of hypertrophic obstructive cardiomyopathy and mitral valve prolapse. These are louder and longer with Valsalva strain because of the decreased left ventricular preload and hence decreased cavity size. Though these two murmurs behave similarly with Valsalva maneuver, observation in post ectopic beat can differentiate between the two. In the post ectopic beat, with a longer preceding diastole, larger ventricular volume decreases mitral valve prolapse and its murmur. But in case of hypertrophic obstructive cardiomyopathy, increased inotropy in the post ectopic beat overrides this and enhances left ventricular outflow obstruction and murmur. Calcium utilization is lower during the ectopic beat and more calcium is available during the post ectopic beat for a stronger contraction. Increased end diastolic volume also increases the force of contraction according to Starling’s law. On release of Valsalva strain, right sided murmurs return to baseline intensity earlier than the left sided murmurs.

Hand grip exercise, both isotonic and isometric, can increase murmurs of pulmonary and mitral stenosis. Similar changes may be noted in ventricular septal defect, mitral regurgitation and aortic regurgitation. You may remember that murmur of aortic regurgitation is best heard with the patient leaning forward with breath held in expiration.

Among positional changes, standing and squatting are the most commonly used. Most murmurs, except those of mitral valve prolapse and hypertrophic obstructive cardiomyopathy decrease with standing. Opposite effect is noted on squatting. Sudden standing decreases ventricular preload while squatting increases the preload. Passive leg raising in supine position has effects similar to squatting by increasing the venous return. Passive leg raising is useful in detecting murmur of tricuspid regurgitation better. Mid diastolic murmur of mitral stenosis is better heard in the left lateral position, in expiration.

Murmurs of VSD, MR and AR decrease in the early phase of mild hypotension after inhalation of amyl nitrate. Murmur of aortic stenosis becomes louder due to the increased stroke volume. As AR decreases, this maneuver has been described for the differentiation of Austin Flint murmur from mitral stenosis. Murmur of mitral stenosis increased due to the reflex tachycardia following vasodilatation with amyl nitrate.

Increasing the afterload by transient occlusion of both brachial arteries by inflating BP cuff pressure 20 mmHg above systolic pressure increases murmurs of MR, VSD and AR. MR and VSD murmurs increase because of increased left ventricular afterload. AR increases because of increased resistance to aortic forward flow in diastole.