Continuous Murmurs
PRETEST 
1. How is the sound of a continuous murmur produced?
2. What is a cervical venous hum?
3. Why do the sounds of a patent ductus arteriosus (PDA) murmur change with age?
4. How can you differentiate between a PDA murmur and cervical venous hum murmur?
TWO CAUSES
Continuous murmurs are generated by rapid blood flow through arteries or veins or by shunting. Shunting occurs when an abnormal communication is created between the high-pressure arterial system and the low-pressure venous system. The murmurs begin in systole and persist, without interruption, through the second heart sound (S2) into diastole. Because these murmurs end late in diastole, they are continuous throughout the cardiac cycle.
CERVICAL VENOUS HUM MURMURS
The most common continuous murmur is a normal cervical venous hum, caused by rapid downward blood flow through the jugular veins in the lower part of the neck. (♦Sound 45) A cervical venous hum is present in most individuals, but it’s more pronounced in patients with hyperkinetic circulatory states, such as anemia, pregnancy, and thyrotoxicosis. The hum will disappear if the patient performs the Valsalva’s maneuver, lies down, or has pressure applied over the jugular vein.
Sound characteristics
A cervical venous hum murmur is heard best over the right supraclavicular fossa when the patient is sitting and his head is turned to the left. It has a faint intensity that increases during diastole. The murmur has a long duration: it lasts throughout the cardiac
cycle. Its high pitch is heard best using the diaphragm of the stethoscope. Its quality is soft and its timing continuous. The hum is louder between S2 and the first heart sound (S1). (♦Sound 45) The murmur has a plateau shape in systole and a crescendo-decrescendo configuration in diastole.
cycle. Its high pitch is heard best using the diaphragm of the stethoscope. Its quality is soft and its timing continuous. The hum is louder between S2 and the first heart sound (S1). (♦Sound 45) The murmur has a plateau shape in systole and a crescendo-decrescendo configuration in diastole.
 PCG and ECG showing cervical venous murmur |
PATENT DUCTUS ARTERIOSUS MURMURS
 Auscultatory area for cervical venous hum murmur |
A PDA murmur is the prototype of continuous murmurs. (♦Sound 46) Normally, the ductus is open during fetal life and closes shortly after birth. When the ductus remains open, abnormal blood flow, or shunting, occurs from the high-pressure aorta to the low-pressure pulmonary artery. The PDA murmur extends into diastole. A thrill may be palpable with a loud PDA murmur.
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