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Heart Rate and Pulse

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Special Cases

 

Blood/Fluid Loss

Abnormal orthostatic vital signs are initial indicators of significant blood/ body-fluid loss. After about a liter deficit (about 20% of body fluid) an increase in heart rate occurs to compensate for the decreased volume. A patient has orthostatic tachycardia if the heart-rate increases by 30 or more beats per minute or the person becomes light-headed from supine to standing. Only when about 30% of blood-body-fluid loss occurs—about 2 liters— does the systolic pressure begin to drop. An exception to tachycardia with blood loss is sometimes seen. Bradycardia may occur (paradoxical bradycardia) because of stimulation of afferent vagal fibers in the left ventricle from cardiac contraction around a reduced blood volume.

Doppler Pulse

If one cannot hear the heart or palpate the pulse, a Doppler or ultrasound device may be used. The Doppler transducer, or flow meter, is a transmitter and receiver and detects the movement of red blood cells, converting the frequency shift of the reflected ultrasound to an audible signal. Acoustic gel is applied. After contact with the skin, the probe is angled in different directions over the artery until an optimum sound is heard with earphones or speaker.

Fetal heart tones (FHTs) may be heard with a regular stethoscope after about 18-20 weeks and with a Doppler stethoscope after about 12 weeks. The mother’s heart rate is auscultated prior to the Doppler to avoid confusion. After application of a conducting gel, it is pressed firmly against the abdominal wall. Normal FHTs range from 120-160 beats per minute. Above 160 or below 120 requires urgent obstetric consultation. If fetal bradycardia is present (indicating fetal distress) the mother is placed in the left lateral decubitus position and supplemental oxygen is administered.

Abnormal Heart Sounds

Several normal and abnormal heart sounds are common and may be recognized:
Splitting of the 1st sound. One may hear both AV valves close separately. Usually splitting of the first sound has little clinical significance.
Splitting of the 2nd sound. The aortic valve closes before the pulmonary, sometimes heard in inspiration. If it is heard during expiration it may indicate heart disease. Third sound. This is a weak sound, heard occasionally after the 2nd and caused by distention of the ventricles during filling. It is loud in heart failure because of overfilling of the failing ventricle. Three sounds are heard in cardiac failure and resemble a galloping horse (gallop rhythm).
Fourth sound. This sound precedes the first and is caused by vibrations and decreased compliance of the left ventricle. It is sometimes heard in myocardial infarction. A click may be heard after the 1st or before the 2nd sound, indicating a normal opening of the semilunar valves, aortic valve disease, pulmonic disease or mitral valve prolapse. An opening snap is sometimes heard after the 2nd sound. It is caused by the opening of a narrowed mitral valve.
A friction rub, often heard in infectious pericarditis, is a squeaky or scratchy sound caused by the rubbing together of the dry epicardium against the parietal pericardium. A heart murmur is the “swooshing” sound of blood heard before, during or after (or all three) the heart sounds.

It may originate from several mechanisms:

1. increased velocity of blood flow, as in exercise,
2. normal velocity with lessened viscosity, as in anemia,
3. obstruction to flow, as in valvular disease,
4. flow into a dilated chamber, as in an aortic aneurysm and
5. flow through an abnormal opening, as in a congenital heart defect.

It is commonly heard in valves that are damaged and do not open properly (narrowing, or stenosis), or close properly, letting blood back up through the valve (regurgitation, or insufficiency).
Murmurs occurring after the first heart sound are systolic. Those occurring after the second heart sound are diastolic.

Examples

1. In the setting of an acute myocardial infarction, a new systolic murmur may signal papillary muscle dysfunction or ventricular septal rupture: 3/6 systolic murmur at apex.
2. One may hear the diastolic murmur of aortic regurgitation in a dissecting aortic aneurysm: 5/6 diastolic murmur right sternal border (RSB).

 


 
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