1. What is a normal ejection fraction?
ANS: About 70 ± 10% of the end-diastolic volume that is ejected during systole by angiography.
2. What is the blood pressure response to a Valsalva strain if the ejection fraction is normal, i.e., 70 ± 10% by angiography, or 60 ± 10% by radionuclide methods?
ANS: If the cuff pressure is held at 25 mmHg above systolic pressure during the strain, a few Korotkoff sounds heard at the beginning of the strain reflect the increased intrathoracic pressure. Then the Korotkoff sounds will disappear as the blood pressure falls, because of the decrease in venous return. Post-Valsalva, the Korotkoff sounds will reappear due to an overshoot of at least 25 mmHg if the ejection fraction is normal. If no overshoot is obtained, hold the cuff pressure at 15 mmHg above the control pressure. If there is an overshoot to 15 mmHg, the ejection fraction may be low normal or it may be slightly reduced.
3. What kind of blood pressure response to the Valsalva occurs with a markedly reduced ejection fraction?
ANS: During the entire strain, the blood pressure stays up, and after the Val-salva maneuver there is no overshoot or bradycardia. This is known as
A. The typical normal blood pressure response to a 10-s Valsalva strain showing a good post-Valsalva overshoot, indicating an ejection fraction of about 70 ± 10%.
B. The absent post-Valsalva overshoot suggests an ejection fraction of about 50 ± 10% by angiography.
a square-wave response. This is partly due to the excess lung blood volume in the congested lungs, which continues to empty into the LV during the entire 10 s of strain.
How does the square-wave response relate to ejection fraction and end-diastolic pressure in the LV?
ANS: It has been found that the ejection fraction is about 20 ± 10% by angiography (15 ± 10% by radionuclide methods). The end-diastolic pressure in the LV is likely to be very high (i.e., as much as 40 mmHg).
The square-wave response is present when there is no fall in blood pressure during and no rise in blood pressure after a Valsalva strain. This usually indicates an ejection fraction of 20 ± 10%.
5. What happens to the blood pressure response to the Valsalva if the ejection fraction is reduced to 50 ± 10% by angiography (40 ± 10% by nuclear methods) and has a near-normal ejection fraction only with the help of a high end-diastolic pressure?
ANS: The blood pressure and pulse pressure decrease during the strain, but there is no poststrain overshoot . This is presumably due to the excess sympathetic tone to which hearts with reduced ejection fractions are subject. Therefore, the strain does not stimulate enough further sympathetic drive to produce an overshoot after release of the strain.
6. What can produce a falsely abnormal absence of overshoot despite a normal heart?
ANS: a. Any cause of autonomic imbalance, such as the use of beta blockers.
b. Decreased blood volume.
c. A moderate or large ASD.
Note: A large ASD may even produce a square-wave response.
7. How can you help the patient to perform a Valsalva if he or she cannot comprehend your instructions or cooperate enough to carry out the maneuver?
ANS: a. Press on the abdomen with one hand and ask the patient to push your hand away with the abdomen. If this does not work, then b. Have the patient blow up an aneroid manometer to 40 mmHg through a rubber tube connection. (A 20-gauge needle inserted into the rubber tube will ensure that continuous expiration through an open glottis is moving the manometer needle and prevents the needle from moving if only intra-oral pressure is raised.)
c. Have the patient blow out hard against the resistance of the patient's forefinger inserted into his or her mouth.
Note: Another way to use blood pressure to tell if the patient has low cardiac output is to divide the difference between systolic and diastolic blood pressure. This is known as the proportional pulse pressure. If the difference between systolic and diastolic blood pressure is 25% of the systolic pressure or less, then there is a 90% chance that the cardiac index is 2.2 L/min/m2 or less.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...