Accentuation of heart sounds in anemia: an effect of blood viscosity

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Abstract
The effect of blood viscosity on the intensity of heart sounds was investigated in 25 anemic patients and 41 control subjects. Calibrated phonocardiograms showed that in anemic patients, the aortic component of the second sound was of greater amplitude (54 +/- 3 vs. 33 +/- 3 dyn/cm2) (P less than 0.001). The pulmonary component of the second sound and the first sound were also of higher amplitude in anemic patients (both P less than 0.001). The viscosity of blood of anemic patients was lower (0.029 +/- 0.001 vs. 0.045 +/- 0.001 poise) (P less than 0.001). Blood pressure was comparable among the two groups. Sound produced by closure of a normal porcine valve in an in vitro flow system also showed an accentuated sound with liquids of lower viscosity. Augmented diastolic vibrations of the closed valve, shown by high-speed motion pictures, accompanied the accentuated sound. These observations suggest that the accentuated second sound in anemic patients results from the lower blood viscosity, which reduces the damping forces that act upon the semilunar valve as it vibrates after closure. The reduced damping would allow augmented vibrations that result in an accentuated sound.