In research in cardiology and exercise physiology, it isoften important to know the mass of blood pumped by a person’sheart in one stroke. This information can be obtained bymeans of a ballistocardiograph. The instrument works as follows:The subject lies on a horizontal pallet floating on a film of air.Friction on the pallet is negligible. Initially, the momentum ofthe system is zero. When the heart beats, it expels a mass m ofblood into the aorta with speed v, and the body and platformmove in the opposite direction with speed V. The speed of the blood can be determined independently (e.g., by observingan ultrasound Doppler shift). Assume that the blood’s speed is50.0 cm/s in one typical trial. The mass of the subject plus thepallet is 54.0 kg. The pallet moves at a speed of 6.00 x 1025 min 0.160 s after one heartbeat. Calculate the mass of blood thatleaves the heart. Assume that the mass of blood is negligiblecompared with the total mass of the person. This simplifiedexample illustrates the principle of ballistocardiography,but in practice a more sophisticated model of heart functionis used.
In research in cardiology and exercise physiology, it is
often important to know the mass of blood pumped by a person’s
heart in one stroke. This information can be obtained by
means of a ballistocardiograph. The instrument works as follows:
The subject lies on a horizontal pallet floating on a film of air.
Friction on the pallet is negligible. Initially, the momentum of
the system is zero. When the heart beats, it expels a mass m of
blood into the aorta with speed v, and the body and platform
move in the opposite direction with speed V. The speed of the blood can be determined independently (e.g., by observing
an ultrasound Doppler shift). Assume that the blood’s speed is
50.0 cm/s in one typical trial. The mass of the subject plus the
pallet is 54.0 kg. The pallet moves at a speed of 6.00 x 1025 m
in 0.160 s after one heartbeat. Calculate the mass of blood that
leaves the heart. Assume that the mass of blood is negligible
compared with the total mass of the person. This simplified
example illustrates the principle of ballistocardiography,
but in practice a more sophisticated model of heart function
is used.
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