a method of investigating the mechanical manifestations of heart activity expressed in movements of the subject’s body. It consists of recording these movements, which are caused by “recoil” during heart contractions and discharge of blood into the aorta and pulmonary artery and by the movement of blood through the vascular system. Ballistocardiography became widespread in medical research in 1939, after the work of the American researcher I. Starr and his colleagues. In ballistocardiography special instruments, usually attachments to the electrocardiographs, are known as ballistocardiographs. There are two types of ballistocardiographs—indirect, which register the movements of a movable table on which the subject lies (table movement is caused by movement of the body as a result of discharge of blood), and direct, which record the immediate movements of the body.

Ballistocardiographs consist of a mechanical part, which senses the movements of the subject; a transducer, which transforms these mechanical movements into electrical energy; and an electronic part, which amplifies the electrical phenomena received from the transducer and records them. In indirect ballistocardiographs the movable table on which the subject lies is the mechanical part; in direct ones, it is a pickup attached to some part of the body (usually the tibia), by means of which it is possible to record the movement of that part of the body. The force of the photoelectric or induction current generated by the movements of this part of the body is recorded. Ballistocardiographs are differentiated according to frequency as ultralow-frequency (natural frequency 0.25 or 0.5 Hz), low-frequency (1–4 Hz), and high-frequency (15–30 Hz). Body movements along the longitudinal axis are usually recorded. It is also possible to record the velocity and acceleration of body movements arising as a result of heart activity. The movements are recorded in the form of a curve, known as a ballistocardiogram. Waves or spurs, which are designated by Latin letters from H to O, are discerned on this curve. Waves H, I, J, and K arise during contractions of the ventricles (systole); L and subsequent waves, during relaxation of the heart muscle (diastole). The contractive function of the myocardium and the function of the cardiovascular system as a whole may be judged by changes in the ballistocardiogram. Changes in the ballistocardiogram indicate disruption of cardiac activity but do not allow for diagnosis.