ballistocardiogram

Ballistocardiography is a noninvasive method for recording the mechanical recoil of the human body resulting from the heartbeat. The technique measures the small forces and motions generated when the heart ejects blood into the circulation, producing a ballistic impulse transmitted to the body's center of mass and detected at the surface.

Physiological basis: When the ventricles eject blood at high velocity into the aorta, an equal and opposite reaction occurs. This momentum transfer causes subtle body movements and body-surface vibrations that vary with the cardiac cycle. The amplitude and timing of the signal are related to stroke volume and cardiac output and are influenced by posture and respiration.

Measurement: BCG signals are typically obtained with sensitive force transducers or load cells placed under a bed, chair, couch, or seat, or with floor-embedded platforms. Modern implementations may use accelerometers or piezoelectric sensors. Signals are often recorded alongside electrocardiography (ECG) or phonocardiography to aid interpretation.

Signal interpretation and limitations: The ballistocardiogram comprises characteristic deflections that correspond to phases of the cardiac cycle, though the exact morphology is affected by body habitus, movement, and breathing. Interpretation requires careful calibration and filtering, and direct clinical utility varies. In practice, BCG has historical significance and remains primarily a research tool.

Applications and status: Historically explored as a noninvasive monitor of cardiac function, BCG has largely given way to imaging and Doppler methods but continues to be studied for continuous, unobtrusive monitoring in clinical and home settings and as part of the broader field of seismocardiography.