CARDIAC RESPONSES OF DOGS TO NONSYNCHRONOUS AND HEART SYNCHRONOUS WHOLE-BODY VIBRATION

Changes in cardiac function produced by synchronizing vibration-induced forces with events in the cardiac cycle were compared to those for the nonsynchronous case in eight chronically instrumented, tranquilized dogs. The supine animals received sinusoidal, whole-body vibration (along the spinal ±G(z) axis) at a constant acceleration amplitude (±0.75 G). The vibration frequency (2-3 Hz) was set equal to the paced heart frequency. Synchronization between vibration and cardiac cycles on a beat-by-beat basis produced a specific and sustained cardiovascular response; such a sustained response was not possible with nonsynchronous vibration. With synchronization, relationships could be found and sustained in which changes either exceeded or were below mean nonsynchronous levels, in some cases below previbration values. For the synchronous vs. nonsynchronous states, significant modification of cardiac function was reflected in parameters such as coronary flow (+15% to -34%) and myocardial oxygen consumption (+21% to -51%). Thus, whole-body oscillating acceleration (vibration) is a forcing function that can produce and maintain a particular cardiovascular response.