Canine sternal force-displacement relationship during cardiopulmonary resuscitation

A viscoelastic model developed to model human sternal response to the cyclic loading of manual cardiopulmonary resuscitation (CPR) (K.G. Gruben et al., J. Biomech. Eng., vol. 115, p. 195-201, 1993) was used to evaluate the properties of canine chests during CPR. Sternal compressions with ventilations after every fifth compression were applied to supine canines (n=7) with a mechanical resuscitation device. The compressions were applied at a nominal rate of 90/min with a peak force near 400 N. From measurements of sternal force, sternal displacement, and tracheal airflow, model parameters were estimated and their dependence on time and lung volume evaluated. The position to which the chest recoiled between compressions changed with time at a mean rate of 1.0 mm/min. Within each ventilation cycle (five compressions) the sternal recoil position decreased by 2.0 cm for each liter of decrease in lung volume. The elastic force and damping decreased with time and decreasing lung volume. Canine and human model parameters were found to be similar despite the notable differences in thoracic anatomy between the species, supporting the continued use of canines as models for human CPR. These parameters may be useful in the development of a model relating sternal compression forces to blood flow during CPR.