Objective: To study the effects of underlying bed softness versus stiffness on the effectiveness of chest compressions in CPR. Methods: For a wide range of bed stiffness constants, mathematical models describing compression of the human chest supported by a hospital bed were created for an adult thorax experiencing either a sinusoidal compressive force or a sinusoidal sternal displacement. Results: With 5 cm peak displacement, sternum-to-spine compression fell from 4.3 to 1.0 cm, and peak power fell from 59 to 23 Watts, as bed stiffness decreased from 50,000 to 5,000 N/m. Less than 35% of maximal chest compression occurred at a typical bed stiffness of 10,000 N/m. With 400 N peak force, sternum-to-spine compression decreased from 5.0 to 2.0 cm, and peak power increased from 82 to 226 Watts, as bed stiffness decreased from 50,000 to 5,000 N/m. However, greater than 85% of maximal chest compression was obtained at a typical bed stiffness of 10,000 N/m. Conclusion: The deterioration of chest compression performed on soft beds is technique dependent. If necessary, CPR can be performed effectively on a softer surface using a constant peak force technique. However, a firm surface is most desirable
