Systems, methods and devices for optimizing heat transfer within a device or system used to compress andor expand a gas, such as air, are described herein. More particularly, the present invention relates to therapeutic walkers and devices for preventing tipping of a walker during use. The relationship between the pressures is reversed at a certain timing, to make the pressure of the second space higher than the pressure of the first space. A rivet of the rivet assembly is inserted into at least one object.