What effect does tight clothing and spanx have on my breathing?

There is an effect. In the old days women wore corsets and sometimes their breathing was so restricted they would faint. This was known as "the vapors." nowadays, corsets have been replaced by softer fabrics such as spanx but they still have a restrictive effect especially when combined with tight, inelastic clothing. So if you notice you're short of breath, consider loosening up!
Depends cardiac f(x) This really depends on your cardiac function. In most instances it will not effect your breathing or have a minimal effect (positive or negative) a recent study showed that compressive clothing worn during exercise may improve venous return and overall cardiac function. However this may not be good for patients with compromised cardiac function.