A CK-MB test may be used as a follow-up test to an elevated CK in order to determine whether the increase is due to heart damage or skeletal muscle damage.
Scuba organizations say recreational divers shouldn't go below about 130 feet, but one Egyptian diver recently ventured a bit deeper -- going more than 1,000 feet below the ocean surface and setting a world record in the process.
But even pure oxygen can be dangerous when breathed under pressure. In fact, breathing pure oxygen while scuba diving below 25 feet can be fatal! So for very deep technical dives, the inert gas helium is often added into the gas mix; which can be heliox (oxygen & helium), or trimix (oxygen, helium, and nitrogen).