Fig. 1.

Standardized hypobaric/hyperbaric pressure chamber profile of compression and decompression start at 1.0 bar with a decompression over 60 s–0.8 bar (phase one is passive pressure equalization), remaining at 0.8 bar in isopression for 15 s (phase two), compression to1.2 bar over 120 s (phase three is active pressure equalization phase by means of Frenzel maneuver (first measurement), Valsalva or Toynbee maneuver (second measurement), remaining at 1.2 bar in isopression for 15 s (phase four), decompression to 1.0 bar over 60 s (phase five). The pressure changes were performed with a steady speed of 0.2 bar per minute