[Code of Federal Regulations] [Title 21, Volume 8] [Revised as of April 1, 2008] From the U.S. Government Printing Office via GPO Access [CITE: 21CFR868.1750] [Page 298] TITLE 21--FOOD AND DRUGS CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) PART 868_ANESTHESIOLOGY DEVICES--Table of Contents Subpart B_Diagnostic Devices Sec. 868.1750 Pressure plethysmograph. (a) Identification. A pressure plethysmograph is a device used to determine a patient's airway resistance and lung volumes by measuring pressure changes while the patient is in an airtight box. (b) Classification. Class II (performance standards).