René van der Bel

| Chapter 3 | 56 Abstract It would be desirable to safely and noninvasively measure blood pressure under hyperbaric and/or hyperoxic conditions continuously, in order to explore normal- and pathophysiologic haemodynamic responses in humans under these conditions. A systematic analysis according to ‘failure mode and effects analysis’ principles of a com- mercially available beat-by-beat non-invasive blood pressure monitoring device was per- formed using specifications provided by the manufacturer. Possible failure modes related to pressure resistance and fire hazard in hyperbaric and oxygen-enriched environments were identified and the device modified accordingly to mitigate these risks. The modified device was compared to an unaltered device in five healthy volunteers under normobaric condi- tions. Measurements were then performed under hyperbaric conditions (243 kPa) in two healthy volunteers and two patients. Modifications required included: 1) replacement of the carbon brush motorized pump by pressurized air connected through a balanced pressure valve; 2) modification of the 12V power supply connection in the multiplace hyperbaric chamber, and 3) replacement of gas-filled electrolytic capacitors by solid equivalents. There was concurrence between mea- surements under normobaric conditions, with no significant differences in blood pressure. Measurements under pressure were achieved without problems and matched intermittent measurement of brachial arterial pressure using the Korotkoff sounds. The modified system provides safe and stable continuous non-invasive blood pressure trends under both normobaric and hyperbaric conditions.