Monitoring the respiratory rate is important during procedural sedation. Several methods of measuring the respiratory rate are available, but most are unreliable and the most reliable method (capnography) is not available during the use of High Flow Nasal Cannula (HFNC) oxygen. We hypothesize that measuring the pressure variation in the HFNC-circuit is a reliable method of measuring the respiratory rate.

An experimental study, using healthy volunteers that will breath in three guided respiratory rates, compares the measurements of respiratory rate by the pressure variation in the HFNC circuit with measurements of respiratory rate by an ECG-derived method and a manual count by an physician.

A secondary outcome will be the ability to measure the size of pressure difference, in order to determine its feasiblity to use it as a surrogate for tidal volume or respiratory effort.

The healthy volunteers will be administered HFNC-oxygen and will be instructed to breath normally, rapidly and slowly for 30 seconds. This will be done at two HFNC flow rates (35 L/min and 70 L/min) and with an open and a closed mouth. During these 30 seconds the respiratory rate will be measured by pressure variation in the HFNC circuit, ECG-derived impedance difference and a manual count by a physician.

This will lead to 12 conditions, depending on HFNC flow (35 and 70 L/min), open or closed mouth and respiratory rate (normally, rapidly, slowly). The measurements of the respiratory rates wil be compared per HFNC flow and per open or closed mouth.

A secondary outcome will be the ability to measure the size of pressure difference, in order to determine its feasiblity to use it as a surrogate for tidal volume or respiratory effort.

Inclusion Criteria:

• healthy volunteers

Exclusion Criteria:

• known neurodegenerative diseases
• Pregnancy
• Children (age <18)
• Upper airway obstruction

Available upon reasonable request.

Within 2 years

Available upon reasonable request.