Article Figures & Data
Figures
- Fig. 1.
The high flow nasal cannula (HFNC) system incorporated an air/O2 blender with a flow meter and a heated humidifier. For the HFNC protocols, nasal prongs were connected to the manufacturer's standard circuit. We made 2 holes in a polyvinyl chloride cylinder to simulate adult external nares. The external nares were connected to the TTL test lung via a standard ventilator circuit. Spontaneous breathing was simulated using a mechanical ventilator and TTL test lung. To simulate spontaneous breathing, the muscle and lung compartment of the test lung were connected; consequently, the mechanical ventilator inflated the muscle compartment, whereupon the lung compartment inspired, along with ambient air, medical gas delivered, in turn, via each of the HFNC prongs and a conventional low-flow cannula. To monitor VT delivered to the lung compartment, flow to the lung compartment was measured using a pneumotachometer with a differential pressure transducer. Inspired gas downstream of the external nares was measured using an oxygen analyzer.
- Fig. 2.
Effect of changing VT and flow during high-flow nasal cannula (HFNC) with FIO2 of 0.3 (A), 0.5 (B), and 0.7 (C). With HFNC flows of 20 and 40 L/min, measured FIO2 was affected by VT at all FIO2 settings. With HFNC flow of 60 L/min, measured FIO2 was not affected by VT when FIO2 was set at 0.3 and 0.5; when FIO2 was set at 0.7, however, as VT increased, measured FIO2 decreased. *, P < .01.
- Fig. 3.
Effects of changing VT and flow during low-flow oxygen delivery As VT increased, measured FIO2 decreased significantly at all flow settings. *, P <.001.
