| Background and Objective:From the point of view of machine construction and hydrodynamics,this paper innovatively proposes that the essence of high-flow nasal cannula(HFNC)is a constant-flow mode of non-invasive ventilator(NIVCFM).Due to the mechanisms of nasopharyngeal dead-space wash out and generating a low level airway pressure,NIVCFM/HFNC has been used to treat many respiratory diseases.But further and accurate evidence is needed,especially in adults.Therefore,this study enrolled healthy adults as study subjects to validate the mechanisms and assess the comfort of NIVCFM/HFNC.Aiming to provide a scientific basis for the rational clinical application of NIVCFM/HFNC.Material and Methods:44 healthy adults participated in this study.PetCO2 at the depths of 2,3,4,5cm of the nasal cavity,EEP and EIP at the depths of 2,3,4,5,6cm of the nasal cavity were measured during NIVCFM/HFNC delivered different flow rates to validate the mechanisms of NIVCFM/HFNC.In addition,the noise generated by different flow rates of the ventilator is measured and the comfort of the ventilator at different flow rates is evaluated.The ventilator’s flow rates were set to 0,5,10,15,20,25,30,35,40,45,50,55 and 60L/min.The descriptive statistical analysis of the observed indicators was conducted.The observation indicators were compared by the Kruskal-Wallis nonparametric test or the one-way variance analysis.Fourier function-fitted curves were used to analyze the trend of the observed indicators with ventilator flow rates at different depths of nasal cavity.Results:The results of descriptive analysis showed that when the flow of NIVCFM/HFNC was 60 L/min,the PetCO2 at the 2cm of nasal cavity was 30.2 mmHg、14.9mmHg、8.2mmHg、8.3mmHg respectively.The maximum EEP and EIP of NIVCFM/HFNC were 6.5 cmH2O and 2.9 cmH2O respectively,and the maximum noise was 65.9dB.The mean values of mouth、nasal or pharynx dryness score,dysphagia score,dyspnea score,sore throat score,and other discomfort score were:0.43±0.70,0.48±0.82,1.57±1.13,0.09±0.47,0.61±0.90 respectively when the flow rate was 60L/min.The results of the comparison analysis showed that:At the same depth of nasal cavity,compared with OL/min,PetCO2 had a statistical difference when NIVCFM/HFNC’s flow rate≥20L/min;EEP had a statistical difference when NIVCFM/HFNC’s flow rate≥10L/min;EIP had a statistical difference when NIVCFM/HFNC’s flow rate>15L/min.When the flow rate was the same,there was little difference between EEP and EIP at other depths of nasal cavity compared with 2cm of nasal cavity.There was a statistical difference in PetCO2 at 3 cm,4cm,5cm of nasal cavity but not between PetCO2 at 3 cm,4cm,5cm of nasal cavity.There was a statistical difference in noise level when the flow rate≥15 L/min compared with OL/min.Fourier function curve fitting results showed that there was a nonlinear negative correlation between PetCO2 and the flow rates,and a nonlinear positive correlation between the EEP,EIP,noise level and the flow rates.Conclusions:1.The NIVCFM/HFNC has very limited washing effect on end-expiratory CO2 after nasal limen in healthy adults,and as the depth deepens,the flushing effect on end-expiratory CO2 decreases rapidly.2.The NIVCFM/HFNC can only produce low level EEP(<6.6 cmH2O)and low level EIP(<3.0 cmH2O)in the nasal cavity of healthy adults when breathing with the mouth closed.3.With the increase of flow rate,the PetCO2 decreases,while the EEP and EIP increase,and all of them are nonlinear.4.The grater the flow rate,the greater the noise generated by the ventilator(<65.9dB).5.The maximum flow rate that most healthy adults can able to tolerate is 30 L/min,and the main discomfort is dyspnea. |
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