Nasal high flow (NHF) cannulae are used to deliver heated and humidified air to patients at steady flows ranging from 5-50 l/min. Knowledge of the airflow characteristics within the nasal cavity with NHF and during natural breathing is essential to understand the treatment's efficacy. In this thesis, the distribution and velocity of the airflow in the human nasal cavity have been mapped during natural and NHF assisted breathing with planar- and stereo-PIV in both steady and oscillatory flow conditions. Anatomically accurate transparent silicone models of the human nasal cavity were constructed using CT scan data and rapid prototyping. Breathing flowrates and waveforms were measured in vivo and dimensionally scaled by Reynolds and Womersley number matching to reproduce physiological conditions in vitro. Velocities of 2.8 and 3.8 m/s occurred in the nasal valve during natural breathing at peak expiration and inspiration, respectively; however on expiration the maximum velocity of 4.2 m/s occurred in the nasopharynx. Velocity magnitudes differed appreciably between the left and right sides of the nasal cavity, which were asymmetric. NHF modifies nasal cavity flow patterns significantly, altering the proportion of inspiration and expiration through each passageway and producing jets with in vivo velocities up to 20.8 m/s for 40 l/min cannula flow. The main flow stream passed through the middle airway and along the septal wall during both natural inspiration and expiration, whereas NHF inspired and expired flows remained high through the nasal cavity. Strong recirculating features are created above and below the cannula jet. Results are presented that suggest the quasi-steady flow assumption is invalid in the nasal cavity during both natural and NHF assisted breathing. The importance of using a three-component measurement technique when investigating nasal flows has been highlighted. Cannula flow has been found to continuously flush the nasopharyngeal dead space, which may enhance carbon dioxide removal and increase oxygen fraction. Close agreement was found between numerical and experimental results performed in identical conditions and geometries.

Nasal high flow (NHF) therapy is a recent form of non-invasive respiratory support for patients suffering from respiratory distress that supplies high flows of heated and humidified air, oxygen or a mix via a nasal cannula. A number of in vivo studies have proven its effectiveness at improving blood oxygenation; however, its mechanisms of action remain widely unproven. Two proposed mechanisms of action, the CO2 washout of anatomic dead space and the production of positive airway pressure, are investigated in this thesis for the use of the Fisher & Paykel Healthcare Ltd (FPH) Optiflow™ adult nasal cannula through a range of experiments. Five anatomically correct upper airway models produced from computed tomography (CT) scan data via 3D printing were employed during in vitro experiments and two live subjects participated in in vivo measurements. The human respiratory system was faithfully replicated for CO2 washout experiments with physiological CO2 diffusion into the lung replicated by a constant flow of CO2 into the lung pump. In vivo measurement of a natural breathing flow pattern was scaled to an average population tidal volume and respiratory rate for in vitro use. In vitro measurements of static pressure during natural breathing found similar flow resistances across the nasal passage for inspiratory and expiratory flow directions; however, across the entire upper airway greater resistance was seen for inspiration. Introduction of NHF therapy produced significant increases in all mean and peak airway pressures within the upper airway with a flow rate of 30 LPM fulfilling the inspiratory work requirements presented by the upper airway resistance. In vivo and in vitro hot wire anemometry measurements at the exterior nares indicated low velocity and turbulence intensity flows at peak inspiration and a high velocity jet with high turbulence during peak expiration. At natural breathing an in vitro anterior-posterior velopharynx traverse captured low turbulence intensities during peak inspiration and high turbulence intensities during peak expiration. Introduction of NHF therapy had little influence on the turbulence intensity profile of peak expiration yet did cause significant increases in the turbulence intensities during peak inspiration. Measurements of the CO2 concentration near the lung volume over many breath cycles were used to find time-averaged CO2 concentrations. For the standard airway model an average CO2 concentration of 4.88 ± 0.07 %V/V was determined during natural breathing. Implementation of increasing levels of NHF therapy generated significant washout of CO2 reducing this average concentration to a minimum of 3.81 ± 0.11 %V/V at a flow rate of 80 LPM. It was determined that airway geometry significantly affected the efficacy of the NHF therapy though CO2 washout was observed in all five airway models.

Sammanfattning Bakgrund: KOL är en obstruktiv lungsjukdom med luftflödesbegränsningar pga.  kronisk bronkit och emfysem. De patofysiologiska mekanismer är en progressiv inflammatorisk process som påverkar hela kroppen. De viktigaste behandlingsstrategierna är rökstopp, farmakologisk behandling samt fysisk träning.  Personer med KOL har ofta en nedsatt fysisk funktionsnivå, som inte behöver vara kopplad till sjukdomens svårighetsgrad.  De viktigaste fysioterapeutiska interventionerna för KOL är mätning av fysisk kapacitet, aerob- och muskelstärkande träning, tekniker för sekretmobilisering via motståndsandning samt undervisning i energibesparande arbetssätt. Interventionerna leder till förbättrad funktionsnivå, bromsar upp sjukdomen, minskar risken för samsjuklighet med andra icke smittsamma sjukdomar (NCD), minskar risken för execerbationer, förbättrad livskvalitet, samt minskar risken att dö för tidigt (6MWT >350 m).     God bålkontroll är central för en effektiv biomekanisk funktion i syfte att maximera kraft och minimera skaderisker. En bra bålkontroll har hos friska personer visats ha en positiv effekt på diafragmas funktion, samt att bålkontrollen påverkas av andningen vilket blir extra tydligt vid fysiskt ansträngande arbete.     Sambandet mellan bålkontroll, syrgasmättnad, fysisk funktion och självskattade symtom hos personer med KOL har enligt författarens kännedom inte studerats tidigare. Syfte: Studien syftar till att undersöka om fysisk aktivitet, med fokus på förbättrad bålstabilitet och sluten läppandning, kan förbättra syrgasmättnad, fysisk kapacitet, benmuskelstyrka, balans och självskattade symtom hos personer med KOL, stadium 2. Metod: Single subject experimental design (SSED) med AB design (baslinje undersökning – intervention) användes. Primärt utfallsmått var saturation och gångsträcka mätt med 6MWT. Sekundära utfallsmått var enbensstående balans, CS-30 samt CAT. Data på kvotskalenivå analyserades visuellt med stöd av 2-SD-bands analys och celerationslinje analys. Förändringar i CAT före och efter interventionen redovisas i procent. Resultat: Fyra personer inkluderades i studien. Resultatet visar en möjlig interventionseffekt avseende gångsträcka vid 6MWT och enbensstående balans för två av deltagarna, som vid studiestart låg under eller tangerade förväntade normalvärden i samtliga parametrar. En av dessa stabiliserades avseende lägsta värde på saturation vid 6MWT. Det fanns en effekt/möjlig effekt på förbättrad benstyrka (CS-30) för de deltagare som vid studiestart låg över förväntade normalvärden i samtliga parametrar. Självskattade lungsymtom (CAT) förbättrades hos tre av deltagarna (31–55 procent) och försämrades hon en av deltagarna (-17 procent). Konklusion: Studien visar en möjlig positiv effekt av bålstabiliserande träning på gångsträcka (6MWT), enbensstående balans, antalet uppresningar vid CS-30 samt självupplevda lungsymptom (CAT) för personer med KOL, stadium 2. Fler studier behövs för att stärka validiteten av dessa fynd. / Abstract Background: COPD is an obstructive pulmonary disease with air flow constraints due to chronic bronchitis and emphysema. The pathophysiological mechanisms are a progressive inflammatory process that affects the entire body. The main treatment strategies are smoking cessation, pharmacological treatment and physical exercise. People with COPD often have a reduced physical function level, which not need to be linked to the severity of the disease. The most important physiotherapeutic interventions for COPD are measurement of physical capacity, aerobic and muscle strength training, techniques for mobilization of sputum through resistance breathing techniques and teaching in energy-saving work methods. The interventions lead to improved functional levels, slow down the disease, reduce the risk of comorbidity with other non-communicable diseases (NCD), reduce the risk of exacerbation, improve quality of life, and reduce the risk to die prematurely (6MWT> 350m).     A well-functioning core stability is considered central to an effective biomechanical function to maximize strength and minimize risks of injury and has been shown by healthy individuals to have a positive effect on diaphragm function. It has also been shown that the ability to core-control is affected by deep breathing and especially during hard physical work.    A correlation between oxygen saturation, physical function, self-estimated symptoms and core stability in people with COPD, has to the knowledge of the author not been studied earlier.     Aim: The aim of the study was to investigate whether there are a correlation exercise together with improved core stability and pursed lip breathing, can improve oxygen saturation, physical capacity, leg muscle strength, balance and self-estimated symptoms in people with COPD in stage 2.Methodology: A single subject experimental design (SSED) with AB design (baseline survey - intervention) was used. As primary outcome saturation and walking distance measured at 6MWT were used. Secondary outcomes were CS-30, single balance and CAT. Data at nominal level were analyzed by using Two Standard Deviation Band Analysis and Celeration Line Analysis, Changes in CAT, pre- and post-intervention, was analyzed by percentage. Result: Four participants were included in the study. The result indicates a possible intervention effect regarding walking distance at 6MWT and single leg balance for two of the participants, who at study start were below or dropped below expected normal values in all parameters. One of these participants was stabilized for the lowest value of saturation at 6MWT. There was an effect/possible effect in the CS-30 for participants who at study start exceeded expected normal values in all parameters. Self-estimated symptoms (CAT) were improved in three participants (31–55 percent) and got worse in one participant (17 percent).Conclusion: The study indicates that core stability training focusing on improved motor control for stabilizing core muscles may have a positive effect on walking distance (6MWD) single leg balance, number of up rises in CS-30 and self-estimated lungsymptoms for people with COPD, stage 2. More studies are needed to validate these preliminary findings.