1 / 23

THE AUSTRALIAN NATIONAL UNIVERSITY

THE AUSTRALIAN NATIONAL UNIVERSITY. Pressure Changes and Airflow during Breathing Christian Stricker Associate Professor for Systems Physiology ANUMS/JCSMR - ANU Christian.Stricker@anu.edu.au http:/ /stricker.jcsmr.anu.edu.au/Airflow.pptx. Respiratory Part in Block 2. Week 8 Airflow

eshe
Download Presentation

THE AUSTRALIAN NATIONAL UNIVERSITY

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. THE AUSTRALIAN NATIONAL UNIVERSITY Pressure Changes and Airflow during BreathingChristian StrickerAssociate Professor for Systems PhysiologyANUMS/JCSMR - ANUChristian.Stricker@anu.edu.auhttp://stricker.jcsmr.anu.edu.au/Airflow.pptx

  2. Respiratory Part in Block 2 • Week 8 • Airflow • Week 9 • Mechanical properties of lung / thorax. • Spirometry practical • Pulmonary ventilation • Pulmonary perfusion and matching of perfusion with ventilation • Week 10 • Respiratory control and regulation • Respiratory regulation practical • Week 12 • Wrap-up of Block 2

  3. Aims At the end of this lecture students should be able to • discuss different types of spirometers; • outline how flows, volumes & pressures are measured; • illustrate the phases of the respiratory cycle and what determines them; • define forced volumes and peak flows; • recognise some important features in a flow-volume loop; and • explain the P-V work during respiration.

  4. Contents • Measuring techniques • How to measure RV • Repetition of volumes/pressures • Respiratory cycle • Forced volumes and peak flows • Flow-volume curves • P-V (V-P) work and its optimisation

  5. Static Lung Volumes • Measured with a spirometer. • Static volumes (no flow): only maximal values relevant. • Volumes = cannot be broken down any further. • Capacities ≥ 2 volumes. • TLC reached with maximal inspiration. • RV reached with maximal expiration. • FRC reached when in- and expiratory muscles are “relaxed” (training). • Need training to achieve maxima (coaching). Modified from Boron & Boulpaep, 2003

  6. Bell Spirometers • Bell dome filled with air and immersed in water (separation). • Oldest spirometer type, still used. • Different makes and variants. • Pros: • Direct volume measurement. • Very precise when well adjusted. • Allows for measurements of O2 uptake (metabolic studies). • Cons: • Poor dynamics due to inertia; no flow measurements possible. • Expensive (several K AU$). Wintrich, 1854

  7. Pneumotachographs • Modern spirometers (Lilly; used in practical): measure flow. • Based on Ohm’s law: • ΔP = RI (I = flow = V / Δt). • Volumeobtained by integration. • Pros: • Excellent dynamic response. • Cheap (few 100’s AU$). • Cons: • “Fiddly” - as small pressure changes can cause “drifts” (T). • Need repeated calibrations. • Need a computer. http://www.spirxpert.com/technical3.htm

  8. How to Measure RV (TLC) • Body plethysmograph. • Insp → air flow → ΔV → ΔP. • From ΔPBox, PAand FRC are determined. • If Ppl measured (oesoph.), all respiratory pressures known. • Allows RAWestimation: Modified from Boron & Boulpaep, 2003

  9. Another Method for RV • Helium dilution technique • Requires [He] to be measured. • TLV can be estimated if initial [He] and that after equilibration are known. • Simple and effective method • Problem: Small amount of He is dissolved in plasma → over-estimates of true volume (correction required).

  10. Important Pressures • (always take “inside view”). • Pb = barometric pressure. • Ppl= intrapleural pressure. • PA (alveolar pressure) = 0 at beginning/end of in-/expiration (FRecoil = FThorax). • Volume corresponds to FRC (when all muscles are relaxed). • PL = translung pressure. • Pw = transthoracic pressure. • Prs = resp. system pressure. Modified from Boron & Boulpaep, 2003

  11. Respiratory Cycle within TV Modified from Boron & Boulpaep, 2003 • FRC: Ppl = -PL (no muscle force). (PA=Ppl+PL; PA= 0) • Inspiration: muscles contract (-2.5 cm H2O) →Ppl↓ and-PL↓lags (due to RAW & CL): PA < 0 → air flow into alveoli. • End of I / start of E: Ppl = -PL, but at a larger magnitude. • Expiration: muscles relax → recoil of system →Ppl↑ with lagging-PL↑: PA > 0 → air flow out of alveoli. • 2 parts ofPpl: (Ppl=PA-PL) • PA : air flow. • PL : lung volume (integrated flow).

  12. Reasons Why -PLLags Ppl • There are two major factors: • Airway resistance (RAW) • Total compliance (CT) • Characteristic time (τ) is product: τ = RAW·CT. • For influence of each factor see next lecture. • See also influence on ventilation (later).

  13. Forced/Large Respiratory Cycle • Pmus = 27 cm H2O causes inspiration to ~90% TLC. • Similar story as before. • Muscles build-up considerable recoil: energy not only in elastic lung/thorax tissue, but also in muscles. • At >60% TLC, considerable pressures generated by muscles, which can render thorax recoilinward at end of inspiration. Modified from Hlastala & Berger 2001

  14. Forced Volumes & Peak Flow • Dynamic volumes important in evaluating RAW. • Training required. • Best out of 3 trials. E for 10 s (count down!). • Peak flows: PEF and PIF • PEF more sensitive to RAW. • PIF is normally > PEF (airway distension - next). • FEV1 and FVC (more dynamic) • FEV1 good test of RAW. • FVC > VC (acceleration). Modified from Boron & Boulpaep, 2003

  15. Flow-Volume Diagram • Air flow is plotted against volume change from maximal filling (TLC): 0 @ TLC; maximum = RV; span = FVC. • Maximal efforts required to have indicative curves (training). • Expiration above and inspiration below zero flow. • PEF reached ≥ 20% volume. • Expiratory flow rates at < 2 L are effort dependent: muscle. • Expiratory flow rates at > 2 L are effort independent: limited by lung/thorax elasticity & RAW. Berne et al., 2008

  16. TV and Different Efforts • TV in “middle” of graph. • Inspiratory part of loop unimportant. • Detailed interpretation given later. • Make sure that person puts in best effort (judge it…). • Effort-independent region: flow determined by RAW and recoil / CT. Berne et al., 2008

  17. Respiratory Work - V-P Loop • Inspiration: Winsp + Wela (“loading of recoil”). • Expiration: Wexp - Wela (recoil at TV is sufficient). • For volumes > TV, Wmus(exp) becomes more important.

  18. Optimisation of Respiration • Resistive work↑ with respiratory rate as flow↑(transitional flow). • Elastic work↓ with respiratory rate (time constant of recoil). • Elastic work (Wela) at mimimum~ 30 bpm (“resonance” of elastic system). • Minimum of total work at ~ eupnoea (12 – 20 bpm). Berne et al., 2004

  19. Take-Home Messages • Several methods to measure volumes and pressure; all have their place in clinical practice. • Pneumotachography and He-dilution allow measurement of RV and TLC. • Intrapleuralpressure (Ppl) has 2 components: • PAdetermining flow; and • PL determining volume. • PLlags behind -Pplduring respiratory cycle. • Air flow into lung is determined byRAW and CT. • V-P loop indicates external work during respiration: • at TV: expiration is passive; inspiration via muscle force. • Flow-volume loop reveals most dynamic aspects.

  20. MCQ A 17 year-old woman presents to emergency with an acute asthma exacerbation of moderate severity. Which of the following sets of lung function tests best describes her current condition? • Decreased FVC, FEV1, FEV1/FVC, PEF and increased RV. • Decreased FVC, FEV1, PEF and normal FEV1/FVC, RV. • Decreased FVC, FEV1, FEV1/FVC, and increased PEF, RV. • Decreased FVC, FEV1, PEF and increased FEV1/FVC, RV. • Decreased FVC, FEV1, FEV1/FVC and normal PEF, RV.

  21. That’s it folks…

  22. MCQ A 17 year-old woman presents to emergency with an acute asthma exacerbation of moderate severity. Which of the following sets of lung function tests best describes her current condition? • Decreased FVC, FEV1, FEV1/FVC, PEF and increased RV. • Decreased FVC, FEV1, PEF and normal FEV1/FVC, RV. • Decreased FVC, FEV1, FEV1/FVC, and increased PEF, RV. • Decreased FVC, FEV1, PEF and increased FEV1/FVC, RV. • Decreased FVC, FEV1, FEV1/FVC and normal PEF, RV.

More Related