THE AUSTRALIAN NATIONAL UNIVERSITY

1. THE AUSTRALIAN NATIONAL UNIVERSITY Pulmonary Pressures and VolumesChristian StrickerAssociate Professor for Systems PhysiologyANUMS/JCSMR - ANUChristian.Stricker@anu.edu.auhttp://stricker.jcsmr.anu.edu.au/LungPV.pptx

3. Aims The students should • appreciate the thoracic changes with breathing; • be able to name inspiratory and expiratory muscles; • know different static volumes and capacities; • be cognisant of the sequence by which pressure changes arise; • know intrathoracic pressures and differences; and • be aware of the concepts of airway resistance and static lung compliance.

4. Contents • Respiratory muscles • Static lung volumes • Changes during aging • Intrapleural pressure (Ppl) • Pneumothorax • Generation of intrathoracic pressures • 3 ways to ventilate the lungs • Air way resistance • V-P relationship: lung compliance

5. Thorax during In- and Expiration • Inspiration • Lifting up of thorax • Widening of thorax • Lowering of diaphragm • Expiration • Lowering of thorax • Narrowing of thorax • Relaxation of diaphragm • Volume change: ~4 L (for the vital capacity). Modified from Schmidt/Thews 1977

6. Breathing Muscles Modified from Hlastala & Berger 2001

7. Static Lung Volumes • Measured with spirometry. • Static volumes (no flow): only maximal/peak values relevant. • Volumes cannot be broken down any further. • RV reached with maximal expiration; measurement not simple (see Block 2). • Need for training to achieve maxima (coaching). Modified from Boron & Boulpaep, 2003

8. Static Lung Capacities • Capacities = ≥ 2 volumes. • VC is volume exchanged with maximal expiration followed by maximal inspiration (or vice versa). • FRC reached when in- and expiratory muscles are “relaxed” (training).= TLC - IC = RV + ERV. • TLC reached with maximal inspiration.= VC + RV (not simple to determine). Modified from Boron & Boulpaep, 2003

9. Properties of Static Volumes • Dependent on • age (VC90 ~ 0.5 VC40), • sex (male > female), • body height, and • race. • Varies between populations/countries. • Standards available for each population /country. • See spirometry practical for Oz values. after Schmidt/Thews 1977

10. Thorax - Lung System http://www.nlm.nih.gov Hillig et al. (2007) Intern. J . Rheumatol. 3:1 • Thorax is kept under tension such that it bursts open when lacerated (elastic recoil to outside). • Lung has a tendency to collapse if exposed to barometric pressure (elastic recoil to inside). • Two recoils are in “balance” during breathing: system kept in intermediate “position”.

11. Recoils and Intrapleural Pressure • Situation at FRC: • Thorax tends to expand. • Lung tends to collapse. • Generates negative intrapleuralpressure. • FRC:RecoilL = -RecoilTh. • Intrapleural pressure (Ppl) in a virtual space (between 2 pleurae): • ~ –5 cm H2O (FRC). • space volume ~ 0 mL. • keeps lungs unfolded and thorax under tension. Modified from Boron & Boulpaep, 2003

12. Intrapleural Pressure (Ppl) • However, hydrostatic pressure difference between apex and base of lung: generated by blood column in lung tissue. • Ppldetermined by • posture (upright vs laying) and • height within thorax. • Measured clinically in oesophagus (Poe ≥ Ppl). • Poe and Ppl dependent on height of measurement: at top < at base. • Ppl remains negative at TV, but can become positive (forced expiration - sneezing). Modified from Boron & Boulpaep, 2003

13. Pneumothorax • Opening of chest wall and/or visceral pleura leads to Ppl ≈ 0 with air exchange: lung collap-ses - pneumothorax. • If openings pass air when Ppl < 0 (insp.), but close when Ppl > 0 (exp.), over time Ppl » 0: tension pneumothorax. • Therapy: re-establishing Ppl < 0 (surgery Y3/4). Modified after Boron & Boulpaep, 2003

14. Primary Static Lung Pressures • Pb = barometric pressure. = 101.3 kPa = 760 torr. = reference pressure (~ 0). = “constant” during I/E. • PA = alveolar pressure. = 0 = no air flow in bronchi. = 0 at beginning of I. = @ FRC (mus. relaxed). = 0 at beginning of E. = muscles produce force. = variable at other times. • Ppl= intrapleural pressure. = variable during I/E. Modified from Boron & Boulpaep, 2003

15. Composite Static Lung Pressures • (always take “inside view”). • PL= translung pressure. = transpulmonary pressure. = transmural pressure across lung. • Typically positive with tidal breathing. • at FRC: PL = 0 - Ppl(thorax recoil). • Determines the lung volume. • Larger during I than during E. • Pw= transthoracic pressure. = Pressure across thorax wall. • Prs= resp. system pressure. = net recoil of resp. system when airflow = 0 (end of I & E). Modified from Boron & Boulpaep, 2003

16. Generation of Pressures • What generates PA? • When glottis is closed, increase in thoracic volume causes decrease in PA. • V1(FRC) = 3 L; PA1 = 101.3 kPa • V2(TV) = 3.5 L; PA2 = ? • If glottis opens, air flows into lungs, not instantaneously, but over time: flow over con-siderable airway resistance. Modified from Boron & Boulpaep, 2003

17. 3 Ways to Ventilate Lung • Muscle force: PL • Normal breathing. • PMouth> Pb: • PMouth- PA: pressure along airways (drives air). • Ventilation with positive external pressure (bag, mouth-to-mouth, etc.). • PS < Pb: • Requires tight seal around neck. • Ventilation with negative outside thorax pressure (iron lung). Modified from Boron & Boulpaep, 2003

18. Air Flow into Lungs • Flow in airways follows Ohm’s law: • What derminesRAW? • Smallest bronchi (similar to vessels). • Not only diameter, but also flow important (Block 2). • Larynx. • For tidal breathing, inspiration active, expiration passive (thorax/lung & muscle recoil). Modified from Boron & Boulpaep, 2003

19. Relationship between P and V • Which relationship describes lung volume and pressure? • If airflow = 0, static compliance. • Compliance • Measure of “ease of inflation”. • “Linear” in range of TV. • Inverse of “elastance”: E = 1/C. • Lungs with a large compliance have a small elastic lung recoil (emphysema…), and vice versa (pulmonary fibrosis). Modified from Boron & Boulpaep, 2003

20. Take-Home Messages • FRC is reached when all muscles are relaxed. • VC is ~ 4 L; RV cannot be measured directly. • Lung capacities are made up of ≥ 2 volumes. • Intrathoracic pressures determine lung volume. • At FRC, recoils of thorax and lung are balanced. • Pplvaries with the hydrostatic pressure/level. • Change in PL causes a change in VL. • Air flow is limited by RAW. • Lung compliance (CL)relates VL to PL.

21. MCQ Which of the following statements best describes the functional residual capacity (FRC)? • It is the lung volume after a forced expiration. • It is the lung volume between total lung capacity and residual volume. • It is the lung volume after a tidal expiration. • It is the lung volume change between maximal expiration and inspiration. • It is the lung volume comprising tidal volume and inspiratory reserve volume.

22. That’s it folks…

23. MCQ Which of the following statements best describes the functional residual capacity (FRC)? • It is the lung volume after a forced expiration. • It is the lung volume between total lung capacity and residual volume. • It is the lung volume after a tidal expiration. • It is the lung volume change between maximal expiration and inspiration. • It is the lung volume comprising tidal volume and inspiratory reserve volume.