1. CS 2016 Pulmonary Pressures and Volumes Christian Stricker Associate Professor for Systems Physiology ANUMS/JCSMR - ANU Christian.Stricker@anu.edu.au http://stricker.jcsmr.anu.edu.au/LungPV.pptx Christian.Stricker@anu.edu.au http://stricker.jcsmr.anu.edu.au/LungPV.pptx THE AUSTRALIAN NATIONAL UNIVERSITY

2. CS 2016

3. Aims At the end of this lecture students should be able to demonstrate the thoracic changes with breathing; locate inspiratory and expiratory muscles; identify different static volumes and capacities; explain sequence by which pressure changes arise; recognise intrathoracic pressures and differences; and discuss the concepts of airway resistance and static lung compliance.

4. CS 2016 Contents Respiratory muscles Static lung volumes Changes during aging Intrapleural pressure (P pl ) Pneumothorax Generation of intrathoracic pressures 3 ways to ventilate the lungs Air way resistance V-P relationship: lung compliance

5. CS 2016 Thorax during In- and Expiration Modified from Schmidt/Thews 1977 Inspiration –Lowering of diaphragm –Lifting up of thorax –Widening of thorax Expiration –Relaxation of diaphragm –Lowering of thorax –Narrowing of thorax Volume change: ~4 L (vital capacity).

6. CS 2016 Breathing Muscles Modified from Hlastala & Berger 2001

7. CS 2016 Modified from Boron & Boulpaep, 2003 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; it’s measurement is not simple (see Block 2). Need training/coaching to achieve maxima.

8. CS 2016 Static Lung Capacities Modified from Boron & Boulpaep, 2003 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).

9. CS 2016 Properties of Static Volumes Dependent on –age (VC 90 ~ 0.5 VC 40 ), –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. CS 2016 Thorax - Lung System 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”. http://www.nlm.nih.govHillig et al. (2007) Intern. J. Rheumatol. 3:1

11. CS 2016 Recoils and Intrapleural Pressure Situation at FRC: –Thorax tends to expand. –Lung tends to collapse. –Generates negative intrapleural pressure. –FRC: Recoil L = -Recoil Th. Intrapleural pressure (P pl ) in a virtual space (between 2 pleurae): –~ –5 cm H 2 O (FRC). –space/volume ~ 0 mL. –keeps lungs unfolded and thorax under tension. Modified from Boron & Boulpaep, 2003

12. CS 2016 Intrapleural Pressure (P pl ) However, hydrostatic pressure difference between apex and base of lung: generated by blood column in lung tissue. P pl determined by –posture (upright vs laying) and –height within thorax. Measured clinically in oesophagus (P oe ≥ P pl ). P oe and P pl dependent on height of measurement: at top < at base. P pl remains negative at TV, but can become positive (forced expiration - sneezing). Modified from Boron & Boulpaep, 2003

13. CS 2016 Pneumothorax Opening of chest wall and/or visceral pleura leads to P pl ≈ 0 with air exchange: lung collapses - pneumothorax. If openings pass air when P pl 0 (exp.); over time P pl » 0: tension pneumothorax. Therapy: re-establishing P pl < 0 (surgery Y3/4). Modified after Boron & Boulpaep, 2003

14. CS 2016 Primary Static Lung Pressures P b = barometric pressure. = 101.3 kPa = 760 torr. = reference pressure (~ 0). = “constant” during I/E. P A = 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. P pl = intrapleural pressure. = variable during I/E. Modified from Boron & Boulpaep, 2003

15. CS 2016 Composite Static Lung Pressures (always take “inside view”). P L = translung pressure. = transpulmonary pressure. = transmural pressure across lung. –Typically positive with tidal breathing. –at FRC: P L = 0 - P pl (thorax recoil). –Determines the lung volume. –Larger during I than during E. P w = transthoracic pressure. = Pressure across thorax wall. P rs = resp. system pressure. net recoil of resp. system when airflow = 0 (end of I & E). = net recoil of resp. system when airflow = 0 (end of I & E). Modified from Boron & Boulpaep, 2003

16. CS 2016 Generation of Pressures Modified from Boron & Boulpaep, 2003 What generates P A ? When glottis is closed, increase in thoracic volume causes decrease in P A. –V 1 (FRC) = 3 L; P A1 = 101.3 kPa –V 2 (TV) = 3.5 L; P A2 = ? If glottis opens, air flows into lungs, not instantaneously, but over time: flow over considerable airway resistance.

17. CS 2016 3 Ways to Ventilate Lung Muscle force: P L –Normal breathing. P Mouth > P b : –P Mouth - P A : pressure along airways (drives air). –Ventilation with positive external pressure (bag, mouth- to-mouth, etc.). P S < P b : –Requires tight seal around neck. –Ventilation with negative outsi- de thorax pressure (iron lung). Modified from Boron & Boulpaep, 2003

18. CS 2016 Flow in airways follows Ohm’s law: What determines R AW ? –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). Air Flow into Lungs Modified from Boron & Boulpaep, 2003

19. CS 2016 Relationship between P and V Modified from Boron & Boulpaep, 2003 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).

20. CS 2016 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. P pl varies with the hydrostatic pressure/level. Change in P L causes a change in V L. Air flow is limited by R AW. Lung compliance (C L ) relates V L to P L.

21. CS 2016 MCQ Which of the following statements best describes the functional residual capacity (FRC)? A.It is the lung volume after a forced expiration. B.It is the lung volume between total lung capacity and residual volume. C.It is the lung volume after a tidal expiration. D.It is the lung volume change between maximal expiration and inspiration. E.It is the lung volume comprising tidal volume and inspiratory reserve volume.

22. CS 2016 That’s it folks…

23. CS 2016 MCQ Which of the following statements best describes the functional residual capacity (FRC)? A.It is the lung volume after a forced expiration. B.It is the lung volume between total lung capacity and residual volume. C.It is the lung volume after a tidal expiration. D.It is the lung volume change between maximal expiration and inspiration. E.It is the lung volume comprising tidal volume and inspiratory reserve volume.