1. MECHANICS Of breathing/Tests of lung function
Aims:
How is breathing affected by changes in pressures, resistance, compliance and surface tension?
How do these factors change in respiratory disease?
What tests can be used to assess the function of the lungs?
How do you distinguish between an obstructive and a restrictive respiratory disease ? 2

2. MECHANICS PRESSURES - pleural, alveolar RESISTANCE - airways
COMPLIANCE - ability to expand
SURFACE TENSION - surfactant 2

3. PRESSURES
PLEURAL- Pressure between lungs and chest wall (-ve) =- 5cmH2O
lung elastic recoil pressure
lungs (visceral), chest wall (parietal)
lung tissuel inwards whilst chest wall outwards
I= more -ve; E= less -ve
ALVEOLAR- pressure within alveoli
I= PA -ve
E= PA +ve
THORAX= -ve pressure pump
ARTIFICIAL VENTILATION- +ve pressure at mouth, CPAP,NPPV
PNEUMOTHORAX-air entry into pleural space due to lung disease or chest wall injury; causes lung collapse, rib cage springs outward, diaphragm depressed 3

4. AIRWAYS RESISTANCE Raw= (mouth pressure-PA)/ airflow
40-50% of resistance in upper airways- nose, pharynx,larynx
majority of the remainder (40%) in trachea and medium size bronchi(div. 1-8, 2-4mm), rest in size 1-2mm
INCREASED- smooth muscle contraction, falls in lung volumes, secretions, obstructive disease, mediators, histamine, air pollution, PNS (Ach)
DECREASED- smooth muscle relaxation, bronchodilators, nitric oxide, increase in lung volumes 4

5. COMPLIANCE Ability to distend lungs
change of lung volume/change of pressure
0.2 l/cmH2O
increased- age, emphysema, lung size, low volumes and low pressures
decreased- oedema, atelectasis, fibrosis, at high lung volumes and pressures, high pulmonary venous pressures, supine 5

6. SURFACE TENSION Force- produced at a gas/liquid interface
collapse of alveoli in lungs
pulls fluid from capillaries into alveoli- stiff lungs
smallest alveoli - largest surface tension
LAPLACE’S LAW- pressure  1/radius
SURFACTANT (dipalmitoyl lecithin)- complex lipoprotein
surface tension
produced by type II cells
prevents collapse of alveoli, keeps alveoli dry
normally secreted by 22 weeks in foetus
lack- infant respiratory distress syndrome (RDS)
RDS- atelectasis, fluid in lungs, decreased compliance
ARDS - adult RDS 6

7. RESPIRATORY INVESTIGATIONS
SYMPTOMS-chest pain, cough, sounds, breathlessness
ANATOMICAL- sputum,CXR, blood, bronchoscopy, scans (PET, CT, MRI)
PHYSIOLOGICAL- skin prick tests, blood gases, exercise tests, spirometry (LUNG FUNCTION TESTS) 1

8. LUNG FUNCTION TESTS TESTS OF FORCED EXPIRATION
FEV1, FVC, PEF, FEV1/FVC ratio
Effort dependent
Obstructive & Restrictive
TLC, RV, FRC, Raw
GAS TRANSFER- TCO, KCO
FLOW-VOLUME LOOPS
Vitalographs, spirometers
Body plethysmographs
COTES, J.E. (1993). LUNG FUNCTION. Blackwell Scientific Publications.
QUANJER, Ph. H et al (1993). LUNG VOLUMES AND FORCED VENTILATORY FLOWS. EUR RESPIR. JOURNAL, SUPPL 16, 5-40.

9. LUNG VOLUMES SPIROMETER- SPIROGRAM VOLUMES Tidal volume (VT) - 0.5l
Inspiratory capacity(IC)-3.6l
Inspiratory reserve volume (IRV)- 3.1l
Expiratory reserve volume (ERV)-1.2l
Functional residual capacity (FRC)- 2.4l
vital capacity (VC) - 4.8l
Residual volume (RV)- 1.2l
Total lung capacity (TLC) - 6l
VOLUMES
Body size, Age,
Sex, Muscular Training
Ethnicity, Diseases

10. FRC 40% OF TLC, 10% less in females,  height IMPORTANCE: VARIATION:
Minimum amount of air for gas exchange at all times
Keeps alveoli & small air tubes open after expiration
Provides stability of oxygen pressure (PO2)
VARIATION:
Obesity, pulmonary fibrosis, kyphoscoliosis, supine
standing, decreased elastic recoil

11. CONCLUSIONS
1. The work of breathing is increased by compliance and resistance & surface tension.
2. Changes in pleural and alveolar pressures are essential in creating pressure gradients and thus airflow, inflation and deflation of lungs.
3. Obstruction of airways(e.g mucus, bronchoconstriction), oedema, atelectasis and fibrosis resistance, surface tension and compliance of lungs.
4. Lung function assessed by anatomical (eg Bronchoscopy, CXR) and physiological tests (eg blood gases, expiratory tests).
5. Obstructive diseases-airways obstruction(mucus, smooth muscle enlargement, airway hypersensitivity), thus FEV1,PEF & FEV1/FVC.
6. Restrictive diseases-impairment of lung inflation( muscular, rib cage), thus VC,TLC, same or FEV1/FVC.