1. Lung Mechanics
Lung Compliance (C)
Airway Resistance (R)

3. Determinants of CL
Stretchability of the lungs
Surface tension (type II alveolar cells secrete surfactant which lowers surface tension and increases CL)
Respiratory-distress syndrome of the newborn (surfactant is deficient)

4. Some important facts about pulmonary surfactant
1. A mixture of phospholipids and protein
2. Secreted by type II alveolar cells
3. Lowers surface tension of the water layer at the alveolar surface, increases lung compliance
4. A deep breath increases its secretion (by stretching the type II cells)
5. Concentrations decreases when breaths are small

5. Airway Resistance (R)
Inversely proportional to the fourth power of the airway radii
Physical factors: transpulmonary pressure lateral traction (mucus accumulation)
Neuroendocrine factors:
bronchodilators- Epinephrine (b receptor), VIP
bronchoconstrictors- leukotrienes, histamine, ACh

6. Pathological conditions of airway resistance
Asthma: treated with anti-inflammatory drugs, bronchodilator drugs
Chronic obstructive pulmonary disease (COPD):
1. emphysema (destruction of alveolar walls)
2. chronic bronchitis (excessive mucus production in the bronchi and chronic inflammatory changes in the small airways)
3. a combination of the two

7. Lung volumes and capacities

8. Lung volume and capacities
Lung Volumes
Tidal volume (VT): 500 ml
Inspiratory reserve volume (IRV): 3000 ml
Expiratory reserve volume (ERV): 1500 ml
Residual volume (RV): 1000 ml
Lung Capacities
Vital capacity (VC) = VT +IRV+ERV
Functional residual capacity (FRC) = RV+ERV
Inspiratory capacity (IC) = VT+IRV
Total lung capacity (TLC) = FRC+IC

9. Ventilation VE=VT x f VE: minute ventilation (l/min)
VT: tidal volume (l)
f: respiratory frequency (cpm)

10. Alveolar Ventilation (VA)
VE=VT x f
the total volume of fresh air entering the alveoli per minute
VA =(VT – VD) x f

11. Dead Space (VD)
Definition: the space within them gas exchange is not permitted
Anatomical dead space: conducting airways
Alveolar dead space: some fresh inspired air is not used for gas exchange if the alveoli have little or no blood supply
Physiological dead space: the sum of the anatomical and physiological dead spaces

12. Effects of VD on VA

13. Effect of breathing patterns on alveolar ventilation

14. FEV1: forced expiratory volume in 1 sec
FVC: forced vital capacity
Obstructive lung diseases: increased airway resistance
Restrictive lung diseases: impaired respiratory movements because of abnormalities in the lung tissue, the pleura, the chest wall, or the neuromuscular machinery

15. Examples:

16. Gas Exchange

17. Respiratory Quotient (RQ)
(in the steady state)
RQ = VCO2/VO2
1 for carbohydrate
0.7 for fat
0.8 for protein or mixed diet

18. Typical O2 and CO2 exchanges during 1 min at rest

19. The individual pressures in a mixture of gases; eg, PO2, PCO2
Partial Pressure
The individual pressures in a mixture of gases; eg, PO2, PCO2
Dalton’s law
In a mixture of gases, the pressure exerted by each gas (x) is independent of the pressure exerted by the others
Px = P x Fx

20. Partial pressures of CO2 and O2

21. Alveolar gas pressure
Factors that determine PAO2 PO2 of inspired air VA O2 consumption
Factors that determine PACO2 VA VCO2

25. Gas exchange (Diffusion)