This document discusses mechanical ventilation and the mechanics of breathing. It explains that breathing can occur spontaneously through the work of respiratory muscles, or through positive pressure ventilation using devices like endotracheal tubes. The balance between the lungs' elastic recoil inward and the chest wall's recoil outward determines the lung volume. Transpulmonary pressure, the difference between alveolar and pleural pressures, controls lung volume and inflation. Boyle's law states that for a fixed amount of gas, pressure and volume are inversely proportional.

1. Mechanical Ventilation – 01
Fakhir Raza Haidri
SIUT
23-September-2020

2. Ventilation
• In and Out of Air

3. Spontaneous Breathing
• Movement of air into and out of the lungs as a result of work done by
an individual’s respiratory muscles.

4. Positive pressure ventilation
• The movement of air into the lungs by the application of positive
pressure to the airway through an endotracheal tube, tracheostomy
tube, or noninvasive mask.

5. Composition of Lung
• Lungs – Elastic Tissue -
Tendency to recoil inwards
• Chest Wall – Tendency to
spring outwards
• Pleural Space – Potential
space between Chest wall
and Lungs

6. Pleural Pressure (Ppl)
• At the end of the expiration it is negative (less then atmospheric
pressure)
• It prevents the lungs from collapsing and Keeps the Chest wall at its
position

7. Key Concept
• Balance between lung recoil inward and chest wall recoil outward
determines lung volume at end of expiration

8. Transpulmonary Pressure (PAlv)
• The difference
between alveolar
pressure and
pleural pressure,
known as
transpulmonary
pressure (Ptp)
• equal and opposite
to lung elastic recoil
pressure for a given
lung volume
Ptp = Palv− Ppl
Ptp = − Pel

9. Ptp = Lung Volume
• Transpulmonary pressure determines lung volume
• To inflate lungs, Ptp must increase
• Ptp = Palv− Ppl
• To increase Ptp, either decrease Ppl (spontaneous breathing) or
increase Palv (positive pressure ventilation)

14. Boyle’s law
• For a fixed amount of gas kept at constant temperature, pressure and
volume are inversely proportional
• pressure = 1/volume

15. How Does Boyle’s Law Explains Breathing
• Inspiration
Increase Thoracic Volume – Lower Pleural Pressure – Lower Alveolar Pressure
(below atm pressure) – Inward Movement of Air from Atmosphere
Expiration
• Expiration
• Passive Recoil – Diaphragm and Inspiratory muscles relax – Abdominal
contents returns to previous position – Chest wall recoils – Decreased
intrathoracic volume – increase intrathoracic pressure – increased pleural
pressure – decrease in Ptp – Alveolar pressure more then atm Pressure – Air
moves out of lungs

16. Flow – Air Pressure – Alv Pressure – Resistance