Respiratory Physiology Lecture 2 part 11: More on ventilation Flashcards
What are the two mechanics of ventilation?
- static properties of the lung
- Dynamic properties of the lung
Static lung properties
mechanical properties when no air is flowing (Necessary to maintain lung and chest wall at a certain volume)
What are the static properties of the lung?
- Intrapleural pressure (PIP)
- transpulmonary pressure (PTP)
- Static compliance of the lung
- Surface tension of the lung
Dynamic lung properties
mechanical properties when the lungs are changing volume and air is flowing in and out (Necessary to permit airflow)
What are the dynamic properties of the lungs?
– Alveolar pressure (PALV)
– Dynamic lung compliance
– Airway and tissue resistance
What are static and dynamic properties of the lung necessary for?
- static: Necessary to maintain lung and chest wall at a certain volume
- dynamic: Necessary to permit airflow
What is the main pressure for generating flow?
Alveolar pressure (PALV)
Ventilation
exchange of air between the atmosphere and the alveoli
What kind of flow is ventilation?
bulk flow
bulk flow
gas moves from high pressure to low pressure
Boyles Law
for a fixed amount of an ideal gas kept at a fixed temperature, P [Pressure] and V [Volume] are inversely proportional
ie. While one increases, the other decreases
P1V1= ?? (At constant T)
P1V1 = P2V2 (At constant T)
What exerts pressure in lungs?
- Change in lung volume translated into a change in lung pressure according to Boyle’s Law
- Gas molecules are constantly in motion and this motion exerts a pressure
Alveolar volume/ pressure during expiration and inspiration
expiration: ⇡ pressure ⇣ volume
inspiration: ⇣ pressure ⇡ volume
What produces airflow?
A change in volume, and then in pressure, produces airflow
- Once pressure difference is generated between inside and outside of the lung (alveoli and atm), air moves via bulk flow (F) from a region of high pressure to a region of low pressure
F
bulk flow
bulk flow (F) = ??
F=ΔP/R
What are the two pressures of interest in bulk flow?
Two pressures of interest:
Palveoli (Palv) & Patmosphere (Patm)
F=(Palv – Patm)/R
When is F = 0?
When Patm = Palv, F = 0
What relates the the lungs to the thoracic wall?
The pleurae
Pleurae
thin double-layered envelope
What are the layers of the pleurae?
visceral pleura & parietal pleura
visceral pleura
covers the external surface of the lung
Parietal pleura
covers thoracic wall and superior face of the diaphragm
What is between the visceral and parietal pleura?
Intrapleural fluid (~ 10 mL)
Purpose of intrapleural fluid
Reduces friction of lung against thoracic wall during breathing
(Extremely thin, 5 - 35 μm)
What interaction determines lung volume?
Interaction between lungs and thoracic cage determines lung volume
What is the elastic recoil of lungs and chest wall?
‒ Lungs → tendency to collapse due to elastic recoil
‒ Chest wall → pulls thoracic cage outward due to elastic recoil
Elastic recoil of lungs and chest wall at equalibrium
At equilibrium, inward elastic recoil of lungs exactly balances outward elastic recoil of chest wall
How does interaction between lungs and chest wall occur?
Interaction between lungs and chest wall does not occur by direct attachment but through the intrapleural space between visceral and parietal pleurae
