Respiratory Physiology Part A + B: Air Exchange Flashcards
3 processes involved in exchange of air
- Pulmonary Ventilation
a) inspiration
b) expiration - External Respiration
- Internal Respiration
Pulmonary Ventilation
result of pressure gradients caused by changes in thoracic cavity volume
Boyle’s Law
- Gas volume is inversely proportional to pressure
- As increase in volume, decrease in pressure (+ vice versa) - for same number of molecules of air (gas amount remains constant)
3 Pressures involved in Pulmonary Ventilation
- Atmospheric Pressure
- Intrapulmonary Pressure
- Intrapleural Pressure
Atmospheric Pressure =
760 mmHg (sea level)
Intrapulmonary Pressure =
air pressure inside lungs (between breaths is = atmospheric pressure)
Intrapleural Pressure =
- Fluid pressure in pleural cavity
- always < intrapulmonary pressure
- usually < atm pressure = ~4 mmHg less = 756 mmHg (at rest)
- thoracic wall recoils out, lungs recoil in - but fluid holds them together, therefore intrapleural pressure decreases
Types of Pulmonary Ventilation
- Quiet Inspiration
- Forced Inspiration
- Quiet Expiration
- Forced Expiration
Quiet Inspiration
- active process (muscles contract)
- at start Patm = Ppul (760 mmHg) – no air moves, then:
i. diaphragm , external intercostals contract, ⇑ volume of thoracic cavity
ii. lungs resist expansion ∴ Pip ⇓ (756 ⇒ 754 mmHg)
iii. higher pressure difference between Ppul and Pip pushes lungs out ⇒ lungs expand ∴ Ppul ⇓ (760 ⇒ 758 mmHg)
iv. air moves in down P gradient (until Ppul = Patm)
Forced Inspiration
- involves diaphragm, external intercostals and sternocleidomastoids, pectoralis minors, scalenes contract (∴ active)
- ⇑⇑ vol of thoracic cavity ∴ pressure gradient ⇑, and more air moves in
Quiet Expiration
-relax muscles ⇒ lungs to resting size ∴ ⇓ thoracic cavity size (passive process)
-vol ⇓ Pip ⇑ (754 ⇒756 mmHg)
∴ Ppul ⇑ (760 ⇒ 762 mmHg) ⇒ air moves out down pressure gradient
Forced Expiration
- laboured or impeded (e.g. asthma) breathing
- relax diaphragm, ext. intercostals and contract internal intercostals, abdominals (ACTIVE process)
- Pip ⇑ - lung volume ⇓ ∴ Ppul ⇑ and air moves out
Stretch in lungs is determined by:
- Compliance = effort needed to stretch lungs; low = much effort
- Recoil = ability to return to resting size after stretch
- both = result of elastic CT + surfactant
Pip is always below Ppul
What does the prevent?
Prevents lung from collapsing.
- pneumothorax = air into pleural cavity
- Patm = Ppul = Pip ∴ lungs collapse, thoracic wall expands
Presence of surfactant prevents:
Prevents lung from collapsing.
- = lipoprotein/phospholipid mixture
o in watery film coating alveoli - ⇓ surface tension
o allows easier stretch of lungs (⇑ compliance)
o prevents alveolar collapse
-Respiratory distress syndrome
o newborns < 7 months gestation
o inadequate surfactant ∴ alveoli tend to collapse (low compliance)
o ∴ effort high ⇒ exhaustion, death
