Respiratory Physiology Flashcards
Overview
3 Processes involved in exchange of air:
1) Pulmonary Ventilation
a) Inspiration
b) Expiration
2) External Respiration
3) Internal Respiration
Pulmonary Ventilation
- Results of pressure gradients caused by changes in thoracic cavity volume
- Boyle’s Law
- Gas volume is inversely proportional to pressure
- As vol increases, P decreases (+ vice versa) - for the same # of molecules of air (gas amount remains constant)
Pulmonary Ventilation Pressures Involved
a) Atmospheric pressure = Patm = 760 mmHg (sea level)
b) Intrapulmonary Pressure = Ppul = air pressure inside lungs (= Patm between breaths)
c) Intrapleural Pressure = Pip = fluid pressure in pleural cavity
- always < Ppul (healthy individual)
- Usually < Patm = ~4mmHg less = 756 mmHg at rest
- Thoracic wall recoils out, lungs recoil in - but fluid holds them together = Pip lowers slightly
Pulmonary Ventilation Processe
1) Quiet Inspiration
2) Forced Inspiration
3) Quiet Expiration
4) Forced Expiration
Quiet Inspiration
- Active process (muscle contract)
- At start Patm = Ppul (760 mmHg) - no air moves, then:
1) Diaphragm, ext intercostals contract (active), higher volume of thoracic cavity
2) Lungs resist expansion = Pip lowers (756 -> 754 mmHg)
3) Higher pressure difference between Ppul and Pip pushes lungs out –> lungs expand = Ppul lowers –> 758 mmHg)
4) Air moves in down P gradient (until Ppul = Patm)
Forced Inspiration
- Active process
- diaphragm, external intercostals + sternocleidomastoids, pectorals minors, scalene contract (active)
- Great increase in volume of thoracic cavity - pressure gradient higher, and more air moves in
Quiet Expiration
- Relax diaphragm, ext. intercostals = lungs to resting size = lower thoracic cavity size (passive process)
- Vol lower, Pip higher (754 -> 756 mmHg) = Ppul increased (760–> 762 mmHg) –> air moves out down pressure gradient
Forced Expiration
- Laboured or impeded (e.g. asthma) breathing
- Relax diaphragm, ext. intercostals + contract internal intercostals, abdominals (active process)
- Pip increased –> lung volume decreased = Ppul increased and air moves out
Stretch in Lungs 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
Lungs Collapse Prevented by
1) Pip is always below Ppul
- Pneumothorax = air in pleural cavity
- Patm = Pip = Ppul : lungs collapse, thoracic wall expands
2) Presence of Surfactant
= lipoprotein/phospholipid mixture
- in watery fil coating alveoli - decreased surface tension
- Allows easier stretch of lungs (increases compliance)
- Prevents alveolar collapse
- Respiratory Distress Syndorme
- newborns <7 months gestation
- inadequate surfactant : alveoli tend to collapse (low compliance)
- Effort high –> exhaustion, death
Air Flow and Airway Resistance Formula
F = P/R F= air flow P = Patm - Ppul R= airway resistance
Resistance of Airway Determined by:
Resistance determined by diameter of bronchi, bronchioles
- Asthma, bronchitis, emphysema increased airway R - more difficult to expire than to inspire
- Inspiratory mechanics open airways/ expiratory close airways
- SNS - dilates bronchiolar smooth muscle (bronchodilation)
- PSNS - contracts it (bronchoconstriction)
Respiratory Volumes
- Measured using a spirometer ; 1 respiration = 1 inspiration + 1 expiration
- Volumes:
a) Tidal Vol (TV) - inspired or expired air during quiet respiration (~500ml)
b) Inspiratory Reserve Volume (IRV) - excess air over TV taken in on a max inspiration (~3000 ml)
c) Expiratory Reserve Volume (ERV) - excess air over TV pushed out on max expiration (~1200 ml)
d) Residual Vol (RV) - volume of air in lungs after maximal expiration (~1200 ml)
e) Minute Respiratory Vol = TV X Respiratory Rate e.g. = 500mL X 12 breaths/minute = ~6 L/min (on average)
f) Forced Expiratory Volume in 1 second (FEV1) - volumes expired in 1 sec., with max. effort, following max. inspiration
Respiratory Capacities
- 2 or more volumes
a) Inspiratory Capacity (IC) = TV + IRV
b) Vital Capacity (VC) = TV + IRV + ERV - largest volume in and out of lungs
c) Total Lung Capacity (TLC) - max amount of air lungs can hold = TV + IRV +ERV + RV (=VC + RV)
Clinical Application
- FEV1 is measured while measuring VC + expressed as %VC (allows correction for body size)
- Usually FEV1 = ~80% VC