Pulmonary mechanics and ventilation (physio) Flashcards
What happens when air is inspired?
Diaphragm and inspiratory chest wall muscles contract -> chest cavity expand
Lungs expand -> intrathoracic vol increase -> air pressure in lungs decrease
Pressures in thorax and pleural cavity decrease
Active -> contract
What happens when air is expired?
Diaphragm and inspiratory chest wall muscles relax
Lungs recoil -> form smaller vol -> air pressure in lungs increase
Pressures in thorax and pleural cavity increase
Passive -> relax
What happens when ventilation is stimulated (i.e: exercise)?
Extra muscles are recruited in inspiration and expiration -> enhance movement of chest wall
- stronger inspiratory effort -> increase lung vol further -> increased air drawn into lungs per unit time
- stronger expiratory efforts -> decrease lung vol further -> increased air expelled from lungs per unit time
What is pleura space?
Potential space btw 2 layers
- 2 layers in very close contact -> glide over one another
What is intrapleural pressure?
Pressure in the pleural space
What is pressure in the lungs like before inspiration?
No net flow btw alveoli and atmosphere -> intra-alveolar pressure similar to atmospheric pressure
Intrapleural pressure is neg -> created by lung recoil against chest wall
How does pressure in the lungs change during inspiration?
Chest wall, pleura and lungs expand
Intra-alveolar pressure decrease -> become less than atmospheric pressure -> air flows in
Intrapleural pressure decrease -> become more neg
How does pressure change during expiration?
Chest wall, pleura and lungs recoil
Intra-alveolar pressure increase -> become more than atmospheric pressure due to additional air taken in during inspiration -> air flows out
Intrapleural pressure returns to original levels
How can the pleural space expand?
Filled w/ excess fluid
Filled w/ excess air
What happens when the pleural space expands?
Intrapleural pressure increase -> lung collapses/have difficulty expanding -> disrupts ventilation
How does pressure change during a pneumothorax?
Air flow in from atmosphere into pleural space/leak out from punctured lung into pleural space -> intrapleural pressure increase -> lung collapse
What affects ventilation?
Changes in thoracic vol and pressure
Integrity of lungs and pleura, muscles and innervation, rib cage
What is physiologic dead space?
Vol of air breathed in that does not undergo gas exchange w/ blood
Why does dead space exist?
Not all air taken in undergoes gas exchange as it doesn’t reach alveoli due to anatomic dead space (air in airways up to respi bronchioles, just short of alveoli)
What is tidal vol at rest (TV)?
Vol of air entering respi sys at each resting breath/exiting respi sys on passive expiration
What is inspiratory reserve vol (IRV)?
Extra air entering lungs w/ maximal inspiration (on top of TV)
What is expiratory reserve vol (ERV)?
Extra air expelled from lungs w/ maximum expiration (aft passive expiration)
What is residual vol (RV)?
Vol of air left in lungs aft max expiration -> prevent lungs from collapsing
Factors affecting ventilation vol
Size
- small size person -> smaller ventilation vol
Age
Physical fitness
- less fit -> smaller ventilation vol
Gender
- male usually have larger ventilation vol thn women
-ERV and IRV higher as men have more muscular framework and muscular chest wall -> take in additional vol of air during forceful inspiration/exhale additional vol of air during forceful expiration
How can tidal vol change?
Depends on how much ventilation is stimulated (eg: activity of a person -> resting TV < exercising TV as exercising TV recruits other lung vol at rest)
What affects ability to ventillate?
Factors which affect breathing
- properties of chest wall
- muscle power -> whether it’s adequate for breathing movement
- skeletal deformities -> hinder breathing movement
- properties of lungs
- resistance to air flow -> high -> more difficult to breathe
- areas of stiffness -> hard to expand lung
- areas of collapse -> predispose to difficulty in expansion
- restriction of diaphragm movement
What is hyperventilation?
Increased ventilation
What is hypoventilation?
Decreased ventilation
What is tachypnoea?
Increased rate of breathing/respi rate
What is dyspnoea?
Distressful sensation of breathing
Define minute ventilation
TV of air breathe per min
Formula to calc minute ventilation
TV x respi rate
Define alveolar ventilation
Volume of air that reaches alveoli per min
- component of min. ventilation that can undergo gas exchange
Formula to calc alveolar ventilation
(TV - dead space) x breaths per min
