Ventilation- The Physics of Breathing Flashcards
What occurs in inspiration to increase size of lungs?
Change in volume leads to change in pressure
Role of the diaphragm – main muscle of respiration. Contraction flattens domes. Abdominal wall relaxes to allow abdominal contents to move downwards
Role of the intercostals – externals – with first rib fixed, two movements, forward movement of lower end of sternum, and upward and outward movement of ribs
By how much does inspiration increase thorax volume?
By 500 ml
What is normal intrapleural pressure?
756mmHg
What is intrapulmonary pressure?
760mmHg
What is the collapsing force of the lungs?
4mmHg
What happens to the different pressures during inspiration?
Intrapleural drops to -6mmHg
Intrapulmonary pressure drops by 1mmHg allowing air to enter the lungs
Describe quiet expiration
Passive – no direct muscle action normally
Cessation of muscle contraction
Elastic recoil – drives air out of lungs
Thoracic volume decreases by 500 ml
Intrapulmonary pressure increases
Air moves down pressure gradient
Describe forced expiration
Contraction of abdominal walls, forces abdominal contents up against diaphragm, and internal intercostals – pull ribs downwards
What is energy required to do?
Contract the muscles of inspiration
Stretch elastic elements
Overcome airway resistance
Overcome frictional forces arising from the viscosity of the lung and chest wall
Overcome inertia of the air and tissues
What is the most significant non-elastic source of resistance?
Airway resistance
What is the amount of air that flow determined by?
Change of pressure divided by the resistance
What is turbulent flow more likely to occur with?
High velocities
Where is the greatest resistance to airflow?
Segmental bronchi
Why is the greatest resistance found in the segmental bronchi?
Cross sectional area is relatively low and airflow is high and turbulent
How does airway resistance change?
In inspiration airway resistance decreases
What diseases cause an increase in airway resistance?
Asthma
COPD
What is compliance?
Describes the distensibility or ease of stretch of lung tissue when external force applied, or the ease with which the lungs expand under pressure
What does high compliance mean?
A large change in volume for a given change in pressure
What are the major determinants of compliance?
Elastic components and alveolar surface tension
What is compliance in an average person?
1L per kPA
What changes compliance?
Changes in volume of the chest that results from a given change in intrapleural pressure
How do we reduce compliance?
replacing elastic tissue with non-elastic tissue –pulmonary fibrosis – lungs become stiffer.
Blocking smaller respiratory passages
Increasing alveolar surface tension
Decreasing the flexibility of the thoracic cage or its ability to expand
How can we increase compliance?
Pulmonary emphysema. Due to alveoli rupture, creating larger air space and thus reducing surface area of lung. Impaired elastic recoil leads to poor deflation, trapping more air.
When is lung compliance at its greatest?
Lower lung volumes and smallest at higher lung volumes
How does compliance differ from the apex and base of lung?
Apex is less compliant than the base allowing the bsae to expand more
What would happen if the alveoli were lined with polar water?
They’d collapse
How does the body stops the alveoli from collapsing?
Type II alveolar cells produce surfactant
Surfactant is made up of phospholipids
Increases lung compliance by reducing surface tension- allowing for greater expansion
How can we measure respiratory volume?
Spirometry
Vitalograph
SEE LECTURE
What are the four different lung volumes?/
Tidal
Inspiratory reserve volume
Expiratory reserve volume
Residual volume
What is tidal volume?
Volume of air breathed in and out in a single breath
What is inspiratory reserve volume?
Volume breathed in by max inspiration at end of normal inspiration
What is expiratory reserve volume?
Volume of air expelled by max effort at the end of normal expiration
What is residual volume?
Volume of air in lungs at the end of maximum expiration
What is inspiratory capacity?
TV add IRV
Volume of air breathed in by max inspirations at the end of normal expiration
What is functional residual capacity?
ERC add RV
Volume of air left in lungs at end of normal expiration
What is vital capacity?
IRV add TV add ERV
Volume of air that can be breathed by max inspiration following a max expiration
What is total lung capacity?
VC + RV
What can’t you use a spirometer to measure?
Residual volume
Functional residual capacity
Total lung capacity
What is dead space?
Areas of airway not involved in gas exchange- 150ml on average
Alveolar with poor perfusion as well- 5ml
What is intrapleural pressure?
Always more negative than the alveolar
Slde 7
Exam question
What is a normal volume for inspiratory capacity?
3.8L
what is a normal function residual capacity?
2.2-2.4L
What is a normal vital capacity?
4.8L
What is a normal total lung capacity?
6L
What does a vitalograph measure?
Measure the maximum forced breath out
Forced expiratory volume
FEV1- volume exhaled during the first second of forced expiration
How long should a breath roughly take?
4 seconds
Describe the effect of expiration and inspiration on intrapulmonary, trans-pulmonary and intrapleural pressures
All decreases during inspiration but intrapleural pressure decreases more
Intrapleural pressure stays lower for linger during in expiration but they do both rise again
