Physics of Breathing Flashcards
What is pulmonary ventilation?
movement of air into and out of the lungs
What causes airflow into and out of the lungs?
- Δ volume
- Δ pressure
- Airflow follows a change in pressure resulting from the change of volume of the lungs
How does air flow?
From an area of high pressure to an area of low pressure
How is low pressure created inside the lungs?
Increasing the volume by expanding the chest and lungs
What is intrapulmonary pressure?
pressure within the alveoli
How does intrapulmonary pressure change within a respiratory cycle?
falls and rises over one respiratory cycle
What is intrapleural pressure?
pressure within the pleural cavity, which is always more negative than alveolar pressure
-4mmHg
What is responsible for trying the pull the visceral pleura away from the parietal pleura?
elastic nature of the lung tissue versus the ribcage and thorax (more rigid structures)
What is usually contained within the pleural cavity?
fluid
Draw a diagram of the lungs indicating the intrapleural and intrapulmonary pressure and the collapsing force of the lungs
What leads to change in pressure in inspiration?
change in volume
What is the main muscle of respiration?
Diaphragm
What is the role of the diaphragm in inspiration?
- contraction flattens domes
- abdominal wall relaxes to allow abdominal contents to move downwards
What muscles are used in forced inspiration (respiratory distress)?
accessory muscles
e.g. trapezius
What is the role of the intercostal muscles in inspiration
external intercostal muscles
with first rib fixed, the have 2 movements:
- forward movement of lower end of sternum
- upwards and outwards movement of the ribs
What is the normal tidal volume of an average person?
500ml
What happens to the intrapleural pressure in inspiration?
drops to -6mmHg
What happens to the intrapulmonary pressure in inspiration?
decreases by ~1mmHg
What occurs in quiet expiration?
- passive - no direct muscle action
- cessation of muscle contraction
- elastic recoil
- thoracic volume decreases by 500ml
What happens to the intrapulmonary pressure during quiet expiration?
increases (by 1mmHg)
What happens to air in quiet expiration?
moves down the pressure gradient and out of the lungs
What occurs in forced expiration?
Contraction of abdominal walls, forces abdominal contents up against diaphragm and internal intercostals
What pressure indicates the differnce beywen intrapleural and intrapulmonary pressure?
transpulmonary pressure
Draw a diagram showing the pressure changes that occur during inspiration and expiration with values
During breathing what is energy required to do?
- contract muscles of inspiration
- stretch elastic elements
- overcome airway resistance
- overcone fricitional forces arising from viscosity of the lungs and chest wall
- overcome inertia of the air and tissues
What is the most significant source of non-elastic resistance?
airway resistance
F = ΔP/R
the amount of air that flows is determined by the change in pressure divided by resistance
How much does the upper respiratory tract contribute to airway resistance?
1/3
Where os the greatest resistance to airflow found? And why?
segmental bronchi
cross-sectional area is relatively low and airflow is high and turbulent
What type of flow is found in the smallest airways?
laminar
What happens to airway resistance in inspiration?
decreases
What occurs to airway resistance in asthma?
inflammatory mediators change smooth muscle tone narrowing the airway and increasing resistance
What is compliance?
describes the distensibility or ease of stretch of lung tissue when external force is applied, or the ease with which the lungs expand under pressure (ease of stretching with external force)
What is the meaning of high compliance?
there is a large change in volume for a given change in pressure
What occurs due to compliance?
Change in volume of the chest that results from a given change in intrapleural pressure
What are tje major determinants of compliance?
elastic components
alveolar surface tension
What can compliance be reduced by?
- replacing elastic tissue with non-elastic tissue –> pulmonaru fibrosis (lungs become stiffer)
- blocking smaller respiratory passages
- increasing alveolar surface tension
- decreasing the flexibility of the thoracic cage or its ability to expand e.g. rib fracture
What can compliance be increased by?
- pulmonary emphsema (easier to breath in but harder to expel air due to impaired elastic recoil)
- alveolar rupture creating large air spaces and reducing the SA of the lung
- impaired elastic recoil leads to poor deflation, trapping more air
What does compliance vary with?
lung volume
When is compliance greatest?
at lower lung volumes
When is compliance lowest?
higher lung volumes
What does compliance help explain? And what part of the lung is most compliant
the difference in ventilation between the apex and base of the lung
Apex is more complaint
What helps reduce the alveolar surface tension?
Surfactant
What is surfacant made of and what produces it?
phospholipid
type II alveolar cells
What does surfactant prevent?
alveolar collapse
What is the main purpose of surfactant?
Increases lung compliance by reducing alveolar surface tension. Allows for greater expansion for a given change in pressure
Draw a diagram indicating all the major lung volumes and capacities
What is tidal volume?
Volume of air breathed in and out in a single breath
500ml
What is inspiratory reservce volume?
volume breathed in by maz inspiration at the end of normal inspiration (max in after normal breath)
3.3L
What is expiratory reserve volume?
volume of air expelled by max effort at the end of normal expiration
1L
What is residual volume?
volume of air in the lungs at the end of maximal expiration (you cannot expel all of the air in the lung)
1.2L
What is inspiratory capcity?
Tidal Volume + Inspiratory Reserve Volume
volume of air breathed in by maximal inspiration at the end of a normal expiration
3.8L
What is functional residual capcity?
Expiratory reserve volume + residual volume
Volume of air left in the lungs after normal expiration. Buffer against extreme changes in alveolar gas levels in each breath
2.2-2.4L
What is Vital Capcity?
Inspiratory Reserve Volume + Tidal Volume + Expiratory Resvere Volume
Volume of air that can be breath by maximal inspiration following maximal expiration
4.8L
What is Total lung capacity?
Vital Capcity + Residual Volume
Total capcity of the lungs
6L
What is spirometry?
Measures how much air you inhale and exhale and how fast you can exhale.
Indicates lung capacity
What is FEV1.0 ?
Forced expiratory volume
The amount of air you can force out of your lungs in 1 second
What is anatomical dead space?
areas of airways not involved in gaseous exchange
e.g. nose and mouth, pharynx, larynx, bronchioles etc
What is alveolar dead space?
gas exchange suboptimal in some parts of the lung (less ventilation)
What is physiological dead space
anatomical plus alveolar
What can increase alveolar dead space?
altering the ventilation:perfusion ratio
