Respiratory System 2 Flashcards
Understand the physical law that governs the movement of air into and out of the lungs
Boyle’s Law
- Defines the relationship between gas pressure and volume
- Determines how air moves into and out of the lung
Decrease volume of container = collisions occur more often over time = increasing pressure of gas
Increase volume = free collisions = because it takes longer for gas molecule to travel from one wall to another = decrease gas pressure
Describe Atmospheric pressure involved in pulmonary ventilation
Pressure of the air outside the body
~760 mmHg
Inhalation
- Air pressure within lungs is lower than atmospheric pressure
Exhalation
- Air pressure within lungs rises above atmospheric pressure
Describe Intrapulmonary pressure involved in pulmonary ventilation
Pressure inside the alveoli of the lungs
- At rest, no change in the volume of the thoracic cavity
- ~760 mmHg
- Difference in pressure is 0 mmHg (at rest)
Inhalation
- Decreases intrapulmonary pressure relative to atmospheric pressure
Exhalation
- Volume decreases, intrapulmonary pressure increases → air flows out
Describe Intrapleural pressure involved in pulmonary ventilation
Pressure within the pleural cavity
~756 mmHg
Lower than atmospheric and intrapulmonary pressure (subatmospheric) (Decrease pressure)
Due to elastic lung
Difference -4 mmHg
Describe the processes of inhalation
During deep forceful inhalation accessory muscles of inhalation participate to increase size of thoracic cavity
- Sternocleidomastoid – elevate sternum - Scalenes – elevate first two ribs
During quiet breathing contraction of diaphragm and external intercostals expands thoracic cavity (Air flows into lungs & Diaphragm contracts )
Decreases intrapulmonary pressure relative to atmospheric pressure
Air flows down pressure gradient
Pressure outside is greater = which means travel from outside to inside (Air pressure within lungs is lower than atmospheric pressure )
Describe the processes of exhalation
Deep Exhalation
During forceful breathing is active process
- Muscles of exhalation increase pressure in abdomen and thorax
- Abdominals
- Internal intercostals
Passive process during quiet breathing
Relaxation of muscles (Diaphragm relax)
Thoracic volume decrease; lungs recoil
Elastic recoil of chest wall and lungs, due to:
- Recoil of elastic fibres
- Inward pull of surface tension of alveolar fluid
Volume decreases, intrapulmonary pressure increases → air flows out (Air pressure within lungs rises above atmospheric pressure)
Describe the factors that affect pulmonary ventilation
- Lung compliance
- How much effort (force) required to deform a body e.g. stretch or distend lungs (i.e. ΔV/ ΔP)
- Most work due to overcoming resistance of elastic lungs and thoracic cage to stretching
- Less compliant → more work ( ↑ pressure) required to produce a given degree of inflation
- Elastance (=Elasticity)
- Inverse of compliance; how readily lungs rebound after being stretched; i.e. natural tendency to collapse
- Due to elastic fibres and surface tension
- If Compliance goes up, elastance goes down, If Elastance goes up, compliance goes down
- Needs some surface tension to move lungs inwards
- Surface tension of alveolar fluid
- Surfactant reduces surface tension of water
- Low surface tension increases compliance & decreases elastance
- Airways resistance
- Airflow inversely proportional to airway resistance
- Primary determinant of resistance is radius of conducting airways
Identify the various lung volumes
Tidal (~500 ml)
- Volume of air entering or leaving lungs during a single breath
Inspiratory reserve (~3100 ml) - Extra volume of air that can be maximally inspired over and above the typical resting tidal volume
Expiratory reserve (~1200 ml) - Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
Residual (~1200 ml)
- Minimum volume of air remaining in the lungs even after a maximal expiration
Identify the various lung capacities
Inspiratory (~3600 ml)
- Maximum volume of air that can be inspired at the end of a normal quiet expiration (IC = IRV + TV)
Functional residual (~2400 ml) - Volume of air in lungs at end of normal passive expiration (FRC = ERV + RV)
Vital (~4800 ml)
- Maximum volume of air that can be moved out during a single breath following a maximal inspiration (VC = IRV + TV + ERV)
Total lung (~6000 ml) - Maximum volume of air that the lungs can hold (TLC = VC + RV)
Understand the concepts respiratory minute volume, alveolar ventilation & anatomic dead space
Respiratory minute volume
- Amount of air moved into & out of lung per minute
- Respiratory rate x Tidal volume
- Also called Pulmonary Ventilation
Alveolar ventilation
- Relative rate & depth of breathing determine efficiency of alveolar ventilation
- Respiratory Rate x (Tidal Volume – Anatomical Dead Space)
Anatomic dead space
- Fresh air in conducting airways (trachea, bronchi & bronchioles) does not participate in gas exchange
- Known as anatomic dead space (physical limitation)
What is the function of pleura
- Allow optimal expansion and contraction of the lungs during breathing
- The pleural fluid acts as a lubricant, allowing the parietal and visceral pleura to glide over each other friction free
Lung compliance that affect pulmonary ventilation
Lung compliance
- How much effort (force) required to deform a body e.g. stretch or distend lungs (i.e. ΔV/ ΔP) - Most work due to overcoming resistance of elastic lungs and thoracic cage to stretching - Less compliant → more work ( ↑ pressure) required to produce a given degree of inflation
Elastance (=Elasticity) affect pulmonary ventilation
Elastance (=Elasticity)
- Inverse of compliance; how readily lungs rebound after being stretched; i.e. natural tendency to collapse - Due to elastic fibres and surface tension - If Compliance goes up, elastance goes down, If Elastance goes up, compliance goes down - Needs some surface tension to move lungs inwards
Surface tension affect pulmonary ventilation
Surface tension of alveolar fluid
- Surfactant reduces surface tension of water - Low surface tension increases compliance & decreases elastance
Airways resistance affect pulmonary ventilation
Airways resistance
- Airflow inversely proportional to airway resistance - Primary determinant of resistance is radius of conducting airways
