Physiology 1: Ventilation (L-1&2) Flashcards
What is internal respiration?
- Intracellular
- Biochemical reactions converting food and oxygen into energy and carbon dioxide
What is external respiration?
The exchange of oxygen and carbon dioxide between the external environment and cells
List the steps of external respiration
- Ventilation
- Alveolar gas exchange
- Transport in blood
- Gas exchange at tissues
Define ventilation
The mechanical process of moving gas in and out of the lungs
Define alveolar gas exchange
The exchange of oxygen and carbon dioxide between air in the alveoli and the blood in the pulmonary capillaries
Define gas transport in the blood
The binding and transport of oxygen and carbon dioxide in the blood
Define tissue gas exchange
The exchange of oxygen and carbon dioxide between the blood in systemic capillaries and cells
Which 4 body systems are involved in external respiration?
- Respiratory system
- Cardiovascular system
- Hematology system
- Nervous system
What term describes the intake of gas into the lungs?
Inspiration
What term describe the outflow of gas from the lungs?
Expiration
Describe the relationship between intra-alveolar and atmospheric pressures to allow inspiration
For inspiration:
Intra-alveolar pressure must be less than atmospheric pressure
Describe the relationship between intra-alveolar and atmospheric pressures before inspiration
Intra-alveolar pressure is the same as atmospheric pressure
Describe Boyle’s Law
- As the volume of a set amount gas increases, the pressure it exerts decreases
- At a constant temperature
(At a constant temperature the pressure exerted by a gas varies inversely with the volume of the gas)
What forces hold the thoracic wall and lungs together?
- Intrapleural fluid cohesiveness
- Negative intrapleural pressure
(*INTRApleural not INTERpleural)
Are there physical connections between the thoracic wall and the lungs?
No, they are not linked
Describe intrapleural fluid cohesiveness
- The water molecules in the intrapleural fluid resist being pulled apart
- Pleural membranes stick together
Describe negative intrapleural pressure
- Intrapleural pressure is sub-atmospheric
- Creates a transmural pressure gradients across the lung wall and across the thoracic wall
- Pulls lungs out towards thoracic wall, and pulls thoracic wall in towards lung
(*See L1 slide 13 for explanation)
Describe the pressures that are important in ventilation
Atmospheric
Intra-alveolar
Intrapleural (intrathoracic)
Describe the process of inspiration
- Active process due to muscle contraction
- Thorax volume is increased by contraction of the diaphragm and external intercostal muscles
- Increased thorax volume –> increases the lung volume –> increase in alveolar volume
- Decrease in alveolar pressure (Boyle’s Law), causing the influx of air down its conc. gradient
Which muscle contracts to vertically expand the thoracic cavity?
Diaphragm
It flattens as it contracts
Describe the effect of the contraction of the external intercostal muscles on the volume of the thoracic cavity
Increases it by elevating the ribs, causing:
- Increase side to side dimension
- Sternum to move anteriorly and superiorly, increasing the front to back dimension
Describe the process of expiration
- Passive process due to muscle relaxation
- The thoracic cavity and lungs recoil to their pre-inspiratory size
- Lung recoil decreases alveolar volume
- Increasing intra-alveolar pressure (Boyle’s Law)
- Outflow of air down its conc. gradient
Which muscles relax during normal expiration
- Diaphragm
- External intercostal muscles
Define a pneumothorax
When there is air in the pleural cavity
Abolishing the transmural pressure gradient
Can lead to a collapsed lung
Define a transmural pressure gradient
Transmural pressure gradient is the pressure gradient between two sides of a wall or separator
e.g. across the visceral pleura
What are the types of pneumothorax
- Spontaneous
- Traumatic
Describe a spontaneous pneumothorax
- Hole in the lung
- Air moves down conc. gradient from lung into pleural cavity
- Abolishing transmural pressure gradient
- Lung collapses to its unstretched size
Describe a traumatic pneumothorax
- Puncture in chest wall
- Air moves down conc. gradient from atmosphere into pleural cavity
- Abolishing transmural pressure gradient
- Lung collapses to its unstretched size
What causes the lungs to recoil during expiration?
- Elastic connective tissue
- Alveolar surface tension
Describe alveolar surface tension
- Attraction between the water molecules (surface tension) on the inner surface of the alveoli
- This resists the expansion of the lungs
- Important in lung recoil
Describe pulmonary surfactant
- Mix of lipids and proteins
- Secreted by type II alveolar cells
- Lowers alveolar surface tension, by disrupting the water molecules interactions
- Lowers the surface tension of smaller alveoli more than that of larger alveoli
Describe the relationship between alveolar size and their tendency to collapse
- Smaller the alveoli, the more likely it is to collapse
- Due to LaPlace’s Law
What is newborn respiratory distress syndrome
- Fetal lungs don’t produce enough surfactant until late pregnancy
- Thus premature babies may not have enough
- Causes difficulty with inspiration
Describe alveolar interdependence
- Alveoli exist in clusters
- If one alveolus in the cluster starts to collapse it will stretch the surrounding alveoli
- They will then recoil exerting expanding forces of the collapsing alveolus, opening it
List the factors keeping alveoli open
- Transmural pressure gradient
- Pulmonary surfactant
- Alveolar interdependence
List the factors promoting alveolar collapse
- Elasticity of lung connective tissue
- Alveolar surface tension
List the accessory muscles of inspiration
- Sternocleidomastoid
- Scalenus
- Pectoral
When are the accessory muscles of inspiration used for ventilation?
Only during forceful inspiration
List the muscles of active expiration
- Abdominal muscles
- Internal intercostal muscles
When are the muscles of active expiration used for ventilation?
During active expiration
Define the role of the major muscles of inspiration
- Contract every inspiration
- Their relaxation allows passive expiration
What is used to measure the different lung volumes and capacities?
A spirometer
Define tidal volume (TV)
Give an average value
- Volume inspired and expired during a single ventilation
- 0.5L
Define inspiratory reserve volume (IRV)
Give an average value
- Extra volume of air that can be inspired over and above the tidal volume
- 3L
Define expiratory reserve volume (ERV)
Give an average value
- Extra volume of air that can be actively expired by a maximal contraction beyond the tidal volume
- 1L
Define residual volume (RV)
Give an average value
- The air remaining in the lungs after maximal expiration
- 1.2L
Define inspiratory capacity (IC)
Give an average value
- Maximum volume that can be inspired after a normal expiration
- IC = TV+IRV
- 3.5L
Define functional residual capacity (FRC)
Give an average value
- The total volume of air left in the lungs after a normal expiration
- FRC = ERV+RV
- 2.2L
Define vital capacity (VC)
Give an average value
- The maximum volume of air that can be moved out during a single breath following maximal inspiration
- VC = IRV+TV+ERV
- 4.5L
Define total lung capacity
Give an average value
- Maximum volume of air the lungs can hold
- TLC = VC+RV
- 5.7L
Which volumes cannot be determined using spirometry?
- Residual volume
- and thus total lung capacity and functional expiratory reserve
Describe the effect on the lung’s residual volume if the lungs elastic recoil is decreased
Less elastic recoil = Less can be expired = Increased residual volume
List dynamic lung volumes and ratios that can be determined from volume/time curves
- Forced vital capacity (FVC)
- Forced expiratory volume in 1 second (FEV1)
- FEV1/FVC
Define forced vital capacity (FVC)
The max volume that can be forcibly expired from the lungs following a maximum inspiration
Describe why vital capacity and forced vital capacity are different measurements
- If healthy FVC and VC should be the same
- If there is obstructive lung disease then VC>FVC
- Due to difficulty in forcibly expelling the air
Define forced expiratory volume in one second (FEV1)
The volume air that can be expired during the first second of a FVC determination
Define the FEV1/FVC ratio
- Give a normal % value
- The proportion of the forced vital capacity that can be expired in the first second
- Usually >70%
Define normal FEV1/FVC ratios, with those displaying obstructive lung disease
Normal: >70%
Abnormal: <70%
e.g.
Low FEV1/FVC = obstructive, or a mix of obstructive and restrictive
Describe the effect of restrictive lung disease on:
- FVC
- FEV
- FEV1/FVC ratio
FVC:
- Lower than normal
FEV:
- Lower than normal
FEV1/FVC ratio:
- The same as normal (as FEV1 and FVC are both lower)
Describe the effect of a combination of restrictive and obstructive lung disease on:
- FVC
- FEV
- FEV1/FVC ratio
FVC:
- Lower than normal
FEV:
- Lower than normal
FEV1/FVC ratio:
- Lower than normal
Give the equation for airway resistance
F=ΔP/R
F - flow, ΔP - pressure, R - resistance
Airway radius is important in determining airway resistance
Remember it
Describe the effect of parasympathetic stimulation on airway radius
Parasympathetic
Bronchoconstriction
(via M3 Muscarinic ACh receptors)
*(para constricts unlike most other places)
Describe the effect of sympathetic stimulation on airway radius
Sympathetic
Bronchodilation
(via β2 Adrenoceptor)
*(sympathetic relaxes unlike most other places)
With obstructive lung disease is inspiration or expiration harder?
Expiration is more difficult
Describe dynamic airway compression
- When intrapleural pressure increases during active expiration
- Compression of airway and alveoli
Is dynamic airway compression a problem in normal people?
No
Only in people with obstructive lung disease
Describe how dynamic airway compression can cause increased airway compression, or collapse if obstructive lung disease is present
- The driving pressure between the alveolus and airway is lost over the obstruction
- Causes a drop in airway pressure in the proximal airway
- Airways can compress or collapse due to higher expiratory pleural pressure
What sort of lung disease is a peak flow meter useful for detecting
Obstructive lung disease
peak flow = FEV1
Give examples of obstructive lung disease
- COPD
- Asthma
Describe pulmonary compliance
- a measure of the effort required to expand lungs
- Volume change per unit of pressure change
- Less compliant = more work to produce a certain degree of inflation
List factors that decrease pulmonary compliance
- Pulmonary fibrosis
- Pulmonary oedema
- Lung collapse (pneumothorax)
- pneumonia
- Absence of surfactant
Describe the impact and symptoms of a decreased pulmonary compliance
- Greater pressure change required to increase lung volume by a set amount (stiffer lungs)
- Use of accessory inspiratory muscles
- May cause a restrictive pattern of lung volumes
List factors that increase pulmonary compliance
- Loss of elastic recoil (abnormal)
- Emphysema (abnormal)
- Increased age
What factors can increase the work of breathing
- Pulmonary compliance is decreased
- Airway resistance is increased
- Elastic recoil is decreased
- When there is a need for increased ventilation
