Respiratory Physiology 3 Flashcards
Describe the term ventilation
Movement of air in and out of lungs
Can be described in two ways - pulmonary ventilation and alveolar ventilation
Describe pulmonary (minute) ventilation
Total air movement into/out of lungs - relatively insignificant
L/min
Describe Alveolar ventilation
Fresh air getting to alveoli so therefore available for gas exchange - more functionally significant
L/min
Percentage that tidal breathing is effective and why?
75%
When inhaling 500ml (tidal volume), only 350ml of fresh air enters the alveoli as 150ml of dead space stale air enters the alveoli. At end of the inspiration the dead space is filled with fresh air which is exhaled out with 350ml of air from the alveoli
What is hypoventilation
When the alveolar ventilation is lower (3000ml/min) than the normal 4200ml/min
Happens when someone has a low tidal volume and high respiratory rate
Total pulmonary ventilation is the same
What is hyperventilation
Alveolar ventilation is higher than normal (4800ml/min)
Larger Tidal volume of 750ml at a slower respiratory rate
Same total pulmonary ventilation
What id Dalton’s Law
States that total pressure of gas mixture is a sum of the individual gases
What does Partial Pressure mean
The pressure of a gas in the mixture of gases is equivalent to the percentage of that particular gas in the mixture multiplied by the pressure of the whole gaseous mixture
What happens to the alveolar ventilation during hyperventilation?
There is increased alveolar ventilation
Partial pressure of O2 rises to 120mm Hg and partial pressure of CO2 falls to 20mm Hg
What happens to alveolar ventilation during hypoventilation?
There is decreased alveolar ventilation
Partial pressure of O2 falls to 30mm Hg and partial pressure of CO2 rises to 100mg
What happens to the alveolar ventilation from the base of the lung to the apex of the lung?
Declines with height from base to the apex
Compliance is lower at the apex due to being more inflated at FRC. At the base the lungs are slightly compressed by the diaphragm hence more compliant on inspiration
What does the pulmonary artery carry?
Carries deoxygenated blood away from the heart and towards the lungs
What does the pulmonary vein carry?
Carries oxygenated blood away from the lungs and towards the heart
What is the bronchial circulation?
Supplied via pulmonary arteries arising from systemic circulation to supply oxygenated blood to the lung tissues.
Comprises 2% of left heart output. Blood drains to left atrium via pulmonary veins.
What is the pulmonary circulation?
Consists of Left and right arteries originating from the right ventricle. Entire cardiac output is from the RV. Supplies the dense capillary network surrounding the alveoli and returns oxygenated blood to the left atrium via the pulmonary vein
Is a high flow but low pressure system
Describe gas exchange at the alveoli and the tissues - partial pressure
Air diffuses across the membranes down partial pressure gradient
In alveoli: O2 moves from 100 - 40mm Hg and CO2 moves from 46 - 40 mm Hg
In tissues: opposite happens
What does the PACO2 mean?
Partial pressure of carbon dioxide in alveolar air
What does the PaO2 mean?
Partial pressure of oxygen in arterial blood
Explain gas exchange in the lungs
Gas will move across the membrane that is permeable, down its partial pressure gradient (similar to conc.). Will continue to do so until equilibrium is reached
What is the rate of diffusion across membrane proportional to?
Directly proportional to partial pressure gradient
Directly proportional to gas solubility
Directly proportional to the available surface area
Inversely proportional to the thickness of the membrane
Most rapid over short distances
What does partial pressure in alveoli correspond to?
Partial pressure in systemic arterial blood
What does the partial pressures in pulmonary arterial blood (deoxygenated blood) correspond with?
Partial pressure at tissues
Explain how O2 and CO2 diffuse at similar rates
O2 diffuses at 250ml/min and CO2 at 200ml/min
O2 diffuses slightly faster due to its PP having bigger difference
CO2 still diffuses as it is more soluble in water than O2
What are 3 parts of the lung that help maximise gas exchange?
Large surface area of alveoli
Minimal diffusion difference
Thin walled membranes (Type I alveolar cells, capillary cell)
What is emphysema?
Destruction of the alveoli reduces surface area for gas exchange
PO2 is normal or low in alveoli
PO2 is low in veins
What is Fibrotic lung disease?
Thickened alveolar membrane that slows gas exchange. Loss of lung compliance which can decrease alveolar ventilation as stretch of lungs affected.
PO2 is normal or low in alveoli
PO2 is low in the veins
What is pulmonary oedema?
Fluid in the interstitial space increases the diffusion distance. The PCO2 may be normal as CO2 solubility in water.
PO2 is normal in alveoli
PO2 is low in veins
What is asthma?
Increased airway resistance which decreases airway ventilation. The bronchioles are constricted and does not affect diffusion.
PO2 is low in the alveoli so PO2 is low in the veins
What does the fibrotic tissue in fibrotic lung disease cause?
Makes the alveoli resistant to stretch so low compliance
Resists the expansion of lungs during inspiration so can have impact on ventilation.
Also impedes diffusion
What characteristics does an emphysemic lung have?
Loss of elasticity as smoking can produce the enzyme elastase that breaks down the fibres.
Loss of surface area
Low compliance so expiration and muscles need to be used to get air out
Explain obstructive lung disease
Obstruction of air flow especially on expiration
Explain Restrictive lung disease
Restriction of lung expansion
Loss of lung compliance
More effort in the inspiration
What are obstructive lung disorders?
Asthma - reduction in radius
COPD - chronic bronchitis which is inflammation of bronchi so reduction in airway. Emphysema - destruction of alveoli so elastic recoil is damaged and air cant be pushed out through airways.
What are restrictive lung disorders?
Fibrosis - creates stiff lung. Can be idiopathic (cause unknown) or asbestosis.
Infant respiratory distress syndrome - insufficient surfactant production
Oedema
Pneumothorax
What is pneumothorax?
Air is introduced into the pleural cavity which pushes the pleural membranes apart.
Lung is no longer related to the chest wall and diaphragm
Now independent - no expansion or contraction
What is spirometry?
measuring the volume of air that is inspired and expired.
Can be static or dynamic measurements
Explain static measurements
Where the only consideration made is the volume exhaled
Explain dynamic measurements
Where the time taken to exhale a certain volume is what is being measured
What volumes of lung capacity can be measured with the spirometer?
Measures where the residual volume is not a component
TV, IRV, ERV, IC, VC
What is FEV1?
Forced expiratory volume in 1 second - in fit healthy males: 4L
So how fast air can be pushed out
What is FVC?
Forced vital capacity
Total amount o air you can expire over whatever time
In fit healthy males: 5L
What is the FEV1/FVC?
80%
Describe the pressure-volume relationship and compliance during inspiration
There is a decrease in pressure before there is an increase in volume
Compliance increases during inspiration
Requires greater change in pressure to reach a particular lung volume
Requires more negative intrapleural pressure
Describe the pressure-volume relationship and compliance during expiration
Requires less of a change in pressure to maintain the volume in expiration
Low compliance at start of expiration
Why does inspiration require a greater change in pressure to reach particular volume compared to expiration?
Overcome ling inertia during inspiration - reluctance for tissues to change shape
Overcome surface tension - wants alveoli to collapse
During expiration compression of airways means more pressure is required for air to flow along them
Give examples of when inspiration and expiration require more effort
Emphysema - loss of elastic tissue means expiration is more difficult as muscles have to force air out, not elastic recoil
Fibrosis - inert fibrous means more effort on inspiration as thickened alveoli walls meaning lower compliance
Describe inspiration and expiration when someone has asthma?
Inspiration - airways are pulled open by physical forces of inspiration
Expiration - airways are compressed by physical forces of expiration so more effort is needed to expire
