Resp: Physiology Flashcards
What is ventilation?
The process of inspiration and expiration
What is the tidal volume?
The volume of air which enters and leaves the lungs with each breath
Can the lungs be emptied completely?
No. Residual volume will remain
What is the physiological dead space?
Air in alveoli which are not perfused or are damaged do not take part in gas exchange, and ventilation of these alveoli are wasted
What are the lung capacities defined by?
Maximum inspiration
Maximum expiration
End of a quiet expiration
What is the volume of the conducting airways termed as?
Anatomical dead space
What is the equation for the total dead space?
Anatomical dead space + Physiological dead space
What is the equation for tidal volume?
Anatomical dead space + alveolar ventilation
What is the equation for total pulmonary ventilation?
Tidal volume X respiratory rate
What is the equation for the alveolar ventilation?
(Tidal volume - Dead space) X Respiratory rate
What is the inward force acting on the lung at rest?
The lung’s elasticity and surface tension generate an inwardly directed force that favours small lung volumes
What is the outward force acting on the lung at rest?
The muscles and various connective tissues associated with the rib cage also have elasticity. At rest these elastic elements favour outward movement of the chest wall.
What is the result of the inward and out ward force acting on the lung at rest?
They balance each other and create a negative pressure within the intrapleural space relative to atmospheric pressure
How does inspiration occur?
- Contraction of the diaphragm and the external intercostal muscles expands the thoracic cavity outward from equilibrium position
- Pleural seal ensure that the lungs expand along with the thorax.
- Lung volume increase so air pressure within the lungs fall below atmospheric pressure. Air flows into the lungs
What happens in (quiet) expiration?
- Muscle contraction ceases
- Elastic recoil of the lung results in the thoracic cavity and lung returning to the original position
- Passive process
What ensures that the chest wall and lung move together?
-Surface tension due to fluid lining the pleural space which holds the outer surface of the lungs to the inner surface of the chest wall. This ensure that the chest wall and lungs move together.
What happens to the intrapleural pressure during inspiration?
The intrapleural pressure becomes more negative and returns to resting pressure at the end of quiet expiration
What are the muscle of quiet inspiration?
- Diaphragm
- External Intercostal muscles
What muscles are involved in quiet expiration?
None!
Due to elastic recoil
Which muscles are involved in forced inspiration?
Accessory muscles of inspiration.
- Sternocleidomastoid
- Scalene
- Serratus anterior
- Pectoralis major
What muscles are used in forced expiration
- Internal intercostal muscles
- Abdominal wall muscles
What is the stretchiness of the lung known as?
Compliance
What is compliance defined as?
Volume change per unit pressure change
What contributes to the elastic properties of the lung?
- Elastic tissue in the lungs
- Surface tension forces of fluid lining the alveoli
What is contained in the alveolar lining fluid?
Surfactant
What is the purpose of surfactant?
- Reduce surface tension thereby increasing lung compliance
- Stabilise the lungs by preventing small alveoli collapsing into big ones
- Prevents the surface tension in alveoli creating a suction force tending to cause transudation fluid from pulmonary
How does surfactant increase surface tension as the alveolus expands?
Surfactant molecules spread further apart making them less efficient
How does surfactant decrease the surface tension as the area of the alveolus decreases?
Surfactant molecules comes closer together increasing their concentration and act more efficiently thereby reducing the surface tension
What is the effect of the increase in concentration of surfactant in the smaller alveoli?
The force required to expand smaller alveoli is therefore less than that required to expand the large one
What would happen between the different sized alveoli if the surface tension was constant?
-Smaller alveoli would have a higher pressure within it.
-Therefore if two unequaled size alveoli were connected by an airway the smaller alveolus would empty into the larger alveolus due to having a higher pressure
Law of Laplace
What would happens to the surface area for gas exchange if the surface tension was a constant in the variable alveolus sizes?
- The smaller alveoli would collapse into larger alveoli to from huge air filled spaces
- Combined surface area of a few large bubbles would be much less than combined surface area of thousands of small alveoli
- Surface area for gas exchange would decrease
What is the effect of surfactant on the alveoli as the size increases?
As the alveolus expands the surface tension and the radius increase as well.
What is the effect of surfactant on the alveolus as the size decreases?
As the alveolus shrinks
- Radius decreases
- Surface tension reduces
What is the overall effect of surfactant?
Different sized alveoli can have the same pressure within them. This stabilises the lungs preventing small alveoli collapsing into big ones.
What is respiratory distress syndrome of the newborn?
Condition usually seen in premature babies particularly those less than 30 weeks old due to lack of surfactant.
-Without surfactant, surface tension of alveolar sacs is high so increases tendency of the alveoli to collapse.
What is the treatment for RDS?
- Surfactant replacement via endotracheal tube
- Supportive treatment with oxygen and assisted ventillation
What are the sign of RDS in the babies?
- Cyanosis
- Grunting
- Intercostal and subcostal recessions
What is the equation for the minute ventilation?
Tidal volume X Breaths per minute
How do you calculate the tidal volume entering the gas exchange region of the lung?
Resting tidal volume - Amount in anatomical deadspace
What is alveolar ventilation?
Respiratory frequency X volume available for gas exchange
Where in the bronchial tree is the main site of airways resistance?
The upper respiratory tract
-Although resistance increases sharply with lower radius the combined cross sectional area of the bronchioles is a lot bigger than the cross sectional area of the trachea.
What are different mechanism for increased airways resistance?
- Increased mucus (Chronic bronchitis)
- Hypertrophy of the smooth muscle, and/or oedema (Asthma)
- Loss of radial traction (Emphysema)
What is the equation for resistance?
Pressure/Flow=Resistance
Resistance is also directly proportional to 1/r^4
Small change in r makes a big difference in resistance
Why do lungs collapse when air enter the pleural cavity?
Lack of negative pressure in the pleural cavity so the lungs aren’t held against the thoracic wall so they collapse
How can damage to the intercostal vessels and nerves be avoided during procedure requiring insertion into the pleural space?
The costal groove runs underneath each rib so inserting into the lower border of the intercostal space or inserting into superior border of the rib
Explain why lack of surfactant causes difficulty breathing?
- Increased surface tension so alveolar walls held closer together
- Smaller alveoli are not able to expand as well due to increased pressure
- Bigger alveoli will expand
- Higher volume in the thorax is need to lower the pressure in the alveoli
Why is there indrawing of intercostal spaces during respiration?
- Active contraction of external intercostal muscle in order to pull the thoracic wall upwards which will increase volume.
- Pressure decreases as result
- Indrawing is the presence of the active contraction
How does fibrosis affect compliance?
Reduced compliance
How does emphysema affect compliance of the lungs?
Increased compliance
What is the ideal gas equation?
PV=nRT
What is Boyle’s law?
Pressure in a gas is inversely proportional to its volume
What is the total partial pressure exerted in a mixture of gases equal to?
The sum of the partial pressure of the individual gases
What is composition of atmospheric air?
20.9% = Oxygen 78% = Nitrogen 0.03% = CO2
How do gases diffuse in the body?
Down the partial pressure gradient
What happens when gas molecules come into contact with body fluids?
- Gas molecule will enter the fluid to dissolve
- The water molecules evaporate to enter air
What is the saturated vapour pressure at body temperature?
6.28 kPa
What happens to inhaled air in the upper respiratory tract?
Saturated with water
How does water vapour affect the partial pressure of other gases at 101 kPa?
101-6.28
The use the normal ratios
When is the equilibrium of gases established in a fluid?
Rate of gas molecules entering water = rate of gas molecules leaving the water
What is occurring at equilibrium of gas in fluid?
Partial pressure of the gas in the liquid = partial pressure gas in the air above it
Partial pressure is the same as the amount of dissolved gas. True/False. Why?
False
Amount of gas dissolved = Partial pressure X solubility coefficient of gas
When is partial pressure established if there is a component of liquid that the gas reacts with?
Partial pressure is established after the gas reacts with component
What happens when oxygen encounters plasma?
- Enters plasma and dissolves in it
- Dissolved oxygen enter red blood cells to bind to Hb
- Process continues till Hb fully saturated
- After Hb is fully saturated, oxygen continues to dissolve until the equilibrium is established
- At equilibrium pO2 of plasma=pO2 of alveolar air
What happens to the dissolved oxygen in plasma when it encounters tissues?
It is available to diffuse into tissues and is replaced by the oxygen bound to haemoglobin
Why does alveolar air equilibrate with the blood air?
There is constantly gas moving out and into the alveolus. Oxygen move into the blood stream constantly.
What happens to the atmospheric pressure and gases at high altitudes?
- The atmospheric pressure is lower
- There are fewer molecules of gas.
What happens to pressure as you dive further into the sea?
The pressure increase dramatically
Pressure below sea level = Atmospheric pressure+weight of water
What is decompression sickness in divers?
- Nitrogen moves from high pressure in the lungs into the blood during a dive
- A slow return to the surface lets the nitrogen return to the lungs where it is breathed out
- A quick return doesn’t give the nitrogen enough time to leave the blood so instead it can form painful bubbles
What are the features of oxygen binding?
- Reaction has to be reversible
- Oxygen must dissociate at the tissue to supply them
- Oxygen combines reversibly
