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Flashcards in Ventilation of the lungs Deck (18):

What is the resting expiratory level?

Naturally the lungs want to collapse inwards and upwards away from the diaphragm, similarly the thoracic cage wants to pull out and if you were to cut through the sternum during surgery the cage will spring outwards. This is known as the resting expiratory level where the whole respiratory system is at rest before you breath in or out.

At rest all the forces are in balance. This is its least energetic position and will always re assume this position when you relax hence why expiration is a much easier process that breathing in.


Which muscle is most important in inspiration?

Inhalation is done mainly by the diaphragm contracting and pushing downwards, whilst the external intercostal move the ribs up and out to increase the thoracic volume.


What casues the lung and thoracic cavity to adhere to each other?

The intrapleural pressure is always negative so that the lungs and thoracic cavity adhere to each other.


Which other muscles are also used in forced expiration?

Abdominal and back muscles are used during ventilation when you are breathing heavily and this is known as forced expiration – breathing out beyond resting expiratory level requires force. This is also done with respiratory obstruction, disease states and generally to expel extra air. Expiration is almost all elastic recoil.


What is a capacity?

2 volumes make a capacity.


What is residual volume?

Residual volume of the lungs is the volume of air that occupies the dead space in your lungs.


How can obesity, pregnancy and clothing incur on breathing?

Difficulties with breathing can occur due to obstruction of the diaphragm and it can’t move into the abdomen


What is pleural fluid?

Pleural fluid – about 10ml per lung. This fluid ensures that the lungs ahdere to the thoracic cavity securely.


What is lung compliance?

This is the stretchiness of the lungs. It is the volume change per unit pressure change. Low compliance means it is more difficult to stretch, and higher compliance means it is much easier to stretch.


What causes the elasticity of the lungs?

The elasticity of the lungs is due to the elastin fibres and also the surface tension of the fluid lining the alveoli.


How is compliance changed by surface tension of lining fluid?

Compliance is reduced by surface tension of lining fluid.


How is elastic recoil related to compliance?

Elastic recoil is inversely proportional to compliance.


Discuss the importance of surface tension in the lungs

Surface tension – water molecuels attract each other. The interface of air and fluid makes the surface resistant to stretching. Alveoli have a fluid lining and so the higher the surface tension the harder the lungs are to stretch. Surface tension is reduced in the alveoli by surfactant produced by type 2 pneumocytes which interrupts the water molecules (most important protein is surfactant protein A). This makes it easier to inflate for little breaths but not so much for deep breaths.


Explain the importance of surfactant in alveoli?

Bubbles are created when a film of fluid shrinks to compress the gas until equilibirum of the pressure inside and outside are equal. Smaller bubbles have a higher pressure inside and the little bubbles are ‘eaten’ by the big bubbles as there is a movement of air down a pressure gradient. Surfactant equalizes the pressure of the alveoli in the lungs and prevents this from happening in the lungs. This is because surfactant become less effective at bigger radius’ so although the radius is increasing and so decreasing the pressure the surface tension is also increasing (because the surfactants are becoming less effective) and so this cancels out and the alveoli are all at the same pressure.


What is a surfactant and what does it do?

Surfactant = reduced surface tension, increases compliance, stops alveoli from collapsing and stops atelectasis (whole parts of the lung compliance).


What is RDS? (respiratory distress syndrome)

Babies born prematruely have too little surfactant as their type 2 penumocytes haven’t developed properly yet and their lugns are very stuff with large alveoli. This is treated by ventilating the babies lungs using a low pressure system and inserting synthetic surfactant in small amounts as the bab grows.

*Adult RDS is different and must not be confused with this*


Why is the flow resistance through the tubes in lungs not as high as you'd expect?

The ventilatory system is made up of many small tubes which all have a high flow resistance so you’d expect the resistance to be very high however the viscosity of air is very low and as these tubes are all in parallel this decreases the resistance.


Why does high intrathoracic pressure and disease such as asthma or infection cause difficulties expelling air?

When the thorax is compromised and the intrathroacic pressure is high this will cause small airways to narrow, this dramtically increases resistance and traps air inside alveoli. Similarly if the airways becoem narrowed due to disease such as asthma or infection then inspiration is okay as the upper airwyas can expand and lower resistance but resistance in expiration is much higher and so breathing out can be difficult.