Session 3 Flashcards
What is Fick’s first law of diffusion?
Flux of molecules across a barrier is proportional to the product of the permeability of the molecules, transfer surface area for diffusion and concentration gradient.
Is carbon dioxide more or less soluble than oxygen? What effect does this have?
More soluble, allows it to diffuse easily with a smaller gradient.
How are the lungs adapted for diffusion?
Large SA; small diffusion barrier; lung distension makes the diffusion barrier smaller.
How does inspired air differ from expired air?
Dry; lower oxygen content; higher carbon dioxide content; same nitrogen content; same overall pressure.
How is carbon dioxide transported in the blood?
Most as bicarbonate ions in the plasma; some as carboxyhaemaglobin.
What conditions can affect membrane thickness in the lungs?
Oedema of the interstitial space or alveoli; fibrotic disease.
What conditions can affect lung surface area?
Removal of a lung; emphysema.
What is seral dead space?
The volume of the conducting portions of the airways where no gas exchange occurs.
What is distributive dead space?
Parts of the lungs which don’t support gas exchange: dead or damaged alveoli; alveoli with poor perfusion.
What is physiological dead space?
Combination of seral and distributive dead space.
What is alveolar ventilation rate?
Pulmonary ventilation rate - dead space volume x resp rate.
What is the normal value for AVR?
5 litres per minute.
What is normal ventilation-perfusion rate?
1.
What is tidal volume?
Volume in and out with each breath.
What is inspiratory reserve volume?
Additional volume that can be inspired above that at rest.
What is expiratory reserve volume?
Additional volume that can be expired above that at rest.
What is residual volume?
The volume remaining after maximal expiration.
What is vital lung capacity?
The largest breath a person can take.
What is inspiratory capacity?
The maximum volume inhaled from resting expiratory level.
What is functional residual capacity?
The volume in the lungs at resting expiratory level.
What is total lung capacity?
The volume in the lungs at the end of maximal inspiration.
What factors can influence vital capacity?
Compliance of the lungs and force of insporatory muscles on inspiration; airway resistance on expiration.
What does spirometers produce?
A volume/time graph for ventilation.
What can be interpreted from single-breath spirometers?
FEV1.0, FVC.
How is residual lung volume measured?
Helium dilution: set amount of helium is inhaled; helium dilutes gases in the lungs but isn’t metabolised; level of dilution allows amount of air already in the lungs to be calculated.
How is serial dead space measured?
Nitrogen washout: patient breathes in pure oxygen; breathes out through a meter measuring nitrogen concentration; volume expired before nitrogen is found is the serial dead space volume.
Describe what is seen in obstructive pattern respiratory problems.
Airways are narrowed so lungs are easy to fill but hard to empty: FEV1.0 is reduced but FVC is normal.
If obstructive respiratory problems are relieved by bronchodilators, what does this suggest?
Asthma.
Describe restrictive respiratory problems.
Lungs are difficult to fill: FVC is reduced and FEV1.0:FVC is raised.
Why is peak flow useful?
Can be used to screen for airway narrowing.
