lecture 2 (respiratory) Flashcards
(24 cards)
what are the functions of the lungs?
- uptake of oxygen
- elimination of co2
- maintenance of acid-base stability
how much perfusion should occur?
- 5L/min
what is the ventilation rate?
- 5 L/min
what is the composition of mixed venous blood?
- lots of CO2
- low levels of O2
what is the composition of alveolar blood?
- lots of oxygen
- lower levels of co2
what occurs in real life gas exchange?
- ventilation and perfusion is uneven
what is the cause for the unevenness?
- gravity
- patchy diseases of airways, alveoli etc.
what are the consequences of uneven gas exchange?
- efficiency depends on dispersion of ventilation/perfusion
how does gravity affect alveolar distension?
- upper alveoli more distended
what is regional lung compliance?
- larger alveoli are stiffer and expand less during breathing
what is shown in regional tidal expansion?
- less ventilation of upper parts compared to lower parts of lung
- effect of gravity on perfusion
where is there less perfusion?
- towards top of lung
where does more ventilation occur?
- towards the top
what are the mechanisms of hypoxaemia?
- low inspired oxygen
- hypoventilation (not breathing much)
- impaired diffusion
- ventilation/perfusion mismatching
how does hypoxaemia occur due to hypoventilation?
- low levels of oxygen enter
- causes decreased pressure of oxygen
- increased levels of co2 reaching arterial blood
what occurs in hypoxaemia due to impaired diffusion?
- increased distance for oxygen to travel
- high levels of o2 cant enter blood
- thickened membranes
what occurs in hypoxaemia due to perfusion ventilation mismatch?
- alters ratio
- mix in the blood can result in any ratio
what is hypercapnia?
- too high levels of CO2 in the body
what are the causes of hypercapnia?
- hypoventilation
- neuromuscular diseases
- chest wall deformities (scoliosis)
- sedation
- COPD
- severe asthma
what is the CO transfer factor (TLCO)?
- carbon monoxide diffusing capacity
what does the CO transfer factor measure?
- rate of uptake of CO during breath-holding after full inspiration of air containing CO and helium
what are the factors affecting TLCO?
- distribution of inspired gas
- integrity and number of alveoli
- thickness of alveolar-capillary membrane
- function of pulmonary capillaries
- haemoglobin concentration
how is effective alveolar volume tested in this test?
- by comparing inspired and expired helium concentration
what is KCO?
- rate of uptake of CO pr litre of effective alveolar volume
