Pulmonary (minute) Ventilation (L/min)
total air movement in/out of lungs
Alveolar Ventilation(L/min)
Fresh air getting alveoli and therefore available for gas exchange
Air from deadspace
150mL
Total Pulmonary Ventilation =
Tidal Volume x Respiratory Rate
Tidal Volume
A measure of the amount of air a person inhales during a normal breath
Alveolar Ventilation=
Air to alveoli X Respiratory Rate
Air to Alveoli =
Tidal - dead space (150)
Partial pressure
pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whol gaseous mixture
If the atmospheric pressure is 760mmHg (101kPa) and 21% of air we breath is O2 what is the partial pressure of the oxygen we breath
760 X 0.21 = 160mmHg (21kPa)
Increased alveolar ventilation
Hyperventilation, PO2 rises and Pco2 falls
Decreased alveolar ventilation
Hypoventilation, PO2 falls and PCO2 rises
Law of Laplace
Inward directed pressure. The pressure required to keep the alveoli open
P= 2T/r
P= 2T/r
T= surface tension r= radius
When does surfactant start to be produced
25 weeks gestation and completes by 36 week
Why do babies no need a high change in pressure to inflate lungs
Lungs are filled with fluid and do not need to overcome surface tension (no air-water interface)
Compliance
Change in volume relative to change in pressure
High Compliance
Large increase in volume for a small decrease in ip pressure- easy for air to enter lungs- steep line
Low Compliance
Small increase in lung volume for a large decrease in pressure- difficult to inspire- less steep
Emphysema
loss of elastic tissue means expiration requires effort
Fibrosis
inert fibrous tissue means effort on inspiration increases
Compliance decreases from
base to apex, because of gravity apex is already stretched due to gravity and base is able to expand
Small change in intrapleural pressure brings about a larger change in volume at
the base compared to the apex
Obstructive
Increased compliance
Increased inspiration
Decreased expiration
Restrictive
Loss of lung compliance
Decreased inspiration
Examples of Obstructive
Asthma
Emphysema
Chronic Bronchitis
Examples of Restrictive
Fibrosis
Infant respiratory distress syndrome (insufficient surfactant)
Oedema
Pneumothorax
Technique used to measure abnormal lung fucntion
Spirometry
Spirometry measurements can be
Static: volume exhaled
Dynamic: time taken to exhale is being measured as well
What volumes can be measured by spirometry
everything except residual volume
Functional residual volume
Expiatory reserve volume + residual volume
Vital capacity
Expiatory reserve + Inspiratory Capacity + Inspiratory reserve
FEV1/FVC ratio is restrictive
High
FEV1/FVC in obstructive
low (both FEV1 and FVC fall so air comes out more slowly)
FEF (25-75)
Average expired flow over the middle of an FVC
Expiratory Reserve Volume
the additional amount of air that can be expired from the lungs by determined effort after normal expiration
Functional Residual Capacity
the volume of air present in the lungs at the end of passive expiration
Residual Volume
the amount of air that remains in a person’s lungs after fully exhaling
Vital Capacity
the maximum amount of air a person can expel from the lungs after a maximum inhalation