Respiratory physiology I: Lung Mechanics Flashcards
Describe breathing and ventilation
this is the flow in and out of the respiratory system
what is the movement of air into the body due to
the movement of air in and out of the lungs occurs due to pressure differences
how are pressure differences created
- Pressure differences are created by changes in lung volume because air flows from a region of a high pressure to a region of low pressure
describe what drives inhalation
- driven by diaphragm which contracts and flattens leading to an increase in lung size and consequently air moves into the lungs
what drives exhalation
– diaphragm relaxes which leads to a decrease in lung size and therefore pressure increases and air moves out of the lungs
How do we measure lung function
spirometry
define tidal volume
amount of air you move into and out of your lungs during rest, not the sum of the two
define inspiratory capacity
total volume of air that you can breathe in at maximum lung capacity at rest
define expiratory capacity
total volume of air that you can breath out of the lungs at maximum lung capacity at rest
define forced vital capacity
maximum volume of air into and out of the lungs in a single respiratory cycle
define residual volume
volume of air that remains in the lungs even after maximal exhalation
How do you calculate the forced vital capacity
- Inspiratory reserve capacity+ tidal volume + expiratory reserve volume = forced vital capacity
what is FEV1/FVC
• FEVI/FVC is a ratio of Forced Expiratory Volume in 1 sec & Forced Vital Capacity
what is the normal FEV1/FVC ratio
values above 70-80% = normal. Age/gender adjusted
what causes the decrease of the FEV1/FVC
• Airflow limitation (e.g. Asthma)
what generates the pressure differences for breathing
it is the respiratory muscles that generate the pressure differences for breathing
what happens during inspiration of quiet breathing
- inspiration: active part of passive breathing
- Diaphragm and external intercostal muscles
what happens during inspiration in forced breathing
- Inspiration: diaphragm, external intercostal muscles and accessory muscles such as pectoralis major and minor and serratus anterior
what is the diaphragm innervated by
- it is innervated by the phrenic nerve
describe measurements of the diaphragm
- rest – 1-2cm
- forced breathing < 10cm
what are the two muscles that the external intercostal muscles do
- pump handle movements; anterior end of each rib is elevated
- bucket handle movements; dimeter of chest increases
what happens during expiration in quiet breathing
- expiration; largely passive as a result of elastic recoil of the lungs
what happen during expiration in forced breathing
- active
- involves accessory respiratory muscles
- E.g. Anterior abdominal muscles & quadratus lumborum
define alveolar ventilation
- Defined by portion of the total ventilation that reaches the alveoli and participates in gas exchange
How do gasses move between air and blood
move between air and blood by passive diffusion
- movement of gases is defined by partial pressure gradients
what is hypoventilation or hyperventilation a sign of
lung diseases
what decreases as you descend the airways
airway ventilation and perfusion decrease
what is dead space
• Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles
it is the volume of air that does not exchange in gas
how large is the anatomical dead space
150 ml does not exchange gas
what is the anatomical dead space made out of which structures
made up of upper respiratory tract, trachea, bronchi, bronchioles, terminal bronchioles
what is alveolar dead space
alveoli that have insufficient blood supply to act as effective respiratory membranes therefore do not take part in gas exchange
How do you work out physiological dead space
anatomical dead space and alveolar dead space
how do you work out the rate at which new air reaches the alveoli
(tidal volume - dead space) x respiratory rate
describe the example of how you work out the rate at which new air reaches the alveoli
tidal volume – dead space) x respiratory rate
- Tidal volume=500 mL
- Anatomic dead space=150 mL
- Fresh air entering the lungs=350 mL
- Respiratory rate=12 breaths/min
- Alveolar ventilation (ml/min)
- 12X350=4200 mL/min (4.2L/min)
- This is the effective ventilation that brings about the exchange of O2 and CO2.
describe alveolar ventilation and respiratory exchange
Room = Almost zero CO2 & alveolar gas = 5.5% giving an output of:
4.2 X (5.5-0/100)=0.231 L/min or 231 mL/min
Oxygen forms 21% of atmospheric air and alveolar gas contains about 14% giving an uptake of:
4.2 X (21-14/100)=0.294 L/min or 294 mL/min
How do you see the spirometers restyles
- look at flow volume loops on the graph, where the Y axis is and X axis is
- after the starting point the curve rapidly mounts to a peak (peak expiratory flow)
- after the PEF the curve descends = the flow decreases as more air is expired, a normal non pathological F/V loop will descend into a straight or a convex line form top PEF to bottom FVC
