F Respiratory System

Question 1

Tidal Volume

Answer 1

Amount of air inspired or expired during normal breathing. Normal range is about 500ml
7ml/kg

Question 2

Inspiratory Reserve Volume

Answer 2

The maximum amount of air that can be inspired in addition to normal tidal volume, Normal range is 2500 -3000ml
45ml/kg

Question 3

Expiratory Reserve Volume

Answer 3

The maximum amount of air that can be exhaled after a normal tidal volume exhalation. Normal range is around 1000ml to 1200ml.
15ml/kg

Question 4

Residual Volume RV

Answer 4

The volume of air remaining in the lungs after maximal exhalation. Normal range is around 1200ml.
15ml/kg

Question 5

Vital Capacity

Answer 5

The maximum amount of air that can be exhaled after maximal inhalation.
It is the sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume.
TV + IRV + ERV
Normal range is around 4000ml-5000ml
67ml/kg

Question 6

Functional Residual Capacity (FRC)

Answer 6

Volume of air remaining in the lungs after a normal tidal volume exhalation.
It is the sum of expiratory reserve volume and residual volume. Normal range is around 2200-2500ml.
30ml/kg

Question 7

Total lung capacity (TLC)

Answer 7

The volume of air in the lungs at the end of maximal inspiration.
Sum of Vital Capacity (VC) and Residual Volume (RV).
Normal range is around 5500-6000ml
82ml/kg

Question 8

Volume v Capacity

Answer 8

Volume is set amount measured by spirometry or gas equation, Capacity is a derived value from the addition of multiple volumes
Capacity is a measure of the lungs ability to hold a gas.

Question 9

Inspiratory Capacity

Answer 9

The maximum volume of gas that can be inspired from FRC
52ml/kg

Question 10

Graph of Lung volumes and capacities

Answer 10

See notes

Question 11

Functions of FRC

Answer 11

It keeps small airways open.
It is representative of compliance
It represents optimal compliance
It keeps a gas reserve between breaths
It keeps pulmonary vascular resistance at a minimum
Relationship between FRC and closing capacity influences the development of atelectasis and shunt.

Question 12

How does the FRC keep small airways open

Answer 12

At FRC small airways are splinted open by the tension of the surrounding lung tissue.
If FRC is reduced below the closing capacity, there will be gas trapping and atelectasis

Question 13

How is FRC representative of compliance

Answer 13

Any decrease in lung compliance causes a decrease in FRC

Question 14

How does FRC represent optimal compliance?

Answer 14

At FRC the pressure volume curve which represents compliance is at its steepest.
Which means, the work of breathing required to inflate the lung from FRC is at it’s minimum.
In other words, ventilating tidal volumes whihc start and end at FRC is the most energy efficient form of breathing.

Question 15

How does FRC keep a gas reserve between breaths

Answer 15

Breathing is an intermittent phenomenon, during 2 thirds of which there is no gas entering the chest.
IF there was no FRC, there would be no gas exchange and the pulmonary circulation would return deoxygenated blood to the left atrium for the majority of the resp cycle.
Because some gas remains in the lung, gas exchange can carry on during the entire cycle.
Eg in anaesthetisia, peri intubation time dependent on o2 stores in FRC

Question 16

How does FRC keep pulmonary vascular resistance at a minimum?

Answer 16

The alveolar and extra-alveolar vessels change there resistance characteristics as lung volume changes.
Small lung volumes: everything collapsed, PVR high.
As inflates to FRC arteries can increase in diameter and the resistance decreases.
At higher inflation expanding alveoli compress the small interalveolar vessels and increase PVR again.
Ergo: FRC is where PVR is at its lowest, representing the bottom of the U shaped PVR volume curve.

Question 17

Factors which influence FRC - Increase

Answer 17

Increased lung size :
Increased height
Male gender
Age:Ratio of FRC to TLC increases but absolute FRC remains the same
Increased compliance
Emphysema
Increased end expiratory pressure, eg PEEP or auto PEEP
Open chest or mediastinum
Upright position and prone position

Question 18

Factors which decrease FRC

Answer 18

Short stature
Female gender
Decreased lung compliance due to disease eg ards
negative end expiratory pressure
increased intra abdominal pressure
Pregnancy ascites etc
Decreased resp muscle tone eg anaesthesia, sedation
Supine and head down position
Obesity
Circumferential burns
Chest binder devices

Question 19

Consequences of a decreased FRC on lung mechanisms

Answer 19

Decreased lung compliance
Increased airway resistance
Increased work of breathing
Decreased tidal volume and increased respiratory rate due to decreased lung compliance
Decreased tolerance of position changes

Question 20

Effect of decreased FRC on gas exchange

Answer 20

Decreased o2 reserves
increased atelectasis
increased shunt

Question 21

Effects of decreased FRC on the pulmonary circulation

Answer 21

Increased pulmonary vascular resistance
Increased RV afterload

Question 22

How does decreased FRC cause decreased lung compliance?

Answer 22

The decreasing size of alveoli at lower FRCs results in an increased amount of work required ot inflate them, according to the law of Laplace, which holds that the pressure or surface tension inside an elastic sphere is inversely proportional to the radius

Question 23

Law of Laplace

Answer 23

The pressure or surface tension inside an elastic sphere is inversely proportional to the radius.