Ventilation Flashcards
What does “volume” refer to
discrete sections of a lung volume graph that do not overlap
What is capacity
the sum of two or more volumes
What can vital capacity be thought of as
useful air
What is tidal volume
normal breathing at rest
What is the residual volume
volume that is not expelled in ventilation to allow the lungs to inflate again as wet surface will stick together
What factors affect volumes and capacities
Sex Disease Body size Fitness Age
Define anatomical dead space
The capacity of the airways incapable of undertaking gas exchange
Define alveolar dead space
Capacity of the airways that should be able to undertake gas exchange but cannot e.g. hypoperfused alveoli
Define physiological dead space
Equivalent to the sum of alveolar and anatomical dead space
conducting zone + non-perfuse parenchyma air
Describe the respiratory zone
7 generations
Gas exchange
350mL
air here is equivalent to alveolar ventilation
Describe the conducting zone
16 generations
No gas exchange
140mL
equivalent to anatomical dead space
Describe non-perfuse parenchyma
alveoli with no blood supply
No gas exchange
0mL
alveolar dead space
Give 2 reversible procedures to alter the dead space
Tracheostomy or cricothyrotomy to decrease dead space
Anaesthetic circuit or snorkelling to increase dead space
How does changes in pressure alter the work that must be put in for inflation
The greater the pressure, the more work that must be put in to expand the lungs
Describe what occurs during ventilation in terms of dead space
- Functional residual capacity initially
- Alveolar pressure inside decreases
- Air flows in due to gradient
- Tidal volume reached
- Lungs recoil and the air is compressed
- Pressure gradient forces air out
- Ends at functional residual capacity
Define pulmonary ventilation
Air ventilating the entire airway
Define alveolar ventilation
air ventilation the respiratory exchange surface
When is ventilation +ve or -ve pressure
\+ve= ventilation or CPR -ve = normal breathing
Describe the healthy chest
Single unit
Pleural cavity is a partial vacuum
Describe tidal breathing
Tidal breathing is predominantly diaphragm-induced
Maximum ventilation involves full inspiratory muscle recruitment
Describe the chest wall relationship
The chest wall has a tendency to spring outwards and the lung has a tendency to recoil inwards
These forces are in equilibrium at end-tidal expiration (functional residual capacity, FCR) which is the neutral position of the intact chest
What leads to inspiration and expiration in terms of the chest wall relationship
inspiratory muscle effort and chest recoil > lung recoil = inspiration
chest recoil expiration
Describe the membranes surrounding the lung
The lungs are surrounded by a visceral pleural membrane
The inner surface of the chest wall is covered by a parietal pleural membrane
The pleural cavity is a fixed volume and contains protein-rich pleural fluid
What can interruptions to the pleural cavity cause
haemothorax or pneumothorax
Describe the 3 compartment model
Transmural pressures = (Pinside – Poutside)
A negative transrespiratory pressure will lead to inspiration
A positive transmural pressure leads to expiration
Describe the procedure for the volume time curve
- Patient wears a noseclip
- Patient inhales to TLC
- Patient wraps lips around mouthpiece
- Patient exhales as hard and fast as possible
- Exhalation continues until RV is reached or six seconds have passed
What should be assessed on the volume time curve
Slow starts
Early stops
Intramanouever variability
How is a volume time graph interpreted
FVC = top of the curve FEV = volume in 1 second
Describe what a volume time graph may look like for a restrictive and obstructive disease
restrictive = slightly reduced FVC, similar FEV, time breath is held for is short obstructive = reduced FVC and FEV
Describe the procedure for peak flow
- Patient wears noseclip
- Patient inhales to TLC
- Patient wraps lips around mouthpiece
- Patient exhales as hard and fast as possible
- Exhalation does not have to reach RV
- Repeat at least twice. Take highest measurement
Describe the procedure for the flow-volume loop measurement
- Patient wears a noseclip
- Patient wraps lips around mouthpiece
- Patient completes at least one tidal breath (A&B)
- Patient inhales steadily to TLC (C)
- Patient exhales as hard and fast as possible (D)
- Exhalation continues until RV is reached (E)
- Patient immediately inhales to TLC (F)
- Visually inspect performance and volume time curve and repeat if necessary
What should be looked out for when assessing the flow-volume loop
Inconsistencies with clinical picture
Interrupted flow data
