Lecture 3.1: Lung Ventilation Flashcards
How much oxygen should blood pick up in the lungs at rest?
5 liters of blood must pick up 12 mmol of oxygen per minute
How many alveoli do we have?
300 million alveoli (each surrounded by a capillary)
What is the order of sub-divisions in the lung airways?
• Trachea branches
• Main bronchi (right and left)
• Lobar bronchi (3 on right 2 on left)
• Segmental bronchi
• Sub-segmental bronchi
• Bronchioles
• Terminal bronchioles
• Respiratory bronchioles
• Alveolar ducts
• Alveoli
What is the difference between the walls of bronchi and bronchioles?
• Bronchi have cartilage in walls
• Bronchioles do not but do have more
smooth muscle
What is the importance of the hydrostatic pressure gradient?
Drives fluid from the pulmonary microcirculation into the interstitium
What is the importance of the oncotic pressure (colloidal osmotic pressure)?
Gradient favours movement of fluid in the opposite direction
How does ‘alveolar air’ have a different composition to the atmosphere?
• Less Oxygen
• More Carbon Dioxide
• As gas exchange removes oxygen from and
adds carbon dioxide to alveolar air
Mixed Venous Blood: pO2? pCO2?
• Returns to the lungs from the body
• pO2 typically 6.0 kPa
• pCO2 typically 6.5 kPa
• This varies with metabolism
Alveolar Air: pO2? pCO2?
• pO2 normally 13.3 kPa
• pCO2 normally 5.3 kPa
What are the 3 factors that affect Diffusion?
1) Area: Large (exchange area in normal lung
70m2)
2) Gradients: Large
3) Diffusion Resistance
Diffusion Barrier
• Diffusion through gas to alveolar wall
• Epithelial cell of alveolus
• Tissue Fluid
• Endothelial Cell of Capillary
• Plasma
• Red Cell Membrane
What machine is used to measure ventilation?
Spirometer
How to use a Spirometer?
• Subject breathes from a closed chamber
over water
• Whose volume changes with ventilation
What is Tidal Volume?
• Volume in and out with each breath
• In males: 0.5L
• In females: 0.5L
What is Inspiratory Reserve Volume?
• Extra volume that can be breathed in over
that at rest
• In males: 3.3L
• In females: 1.9L
What is Expiratory Reserve Volume?
• Extra volume that can be breathed out
over that at rest
• In males: 1.1L
• In females: 0.7L
What is Residual Volume? How to measure it?
• Volume left in lungs at maximal expiration
(0.8L)
• Volume does not change
• Cannot be measured by spirometer
• Use helium dilution
Lung Capacities vs Lung Volumes
• Lung volumes change with breathing pattern
• Capacities do not change
• Because measured from fixed points in breathing cycle
What are the 4 measured Lung Capacities?
- Vital capacity (VC) (can be measured by spirometers)
- Total lung capacity (TLC)
- Inspiratory capacity (IC) (can be measured by spirometers)
- Functional residual capacity (FRC)
What is Vital Capacity?
• Measured from max inspiration to max expiration
• Often changes in disease
• Typically 5L
• Total Lung Capacity = Vital Capacity + Reserve Volume
What is Inspiratory Capacity?
• Biggest breath that can be taken from resting expiratory level
• Typically 3.8L
What is Functional Residual Capacity?
• Volume of air in lungs at resting expiratory level
• Typically 2L
• Functional Residual Capacity = Expiratory Reserve Volume + Residual Volume
What is Ventilation Rate?
The amount of air moved into and out of a space per minute product of:
1) Volume moved per breath
2) Respiratory Rate
What is Pulmonary Ventilation Rate?
• Tidal volume x respiratory rate
• Typically 8l.min-1 at rest
• Can exceed 80 l.min-1 in exercise
What is Dead Space?
• The volume of air that is inhaled that does not take part in the gas exchange
• Because it either remains in the conducting airways
• Or reaches alveoli that are not perfused or poorly perfused
What is Serial Dead Space?
Anatomical Deadspace
What is Distributive Dead Space?
Alveolar Deadspace
What is Alveolar Ventilation Rate?
• The amount of air that actually reaches the alveoli
What is the calculation for Physiological Dead Space?
• Serial Dead Space + Distributive Dead Space = Physiological Dead Space
• Typically 0.17l
What is the calculation for Alveolar Ventilation Rate?
Alveolar Ventilation Rate = Pulmonary Ventilation Rate - Dead Space Ventilation Rate
How to calculate DSVR?
DSVR = DS vol x Respiratory Rate
How to calculate Pulmonary Ventilation Rate?
PVR = Tital Volume x Respiratory Rate
How to calculate Alveolar Ventilation Rate?
AVR = PVR - DSVR
How much Inspired Air is ‘wasted’ in normal breathing?
1/3
How much Inspired Air is ‘wasted’ in shallow, rapid breathing?
2/3
But why do we not take slow, deep breaths if less inspired air is ‘wasted’?
It is hard work so at rest we adopt an intermediate rate and depth
What is Ventilation Perfusion Matching (Ratio)?
A ratio used to assess the efficiency and adequacy of the matching of two variables:
• V – ventilation – the air that reaches the alveoli
• Q – perfusion – the blood that reaches the alveoli via the capillaries
• V/Q
Why can Ventilation Perfusion Mismatch occur? (3)
Reduced ventilation to a well perfused area of the lung:
• Airway obstruction
• Alveolar disease, damage
Reduced perfusion to well ventilated areas of the lung:
• Pulmonary embolism
