Lecture 15 - Ventilation Flashcards
Assertion question: FEV1/FVC ratio does not decrease below 70% in restrictive lung disease BECAUSE restrictive lung disease does not affect the airway resistance
A. Both statements (the one before and the one after “BECAUSE”) are true, and are causally related (the
fact presented in the first statement is a result of the fact presented in the second statement).
What do forced breathing measurements give us?
Info about air flow rates
What is forced vital capacity (FVC)?
maximum breath into maximum breath out (VC) - forced out as hard as possible
Variant of vital capacity (VC), useful diagnostic tool for the diagnosis of lung diseases – indicator of airway resistance
What is FEV1?
Forced expiratory volume in one second
What are the air flow rates in healthy lungs?
In healthy lungs -FEV1 / FVC = ~80%, (80% expirated in 1 second)
What happens to air flow rates in obstructive lung disease?
FEV1 big decrease & FVC decrease, thus FEV1/FVC = decrease
Ratio of less than 70%, indicative of increased airway resistance
What happens to air flow rates in restrictive lung disease?
FEV1/FVC ratio doesn’t change (or increased) - no change in airway resistance
What airway resistance disease affects air flow rates?
Obstructive lung disease
How can we measure total (mouth) ventilation (V̇E)?
Total (mouth) ventilation (V̇E)= frequency (f) x tidal volume (VT)
When can change V̇E?
To match metabolic demands (involuntarily, e.g exercise)
Voluntarily (changing breathing behaviour)
What is dead space?
Some of the inhaled air never gets to the alveoli
so cannot gas exchange – known as dead space
ventilation ( VD )
What are the two types of dead space that contribute to VD?
- Anatomical dead space
- Physiological dead space
VD = anatomical dead space + functional dead space
Where and what is our anatomical ‘dead space’?
Conducting airways (including mouth, trachea)
Ventilated but no respiration (no gas exchange)
Where and what is our functional ‘dead space’?
Respiratory area (gas exchange) could exchange gases but not happening - unused respiratory area
How big is dead space?
Dead space is approximately 1/3rd of the inspired air.
Dead space (VD) is approx. = 150 ml
145 ml air will stay in mouth,
trachea and Airways - 145 ml not available for respiration 355 ml air get into the respiratory area - approx. 5 ml of this air is not available for gas exchange
How can VD determine VA?
VE = VD + VA
How does Pulmonary Fibrosis affect VD?
Increases dead space by transforming
respiratory tissue into fibrotic tissue (e.g. cystic fibrosis, pulmonary fibrosis)
Scared alveoli that don’t work
How does Pulmonary Hypertension affect VD?
Increased dead space by impairing pulmonary
perfusion (pulmonary arteries not functioning properly)
What is the affect of fast shallow breathing on VA?
Decreased AV – causing hypoxia (↓PAO2), hypercapnia (↑PACO2) and acidity
From a gas exchange point of view, wastes ventilation in the dead space
Is energetically costly for the respiratory muscles
Less gas exchange (when the tidal volume (VT) is low)
What is the affect of slow deep breathing on VA?
Increased alveolar ventilation – causing hyperoxia (↑PAO2), hypocapnia (↓PACO2) and
alkalinity
↑ Gas exchange
Is energetically costly for the respiratory muscles
What is Dalton’s Law?
Partial Pressure = fraction of individual gas x total gas pressure
Pgas= Fgas X Ptotal
What is partial pressure (P)?
In a gas mixture (air), each gas exerts its own individual pressure, called a partial pressure (P), in direct proportion to its fractional concentration in the mixture.
What is alveolar ventilation in a healthy lung?
4 L/min
What is Pulmonary blood blow in a healthy lung?
5 L/min
What is the ventilation and perfusion relationship defined by?
Defined as the ratio of ventilation to perfusion
Normal = 0.8
Any change in the ratio – impairs O2 and CO2
transfer
What is the ventilation and perfusion relationship defined by?
Defined as the ratio of ventilation to perfusion
Normal = 0.8
Any change in the ratio – impairs O2 and CO2
transfer
What happens to ventilation and perfusion relationship during physiological shunt?
Ratio does not = 0.8
Decreased ventilation
Constant perfusion
What happens to ventilation and perfusion relationship during anatomical shunt?
Ratio does not = 0.8
What happens to ventilation and perfusion relationship during Low ventilation/perfusion?
Ratio does not = 0.8
Decreased ventilation
Constant perfusion
What lung diseases impair ventilation?
• Atelectasis (fibrosis)
• Emphysema
• Pulmonary oedema (fluid)
What lung diseases impair perfusion?
• Pulmonary hypertension
• Heart failure
• Vascular disease associated with COPD
