Physiology Lecture 1: Lung Statics Flashcards
Define tidal volume
Volume of air inspired and expired during regular breathing
Define vital capacity
Maximum volume of air that you can inspire and forcibly expire
Define residual volume
Volume in lungs that can never be expired (always there)
Equations for FRC
FRC = RV + ERV
(ERV = Expiratory reserve volume)
Equations for total lung capacity (TLC)
- TLC = IC + FRC
- (IC = Inspiratory capacity)
- TLC = RV + ERV + VT + IRV
Equations for vital capacity
- VC = ERV + VT + IRV
- IRV = inspiratory reserve volume
- VC = ERV + IC
Four major methods of volumes
- Spirometry
- Gas dilution
- Plethysmography (body box)
- Radiographic Techniques (x-ray; CT scan)
Function of spirometer
- Measure the volume of gas entering or leaving the mouth (changes in lung volume)
What divisions of lung volume can spirometry measure?
Subdivisions of vital capacity (VC, IRV, ERV, VT)
4 uses of spirometry
- Diagnosis of lung disease in patients
- Determine severity of disease
- Evaluate the evolution of disease
- Evaluate treatment effect
Define FEV1
Volume of air that can be forcibly expelled from maximum inspiration in the first second
Define FVC
Volume of air that can be forcibly expelled from maximum inspiration to maximum expiration
Define PEF
Maximum flow attained during a forced expiratory maneuver
What is the important ratio in determining the health state of lungs using spirometry?
FEV1/FVC
What is a normal FEV1/FVC ratio?
0.70
Describe the changes in the flow volume curve and volume-time curve in obstructive lung disease
- FEV1 and PEF are decreased
- FVC is decreased or unchanged
- **FEV1/FVC is decreased

Describe the changes in the flow volume curve and the volume-time curve of restrictive lung diseases
- FEV1 decreased
- Peak flow increases
- FVC decreases
- FEV1/FVC are normal or increased
Equation used in gas dilution (explain components)
C1V1=C2V2
where V2 = V1 + FRC if measured at the end of usual breath
Limitation of gas dilution
May underestimate lung volume of people with certain diseases (i.e. asthma) where air cannot accuss all parts of the lung
Plethysmography equation
Boyle’s Law: P1V1 = k
Why use plethysmograph?
Can measure trapped air volume not accessible by gas dilution
3 determinants of lung volume
- Pulmonary compliance
- Chest wall compliance
- Respiratory muscles
Define transpulmonary pressure
Ptp = Pao - Ppl
Define transrespiratory pressure
PRS = Pao - Patm
Define transmural pressure
The pressure across the wall of a structure (i.e. chest wall, airway wall or alveolar wall)
Define compliance (in general)
- A measure of stiffness
- (Stiff = low; loose = high)
- The slope of the P-V curve
CL = ΔV/ΔP
How is pulmonary compliance obtained?
Using the transpulmonary pressure (Ptp)
What is Ptp a measure of?
Elastic recoil pressure (Pel)
When there is no flow, what is the Palv?
Pao = Palv
2 determinants of compliance
- Tissue Forces
- Surface tension
Where do the tissue forces of the lung come from?
Elastin-collagen proteoglycan network of the lung tissue
When are tissue forces reduced?
When the lung parenchymal architecture is destroyed (i.e. in emphysema)
When are tissue forces increased?
When lung scarring occurs (i.e. fibrosis)
2 vital properties of pulmonary surfactant
- Lowers surface tension to make it easier to inflate and delfate the lungs
- Promotes alveolar stability, reducing the chance that alveoli will collapse
Laplace’s Law
P = 2T/r
Airflow according to Laplace’s law in the alveoli. How does this relate to pulmonary surfactant?
Decreased alveolus size = increase pressure = wair wants to go to bigger alveoli (P gradient)
Therefore, without pulmonary surfactant, the smaller alveoli would all collapse
Describe the Pressure-Volume curve
Describe the pressure-volume curves in disease
3 determinants of residual volume
- Limit of chest wall (i.e. youth)
- Lung recoils inward
- Chest wall reocils outward
- Limit of emptying of the lung (i.e. elders)
- Obstruction = more time to exhale (notion of closing volume)
- Limit of expiratory force
- Too weak = cannot blow
Lung and chest recoil direction at TLC
Inward
FRC lung and chest wall recoil
Lungs = inward
Chest wall = ouitwards
(Balance)
RV lung and chest wall recoil direction
Lungs = inward
Chest wall = outward
+ effect of age and muscle strength