Normal physiology Flashcards
What is Spirometry? What is it’s usefulness ? What can it mesure ?
- Measures the volume of gas entering or leaving the mouth
- Useful to
- diagnose lung disease in patient
- determine severity of disease
- evaluate evolution of disease
- evaluate treatment effect
- Mesure
- vital capacity (VC)
- tidal volume (VT)
- doesn’t mesure RV (so no TLC, FRC)
What is gas dilution?
- Absolute lung volume cannot be measured by a spirometer because there is no way of expelling the RV into the spirometer (this would require complete collapse of the lungs).
- The subject rebreathes from a bag of volume V1 initially containing helium at concentration C1. After a while, the helium will equilibrate between the bag and the lungs as the helium becomes uniformly mixed throughout the whole closed system. This equilibrium concentration is C2 (and, of course, C1 > C2). However, helium is insoluble and not absorbed to any significant degree by the lungs so the total amount of helium at the end of the manoeuvre is the same as at the start, which is expressed as C1V1=C2V2
-
First bag volume and helium concentration are easily measured. Therefore, the only unknown quantity in this expression is V2, which is the sum of the bag (V1) and lung volume.
- C1V1 = C2(lung volume - V1)
What are the 4 major methods available to mesure lung volume ?
- spirometry
- gas dilution
- plethysmography (body box)
- radiographic techniques (x-ray, CT scan)
On a diagram of airflow and lung volume, where does the curve of obstructive lung disease shifts?
To the left (higher lung volume)

On a diagram of airflow and lung volume, where does the curve of restrictive lung disease shifts?
To the right (lower lung volume)

What is the 2 relations of lung pressure ?
- Ptp = Palv (Pao)-Ppl
- PRS = Palv (Pao)-Patm
What is pulmonary compliance?
The relationship between volume and pressure, a measure of how stiff a lung is (stiff lungs have low compliance)
CL= ∆V
∆P
- compliance is the slope of the P-V curve

In a Volume-Pressure curve, where is the curve of a person with emphysema compared to a person without this disease ?
- Left and up.
- the lung is easier to strech since there’s already air stuck in the alveoli
- The higher TLC is due to the fact that an unstiff lung won’t let you get all the air out

In a Volume-Pressure curve, where is the curve of a person with pulmonary fibrosis compared to a person without this disease ?
- RIght and down
- it takes a lot of pressure to make a big change in your lung volume

What are the determinants of lung volume?
- Pulmonary Compliance
- Chest Wall Compliance
- Respiratory Muscles

By what it influenced pulmonary compliance?
-
Tissue forces
- mesure of the elastin-collagen network
- increase in fibrosis
- decrease in ephysema
- mesure of the elastin-collagen network
-
Surface tension: modified by presence of pulmonary surfactant.
- Two vital properties of pulmonary surfactant
- lowers surface tension to make it easier to inflate and deflate the lungs
- promotes alveolar stability, reducing the chance that alveoli will collapse.
- Two vital properties of pulmonary surfactant
The top and the bottom of the lungs have difference compliance. In the compliance curve, when the lung is at TLC, what part of the lung is more difficult to fill in an upright posture?
BOTH: top and bottom of lungs are at the top portion of the compliance curve, they want to get emptied

The top and the bottom of the lungs have difference compliance. In the compliance curve, when the lung is at FRC, what part of the lung is more difficult to fill in an upright posture?
TOP PART: top is higher in the curve; bottom is in the middle (filled up more easily)

The top and the bottom of the lungs have difference compliance. In the compliance curve, when the lung is at RV, what part of the lung is more difficult to fill in an upright posture?
BOTTOM PART: top part is in the middle (filled up more easily); the bottom part is in the bottom

What are the 2 vital properties of pulmonary surfactant?
- Lowers surface tension to make it easier to inflate and deflate the lungs.
- Promotes alveolar stability, reducing the chance that alveoli will collapse
On what does the flow of the respiratory system depend on?
- Length of the tube
- Diameter of the tube
What are the 2 types of flow ?
- Laminar flow (more energy efficient, smaller airways)
- Turbulent flow (less energy efficient, bigger airways)
The nature of the flow changes as the gas moves from the mouth to the alveoli and back again

How can you change a turbulent flow to a laminar flow?
By changing the gas density (Reynold’s number)
What is the formula of resistance?
Resistance is the energy cost of flow. To calculate it:
V̇ = ∆P or R = ∆P
R V̇
True or false: the harder a person forces air out of their lungs, the faster gas will come out.
FALSE: Not in the effort-independant phase of expiration. Surprisingly, once flow reaches a certain level, no matter how hard the expiratory muscles push, flow will not increase any further. This phenomenon is called flow limitation.
there’s an effort-independant region in the flow curves
- As expiration proceeds the airways become narrowed at different sites creating choke points : at this point, the more you make an effort to expire, the more you squeeze the tubes and the more flow is limited.

What are the 2 large categories of lung disease?
- Obstructive: emphysema and brochitis
- Restrictive: pulmonary fibrosis and chest wall disease
On what depends maximum expiratory flow?
- Airway resistance
- Elastic recoil of the lungs
- Expiratory muscle strength
What is the index of obstruction? What does it means when it’s low ?
FEV1/FVC (>0.7 when normal) in expiratory spirometry
- when low, it indicates that it’s taking longer than usual to get air out.
What is dead space?
The total dead space, also refered to as physiological dead space, is the volume of inspired gas hat doesn’t exchange CO2
- Anatomic dead space (about 150 ml of inspired gas that get lost in the conducting zone)
- Alveolar dead space
- VD (physiological dead space) = anatomical dead space + alveolar dead space




































