Lecture 3: Respiratory Mechanics Flashcards
Compliance of the lung _________ with _________ lung volume; relate to compliance and elastance
Decreases with increasing (more –> less compliance, less –> more elastance)
If the pleural plessure _______ 0, what happens to the lungs? To the chest wall?
Lungs collapse, chest wall springs outward
At the functional resting capacity, the pressure of the lungs equals what?
The negative pressure of the chest wall
What size of alveoli is unstable? What’s the equation?
Small; P = 2T / r
Describe surfactant
Phospholipids that migrate to surface of alveoli w/ hydrophobic ends sticking out, decreasing surface tension
What is hysteresis?
Change in mechanical properties due to the volume history of the lung (lung volume depends not only pressure but also whether your inspiring or expiring)
Higher pressures are required to open/close airways
Open
Lungs filled with water are more/less compliant? What does this mean?
More (surfactant is more important for compliance than lung’s intrinsic properties)
Laminar flow is proportional to…Turbulent flow is proportional to…
Pressure difference; the square root of pressure difference
Reynold’s number
Determines laminar (smaller numbers) or turbulent (larger numbers) flow; = pdV / viscosity of gas
While each airway by itself gets smaller through the respiratory track…
Entire cross-sectional area of peripheral airways is much greater than that of central areas
In large airways, what kind of flow do we get?
Turbulent
In peripheral airways, what kind of flow do we get?
Peripheral
Where do we get the most resistance in the airways?
Early (bronci)
Resistance is proportional to gas _______ in turbulent flow. Give a clinical indication of this.
Density; heliox (helium/oxygen mixture less dense than air) can be given to patients with upper airway narrowing to decrease airway resistance
Functional residual capacity (FRC) equals…
ERV (expiratory reserve volume) + RV (residual volume)
Vital capacity (VC) equals…
IRV (inspiratory reserve volume) + TV (tidal volume) + ERV (expiratory reserve volume)
What is spirometry
Amount (volume) and speed (flow) of air that an be inhaled/exhaled from lungs
Can you measure residual volume with spirometry? What else can you NOT measure?
No (it is not actually breathed); FRC and TLC (total lung capacity)
What is FEV1 and FVC? What is normal ratio?
Forced expiratory volume in one second; forced vital capacity; 80%
If it takes you longer than one second to get out 70% of your air, this suggests what kind of…
Obstructive ventilatory defect
Normal or elevated FEV1/FVC suggests…
Restrictive ventilatory defect
What is a restrictive ventilatory defect defined by?
Reduced TLC
Flow-volume loop: obstructive
Peak expiratory flow may be low, but will drop with scooped out shape (long exhale)
Flow-volume loop: restrictive
No scooped out shape, but much lower vital capacity
Obstruction can be (2)
Intrathoracic or extrathoracic
Stridor is what kind of obstruction? What happens to flow-volume loop?
Extrathoracic; flat inspiratory curve
Wheezes is what kind of obstruction? What happens to flow-volume loop?
Intrathoracic; flat expiratory cure
Fixed obstruction will cause what to flow-volume loops
Flattening of both inspiration and expiration
How do you measure FRC? (2)
Plethysmography and helium dilution
At the top of inspiration, the intrapleural pressure is more/less negative than at rest
More negative
Describe the pressure of the alveolar space through inspiration and expiration
Inhale: 0 –> (-) –> 0 (at top of inspiration); exhale: 0 –> (+) –> (0) (think of it driven by the diaphragm’s actions)
