Lung Mechanics Flashcards
How does air flow during inspiration?
Alveolar pressure is less than atmospheric so air can flow in
How does air flow during expiration?
Alveolar pressure is greater than atmospheric so air can flow out
What are the muscles of inspiration?
- Diaphragm
- External Intercostals
What are the muscles of expiration?
-Internal Intercostals
How do the muscles act on inspiration?
The diaphragm flattens and moves downward, expanding the thorax vertically.
The external intercostals move the ribs up and out enlarging the thorax lateral as well as anterior and posteriorly.
How do the muscles act on expiration?
Expiration is a mostly passive process in quiet breathing.
What is the action of the external intercostals similar to?
Lifting the handle of a bucket
How do the muscles act on forced expiration?
The internal intercostals contract and pull down on the ribs and make the thoracic cavity smaller
What are the accessory inspiratory muscles?
Sternocleidomastoid
Scalenus
How do the muscles act on forced inspiration?
The accessory inspiratory muscles raise the sternum and elevate the first 2 ribs in order to expand the chest cavity further. Only occurs during forced inspiration.
What is the Tidal Volume (Vt) of the lung?
It is the change in volume during quiet breathing
What is the Inspiratory Reserve Volume (IRV) of the lung?
It is the additional amount of air that can be inhaled in addition to the Tidal Volume.
What is the Expiratory Reserve Volume (ERV) of the lung?
It is the additional amount of air that can be exhaled in addition to the Tidal Volume.
What is the Residual Volume (RV) of the lung?
It is the volume remaining in the lungs after forced expiration and it cannot be exhaled.
What volume of the lung cannot be measured with spirometry?
Residual Volume as it is not physically blown out from the lungs.
What is the Inspiratory Capacity?
IC = IRV +Vt
It is the volume that can be inhaled after all respiratory muscles are relaxed.
What is the Functional Residual Capacity?
FRC = ERV + RV
It is the volume of air in the lungs when all of the respiratory muscles are relaxed.
What is the Vital Capacity?
VC = IRV + Vt + ERV
It is the maximum amount of air that can be moved when going from deep inspiration to deep expiration.
What is the Total Lung Capacity?
TLC = IRV + VT + ERV + RV
It is the total volume of air held by the lungs.
How can the FRC be measured?
It can be done by helium dilution.
How does the compliance of the lung change with its volume of air?
At volumes near the FRC, the compliance of the lung is maximized, but the compliance decreases as the volume of the lung increases.
What is the difference between specific lung compliance and lung compliance?
The specific lung compliance adjusts for different lung volumes so that they can be compared to each other, such as in the case of a child vs an adult. Specific compliance will not change with volume.
The lung compliance found is divided by its volume.
What is the normal compliance of the adult lung?
0.2 L/cm H2O
What forces must the inflation of the lung overcome?
- Viscoelastic properties of lung stretching
- Surface tension of the lungs
What happens to the compliance in emphysema?
It will increase the compliance as the disease will eat away at the elastin and collagen so that alveoli will stretch more but also have less surface area.
The FRC will increase and the intrapleural pressure will increase as well due to less recoil of the lungs.
What happens to the compliance in fibrosis?
The compliance decreases due to the scarring resulting in fibrotic tissue that is stiffer and also thickens the gas diffusion pathway.
The FRC decreases due to increased lung recoil and the intrapleural pressure becomes more negative.
What is hysteresis?
Dissipating energy between inflation and deflation
When does the compliance of the lung drastically decrease?
When the lung is inflated close to the TLC or deflated below the FRC.
Describe the movement of the lung and chest wall from deflation to inflation.
With shallow inflations from FRC to the equilibrium position of the chest wall, the lung is stretched and the chest wall relaxed.
With deep inflations from FRC to above the equilibrium position of the chest wall, both the chest wall and lung are stretched out.
With deflations of any volume below FRC, the chest wall is always stretched inward.
How is the intrapleural pressure like compared to the pressure within the lungs?
It is lower
What is a pneumothorax?
It occurs when the pleural space is punctured and its pressure equilibrates with atmospheric pressure. It causes the expansion of the chest wall and recoil of the lung to 10% of its size.
What are the 3 phases during quiet breathing?
Dynamic Inspiration
Dynamic Expiration
Static Pause
Which is active breathing?
Inspiration
Which is passive breathing?
Expiration
At points of no air flow, what is the pressure across the respiratory system?
0
During quiet breathing, what is intrapleural pressure like?
It is always below atmospheric pressure.
What are the factors that determine airflow?
Pattern of airflow
Resistance to airflow by airways
What are the patterns of airflow?
Laminar
Transitional
Turbulent
What is laminar airflow?
It is flow is parallel to the tube where the center travels around twice as fast as the average.
What is transitional airflow?
It occurs in branches where eddies of air occur.
What is turbulent airflow?
It is non uniform flow where to increase the flow two times pressure must be increased four times. This shows that the pressure and flow are related in a non-linear relationship.
Where is turbulent airflow found in the airway?
Trachea
Where is laminar airflow found in the airway?
Small bronchioles
What kind of airflow is found in the respiratory bronchioles?
Diffusion
At what value of Reynold’s number does turbulent flow occur?
> 2000
What are the types of airflow found in the conducting zone?
Turbulent and Laminar
What are the types of airflow found in the respiratory region?
Diffusion
Based on Pouselle’s Law, what happens to the resistance as the radius of the vessel decreases?
As radius decreases, the resistance will increase dramatically.
As the generations of airways increases, what happens to the radius of the airways?
Decreases
As the generations of airways increases, what happens to the resistance of the airways?
Decreases
Why does the resistance of the airways decrease as their radii decrease even though Pouselle’s Law says that it should increase?
The resistance decreases dramatically in the later generations as the lung volume is increasing more. Increases in the lung volume decreases the resistance dramatically by increasing the lung diameter.
What is the most important factor affecting the airway resistance?
Lung Volume
Where is the highest resistance in the airway found?
In the first 6 or 7 generations due to the turbulent flow found in the conducting zone
How does sympathetic stimulation affect the airway resistance?
It will decrease the airway resistance by increasing the lung volume.
How does parasympathetic stimulation affect the airway resistance?
It will increase the airway resistance by decreasing the lung volume.
What is the forced vital capacity (FVC)?
It is where the patient first inhales as much as possible and then exhales as much as possible.
What is forced expiratory volume 1 (FEV1)?
It is the volume that can be forcefully exhaled in 1 second
What should the FEV1 be around?
> 75%
What is the peak expiratory flow rate (PEFR)?
It is the most positive airflow in a Flow-Volume Loop
When does the PEFR generally occur on the F-V Loop?
It generally occurs early on, at around 20% of the first cycle
What is the peak inspiratory flow rate (PIFR)?
It is the most negative airflow in a Flow-Volume Loop
What happens to force of the inspiratory muscles as the lung volume increases during inspiration?
It decreases
What happens to the lung recoil pressure as the volume of the lung increases?
It increases
What happens to the airway resistance as the lung volume increases?
It decreases
When does the max inspiratory flow rate occur?
Halfway between the TLC and the RV.
What happens the expiratory flow rate as it approaches the RV?
It decreases
What is expiratory flow limitation?
It is a point in expiration where it becomes effort independent because of the limited flow as the RV is approached.
What causes flow limitation?
It is caused by the dynamic compression of the airways when the pressure outside of the airways is greater than the pressure within the airways.
What is the equal pressure point?
It is the point where the airflow becomes independent of the total driving pressure due to the extra-airway pressure being equal to the intra-airway pressure.
What happens to the airflow in obstructive diseases like asthma and COPD?
The FEV1 is drastically reduced due to the airway resistance increasing a lot.
What happens to the airflow in restrictive lung diseases like fibrosis?
The FVC is reduced because the lung cannot fill as much compared to a normal lung due to lowered compliance.
How is asthma diagnosed?
It is done so by looking at the FEV1 to FVC ratio, with abnormally low ratios being possible cases of asthma.
What is used to treat asthma and how does it work?
Albuterol. It works as a beta-2 agonist which results in bronchodilation.
What is elastic work?
It is the work done to overcome the elastic recoil of the lung and expand the thoracic cage and it is related to the tidal volume.
What is the non-elastic work?
It is the work done to overcome the airflow resistance and is related to the breathing frequency.
What are some factors that can increase the work of the lungs?
– Pulmonary compliance is reduced – Airway resistance is increased – Elastic recoil is decreased – Exercise, however total energy is also increased, proportion remains at ~5%
What happens to the breathing of fibrosis patients?
It becomes shallow and rapid because the elastic work is increased a lot.
What happens to the breathing of COPD patients?
It becomes more slow and deep as airway resistance is increased and it becomes flow limited.
