Respiratory Mechanics Flashcards
FRC
“Functional Residual Capacity”
-Amount of air in the lungs with the mouth is held open; elastic recoil of the lungs and thoracic wall are equal and opposite
Most common cause of pleurisy
Viral infection
2 Forces of Lung Elastic Recoil
- Collagen and elastin fibers
2. Surface tension from the water lining the alveoli
Laplace’s Law (Surface Tension)
P=T/ r/2
*Pressure is inversely proportional to radius
Shunt
Vascular pathway in the lung which has no gas exchange
Dipalmitoyl phosphatidyl choline
“SURFACTANT”
-Surfactant inserts itself b/w water molecules lining the alveoli to decrease the cohesive forces b/w them
Net Result= Decreased surface tension
Tripod Position
Assumed by COPD pts. in an effort to force expiration of air
Pressures in Inspiration
Start: Transmural Pressure = -5 cm H2O; lung elastic recoil = 5 cm H2O
=>No air-flow
Begin inhalation: Pleural volume increases; decrease in Ppl
=> Lungs begin to expand
During Inhalation: Increased lung volume increases the volume of alveoli; Patm> Pa
=>Air flows in
End Inhalation: Elastic recoil is stretched to limits and it balances forces around the lung
=>Airflow stops
Flail Chest
Damage thorax causes chest cavity to move inward during inspiration
-Ppl is not sufficiently negative causing no air to flow in
Tension Pneumothorax
Air accumulates in pleural cavity after collapse of lung
*Mediastinum will shift to opposite side of lung
Transmural Pressure
Ptm= Palv- Ppl
Compliance in emphysema and fibrosis
Emphysema= INCREASED
Fibrosis= DECREASED
Specific Compliance
A measure of compliance as a function of size
C= P/V
Specific Compliance= C/volume of lungs
Total pulmonary compliance
1/total compliance= 1/lung compliance + 1/ chest wall compliance
Alveolar Simplification
Breakdown of structural proteins due to increased levels of trypsin in the lungs
=>Decreased # of alveoli
Centrilobar emphysema
Most common subtype of emphysema that affects the central region around the secondary pulmonary lobules; (Upper lobe)
- Spreads peripherally
- Assoc. w/ long-term smoking; inhalation of chemicals
Panacinar Emphysema
Uniform destruction of alveoli predominantly in the lower lungs
-Assoc. w/ AAT deficiencies of Ritalin abuse
Predict compliance in the following situations:
Decreased pulmonary surfactant
Removal of lobe
Obesity
Pulmonary Vascular Congestion
Decreased in all
Areas of greatest airway resistance
Large airways
Passive Exhalation
Elastic recoil forces in alveoli move air out of the airway; airway is held open by expansile forces since Ppl is negative
Forced Exhalation
When the rib cage pushes in and abdominal muscles push upwards, Ppl increases
Alveolar pressure becomes more positive pushing air out faster
Dynamic Compression
Increased Ppl during forced exhalation can cause collapse of the alveolar airways => Decreased air release
*Common in emphysema; decreased elastic recoil means air must be forced out of alveoli
Greatest flow rate in lungs
Large Airways
*Must have cartilaginous rings because fast air flow=decreased pressure; airway could collapse
Tethering
The attachment of alveoli to neighboring alveoli
=>Decreases the tendency for vessels to collapse
*Decreased in emphysema
Dead Space Volume
Volume of air person breathes but is not used for gas exchange
-Fills nose, pharynx, trachea (respiratory passages); part of first 17 divisions of respiratory system
FVC
“Forced Vital Capacity”
Amount of air that can be quickly expired
Cannot be measured w/ spirometry
RV, TLC, and FRC
-All include the RV
FRC measuremetn
Pbag X Vbag= PHe X (Vbag + FRC)
PHe=new pressure of helium in the lungs after mixing
Body Box Plethysmogrophy
Used to measure FRC in pts. w/ emphsyema because it takes them a long time to expire into the bag
Predict FRC in the following conditions:
Emphysema
Age
Laying Down
Obesity/Pregnancy
Kyphoscoliosis
Increased
Increased
Decreased
Decreased
Decreased
Barrel chest symptom
Residual pockets of air in emphysema pts. can lead to “barrel chest”
Bronchitis
Inflammation of the mucous membranes of the bronchi; affects the upper pathways of the respiratory system
COPD
Co-existence of emphysema and chronic bronchitis; assoc. w/ chronic narrowing of the pathways and shortness of breath
Sarcoidosis
The formulation of granulomas in the lungs due to the accumulation of chronic inflammatory cells; cause unknown
Flow Volume Loops of Emphysema
Expiration is low and prolonged due to high compliance and dynamic collapse; graph is shifted to the right
-Top part of graph has significant scooping
Flow Volume Loops of Restrictive Disease
Lungs are stiffer=> only small volume is inhaled and exhaled
*Top part of graph looks like a witch-hat
Diagnosis of Lung Diseases
Examine FEV1/FVC ratio
Examine the shape of the PV-loop
Perform methacholine and DLco test
Variable Intrathoracic Legions
Cause dynamic compression during forced expiration; legions will further compress airways along with increased Ppl
Variable Extrathoracic Legion
Cause dynamic compression during forced inhalation; negative Ppl causes the region near the trachea to collapse
*Vocal chord paralysis; fat deposits
Fixed Obstructions
Affect both inspiration and exhalation; caused by fibrosis or scarring
Methacholine Challenge Test
Give the pt. successively increased dosages of methacholine
(.0625-16mg/mL)
- 20% reduction in FEV before 16mg/mL => airway hyperreactivity
- Not all pts. may have asthma, pts. who do may test negative if they are on drugs or it has not been triggered
DLco
Diffusing Capacity of the Lung
DLco is directly related to surface area; indirectly rated to membrane thickness
*Emphysema=decrease A; Fibrosis=thickened membrane
Hypoxia stimulates what receptors?
Peripheral; during lung disease, patients respiration is being maintained by hypoxic stimulus of these receptors so they should NOT be placed on a ventilator
Causes a great increase in anatomical dead space
Mechanical ventilation
- This is due to P1V1=P2V2; use Va1/Va2=PaCO2/PaCO1 w/ before and after PaCO2s
- Equation possible due to inverse nature of the two
FEV1
Measurement of airway resistance; big FEV/small resistance
FEF25-75%
Slope of FEV1; directly related to FEV1
Fixed intra/extra thoracic legion
Causes compression on inspiration and expiration; caused by scarring and inflammation
O2 delivery
CO x O2 content
