35 - Pulmonary Pathophysiology Flashcards
What are the three major factors which will set off the peripheral chemo receptors and trigger an increase in respiratory rate?
1 - Increase in PCO2 ***
2 - Decrease in O2
3 - Decrease in pH
Describe the basic branching of the airway
The trachea bifurcates into two main stem bronchi, which then divide into lobar bronchi (one for each lobe), which in turn divide into segmental bronchi and into smaller and smaller branches until reaching the alveolus
Note that there is no gas exchange in the conducting airway
Describe the surface area achieved by the airway branching
Each branching of the respiratory bronchioles results in decreased diameter; however, the total surface area for that generation increases in size and number
Describe how gas exchange is maximized in the airway
In order to maximize gas exchange, capillaries branch as well as the airway
What is the KEY feature of obstructive airway diseases?
Increased resistance to airflow***
Give examples of obstructive airway diseases
- Inflammation of bronchial epithelium in bronchitis
- Secretions from epithelium (asthma, infection, decreased cilia)
- Constriction of smooth muscle in asthma
- Physical blockade (tumor, aspiration)
How do you calculate airway resistance?
Reynold’s formula
- Radius of the airway is the most influential factor determining airflow resistance.
- Resistance to airflow in the lower respiratory tract comes mainly from bronchioles and bronchi
What is Reynold’s formula?
R = (8nl)/(pi*r^4)
R = airway resistance n = viscosity of inspired air l = length of airway r = radius of the airway
What is the effect of parasympathetic activation on the airway resistance?
Increased airway resistance
- M3 activation occurs
- Examples: asthma, taking muscarinic agonists
What is the effect of sympathetic activation on the airway resistance?
Decreased airway resistance
- B2 activation occurs
- Examples: taking epinepherine or albuterol
What is the effect of bronchiolar size on the airway resistance
- Most important factor
- As bronchiolar size decreases, airway resistance increases
- Note that medium-sized bronchioles have the highest resistance compared to other bronchioles (most determinant factor on resistance)
What are three obstruction diseases that result from conditions in the airway wall?
1 - Asthma
2 - Acute bronchitis
3 - Chronic bronchitis
What is an obstructive disease that is related to the loss of lung parenchyma?
Emphysema
What are six obstruction diseases which are related to obstruction of the airway lumen?
1 - Bronchiectasis 2 - Bronchiolitis 3 - Cystic fibrosis 4 - Acute tracheobronchial obstruction 5 - Epiglottitis 6 - Croup syndrome
Describe why the respiratory surface between the air and blood is clinically relevant
Getting back to airway branching, you need to know the relationship between the air and the blood
- Very commonly affected by many disease states
- We want tot make sure the interface between the air and the blood is clear and free of infection
Describe the respiratory unit
The respiratory unit is where respiration takes place
- Consists of a respiratory bronchiole, alveolar ducts, atria and alveoli
- It is the site of gas exchange of the lung
Describe the pulmonary capillary network and “sheet of flow” concept
each alveolus contains 500 – 1000 capillaries that form a “sheet of flow” around it, substantially facilitating
gas exchange between the alveoli and the blood
Describe the capillary endothelium
- The endothelium of the capillary and the epithelium of the pulmonary unit are closely apposed
- There is only an ultra-thin barrier between the two surfaces
- There are NOT tight junctions here, but rather “leaky” cell junctions
Describe the function of this relationship between the capillary and respiratory unit
- The ultra thin barrier promotes gas exchange
- Water and solutes are able to move back and forth between the plasma and interstitial space due to “leaky” cell junctions
What is the respiratory membrane?
The basic respiratory membrane constitutes the
barriers that gas has to pass through for exchange
between the alveoli and the pulmonary capillary blood
What does the respiratory membrane consist of?
- a layer of fluid lining the alveolus containing surfactant - alveolar epithelium - epithelial basement membrane - interstitial space capillary basement membrane - capillary endothelial membrane
What is the effect of pathological conditions which affect the respiratory membrane?
Pathological conditions that
affect the thickness or integrity of any component of
the respiratory membrane will affect gas exchange at
the involved respiratory unit.
What is the lung interstitium?
The lung interstitial space or interstitium is
composed of connective tissue, smooth muscle,
lymphatics, capillaries, and a variety of other cells
What is the prominent cell in the interstitium?
Fibroblasts
Why are fibroblasts so important in the lung interstitium?
Fibroblasts produce collagen and elastin and therefore effect the distensibility and elastic recoil of the lungs
What is clinically relevant about the lung interstitium (interstitial space)?
Lung interstitium is very small under normal condition, but can become enlarged with inflammatory cells & edema fluid –> interfere with gas exchange
What is recoil?
Recoil is the ability of the lung to collapse once expanded (KNOW THIS)
What is distensibility?
Distensibility is the ability of the lung to expand once expanded (KNOW THIS)
What are the factors that affect gas diffusion across the respiratory membrane?
There is an equation for this…
D = (∆P × A × S)/ (d × √ MW)
D = diffusion of gas across respiratory membrane ∆P = partial pressure difference between alveoli and blood A = surface area d = distance between two sides of the membrane (thickness
What factors affect the partial pressure difference between alveoli and blood?
- High altitude
- O2 mask
- Restrictive lung disease
What factors affect the surface area?
- Atelectasis (collapsed lung)
- Tumors
What factors affect the distance between the two sides of the membrane (thickness)?
- Pulmonary edema
- Pneumonia
Describe the pleura of the lungs
Lungs are covered by the visceral pleura and
are encased by the parietal pleura. The interface of the two pleuras allows for smooth gliding of the lung as
What is pleural fluid?
Pleural fluid is interstitial liquid of the parietal pleura
Which layer of pleura contributes more to pleural fluid?
The main contribution to the pleural fluid is from the parietal pleura which smooths and lubricates the membrane
What is pleural effusion?
A pathological condition where a patient has a build up of pleural fluid
When do we most commonly see pleural effusion?
Congestive heart failure
- There is increased pulmonary venous hydrostatic pressure from the visceral side
- This means fluid is getting pushed out
What other things can cause or contribute to pleural effusion (think forces)
- Decreased microvascular oncotic pressure (less pull back into vasculature - can occur in nephrotic syndrome or liver disease when you lose a lot of plasma proteins)
- Decreased pleural pressure (negative pressure within the cavity pulls fluid in from the tissues - happens in collapsed lung aka atalectasis)
- Blockade of lymphatic drainage via the stoma (tumors and cancer can cause this)
What is a restrictive pulmonary disorder?
The result of decreased expansion of the lungs due to alterations in the lung parenchyma, pleura, chest wall, or neuromuscular function.
Most common restrictive pulmonary disorder is pneumonia
What are the four main categories of restrictive lung disorders?
***
1 - Lung parenchyma disorders
2 - Pleural space disorders
3 - Neuromuscular, chest wall and obesity disorders
4 - Infection or inflammation of the lung
Which diseases fall into the “lung parenchyma disorders” category of restrictive lung diseases?
- Fibrotic interstitial lung diseases
- Atelectasis disorders
List the fibrotic interstitial lung disease
- Diffuse Interstitial Lung Disease
- Sarcoidosis
- Hypersensitivity Pneumonitis
- Occupational lung diseases
List the atelectatic disorders
- Adult Respiratory Distress Syndrome (ARDS)
- Infant Respiratory Distress Syndrome
List the pleural space disorders
- Pneumothorax
- Pleural effusion
Pneumothorax occurs when air leaks into the space between your lungs and chest wall. This air pushes on the outside of your lung and makes it collapse.
What are the two categories of neuromuscular, chest wall and obesity disorders?
- Neuromuscular disorders
- Chest wall deformities
List the neuromuscular disorders
- Poliomyelitis
- Amyotropic Lateral
- Sclerosis
- Muscular Dystrophies
- Guillain Barre Syndrome
- Myasthenia Gravis
List the chest wall deformities
- Kyphoscoliosis
- Ankylosing Spondylitis
- Flail Chest
- Disorders of obesity
List the infections or inflammations of the lungs
- Pneumonia
- Severe acute respiratory syndrome
- Pulmonary tuberculosis
Describe the pulmonary circulation
- Largest vascular bed in the body
- Highly compliant vessels due to the thin walls ***
- Accommodates the entire cardiac output
Describe the bronchial circulation
- Only receives 1-2% of the cardiac output
- Bronchial circulation empties into the pulmonary veins then into the systemic circulation
- Generates a physiological shunt ***
Describe the physiological shunt created by the bronchial circulation
Approximately 1/3 of the blood from the bronchial circulation returns to the right atrium through the bronchial veins
- The remainder drains into the left atrium (with oxygenated blood) via pulmonary veins, generating physiological shunt of blood
What is hypoxic pulmonary vasoconstriction?
- A unique phenomenon to the lungs
- A mechanism for control of pulmonary blood flow distribution
- There is a “matching” between ventilation and perfusion/pulmonary blood flow
- If you have low ventilation in an area of the lung, the blood flow will shunt away from that area to increase efficiency
What happens over a long period of time to a low ventilated area?
- If this happens over a long period of time, there will be pathologic changes in the tissues
- Hypertrophy of vascular smooth muscle and others, leading to pulmonary hypertension
- The right heart will be effected by this, right heart failure will eventually occur
Describe the equation for ventilation-perfusion
The average normal value of V/Q is 0.8
Matching ventilation (V) to perfusion (Q) is critically important for ideal gas exchange: It is useless for alveoli to be ventilated but not perfused, or for alveoli to be perfused but not ventilated.
What is “dead space”? What is a clinical example of “dead space”?
- Dead space is ventilation of lung regions that are not perfused
- Dead space is illustrated by pulmonary embolism, in which blood flow to a portion of the lung (or even the entire lung) is occluded
What does spirometry measure?
- Static volumes of the lung are measured with a spirometer
- The spirometer is a simple
device for measuring gas volumes
What is tidal volume?
The volume of air entering or leaving the nose or mouth per breath
500 mL in normal adults
What is residual volume?
- the volume of gas left in the lungs after a maximal forced expiration
- Residual volume cannot be measured by spirometry
What is forced vital capacity?
Forced Vital Capacity (FVC): is the total volume of air that can be forcibly expired after a maximal inspiration.
What is FEV1?
Forced Expiratory Volume in the first second of exhalation (FEV1): the air volume that can be forcibly expired in the first
second.
What is FEV1/FVC??
FEV1/FVC ratio: the fraction of total FVC that can be expelled in the first second. Normal value is 0.8. This ratio reflects the resistance to airflow
What is a flow volume curve?
- Spirometry is usually
performed to obtain a flow-volume curve. - From a flow-volume curve, lung performance during both
inspiration and expiration is assessed. - Useful parameters are obtained such as peak flow (PEF, peak expiratory flow; or PIF, peak inspiratory flow),
or forced expiratory flow at 25, 50, or 75% of the
exhaled vital capacity
Describe obstructive lung diseases such as asthma in terms of the FEV1/FVC ratio
- In obstructive lung diseases, such asthma, both FVC
and FEV1 are decreased, but FEV1 is decreased
more than FVC is. Thus the ratio FEV1/FVC also is decreased
Describe restrictive lung diseases such as pneumonia in terms of the FEV1/FVC ratio
- the compliance of the lungs is decreased, leading to compressed lung volumes.
- In these conditions, both FVC and FEV1 are decreased, but FEV1 is decreased less than FVC is.
- So the FEV1/FVC ratio can actually be increased compared to normal individuals.
What does an obstructive lung disease look like on a flow-volume curve?
- Small high peak followed by big dip on top
- Near normal below the line
What does an upper airway obstruction look like on a flow-volume curve?
- The “tip of the iceberg” of the normal curve is missing on top
- The bottom half of the flow volume curve is missing on bottom
- Decreased inspiratory and expiratory volumes
What does a restrictive lung disease look like on a flow volume curve?
- Similar shape, uniformly decreased in size compared to a normal curve
- Far to the right - not in the normal location
