Respiratory Physiology- Mechanisms I Flashcards
Functions of the respiratory system
- Exchange of gases between the atmosphere and the lung
- Homeostatic regulation of body pH
- Protection from inhaled pathogens/ irritants
- Vocalization, signing, and production of audible sounds
Contraction of the diaphragm _________ (increases/decreases) thoracic volume.
Increases
Muscles of inspiration
Principal
- External intercostalis
- Diaphragm
- Interchondral part of internal intercostalis
Accessory
- Seratus anterior
- Scalene
- Sternocleoidomasteoid
Muscles of expiration
Active breathing
- Internal intercostalis, except interchondral part
- Abdominal muscles
- Recutus abdominis
- External oblique
- Transversus abdominis
NOTE: There are no muscles involved in quiet expiration
Functional Residual Capacity
The volume of air present in the lungs at the end of passive expiration.
Compliance equation
Change in volume/Change in pressure
Transpulmonary pressure
The difference between the alveolar pressure and the intrapleural pressure
At _________ (low/high) lung volumes, large changes in transpulmonary pressure only produce small changes in lung volume.
High
Emphysema results in a ____ (less/more) complaint lung.
More
NOTE: In emphysema, Type I alveolar cells are destroyed.
Pulmonary fibrosis results in a ____ (less/more) complaint lung.
Less
NOTE: Proliferation of connective tissue is seen here. Lungs are stiff
Which diseases result in a reduced complaince?
- Pulmonary edema
- Pleural effusion
- Hemothorax
- Empyema
- Obesity
- Musculoskeletal disease (like kyphoscoliosis)
Individuals with decreased compliance have to exert an increased work load for breathing. Why?
Becuase individials with decreased compliance must generate greater transpulmonary pressure to produce changes in the lung volume than those with normal compliance
Specific compliance
Demonstrates that the complaince does not change when normalized with a volume
NOTE: This is usually calculated by dividing the compliance by the functional residual capacity
What are the primary determinants of lung volumes?
Balanced interactions between lung and chest wall
NOTE: High recoil properties of the lung parenchyma shrink to approxiamtely 10% of TLC in the absence of chest wall. Recoil of lung parenchyma is opposed by external force of the chest wall, leading to an increase to approximately 60% of the TLC in the absence of lung parenchyma.
The maximal amount of air that the lung-chest wall can hold is determined primarily by the force that can be generated by the ________.
Diaphragm
When does inspiratory airflow stop?
Once the pressure gradient is absorbed.
NOTE: Once the inspiratory muscles can no longer generate force for the movement of air, as the volume increases, the ability to stretch further decreases.
Residual volume
Volume of gas that remains in the lungs after maximal expiratory effort
Functional residual capacity
Represents the volume of air within the lung-chest wall at a point where the two are balanced
*Each breath begins and ends at FRC
Why does muscle weakness cause a reduction in FRC?
Becuase the lung elastic recoil exceeds the chest wall muscle force
FRC is equal to..
The lung volume at which the outward recoil of the chest wall is equal to the inward elastic recoil of the lung
Obstructions to airflow cause increases in FRC. Why?
Due to premature airway closure
REMEMBER: Each breath begins and ends with FRC
What is a normal RV/TLC ratio?
Less than 0.25
An elevated RV/TLC ratio is seen with both obstructive and restrictive pulmonary disease. Which component of the ratio is abnormal in obstructive pulmonary disease?
RV is elevated. Due to air trapping 2nd to airway obstruction
An elevated RV/TLC ratio is seen with both obstructive and restrictive pulmonary disease. Which component of the ratio is abnormal in restrictive pulmonary disease?
Decreased TLC.
Transmural pressure
Pressure difference between the pleural pressure and the barometric pressure
During inspiration, what happens to the pleural pressure?
It becomes more negative due to an increase in chest wall volume
REMEMBER: Volume and pressure are inversely proportional
If alveoli pressure is greater than the baromeric pressure, air will ______ (enter/leave) the alveoli.
Leave
*pressure flows from high concentration to low concentration
Vital capacity
the maximum amount of air a person can expel from the lungs after a maximum inhalation
Vital capacity calculations
Sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume .
The resting volume of the chest wall is approximately ______ % of vital capacity.
60
*Thus in the absence of the lungs the resting volume of the thorax would be approximately 60% of VC
Below 60% of the VC, teh chest wall has an _________ (inward/outward) elastic recoil. Above 60% of the VC, the chest wall has an ____ (inward/outward) recoil tendency.
Outward; inward
NOTE: Above 60% of VC the chest wall has the same recoil tendency as the lungs
Pressure responsible for distending the lungs.
Transpulmonary pressure
Pressure tending to collapse the lung
Elastic recoil pressure
The driving pressure for expiratory gas flow
Elastic recoil pressures (PEL)
What is the relationship between the pressures listed below?
Transpulmonary pressure (PL)
Pleural pressure (PPL)
Alveolar pressure (PA)
Elastic recoil pressure (PEL)
- PA= PPL+ PEL
- PL= PA-PPL
- PL=PEL
Why does the lung volume decrease in cases of pneumothorax?
The seal is broken. So inward recoil of the lung is no longer opposed by the outward spring of the chest wall. The lung volume will decrease and the alveoli of the affected side will collapse.
In pneumothorax, chest wall will _________ (expand/collapse).
It will expand because it is no longer opposed by inward elastic recoil of the lung parenchyma
When the diaphragm contracts, the thoracic volume _____ (increases/decreases)
Increases
NOTE: This would mean that the thoracic pressure decreases
Surface tension
The attractive force that causes the molecules on the surface of a liquid to come together and form a layer
Normal surface tension for lungs
25 dyn/cm
Surfactant
Reduces surface tension to almost zero at the end of expiration
What factors contribute to the elastic properties of the lung?
Elastin
Collagen
Surface tension
Atelectasis
Collapse or closure of a lung resulting in reduced or absent gas exchange
Law of LaPlace
P=2T/r
P= Pressure
T= Tension
r= radius
According to the law of LaPlace, if two bubbles have the same surface tension, the smaller bubble will have higher pressure
The most abundant components in surfactant are ___ and ___________.
Dipalmitoyl phosphotidylcholine
Phoshotidylglygerol
Surfactant is secreted by _______ cells.
Alveolar Type II
NOTE: These cells occupy aprroximately 2.7% of the alveolar gas exchanve surface area. Alveolar Type II cells are more plentiful.
What is the standard treatment of respiratory distress syndrome?
Surfactant replacement therapy
What is the importance of alveolar interpedendence?
- Increased stability of the alveoli
- Collapse of one alveolus is opposed by the surrounding alveolo which help to overt atelectasis
- Collateral ventilation
________ is the resting volume of the lung and represents the point where the lung recoil and the chest wall are at equilibrium; no pressure difference across the respiratory system.
FRC
What is the leading cause of Chronic obstructive pulmonary disease?
Smoking
Symptoms of Chronic obstructive pulmonary disease
Constant coughing, sometimes called “smoker’s cough”
Shortness of breath while doing activities you used to be able to do
Excess sputum production
Feeling like you can’t breathe
Not being able to take a deep breath
Wheezing
___________is an early diagnostic tool for COPD.
Spirometry
NOTE : Spirometry is great for early detection
Amount of air moving into and out of the lung during quiet respiration.
Tidal volume
Normal tidal volume
500 mL
Additional volume that you can maximally inspire beyond tidal volume
Inspiratory Reserve Volume
Normal Inspiratory Reserve Volume
3000 mL
Maximum amount of air that can be forcefully expelled at the end of a normal expiration
Expiratory Reserve Volume
Normale expiratory Reserve volume
1100 mL
Volume of air remaining in the lungs after a maximal expiratory effort
Residual volume
Normal residual volume
1200 mL
How are the following lung capacities calculated?
Inspiratory Capacity (IC)
Vital Capacity (VC)
Functional residual capacity (FRC)
Total Lung Capacity (TLC)
- IC= Tidal volume + Inspiratory Reserve Volume
- VC= Tidal volume + Inspiratory reserve volume + Expiratory reserve volume
- FRC= Residual volume + Expiratory reserve volume
- TLC= Vital capacity+ Residual Volume
Normal Inspiratory capacity
3500 mL
Normal vital capacity
4600 mL
Normal function residual capacity
2300 mL
Normal TLC
5800 mL
Spirometry & the spirogram tracing
What does a plethysmography (body box) measure?
The amount of air remaining in teh lungs after a normal exhalation including gas that gets trapped during premature airway closure. This distorts the FRC and makes its appear larger
NOTE: The FRC would appear lower when using the helium dilution technique. The two test only product similar results in normal subjects
What does the helium dilution technique measure?
The functional residual capacity of the lungs.
How do you calculate the lung volume using the helium dilution technique?
V2= [V1 (C1-C2)]/ [C2]
V2= Lung Volume
V1= Helium Volume
C1= Helium Concentration
C2= Diluted helium concentration
What does the nitrogen-wash out techinque measure?
The dead space of the lungs
V1C1=V2C2
What does the effort- dependent forced vital capacity maneuver identify?
Normal, obstructive, and restrictive ventilatory disease states
_____________ is a volume/time curve that shows the volume of exhaled air plotted against time.
Spirogram
What tests are reported by the spirogram?
- The forced vital capacity (FVC); volume in liters
- The forced expiratory volume in 1 second (FEV1).
- The ratio of the FEV1 to the FVC (FEV1/FVC).
- The average mid-maximal expiratory flow (MMEF) of more commonly referred to as the FEF25-75
How is the FVC maneuver performed?
The subject stands or sits and initially inspires to TLC while connected to a spirometer
What are the 3 major determinants of maximal air flow during inspiration?
- Force generated by inspiratory muscles
- Increase of static recoil pressure of the lung
- Airway resistance
When is inspiratory force greatest?
At RV, then force decreases as lung volume increases above RV
What are the determinants of maximal expiratory flow?
- Increases in effort (effort dependent)
- Modest effort (effort independent)
When does maximal expiratory flow occur?
During the first 20% of the FVC maneuver
What are important elements of a well-performed FVE maneuver?
- Rapid Rise
- Smooth decrease in expiratory flow
- A decrease in flow to the baseline
What happens to the FEV1/FVC ratio in obstructive disease?
Decreased, due to a decrease in FEV1
What is PEFR?
Peak-expiratory flow (for the FVC maneuver)
What happens to the FEV1/FVC ratio in restrictive disease?
The ratio should be about normal or maybe slightly elevated because both the FEV1 and FVC are reduced.
Aside from a decrease in FEV1, what other signs are seen on spirogram of a patient with asthma or emphysema?
- High residual volume
- High functional residual capacity
- Low vital capacity
NOTE: Though Bronchitis is considered an obstructive disorder, it rarely cause a high RV.
____________ is a disease characterized by dilation of the alveolar spaces and descruction of the alveolar walls.
Emphysema
NOTE: In cases of emphysema, compliance is increased and elasticity is decreased. So the lung becomes easy to distend but empties slowly.
How is the pressure gradient related to the air flow in emphysema?
Air flow is reduced in emphysema because the diaphragm is less efficient at generating pressure gradients that are necessary for breathing.
What are the test results of restrictive disease?
- Low TLC
- Low FRC
- Low RV
- Normal FEV1/FVC
Bronchitis
A condition which is clinically defined as a chronic cough with mucus production most months of the year
NOTE: The mucus secretions and inflammation in the bronchi tend to narrow the airways and provide an obstacle to airflow, thus increasing the resistance of the airways
What is a normal FEV1/FVC ratio?
90-95%
Why does bronchitis rarely result in a high RV?
Because the air flow obstruction found in bronchitis due to increased resistance, which does not generally cause the airways to collapse prematurely and trap air in the lungs.
What are the test results for asthma?
- Decreased maximal expiratory air flow
- Decreased FVC
- Decreased FEV1
- Decreased FEV1/FVC ratio
NOTE: With asthma, significant effort is required to create an extremely negative pleural pressure
Characteristics of asthma
- Airway hyper-responsiveness
- Reversible increases in bronchial smooth muscle tone
- Inflammation of the bronchial mucosa
- Broncho-spasm, which leads to increased airway resistance
Normal Values for Lung Volumes and Pulmonary Function mechanics
Lung Volume Abnormalities in Obstructive and Restrictive Pulmonary Diseases
Causes of Abnormal Vital Capacity
FRC ________ (increases/decreases) with age.
Increases
*This is associated with the decrease in elasticity
With age, there is a _______ (decrease/increase) in arterial tension.
Decrease
*This is as a result of ventilation-perfusion mismatch
Constrast the reflective events that occur early in the FVC maneuver with the events that occur late in the FVC maneuver.
Early
- Large airway function
- Effort dependent
Late
- Small airway function
- Effort independent
