Ch2 Part2 Flashcards
What must be overcome to move air into or out of the lungs?
Factors include inertia of the respiratory system, frictional resistance of lung and chest wall tissue, and frictional resistance of the airways
Inertia of the system is negligible.
What is pulmonary resistance composed of?
Pulmonary tissue resistance and airways resistance
Pulmonary tissue resistance contributes about 20% and airways resistance about 80%.
What conditions can increase pulmonary tissue resistance?
Pulmonary sarcoidosis, silicosis, asbestosis, and fibrosis.
What is the formula relating pressure difference, flow, and resistance?
Pressure difference = flow × resistance
How is resistance defined in terms of airflow?
Resistance = pressure difference (cm H2O) / flow (L/s)
How are resistances in series and parallel added?
Series: Rtot = R1 + R2 +…; Parallel: 1/Rtot = 1/R1 + 1/R2 +…
What governs the behavior of laminar flow in tubes?
Poiseuille’s law.
What is the relationship described by Poiseuille’s law?
ΔP ∝ V˙R1
What factors does resistance depend on according to Poiseuille’s law?
- Viscosity of the fluid
- Length of the tube
- Inversely proportional to the fourth power of the radius of the tube
What happens to resistance if the radius of a tube is cut in half?
Resistance is multiplied by 16.
When does flow change from laminar to turbulent?
When Reynolds’ number exceeds 2000.
What is Reynolds’ number?
Reynolds number = ρ × Ve × D / η
What occurs during turbulent flow?
Pressure difference is proportional to the flow squared.
What is transitional flow?
A mixture of laminar and turbulent flow, often at branch points or distal to partial obstructions.
What percentage of total resistance to airflow is located in the upper airways in a normal adult?
35% to 50%.
How does resistance differ when breathing through the nose versus the mouth?
Resistance is greater when breathing through the nose.
What is the component with the highest individual resistance in the tracheobronchial tree?
The smallest airway.
What controls the smooth muscle of the airways?
Efferent fibers of the autonomic nervous system.
What causes constriction of bronchial smooth muscle?
Stimulation of cholinergic parasympathetic postganglionic fibers.
What mediates dilation of bronchial smooth muscle?
Beta2 (β2) receptors.
What substances can cause reflex constriction of the airways?
- Chemical irritants
- Smoke
- Dust
- Histamine
What happens to airways resistance with increasing lung volume?
Airways resistance decreases.
What is the primary reason for decreased airways resistance at higher lung volumes?
Increased transmural pressure difference across small airways.
What is dynamic compression of airways?
High airways resistance at low lung volumes due to positive intrapleural pressures.
What generates positive intrapleural pressure during forced expiration?
Contraction of the muscles of expiration.
What is the effect of small airway collapse on airways resistance?
It causes airways resistance to appear to be approaching infinity at low lung volumes.
What is the main reason that airways resistance appears to be approaching infinity at low lung volumes?
Small airway collapse
This occurs due to the lack of cartilaginous support and reliance on alveolar septa traction.
What is the transmural pressure gradient across the smallest airways during passive expiration?
+9 cm H2O
Calculated as +1 cm H2O minus (−8) cm H2O.
What is dynamic compression of airways?
Increased resistance during forced expiration
Occurs when the transmural pressure gradient is reduced.
What happens to intrapleural pressure during maximal forced expiration?
It becomes more positive
Leading to increased dynamic compression.
What is the equal pressure point hypothesis?
A point where airway pressure equals outside pressure
At this point, the airway may collapse if insufficient support exists.
What occurs as the equal pressure point moves down the airway during forced expiration?
Dynamic compression increases
Eventually leading to airway closure.
What is the effective driving pressure for airflow during a forced expiration when dynamic compression occurs?
Alveolar elastic recoil pressure
This pressure opposes dynamic compression.
What is the formula to calculate airways resistance?
R = ΔP/V˙
This formula approximates resistance assuming laminar flow.
What does FVC stand for in respiratory assessments?
Forced Vital Capacity
It measures the volume of air expired after maximal inspiration.
What is FEV1?
Forced expiratory volume in 1 second
It is a key indicator of expiratory airways resistance.
What does an FEV1/FVC ratio of less than 0.80 indicate?
Possible airway obstruction
Common in conditions like asthma.
What does FEF25%-75% represent?
Forced expiratory flow between 25% and 75% of FVC
Indicates airflow in smaller to medium-sized airways.
How does airflow behave at high lung volumes according to flow-volume curves?
Effort-dependent
Airflow increases with increased effort.
What occurs at low lung volumes in terms of airflow and effort?
Airflow becomes effort-independent
All expiratory efforts merge into the same curve.
What does the Bernoulli principle suggest about airflow in small compressible airways during forced expiration?
Pressure decreases as airflow velocity increases
This can contribute to dynamic compression.
What is the relationship between intrapleural pressure and airflow during forced expiration?
Intrapleural pressure becomes positive
Leading to potential dynamic compression in the airways.
What is the significance of the isovolumetric pressure-flow technique?
Demonstrates the pressure-flow relationship during expiratory maneuvers
It is not commonly used clinically due to complexity.
What is the relationship between airflow rate and lung volume at high lung volumes?
Airflow rate is effort-dependent.
This means that the rate of airflow varies with the effort exerted during expiration.
What occurs at low lung volumes regarding expiratory efforts?
Expiratory efforts of different initial intensities merge into the same effort-independent curve.
This is due to dynamic compression requiring sufficient intrapleural pressures.
What is the purpose of the maximal flow-volume curve?
It helps distinguish between obstructive and restrictive pulmonary diseases.
Obstructive diseases interfere with airflow, while restrictive diseases limit lung expansion.
What characterizes obstructive diseases?
They are associated with low peak expiratory flow (PEF) and a low FEV1/FVC ratio.
Examples include asthma, bronchitis, and emphysema.
What is the impact of restrictive diseases on peak expiratory flow (PEF)?
PEF may be decreased due to reduced total lung capacity (TLC) and vital capacity (VC).
The FEV1/FVC ratio is usually normal or above normal in these cases.
What distinguishes fixed obstructions from variable obstructions in flow-volume loops?
Fixed obstructions affect both expiratory and inspiratory airflow, while variable obstructions show changes based on inspiratory or expiratory effort.
Examples of fixed obstructions include tumors and foreign bodies.
What happens to the cross-sectional area of a variable extrathoracic obstruction during forced expiration?
The cross-sectional area increases as pressure inside the airway increases.
This results in a nearly normal expiratory flow-volume curve.
How do variable intrathoracic obstructions affect airflow during forced inspiration?
The inspiratory flow-volume curve is nearly normal or not affected due to increased cross-sectional area.
These obstructions are often caused by tumors.
What is dynamic compliance?
Dynamic compliance is the change in lung volume divided by the change in alveolar-distending pressure during breathing.
It reflects the mechanics of airflow and lung compliance.
What happens to the ratio of dynamic compliance to static compliance at high breathing frequencies in patients with obstructive diseases?
The ratio decreases dramatically.
This indicates increased airflow resistance.
What defines the work of breathing?
It is proportional to the pressure change times the volume change.
This includes both elastic and resistive work.
What is elastic work in breathing?
It is the work done to overcome elastic recoil of the chest wall and pulmonary parenchyma, as well as surface tension of the alveoli.
Increased elastic work is seen in restrictive diseases.
What is resistive work in breathing?
It is the work done to overcome tissue resistance and airways resistance.
Elevated airways resistance is common in obstructive diseases.
What is the oxygen cost of eupneic breathing?
Less than 5% of total body oxygen uptake.
This can increase to 30% during maximal exercise.
What determines the volume of gas in the lungs at the end of a normal tidal expiration?
The balance point of inward recoil of the lungs and outward recoil of the chest wall.
This volume is referred to as Functional Residual Capacity (FRC).
What effect does pulmonary surfactant have on alveoli?
It increases alveolar compliance and helps prevent atelectasis.
Surfactant reduces surface tension, especially in smaller alveoli.
What occurs during forced expiration when intrapleural pressure becomes positive?
Small airways are compressed leading to dynamic compression.
This can cause airway collapse in certain conditions.
What are the two main components of the work of breathing?
The elastic recoil of the lungs and chest wall, and the resistance to air flow.
Intrapleural pressure before a woman’s inspiratory effort was measured at ____ cm H2O.
-5 cm H2O
What was the intrapleural pressure at the end of the woman’s inspiration?
-10 cm H2O
How is pulmonary compliance calculated based on inspiratory effort?
Change in volume / Change in pressure
What is the tidal volume for the postoperative patient maintained by a respirator?
500 mL
At end expiration, the intrapleural pressure of the postoperative patient is ____ cm H2O.
-3 cm H2O
At peak inspiration, the alveolar pressure of the postoperative patient is ____ cm H2O.
+20 cm H2O
At peak inspiration, the intrapleural pressure of the postoperative patient is ____ cm H2O.
+10 cm H2O
Which condition is NOT a reasonable explanation for decreased static pulmonary compliance?
All of the above
Which factors tend to increase airway resistance?
Stimulation of parasympathetic fibers, low lung volumes, forced expirations, breathing through the nose.
True or False: Alveolar pressure is lower than atmospheric pressure during a normal negative-pressure inspiration.
True
What is the relationship between alveolar pressure and atmospheric pressure at the end of a normal tidal expiration?
Alveolar pressure equals atmospheric pressure.
Which statements concerning small airways are true?
Total resistance decreases with successive generations, linear velocity decreases as size decreases, alveolar elastic recoil plays a role, airflow is usually laminar.
During forced expiration at high lung volumes, airway resistance is ____ than at low lung volumes.
Greater
What is a primary spontaneous pneumothorax?
A pneumothorax that occurs suddenly and is not attributable to underlying pulmonary disease or trauma.
In a tension pneumothorax, air enters the pleural space on inspiration but cannot ____ on expiration.
Leave
What is a potential consequence of a tension pneumothorax?
Compression of structures on the affected side and eventually on the other side.
Which demographic is most commonly affected by primary spontaneous pneumothorax?
Tall thin males between 10 and 30 years of age.
If a pneumothorax is mild and the patient is not in distress, it may resolve with ____.
Observation
What is the role of alveolar elastic recoil in small airways?
It helps to oppose dynamic compression.
