Ch 7 Mechanics Part 2 Flashcards
What causes regional differences in ventilation in the lungs?
The weight of the lung affects intrapleural pressure, which is less negative at the base than at the apex
This results in the base being relatively compressed and better ventilated compared to the apex.
How does intrapleural pressure vary from the base to the apex of the lung?
The intrapleural pressure is less negative at the base than at the apex
This is due to the weight of the lung and the need for greater pressure below to balance downward forces.
What is the effect of lung volume on its compliance during inspiration?
The lung is easier to inflate at low volumes than at high volumes, where it becomes stiffer
This is reflected in the pressure-volume curve.
What paradox exists regarding lung ventilation between its base and apex?
The base of the lung has a smaller resting volume but greater ventilation compared to the apex
This is due to larger changes in volume at the base during inspiration.
What happens to intrapleural pressure at very low lung volumes?
Intrapleural pressures are less negative, and at the base, they can exceed atmospheric pressure
This leads to airway closure and prevents ventilation at the base.
What is airway closure, and when does it occur?
Airway closure occurs when small airways close at low lung volumes, trapping gas in distal alveoli
This can happen at higher volumes in elderly individuals due to loss of elastic recoil.
What is the equilibrium volume of the lung and chest wall?
The equilibrium volume is the functional residual capacity (FRC)
At FRC, the elastic recoil of the lung balances the outward spring of the chest wall.
What is the relationship between lung and chest wall compliance?
Total compliance is the sum of the reciprocals of lung and chest wall compliances
It is expressed as 1/CT = 1/CL + 1/CCW.
What are the types of airflow in tubes?
Laminar flow, transitional flow, and turbulent flow
Each type has different pressure-flow characteristics.
What does the Reynolds number indicate?
The Reynolds number indicates the ratio of inertial to viscous forces
Turbulence is likely when the Reynolds number exceeds 2,000.
How does resistance in laminar flow relate to tube radius?
Resistance is inversely proportional to the fourth power of the radius of the tube
Halving the radius increases resistance 16-fold.
What is the formula for airflow resistance in laminar flow?
R = 8nl / (πr^4)
Where R is resistance, n is viscosity, l is length, and r is radius.
What happens to pressure in turbulent flow?
Pressure is approximately proportional to the square of the flow rate
This differs from laminar flow, where pressure is directly proportional to flow rate.
How is airway resistance measured?
Airway resistance is the pressure difference between the alveoli and the mouth divided by flow rate
Alveolar pressure is deduced from body plethysmograph measurements.
What is the typical intrapleural pressure before inspiration?
The intrapleural pressure is typically -5 cm water before inspiration
This is due to the elastic recoil of the lung.
What is the intrapleural pressure before inspiration begins?
−5 cm water
This pressure is due to the elastic recoil of the lung.
What is the alveolar pressure before inspiration?
Zero (atmospheric)
This occurs because there is no airflow, resulting in no pressure drop along the airways.
What happens to alveolar pressure during inspiration?
It falls, establishing the driving pressure for airflow.
The extent of the fall depends on flow rate and airway resistance.
How much does alveolar pressure typically change in normal subjects during inspiration?
About 1 cm water
In patients with airway obstruction, this change may be significantly larger.
What causes the fall in intrapleural pressure during inspiration?
Expansion of the lung and reduction in alveolar pressure.
The actual path of pressure change is represented by the hatched area in the pressure diagrams.
During expiration, how does intrapleural pressure change?
It becomes less negative due to positive alveolar pressure.
With forced expiration, intrapleural pressure can exceed zero.
What is the chief site of airway resistance?
Medium-sized bronchi
This is contrary to the earlier belief that resistance was mainly in the narrow airways.
What percentage of airway resistance is attributed to airways less than 2 mm in diameter?
Less than 20%
Most resistance occurs in the airways up to the seventh generation.
How does lung volume affect airway resistance?
Higher lung volumes decrease airway resistance.
As lung volume decreases, airway resistance rises rapidly.
What happens to small airways at very low lung volumes?
They may close completely.
This is particularly true at the bottom of the lung.
What role does bronchial smooth muscle contraction play in airway resistance?
It narrows the airways and increases resistance.
This contraction can be reflexive due to irritants like cigarette smoke.
What is the role of β2-adrenergic receptors in the respiratory system?
They relax smooth muscle in the bronchi, leading to bronchodilation.
Epinephrine and isoproterenol stimulate these receptors.
True or False: The shape of the alveolar pressure tracing is identical to the flow tracing if airway resistance remains constant.
True
This indicates a direct relationship between flow and pressure during respiration.
Fill in the blank: The equation of pressures can be represented as (mouth − intrapleural) = (mouth − ______) + (alveolar − intrapleural).
alveolar
This equation reflects the relationship between the different pressures during the breathing cycle.
