airway resistance Flashcards
what is airway resistance?
resistance to flow of air in the airways
What is airway resistance due to?
1) internal friction between gas molecules 2) friction between gas molecules and the walls of the airways
What are the types o flow?
Laminar turbulent transitional
What are features of laminar flow?
Laminar flow is parallel streams of flow in the small airways Velocity in the center of airway is twice as fast than at the edges
What is poiseuilles law for laminar flow
R=8nl/(pie)r^4= Change pressure/V
n=viscosity l= length r=radius
Where does turbulent flow occur?
Turbulence occurs at higher flow rates or air velocity in large airways, e.g., nose, mouth, trachea.
Which have a higher resistance turbulent or laminar flow?
Resistance of turbulent flow is much greater than laminar flow
What are the result of local eddies?
Local eddies form at sides of airway and flow becomes disorganized. Pressure no longer proportional to flow.
What makes turbulent flow more probable?
Increases in density, viscosity & airway resistance make turbulence more probable
What does breath sounds heard with a stethoscope reflect?
Breath sounds heard with a stethoscope reflect the turbulent airflow
What are the following airways contribute the most to the overall airway resistance in the respiratory system?
b. Midsize airways, like bronchi
Where is the chief site of airway resistance?
Major resistance is at the medium-sized bronchi
Where is the greatest pressure drop and resistance and why?
Most of pressure drop occurs at seventh division Very small bronchioles have very little resistance because of the very small airways in parallel air velocity becomes low and diffusion takes over
What are the factors affecting airway resistance?
Airway diameter Any factor that decreases airway diameter increases resistance, e.g. in asthma, parasympathetic stimulation.
Turbulent Flow increases airway resistance. Rapid breathing causes turbulence.
Medium-sized airways provide greater resistance to flow than the small airways do.
Lung Volume High lung volume has low resistance and low lung volume increases airway resistance.
Density & Viscosity Of Inspired Gas Increased density & viscosity increase airway resistance
What is dynamic compression of airways?
This is when the the intraplueral pressure is high and forced expiration is determined by intrapleral pressure instead of atmospheric pressure. occurs in patients with some obstructive lung disease. This accounts for the wheezing during forced expiration
What is forced expiration equal to in dynamic compression of airways?
alveolar pressure minus intraplueral pressure
What is the pressure gradient to determine the air flow during passive expiration?
d. 2 cm H2O
What is the pressure gradient to determine the air flow during forced expiration?
c. 10 cm H2O
What exaggerate dynamic compression of airways in COPD?
Increase in resistance of the peripheral airways
What exaggerate dynamic compression of airways in emphysema?
Reduced lung elastic recoil and loss of radial traction on airways
What is obstructive airway diseases?
diseases that increase airway resistance
What are obstructive airway diseases?
Asthma, Emphysema, Bronchitis, and Chronic obstructive pulmonary disease (COPD).
What are restrictive airway diseases?
disease restricts lung expansion.
What are restrictive airway diseases?
Decreased lung volume
Decreased compliance
Increased work of breathing
Diseases include pulmonary fibrosis, asbestosis, silcosis tumor.
On this this graph what is decreased for restrictive diseases ad what is increased for obstuctive diseases?
Restrictive disease: peak expiratory flow (PEF) and total lung capacity (TLC) are decreased. The effort-independent part of curve is similar to the normal.
Obstructive disease: the residual volume (RV) is greatly increased. The effort-independent portion of curve is depressed inward.
