Dynamic Properties Flashcards
what are respiratory dynamics?
the properties of the respiratory system that depend on motion
- not statics but the movements of air
what are the different types of air flow?
- laminar = orderly, smooth flow
- turbulent = bounces around
- tracheo-bronchial = mixture of both due to the branching and/or blockage (turbulent at branching, laminar in tubes)
what is the relationship between the driving pressure and flow of:
laminar flow and turbulent flow?
- in laminar flow, the flow rate is directly (linear) related to the driving pressure so if you increase driving pressure, you increase flow rate (because there is minimal resistance)
- in turbulent flow, they are directly related (not linear) so you still increase flow rate as you increase driving pressure, but not as significantly because when you increase turbulent flow you increase resistance
what is the most influential factor influencing resistance?
radius
what is turbulent flow? what direction does it move? pressure required?
when does turbulence occur?
when Reynold’s number exceeds 2000 which occurs when:
- density of liquid is higher
- diameter of tube is higher
- velocity is higher
- viscosity is lower
what is Reynold’s number and what does it represent?
- basically = turbulence
- incorporates the factors of density of fluid or gas, diameter of tube, velocity of fluid or gas movement, and viscosity into how turbulent the flow is
what happens when you increase density of a fluid or gas? how does this correlate to a real life scenario?
- you increase reynold’s number and increase the chance for turbulent flow
- the air we breath is 80% nitrogen 20% oxygen, so for patients in respiratory distress, we give the patient 80/20 helium and oxygen instead because the He is less dense than nitrogen and decreases the turbulence for better movement of air
what happens when we increase the diameter of the tube? in this case, the trachea/airways
- the trachea itself has a large diameter and always has turbulent flow
- increase diameter, then you increase the turbulence
- this is why as you go down the airway, you reach the smaller branches and decrease turbulence and have more laminar flow
what happens when you increase the velocity?
- so technically when you increase velocity, you increase the flow rate because they are directly proportional
- but in terms of the respiratory system, the flow rate stays the same
- when you branch into bronchi and bronchioles, etc the velocity decreases
- this is because the more branching that you have, increases the TOTAL cross sectional area, thus decreasing velocity
- has to add up to the whole flow
- increase the turbulence
how does the total cross sectional area change as you go down the airways?
- increase total CSA
- this is why the velocity in the branches decrease but the flow is the same
- decrease in velocity = decrease in turbulence
what is the airflow like in the respiratory tract?
- larger vs smaller airways
- larger airways = always turbulent
- smaller airways = never turbulent
what factors affect airway radius?
- bronchiolar smooth muscle
- radial traction
- dynamic airway compression
- obstructions
how does autonomic control affect the radius?
sympathetic
- release of noradrenaline
- causes smooth muscle dilation (bronchodilation) = relaxation of bronchioles
- inhibits mast cells and reduces mucous secretion bc mucous causes radius reduction (so we stop that)
- increases beating of cilia
- result: increased air flow via increase of radius
how does autonomic control affect the radius?
parasympathetic
- release ACh
- smooth muscle contraction (bronchoconstriction)
- mucous secretion is increased (caused radius reduction)
what is radial traction? how does it change when we breathe? how does it work?
- when you inhale = you increase lung volume = you decrease resistance
- this occurs because the increasing tension in the alveolar walls pulls the conducting airways open – essentially increasing radius which decreases resistance and increases flow
- when the lungs recoil, the alveoli are compressed and the traction to the airway pulls the airway open upon exhalation
what happens when you compress the airways?
= forceful expiration
- pressure is applied to the alveoli so the chest is compressed and air is forced out of the lungs
- during this time, some pressure can squeeze the bronchioles because the pressure is so high – this limits how much air flow can be pushed out – also why the system has cartilage to help prevent breaking/resistance against pressure
- like a balloon – can get air out of the system with some effort, but extra effort is needed to increase how much air is let out
- although with extra effort, there is no increase in the maximal air FLOW
how does the forced expired volume change over time?
- if you forcefully exhale, 80% of air leaves in the first second
- remember - you can’t expire 100% of the air volume in your lungs
- maximal expiration for 6 seconds – 3-6+ seconds there is no real change in volume expired and almost nothing is coming out
FVC = forced vital capacity
FEV = forced expiring volume
where is airway resistance the highest?
upper airways
- about 40% of total resistance is here
what happens when you have asthma?
- it’s an immune reaction
- obstructive
- causes constriction of smooth muscle because of fluid release and a thickened wall
- overall decrease in diameter
what happens when you have emphysema?
- there is weakened and collapsed air sacs with excess mucus
- due to break down of elastic tissue
what is emphysema? what does it cause?
- a lung disease that destroys alveolar walls
- lung recoil is decreased, radial traction is lost causing the airway to be more collapsible
- tendency for the airway to close and trap gas, increasing the residual volume
- obstructed airflow and increased resistance
- usually due to smoking because it alters elastin production
what are the 2 types of disorders of pulmonary mechanics? what are examples? how do you test for them?
- obstructive defects (decreased expiratory flow) like asthma, chronic bronchitis, emphysema
- restrictive defects (reduced lung volumes) like fibrosis, pleural effusion, kyphoscoliosis, paralysis of diaphragm, polio
- tested for by spirometry
what happens to spirometry measurements with obstructive defects?
normal:
- TV = 2L
- FEV1 = 4L
- FVC = 5L
- FEV1/FVC = 0.8 = GOOD
obstructive:
- TV = 2L
- FEV1 = 2L
- FVC = 4L
- FEV1/FVC = 0.5 = BAD – indicative of obstructive pattern
what happens to spirometry measurements with restrictive defects?
normal:
- TV = 2L
- FEV1 = 4L
- FVC = 5L
- FEV1/FVC = 0.8 = GOOD
restrictive:
- TV = 1L
- FEV1 = 3L
- FVC = 3.5L
- FEV1/FVC = 0.88 = BAD – indicative of restrictive defects
