Respiratory Mechanics Flashcards
To alter lung volumes we need:
Respiratory muscles to change size of thoracic cavity
Overcome tissue elastance (need to recoil)
Overcome surface tensionwithin alveoli
Which direction does air flow?
down the pressure gradient
When PA is less than PB…
PA - alveolar; PB - atmospheric
Air enters lung
When PA is greater than PB…
Air exits lungs
As volume increases, pressure exerted by gas…
Boyle’s Law
decreases
The pressure and volume of a gas are inversley related
Double volume, 1/2 pressure
How does Boyle’s Law work in us?
As the lungs expand in volume, P goes down
As the lungs shrink in volume, P goes up
How do respiratory muscles act on lungs?
Indirectly
Lungs and thoracic wall linked
How do muscles effect the thoracic cavity?
Muscles change the volume of the thoracic cavity
As cavity increases, lungs follow
Define
Inspiration
The active phase of breathing cycle
expending energy
Increase thoracic cavity volume
Decrease alveolar and intrapleural pressre
What is happening in the thoracic cavity before inspiration?
Respiratory muscles are relaxed
No air is flowing, PA=PB
What needs to happen in the thoracic cavity in order for air to move?
Lung volume has to change
What occurs in the thoracic cavity during inspiration?
Motor impulses from brainstem activate muscle contraction
Thoracic cavity expands - PA and Pip drop
Intrapleural pressure drops by association when thoracic cavity volume increases
What is happening during inspiration when PA drops?
Fresh air flows in until pressures are equalized
What happens during inspiration when Pip drops?
Increase in transpulmonary pressure gradient
needed to overcome increases elastic recoil force of stretched lungs
Diaphragm
The major muscle of inspiratory effect
Sheet of skeletal muscle forms floor
Diaphrgam when relaxed:
Dome shape protrudes upward into throax
Diaphragm when contracted:
It increases thoracic cavity by descending downward
Innervated by phrenic nerve
Diaphragm movement during normal inspiration…
moves 1 cm
Diaphragm movement during forced inspiration…
Diaphragm can move 10cm
Muscles of Inspiration
External Intercostal Muscles
What do they do? How do they work?
Run between ribs
Responsible for 25% of inspiratory effort:
Lie on top of internal intercoastal
Activated b intercostal nerves
Contaction: elevate ribs and thus sternum
Muscles of Inspiration
External Intercostal Muscles: Pump Handle Movement
Increasing interior/posterior pressure
Muscles of Inspiration
Accessory Muscles
What do they do?
Assist with forced inspiration eg, exercise
Muscles of Inspiration
External Intercostal Muscles: Bucket Handle Movement
Increasing transverse volume
Muscles of Inspiration
What are the two types of accessory muscles?
Scalene Muscles: elevated the first 2 ribs
Sternocleidomastoid Muscle: raises sternum
cause even greater drops in PA and Pip
Use of accessory muscles for inspiration is a sign of…
respiratory distress
What is the driving pressure for airflow in to the lungs?
Decreasing alveolar pressure
What initially creates the driving pressure for airflow into the lungs?
Increases thoracic cavity volume/lungs
Why does alveolar pressure decrease and then swing back up, but pleural pressure decreases continuously during inspiration?
Alveolar pressure comes back up because it is in communication with outside world
Intrapleural content decreases because it has no outside communication
The act of inhaling is _ ventilation
negative-pressure
Define
Expiration
What is it?
The passive phase of the breathing cycle
No energy
What occurs during Expiration?
Inspiratory muscles relax
Lungs recoil due to elastic properties
Pleural and alveolar pressures rise
Gas flows passively out of lung due to elastic recoil
What are the muscles of active expiraton?
abdominal and intercostals
How does the body empty air more completely?
need to increase PA even more
How do you further increase PA to empty the lungs more completely?
Need more force than accomplished by simple relaxation
Exercise or disease states (asthma)
What effect does contraction of abdominal wall and internal intercostals cause?
increasing intra-abdominal pressure
When is it difficult/unable to expand the lungs?
Scar tissue
Reduced surfactant
Mucous
Fluid
Hard to increase volume, difficult to decrease pressure and breath in
When is the lung unable to contract?
Emphysema - destroyed alveoli and elastic tissue
Hard to decrease volune, difficult to increase pressure and breath out
What are the 2 major patterns of gas flow?
Laminar
Turbulent
Define
Laminar flow
Air flows in same direction
parallel to walls
low flow rates
gas in center travels most rapidly
Define
Turbulent Flow
As air flow rate increases - air moves irregularly
Creates resistance to flow which requires higher pressure
How do you change turbulent flow?
Increases drive in pressure
Turbulence is most likely to occur when…
Average velocity is high and radius is large
Gas flow in larger airways is…
turbulent
Breath sounds heard with stethoscope are due to…
turbulent flow
Laminae is silent
What causes airflow?
Normal airways offer such low resistance, that only very small pressure gradients needed for adequate airflow
Poiseuille’s Law of Resistance for laminar flow:
R = 8+L+n/3.14r
Where is the cheif site of airway resistance?
Medium sized bronchi
Airway resistance
Large airways have _ flow but large _
Decreases but vast cross sectional area and in parallel
Define
Lung Volume
How much air is in the lungs
Lung Volume
Diameter of airways change with…
lung volume
Lung Volume
How does airway diameter change with Lung Volume?
Airways are supported by radial traction nof surrounding lung connective tissue
As lung expands, it pulls open airways
As lung volume decreases, smaller airways may be compressed at low lung volumes (increasing R)
What assists in contraction of airways?
Bronchial smooth muscle tone increasing resistannce
Bronchoconstriction
Decreases radius and increase resistance to airflow
What are the major control factors of bronchoconstriction?
Neural Control: PNS
Local Control: Decreases CO2
Patholigical factors can produce bronchoconstriction (allergies, asthma)
Neural control of bronchoconstriction
During quiet relaxed situations demand not high
ACh on muscarinic receptors
Many inhalers block ACh to prevent constriction
Bronchiole pathway
relation of blood flow and airflow
Small blood flow -> decrease CO2 area -> Increase contraction of local-airway smooth muscle -> constriction of local airways -> increase airway resistance -> decrease airflow -> helps balance large airflow
Airflow influences _ radius
airway
Blood flow influences _ radius
vascular
Pulmonary vascular Smooth Muscle pathway
relation of blood flow and airflow
Small blood flow -> Increased O2 in area -> relaxation of local pulmonary arteriolar smooth muscle -> dilation of local blood vessels -> decreases vascular resistance -> increase blood flow -> helps balance Large airflow
Bronchodilation
Increase radius, decrease resistance to airflow
What are the major control factors of bronchodilation?
Hormonal: EPI
Local Control: Increasing CO2
neural factors have minimal effect: SNS
How does hormonal control effect bronchodilation?
EPI when demand is high, bind Beta-2 adrenergic agonists to increase airway radius
How does gas density affect airway resistance?
Elevated gas density increases resistance
deep sea diving
How does forced expiration affect airway resistance?
Airway compression increases resistance
How does bronchial smooth muscle tone affect resistance?
Contraction of airways increases resistance
How does lung volume affect resistance?
As lung volume decreases, resistance increases
Forced Expiration
In normal breathing, resistance…
Doesn’t change much
Pip is less than airway pressure; airways open
During forced expiration, resistance…
significantly inceases
Forced expiration
AS elastic recoil decreases…
what happens to PA
PA decreases
When does exhaling air lose pressure?
When it hits R
Equal Pressure Point (EPP)
The point when Pairway = Pip
If Pip is greater than Pairway….
What can occur?
collapse can occur
How does EPP prevent lung collapse?
In healthy lungs, the EPP occurs normally where cartilage is present and prevents closure of the airway
Why do the first four generations of the conducting zone contain alot of cartilage?
They ae subject to negative and positive pressures, the cartilage prevents collapse of the lung due to the changing pressures
Forced Inspiration
What causes emphysema?
The loss of alveoli and thus elastic recoil, lowers PA further during forced expiration
EPP occurs closer to the alveoli, where the cartilage cannot prevent airway collapse
What is the result of emphysema?
More air is trapped in the lungs
EPP is influenced by…
Lung elastic recoil
In a healthy lung, EPP sequence:
Recoil -> increasing PA-> EPP established in larger airways; collapse is minimal
In emphysema, EPP sequence is:
Low recoil -> decreasinig PA -> EPP established in small airways; easily compressed
Define
Chronic Obstructive Pulmonary Disease (COPD)
Umbrella term used to describe chronic lung diseases that cause limitations in lung airflow -> increases resistance
When R increases, larger pressure gradient needed to maintain normal flow rate
COPD causes what changes in the respiratory system?
Alveoli lose their ability to recoil
Alveolar walls are destroyed
Airway walls become thickened and inflamed
Airways become clogged with mucus
What are the two main forms of COPD?
Chronic Bronchitis
Emphysema
Define
Pulmonary Function Tests
What are they?
A series of tests that evaluate how well lungs are working
What are pulmonary function tests used for?
To differentiate and monitor lung diseases
Is SOD due to worsening emphysema or new heart failure?
Is cough due to emphysema or asthma?
Types of PFTs
Spirometry
1st test performed
Compare measured values with normal values from population studies
Lung volumes and capacities determine…
the amount (volume) of air someone can move in and out
seen on Volume-time curve
Flow/Volume Loops
get more spirometry information
determine speed of flow
What variables can impact lung function?
Age, height, weight, sex, race, disease/trauma
How does the spirometry work?
Seated subject breathes into a closed system
Pneumotachometer
What affect does emphysema have on residual volume?
It increases residual volume
Define
Inspiratory Reserve Volume (IRV)
All we can inspire above a normal inspiration
Define
Expiratory Reserve Volume (ERV)
Everything we are capable of exhaling
Define
Inspiratory Capacity (IC)
Everything we can inspire
Define
Residual Volume (RV)
All air trapped in our lungs no matter how hard you expire
Makes easier to move air in and out
Define
Functional Residual Capacity (FRC)
All the air left over after a normal expiration
Define
Vital Capacity (VC)
All air we can move out of lung in a single breath
Define
Total Lung Capacity (TLC)
All air we can and cant move in and out during a single breath
What is the average value of VT?
500 mL
Equation
IC
IC = IRV + VT
Equation
FRC
FRC = ERV + RV
Equation
VC
VC = IRV + VT + ERV
Equation
TLC
TLC = VC + RV
What is the average value of VC?
4800 mL
What is the average value of TLC?
6000 mL
Lung function is divided into _ and their combinations give us…
4 volumes
4 Capacities
Spirometry measures…
amount of air entering and leaving lungs
Can not provide info about absolute lung volumes (RV, FRC, TLC)
What techniques are used to determine RV, FRC, and TLC?
Gas dilution
Body plethysmography
What are the 2 types of dysfunctions yielding abnormal spirometry results?
Obstructive
Restrictive
Obstructive Lung Disorders
How does it affect lung volumes and capacities ?
Decreases VC, IRV, ERV
Increases RV, FRC, TLC
Obstructive Lung Disorders
Slow flow rates
Hyperinflation
Decreased recoil
decrease capacity to get air out
What is the result of increased RV in obstructive lung disorders?
Air trapped
Barrel Chest
What affect do restrictive lung disorders have on lung volumes and capacities?
Decreases VC, RV, FRC, VT, and TLC
Restrictive Lung Disorders
Increase recoil
Decrease volume
Decrease capacity to get air in
What is the result of decreased TLC in restrictive lung disorders?
Difficulty to expand
What is an example of an Obstructive Lung Disorder?
COPD
What is an example of a Restrictive Lung Disorders?
Pulmonary Fibrosis
