Mechanics of Breathing, Pressures & Work Flashcards
FIO2
fraction of inspired oxygen
FRC
Functional Residual Capacity
Patm
atmospheric pressure
Ptp
transmural pulmonary pressure
Ppl
intrapleural pressure
Palv
intrapulmonary/intra-alveolar pressure
PTM
pressure at the mouth
RAW
airway resistance
RR
respiratory rate
RV
residual volume
TLC
Total Lung Capacity
Respiratory system slide
complete
Tidal Volume definition and is at rest
volume of each breath
500mL at rest
Dalton’s Law
when two or more gases which do not chemically react are present in the same container (lungs) the total pressure is the sum of the partial pressure of each gas
Dalton’s Law problem
complete
Boyle’s Law
pressure exerted by gas (CO2) in a closed container (lungs) is inversely proportional to the volume of gas in the container
occurs at a constant temperature
P is inversely proportional to V
Charles’s Law
V is proportional to T
Henry’s Law
Applies to gases dissolved in liquids
The number of molecules of a gas dissolving in the liquid is proportional to the partial pressure at the surface of the gas = solubility
Inspiration:
- intercostal muscles —– and —– the ribs
- diaphragm moves —-
- Scalene muscles inserted into ribs —- and —–, ——— the upper ribs and ——- the sternum ——- in —— action, which —— the anterior-posterior diameter of the thoracic cavity
- sloping lower ribs rise and move out = ———- action and increases the ——— diameter of the chest wall
- elevate and evert
- downward
- 1 & 2, raising, pushes, forward, pump, increases
- bucket handle, transverse
What percentage increase in volume when the diaphragm contracts?
75%
At the end of inspiration, pressures are equal.
True or False?
True
Expiration occurs due to
elastic recoil of the lungs and the chest wall
Forced contraction (eg: ——-) requires
- coughing/sneezing
- contraction of the abdominal walls, which push the diaphragm upward
During forced expiration, intrapleural pressures may rise to
+8kPa
60mmHg
Intrapleural pressure equilibrates with the atmosphere.
True or False?
False
Why does intrapleural pressure not equilibrate with the atmosphere?
As the pleural space is closed and fluid filled, it is slightly sub-atmospheric due to the recoil of the chest and lungs away from each other - stops the lungs from collapsing.
Ptp: Transmural Pulmonary Pressure is
The distending pressure on the pleural space, which is transmitted to the alveoli to increase their volume, lower the pressure and generate airflow inwards.
Under physiological conditions (quiet breathing):
Ptp: Transmural Pulmonary Pressure is always positive or negative?
Positive
Under physiological conditions (quiet breathing):
Ppl: Intrapleural Pressure is always positive or negative?
Negative
Under physiological conditions (quiet breathing):
Palv: intrapulmonary/alveolar pressure is always positive/negative?
Moves from slightly negative to slightly positive as we breathe, it is always higher than the intrapleural pressure because of the recoil of the lungs; it is 0 at the end of inspiration and expiration, so there is no airflow
For a given lung volume, the Ptp; the transmural pulmonary pressure is less than the elastic recoil pressure of the lung.
equal and opposite to the elastic recoil pressure of the lung.
What “sucks the lungs out and sucks the lungs back in”?
transmural pulmonary pressure
Ptp
ensures the lungs don’t collapse
During inspiration, atmospheric pressure in relation to alveolar pressure
greater
hence air flows in
At the end of expiration, atmospheric pressure in relation to alveolar pressure
equal, FRC, no air flow, outward and inward recoil of lungs are equal
FRC: Functional Residual Capacity
- volume of air left in the lungs at the end of a normal breath
- at FRC respiratory muscles are relaxed and the lungs and the chest wall recoil in opposite directions and inward and outward recoil are exactly balanced
Volume of FRC is determined by the
elastic properties of the lungs and the chest wall
Pulmonary Fibrosis affecting FRC
- lungs are stiff and small
- increase in elastic recoil
- decrease in FRC
Emphysema affecting FRC
- loss of alveolar tissue, break down of alveolar sacs
- decrease in elastic recoil
- increase in FRC
Impedance
Frictional Airway Resistance and Elastic Resistance to the stretching of the lungs and chest wall
inspiratory muscles contract to overcome the —— offered by the lungs and chest wall.
impedance
Lung compliance refers to
the ability of the lungs to stretch and recoil during ventilation
CL =
change in lung volume/unit change in distending pressure
The distending pressure is
the pressure difference across the lung = alveolar-intrapleural pressure
Static pressure-Volume loop
A dynamic pressure volume loop is obtained from
continuous measurements of intrapleural pressure and volume during a normal breathing cycle
How can we find dynamic compliance from a dynamic pressure-volume loop?
At the end of inspiration airflow is 0
At the end of expiration alveolar pressure is 0
The slope of the line joining these points is the dynamic compliance
In lung diseases (stiff lungs) dynamic compliance is similar to static compliance.
True or False?
False
- in healthy lungs are similar
- different in stiff lungs
In lung diseases (stiff lungs) dynamic compliance is similar to static compliance.
True or False?
False
- in healthy lungs are similar
- different in stiff lungs
What is hysteresis?
- frictional resistance changes, hence compliance curves are different for inspiration and expiration.
Is the lung more or less compliant at higher volumes?
Less compliant
altered lung compliance in lung disease
altered lung compliance in lung disease
insert
altered lung compliance in disease
enter
Laminar and Turbulent Flow
during quiet breathing there is laminar air flow in airways
gas particles move parallel to the walls of bronchi
center layers move faster than outer ones creating a cone shaped front
turbulent flow occurs at higher linear velocities in wide airways and near branch points
Turbulent flow occurs in the trachea during exercise
laminar and turbulent airflow diagram
RAW: Airway Resistance
- originates from friction between air and mucosa
- affects ventilation and has to be overcome along with elastic recoil and inflate the lung
- pressure difference between the alveoli and mouth divided by the flow rate
- inversely proportional to the 4th power of the radius
- inversely proportional to the viscosity of fluid
How can RAW be indirectly assessed?
From Forced Expiratory Measures (FEV1,FVC, FEV1/FVC)
airflow equation
(mouth-alveolar pressure)/RAW
Halving radius of airway increases laminar flow (airway resistance) by
16x
Which areas offer the most resistance during respiration?
Nose, pharynx and trachea
Mouth breathing (eg: during exercise) increases or decreases resistance?
Decreases
Disease that affects peripheral, smaller airways effect on RAW?
Increases airway resistance
Tone of bronchial smooth muscle and epithelium as a factor affecting laminar flow
parasympathetic nerve supply affects bronchomotor tone (Ach and M3 receptors)
Beta adrenergic receptors activated, cause relaxation (broncho)
mmHg is the millimeters of mercury and is used for
blood pressure
SI unit of pressure is, which is equal to
1 pascal = 1Newton per m^2
cmH2O used for
Intrapleural Pressure
Central Venous Pressure
Inspiration and Expiration are active processes.
True or False?
False
Expiration is a passive process
inspiratory muscles diagram
Q =
flow rate =
Q = (piPr^4)/8nl
flow rate = (pipressureradius^4)/ (8fluid viscositylength of tubing)
Nitric Oxide causes bronchodilation or bronchoconstriction?
Bronchodilation
Resting bronchomotor tone during bronchoconstriction:
- radius
- resistance
- airflow
- radius decreases
- resistance increases
- airflow decreases
Resting bronchomotor tone during bronchodilation:
- radius
- resistance
- airflow
- increases
- decreases
- increases
Acute Asthma affecting RAW:
- bronchonstriction
- mucosal oedema
- mucus hypersecretion
- mucus pluggin
COPD affecting RAW:
- bronchoconstriction
- chronic mucosal hypertrophy
Surface Tension in lungs are caused by
explain
name
air-fluid interface in alveoli
cohesive forces between molecules at the surface of an alveolus creates a tension that causes the alveolus to shrink
Alveoli and small airways are inherently unstable and can collapse during expiration = atelectasis
Surface tension of alveolus changes with (2)
age
disease
Pulmonary Surfactant is
a mixture of phospholipids (phosphatidylcholine and proteins)
Where is pulmonary surfactant found?
Floats on the surface of alveolar fluid
Pulmonary surfactant are produced by
Type 2 pneumocytes
How does pulmonary surfactant reduce surface tension?
Hydrophilic and Hydrophobic ends repel each other and interfere with liquid molecule attraction, which lowers surface tension.
Why is pulmonary surfactant important? (5)
- increases lung compliance by reducing surface forces
- promotes alveolar stability
- prevents alveolar collapse as small alveoli do not get smaller and large alveoli don’t get bigger
- reduces surface tension which reduces hydrostatic pressure in tissue outside capillaries and hence keeps lungs dry
- important defense against infection
How does pulmonary surfactant help keep the lungs dry?
- surface tension will suck fluid from the capillaries into the alveoli
- reduction of the surface tension reduces the hydrostatic pressure in tissue outside capillaries and keeps the lungs dry
Lack of surfactant in premature babies (<28 weeks) causes
neonatal respiratory distress syndrome
lung volume and capacity
