Respiratory Physiology Flashcards
What are the muscles of inspiration
Diaphragm and external intercostals
The reduction in thoracic pressure and the increase in thoracic volume is an example of what law?
Boyles law
What is boyles law?
Pressure is inversely proportional to 1/volume
(I.e. an increase in volume results in a DECREASE in pressure)
What muscles are activate during exhalation?
Exhalation is PASSIVE!
Active exhalation is carried out by the abdominal musculature (abs, internal oblique, external oblique)
Why vital capacity is required for an effective cough?
15 mL/kg
What are the three divisions of the airway?
Conducting zone, transitional zone, respiratory zone
What is the conducting zone? Where does it begin/end?
Begins at the nares and ends with the terminal bronchioles
This is anatomical dead space
What is the transitional zone?
Respiratory bronchioles
Dual function of gas exchange and air conduit
What is the respiratory zone? Where is it?
Begins at the alveolar ducts and ends in the alveolar sacs
This is where gas takes place
What is alveolar pressure?
Pressure inside the airway
what is intrapleural pressure?
The pressure outside the airway
What is transpulmonary pulmonary pressure (TPP)?
This is the difference between the pressure inside the airway and the pressure outside of the airway.
Alveolar pressure - Intrapleural pressure
What happens if Transpulmonary Pulmonary Pressure (TPP) is positive?
Airways stay open
What happens if transpulmonary pulmonary pressure is negative?
The airways collapse
What is a normal tidal volume?
6-8 mL/kg
What is normal dead space?
2 mL/kg or about 150
What causes an increase in the PaCO2-EtCO2 gradient?
And increase in dead space
What is Minute Ventilation?
Tidal volume x respiratory rate
What is alveolar ventilation?
(Tidal volume - dead space) x respiratory rate
What conditions increase dead space
Conditions that increase the volume of the conducting zone OR decrease pulmonary blood flow
(Ex: hypotension, positive pressure ventilation, atropine)
The fraction of tidal volume that contributes to dead space is called what?
Vd/Vt ration
What is the most common cause of increased Vd/Vt under general anesthesia?
Reduction in cardiac output (rule out hypotension)
Name some things that increase Vd
Face mask
HME
Positive pressure Ventilation
Atropine
Old age
Extension
COPD
PE
Decreased CO
Sitting
Name some things that decrease Vd
ETT
LMA
Trach
Flexion
Supine
T-berg
In the circle ventilators system, where does dead space begin?
At the y-piece
In the textbook patient, what is ventilation and perfusion?
Ventilation is 4 L/min
Perfusion is 5 L/min
In the textbook patient, a normal V/Q ratio would be what?
0.8
(4L/5L)
Where is ventilation the greatest? And why?
It is highest at the lung base due to higher alveolar compliance
Where is perfusion the greatest? And why?
Perfusion is the greatest at the lung base due to gravity.
What is ventilation and perfusion like in the NON-dependent lung?
Decreased alveolar ventilation
Decreased alveolar compliance
Decreased PACO2
Increased PAO2
Decreased blood flow
Decrease vascular pressure
Increased vascular resistance
What is ventilation and perfusion like on the dependent lung?
Increased alveolar ventilation
Increased alveolar compliance
Increased PACO2
Decreased PAO2
Increased blood flow
Increased vascular pressure
Decreased vascular resistance
What is the most common cause of hypoxemia in the PACU?
V/Q mismatch (specifically atelectasis)
What does the body do to combat dead space (aka zone 1 of the lungs)
Constriction of bronchioles to minimize of poorly perfused alveoli
What does the body do to combat shunt (aka zone 3)
Hypoxic vasoconstriction reduced pulmonary blood flow to poorly ventilated alveoli
What is the Law of Laplace
Decrives the relationship b/t pressure, radius, and tension
Tension = pressure x radius (cylinder ~ blood vessels)
Tension = pressure x radius / 2 (spherical ~ alveoli)
what is surfactant
This is a substance produced by type 2 pneumocytes to modulate surface tension and prevent alveolar collapse.
When do type 2 pneumocytes begin producing surfactant?
22-23 weeks
When does surfactant production peak?!
35-36 weeks
Zone 1 (of the West Zones)
PA (alveolar) > Pa > Pv
Ventilation, but no perfusion
(I.e PE, hypotension)
Zone 2 (of the West Zones)
Pa > PA > Pv
V/Q = 1
Directly proportional to the difference between Pa - PA
Zone 3 (West zones)
Pa > Pv > PA
V/Q = 0
Shunt
Blood flow is a function of arteriovenous pressure (Pa - Pv)
Zone 4 (West Zones of the lung)
Pulmonary edema
Pa > Pist > Pv > PA
What is the alveolar gas equation?
Alveolar Oxygen = FiO2 x (atmospheric pressure - 47) - PaCO2/RQ (0.8)
What is the respiratory Quotient?
Carbon Dioxide Production/oxygen concentration
200 mL/250 mL = 0.8
What are the 5 causes of hypoxemia
Hypoxic mixture, hypoventilation, diffusion limitation, V/Q mismatch, and shunt
What are the 3 causes of an increased A-a gradient?
V/Q mismatch l
Diffusion impairment
Shunt
What is hypoxemia
A low state of oxygen in the blood (PaO2 <80)
What is hypoxia
Insufficient oxygen to support the tissues
What are examples of an increase A-a gradient in hypoxemia
V/Q mismatch
Diffusion impairment
Shunt
What are examples of a normal A-a gradient in hypoxemia
Hypoventilation
Reduced FiO2 (think high altitudes)
What are examples of a V/Q mismatch?
COPD
Impaired Hypoxic Pulmonary Vasoconstriction
One-lung ventilation
Embolism
What are examples of impaired diffusion?
Pulmonary fibrosis
Emphysema
Interstitial lung disease
What are examples of Shunt?
Pneumonia
Atelectasis
Bronchial intubation
Intracardiac shunt
What are examples of reduced FiO2?
High altitude
Oxygen pipeline failure
Hypoxic mixture
What are examples of Hypoventilation?
Opioid overdose
Residual neuromuscular blockers
Residual anesthetic
Neuromuscular disease
Obesity hypoventilation
What is the normal A-a gradient?
Less than 15 mmHg
How do you estimate the percentage of shunt using the A-a gradient?
Shunt increases 1% for every 20 mmHg of A-a gradient
For example, if the A-a gradient is 218, the shunt would be about 11% (218/20 = 11)
What is a normal inspiratory reserve volume?
3,000 mL
What is a normal tidal volume?
500 mL
What is a normal expiratory reserve volume?
1,100 mL
What is a normal residual volume?
1,200 mL