Intro to Pulm Physiology Flashcards
Gas flow rate
E
expired gas
I
inspired gas
A
alveolar gas
a
arterial blood
v
venous blood
mixed venous blood = pulmonary arterial blood, bc it’s a mixture of all the venous blood from all over the body
What is the difference between ventilation, gas exchange, and gas transport?
Ventilation = Atmosphere <–> Alveolar space
Gas exchange = Alveolar space <–> Blood
Gas transport = Blood <–> Tissues
Hypercapnia
Too much CO2 in the blood
Leads to increased cerebral blood flow/intracranial pressure, acedemia
Hypoxemia
Not enough O2 in the blood
Leads to tissue hypoxia, inhibition of cellular aerobic respiration, death
What is the relationship between partial pressure of a gas and the fraction of the gas? Equation?
Partial pressure and fraction of gas are directly proportional
Pgas = Fgas x Ptotal
What is atmospheric pressure at sea level?
760 mmHg
What makes inspired gas different than atmospheric gas?
Your body warms it up and adds water vapor to saturate it
How much partial pressure of water vapor is added to air that you breathe in?
47 mmHg
Negative pressure ventilation
Subatmospheric pressures in the chest generate air flow
“spontaneous” breathing = tidal breathing
Iron lung
Positive pressure ventilation
Suparatmospheric pressure outside the chest generate air flow
Machine/ventialator does this
What is normal RR?
10-16 breaths per minute
Tidal volume = VT
Volume of gas inspired in a normal breath
About 0.5 L
Minute ventilation
Volume of gas expired or inspired in a minute
About 6-7 L/min
Tachypnea
Increased RR
Hypopnea
Small tidal volume
Synonymous to shallow breathing
Dead space
Ventilated but does not participate in gas exchange
Anatomic dead space
Normal, part of your anatomy
Includes trachea, bronchi, bronchioles
About 1 ml/lb ideal body weight
Physiologic Dead Space
Anatomic dead space + diseased areas not participating in gas exchange
Which parts do participate in gas exchange?
Alveolar space = respiratory bronchioles, alveolar ducts, alveolar sacs
What is the relationship between minute ventilation, dead space ventilation, and alveolar ventilation?
Where V(dot)E = minute ventilation
V(dot)D = dead space ventilation
V(dot)A = Alveolar ventilation
What are the 4 main ways that alveolar ventilation are regulated?
peripheral chemoreceptors (CO2, O2, H+), central chemoreceptors (H+), lung stretch receptors, muscle and joint receptors
Includes: inspiratory inhibition reflex/Hering-Breuer reflex, Irritant receptors, J receptors (respond to pulm edema)
What is the strongest influence of control over breathing?
Central chemoreceptors: sense H+ in brain arterial blood
If pH goes down, tells your body to breathe faster
What is the relationship between CO2 and H+ in the blood?
CO2 <–> H2CO3 <–> H+ + HCO3-
If CO2 levels rise, then H+ levels increase and pH goes down, which is a signal to the brain to increase ventilation
What can the peripheral chemoreceptors sense?
Located in carotid and aortic bodies
Elevated H+ (low pH)
Increase in arterial PCO2
Decrease in arterial PaO2
What is the best way to measure alveolar ventilation?
Measure alveolar CO2!
Unlike O2, it’s pretty constant: there is no inspired CO2
Transferred VCO2 messes with the value of VCO2 a little bit BUT the rate of transfer of CO2 from pulm circ/tissue to alveolus is constant when you are at rest
What is the equation for partial pressure of CO2 in the alveolus?
PACO2 = 863 x V(dot)CO2/V(dot)A
The amount of CO2 in your alveoli is:
- directly proportional to the amount of CO2 moving from capillary blood to alveolus (this is your “input” of CO2)
- inversely proportional to your alveolar ventilation (this is your “drainage:” if you increase alveolar ventilation, you’ll take more CO2 out of the lung & ppCO2 will go down)
What is a simplified version of the equation for PCO2?
Why can we rewrite the equation in this way?
PACO2 = K’/V(dot)A
Because V(dot)CO2 is constant at rest
What is the easiest way to calculate alveolar flow?
V(dot)A = K’/PaCO2
We can measure arterial PCO2!!! Alveolar PCO2 = arterial PCO2 because the CO2 has equilibrated between the alveolus and pulmonary capillary PCO2, which becomes pulmonary venous & becomes left atrial & aortic & all the arteries
What is the normal range for PaCO2 (arterial)?
37-42 mmHg
What does low PaCO2 indicate?
Less than 37 mmHg
Hypocapnia/hypocarbia
Due to alveolar hyperventilation
What does high alveolar PaCO2 indicate?
Hypercapnia/hypercarbia: elevated alveolar PCO2
Due to alvolar hypoventilation
What causes alveolar hyperventilation?
Hypoxemia
Acidemia
Stimulation of lung receptors
Drugs: aspirin, progestins
Pain
Anxiety
Fever
Pregnancy
Exercise
Note: hypercapnia causes increased respiratory drive but it’s impossible to have both hypercapnia and alveolar hyperventilation at the same time
What are signs of increased work of breathing?
Accessory muscle use
Tachypnea
Nasa flaring
Paradoxical breathing: when belly moves in while chest moves out secondary to diaphragmatic weakness which is due to muscle fatigue
What can cause alvolar hypoventilation?
Decreased respiratory drive/effort (drugs, sleep, breath holding)
Neuromuscular incompetence i.e ALS patient with weak muscles
Muscle fatigue due to increased load i.e. AIDS patient has increased dead space due to pneumonia
Loss of respiratory system integrity (crushed chest, complete airway obstruction)
What are sources of dead space that’s not normal?
Adding external dead space: scuba, ventilator tubing, breathe through a straw
New dead space created from alveolar space: due to a pulmonary embolism that blocks blood flow to a section of alveoli
Why does increased dead space due to pulmonary embolism lead to alveolar hypoventilation?
Normal homeostasis leads to increased PaCO2 which leads to increased minute ventilation and increased alveolar ventilation which ultimately brings down the PaCO2 to normal levels
But when you have dead space due to pulmonary embolism, you get increased PaCO2 which leads to increased minute ventilation & increased ventillation of the dead space –> eventually you get increased work of breathing & your muscles get fatigued –> alveolar hypoventilation
