Respiratory II Flashcards
Pulmonary System is a ___ flow, ___ resistance, ___ pressure system
high flow, low resistance, low pressure system
Ventilation
how gas gets from the atmosphere to the alveoli
What does Boyle’s Law mean and how does it apply to us?
a gas in a closed container has a given pressure → ⇡ volume, ⇣ pressure
when the diaphragm contacts the volume of the thoracic cavity ⇡ and intrapleural pressure ⇣
⇣ in Pip causes lungs to expand
Henry’s Law
- the amount of gas that dissolves into a fluid is related to:
- the solubility of the gas into the fluid → CO2 is more soluble than O2
- the temperature of the fluid → the higher the temp the lower the solubility
- the partial pressure of the gas → the greater the pp gradient the better we can get a gas into a fluid
Dalton’s Law
the total pressure of a gas mixture is equal to the sum of the pressures that each gas exerts independently
What does Dalton’s Law mean for respiratory physio?
- air is composed of multiple gases → mostly N2 and O2
- each gas has a pressure (partial pressure) that is independent of other gasses
- add up partial pressures of all gases for total pressure
total partial pressure: PB = PO2 + PN2…
to calculate PP
PO2 = PB x FO2 (fraction of gas that is oxygen)
What happens to PO2 as you go up in altitude?
it decreases
Why does the function of inspired air stay the same but atmospheric pressure drop as you go up?
because gravity decreases as you go up
Inspiration begins
- ambient air brought into airways warmed and humidified
- by larynx, saturated with water vapor (water vapor = a gas (PH2O = 47 mmHg)
- PP of other gases diluted
- PO2 in a humidified mixture → PO2trachea = 150 mmHg
water vapor does not change the % of O2, it decreases PP
Total ventilation (VE)
VE (ml/min) = tidal volume (VT) (ml/breath) x respiratory rate (f)(breaths/min)
rest: 6,000 mL = 500 mL/breath X 12 breaths/min
Max: 150L (2X rest) = ⇡⇡ X ⇡ → both VT and f ⇡ but depth of breathing increases more because of anatomical dead space
Dead Space
- Not all inspired air gets to site of gas exchange
- part remains in conducting pathway
- useless for gas exchange
- anatomical dead space (= 150 mL)
- Pronounced effect on efficiency of VE
- 500 mL air moved in and out/breath → only 350 mL exchanged between atmosphere and alveoli
must be considered to determine alveolar ventilation
2 types of dead space
- anatomical dead space (=150mL)
- in conducting airways → everyone has it
- Alveolar dead space (later)
- in alveoli with poor circulation
- insignificant in healthy lung; lethal in diseased lung
physiological dead space (anatomical + alveolar dead space) is the same as anatomical in healthy people
What is more important: Tidal Volume or Total Ventilation?
Tidal volume
Alveolar Ventilation (VA)
Alveolar Ventilation (VA) = (tidal volume (VT) - anatomic dead space (VD)) x respiratory rate (f)
4200 mL = (500 ml/breath - 150 ml) x 12 breaths/min
- at the end of expiration → old air from previous breath is in dead space
- next inspiration → old air is pushed into alveoli
Alveolar ventilation is best increased by….
increasing tidal volume
Wasted ventilation
drawing air in and out of dead space and not inspiring fresh air
PCO2 Equation
PaCO2 = (VECO2 x 0.863)/VA
PCO2 in arterial blood is inversely related to alveolar ventilation (VA)
- if you hyperventilate (high level of ventilation), PaCO2 goes down
- if you hypoventilate (under ventilate), PaCO2 goes up
How do you regulate PaCO2 and pH?
changing VA
- if PaCO2 is high, VA is not adequate for level of CO2
- not enough ventilation (CNS depression or respiratory muscle weakness)
- too much ventilation ending up as dead space ventilation (COPD or rapid, shallow breathing
Eucapnia
PaCO2 = 35-45 mmHg
alveolar ventilation = normal
Hypercapnia
PaCO2 = >45 mmHg
alveolar ventilaiton = hypoventilation
Hypocapnia
PaCO2 = < 35 mmHg
alveolar ventilation = Hyperventilation
How do we measure the amount of O2 reaching the alveoli?
The alveolar gas equation → PAO2 = PIO2 - (PACO2/R)
R = respiratory exchange ratio → ratio of how much CO2 is produced and how much O2 is taken in
PAO2 = 102
Respiratory Quotient
Ratio of CO2 produced (VCO2) to O2 taken up (VO2)
depends on the rate of metabolism and substrate burned (0.7-1); assumed to be 0.8
Alveolar Gas Composition
PP of gases and H2O from atmosphere to blood
- in healthy individuals, PAO2 is very close to PaO2
- difference is the A-a gradient
- 50% due to regional differences in VA/Q (⇡ at top of lung)
- 50% due to anatomic shunt (blood bypasses alveoli); bronchial veins drain into pulmonary veins
- due to high diffusibility, PACO2 = PaCO2