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SMP - Cardiopulmonary Exam 2 > Lecture 22 - Ventilation and Gas Exchange > Flashcards

Lecture 22 - Ventilation and Gas Exchange Flashcards

1
Q

Functions of conducting zone?

A
  1. Warms and humidifies the air as it flows through
  2. Secretes mucus to trap particles in the inspired air
  3. Expectorates phlegm with cilia
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2
Q

Describe how spirometry works.

A

Water filled bucket with an inverted bucket placed inside

Water filled bucket connected to an air tube through which the patient breathes

Inverted bucket connected to pulley system connected to a pen on paper recording changes in rise/fall

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3
Q

How many lung volumes are there? Describe each. WHICH ONES ARE DIRECTLY MEASURED via spirometry?

A
  1. ***Tidal volume (TV) = amount of air breathed out/in under normal conditions
  2. ***Inspiratory reserve volume (IRV) = max amount inspired above the tidal volume
  3. ***Expiratory reserve volume (ERV) = max amount expired below the tidal volume
  4. Residual volume (RV) = remaining amount of air left after max expiration
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4
Q

How many lung capacities are there? Describe each. WHICH ONES ARE DIRECTLY MEASURED via spirometry?

A
  1. Total lung capacity (TLC) = sum of all lung volumes = TV + IRV + ERV + RV
  2. ***Vital capacity (VC) = largest breath you can take = TV + IRV + ERV
  3. ***Inspiratory capacity (IC) = maximal inspiratory volume = IRV + TV
  4. Functional residual capacity (FRC) = amount of air left after residual expiration = ERV + RV
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5
Q

During spirometry, does the bucket move up or down during expiration?

A

Up

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6
Q

During spirometry, does the bucket move up or down during inspiration?

A

Down

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7
Q

During spirometry, does the pen move up or down during inspiration?

A

Up

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8
Q

During spirometry, does the pen move up or down during expiration?

A

Down

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9
Q

What is a lung capacity?

A

Summation of 2 or more lung volumes

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10
Q

How is RV measured?

A
  1. Via helium dilution
  2. Via nitrogen washout
  3. Via body plethysmography
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11
Q

Does the residual volume ever leave the chest?

A

NOPE

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12
Q

What is special about helium gas? What does this mean?

A

It is inert = it cannot pass alveolar capillary membranes

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13
Q

Describe the helium dilution technique to calculate RV.

A
  1. Add a certain quantity of helium gas in the upside down bucket (C1 x V1)
  2. Let the patient breath until the helium equilibrates throughout the lungs, the tube, and the bucket (aka at FRC)
  3. Record C2 in the bucket
  4. Calculate VT = V1 + V2 = C1 x V1 / C2
  5. VT - V1 = V2 = FRC
  6. FRC - ERV = RV
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14
Q

Describe the nitrogen washout technique to calculate RV.

A
  1. Patient starts at FRC
  2. Measure [N2] expired
  3. Use 100% O2 gas to wash all of the N2 out into a collecting bag
  4. Measure volume and N2 concentration in bag once it has reached a steady state and no more N2 is exiting the lungs = quantity of N2 which was in the FRC
  5. FRC x 0.8 = VB x FN2 (in bag) OR FRC = VB x FN2 / 0.8
  6. FRC - ERV = RV
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15
Q

What is FN2 at FRC?

A

0.8

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16
Q

What is the caveat of both GAS techniques to indirectly measure RV? Does this apply to body plethysmography?

A

Both techniques assume that gases reach all sections of the lungs evenly, so if there are pathologies causing some alveoli to be occluded or stop functioning (asthma, emphysema, COPD), the helium will not reach all of them OR all of the N2 will not be expelled, and therefore the RV will be underestimated

NOPE, it does not because body plethysmography measures all of the gases in the lungs whether it is communicating or not

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17
Q

What is Boyle’s Law?

A

P x V will stay constant at the same temperature

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18
Q

Describe the body plethysmography technique to calculate RV.

A
  1. Place patient in a box with a pressure monitor and a tube they can breath through
  2. As patient inspires, the chest expands and the pressure within the box increases and the volume will decrease
  3. Boyle’s Law:
    - P1 x V1 = P2 x (V1 - ΔV)
    - P3 x V2 = P4 x (V2 + ΔV)
ΔV = volume change caused by expanded chest 
P3/P4 = pressure at patient's mouth
V2 = FRC = volume inside the chest
19
Q

In which case is the body plethysmography technique not valid?

A

If a child has an ear tube

20
Q

What is minute ventilation?

A

Volume of gas moved in and out of the body during regular breathing = VE = TV x respiratory rate = dead space minute ventilation + alveolar minute ventilation

21
Q

Normal respiratory rate?

A

15 breaths/min

22
Q

Normal minute ventilation?

A

500 mL x 15 breaths/min = 7,500 mL/min

23
Q

What is the tidal volume equal to? Describe the proportions.

A

VT = VD (40%) + VA (60%) = 150 mL + 350 mL = 500 mL

VD = Dead space volume
VA = Alveolar volume
24
Q

What is the ventilation to perfusion ratio?

A

V/Q ~ 1

25
Q

What is the alveolar ventilation?

A

350 mL x 15 breaths/min = 5,250 mL/min

26
Q

PvO2 in pulmonary artery?

A

40 mmHg

27
Q

PvCO2 in pulmonary artery?

A

45 mmHg

28
Q

PaO2 in pulmonary vein?

A

100 mmHg

29
Q

PaCO2 in pulmonary vein?

A

40 mmHg

30
Q

PAO2?

A

100 mmHg

31
Q

PACO2?

A

40 mmHg

32
Q

How to measure the volume of the anatomical dead space aka the conducting zone? Describe this technique.

A

Fowler’s method:

  1. Ask patient to inhale 100% O2 in one maximal inspiration
  2. Measure amount of O2 exhaled: first portion will include 100% O2
  3. As more air travels up from the respiratory zone we will also detect CO2/N2
  4. As soon as CO2/N2 starts to appear, we can deduce it is the end of the anatomical dead space => on a graph use the midpoint of the rise to measure the anatomical dead space volume because at the dead space/respiratory zone limit some CO2 will diffuse into the dead space and mix with the pure O2
33
Q

What is the physiological dead space?

A

Regions of alveoli that are not capable of exchanging gas + anatomical dead space = volume of gas that does not eliminate CO2

34
Q

How to measure the volume of the physiological dead space? What to note?

A

The Bohr method: you can measure TV, exhaled volume of CO2 (=VT x FeCO2), and alveolar CO2 (aka arterial CO2) to calculate alveolar volume (VA) and then VD = VT - VA

VT x PeCO2 = VA x PACO2
VT x PeCO2 = VA x PaCO2
VA = VT – VD
VT x PeCO2 = (VT-VD) x PACO2
Bohr equation: VD/VT= PACO2- PeCO2/PACO2

Note: since physiological dead space includes alveoli that are not capable of exchanging gas, the CO2 that we expire only comes from alveolar gas space

35
Q

What is an example of a case in which an alveolus would be incapable of exchanging gas?

A

Pulmonary embolism

36
Q

What is the minute ventilation of CO2 equal to in a steady state?

A

oVeCO2 = oVA x PaCO2 / 0.8

37
Q

How to relate alveolar minute ventilation to VD and VT?

A

◦VA = VA x RR = (VT - VD) x RR = ◦Ve x (1 - VD/VT)

1 - VD/VT = % of TV that is alveolar

38
Q

What does VD/VT represent?

A

% of tidal volume that is dead space

39
Q

What can be said of the CO2 production during stead state?

A

It is constant

40
Q

When is minute ventilation Ve x PaCO2 constant? What does this mean?

A

When CO2 production and VD/VT are both constant:

Ve x PaCO2 = VeCO2 x 0.862 / (1 - VD/VT)

Means that if you double the minute ventilation BY ADJUSTING RESPIRATORY RATE you are halving the PaCO2, therefore PACO2

41
Q

If the PaCO2 increases but the minute ventilation stayed constant, what happened?

A

One of 2 things:

  1. Either the CO2 production rose
  2. Or the volume of physiological dead space increased
42
Q

What is total ventilation equal to?

A

= VT x RR

43
Q

Are physiologic and anatomical dead space usually the same value?

A

Yes, but physiologic can be increased in many lung diseases

44
Q

Normal anatomical dead space?

A

150 mL

SMP - Cardiopulmonary Exam 2 (15 decks)

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