Chemical Control of Breathing DEMO - Forster Flashcards Preview

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Flashcards in Chemical Control of Breathing DEMO - Forster Deck (23):
1

Define: VE (V may have a dot over it)

 

Minute expired ventilation

The volume of air expired from a person's lungs per minute.

2

Define:

1) FETCO2 / FETO2

2) PETCO2 / PETO2

1) Fraction of CO2 / O2 at the End of a Tidal breath 

(unitless / %)

2) Pressure of CO2 / O2 at the End of a Tidal breath

(mmHg)

3

1) What formula do you use to convert the measured FETCO2 to PETCO2 (or likewise for O2)?

2) What other equation will be used in this calculation?

1) PETCO2 = FETCO2 x Pnorm

(This should be intuitive: knowing the fraction of a gas within a system, one can calculate the pressure of that gas as a fraction of the total pressure of gas in the system)

2) To calculate the normalized pressure, Pnorm, subtract pressure due to water vapor from the atmospheric pressure:

Pnorm = PATM - PWV

(For our class example, PATM in Milw was 740mmHg and PWV was 47mmHg)

4

Define: CO2 sensitivity of VE

CO2 sensitivity of VE

Change in VE per 1mmHg increase in CO2

(In class, the student's VE increased by 1.6L/min per 1mmHg increase in CO2)

5

Describe the ventilatory response of hypercapnia.

1) Which chemoreceptors are largely responsible for the response?

2) What is the response? To what extent?

3) Is the response sensitive or insensitive?

4) What parameters of the response change, and how?

1) Brain chemoreceptors

2) Increased ventilation (aka VI, in L/min) to reach a new steady state of CO2

3) Sensitive - Gradual changes in response to small CO2 changes

4) Tidal volume increases first, and does so substantially. Frequency increases second, and less so than VT (at least to the extent of hypercapnia demonstrated in class)

6

1) Does PETCO2 increase or decrease when breathing a hypercapnic air mixture? Why?

2) Does PETO2 increase or decrease when breathing a hypercapnic air mixture? Why?

Hypercapnic air mixture:

1) PETCO2 inceases - there is more in the air

2)PETO2 increases - metabolic requirements have not increased, and the subject has increased their ventilation in response to the hypercapnia.

7

How would you characterize a subject's [H+] status while breathing CO2-enriched air?

Respiratory acidosis

8

What are the effects on breathing and plasma [H+] of chronic alveolar hypoventilation?

Loss of baroreceptor CO2 sensitivity over time, leading to chronically elevated plasma [H+].

9

Describe the ventilatory response of hypoxia.

1) Which chemoreceptors are largely responsible for the response?

2) What is the response?

3) Is the response sensitive or insensitive?

4) What parameters of the response change, and how?

1) Peripheral (carotid) chemoreceptors respond to decreased O2

2) Increase in ventilation (aka VI, in L/min)

3) Insensitive - a large O2 drop is required before there is a reponse, but once the drop is sufficient, the response is fast

4) Tidal volume increases suddenly and markedly. Frequency changes more gradually but more significantly than in hypercapnia (at least to the extend of hypoxia demonstrated in class)

10

1) Does PETCO2 increase or decrease when breathing a hypoxic air mixture? Why?

2) Does PETO2 increase or decrease when breathing a hypoxic air mixture? Why?

Hypoxia

1) PETCO2 decreases because of hypoxia-induced tachypnea without an increase in metabolic rate (more CO2 is breathed off than produced)

2) PETO2 decreases because there is less O2 in the inspired air.

11

How would you characterize a subject's [H+] status during hypoxia?

Respiratory alkalosis

12

How do high-altitude natives maintain a higher PO2 despite lower VE (as compared to a visitor to high-altitude)?

Would you say high-altitude natives have a increased or decreased response to hypoxemia?

Increased diffusion capacity due to increased respiratory surface area in the lungs.

Decreased response

13

1) The carotd body is innervated by sensory fibers that originate from what ganglion?

2) What nerve do these fibers constitute?

3) Further back, these fibers originate from what part of the brain?

1) Petrosal ganglion

2) Nucleus Tractus Solitarius

3) Carotid Sinus Nerve

14

What cell types can be found in the carotid body?

  1. Chemoreceptor cells
    • contain cytoplasmic synaptic vesicles near their interface with:
  2. Endings of sensory nerve cells
  3.  Sustentacular cells
    • a type of supportive cell
  4. Endothelial cells
    • of capillaries that surround the clusters of other cells

15

What is the biochemical origin of the chemoreceptor signal?

Controversial / Not known

Likely involves:

  • K+ channel conductance
  • Intracellular Ca2+
  • Serotonin
  • ACh

16

How does the frequency of the carotid chemoreceptor signal change in response to:

1) Increasing CO2?

2) Decreasing O2?

1) Increased CO2: Increased frequency

2) Decreased O2: Increased frequency

Because both CO2 and O2 can alter the frequency rate, you can think of increased CO2 as increasing the sensitivity of the chemoreceptors to decreased O2 and vice versa.

17

Are the carotid chemoreceptors more sensitive to hypoxia or hypercapnia?

Hypoxia

18

What would happen if the carotid chemoreceptors were surgically denervated?

  • Pronounced hypoventilation
  • Attenuation of CO2 sensitivity

(I would think attenuation of O2 sensitivity as well, but it's not listed...)

19

Why can plasma [H+] not stimulate the brain chemoreceptors?

The blood-brain barrier is impermeable to H+. CO2 must diffuse across, reacting with H2O to form HCO3- and H+, decreasing pH that way.

20

Where are central chemoreceptors found?

All are found at various spots throughout the brainstem.

  • Locus coeruleus
  • Pontine & Medullary raphes
  • Fastigial nucleus
  • Medial & Lateral parapyramidal areas
  • Nucleus tractus solitarius
  • Retrotrapezoidal area
  • pre-Bötzinger complex

21

Is the ventilatory response to respiratory or metabolic acidosis greater?

Response to respiratory acidosis is greater

(However, lung pathology may prevent the lungs from adequately responding and neccessitate metabolic compensation via HCO3-)

22

What are major excitatory factors for chemoreceptor firing?

Major inhibitory factors?

Excitatory:

  • Serotonin
  • ACh
  • Substance P
  • NE
  • Orexin

Inhibitory:

  • GABA
  • Glycine

23

Is chemoreceptor stimulation by CO2 obligatory to stimulate breathing?

No, CO2 is not obligatory.

There are experimental models in which breathing does not change when PaCO2 in increased by increasing inspired CO2.

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