Respiration Question

[Giovanotto]

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Hope I'm not asking this in the wrong part of the forum, but I was wondering:

Why/How does hypoventilation cause hypercapnia? Everywhere I search it says it causes it by definition, without further explanation. I'm assuming there is a mathematical correlative and that's why I'm not getting a physiological explanation.

 

[VictorAlpha]

respiration, metabolism generates CO2...if you do not ventilate; CO2 builds up

 

[Giovanotto]

respiration, metabolism generates CO2...if you do not ventilate; CO2 builds up

Hypercapnia = increase CO2 in the alveoli.
Metabolism generates increased CO2 in the blood.

So are you saying that if there is an increase in plasma pCO2 (>46mmhg) than the driving force at the alveoli for CO2 (>46-40mmhg) is greater and therefore more CO2 diffuses at the alveoli. And because the rate of breathing is reduced then CO2 builds up in the alveoli?

 

[VictorAlpha]

I mean as I understand things CO2 builds within the blood from metabolic activity. That blood flows through pulmonary capillaries where it is dumped from blood to the gas of the alveolar space. If there is insufficient gas exchange between that space and the air outside of the body's airway, then the partial pressures of CO2 in the alveolar airspace will not allow more CO2 to be dumped from blood into that alveolar airspace. This means that CO2 will continue to build up. That might be what you said...

 

[terra330]

You're overthinking it. Reduced breathing means less oxygen coming in and less CO2 leaving. Metabolism still generates CO2, so the end result is CO2 levels build up in the blood stream. It will diffuse more readily into the lungs. And since you're not ventilating, the CO2 level will rise.

 

[Giovanotto]

I mean as I understand things CO2 builds within the blood from metabolic activity. That blood flows through pulmonary capillaries where it is dumped from blood to the gas of the alveolar space. If there is insufficient gas exchange between that space and the air outside of the body's airway, then the partial pressures of CO2 in the alveolar airspace will not allow more CO2 to be dumped from blood into that alveolar airspace. This means that CO2 will continue to build up. That might be what you said...

Vice-versa (from alveolar space into blood) and then, yes, that's what I said, unless I'm looking at this from the wrong perspective. I thought that the pCO2 in the blood which is > pCO2 in the alveoli would drive transport and not the pCO2 in the alveoli stopping transport.

 

[Bacchus]

SDN is not a place for homework help. Pick up a biochemistry text or Robbins (Internal Medicine) text.