Hacker News Reader

Comment by ordu | Hacker News Reader

I read somewhere, that COVID-19 attacks alveoli first, in contrast with other viruses who start with attacking bronchi. It leads to problems with bloog oxygenation, but human body doesn't control for oxygen levels, monitoring instead levels of CO2. So it leads to hypoxia which goes undetected for a some time. Damage to alveoli also goes undetected, because alveoli lack pain receptors.

I'm not a medic, I don't know is it plausible explanation or not (I'm even not sure whether I succeeded to use correctly all the anatomical words like "bronhi" or "alveoli") but I'd like someone knowledgeable to comment on this. I wander if it was true, could hypoxia explain other symptoms, like heart damage.

View on HN

> human body doesn't control for oxygen levels, monitoring instead levels of CO2. So it leads to hypoxia which goes undetected for a some time.

I don't think that's quite correct. Hypercapnia (excess CO2) triggers a reflex to inhale, that's what you feel when you hold your breath for a long time. That reflex doesn't trigger when you're inhaling CO, for instance.

But the body does have sensors to detect oxygen levels in the carotid body (and maybe the aortic body?). These do impact breathing as well, but they do so via the parasympathetic nervous system so you're not as aware of it. IIRC the way this works is poorly understood, and its dysfunction been thought to play a role in sleep apnea.

That would possibly explain why some people have trouble with oxygen deprivation in high altitudes while others inexplicably do not. I wonder if people who see a lot of benefit from breathing techniques like Pranayama and Wim Hoff have issues with that mechanism.

A few weeks ago they were investigating symptoms similar to HAPE - High Altitude Pulmonary Edima.

Basically, you get blood clots and those go into the heart to the lungs and block the blood vessels (killing parts of the lungs) and presumably other parts of the body. You also get the cyto storm.

So it's not surprising that it's causing damage everywhere. I wouldn't be surprised if asymptomatic people have some damage, but not enough to cause noticable symptoms.

The article has a section that talks about how the virus affects the brain and that the low oxygen level is because the virus may somehow suppress the brain stem reflex that causes gasping when oxygen levels are low.

This theory doesn't seem plausible, the very place where the body releases CO2 is the same for O2.

The comment about "not controlling for O2" is referring to the fact that the human body can't directly detect blood oxygen levels, and only infers them from blood CO2 levels. So if something's going wrong with the oxygen absorption process but the CO2 exhalation process is still fine, that would explain why patients have dangerously low blood oxygen but aren't panting or otherwise showing respiratory distress.

(Incidentally this is also why it's really dangerous to hyperventilate before free diving, because you can put your O2 / CO2 ratio out of whack which can cause you to black out without warning while under water.)

> the human body can't directly detect blood oxygen levels, and only infers them from blood CO2 levels

This is not quite accurate. The body monitors blood chemistry centrally (in the brain and spinal cord) and peripherally (in the blood vessels).

Central chemoreceptors only monitor pH of the cerebrospinal fluid, which indirectly tracks blood CO2, but don't monitor O2.

Peripheral chemoreceptors monitor O2, CO2, and pH.

https://courses.lumenlearning.com/boundless-ap/chapter/respi...

But there there was low levels of O2, wouldn't it mean low levels of CO2? Body doesn't have enough O2 to produce much of CO2, seems plausible for me.

CO (carbon monoxide) poisoning happens the way it does for this reason: You don't feel lack of oxygen - you feel abundance of (uncleared) CO2. If you have too much CO, you lack oxygen but don't have too much CO2, you just feel sleepy/drowsy but suffocate and die unless you do something.

Whether the rest of OPs theory makes sense, I don't know - but this part is indeed factual AFAIK.

The virus appears to impair hematic function in the lungs. The oxygen builds up, and it is quite caustic. It creates what are called ground glass bodies. Since the oxygen is trapped in the lungs and does not move the blood very efficiently, you get hypoxia.

Reply on news.ycombinator.com