Monday, February 2, 2015

Study group discussion: Respiratory physiology

Does anyone have a mnemonic for respiratory centers?

DIVE!
The Dorsal nucleus is for Inspiration (tidal).
The Ventral nucleus for Expiration.

The ventral nucleus is especially important for forced respiration because expiration in general is passive. In tidal respiration, during the inspiration phase, the diaphragm and external intercostal muscles work. But the tidal expiration is completely passive because of elastic recoil.

Review question: Which all values of lung volumes you cant measure by spirometry? And why?

Reserve volume.
Functional residual capacity.
Vital capacity.

It's because spirometry measures through expiration. And the stuff that stays inside the lungs can't be measured!

What is the importance of residual volume? Why is it crucial for your body to retain air even after forceful expiration?

So that the lungs don't collapse on themselves. That's the most important one. There are two other uses!

Gas exchange is a continuous process, just because you expire, doesn't mean the gas exchange stops.

Third, the residual volume doesn't allow sudden changes in the outside concentration of air to affect your internal homeostasis. It takes 16 to 20 breaths for the outside air to affect your residual volume. This gives ample of time for your chemoreceptors to detect the slight changes in pH and respond.

Oh wow.. I didn't know this. Cool stuff. The breaths part though. Our body is waaay ahead of us than we think.

Totally!

Another review question! Mechanism of chemoreceptors? What passes through the BBB?

CO2 is not polar and is small, the BBB allows hydrophobic substances to pass through, so CO2 would pass the BBB.
The chemoreceptors monitor the H+ concentration of cerebrospinal fluid (CSF), including the brain interstitial fluid.
CO2 readily penetrates membranes, including the bloodbrain barrier, whereas H+ and HCO3– penetrate slowly. The CO2 that enters the brain and CSF is promptly hydrated. The H2CO3 dissociates, so that the local H+ concentration rises. The H+ concentration in brain interstitial fluid parallels the arterial PCO2.

Mechanism of peripheral receptors?

Oxygen potassium sensitizer channel. Lack of oxygen closes this channel, leading to increase in potassium in the ICF, depolarising it.

Do you know about the conditions in which you do not give 100% oxygen to the patient?

In cases where the CO2 levels are increased. Example, emphysema.. Cause the problem here is the respiratory drive is completely dependent on the blood CO2 level. So if you give 100% O2 the patient will go in apnea.

Yep. There's one more besides the CO2 indication. The neonate. Why?

Causes retinopathy of prematurity due to oxidative stress!

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