What is dead space of lungs?

There are two types of dead space-

1.       Anatomical

2.       Physiological

Anatomical dead space is the area included in the first 16 generation of the bronchial tree. Its by virtue of the normal anatomical structure that this area is unable to take part of in the exchange of gases

The physiological dead space is when there is decreased blood supply to a particular part of the lung, but the air entering the same part is normal. Hence there is no exchange of gases. In other words there is an increase in V/Q ratio.

Extra-

Why secondary tuberculosis affects the upper lobe?

There is an entity called ventilation perfusion ratio (V/Q)

meaning the degree of air entering the alveoli of lung and the corresponding pulmonary blood supply to the same. The normal value of the V/Q ratio is 0.8

Pulmonary blood capillaries are a low pressure system, with an average pressure of 25/8 mm of Hg. Out here comes the effect of gravity, pulmonary blood is unable to perfuse the upper lobes that well .

On the other hand, Air when it enters the lungs it enters the upper lobes better than the middle and lower lobes

This fact can be applied to

Study group discussion: Legionella confusion

A few days back, we had a discussion on legionella.

Legionella affects three systems - Lungs, GIT (diarrhoea) and CNS (Altered sensorium, confusion, etc).

Why does it cause CNS symptoms?

Study group discussion: Case control and cohort study mnemonic

Any mnemonic for case control study vs cohort study and how to identify which study to conduct or not?

Study group discussion: Transpulmonary pressure

What is transpulmonary pressure and its significance?

I remember it's something like... General lung pressure without alveolar pressure. I don't know.

It's the difference between the intrapleural pressure and the alveolar pressure. The athmosphere pressure is constant, but air still needs to flow in and out of our lungs, so we adjust the pressure inside our body.

The basic principle is that air flows from higher pressures to lower, so we constantly change the pressure in our lungs to higher or lower than the atmosphere.

Transpulmonary pressure (when everything is fine) is always positive.

I'm getting what he is saying, go on!

Transpulmonary pressure is always positive, intrapleural is always negative and alveolar fluctuates.

That's how I remember from my physiology classes, anyway.

Yeah, alveolar fluctuates so that air can flow in and out easily.

Transpulmonary pressure is basically the elasticity of the lungs. The recoil.

Since atmospheric pressure is relatively constant, pressure in the lungs must be higher or lower than atmospheric pressure for air to flow between the atmosphere and the alveoli. It is nothing but the elastic recoiling of the lungs. If 'transpulmonary pressure' = 0 (alveolar pressure = intrapleural pressure), such as when the lungs are removed from the chest cavity or air enters the intrapleural space (a pneumothorax), the lungs collapse as a result of their inherent elastic recoil. Under physiological conditions the transpulmonary pressure is always positive; intrapleural pressure is always negative and relatively large, while alveolar pressure moves from slightly positive to slightly negative as a person breathes. For a given lung volume the transpulmonary pressure is equal and opposite to the elastic recoil pressure of the lung.

Study group discussion: Physiology books

Which is the best physiology book? I find Guyton to be really dull and Rhoades lacks details.

Ganong is okay, I guess.

Ganong has always been my first love.

I usually go for Ganong, but Costanza and Berne-Levy are also pretty good.

Costanza is not as detailed though, it's good for refreshing your memory the week before exams.

Yep. BRS is good for last minute revision!

Which are the simpler books for physiology? I know of Ganong.

Which was the other one?

Guyton?

Guyton is too extensive.

I read Guyton only in 1st year.
Good for clearing basics.

Yes, I find Guyton better than other physiology books.

Try BRS physiology.. It's little and has everything you need to know. Like it's smaller than Ganong.

Smaller the better!

I think it's 100 -  200 pages.

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!

Study link!  http://medicowesome.blogspot.ae/2013/12/case-scenarios-when-you-dont-give.html

Study group discussion: Cause of decreased glucose levels in CSF in bacterial meningitis

I have a question, my professor told us that the cause of decreased glucose in CSF relates to permeability changes caused by the exudates. Which I find a good reason for the protein levels but glucose is not the same. In books and other references, I found the reason being bacterial and brain tissue consumption of glucose and non replenishment of it being the cause.

Can someone tell me for sure the cause for glucose depletion in csf in meningitis?

I think it's the glucose consumption. Permeability changes play a minor role.

Yes I'd also go with consumption.

Because permeability changes occur in viral meningitis as well.

That's what I also thought because permeability changes occur in all of the forms even the non infective ones.

Study group discussion: How to do percussion

I can't seem to get the hang of percussion and I have OSCE exams coming up :(
Any tips?

What exactly are you having trouble with?

I was always told to just hit once and not repeatedly like a drum, just once or twice and listen.

Ok well I know the technique it just doesn't sound as loud as the docs that are training us.

Ahh i know that you mean, happens to me too, but I don't know how to make it louder, I just try really hard to focus and block all external sounds... Plus, I lean as close as I can to the patient without it being obvious.

I think in part it just comes with practice and gaining experience.

Yeah I'll keep practicing.

When I was first learning it the sound was very dull and I had to try a few times to hit the correct spot.
But now it's just two quick taps.

Make sure that you're not resting your palm on the patient since that can dull the sound.

Ok, I see.

And when tapping make it fast and strong, as if your fingers were hot and you just wanted to get it over with.

Some people tap and let the finger rest, which can also full the sound.

Someone told me to press the pleximeter firmly, it gives better results than trying to strike harder with the plexiform during percussion.

Our supervisor usually sits a far from the patients and asks one to tap until she can hear from a far.

But yeah..Quick double strikes and fast finger withdrawal.

Yes, you can tap as hard as you like but if you aren't pressing your finger down firmly you're not gonna get much.

Note that firmly does not mean hard.

You should not get tired from pressing down your finger.

Plus concentrate on the feel of the vibration against your fingers.

My taps are never really loud enough, but then I practised by percussing myself to know the feel. That's good enough.

Study group discussion: Schizophrenia and Schizotypal disorder

What's difference between schizophrenia and schizotypal?

Schizotypal have odd behaviour and magical thinking.

Why schizophrenia is not placed in personality disorder?

Schizophrenia is a much more serious mental disorder, while schizotypal personality disorder is a (relatively) mild condition where the patient has social anxiety, extreme need to be alone and usually believes in odd things.

For example, have you seen or read Harry Potter? Luna Lovegood could be an example for a schizotypal personality disorder.

Schizophrenia on the other hand, could be... Hmm... Couldn't think of a HP reference.
Anyway, a person who is delusional, has hallucinations, hears voices, again believes odd things but on a much more serious level and is willing to do a lot of things to support those beliefs or because of them.

"Personality" is like, the things that make you YOU... That makes you different from other people.

Our teachers says prophets were schizotypial.. No offense, Living alone in deserts and hearing voices!

Personality disorders are classified as the differences from the norm, they are not always extremely dangerous/harmful mental disorders like schizophrenia. "personality disorders" are just a certain behavioral pattern.

Hahah well that could be said actually, if a person came to my hospital claiming he was a prophet we would give him medication probably!

Can you help me differentiate thought content vs thought form and thought process?

I can try to help.
Thought content is what you are thinking about. Say, you are sitting in your house looking out the window, there are 2 people walking and they have a dog. Looking at them your thought content would be those 2 people, the dog, and that they are walking.

This is in the beginning..

Then you start to form more complex thoughts, the way those develop are your thought process.

"Those people are walking. They are walking in front of my house. They have a dog. Why do they have a dog? Why are they in front of my house? Are they watching me? Who sent them here?"

This is an example of a thought process, the way ideas are forming and developing in the person's head.

This was an example of a paranoid way of thinking by the way, which is common in schizophrenia.

Hey buddy thanks it was very helpful!

You are welcome :)

Renal tubular acidosis types mnemonic

Hi everyone!

We were discussing RTA on our study group when we decided we needed a mnemonic for it!

Study group discussion: Malignant hypertension

What the difference between essential & malignant hypertension?

Essential is of unknown cause. Also known as the primary hypertension.
Malignant hypertension is also known as hypertensive emergency.

Malignant hypertension is an acute form that effects one or more organ systems.
Cardiovascular system, central nervous system and renal systems are irreversibly damaged.

Also papilledema! Remember reading it in ophthalmology.

In malignant hypertension, BP shd be lowered asap with antihypertensive agents. Mostly, iv injection of sodium nitroprusside is given for immediate effect so that BP is lowered.

There was also something about nitroglycerin and nitroprusside.. Which should be used when in malignant hypertension.
Don't remember what it was.. Like if cerebral edema is more use this stuff and if some other symptom is more you'll use the other one of the two.

Just read it up.. They say you choose based on the end organ damage.
Nitroprusside is widely used, especially if the person has neurological symptoms, cerebral edema.
Nitroglycerine will be the drug of choice if the heart is involved (Ischemia, acute coronary syndrome)

I'll have to correct myself, nitroglycerin isn't used anymore in hypertensive emergencies because of the side effect profile. If used, it's used as an adjunct.

Read a ncbi article on the same: Nitroglycerin is a potent venodilator, and only at high doses does it affect arterial tone. It causes hypotension and reflex tachycardia, which are exacerbated by the volume depletion characteristic of hypertensive emergencies. Nitroglycerin reduces blood pressure by reducing preload and cardiac output, which are undesirable effects in patients with compromised cerebral and renal perfusion. Low dose (60 mg/min) nitroglycerin may, however, be used as an adjunct to intravenous antihypertensive therapy in patients with hypertensive emergencies associated with acute coronary syndromes or acute pulmonary edema.

*After a lot of unsure discussions on hypertensive emergency, hypertensive urgency and malignant hypertension we concluded this*

Emergency: End organ damage.
Urgency: No end organ damage.

Malignant hypertension = Hypertensive emergency.

Hypertensive crisis: Severe elevation in blood pressure, with diastolic blood pressure (DBP) > 120-130 mmHg.

Nitroprusside is given in hypertensive emergency. However, watch out for cyanide toxicity when you choose to administer it.

Got a revision question! Which drug is used in cyanide toxicity?

Nitrites.
Sodium thiosulphate.
Cyanide toxicity - GTN.

Yes!

Study group discussion: Migraine, aura and floaters

What did Leonardo have in the movie Shutter Island?

Migraine, I think.

Migraine? When was that?

Migraine was what he started having as a symptom may be.

Oh yes, the headaches and flashes of light.

Auras?

Yes, those.

What are auras?

The lights some people see before they have a migraine headache.

Auras can present in any way of sensation.

Some patients also complain that something smells before the attack.. Smell of burning rubber or something. It's also a part of the aura.

You can have flashes of light, ringing in ears, sensation on hands and even sudden salivation. 

In migraine I guess the most common type of aura is of the visual type.. Seeing flashes of light.

In reality, it moves and vibrates. then expands and fades away.

I see bits and pieces of light too against a very bright room.. I read it's the pieces of proteins in the vitreous of your eye moving around.

Oh yes, I found those proteins very fascinating as a kid.

Would rub my eyes intentionally to see them and wondered if others could see them as well.

Seemed like little bubbles floating!

Floaters!

And when it is sudden and excessive.. It is a sign of retinal detachment!

Floaters.. I once argued with an opthalmologist, I kept telling him it was normal and he kept saying they're pathological.

Did he said why?
If the person has no other symptoms.. Just floaters once in a while.