Respiratory

Question 1

What are the 5 causes of hypoxaemia

Answer 1

reduced pi02
hypoventilation
V/Q mismatch
diffusion
R-L shunt

Question 2

How can drug induced collapse cause hypercapnia?

Answer 2

she has high co2 and has alveolar hypoventilation (this was due to narcotics reducing respiratory drive due to generalised cerebral depression after drug)

Question 3

Spinal cord levels responsible for resp muscles?

Answer 3

anterior horn cells, major resp muscles - the spinal cord would be C3,4,5

Question 4

3 main causes of hypercapnia

Answer 4

• Respiratory drive from brainstem - how much output is there causing you to breathe e.g heroin, morphine
• Neuromuscular transmission - need this to be intact, could be interrupted at any part of tract e.g C3,4,5, nerves exiting , could be effecting neuromuscular transmission, or something wrong with muscle
• Load (work of resp muscles) - resp muscles need to do two types of work - resistive work and elastic work, amount of work may be increased e.g lung disease or weight gain, also fatigue of muscle

Question 5

3 main causes of hypercapnia

Answer 5

• decreased respiratory drive from brainstem- how much output is there causing you to breathe e.g heroin, morphine
• Neuromuscular transmission - need this to be intact, could be interrupted at any part of tract e.g C3,4,5, nerves exiting , could be effecting neuromuscular transmission, or something wrong with muscle, muscle weakness/fatigue
• Load (work of resp muscles) - resp muscles need to do two types of work - resistive work and elastic work, amount of work may be increased e.g lung disease or weight gain, also fatigue of muscle (lung elastic load increases)

Question 6

Equation for A-a gradient

Answer 6

A-a gradient = 20- Pac0/0.8 - Pa02

Question 7

How can we measure diffusion of gas ?

also can use exercise test

Answer 7

use CO because this binds to haemoglobin straight away so then we can tests its diffusion capability - is diffusion not perfusion limited, soluble, binds Hb

-often poor diffison can be masked until you try exercising as oxygen requirements increase so CO increases and if diffusion is imparied will not beable to get enough oxygen across membrane - time for rbc to travel the same distance will increase, so if problem wont get as much perfusion (graph of alveolar p02 vs time in capillary)

Question 8

What does diffusion depend on?

3 reasons causing bad diffusion

Answer 8

• gas
• diffusion distance/thickness
• surface area
• haemoglobin
• capillary volume

-alveolar capillary block (increase fibrous tissue due to aspestos - thickened walls)
-loss of diffusing surface - emphysema
-Capillary volume / haemoglobin
pulmonary capillaries e.g if someone has pulmonary hypertension or embolism then will have abnormal diffusion thing, anaemia

Question 9

Chronic obstructive pulmonary disease
-what is it
-FVC FEV1
-

Answer 9

airway limitation that is not fully reversible. The airway limitation is usually both progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases

• Lower FVC and FEV1 - ratio is low
• get an inflammatory reaction to cigarette smoke and this causes damage to collagen and structure of lungs
• shortness of breath, cough, excess mucous production, reduced gas exchange

Question 10

V/Q mismatch

what happens when you hyperventilate

Answer 10

• can only ventilate the normal compartment
• co2 and o2 saturation curves have very different shapes - which means we reduce content of CO2 but dont increase o2 much
• when you hyperventilate, then you get a decrease in co2 but not o2
• maintain pH by metabolic compensation, but can get worse V/Q

Question 11

Worsening disease

-why is it bad to give oxygen ?

Answer 11

• unable to undertake compensatory hyperventilation
• increase paCO2 - ph is normalised by renal mechanisms
• dangers - high inspired o2, monitorign o2 saturatin
• bad to give o2 - because the only thing keeping ventilation going is the hypoxic drive due to low 02, so if this gets worse then will not get as much ventilation

Question 12

what is dead space, and what is a shunt?

Answer 12

• Dead space is when there is no perfusion so get very low V/Q
• when there is a trapped alveolr, then cannot get ventilation, and have a shunt

Question 13

How to test cause of V/Q mismatch vs a r-l shunt

Answer 13

if administer 100% oxygen and then measure pa02 would rise

• get not much improvement with a right to left shunt
• also would have normal lung function test
• widened A-a gradient

Question 14

Why can some people go red when they are hypoxaemic?

Answer 14

-due to having erythropoietin because they are trying to stimulate more red blood cells to be made so that there can be more oxygen carrying

Question 15

Advantages and disadvantages of FEV testing and peak expiatory flow

Answer 15

FEV
-reduced variability
-less effort dependent
-tight normal range - can distinguish between abnromal and normal easily
FEV1
-can classify between obstructive and restrictive lung disease

PEF - easy, cheap, effort dependent, high variability - not very good

Question 16

Exercise induced Asthma

• what is it
• how is it caused?
• how to measure this

Answer 16

• FEV1 gets worse on exercise
• drying of airways, and this can cause the activation of mast cells and active mediators- worse on exercise and winter
• airway hyper-responsiveness with bronchoactive mediators leading to the narrowing of airway smooth muscle and release of mucous.

Can measure this in the lab - fev1, also give narrowing agents e.g histamine - see response

wheeze - airway narrowing

Question 17

stridor

Answer 17

wheeze on inspiration

airway narrowing on inspiration is rare

Question 18

Obstructive

Answer 18

• problem with expiration
• increase residual volume
• increase functional residual capacity
• fev1 reduced (x2)
• fvc reduced (x1)
• FEV1/FVC - decreased
• TLC unchanged
• decrease flows at all lung volumes
• breaths at higher lung volumes to decrease resistive work of breathing by doing more elastic work of breathing
• for same change in pressure get a smaller change in volume
• tidal volume is at large lung volumes to reduce work of breathing

Question 19

Restrictive Lung disease

Answer 19

• fibrosis - stifness of lung so they are non-compliant
• reduced pulmonary complaince
• decrease TLC (x2)
• decreasse FVC (x2)
• decrease FEV1 (x1)
• normal or increased FEV/FVC
• increased flow at same lung volume due to more elastic recoil

Question 20

Aspestos -

fine late inspiratory crackles

Answer 20

causes increased in fibrosis material

• get the lower airways shut off, because cannot get enough pressure to open them
• however on late inspiration can generate enough pressure and then can get them snap open and thats the sound we hear

Question 21

Why shortness

of breath in restrictive lung disease

Answer 21

• due to increased work of breathing

- much lower lung compliance so harder to breath