resp

Question 1

define hypoxia

Answer 1

failure to adequately oxygenate arterial blood

Question 2

define hypercapnic

Answer 2

failure to prevent CO2 retention

Question 3

causes of hypoxaemia

Answer 3

• reduced inspired oxygen
• hypoventilation
• V/Q mismatch
• R-L shunt
• diffusion

Question 4

causes of hypercapnia

Answer 4

• caused by alveolar ventilation (also V/Q mismatch)
• PaCO2 inversely proportional to alveolar ventilation
• Ve = Va - Vd

respiratory drive
neuromuscular transmission
load

Question 5

factors influencing alveolar ventilation and how it causes hypercapnia

Answer 5

• respiratory drive (e.g. depression by drugs)
• neuromuscular competence (e.g. muscular dystrophy, myasthenia gravis, spinal cord injury)
• load (gives resistive & elastic work) e.g. obesity, kyphosis-scoliosis

Question 6

describe COPD

Answer 6

• airflow limitation (not fully reversible)
• progressive limitation, association w/ abnormal inflammation response to noxious particles/gases
• often due to cigarettes

Question 7

features of COPD

Answer 7

• chronic mucus hyper-secretion
• emphysema
• small airway inflammation

Question 8

what is gas exchanged influenced by

Answer 8

• diffusion
• V/Q mismatch
• R-L shunt

Question 9

describe V/Q mismatch

Answer 9

is a RATIO between ventilation and perfusion

Question 10

what is another name given to an area that is ventilated but not perfused

Answer 10

dead space

V/Q = 1

Question 11

shunt

Answer 11

whens theres an anatomical abnormality, blood doesn’t come anywhere near the alveolus

= (venous admixture)

Question 12

in the early stages of COPD why are patients hypoxemic but normocapnic

Answer 12

COPD patients have decreased airways, therefore have a V/Q mismatch (shunt). As a result of the mixed venous blood from shunt, theres decreased O2 and increased CO2 levels. Hypercapnia is the major central drive causing hyperventilation. This brings CO2 levels to normal however decreases oxygen levels.

Question 13

effects of worsening COPD and the dangers

Answer 13

overtime they’re unable to undertake compensatory hyperventilation. As a result, theres increased PaCO2 (pH is normalised by renal and other mechanism)

dangers
- high inspired O2 (chemoreceptors in the brain turn off their response to O2 - drive then depends on hypoxemia)
- monitoring O2 saturations only
therefore if you remove that hypoxic drive for ventilation you stop them breathing all together

Question 14

describe R-L shunt

Answer 14

• venous blood being mixed with arterial blood
• distinguish from V/Q mismatch by administration of 100% O2
• in the heart
• reduced PaO2 in the arteries

Question 15

what does diffusion depend on

Answer 15

• gas
• diffusion distance/thickness
• surface area
• (Hb)
• capillary volume

Question 16

what are causes of abnormal diffusion and what are some examples of pathologies

Answer 16

alveolar-capillary block
- diffuse lung disease

loss of diffusing surface
- emphysema

capillary volume / Hb

• pulmonary hypertension
• anaemia

Question 17

what initially happens to FEV1 during exercise and why

Answer 17

• initially increases as exercising produces catecholamines and reduce vagal tone. Causing dilation of airways (parasympathetic supply)
• increases lung function

Question 18

how do you calculate alveoli pressure

Answer 18

it is the sum of intrapleural pressure and elastic recoil pressure

Palv = Pel + Pip

Question 19

wheeze in asthma

Answer 19

wheeze on expiration

airway narrowing by bronchospasm gives ↑ velocity & ↓P (Bernoulli’s principle) - contributing to dynamic compression → wheeze

Question 20

explain how exercised induced asthma lowers FEV1

Answer 20

• exercise causes drying of airways, this increases the tonicity of fluid lining the airways. Mast cells then degranulate and release broncho-active mediators. Causing airway constriction which lowers FEV1