ventilation and perfusion relationship Flashcards
(10 cards)
Gas exchange occurs in the — between — air and the — of the — For effective gas exchange to occur, alveoli must be — and —-.
Ventilation (V) refers to the flow of – into and out of the — , while perfusion (Q) refers to the flow of — to —
lungs
alveolar air
blood
pulmonary capilaries
ventilated and perfused
air
alveoli
blood
alveolar capillaries
Alveolo-capillary membrane (Blood-air barrier):
—- of gaseous exchange in the lungs
Applied aspects:
Failure of the barrier: Pulmonary — due to blast injury, swimming-induced pulmonary —, and gas — or — in the lung during depressurization (which can occur during — from underwater diving or loss of — from a pressurized vehicle, habitat or pressure suit)
Rupture of the barrier: Arterial gas — and — .
functional unit
barotrauma
oedema
entrapment or retention
ascent
pressure
embolism
hemptypoysis
Diffusing capacity is the — of a gas to diffuse as a result of a given —
Diffusing capacity = Net — of — / —
Factors affecting diffusing capacity include:
1- Factors which influencegas properties
The — of the gas
— of the molecules
The — of the medium
2- Factors which influence the gas exchange
- —
- — (with increasing age, total available surface area decreases, irrespective of the other factors)
Body — : height influences the size of the lungs
—- volume
—, — space and – inequality—
3-Factors which influence the membrane characteristics
- —-
Interstitial — disease, eg. —
4- Factors which influence uptake by erythrocytes
The affinity of — for oxygen
— concentration
— (insofar as it affects capillary transit time)
propensity
pressure gradient
net rate of gas transfer / partial pressure gradient
density
size
tempretute
age
body size
lung volume
shunt , dead space , q/v
pulmonary oedema
lung as pulmonary fibrosis
haemoglobin
haemoglobin
cardiac output
pulmonary ventilation:
moving in and out of — in a given unit of time during — It is also called — or —-
Pulmonary ventilation is a — process, by which – air enters the – and an — volume of air leaves the lungs.
pulmonary ventilation = —-
respiratory tract
quiet breathing
minute ventilation or respiratory minute volume (RMV).
cyclic
fresh air
lungs
equal volume
tidal volume x respiratory rate
= 500 ml x 12/min = 6,000 ml/min
Alveolar ventilation is the amount of air — for — every minute.
Alveolar ventilation is different from pulmonary ventilation. In pulmonary ventilation, — of air moves in and out of respiratory tract every minute. But the whole volume of air is not — for exchange of
gases.
Volume of air subjected for exchange of gases is the — ventilation. Air trapped in the respiratory passage ( — ) does not take part in gaseous exchange.
-Normal value of alveolar ventilation is — mL (— L)/ minute.
It is calculated by the formula: —
utilised
gaseous exchange
6 L
utilised
alveolar
dead space
4,200 ( 4.2 L )
( tidal volume - dead space ) x respiratory rate = 500-150 x 12/min
factors affecting ventilation:
Gravity:
Plural pressure is lower at the — than at the — .
This further influence the — and — of the alveoli.
Compliance is more at the — than at –
Hence, Ventilation is more at — than at –
Asthma vs Emphysema ?
concept of partial pressure:
- the standard barometric pressure Pb is — which is at sea level so to determine the partial pressure:
pn2 nitrogen = 79.04% x 760
p02 oxygen = 20% x 760
( c02 has the lowest )
- partial pressure from atmosphere to capillaries;
partial pressure of gas - Fgas x atm pressure
For Oxygen
In inspired air PI O2= FO2 X 760mmHg
In trachea PHT O2= FO2 X (760-PH2O) humidified
In Alveoli PA O2= PiO2 – (PACO2/R) alveolar air
- partial pressure changes in –
apex ( -7 , more inspiratory air)
base (-2)
volume and compliance
base
apex
base
apex
760 mmhg
blood
pulmonary perfusion:
Pulmonary circulation is – , influenced greatly by —
PVR is – times – than that of in systemic circulation because of highly — vessels
Alveolar capillary bed accounts for — of total PVRpu
During inhalation:
Inflated alveoli — the PVR in alveolar capillaries
Meantime due to radial traction and elastic recoiling, PVR — in Extra alveolar capillaries distends
During exhalation
Alveolar PVR — ..
Extra alveolar PVR — due to higher pleural pressure
- distribution of pulmonary blood flow:
P alv : Pulmonary alveolar pressure
P A: Pulmonary Arterial pressure
P V: Pulmonary Venous pressure
pulsatile
pulmoanry vasular resistance PVR
10
less
distensible
40%
increases
decreases
decreases
increases
VENTILATION-PERFUSION RATIO (V/Q ratio):
DEFINITION
Ventilationperfusion ratio is the ratio of —- and the amount of — that — the —.
It is expressed as VA/Q. VA is — and Q is the – flow ( — ).
- alveolar ventilation = 4,200 ml/min
- pulmonary blood flow = 5,000
- v/q ratio = 4,200 / 5,00 = 0.84 ( normal value)
alveolar ventilation
blood
perfuses
alveoli
alveolar ventilation
blood ( perfusion)
1- significance of v/q ratio :
Ventilation-perfusion ratio signifies the —
It is affected if there is any change in — or in —
Ventilation without perfusion = —
Perfusion without ventilation = —
2- alveolar-artel P02 ( AaDO2) :
In Normal healthy individual, partial O2 pressure in alveolus (PAO2) is slightly — than partial O2 pressure in arteries (PaO2) .
PAO2> PaO2
The difference between PAO2 and PaO2 is called as —
Why? Because of —
example of anatomical shunt is — to – shunt which breathing is — oxygen less effective
example of physiological shunt —
gaseous exchange
alveolar ventilation or blood flow
dead space
shunt
greater
Alveolar-arterial P02 gradient.
anatomical shunt
right to left
100%
Atelectasis
wasted air and wasted blood:
Ventilation perfusion ratio is not perfect because of existence of two factors on either side of alveolar membrane.
These factors are:
1. Physiological dead space, which includes —
2. Physiological shunt, which includes —
important info:
Hypoxic Pulmonary Vasoconstriction (HPV) is a unique physiological response where small pulmonary arteries constrict in the presence of low alveolar oxygen levels (low
PAO2P AO2). This mechanism helps match ventilation to perfusion (V/Q matching) by redirecting blood flow away from poorly ventilated (hypoxic) alveoli to better-ventilated regions of the lung
wasted air
wasted blood
