L15 Flashcards
Lung compliance is increased in emphysema
BECAUSE
chronic emphysema increases airway resistance.
Both statements are true but are not causally related
what does Spirometry measure
Lung volumes – How much?
Air flow rates – How fast?
what do you use to mesure lung function
Pulmonary Function tests, Lung Function tests
define tidal volume (VT or TV)
Volume of air moved in and out during normal quiet
breath
what is the approx value of tidal volume
~ 500 ml
define Inspiratory reserve volume (IRV)
Extra volume that can
be inspired with
maximal inhalation - external intercostal
muscles.
define Expiratory reserve
volume
Extra volume that can
be exhaled with
maximal effort - internal intercostal and
abdominal muscles.
define residual volume (RV).
Volume remaining
in lungs after maximal
exhalation.
when exercising what lung volumes will increase
When you are exercising you need to breath in more O2 (inspiratory reserve) and breathe out CO2 (expiratory reserve)
define Inspiratory capacity
maximal breath in
Vt + IRV
define Vital capacity
Maximal breath into out
Volume of air can shift
in/out of lungs (IC +ERV)
define functional residual capacity
• Lung volume at the end of a normal
expiration when there is no inspiratory
or expiratory muscle contractions (ERV +RV)
define total lung capacity
Total volume in lungs
when maximally full =
(VC + RV)
which of the lung capacities is not clinically relevant
inspiratory capacity
which of the lung capacities is the most clinically relevant
vital capacity
because it is vital
what is the “resting equilibrium” position for the lungs + thorax (in “elastic” combination)
functional residual capacity
what are the normal values for functional residual capacity
Normal large FRC ~2.4 L (~40% of TLC),
“Topped up” each breath by the smaller
resting Vt ~500 ml (only ~20% top up!)
what is the importance of large FRC
At all times during the breath cycle O2 and CO2 exchange can occur between alveolar gas and the pulmonary capillaries.
Prevents large fluctuations in the composition of alveolar gas
eg you don’t want to go from 0% O2 - 100% O2 or from 0% CO2 to 100% CO2
when you have a restrictive lung disease what does that do to your breathing
breathe more shallowly and rapidly
what happens in terms of lung volumes in restrictive lung disease
decrease in compliance means that you need to do a lot of work to get air in
Therefore people with this breath more shallow
The whole spirometry trace has gone down
This is because the lung is not expanding
VC ↓ IRV ↓ ERV ↓ RV↓ FRC ↓ TLC↓
what happens to the way someone breathes in OBstructive lung disease
Increased work due to increased airway resistance,“narrow pipes”, breathe more slowly and deeply
what happens to the spirometry trace in obstructive lung disease
why
Bronchi constricted, air
obstructed in alveoli, more air remaining in the lung therefore the trace gets shifted up
VC IRV ERV RV ↑ FRC ↑ TLC ↑
Forced measurements give info about what
air flow rates
Air flow rates – how fast?
what is Forced Vital Capacity FVC
– maximum breath into maximum breath out
(VC) - forced out as hard as possible
Variant of vital capacities (VC) are useful for what
useful diagnostic tool for the diagnosis of
lung diseases – indicator of airway resistance
in healthy lungs what % of your total forced expiratory volume is breathed out in 1 sec
80%
in obstructive lung disease FEV1 & FVC decrease. what effect would this have on the ratio of volume expired in 1 second
what does that mean
Ratio of less than 70%, indicative of increased airway resistance.
Restrictive lung disease: FEV1/FVC ratio doesn’t change (or increased) what does this mean for airway resistance
no change in airway resistance
why is there no change in airway resistance/FEV1 for restrictive lung disease
Fibrotic lungs are quite stiff therefore it is hard to get air in but they are going to recoil very quickly
FEV1/FVC ratio does not decrease below 70% in restrictive lung disease
BECAUSE
restrictive lung disease does not affect the airway resistance
both are true and causal
define Ventilation
process by which air moves in and out of the lungs
It is ONE process of respiration
however Ventilation ≠ Respiration. processes are interdependent
Ventilation determines Respiration and vice versa
what is the symbol for volume and time venterlation
a V with a dot on top
a dot over anything means per minute
what is Dalton’s law of partial pressures
In a gas mixture (air), each gas exerts its own individual pressure, called a partial pressure (P), in direct proportion to its fractional concentration in the mixture.
what is the equation for PP
Partial Pressure = fraction of individual gas x total gas pressure
Pgas= Fgas x Ptotal
Need to know the % concentration of each gas and the atmospheric
pressure
O2 =20.93 % FIO2= 0.2093
CO2 =0.03 % FICO2 = 0.0003
N2 =79.04 % FIN2 = 0.7904
• Barometric pressure PB at sea level ~ 760mmHg.
• The partial pressures are calculated as:
PO2 = 159 mmHg at sea level
PCO2 = 0.23 mmHg at sea level
PN2 = 601 mmHg at sea level
what is Water vapour pressure at body temperature
– 47mmHg
Air gets warmed
as it moves down the respiratory tract, therefore how would you calculate PP at the trachea
(Barometric pressure PB at sea level ~ 760 mmHg.)
(Water vapour pressure at body temperature =-47mmHg)
• The partial pressures at trachea are calculated as:
Pgas= Fgas x (Ptotal - 47)
what is the respiratory quotient (RQ)
- The amount of CO2 produced in relation to the amount of O2 consumed by metabolism and is dependent on caloric intake.
- Considered as a measure of cell metabolism
how do you calculate respiratory quotient (RQ)
𝑅Q =𝑉𝐶O2/𝑉𝑂2
V̇CO2 = amount of CO2 excreted/produced
V̇O2 = amount of O2 taken up
what are the RQ values for exclusive FA metabolism, exclusive carbohydrate metabolism and normal conditions
RQFA= 0.7
RQC = 1
QRN = 0.8
what is total mouth venterlation = to
Total (mouth) ventilation (V̇
E ) = frequency (f) x tidal volume (VT)
VT= 500mL
frequency of breaths per minute = 10-12
therefore at rest approx 5L/min
when would VE ( total mouth ventilation) change
To match metabolic demands (involuntarily, e.g exercise)
Voluntarily (changing breathing behavior) eg when you hold your breath
what is dead space
• Some of the inhaled air never gets to the alveoli
so cannot gas exchange – known as dead space
ventilation ( VD )
• There are two types of dead spaces contributing to VD. what are they
- Anatomical dead space
- Physiological dead space (also known as functional dead space)
VD = anatomical dead space + functional dead space
what is anatomical dead space
- Conducting airways
(including mouth, trachea)
Ventilated but no respiration (no gas exchange)
what is functional/physiological dead space
- respiratory area (gas exchange) could exchange gases but not happening
unused respiratory area (some alveoli that are not used all the time)
Knowing the dead space allows to determine alveolar ventilation (VA)
AV = ventilation - VD
what happens to the dead space in Pulmonary Fibrosis
increases dead space by transforming
respiratory tissue in fibrotic tissue (e.g. cystic fibrosis)
what happens to VD in Pulmonary Hypertension
increased dead space by impairing pulmonary
perfusion (pulmonary arteries not functioning properly)
what is Pulmonary Hypertension and fibrosis’s effect on respiration and ventilation
In both cases respiration is impaired and this also
affects the ventilation
what is the effect of Fast Shallow Breathing
↓ alveolar ventilation
– causing hypoxia (↓PAO2), hypercapnia (↑PACO2) and acidity
• From a gas exchange point of view, wastes ventilation in the
dead space
• Is energetically costly for the respiratory muscles
• No gas exchange (when the tidal volume (VT) is low)
what is the effect of Slow Deep Breathing
• alveolar ventilation
– causing hyperoxia (↑PAO2), hypocapnia (↓PACO2) and
alkalinity
• ↑ Gas exchange
• Is energetically costly for the respiratory muscles
The respiratory quotient (RQ) is:
A. V̇O𝟐/V̇CO2
B. a measure of cell
metabolism.
C. V̇CO𝟐/V̇O2
D. A and B are both correct.
E. B and C are both correct.
E
Lung disease -> ventilation impaired
• Atelectasis (fibrosis)
• Emphysema
• Pulmonary oedema (fluid)
Vascular disease -> perfusion impaired
• Pulmonary hypertension
• Heart failure
• COPD
various reasons same consequences
