5. CP Respiratory Cycle Flashcards
What is the normal intrapleural pressure?
-5 cm H2O
What is the average intrapleural pressure upon full, normal inspiration?
-8 cm H2O
What is the alveolar pressure during inspiration?
-1 cm H2O
How much does the volume of the lungs increase during a normal breath?
500ml (.5L)
When are the expiratory muscles used?
During forced expiration only! Gentle expiration is passive.
What is the alveolar pressure at mid expiration?
+1 cm H2O
How do we calculate minute ventilation?
Tidal volume x breaths per minute
How do we calculate minute alveolar ventilation?
(Tidal volume - dead space) x breaths per minute
How do we calculate transpulmonary pressure?
Alveolar pressure - intrapleural pressure
How does air enter the lungs (Boyle’s Law)?
pressure and volume are inversely proportional
V1P1=V2P2
when there is an increase in lung volume, the pressure decreases and air enters
when there is a decrease in lung volume, pressure increases and air exits
(the pressure of the air outside the lungs is higher than the pressure inside the lungs when the volume is increased, so O2 rushes into the lungs moving from a high to low gradient)
How do the inspiratory muscles contract to allow for inspiration?
the diaphragm and external intercostal muscles contract to increase thoracic volume
these muscles are not directly in contact with the lungs but allow the chest wall to expand despite the lungs wanting to collapse
this interplay allows for inspiration (along with pressure/volume relationship)
Describe intrapleural pressure
(Ppl)
less than atm. (neg) -5 cm H2O at rest
basically the intrathoracic pressure everywhere in the thorax except the blood vessels/lymph and airways
What happens to the intrapleural pressure during quiet inspiration?
volume increases so Ppl decreases to -8 cm H2O
What happens to alveolar pressure as thoracic cavity increases in volume during quiet inspiration?
alveolar pressure decreases from 0 cm H2O (at rest) to -1 cm H2O
this is because the volume in alveoli increases
this pressure gradient allows air to flow into the lungs
What is transpulmonary pressure?
It is the pressure of the Palv-Ppl
Palv-alveolar pressure
Ppl-intrapleural pressure
transpulmonary pressure is -5cm H2O at rest
What would happen if transpulmonary pressure was 0?
pretty sure no gas exchange or air flow would occur because 0 cm H20 is equivalent to atm. pressure.
?
Respiratory Cycle at Rest
Volume
Palv
Ppl
Air flow
Volume=0
Palv=0
Ppl=-5
AF=0L/s
Respiratory Cycle Mid-Inspiration
Volume
Palv
Ppl
Air flow
Volume=increasing (250)
Palv=decreasing (-1)
Ppl=decreasing (-5 to -8)
AF=air flowing into lungs (-1)
Respiratory Cycle-End Inspiration
Volume
Tidal Volume
Palv
Ppl
Air Flow
volume=reached peak
TV=500ml
Palv=returned to zero
Ppl=decreased to -8cm H2O
AF=ceased
Respiratory Cycle-Mid Expiration
Volume
Palv
Ppl
Air Flow
Volume=decreasing (250)
Palv=rises (+1)
Ppl=starts to rise (-8 to -5)
AF-exits (+1)
Respiratory cycle-End Expiration
Volume
Palv
Ppl
Air Flow
volume=returned to resting
Palv=decreases to zero
Ppl=returns to resting
AF=exited lungs
What is the change in transpulmonary pressure throughout the respiratory cycle?
rest
mid-insp.
end insp/start exhal.
mid-exhal.
rest 5cm
mid-insp.5.5cm
end-insp/start exhal. 8cm
mid-exhal. 7.5
What is minute volume and how is it calculated?
Minute Volume (Ve) is the volume of air inhaled every minute
TV=Vt (tidal volume)
Ve=Tv x Frequency
ex: 14 breaths per min x 500ml/breath=7000ml/min (normal)
What is anatomic dead space?
space in respiratory system other than alveoli
150lb person=150ml of Vds
What is physiologic dead space?
aka alveolar dead space
alveoli receive air but no blood
should be nearly 0 in healthy ppl
Is dead space a feature of inspiration or expiration?
inspiration
at end expiration, there is residual volume left over
at end inspiration, there is air filling conducting system, air in the lungs doing gas exchange and left over air from expiration
the air that is in the conducting system is the “dead space” because there is no gas exchange occuring
how is minute alveolar ventilation calculated?
alveolar volume is found by subtracting dead space volume from tidal volume
Valv=Vt-Vds
~350 (for 150lb person)
can find minute alveolar ventilation by taking V(dot)alv=Valc x frequency
Describe the pressure-volume curve of the normal lung and explain the inspiration piece
at the start of inspiration, the lung has lower volme and must work harder to get a little increase in volume. At this point, the lungs are harder to stretch (like a balloon animal type balloon)
once there is a little air in the lungs, a little pressure change will produce a large volume change (easier to stretch lungs, like a “started” balloon”)
as lungs expand toward TLC, it becomes difficult to stretch again. A small pressure change produces small change in volume.
Why does exhalation look different on the pressure-volume curve than inhalation?
due to surfactant reducing the surface tension moreso in the smallest alveoli than in the larger ones
This occurs according to LaPlace’s Law
contributes to hysteresis (difference between inspiration and expiration)
what is compliance?
How do you calculate it?
when is it highest?
how easy the lungs can stretch
higher compliance means easier to stretch (reduces workload)
C=change in V/change in P
highest during normal breathing range, normal TV
If compliance is too high or too low, what happens?
What is the opposite of complance?
the lung has to work harder
Elasticity (recoil/bounce back ability)
What is the compliance and workload of a newborn’s lungs?
compliance is low/lung volume is low
effort is high
How does fibrosis effect compliance?
lowers compliance such that more change in pressure is required for change in volume
same applies for obesity
requires shallower volume and more frequent breaths
How does age effect compliance?
increases with age as elasticity decreases with age due to loss of elastin and increased collagen
How does compliance change with Emphysema?
increases compliances as it destroys alveolar septal tissue that normally opposes lung expansion
How do the lungs and chest wall work against each normally and in a PTX?
lungs have a lot of elastic fibers so they want to shrink (minimal volume)
rib cage has joints/cartilages that want to allow it to expand
in the intact system, the elastic recoil of the lungs and chest wall counter each other at Functional Residual Capacity
In a PTX, they both get what they want (lung collapses, chest wall expands)
Normally, the elastic in the lungs would make them collapse. What helps them to stay structurally intact?
shared walls of alveoli and airways prevents collapse as recoild opposes each other
losing some of the walls will alter or lose forces that would normally counter collapse
when alveoli walls are destroyed (smoking, age) the remaining alveoli can collapse during expiration
When is the work of breathing increased?
as airway resistance increases, it takes a greater pressure change to generate flow into the lungs
therefore, it takes more pressure to generate a change in volume
there will be increased work with increased tidal volume
Draw and memorize resp cycle graphs
and pressure volume curve
What are general age related changes in lung capacity?
What are general obesity related changes in lung capacity
no change in TLC
INcrease in FRC and RV
decrease in FRC with minmal change between seated and supine
What changes do you see in a non-obese person with seated and supine measurements of lung capacity?
decrease in IRV and TLC (?)
decrease in Vt
decrease in ERV
no change in RV
(FRC is lower in obese indiv.)
