Respiratory cycle and mechanics Flashcards
what is Boyle’s law?
P1V1=P2V2
pressure of gas is inversely proportional to its volume
what happens when there is an increase in lung volume?
pressure decreases- air enters
what happens when there is an decrease in lung volume?
pressure increases- air exits
what happens when inspiratory muscles (external intercostal muscles) contract?
it increases thoracic volume
causes an interplay between the chest wall wanting to expand and the lungs wanting to collapse
is intrapleural pressure (PPL) more or less than atmospheric pressure?
less (negative)
*think of it like intrathoracic pressure
what is the PPL at rest?
during inspiration?
- 5 cm H20
- 8 cm H20 (decreases)… lungs expand (increase volume) as thorax does because of coupling
what is alveolar pressure at rest?
what is PA at mid- inspiration? what does this cause?
0 cm H20 (equal to PB)
-1 cm H20 (decreases as alveolar size increases)
causes air to enter lungs
what is transpulmonary pressure?
pressure between alveoli and pleura (PTP=Palv-PPL)
5 cm H20 at rest
at end inspiration, what is the volume in the lungs?
peak volume in lungs– 0.5 liters (500 mL)
at end inspiration, what is happening to alveolar pressure?
returns to 0 cm h20
at end inspiration, what is happening to the PPL?
at its lowest: -8 cm H20
at end inspiration, what is happening to air flow?
stops
(at 0 L/sec)
what is happening during mid-expiration for volume?
decreasing
what is happening during mid-expiration for PAlv?
increasing (peaks at 1 cm H20)
due to recoil of alveoli
what is happening during mid-expiration for PPL?
increasing
what is happening during mid-expiration for air flow?
exiting lungs (at about 1 L/sec)
what is happening at end expiration for volume?
return to rest
what is happening at end expiration for Palv?
decreases to 0
what is happening at end expiration for PPL?
returns to rest
what is happening at end expiration for air flow?
has exited the lungs
at rest, what is the volume in the lungs?
0 L
at rest, what is air flow in lungs?
0 L/sec
during mid-inspiration, what is happening to volume?
increasing
during mid-inspiration, what is happening to Palv?
decreasing (hits about -1 cm H20)
during mid-inspiration, what is happening to PPL?
decreasing
during mid-inspiration, what is happening to air flow?
entering lungs
what is PTP at rest?
+5 cm H20
what is PTP at mid-inspiration?
+5.5 cm H20
what is PTP at end-inspiration/start of expiration?
+8 cm H20
what is PTP at mid-expiration?
+7.5 cm H20
what is tidal volume?
air inhaled and exhaled in single breath
what is minute ventilation? what is the equation? what is the normal value?
volume of air inhaled every minute
VE=VT*frequency
7 L/min (for 14 breaths per min)
what is dead space? what are the two types?
regions of lungs that recieve air but no blood so no gas exchange
- anatomic dead space- space in respiratory system other than alveoli
- physiological- alveoli (should be zero!!)
what air is left in lungs at end-expiration?
alveolar air from previous breath
what air is in lungs at end-inspiration?
- alveolar air from previous breath (bottom)
- inspired air that does gas exchange (350 mL)
- inspired air that fills conducting pathways (anatomic dead space)
** 2 and 3 make up tidal volume
how do we calculate minute alveolar ventilation?
Valv= VT- VDS(dead space)
Vdot alv= Valv * f
when the lungs have low volume, is it hard or easy to get more volume into them?
hard- small increase in volume because it’s harder to stretch them
is it easy or hard to add more volume to lungs during quiet breathing?
easy- it becomes easier to stretch the lungs and they will have a big increase in volume
is it easy or hard to add more volume to lungs at high lung volume (total lung capacity)?
hard- they become difficult to stretch again and experience small increase in volume
in a controlled system, the lungs inflate and deflate the same way. why is it not like this in real life?
- surfactant- reduces tension in smallest alveoli more than larger alveoli
- LaPlace’s law- contributes to hysteresis (difference between inspiration and expiration)
what is compliance in the lungs? (fml it’s back)
how easy it is to stretch the lungs (change in volume/ change in pressure)…. reduces work lungs have to do
when is lung compliance highest?
during normal breathing/ normal VT
when is lung compliance low?
when there is either too little or too much pressure around the lungs (at either extreme of the graph)… lungs have to work harder
how is compliance different than elasticity?
elasticity is actually how easy it is to recoil, while compliance is how easy it is to stretch
when baby is born and before its first breath, what is the volume, compliance, effort?
volume= very low
compliance= low
effort= high
in fibrosis and obesity, what are the changes of volume, compliance, effort?
volume= lower (because they take shallower breaths)… pressure must increase
compliance= lower
in aging, what are the changes in volume, compliance, effort?
volume= ?
compliance= increases (elasticity decreases because of loss of elastin and collagen)
in emphysema, what are the changes in volume, compliance, effort?
volume= increase?
compliance= increases (destroys alveolar septal tissue that normally opposes lung expansion)
when lung is at relaxation, what is its volume?
volume= low (at residual volume)
** lungs want to shrink to an even smaller volume than this and is known as minimal volume (below residual volume) because lungs have a lot of elastic fibers
when chest wall is relaxed, how does its pressure compare to the lungs? its volume?
** I think this concept is using chest wall synynomly with intrapleaural pressre
lower than lung
volume= high volume (because of joint arrangement)
** PPL wants to have as much volume as possible which is why lungs want to collapse and chest wall expand
when are the recoil of the lungs and chest wall balanced with each other?
functional residual capacity (FRC)–> amount of air that remains in lungs following normal expiration (ERV+RV)
*kinda like lungs are at rest
in other words, where they exactly counter each other
what happens to the pressure-volume curve in a pneumothorax?
shifts to the left
lungs collapse, chest maximally expands
they both get what they want!
what is the equation for airway resistance?
R= 8hL/r4
h= viscosity
L=length
what is interdependence?
how does it influence airway resistance?
what happens if we lose it (thru smoking, aging, etc)?
structural stability of small airways and alveoli depends on their connectivity
the elastic recoil in one alveolus is countered by the recoil in an adjacent alveolus
if we lose these shared walls then the alveoli will collapse during expiration
when airway resistance increases, what compensation must take place?
increase pressure to change volume of air in lungs (allow air flow into lungs)
what 2 forces does breathing overcome?
- 0AECD0- elastic forces
- ABCEA- resistive forces
does increase VT increase or decrease work?
increase
