Respiratory cycle and mechanics Flashcards
what is the Pressure volume relationship in the lung
pressure of gas is inversely proportional to its volume (Boyle’s law)
P1xV1 = P2xV2
since the atmosphere Pressure does not change Patm = 760mmHg
the increase in lung volume during inhalation will decrease the alveolar pressure
decrease in lung volume during expiration the pressure in the alveolar increases
What are the events of Inspiration
Contraction of the inspriatory muscles will increase the thoracic volume and even though the lungs and muscles or the ribs are not connected the surfactant of the pleura help generate the negative pressure to open the lungs due to the expansion of the chest
what is the Intrapleural pressure
Ppl
Pip
it is between the visceral and parietal pleura where there is a fluid
less than the atmospheric pressure (negative)
it is the pressure everywhere in the thorax except the lumens of the blood vessels, lymphatics, or airways
what are the units of pressures in the respiratory physilology
pressure measured in cm H20
and the atmospheric pressure is normalized to 0 cmH20 (normally 760)
what is the pressure of the intrapleural at rest and during inspiration
Ppl at rest is -5 cm H20
during inspiration volume will increase so Ppl will decrease to near -8 cm H20
this is due to the coupling of the lungs and the chest wall
what happens if the transpulmonary pressure is zero and what is it normally at rest
the lungs will deflate
can be caused by pneumothorax
Ptp = PALV - Ppl
Ptp = 5 cm at rest
Respiratory cycle, Volume, PA, Ppl, and air flow at stage: rest
Volume = 0L
PA = 0cm H20
Ppl = -5cm H20
Air flow = 0 L/s
Respiratory cycle, Volume, PA, Ppl, and air flow at stage: Mid inspiration
Volume is increasing = 250mL
PA = is decreasing -1 cm H20
Ppl = is decreasing half way between -5 and -8
Air flow is flowing into the lungs (negative 1)
Respiratory cycle, Volume, PA, Ppl, and air flow at stage: End of inspiration
Volume has reached peak increase = Vidal volume Vt = 500mL
PA = has returned to zero
Ppl = has decreased to - 8 cm H20
Air flow has ceased
Respiratory cycle, Volume, PA, Ppl, and air flow at stage: mid expiration
Volume is decreasing = 250mL
PA = rises to drive out air 1 cm H20
PpL = begins to rise from -8 cm H20
Air exits lung, positive air flow
Respiratory cycle, Volume, PA, Ppl, and air flow at stage: end of expiration
Volume has returned to resting (O)
PA = decreases to zero
Ppl = returns to resting -5
Air has exited the lungs = no air flow
how does the transpulmonary pressure act throughout the respiratory cycle
Ptp: rest = +5 mid inspiration = 5.5 End of inspiration = 8 Mid expiration = 7.5 rest = 5
What is Minute Ventilation
Minute ventilation: Ve is the volume of air inhaled every minute
Ve = Vt x frequency
tidal volume times the respirations a minute
14 breaths a min x 500ml/breath = 7 L/min
What are the three types of dead space
Regions in the lung that recieve air but not blood = no gas exchange
Anatomic dead space: space in respiratory system other than alveoli
-150 lb person = 50 mL of Vds
Physiological dead space: air that functionally doesnt participate in gas exchange (not all air is expired)
Alveolar dead space: alveoli that recieve air but not blood
-healthy people this is nearly zero
what is the equation for the physiological dead space
Vt x (PaCO2 - PeCO2)/ PaCO2 = Physiological dead space
what is the significance of the Dead space at the end of the expiration
not all air leaves the conducting airways, this air is not as oxygen rich as new air coming in, therefore lots of air not getting out after each expiration can lead to dilution of the new inspired air
Minute Alveolar Ventilation
calculated by subtracting dead space volume from tidal volume
Valv = Vt - Vds 350ml = 500ml - 150ml (body weight)
then take alveolar ventilation x the frequency
V(dot)alv = Valv x F
how is the Volume/ pressure relationship during inspiration
at the beginning a low slope, much harder to overcome pressure to fill lung
at middle higher slope, easier to increase volume with little pressure changes (Tidal volume)
at end the slope is low, have to increase lots of pressure to increase volume
how is the Volume/ pressure relationship during expiration
deflate much different than they inflate, the expiration graph starts with a small slope and then the slope gets greater and greater the more the volume drops
what makes the pressure and volume relationships different between the inhalation and exhalation
surfactant causes the hysteresis (difference between the inspiration and expiration)
the surfactant reduces tension in smallest alveoli more than larger alveoli
-LaPlace’s Law
without this it would take much more work to inflate and deflate the lungs
where is compliance highest and lowest in the pressure volume relationships for inspiration
lowest at the beginning and end
it is the highest compliance (easiest to stretch) in the middle of the graph, this is where our tidle volume takes place
c = change in V/change in V
how is compliance and elascity related
inverse of each other
e = p/v
c = v/p
if something has a high compliance it has a low elascity
what is the compliance for a baby right at birth
very low because the baby is trying to inflate its lungs for the first time and since their is no volume in the lung the baby has to work harder to overcome the pressure
How does Fibrosis change the compliance of the lung
LOwers compliance, more change in pressure required to change volume
- also occurs in obesity
- usually breath at shallower volume and more frequently
How does age affect the compliance of the lung
compliance increases with age as elasticity decreases with age due to the loss of elastin and increased collagen
how does emphysema affect the compliance of the lung
increases compliance as it destroys alveolar septal tissue that normally opposes lung expansion
however more dead space
how does the chest and lung normally want to be in a relaxation pressure volume curve
lung wants to be collapsed therefore no volume
chest at zero pressure wants to be fully expanded
what is the significance of the point the chest wall + lungs curve crossing the y axis of a relaxation pressure volume curve
the elastic recoil of lungs and that of the chest wall exactly balance each other out (0 pressure) this point is the FRC (functional residual capacity)
what happens to the lungs and chest if the pneumothorax happens
lung will collapse and chest will expand maximally
this is because the lungs have lots of elastic fibers and want to get smaller
rib cage wants to get larger due to the joint arrangement in the body
what is the equation for the airway resistance
R = 8nl/r^4
changing of the radius affects the resistance of the vessel
what is interdependance, and significance of losing it
The elastic recoil of the lung wouuld normally create collapse of the small airways and alveoli
but the shared walls of the alveolar and airways prevent collapse as recoil opposes each other
therefore, losing some of the walls will alter or lose forces that normally would counter collapse
some ways of losing this is smoking or other pulmonary diseases
what happens to breathing as airway resistance increases
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 (decrease in compliance)
what are the two forces that breathing overcomes
Elastic force which represents the elastic recoil of the lungs
resistive force: which represents the work done to overcome resistance to airflow
