Respiratory cycle and mechanics

Question 1

what is the Pressure volume relationship in the lung

Answer 1

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

Question 2

What are the events of Inspiration

Answer 2

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

Question 3

what is the Intrapleural pressure

Answer 3

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

Question 4

what are the units of pressures in the respiratory physilology

Answer 4

pressure measured in cm H20

and the atmospheric pressure is normalized to 0 cmH20 (normally 760)

Question 5

what is the pressure of the intrapleural at rest and during inspiration

Answer 5

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

Question 6

what happens if the transpulmonary pressure is zero and what is it normally at rest

Answer 6

the lungs will deflate

can be caused by pneumothorax

Ptp = PALV - Ppl

Ptp = 5 cm at rest

Question 7

Respiratory cycle, Volume, PA, Ppl, and air flow at stage: rest

Answer 7

Volume = 0L

PA = 0cm H20

Ppl = -5cm H20

Air flow = 0 L/s

Question 8

Respiratory cycle, Volume, PA, Ppl, and air flow at stage: Mid inspiration

Answer 8

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)

Question 9

Respiratory cycle, Volume, PA, Ppl, and air flow at stage: End of inspiration

Answer 9

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

Question 10

Respiratory cycle, Volume, PA, Ppl, and air flow at stage: mid expiration

Answer 10

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

Question 11

Respiratory cycle, Volume, PA, Ppl, and air flow at stage: end of expiration

Answer 11

Volume has returned to resting (O)

PA = decreases to zero

Ppl = returns to resting -5

Air has exited the lungs = no air flow

Question 12

how does the transpulmonary pressure act throughout the respiratory cycle

Answer 12

Ptp: rest = +5
mid inspiration = 5.5
End of inspiration = 8
Mid expiration = 7.5
rest = 5

Question 13

What is Minute Ventilation

Answer 13

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

Question 14

What are the three types of dead space

Answer 14

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

Question 15

what is the equation for the physiological dead space

Answer 15

Vt x (PaCO2 - PeCO2)/ PaCO2 = Physiological dead space

Question 16

what is the significance of the Dead space at the end of the expiration

Answer 16

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

Question 17

Minute Alveolar Ventilation

Answer 17

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

Question 18

how is the Volume/ pressure relationship during inspiration

Answer 18

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

Question 19

how is the Volume/ pressure relationship during expiration

Answer 19

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

Question 20

what makes the pressure and volume relationships different between the inhalation and exhalation

Answer 20

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

Question 21

where is compliance highest and lowest in the pressure volume relationships for inspiration

Answer 21

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

Question 22

how is compliance and elascity related

Answer 22

inverse of each other

e = p/v

c = v/p

if something has a high compliance it has a low elascity

Question 23

what is the compliance for a baby right at birth

Answer 23

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

Question 24

How does Fibrosis change the compliance of the lung

Answer 24

LOwers compliance, more change in pressure required to change volume

• also occurs in obesity
• usually breath at shallower volume and more frequently

Question 25

How does age affect the compliance of the lung

Answer 25

compliance increases with age as elasticity decreases with age due to the loss of elastin and increased collagen

Question 26

how does emphysema affect the compliance of the lung

Answer 26

increases compliance as it destroys alveolar septal tissue that normally opposes lung expansion

however more dead space

Question 27

how does the chest and lung normally want to be in a relaxation pressure volume curve

Answer 27

lung wants to be collapsed therefore no volume

chest at zero pressure wants to be fully expanded

Question 28

what is the significance of the point the chest wall + lungs curve crossing the y axis of a relaxation pressure volume curve

Answer 28

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)

Question 29

what happens to the lungs and chest if the pneumothorax happens

Answer 29

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

Question 30

what is the equation for the airway resistance

Answer 30

R = 8nl/r^4

changing of the radius affects the resistance of the vessel

Question 31

what is interdependance, and significance of losing it

Answer 31

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

Question 32

what happens to breathing as airway resistance increases

Answer 32

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)

Question 33

what are the two forces that breathing overcomes

Answer 33

Elastic force which represents the elastic recoil of the lungs

resistive force: which represents the work done to overcome resistance to airflow