Lecture 4: Respiratory Cycle

Question 1

Is inspiration passive or voluntary?

Answer 1

Voluntary

Question 2

Is expiration passive or voluntary?

Answer 2

Passive

Question 3

What are the muscles of inspiration?

Answer 3

1. Diaphragm
2. External intercostal muscles

Question 4

Diaphragm and inspiration

Answer 4

The diaphragm is innervated by the phrenic nerve and moves moves down to increase the volume of the thorax

Question 5

External intercostal muscles and inspiration

Answer 5

The external intercostal muscles are located in between the ribs. When contracting, the raise the ribs by increasing the anteriorposterior diameter of the thorax (bucket handle motion). This increases the area, allowing us to breathe in.

Question 6

What are the other muscles for inspiration?

Answer 6

1. Scalene muscle- raises the 1st and 2nd rib
2. Sternomastoid muscle- raises the sternum
3. Muscles in the head and neck

Question 7

What kind of muscle are the respiratory muscles?

Answer 7

Skeletal muscle

Question 8

What are the 2 pros of respiratory muscles being skeletal muscle?

Answer 8

1. Activation is uniform and rapid.
2. Can respond rapidly to changes in conditions

Question 9

What are the 2 cons of respiratory muscles being skeletal muscle?

Answer 9

1. Damage to the brain and spinal cord can stop breathing.
2. If the lungs get too big, it can stretch the muscle (length-tension curve)

Question 10

What are the events during inspiration?

Answer 10

1. Inspiratory muscles contract, increasing the thoracic volume.
2. Intrapleural pressure decreases from -5cm H₂0 –> -8cm H₂0. Pressure stays -8cm until the end of inspiration.
3. As the lungs increase, the alveolar pressure decreases from [0cm H₂0 –> -1cm H₂0] due to an increase in alveolar size. At the end of inspiration, alveolar pressure will go back to [0cm H₂0].

Question 11

Pressure changes during 1 inspiration

Answer 11

Intrapleural pressure: -5cm H20 –> -8cm H20

Alveolar pressure: 0 –> -1 (at mid breath) –> 0

Question 12

Are the lungs and mucles/ribs physically connected to one another?

Answer 12

No. The viseral pleura and parietal pleura, plus the fluid in between, adhered the lungs with the ribs and muscles.

Question 13

Intrapleural pressure at rest

Answer 13

-5cm H20

This means that the pressure is 5cm lof H20 less than the outside.

Question 14

Alveolar pressure at rest

Answer 14

Same as atmospheric because there is no air movement: 0cm H20

Question 15

Air flows into the lungs when alveolar pressure _____ atmospheric pressure

Answer 15

**P_alv

atm**

_{When alveolar pressure drops below atmospheric pressure.}

Question 16

Intrapleural pressure reaches its lowest point when?

Answer 16

At the end of inspiration (-8cm H20)

Question 17

Airflow into the lungs will decrease as …

Answer 17

alveolar pressure returns back to 0cm H20

Question 18

What is tidal volume (V_T)?

Answer 18

Tidal volume (V_T​)

The amount of air inhaled in a given breath.

Typically, it is about 500 mL.

Question 19

Expiratory Muscles

Answer 19

1. Abdominal muscles- push into the abdomen to move the diaphragm up
2. Internal intercostal muscles- decrease the AP diameter of the thorax
3. Accessory muscles

Expiration is passive because the lungs WANT to be smaller.. Thus, in a normal breath we do not use these muscles.

Question 20

What are the events during expiration?

Answer 20

1. Inspiratory muscles relax, allowing the volume of the thorax decreases and the diaphragm and rib cage go back starting position.
2. Decrease in volume causes the intrapleural pressure to go back to normal (-5cm H20).
3. Alveolar pressure will increase to +1cm H20 at midbreath due to the action of the rib cage.
4. A pressure gradient is created that produces airflow OUT of the lungs—
5. As expiration proceeds and the volume of air in the lungs decrease, the alveolar pressure will go back to 0.
6. Eventually, all of the air that entered during inspiration is exhaled.

Question 21

What is the intrapleural pressure and alveolar pressue at rest?

Answer 21

Intrapleural pressure: -5cm H20

Alveolar pressure: 0cm H20

Question 22

Intrapleural pressure becomes more ____ with inspiration

Answer 22

Negative

Question 23

When does the peak negative value of the intrapleural pressure occur?

Answer 23

At the end of inspiration

Question 24

In normal expiration, the intrapleural pressure remains _____

Answer 24

Negative

Question 25

Alveolar pressure becomes ______ with inspiration

Answer 25

negative

Question 26

Peak negative alveolar pressure occurs when?

Answer 26

Mid-inspiration

Question 27

In any expiration, the alveolar pressure becomes ______

Answer 27

Postive.

Question 28

Peak positive value of alveolar pressure occurs when?

Answer 28

Mid-expiration

Question 29

Why does the intrapleural pressure not return to resting value until the end of the respiratory cycle?

Why did the alveolar pressure return to 0 at the end of each phase?

Answer 29

Because air enters the alveoli (more molecules takes up the added space), but nothing should enter the intrapleural space.

Thus, the intrapleural space has the same number of molecules spread out over a bigger volume.

Question 30

What is minute ventilation?

Answer 30

Minute ventilation–> how much air is inhaled every minute

V(dot)= V_t (tidal volume) * frequency

Question 31

What are anatomic deadspaces?

Answer 31

The first 16 generations of the airway do not have alveoli, thus, they are called anatomic dead spaces because they do not particpate in gas exhange.

To figure out ones anatomic deadspace, take their weight in lbs and change it to mL.

150 lbs–> 150 mL of dead space

Question 32

What is alveolar ventilation?

Answer 32

How much of every breath gets into the alveoli

V_T-V_DS

_{Tidal volume minus the volume of the anatomic dead space}

Question 33

Alveolar ventilation.

150lb person who breathes 500 Lm with each breath

Answer 33

500- 150= 350 mL of every breath gets into the alveoli

Question 34

Minute alveolar ventiliation

Answer 34

How much of every breath gets into the alveoli/minute

V_alv*frequency

Question 35

What is the minute alveolar ventilation?

Same 150lb patient is breathing 12 breaths/minute.

Answer 35

350 * 12= 4,200 mL/minute

Question 36

Transpulmonary pressure

Answer 36

P_alv-P_IP