Unit 5 - Breathing PART D-F

Question 1

Pulmonary Ventilation

Answer 1

Exchange of gasses between the atmosphere and the lungs

Question 2

Pulmonary Ventilation

pressures involved:

Answer 2

1. Atmospheric pressure (Patm)
2. Intra-alveolar pressure (Palv)
3. Intrapleural Pressure (Pip)
4. Transpulmonary (transmural) pressure (Tp= Palv – Pip)

Question 3

Atmospheric pressure (Patm) =

Answer 3

pressure of the air outside the body (~760 mmHg at sea level). All other pressures are calculated relative to Patm.

Question 4

Intra-alveolar pressure (Palv) =

Answer 4

pressure within the alveoli (-1 to +1 mmHg) (between breaths it is equal to Patm)

Question 5

Intrapleural Pressure (Pip) =

Answer 5

fluid pressure in the pleural cavity (756 mmHg to 753 mmHg, a decrease of -4 to -7mmHg compared to Patm).

Question 6

Intrapleural Pressure (Pip)

Lungs and chest wall are…

Answer 6

both elastic. The thoracic wall recoils outward (like a compressed elastic band) but the lungs recoil inward on themselves (like a stretched elastic band). The cohesive force of the fluid in the pleural cavity holds the lung and the wall together, but the opposing forces create a negative pressure space and so Pip slightly decreases.

Question 7

Intrapleural Pressure (Pip)

ALWAYS ____ during normal breathing and ALWAYS ___ than Palv

Answer 7

NEGATIVE

LESS

Question 8

Intrapleural Pressure (Pip)

ALWAYS negative during normal breathing and ALWAYS less than Palv

Answer 8

if Pip becomes greater than Palv, lungs collapse = pneumothorax. For example stab wounds to the chest that puncture the thoracic wall and enter intrapleural space, would cause Pip = Patm).

Question 9

For air to move into the alveoli, pressure inside the lungs must become…

Answer 9

LOWER than ATMOSPHERIC PRESSURE

Question 10

Intrapleural Pressure (Pip)

According to Boyle’s Law,…

Answer 10

any increase or decrease in pleural cavity volume will respectively cause a corresponding decrease or increase in Pip

Question 11

Transpulmonary (transmural) pressure (Tp= Palv – Pip) =

Answer 11

pressure gradient between the alveoli and the intrapleural sac/cavity. Recoil pressure of lungs.

Question 12

The difference between Palv and Patm…

Answer 12

drives ventilation as air moves down pressure gradients from high to low pressure.

Question 13

F = DP/R.

Where

Answer 13

F = volume of inspiration/expiration,
DP = Patm – Palv, and R = resistance of the airway. The greater the difference between Palv and Patm, the more air will flow.

Question 14

F = DP/R.

Resistance is determined by…

Answer 14

diameter of the bronchi/bronchioles.

Question 15

Resistance is determined by diameter of the bronchi/bronchioles.

For example:

Answer 15

For example: asthma, bronchitis, emphysema all increase airway resistance (and make it more difficult to expire than to inspire, since Inspiratory mechanics open airways whereas expiratory mechanics close/compress the airway)

Question 16

Sympathetic stimulation of bronchiolar smooth muscle causes…

Answer 16

bronchodilation

Question 17

Parasympathetic causes…

Answer 17

bronchoconstriction.

Question 18

Changes to Palv are made by…

Answer 18

contraction and relaxation of the respiratory muscles.

Question 19

Pulmonary Ventilation - Inspiration

Steps for quiet breathing (tidal breathing):

Answer 19

1. Start: Palv = Patm (in between breaths)
2. Diaphragm and external intercostal muscles contract, expanding the thoracic cavity.
3. Pip decreases (flattening diaphragm and lifting thoracic wall away from lungs increases volume of intrapleural cavity, which decreases pressure within the cavity).
4. Tp increases (Tp= Palv – Pip), pushing the lung outward and causing the lungs to expand, which increases lung volume).
5. Increased lung volume causes Palv to decrease below Patm (Boyle’s Law), creating a pressure gradient between the lungs and the atmosphere. Air flows from the area of high pressure in the atmosphere to the area of low pressure in the alveoli.
6. Airflow continues until Palv = Patm.

Question 20

Pulmonary Ventilation - Inspiration

When taking a deep breath in (forced inspiration), the steps are the same, however…

Answer 20

additional muscles are recruited to further increase the expansion of the thoracic cavity (these include the sternocleidomastoid and the scalenes which act to pull the ribcage superiorly)

Question 21

Inspiration

Answer 21

1. contraction of diaphragm and external intercostals
2. chest wall expands
3. ↓ Pip
4. ↑ Tp
5. ↑ lung volum
6. ↓ Palv
7. ↑ Patm - Palv
8. air flows into alveoli until Palv = Patm

Question 22

Pulmonary Ventilation - Expiration

Answer 22

During quiet breathing (tidal breathing), expiration is a passive process (i.e. there is NO contraction of muscles, just relaxation of muscles).

Question 23

Pulmonary Ventilation - Expiration

Steps:

Answer 23

1. Start: Palv = Patm (in between breaths)
2. Diaphragm and external intercostal muscles relax, compressing the thoracic cavity.
3. Elasticity of chest wall causes compression of intrapleural sac/cavity and Pip increases.
4. Tp decreases (Tp= Palv – Pip) causing the lungs (alveoli) to recoil.
5. Recoil causes Palv to increase above Patm, creating a pressure gradient between the lungs and the atmosphere. Air flows from the area of high pressure in the alveoli/lungs to the area of low pressure in the atmosphere.
6. Airflow continues until Palv = Patm.

Question 24

Heavy/Deep expiration (e.g. exercise) is…

Answer 24

an active process that involves contraction of the abdominal muscles and internal intercostal muscles.