Mechanisms of Breathing

Question 1

Pressure air moves

Answer 1

From high pressure to low pressure
The bigger the difference, the faster gazes travel
F(low) = diff pressure / R(esistance)

Question 2

P_ATM

Answer 2

Atmospheric pressure : pressure outside body
760 mmHg
reference point for pressure difference

Question 3

P_Pul

Answer 3

Intrapulmonary pressure : pressure in the lungs -> alveoli
At rest/ end of exhale: 760 mmHg = 0 mmHg(diff)
Changes with lung volume, difference can be pos and neg

Question 4

P_IP

Answer 4

Intrapleural pressure: pressure in pleural cavity
At rest: 756 mmHg = -4mmHg(diff)
Always negative difference

Question 5

Why P_IP smaller pressure ?

Answer 5

Lung elasticity : when expand it pulls back
Surface tension : visceral and parietal pleura pull together (more space between thorax and lungs)
Chest elasticity : when expand it pulls back
Gravity : pressure lower near apex

Question 6

Transpulmonary pressure

Answer 6

Difference intrapulmonary and intrapleural pressure
P_Pul - P_IP = 4mmHg Intrapulmonary pressure higher than intraplural : always positive
Positive pressure means it can inflate !

Question 7

Transthoracic pressure

Answer 7

Difference intrapleural and atmospheric
P_IP - P_ATM = -4mmHg Intrapleural pressure smaller than atmospheric : always negative
Negative means can deflate !

Question 8

Boyle’s law

Answer 8

P1V1=P2V2

Thus if volume goes up, pressure goes down

Question 9

Inspiration general

Answer 9

Diaphragm lowers, rib cage expand & goes up -> intrapulmonary volume goes up -> intrapulmonary pressure goes down : 759 mmHg = -1 mmHg(diff)
Pressure lungs lower than atmospheric -> air enters lung

Question 10

Expiration general

Answer 10

Diaphragm goes up, rib cage constrict & goes down
intrapulmonary volume goes down -> intrapulmonary pressure goes up : 761 mmHg = 1 mmHg(diff)
Pressure lungs higher than atmospheric -> air leave lung

Question 11

mmHg

Answer 11

millimeter of mercury

-> pressure

Question 12

Elasticity

Answer 12

When stretched wants to pull back : recoil
Lungs and thorax have elasticity when they expand -> opposing forces
Creates more volume between thorax & lungs & vacuum from opposing forces

Question 13

Lymphatic vessels pleura

Answer 13

Prevent excess pleural fluid
Drain plural fluid
if too much fluid -> push lungs -> volume goes down

Question 14

Quiet inspiration specific

Answer 14

signal PRG -> DRG -> spine (c1,c2,c3) -> phrenic nerve -> diaphragm goes down
signal PRG -> DRG -> spine (T1-T11)-> intercostal nerve -> external intercostal muscle pull thoracic cage outward and sternum push thoracic forward
=> parietal volume increase -> P_IP goes down : -6mmHg -> lung volume increase -> P_pul goes down : -1 mmHg -> transpulmonary increase = 5 mmHg and transthoracic decrease = -6mmHg
P_pul negative -> O2 goes in lung until 0mmHg difference (pressure gradience)

Question 15

Forced inspiration

Answer 15

accessory muscle also activate
Thoracic cavity volume increase -> pressure decrease
volume increase more than in quiet inspirate thus the pressure decrease more as well
eg: P_IP = - 7mmHg and P_Pul=-2mmg

Question 16

Quiet expiration

Answer 16

no muscles involved
Passive: recoil from elasticity of diaphragm and thorax
Diaphragm goes back up and thoracic cage goes back inward -> thoracic volume decrease -> pressure increase : P_pul =1mmH
E(lasticity) = diff pressure / diff volume

Question 17

Pleural fluid

Answer 17

comes from capillaries in parietal/visceral pleural, interstitial space in lung (space between alveoli and capillaries), parietoneal cavity (potential space between parietal and visceral peritoneum : parietal surround abdominal wall and visceral surround internal organs) with holes in diaphragm

Question 18

Lung collapse

Answer 18

Limited air exchange : O2 goes down and CO2 up

Question 19

Pneumothorax

Answer 19

Air in pleural space : seal visceral and parietal punctured (no vacuum from opposing force) -> lung pulled in -> collapse
types: Spontaneous, traumatic and tension
Spontaneous: alveoli leaks, bullae (air pocket) on lung surface -> break -> hole in visceral pleural -> air in pleural space. Primary if no prior condition (eg: holding breath too long so too much pressure) Secondary if prior condition
Traumatic : puncture from an external object
Tension: air can enter but not leave, the puncture act as a one way valve -> air builds up and push trachea and crompress heart -> CO(cardiac output) decrease
Symptoms: shortness of breath and chest pain
Signs : auscultation reduced breath sounds, percussion hyperresonant
treatment : small heal itself. Big need drainage : between ribs to pleural cavity

Question 20

X-RAY

Answer 20

Lung : mostly black

Pleural space: completly black

Question 21

bronchial breathing sound

Answer 21

Bronchial sounds are high pitched & usually heard over the trachea. Timing includes an inspiratory phase that is less than the expiratory phase. If bronchial sounds are heard in the actual lung fields, this may indicate consolidation

Question 22

Compliance

Answer 22

extent to which lungs expand to each unit increasse in transpulmonary pressure.

Diagram: lung volume changes to pleural pressure: changes to transpulmonary pressure. Determined by elastic forces of lungs(elastin and collagen contracted when deflated). Elastic forces of surface tension from alveoli walls. Expiration and inspiration have different curves. the volume of the lung is higher during expiration than during inspiration. Thus, lung compliance is higher during expiration than during inspiration. If filled with fluid, no surface tension, slope increase and expiration/inspiration are closer together.

Question 23

Surface Tension

Answer 23

water forms surface with air
water strong attraction one another -> water surface contract
surfactant: surface active agent -> reduce surface tension. Secreted by alveolar epithelial cells (pneumocytes type 2). Hydrophilic and hydrophobic part.
Surface tension -> diameter decrease -> pressure up

Question 24

Law of Laplace

Answer 24

Tension within walls filled to a pressure depends on the thickness of the walls
P=2TensionThickness/Radius