Mechanisms of Breathing Flashcards
Pressure air moves
From high pressure to low pressure
The bigger the difference, the faster gazes travel
F(low) = diff pressure / R(esistance)
P_ATM
Atmospheric pressure : pressure outside body
760 mmHg
reference point for pressure difference
P_Pul
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
P_IP
Intrapleural pressure: pressure in pleural cavity
At rest: 756 mmHg = -4mmHg(diff)
Always negative difference
Why P_IP smaller pressure ?
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
Transpulmonary pressure
Difference intrapulmonary and intrapleural pressure
P_Pul - P_IP = 4mmHg Intrapulmonary pressure higher than intraplural : always positive
Positive pressure means it can inflate !
Transthoracic pressure
Difference intrapleural and atmospheric
P_IP - P_ATM = -4mmHg Intrapleural pressure smaller than atmospheric : always negative
Negative means can deflate !
Boyle’s law
P1V1=P2V2
Thus if volume goes up, pressure goes down
Inspiration general
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
Expiration general
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
mmHg
millimeter of mercury
-> pressure
Elasticity
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
Lymphatic vessels pleura
Prevent excess pleural fluid
Drain plural fluid
if too much fluid -> push lungs -> volume goes down
Quiet inspiration specific
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)
Forced inspiration
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
Quiet expiration
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
Pleural fluid
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
Lung collapse
Limited air exchange : O2 goes down and CO2 up
Pneumothorax
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
X-RAY
Lung : mostly black
Pleural space: completly black
bronchial breathing sound
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
Compliance
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.
Surface Tension
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
Law of Laplace
Tension within walls filled to a pressure depends on the thickness of the walls
P=2TensionThickness/Radius
