Block B Flashcards
(13 cards)
Surfactant
Decreases surface tension
- Secretes same amount, regardless of size of alveoli
- Reduces surface tension more in smaller alveoli
Pneumothorax
- Intro of air into pleural cavity
- Pleural pressure increases, becomes equal to Pb
- > alveoli dont expand
- > lung recoil is unopposed
- > lung collapses
PAO2
21%(760-47)= 150mmHg
Aircraft pressure
- Pressurised cabin at 2400m (.: ~564mmHg)
Factors effecting airway resistance
- SM constriction
- SNS: causes bronchioles to dilate (Beta1) -> decreased resistance -> increases flow (also inhibits ACh)
- PSNS: vagus release of ACh -> M3 -> bronchoconstriction -> decreased air flow
- Inflam mediators: e.g. histamine - brochoconstriction -> decreased air flow
Physiological Symptoms During Flying
- Popping and cracking in the ears and nose, due to air expanding in the nasal cavities and ear canals
- Air trapped in GI - feel tight/full -> restrict diaphragm movement in pregnant and obese -> breathing difficulties
- Resp rate increase -> some may experience alkalosis
- Dehydration
- Decreased PaO2 -> reduced cognition, vision, sensation
- Increased HR
- Difficulty sleeping with elevated SNS drive
Compensating for Low O2
Increased Resp rate
BUT there are additional consequences:
- Blows of CO2
-> decreased plasma acidity -> increased pH -> alkalosis
-> Decreased HCO3 -> reduces ability to buffer acid
-> Neg impact during activity -> pH fluctuates dramatically
- Also, if PAO2 is low this predisposes one to a greater degree of anaerobic metabolism and generation of fixed acids
-> causes fluid loss
-> is energy expensive
Central chemoreceptors
- Detect changes in pH
- OVLT triggers vasopressin release -> reneal conservation of water (AQ docking DCT)
- > triggers thirst (but delayed)
- > nausea is also a potent stimulator of vasopressin
Peripheral chemoreceptors
- Detect pH and O22 - hence primary driver of longer term physiological adaption
Renal
Excretion of HCO3 in an effort to normalise pH
- JGA/macula densa detects the flow and sodium and chloride if high -> ATP and adenosine release to constrict afferent arterioles and reduce GFR
- Mesangial cells contract in response to SNS and decrease
Baroreceptors
- Sense low BP due to fluid loss -> activates SNS to increase HR and change in peropheral perfusion
Physical SIgns in Resp to Altitude
- I Resp rate and HR
- D urine vol
- I thirst
- Signs of dehydration
- D appetite
- Cognitive decline
O2 Saturation at High Altitude
- Even if O2 stat of Hb is reduced by 25%, the additional RBCs compensate with additional O2 carrying capacity -> overall the quantity of O22 delivery can be equivalent
