LO - Respiratory Flashcards
What are the forces that keep the lung inflated?
- Negative Intra-pleural pressure
- A slight suction is maintained between the lung pleura and thoracic cavity pleura by the negative pressure gradient. Collapsed lungs are usually brought about by the neutralisation of this pressure. - Surfactant
- Secreted by Type II alveolar epithelial cells. Reduces surface tension of fluid layer coating the alveoli, prevents alveolar collapse.
Composition of Air and Pressures at sea level and 5km altitude
Nitrogen: 78.62%
Oxygen: 20.84%
CO2: 0.04%
H2O: 0.5%
At Sea Level: 760mmHg
At 5km Altitude: 407mmHg
Principle underlying the movement of Air
Gases move from areas of high pressure to areas of low pressure, down their pressure gradient
Inspiration Sequence
- Inspiratory Muscles Contract (Diaphragm moves down toward pelvic floor, external intercostal muscles contract bringing the ribcage up and outward)
- Thoracic cavity volume increases
- Lungs are stretched outward.
- Intra-pulmonary volume increases, Intra-pulmonary pressure decreases to 759mmHg / -1mmHg below atm.
- Air moves in down its pressure gradient until equalisation with atmospheric pressure.
Muscles in Expiration
Quiet Breathing: passive relaxation of inspiratory muscles
Forced breathing: as above, but also contraction of abdominal and internal intercostal muscles
Expiration Sequence:
- Inspiratory muscles relax
- Thoracic cavity volume decreases
- Elastic lungs recoil passively, intra-pulmonary volume decreases
- Intra-pulmonary pressure increases
- Air moves out down its pressure gradient until equalisation with atmospheric pressure
What determines partial pressure of molecules in fluids such as blood?
- Concentration and solubility
- The more soluble a molecule is, the more of that molecule which can dissolve without a significant change in partial pressure.
HENRY’S LAW:
partial pressure = [conc. of diss. gas / solubility coefficient]
Solubility coefficients: Oxygen CO2 CO Nitrogen Helium
Oxygen: 0.024 - weak solubility CO2: 0.57 - strong solubility CO - 0.018 nitrogen - 0.012 Helium - 0.08
How does altitude affect O2 delivery?
- Once you ascend higher than 2000m you alter O2 delivery, because increased altitude means decreased atmospheric pressure, which means decrease PO2.
0-2000m: Decreased PO2 does not significantly affect % saturation of O2.
Over 2000m it does.
2000m: PO2 - 75 - 90%
4000m: PO2 - 60 - 85%
8488m: PO2 - 28 - 45%
Effects of altitude on respiration
0-2500m: decreased PO2, gradual hypoxia, including mild hypocapnia (low blood PCO2), but little effect on respiration because urge to reduce from hypocapnia counteracts urge to increase from PO2.
2500-4500m: decreased PO2, increasing hypoxia, overrides hypocapnia, increased rate/depth of breathing, dysponea (difficult/laboured breathing)
4500-6100m: Increased ventilation becomes less effective at compensating for loss of O2 saturation, profound hypoxia
> 6100m: loss of consciousnous
Types of Mountain Sickness
Acute mountain sickness (AMS)
High Altitude Pulmonary Oedema (HAPE)
Acute Mountain Sickness:
Hypoxia related problems >3500m
Increased ventilation causes hypocapnia, with ensuing alkalosis (high pH because loss of CO2 means loss of H+ ions), including cerebral vasoconstriction.
Symptoms: fatigue, headaches, nausea, vomiting, poor mentation, dizziness, difficulty sleeping
HAPE
Hypoxia related problems experienced at >5000m
Decreased PO2 in the alveoli causes vasoconstriction and increased permeability. This causes increased PULMONARY VASCULAR RESISTANCE - pressure inside the vessels.
Outcome: blood is pushed into the alveoli from the capillaries (OEDEMA)
Symptoms: dry cough followed by frothy blood-stained sputum, breathlessness, dysponea, extreme fatigue
