CVR Mid-Topic Review Flashcards
What is decompression illness?
Diver descends Increase in ambient pressure Increase in lung pressure Increase in PO2 and PN2 And so increased O2 and N2 dissolved into the blood and delivered to the tissues
Why does additional gas dissolve into blood during dive?
What is Henry’s law?
Due to Henry’s Law
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is Boyle’s Law?
The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system
i.e. as volume decreases, pressure increases
What are the consequences of too much oxygen?
Oxygen toxicity = presents as seizures due to increased production of oxygen species that affects neurons - leads to misfiring of the neurons = seizures
How can oxygen toxicity be resolved?
Decreasing ambient pressure = seizure resolved as the oxygen will be metabolised, no long term damage
How can oxygen toxicity be prevented?
60m = 1.6 atm pressure of O2 = leads to O2 toxicity
To go deeper, tank must have a much lower conc of oxygen
Replace most of the N and O with He (inert and small) in tanks to decrease O2 conc and pressure in the tank
What are the consequences of too much nitrogen?
Nitrogen narcosis
Drowsiness and confusion
What is ascending too quickly dangerous?
Rapid decompression - doesn’t allow for N to dissolve out of the tissues into the blood
Nitrogen bubbles can form in the tissues, joints, nerves, blood (as it doesn’t allow enough time for the nitrogen to dissolve in the blood) - leads to joint pain, neurological symptoms and embolisms get trapped in the pulmonary circulation
Large nitrogen gas bubbles may cause pulmonary embolism
Ascending slowly decreases the ambient pressure slowly, so N2 can be steadily cleared
What are the functions of the pulmonary circulation?
Gas exchange
Metabolism of vasoactive substances
Autonomic regulation of blood flow
Local oxygen storage
Filtration of the blood
How does the pulmonary circulation system filter the blood?
Why is it important?
Venous thromboses, ruptured fatty plaques, air bubbles etc. can get caught in the blood, usually on the venous side, and the pulmonary circulation filters these out before the blood enters the systemic arteries
Generally, a small embolus can be eliminated in the pulmonary microcirculation, but a large embolus often gets trapped in the pulmonary microcirculation causing an obstruction to local perfusion
Embolus VS emboli?
Embolus = a ‘mass’ within the circulation capable of causing an obstruction
Embolism = an ‘event’ characterised by obstruction of a major artery
How may air bubbles travel from the venous circulation to the systemic arterial circulation (bypassing the pulmonary circulation)?
Patent foramen ovale(PFO) = foramen ovale that fails to close at birth = leaves a partially open hole between the left and right side of the heart
Most common congenital heart syndrome - hole in the septum between the 2 atria
Found in 25% of general population
What are the features of AS’s and VSDs?
Atrial septal defect
Atrial septal defect
VSD’s are more common
Risk of them is that the hole can lead to a left to right shunt
Blood gets pushed round the pulmonary circulation again
Puts excess pressure on the pulmonary system
Might experience hypertrophy
How do congenital heart defects, such as ASDs (atrial septal defect) and VSDs (ventricular septal defect) present?
How can they be diagnosed?
Babies with this present with breathlessness, fatigue, non-feeding behaviour, doesn’t put on weight
Diagnosed with echocardiogram - look for the hole and directional flow of blood
What differentiates an ASD to a PFO?
ASD = larger
ASDs more commonly present as a right left shunt
