Patho lower (Big ass deck) Flashcards
What happens with altitude?
- With altitude, barometric pressure decreases
- sea lelve 760mmhg
- denver 633mmHg - 83% of sea level
- pikes peak 457 - 60% of sea level
- mt everest 253 - 33% of sea level.
- The percent of oxygen in the air is still 20% but the partial pressure of O2 is lower, thus decreasign the O2 partial pressure in the lungs and the blood.
Partial pressure of oxygen, alveolar-arterial gradient
- Normal A-a gradient is about 5-20mmHg
- Hypoxemia is a decrease in the PaO2
- Hypoxemia secondary to a pulmonary cause will increase the A-a gradient by 30 or more mmHg
- Hypoxemia secondary to extrapulmonary casue will have a normal A-a gradient.
Hypoexemia a-a gradient based on a pulmonary/cardiac problem.
- Hypoxemia secondary to a pulmonary or cardia cause will increase the a-a gradient by 30mmHg.
- entitites which will block gas exchange or shunt deoxygenated blood from the systemic venous to arterial side.
- causes
- ventilatin defect: alvoli perfused, but o2 not delivered to alveoli - atelectasis
- perfusion defect: alveoli ventilated but no perfusion of the alveoil - pulmonary embolism
- diffusion defect: o2 cannot diffuse thorugh alveolar capillary interface- interstitial fibrosis, pulmonary edema, pneumonia
- right to left cardiac shunts - tetraology of fallot, transposition of the great vessels, truncus arteriosus
Why does partial pressure of oxygen change comparing the atmoshperic to alveolar air.
Because of the partial pressure of water vapor and Co2 goes to 47 and 40 compared to 0 in the atmospheric air.
Compare diffusion of Co2 o2 and CO
carbon dioxide diffuses 20x faster than oxygen, and carbon monoxide diffuses 200x faster than oxygen
What is normally the limiting factor of oxygen diffusion in capillaries
- normal conditions
- oxygen diffusion from the alveolar air to the pulmonary capillary blood is perfusion limited, the ability of gas tto fidufse depends on the amount of blood flow through the capillary adjacent to the alveolus
- Under abnormal conditions
- oxygen diffusion becomes diffusion limited.
- Diffusion capacity decreases in
- conditions that increase the alveolar capillary membrane thickness
- pulmonary fibrosis, pulmonary edema
- conditions that decrease the effective area for diffusion
- atelectasis, emphysema, ARDS, pulmonary embolus
- conditions that increase the alveolar capillary membrane thickness
What is normal A-a gradient? What is hypoxemia? Pulmonary hypoxemia a-a vs nonpulmonary hypoxemia a-a
Normal A-a gradient is 5-20
- hypoxemia is a decrease in the PaO2
- hypoxemia secondary to a pulmonary cause will increase the a-a gradient by 30 or more mmHg
- nonpulmonary a-a stays the same.
What does the oxygen-hemoglobin dissociation curve show.
- at low oxygen concentrations, Pv02 (tissues and venous blood) there is uncombined hemoglobin in the blood and low oxyhemoglobin
- at high oxygen concentrations, Pa02 (lungs and arterial blood), there is Hemoglobin saturated with O2, oxyhemoglobin.
- Also shows that in the plateau part that o2 will load onto hemoglobin molecule even if the PO2 falls slightly
- it also means that with increasing levels of Po2 there will not be significant increase in the Hb saturation.
What does the Bohr effect describe
At lower pH tissues, o2 is released from the hemoglobin, facilitating the uptake of O2 in tissues
at lower co2 and h+ concentrations like the lung, there is an increased affinity for hemoglobin for o2 and o2 goes into hemoglobin
What is the haldane effect?
the haldane effect: facilitates the release of Co2 from the rbcs in the lungs. when hemoglobin takes up oxygen, H+ is released and drives the bicarbonate reaction to release Co2 which is then expired.
At low concentrations of o2, the loading of co2 onto hemoglobin is enhanced.
What might cherry red skin imply?
Hemoglobin saturated with CO, aka carbon monoxide poisoning
What are the two important values to know in the alveolar gas equation?
The atmospheric pressure at altitude and the partial pressure of arterial Co2 (PaCo2)
What can acclimitization add in terms of PaO2?
10-13mmHg more Pao2 partial pressure of alveolar air.
What is the color of cyanosis dependent on?
- blue color secondary to low oxygen saturaiton, usually less than 85 to 75%
- the color is dependent on an absolute quantity of deoxyhemoglobin. Seen more easliy in patients with high hemoglobin count than in anemic pts.
what are the three automatic (involuntary) brainstem centers for respiration?
- Medullary respiratory center
- has two components. A rhythm generator
- inspiratory center
- expiratory center
- has two components. A rhythm generator
- apneustic center
- stimulates the medullary inspiratory center and the depth of inspiration
- pneumotaxic center
- turns off inspiration
What does the medullary inspiratory center do?
- its the rhythm generator for breathing getting senosry input from cn 9 and 10, chemoreceptors and pulmonary mechanoreceptors via the vagus nerve. Motor output is via the phrenic n.
- expiratory center is not active in normal breathing, but is in active expiration
- central medullary chemoreceptors are most important determinants for normal breathing and respond to changes in pH or the CSF
- if Co2 increases, there is an increase in CSF Pco2. a decrease in CSF pH and increased ventilation. Hypercapnia leads to hyperventilatoin. The goal is to keep the arterial pH within the normal range
- decreased pao2 stimualtes the peripheral carotid and aortic chemoreceptors to increase ventilation. This is the most sensitive peripheral mechanism for breathing.
- the pons regulates the medulla: apneustic center stimultates prolonged inspiration, the penumnotaxic center turns off inspiratoin.
co2 and cerebral blood flow
with every mmHg decrease in Paco2 there is a 3-4% decrease in cerebral blood flow secondary to vasoconstriction.
What does pulmonary surfactant do?
- surface tension is the tendency for liquid surfaces to shrink to the minimum surface area
- thus alveoli, lined with liquid surface tend to collapse, preventing gas exchange
- Surfactants reduce surface tesnsion and thus preven thte alveoli from collapsing
- Surfactant is a lipoprotein made by type ii cells that reduces surface tensin within alveoli
- This increases pulmonary compliance
- loss of surfactant will make lungs stiffer, decreased compliance
- prevents atelectasis
- re-expands collapsed airways.
When does production of surfactant begin in utero?
28 weeks. NRDS - no surfactant
Elasticity and compliance, when does compliance decrease?
- elasticity is the recoil property of the lungs and chest wall. this is inversely related to compliance
- compliance is a measure of the ability of the lungs and chest wall to expand/distend, this is the change in volume for a given change in pressure
- compliance will decrease in restrictive pulmonary conditions (lungs become stiffer)
- any condition that results in the reduction in the ability of the lung or chest wall to inflate, ie ARDS, restrictive lung dz, diffuse fibrosis or infiltrates.
- diffusion of oxygen across the alveoli in to the blood is decreased if
- the surface area of the lungs is decreased (emphysema),
- the interface is thickened as in fibrosis,
- or there is a decreased partial pressure gradient between the alveoli and the pulmonary capillaries
Elasticity of lungs is related how to compliance?
elasiticity is the ability of the lungs to recoil theri resting volume after stretching force is released
inversely related to compliance
in emphysema, the lung compliance may be increased, patients have no problem inflating lungs but have extreme difficulty exhaling because of narrowing of the bronchi from increased intrathoracic pressure.
What is compliance? how is it related to elasticity?
Compliance is defined as the change in volume for any given applied pressure. Volume chagne per unit pressure change
this ia measure of distensibility (stretchability) and stiffness of the lung
clinically it inlcudes both the lunga nd chest wall in combination
low compliance, stiff lungs, as seen in restrictive disease, more effort is requierd to inflate alveoli
in a stiffer lung, more pressure is needed than normal to breath in a given volume of air and inflate alveoli.
surfactant in the lung will increase pulmonary compliance.
What happens in obstructive lung disease, asthma and COPD
increased inspiratory effort to overcome airway resistance to a degree and move air into the alveoli
However, during expiration, intrathoracic pressures will act to compres airways proximal to the alveoli leading to further obstruction, decreased expiratory flow and distal air trapping.
What happens in increases in intrathroacic pressure?
This will decrease the diamter of the airways and result in increased expiratory resistance
Compression of airways secondary to expiratory effort and increased intra-thoracic intrapleural and intrapulmonary pressures
aggravates obstructive airway disease