Flashcards in L9 Mechanism of sleep apnea and pathophysiology of hypoxemia & hypoxia Deck (21):
What is hypopnea ?
It is significant reduction of air flow for 10 seconds or longer
- more than 50% reduction
- less than 50% reduction + 4% desaturation and more
What is RERA ( respiratory effort related arousal ) ?
When the body is trying with effort to breath for more than 10 seconds that will wake the patient up but it is not fulfilling apnea or hypopnea criteria
What is OSA ?
It is the most common sleep-related breathing disorder that is caused by the collapse of upper airway during lying down
What are the types of OSA ?
1. Excessive daytime sleepiness OSA syndrome
2. OSA- hypopnea syndrome
What is the spectrum of sleep related breathing disorder ?
2. Upper airway resistance syndrome
3. Obstructive sleep apnea ( hypopnea then apnea ) —
What are the factors that determine transmural pressure of upper airways ?
1. Pressure of moving airways
2. Neuromuscular tone
What is bernoulli law ?
Fluids that move faster posses and exert less pressure
What are the body features that increase the risk of having sleep related breathing disorder ?
1. High BMI
2. High neck circumference
3. High cranial index
4. Low facial index
3+4 are only considered for white Americans not African Americans ( they are already more prone )
What is cranial index ?
It is width/length
Low CI = long head = low risk of OSA
High CI = short head = high risk
Why upper airways are collapsing ?
For two reasons : either
1. The dilating muscles are weak and have low tone
2. Patho-anatomical defect that will lead to this narrowing and require more forces to open them
What is the cycle of OSA ?
2. Body do efforts to breath but can’t
3. Arousal ( wake up )
4. Muscle activity increased and airways dilated
5. Over ventilation
6. Return to sleep
7. Increase in UA resistance and decrease in muscle tone
8 . UA narrowing
9. Hypopnea - apnea
What is the importance of EEG ?
It will show you when the patient is awake and when he is asleep
Sleep = low frequency, high amplitude
Awake =high frequency, low amplitude ( desynchronized )
What are the main types of sleep apnea? What is the difference between them ?
1. Obstructive sleep apnea ( our subject )
- it is due an obstruction ( collapse ) of upper airways with body efforts to breath
2. Central sleep apnea
- the body is unable to breath due to central problem without any effort to open them
How OSA is causing cardiovascular diseases ?
1. The hypoxia —
What is severity classification of sleep apnea ?
Apnea-hypopnea index (AHI ):
Mild ( 5-14)
Severe ( more than 30 )
Times Per Hour
What are the main types of hypoxia ?
1. Hypoxic hypoxia ( which is caused by hypoxemia )
2. Circulatory ( stagnant ) hypoxia —> due defects in CVS
3. Anemic hypoxia ( blood has less capacity to carry oxygen )
4. Histological hypoxia ( when the respiratory enzymes are being destroyed by poisons such as cyanide , the cells won’t be able to produce ATP so they will die )
Why hypercapnia is not necessarily associated with hypoxia and hypoxemia ?
As Co2 has high solubility and ability to cross the respiratory membrane so not necessarily accumulate
What are the main causes of hypoxemia ( hypoxic hypoxia ) ?
1. High amplitude ( low available oxygen )
2. Hypoventilation ( improve with pure oxygen )
3. Diffusion impairment ( improve with pure oxygen )
4. Ventilation/perfusion mismatch
5. Abnormal shunt (won’t improve with pure oxygen )
Why Pure hypoventilation can not cause major hypoxemia?
As to reduce 1 mmHg of oxygen there is a need to have a 1mmHg increase in Co2
However Co2 is readily diffuse across membrane so won’t accumulate easily
What are the causes of diffusion impairment ?
- increased thickness
* interstitial pneumonia
* interstitial fibrosis
- smaller surface area
* interstitial lung disease
* pulmonary vessel occlusion
- free fluid
* pulmonary edema
* poisonous gases ( nitrogen dioxide , phosgene)