Pulmonary 9 - Lecture 31 Flashcards
What is the affect of High Altitude on
- Barometric pressure
- PO2
Both decrease!!
What is the PiO2 at a Barometric Pressure of 255 mmHg (high altitude)?
What is the PAO2?
PiO2: 0.21 x (255-47mmHg) = 44 mmHg
PCO2 = 40 mmHg, respiratory ratio = 1
PalveolarO2 = 43 – 40/1 = 3 mmHg !
How is acclimatization achieved at high altitudes where the PO2 is low?
Acclimitization via Hyperventilation
- 5 fold increase in PO2!
PalveolarO2 = 43 – 8/1 = 35 mmHg
How do people achieve hyperventilation in high altitudes with PaCO2 of 33 mmHg?
HYPOXIC STIMULATION of peripheral chemoreceptors
What happens initially at high altitudes due to hyperventilation?
Respiratory Alkalosis due to low PaCO2 and high pH
- this initially inhibits further ventilation, but is adjusted within several days & hyperventilation is further increased
How does Polycythemia normalize O2 concentration? How is polycythemia achieved?
- Increases RBC concentration
- via erythropoietin from Kidney (takes days/weeks) - Increase Hb/O2 carrying capacity
- although Saturation may decrease, the total Oxygen per dL of blood is relatively high due to the increased Hematocrit
(higher Hb = more Oxygen can build up)
What are the normal Hb, SO, and Oxygen content per ml/dl
normal Hb = 15 g/dL
SO = 95%
19.1 mL O2/dl
What is the only blood at high altitude that has relatively similar PO2 to sea level?
Mixed Venous Blood!
- only 7 mmHg difference
What is the initial affect of 2,3- DPG because of high altitudes? What is the secondary affect?
- RIGHTWARD shift of O2 binding curve
- O2 dissociates easier - LEFTWARD shift once alkalosis occurs, due to hyperventilation (low CO2 - better loading of Oxygen)
What is the affect of alveolar hypoxia on Pulmonary Vasculature? (2 clinical correlates)
- Pulmonary Vasocontriction
- Pulmonary Edema
- Right Heart Hypertrophy
Because the air is less dense at high altitudes, what happens to the breathing capacity?
Maximal Breathing Capacity Increases
What is Acute Mountain Sickness? What 2 clinical cases can this progress into?
- Headache, fatigue, dizziness, nausea
- Pulmonary Edema
- Cerebral Edema
What is Chronic Mountain Disease?
Polycethemia, Fatigue, Reduced Exercise TOlerance, Hypoxemia
What is the increase in pressure for every 10 m/33ft depth increase ?
Pressure doubles!
- lung is compressed, so volume decreases (breathing is reduced)
What is the primary and secondary responses of the DIVING REFLEX? What is it induced by?
INDUCED BY APNEA
- Primary - Peripheral Vasoconstriction due to Sympathetic Activity
= initial hypertension - Secondary - Vagal induced Bradycardia & reduction of CARDIAC OUTPUT
= slow HR to spare oxygen
What is the primary purpose of Bradycardia within the context of the diving reflex?
Slow HR = decrease CO and decrease Oxygen Use
What are the 3 important affects of the diving reflex?
- Sympathetic Peripheral Vasoconstriction = increase BP
- Decrease HR (vagally induced bradycardia)
- O2 saturation is maintained - Increase Hb by splenic contraction
What is the pO2 that hypoxic loss of consciousness occurs at?
PO2 of 20-25 mmHg
How does Hyperventilation lead to LOC? What input is overridden?
- Reduces CO2 drive to breath (low CO2 = less of a stimulus to increase ventilation)
- Weak Respiratory Stimulus from Hypoxia is OVERRIDDEN voluntarily by low CO2
(the low CO2 has a greater affect than the low O2)
How does Ascent Blackout occur?
Reduction of Water Pressure & Gas Pressure causes a decrease in pO2 content
(due to lower pressure = lower O2 partial pressure)
- need to slowly ascend to avoid LOC at 20-25 mmHg of PO2
How does carbohydrate depletion lead to Hypoxic Loss of Consciousness?
Less CO2 produced by metabolism
- reduces CO2 drive to breath
What are the 3 reasons that LOC can occur in Breath Holders?
- Hyperventilation - low CO2
- Ascent Blackout - low PO2
- Carbohydrate Depletion - Low CO2
1 and 3 have a common theme = LOW CO2! = loss of CO2 drive to breath
What is the affect of barotrauma of descent?(2) Why does this happen?
- Lung Edema
- Damage
- Atelectasis
- Capillary Rupture
Pressures redistribute & increase in certain areas
ex: Capillary Hydrostatic pressure increases and causes pulmonary edema
Pressures redistribute because LUNG VOLUME redistributes (occurs at low PRESSURES
ex: submerging head underwater)
What is maintained in Barotrauma of Descent & what is lost?
- Compression of lung
- Redistribution of blood volume
LOST:
- Atelectasis
- Edema
- Capillary Rupture
What is Decompression Sickness?
Nitrogen content increases in the tissues as the pressure increases (when diving)
- since more Nitrogen pushed into the tissues, the blood needs time to equilibrate since it is poorly soluble
Nitrogen Diffuses out as you ascend to lower pressures
- causes the formation of NITROGEN BUBBLES
- can function like emboli and lead to pain in joints etc..
What is Inert Gas Narcosis?
High levels of N2 in the blood due to diving to HIGH PRESSURES
at 50 m: EUPHORIA
at deeper levels: Loss of Coordination/Coma
What affects to N2 and O2 have at high pressures?
N2 and O2 affect the CNS
O2 affects the Lung
What is the affect of oxygen toxicity in the CNS? (Hyperbaric O2)
In the lung? What levels must it reach to cause damage in the lung?
- Vomiting, Dizziness, Vision Impairment, seizures
- HIGH LEVELS OF OXYGEN - Must reach FiO2 > 0.4 - 0.5
Damage of endothelial cells of
pulmonary capillaries
Substernal pain during breathing
Impaired gas exchange
Reduction of vital capacity
Atelectasis
Retrolental fibroplasia in premature
infants fibrotic tissue due to increased O2
What is Hyperbaric O2 therapy used for?
- CO poisoning
- Anemic Crisis
- Gas Gangrene (anaerobic bacteria)
- Impaired bone/wound healing
- use dissolved Oxygen for CO poisoning
What is the most important problem at high altitude? How can this be resolved?
Low PO2
- HYPERVENTILATION
How does high altitude lead to the formation of Pulmonary Vasoconstriction, Right Heart Hypertrophy, and Pulmonary Edema?
via ALVEOLAR HYPOXIA
What is the main purpose of the Diving Response?
SPARE OXYGEN
