Diffusion, Hypoxia, Hypercapnia Flashcards
1
Q
3 Conditions that Lower Diffusing Capacity
A
**Loss of interface
1- Emphysema
2- Interstitial lung disease
3- Pulmonary Vascular disease
2
Q
4 Conditions that Inc Diffusing Capacity
A
1- Polycythemia - greater reservoir to bind CO
2- Early CHF - inc cap volume
3- Asthma - expand lung units
4- Alveolar hemorrhage - false; bleeding into lungs so binds w/ CO
3
Q
4 Factors that Affect Rate of Diffusion
A
- A- rate inc w/ in surface area
- D - coefficient proportional to solubility of the gas and inversely proportional to molecular weight of gas
- P1-P2 - partial pressure gradient; greater rate if greater difference
- T - dec rate if thicker interface (diseases like interstitial edema or interstitial fibrosis)
4
Q
What determines concentration / amount of gas dissolved?
A
- C = solubility x partial pressure
- Conc of O2 = .003 x PO2
- Conc of CO2 = .067 x PCO2
- So anything that inc partial pressure will inc the conc of that gas in plasma (more dissolved) and vice versa
- Since CO2 and O2 have relatively low solubilities, partial pressure changes quickly during diffusion
5
Q
How long does diffusion normally take? How is this affected by pathology?
A
- Both CO2 and O2 equilibration takes about .25 seconds while RBC spends about .75 seconds at the interface at rest (done w/ plenty of time)
- Even during exercise (inc perfusion rate so less time at interface) there is enough time for equilibration
- BUT if diffusion impairment, it may take the entire .75 seconds so undetected at rest but “exercised induced de-saturation”
**More dramatic for O2 than CO2 b/c larger P gradient for O2
6
Q
5 Causes of Hypoxia
A
NORMAL PA-aO2 (both dec)
- 1- Hypoventilation
- 2-High Altitude
INCREASED PA-aO2 (only PaO2 is dec)
- 3- V/Q Mismatch
- 4- Shunt
- 5- Impaired Diffusion (thicker interface or dec SA of interface)
7
Q
3 Causes of Hypercapnia
A
- 1- Inc dead space w/o compensatory inc in minute ventilation
- 2- Dec minute ventilation (can be CNS or muscle problem)
- 3- Inc CO2 production w/o compensatory inc in minute ventilation
8
Q
How does respiration change in pregnancy?
A
- Anatomic changes - diaphragm elevates but lower ribs expand to comp - “barrel chest”
- Dec residual volume, dec expiratory reserve
- BUT inc tidal volume so minimal dec in TLC
- Metabolic changes - inc metabolic rate so more CO2 production
- Progesterone –> inc respiratory drive and inc sensitivity of respiratory centers to CO2 –> inc minute ventilation –> inc alveolar ventilation b/c dead space the same
- Overall… inc minute vent/alveolar vent»_space; inc CO2 prod –> overall respiratory alkalosis (pH7.4-7.47)
- *Disproportional rise in minute ventilation**
- If PACO2 is lower than PAO2 is reciprocally higher (so sats close to 100%)
9
Q
Dyspnea in Pregnancy
A
- Common; can start b/f major anatomic change
- Likely due to progesterone-induce in alveolar vent
- Also nasal congestion, inc blood flow, anemia, etc
10
Q
Physiological Changes in Diving
A
- Inc pressure surrounding chest wall (1 atm per 33 ft) –> dec lung volume (PV=nRT)
- Inc partial pressures of ea gas b/c same gas composition … inc PO2 and inc PCO2 (which then means more dissolved b/c C = solubility x PartialP)
- Mechanics affected b/c inc pressure on chest wall dec FRC and TLC (More pressure to overcome in inspiration AKA have to do more work to expand chest wall)
11
Q
4 Steps of Breath Hold Diving
A
- 1- Hyperventilate b/f diving to achieve low starting PCO2 (b/c PCO2 affects drive more) and high starting PO2
- 2- Descent - lung volume dec while total pressure inc; both PO2 and PCO2 inc
- 3-While under, CO2 produce/O2 consumed so inc PACO2 and dec PAO2
- **Respiratory acidosis
- **Stim chemoreceptors that inhibit further breath holding (drive to breath)
- 4-Ascent - total pressure dec so partial pressures also dec; dec PACO2 and now even lower PAO2
- **Can get hypoxic on ascent (may lose consciousness or die)
12
Q
Barotrauma
A
- if scuba diver holds breath on ascent then high starting pressure w/ inc volume while ascending can cause rupture of alveoli
- Can lad to pneumothorax, alveolar hemorrhage, air embolism
- 2nd most common cause of death in SCUBA divers
13
Q
Decompression Illness
A
- when diving there is inc dissolving of O2, CO2 and N2 then dec in amount dissolved during ascent (b/c dec partial pressure of gases) –> bubbles in tissues and blood vessels (goes from solution –> gas)
- Block vessels, rupture tissues, activate clotting and inflammatory cascades, etc
- Bends - bubbles in joints
- Chokes - bubbles in pulmonary blood flow lead to chest pain, dyspnea and cough
- Tx - immediate recompression (hyperbaric oxygen chamber) followed by slow decompression AND 100% oxygen to create nitrogen gradient to get it out of tissues
14
Q
Nitrogen Narcosis
A
- excess nitrogen dissolved in CNS –> alters neuronal cell membranes
- Euphoria, amnesia, clumsiness, irrational behavior
15
Q
Physio Changes at High Altitude
A
- Drop in baro pressure –> inc volume w/ same air composition so partial pressure of O2 decreases proportionally
- Dec PO2 –> chemoreceptor stimulation –> inc minure vent –> respiratory alkalosis
- Inc 2,3-DPG so shift dissociation curve RIGHT
