Gas Exchange, Pathophysiology-Sinclair Flashcards
Barometric Pressure at Sea Level
760 mmHg
Fractional Concentration of Oxygen
0.21 (21%)
Fractional Concentration of Nitrogen
0.78 (78%)
The total pressure in a system is equal to the sum of the partial pressures of each individual gas in the system.
Dalton’s Law
Equation for Partial Pressure
(Barometric Pressure at a certain level) X (Fractional Concentration of gas)
Does the fractional concentration of oxygen ever change with different altitudes?
No. Fractional Concentration is the same at all altitudes.
Does the water vapor pressure ever change with different altitudes?
No. Water vapor pressure never changes.
Water vapor pressure equals…
47 mmHg
Equation for Minute Ventilation
(Tidal Volume) X (Respiratory Rate)
Air which remains in the conducting zone after inspiration and, therefore, does not participate in gas exchange; not pathologic
Anatomic Dead Space
Portion of alveoli which do not participate in gas exchange as a result of a lack of perfusion; usually pathologic
Alveolar Dead Space
Equation for Physiologic Dead Space
(Alveolar Dead Space) + (Anatomic Dead Space)
Normal value for Physiologic Dead Space in normal people
150 mL
Equation for Alveolar (Effective) Ventilation
(Tidal Volume - Physiologic Dead Space) X Respiratory Rate
The amount of dead space in a given individual is highly dependent upon…
Lean Body Weight
Alveolar Gas Equation (Finding the alveolar partial pressure of oxygen)
PIO2 - [(PaCO2)/R], where R=0.8
Value and Calculation of PIO2 (inspired pressure of Oxygen)
(760-47) X 0.21 = 150 mmHg
Normal Value for PaCO2 at Sea Level
40 mmHg
Normal Value for PAO2 at Sea Level
100 mmHg
Best method for attaining PaO2
Arterial Blood gas Test (from Radial Artery)
Equation for A-a gradient/difference
(PAO2-PaO2)
Widened A-a gradient signifies (general)…
Lung disease
Formula for Normal A-a gradient
(Age+4)/4; if value is greater, then lung disease may be evident
Hypoxemia with Normal A-a gradient
No intrinsic lung disease; usually due to hypoventilation secondary to altitude changes.
Equation for PACO2
[VCO2/Alveolar Ventilation] (k); k is a constant that can be ignored most of the time, however.
Causes of Hypoxemia with Normal A-a gradient
1) Hypoventilation
2) Decreased PIO2
Causes of Hypoxemia with a Widened A-a gradient
1) Diffusion Limitation
2) Right-to-left Shunts (VSD/ASD)
3) V/Q mismatch
Hypoxemia due to Diffusion Limitation occurs if:
1) Diffusion capacity is severely decreased
2) Capillary transit time for RBC’s is decreased
Can a shunt be improved with 100% O2 supplementation?
NO. Shunts cannot be improved with oxygen supplementation. V/Q mismatch, however, CAN.
Both ventilation and perfusion are highest at which portion of the lung?
Base of the lung
Diseases associated with Low V/Q values
1) COPD, Asthma [Obstructive Lung Diseases]
2) Pulmonary Edema
3) Shunt [MOST EXTREME DISEASE STATE]
Diseases associated with High V/Q Values
1) Pulmonary Embolism
2) Increase in Dead space [MOST EXTREME DISEASE STATE]
5 Pulmonary Causes of Hypoxemia
1) Decreased PIO2
2) Hypoventilation
3) Shunt
4) V/Q Mismatch
5) Diffusion Limitation
