Term
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Definition
Need to take into account both water vapor pressure and PCO2 in the lungs.
PA O2 = (Pb – PH20) (F02) – PaC02 /R
R normally equals .8
PaCO2 normally equals 40 mmHg |
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Term
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Definition
Total air moved in and out per minute
Ve=Vt x f
Where Ve=minute ventilation
Vt=tidal volume
f= frequency
Roughly 1/3 of minute ventilation is dead space ventilation |
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Term
| Anatomical dead space ventilation |
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Definition
| Amount of air that is in conducting zone (to terminal bronchioles), not used in respiration. Usually equal to 1/3 of minute respiration. |
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Term
| Alveolar Dead Space Ventilation |
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Definition
Alveolar dead space occurs in a variety of lung diseases where lung tissue does not function in gas exchange.
Alveoli that do not participate in gas exchange
i.e. ventilated areas that are not well perfused…….Wasted ventilation
GAS EXCHANGE REDUCED or CAN NOT OCCUR |
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Term
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Definition
Total volume of lung that does not participate in gas exchange
Alveolar VD + anatomic VD = “functional” or physiologic VD
In a healthy individual with normal lungs (well matched ventilation and perfusion): anatomic VD = physiologic VD
Normal VD = .20-.35 or
150 ml (anatomic VD)/500ml (VT)=.3 |
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Term
| Measurements of Physiologic Dead Space |
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Definition
VD/VE = PACO2-PECO2/ PACO2
Patient takes a VT of room air (essentially CO2-free)
Air in the anatomic dead space does not take part in gas exchange and remains 0% CO2
Inspired air (~ 0 mmHg CO2) mixes with alveolar air (~ 40 mmHg, [CO2]A )
Expired air initially 0 CO2….followed by expired air with CO2
Practically, we measure all of the expired air and determine [CO2]E |
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Term
| Alveolar ventilation equation |
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Definition
VA = (VT - VD) x f
or
VA=VT x f - VD x f
VA = (VCO2 x 0.863)/PaCO2
VA = (200ml/min x 0.863)/40= 4.315 L/min |
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Term
| Relationship between CO2 and Alveolar ventilation |
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Definition
Inverse relationship:
PaCO2=0.863 x VCO2 / VA
Double ventilation-reduce PACO2 by ½
Reducing ventilation-increases PACO2 |
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Term
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Definition
| Deep breathing, increased volume |
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Term
| Hypocapnea vs hypercapnea |
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Definition
| Decreased CO2 vs increased CO2 |
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Term
| Relationship of alveolar ventilation and PO2 |
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Definition
| Proportional relationship, increased ventilation increases PO2 and decreases PCO2. |
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Term
| Respiratory exchange ratio |
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Definition
Ratio of CO2 ventilation over oxygen ventilation
R=VCO2/VO2
Normally=.8 |
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Term
| Regional variances in ventilation across lung |
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Definition
| Measure Xenon path throughout lungs to assess regional variations in ventilation. Ventilation happens more at the base than at the apex (alveoli in apex are less compliant). |
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Term
| Ventilation in restrictive lung disease |
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Definition
Happens in cases of pulmonary edema or fibrosis.
Compliance is reduced, results in stiff alveoli.
Reduces volume and ventilation. |
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Term
| Ventilation in obstructive lung disease |
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Definition
Found in asthma, COPD, airway occlusion
Increases resistance or reduces recoil, decreases ventilation. |
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Term
| Ventilation during masses in the lung |
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Definition
Failure to completely expand part of the lung
Example-Tumor, pleural effusion, pneumothorax
No specific effect on resistance or compliance, but compressed lung so
Alters ventilation.
Since part of lung is not taking part in respiration, decreases initial volume. Also reduces change in volume during inspiration because less lung tissue doing respiration. |
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