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15 Intro to Pulmonary Physiology Lung Volumes


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- tidal volume
- volume inspired or expired with normal breath
- Functional Residual Capacity
- sum of ERV and Residual Volume
- cannot be measured by spirometry
- Expiratory Reserve Volume
- volume that can be expired after expiration of tidal volume
- amount left after normal exhalation
- Inspiratory reserve volume
- amount that can be expired over and above tidal volume
- used during exercise
- residual volume
- volume that remains after maximal expiration
- cannot be measured by spirometry
- inspiratory capacity
- Vt + IRV
- normal inspiration and deep breath
- measurement of volume of air entering and leaving lungs
Lung capacities
1) Inspiratory Capacity (Vt + IRV)
2) Functional Residual Capacity (ERV + RV)
3) Vital Capacity (Forced Vital Capacity) (Vt+ IRV + ERV)
- Forced vital capacity
- Vt + IRV + ERV
- air forcibly expired after maximal inspiration
- Total lung capacity
- sum of all four lung capacities
- volume in lung after maximal inspiration
- can't be measured
Dead Space
1) Anatomic Dead space
2) Physiologic Dead Space
anatomic dead space
- volume of conducting airways
- ~150 ml
Physiologic dead space
- volume of lungs not participating in gas exchange
- normal lung = anatomic dead space
- in ventilation/perfusion (V/Q) defects can be greater
-Vd = physiologic dead space (ml)
PaCO2 = PCO2 of arterial blood (mmHg)
PECO2 = PCO2 of expired air

Vd = Vt (PaCO2 - PECO2)/ PaCO2

- tidal volume times (dilution of alveolar PCO2 by dead space air
Minute ventilation
Vt x breaths/min
alveolar ventilation
(Vt - Vd) (breaths/min)
(tidal volume - dead space) x (breaths/minute)
- Vital capacity is 80% of TLC
- Reserve Volume is 20%
- Forced Expiratory Volume in 1st second of forced maximal expiration
- FEV1/FVC = .8
- obstructive lung disease --> Fev1/FVC decreased
- restrictive --> normal or increased
Helium dilution
- from resting, He/O2 mix
- [He] monitored until equilibration reached
- volume of system and initial %He known
- new volume = volume of system + volume remaining in lungs at end of expiration
- FRC = V1(C1-C2)/C2
- boyle's law to find FRC
- airtight box of known V
- P measured in box and at airway during inspiration effort at closed airway
- V1 = volume in box
- V2 = volume after inspiration
- change in volume = volume of thorax
- P3 and p4 are pressure in airway before and after inspiration P3v3 = p4(V3+ change in V)
- V3 = FRC

FRC = P4 (change in V/ change in P)
Fowler Method
- single breath N washout
- measures deadspace
- 100% O2 in, V and [N] measured on exhalation
- no increase in N initially, but incrases to an S curve gradually before a plateau
- horizontal line from plateau, vertical tangent to it, through S curve
- alveolar gas = plateau
- value at which perpendicular intersects Volume axis is anatomic dead space
Bohr Method
- physiological and anatomical dead space
- yield same as Fowlers
- when high physiologic deadspace bohr --> large value
- Vd/Vt =
- (PaCO2 - PECO2)/ PaCO2
PaCO2 = partial pressure of CO2 in arterial blood
PECO2 = partial pressure of CO2 in expired air
- normal is .2 - .4
- graphic display of exhaled [C02] v time or expired volume during respiratory cycle
- plateu = pressure of Alveolar CO2 (PACO2) approximates PaCO2 in normal
- lower than normal PaCO2
- higher than normal PaCO2
Hyper and Hypo ventilation
- refer to PaCO2 levels not rate

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