Alveolar Ventilation Flashcards
What is alveolar ventilation?
The air that comes into and out of the alveoli per time
What is the tidal volume?
The volume of air coming into and out of the nose/mouth per time
Which lung volume is the hardest to measure in a conscious person?
Tidal volume
What is the volume of air in the lungs following a normal tidal expiration?
Functional residual capacity
What determines the functional residual capacity?
The balance point between inward alveolar recoil and outward chest wall recoil
What is the typical functional residual capacity of a 70 kg person?
~3L
What is the volume that remains in the lungs following a maximal expiratory effort?
Residual volume
What determines the residual volume?
The outward recoil of the chest wall and the compression of small airways leading to trapped gas
What volumes are included in the functional residual capacity?
The expiratory reserve volume and the residual volume
What is the expiratory reserve volume?
The air blow out starting at the FRC down to the residual capacity
What is the inspiratory capacity? The inspiratory reserve volume?
The inspiratory capcity is the maximal air taken in from the FRC up to the TLC; The inspiratory reverse volume is the volume of air between the top of a tidal breath to the TLC
What is the vital capacity?
The volume of air expired from the TLC down to the residual volume
What happens to the functional residual capacity moving from standing to laying down? Which volume(s) are changing? Why?
The FRC decreases by a third when laying down because the expiratory reserve volume is decreased and IC and IRV increase; When you are standing, gravity pulls the diaphragm down, which adds to the outward recoil of the chest wall
What lung volumes/capacities are increased in obstructive disease? Decreased?
RV, FRC, and TLC increase; ERV and Vital capacity decreases
What lung volumes/capacities are decreased in restrictive disease?
All values are compressed in restrictive lung disease
What values can be determined by spirometry?
Tidal volume, vital capacity, inspiratory capacity, inspiratory reserve volume and expiratory reserve volume
What percent of the air is nitrogen?
80%
What is the basic process of nitrogen washout?
Person breathes in pure oxygen and then exhales into a different bag. As the pure oxygen is breathed in the nitrogen is diluted and can be measured and multiplied by 1.25 to get TLC
What are the drawbacks of the nitrogen washout method?
If a person has many high resistance, small airways it will take very long to wash all the nitrogen out, and if airways collapse they will trap air which will cause a low measurement of TLC
What is the equation used to calculate lung volume using helium dilution?
Initial helium concentration (FHEi) * initial spirometer volume (VSPi)= Final helium concentration(FHEf)* (final spirometer volume plus lung volume)
What is the gold standard for measuring functional residual capacity?
Body plethysmograph
What concept is the body plethysmograph based on?
Boyle’s Law
How is trapped gas measured using the body plethysmograph?
Breathing in against the close airway will open up the collapsed airways
What is anatomic dead space?
The part of the respiratory tract where gas exchange is not occuring because gas is not in contact with pulmonary capillaries
What is the formula for calculating alveolar volume?
Alveolar volume= tidal volume - anatomic dead space
What is the typical ration of O2:CO2 on a typical western diet?
1 : 0.8
What technique can be used to measure anatomic dead space?
Fowler’s technique
What is physiologic dead space?
Anatomic dead space plus alveolar dead space
What is alveolar dead space?
Alveoli that are ventulated but are not receiving blood supply
What could cause alveolar dead space?
Pulmonary emboli, low right ventricular output (blood loss), or very high alveolar pressure (mechanical ventilation)
How can the Bohr equation be used to calculate alveolar dead space?
1- Calculate physiologic dead space, guesstimate anatomic dead space and subtract it from physiologic dead space
What is the guesstimated value for anatomic deadspace?
1 mL/ lb
What percent of the air is carbon dioxide?
~0.04%
What is displayed on a capnograph? What can it be used for?
Partial pressure of carbon dioxide at the mouth per time; If end-tidal PCO2 is lower than arteriole PCO2 then that person has alveolar dead space
How can hyperventilation caue fainting?
Hyperventiltion lowers PCO2, and lowering PCO2 causes cerebral vasocontriction
Increasing ventilation has what effect on alveolar PCO2?
Alveolar PCO2 goes down
True or False: There is a direct relationship between alveolar PO2 and ventilation
False
What is the partial pressure of water vapor at body temperature?
47 mmHg
What is the alveolar air equation?
Alveolar PO2= Fractional concentration of oxygen in inspired gas (about 0.21 in air) * (barometric pressure in mmHg- partial pressure of water vapor) – alveolar PCO2/ resp. exchange ratio
When upright, where does the most ventilation occur in the lung?
Lower parts
How does the intrapleural pressure at the FRC differ depending on the location within the pleural cavity?
The intrapleural pressure is more negative at upper portions of the lung
How does increased intrapleural pressure at the top of the lung affect the upper alveoli?
They will experience greater transmural pressure, making them bigger and less compliant than bottom alveoli
Where is most of the lungs’ FRC, RV, and IC volume?
RV, FRC is mostly at the top; inspiratory capcity is mostly at the bottom
What is the closing volume?
The lung volume at whoch airway closure begins during a forced expiration
Patients with what condition would liekly have the highest closure volumes?
Emphysema patients
What happens to the FRC, RV, and closing capacity as you age? Why?
They increase because of decreased elasticity
