49: Ventilation Flashcards
P(a)
arterial partial pressure
P(A)
alveolar partial pressure
V(T)
tidal volume
V(D)
dead space
F(A)
fractional concentration alveolar
F(E)
fractional concentration expired
Henry’s Law
V(gas) = P(gas) x solubility
Water vapor
Dry air is water saturated as it moves down respiratory trees to allow for proper gas exchange at alveoli
Minute Ventilation
volume of air moved out of the lungs per minute
Minute Ventilation Equation
V(E) = V(T) x f
V(T): ~500mL
V(E) = (0.5 L) x (12 breaths/min) –> 6L/min
Anatomic dead space
trachea, bronchioles, respiratory tree
don’t contribute to gas exchange
150mL used up in dead space
What is the best way to breath?
Less breaths, deeper breaths
Alveolar Minute ventilation
the amount of ventilation that makes it to gas exchange site
V =(VTx f)–(VDx f)
Functional Residual Capacity
lung not empty when inspire
FRC full of stale air
ventilation of fresh air must be enough to dilute stale air to create gas exchange
Measuring Anatomic Dead Space
Inspire pure O2 and expire out
Measure until no longer pure O2 and Nitrogen is present
Usually 150mL
Measure Alveolar Ventilation
Atmospheric CO2
is zero – all expired CO2 must come from a functional
alveolar unit
alveoli must be well perfused
Physiological Dead Space
Anatomical Dead Space + Not well perfused alveolar (dead space)
Bohr Method
Blood drawn to determine alveolar CO2 from arterial CO2 since they are the same
AND
Measure expired CO2
20-30% of tidal breath wasted on dead space
V(D) / V(T)
((P(a)CO2 - P(E)CO2)) / P(a)CO2
Constant Ventilation
allows maintenance of steady state (gas) b/n alveoli and capillary
PO2 = 100 mm Hg PCO2 = 40 mm Hg
Increased alveolar ventilation
Decrease PCO2
blow out more CO2
increase PO2
Alveolar Gas Equation
** IMPORTANT
calculate global alveolar partial pressure of oxygen
P(Alveolus)O2 = P(Inspire)O2 - (P(Alveolus)CO2 / R))
What happens to arterial pH during increased ventilation?
pH increases b/c less CO2 in blood
Ventilation during exercise
normal metabolic changes:
Hyperpnea
increased ventilation
and cardiac output
arterial gas partial
pressures remain stable, venous CO2 rises
Hyper/Hypo Ventilation changes
pathological changes:
pH increases
PCO2 decreases
Alveolar PO2 increases
Lung Complaince
upper part: low compliance
lower part: high compliance
Hypoventilation
decreased alveolar ventilation with increased PaCO2
Hyperventilation
increased alveolar ventilation with decreased PaCO2
Hypercapnia
increased carbon dioxide in blood
Eupnea
well breath
Hypopnea
decreased ventilation in response to lowered metabolic CO2
production
Hyperpnea
increased ventilation in response to increased metabolic CO2 production (e.g. exercise) – increased ventilation should purge CO2
Tachypnea
(‘swift’ breath) increased frequency of breathing.
Ventilation may or may not change depending on tidal volume
Dyspnea
(‘ill’ breath) shortness of breath / labored breathing
Apnea
temporary cessation of breathing
