Respiratory Acid-Base Disorders Flashcards
How is CO2 regulated?
Alveolar ventilation
Where is the respiratory centre?
Medulla
What receptors are responsible for sensory inputs concerning changes in CO2 and O2
Chemoreceptors
What are the two main stimuli for changes in alveolar ventilation?
Hypoxaemia (pao2< 60mmHg) and pCO2
a lot more sensitive to CO2 changes
Where are most oxygen-sensitive chemoreceptors located?
carotid body and to a lesser extent aortic bodies
play a minimal role in normal ventilation in the absence of hypoxemia
Where are the primary CO2/pH-sensitive receptors noted
in the CNS - retrapezoid nucleus, serotonergic, noradrenergic neurons and Gabaergic neurons
What is the portion of gas not making it to the gas exchange units called?
dead space
From where do respiratory mechanoreceptor inputs come from
chest wall, pulmonary and airway
receptors
Gas diffusion and transport during respiration
How much more soluble is is CO2 when compared to O2
20 to 24x
How do RBCs remain electroneutral when buffering CO2
As HCO3 moves out of the cell easily and H+ is trapped within the cell Cl- moves into the cell to maintain electroneutrality.
How is most CO2 transported to the lungs?
As HCO3 after being buffered by RBCs (approximately 81%), small amount (8%) transported dissolved in plasma, some combined with amino acids (11%)
How much oxygen is dissolved in blood?
0.003 mL dissolved O2 per 100 mL of blood/mm Hg
PO2
What factors aid in the unloading of oxygen to tissues
increased H
þ
ion and carbon dioxide
concentrations (as seen in respiratory acidosis),
increased temperature, and increased 2,3-diphosphogycerate
(2,3-DPG)
How is the aa gradient useful
To determine the degree of pulmonary impairment and excluding hypoventilation as a component
R= diffusability of of CO2 but also the metabolism of CO2 (varies between animals and diet)
What value of aa gradient is considered normal?
bellow 15mmHg
Above what value is pulmonary disease very likely?
25
WHat are the 5 main reasons for hypoxemia?
low fraction of inspired oxygen,
hypoventilation - on room air,
diffusion impairment,
ventilation-perfusion
mismatching,
and shunt
What conditions may result in alveolar hypoventilation?
CNS disease,
respiratory depressant pharmacologic agents, neuromuscular
diseases affecting the respiratory muscles, chest wall
injury, upper airway obstruction, and severe diffuse
pulmonary disease.
What is diffusion impairment ?
whenever there is incomplete
equilibration of alveolar gas and pulmonary end capillary blood. may be seen with
the thickening of the alveolar-capillary membrane. seen in diffuse pulmonary (interstitial disease), or loss of alveolar or capillary surface
area (e.g., emphysema or vasculitis)
What is a normal mammalian V-Q ratio?
approximately 0.8. if V-Q drops to 0.1 blood essentially remains unoxygenated as it moves through the lungs
What conditions may cause derangements in V-Q matching
Low vq - less vent, fine perfusion. –> asthma, bronchitis, pneumonia
High Vq - fine vent, less perfusion –> emphysema, low output states, PE
what is right to left shunting
a severe form of V-Q mismatch
and results when mixed venous blood completely
bypasses ventilated pulmonary alveoli and returns to the arterial circulation.
how much shunting is present in normal animals?
2-3% - due to bronchial perfusion
