RESP: Integrated control of breathing Flashcards
How does varying ventilation rates affect PaCO2 and pH?
- ⬆️Ventilation = ⬇️PaCO2 = ⬆️pH
- ⬇️Ventilation = ⬆️PaCO2 = ⬇️pH
How does varying HCO3 excretion affect HCO3- levels in blood and pH?
⬇️HCO3 excretion = ⬆️[HCO3-] = ⬆️pH
⬆️HCO3 excretion = ⬇️[HCO3-] = ⬇️pH
What might result from respiratory (CO2) or metabolic (HCO3-) dysfunction?
Blood pH is proportional to the ratio of HCO3-:CO2, excessive changes may result from respiratory (CO2) or metabolic (HCO3-) dysfunction.
Decreased pH = acidosis
Increased pH = alkalosis
When does respiratory acidosis occur?
When ventilation is insufficient to metabolic demands of body
Causes an ⬆️ PaCO2, leading to hypercapnia, and therefore acidosis
In the event of chronic hypoventilation, HCO3- excretion must decrease to maintain normal pH
When does respiratory alkalosis occur?
When ventilation is excessive relative to the metabolic demands of the body (in terms of CO2 production)
Causes ⬇️ PACO2, leads to hypocapnia, leading to alkalosis
In the event of chronic hyperventilation, HCO3- excretion must increase to maintain normal pH
What are causes of hyperventilation?
- Anxiety - Causes panic attack, increased ventilation (tachypnoea) without increased metabolic demand, leads to ⬇️ PaCO2, respiratory alkalosis
- High altitude, ⬆️ alveolar ventilation to try and maintain normal PAO2 and PaO2 (via hypoxic drive), increased ventilation, respiratory alkalosis
When does metabolic acidosis occur?
When metabolic production is excessive and/or [HCO3-] is deficient
pH ∝ ⬇️HCO3-/PaCO2
- Unless PaCO2 changes in proportion with [HCO3-] (in opposite direction), acidosis (⬇️pH) will occur
- Respiratory compensation (⬆️ventilation) occurs almost instantly and attempts to return pH back to normal range. However, if patients have simultaneous respiratory pathology, this may not be possible
What are causes of metabolic acidosis?
- Lactic acidosis (sepsis)
- Infection → pathological immune response → septic shock → ⬇️O2 delivery to tissues (hypoxia) → ⬆️Lactic acid production & ⬇️pH → Respiratory compensation to ⬆️O2 delivery and ⬆️lactic acid conversion
- Diabetes ketoacidosis
- ⬆️fatty acid release from liver due to insulin deficiency = ⬆️(acidic) ketone body production
- Renal failure (e.g. decreased HCO3- reabsorption in proximal tubule)
- Diarrhoea (e.g. decreased HCO3- absorption in colon)
When does metabolic alkalosis occur?
When metabolic excretion is excessive and/or [HCO3-] becomes excessive
pH ∝ ⬆️HCO3-/PaCO2
- Unless PaCO2 changes in proportion with [HCO3-] (in the opposite direction), alkalosis (⬆️pH) will occur
- Respiratory compensation (⬇️ventilation) attempts to return pH to normal range
What are causes of metabolic alkalosis?
- Diuretics (changes to H+ and HCO3- reabsorption)
- Antacid ‘abuse’ (⬆️HCO3- consumption)
- Vomiting (loss of H+ in stomach acid)
Describe the effect of acidosis-induced hyperkalaemia
Homeostasis of K+ levels in blood dependent on pH. Cells have multiple mechanisms for indirectly exchanging H+ for K+ (Hydrogen efflux for potassium influx).
1 mechanism is via initial exchange of H+ and Na+ (hydrogen efflux, sodium influx), followed by Na+ and K+ exchange (sodium efflux, potassium influx) - net effect is that potassium ions enter the cell in exchange for hydrogen ions leaving.
Initial step of H+ diffusion out of cell is dependent on a H+ concentration gradient, with H+ higher in concentration within the cell.
In the event of acidosis, this process breaks down as pH falls, meaning there’s an increase in H+ within blood and extracellularly.
Therefore, K+ uptake is reduced in response to acidosis, leading to potassium accumulation within the ECF in blood. Because K+ has critical roles in membrane potential and muscle function, cells such as skeletal muscle and cardiac pacemaker cells are adversely effected.
Describe the effects of alkalosis-induced cerebral vasoconstriction
- CO2 (via conversion to H+) acts as a vasodilator in blood vessels (cerebral arteries particularly sensitive), relaxing smooth muscle and increasing blood flow
- Hyperventilation = ⬇️CO2 and ⬇️H+ (alkalosis)
- Alkalosis causes vasoconstriction of cerebral arteries
- ⬇️cerebral blood flow = headache, lightheadedness, confusion, seizures
How does the respiratory system respond to exercise?
- Minute ventilation of lungs increases rapidly after exercise begins
- In healthy individuals, PaCO2 does not increase during exercise. This is because ventilation increases before the extra CO2 produced by muscles can increase PaCO2.
What are causes and effects of pH disturbances?
Acidosis - pH <7.35, causes hypercapnia (hypoventilation), ⬆️ lactic acid (sepsis), ⬆️ Ketone bodies (diabetes), ⬇️ Kidney acid excretion (renal failure), ⬇️ HCO3- reabsorption (renal acidosis), diarrhoea (loss of HCO3- from gut). Causes tachypnoea, muscular weakness, headache, confusion, coma, cardiac arrhythmia, hyperkalaemia. Compensatory mechanisms are hyperventilation (⬇️PaCO2, respiratory compensation) and ⬇️HCO3- excretion (renal compensation)
Alkalosis - >7.45, Hypocapnia (hyperventilation), vomiting (loss of H+ in HCL), ⬆️ kidney acid excretion (diuretics), ⬆️ alkaloid agent consumption (antacids, NaHCO3). Causes bradypnoea, muscular weakness, cramps, tetany, headache, nausea, lightheadedness, confusion, coma, cardiac arrhythmia, hypokalaemia. Compensatory mechanisms are hypoventilation (⬆️PaCO2, respiratory compensation) and ⬆️ HCO3- excretion (renal compensation)
