Respiratory Control and Arterial Blood Gases Flashcards
What are Central Pattern Generators?
- neuronal circuits that can produce rhythmic motor patterns, for breathing
Various inputs that can modify this rhythm
- Emotional inputs from the cerebral cortex
- Lung mechanoreceptors
- Chemoreceptors (central/peripheral)
What is Minute Ventilation (VE)?
- Respiratory Rate x Tidal Volume
- RR x TT
What is the Pleuritic Chest Pain?
- pain caused by inflammation of the parietal pleura, most pronounced with deep breathing, coughing, sneezing or laughing
What is a Pleural Rub?
- abnormal lung sounds caused by layers of pleura rubbing together during breathing
What are the inspiratory muscles and their innervation?
- Diaphragm: Phrenic nerves from C3-C5
- External Intercostal Muscles: Thoracic nerve T1-T11
Accessory muscles
- Sternocleidomastoid: XI cranial Nerve
- Scalene muscles: C3-C8
What are the expiratory muscles and their innervation?
- Abdominal wall: T5-T12
- External intercostal muscles: T1-T12
Pons and DRG
Explain the Respiratory Centre
- Cerebrum –> Pons –> Medulla Oblongata
Pons
- contains two nuclei
- not essential for respiration but exerts fine control over medullary neurons
Medulla Oblongata
- Dorsal Respiratory Group of Neurons: trigger inspiratory impulses
- Ventral Respiratory Group: trigger inspiratory and expiratory impulses, during exercise and other times of active exhalation
- Central chemoreceptors: detect H+ in the CSF, reflects the amount of CO2 in the blood
What are lug stretch receptors?
- mechanoreceptors in the lungs, in the vagal nerve afferent fibers
- they sense lung stretching, and terminate the breath to prevent over-stretching
- Sense abnormal changes in airway mechanical properties
What are irritants and particulate receptors?
- mechanoreceptors, that are part of the vagal afferent fibers
- C-fiber neurons: activated by oedema and molecules such as bradykinin
- Irritant receptors: respond to punctate mechanical stimuli
What is involved in sensing peripheral PO2 and CO2 ?
- The Carotid body: a bundle of cells outside the bifurcation of the carotid arteries.
- they do the bulk of the sensing
- carotid bodies also sense pH
- The Aortic Body: a bundle of cells within the aortic arch
What is the ventilatory response of peripheral chemoreceptors to PCO2
- the body is very sensitive to changes in PCO2 and the VE (minute ventilation) can be changed to compensate for this
- this effect is reduced when opioids are ingested: this is the most common cause of hypercarbic respiratory failure
- if there is hypercarbia, the body is more sensitive to hypoxaemia
- the body is more sensitive to CO2
What are the two types acidosis?
- Respiratory acidosis: High PCO2
- Metabolic acidosis: Low HCO3-
What types of alkalemia are there?
- Respiratory alkalosis: low PCO2
- Metabolic alkalosis: high HCO3-
What can cause Metabolic Acidosis?
- *Renal Tubular acidosis (RTA)**
- types I-III
- all show loss in urinary bicarbonate and hyperchloremic acidosis
GI Losses
Acetazolamide
Excessive chloride administration (intravenous fluids with NaCl)
What is the anion gap?
the uncounted anions- the uncounted cations
- this consists mainly of albumin, phosphate, sulfate, etc..
- should 12mEq/L
- main cations = K+, Na+
- main anions= Cl-. HCO3-
What is Anion Gap Metabolic Acidosis?
- an increase in the number of anions in the blood sue to metabolic processes
- anion gap is > 12mEq/L
GOLD MARK
What are the causes of Anion Gap Metabolic Acidosis?
- Glycols (ethylene and propylene)
- Oxoproline
- L-lactate
- D-lactate
- Methanol
- Aspirin
- Renal failure
- Ketoacidosis
What are the compensatory mechanisms for both types of acidosis?
- Respiratory acidosis: retain HCO3 through metabolic mechanisms, can take days
- Metabolic acidosis: reduce CO2: increase respiratory rate
What are the compensatory mechanisms for both types of alkalosis?
- Respiratory alkalosis: reduce HCO3 in the body, increased excretion through the kidneys
- Metabolic alkalosis: retain CO2, reduced BR/ hypoventilation
What is Base Excess/Deficit?
- Base Excess: the dose of acid that would be needed to return blood to normal under standard conditions
- Base Deficit: the dose of alkali needed to return blood to normal pH
What is the cause of metabolic alkalosis?
- increased aldosterone
- vomiting
What care causes of respiratory acidosis?
- increased dead space e.g emphysema
- weakness; depression of respiratory centre
What causes respiratory alkalosis?
- hyperventilation due to pain or anxiety
- pregnancy
- hypoxaemia
VE= minute ventilation
What is the definition of hypoventilation with regards to the VE?
- when ventilation is insufficient to maintain a normal PaCO2 and acid-base status
- low ventilation
