45. Breathlessness

Question 1

What 3 main components contribute to dyspnoea?

What do the dorsal and ventral respiratory groups do?

Answer 1

Afferent signals (e.g. baroreceptors, peripheral chemoreceptors, central chemoreceptors, J receptors), efferent signals, central info processing (brain compares afferent and efferent signals, and if mismatch = dyspnoea)

DRG: phrenic nerve (diaphragm), intercostal nerves (intercostals), pharyngeal dilator muscles

VRG: expiratory muscles (don’t fire much b/c expiration mainly passive)

Question 2

List some causes of breathlessness.

Do type 1 and type 2 respiratory failure both cause breathlessness?

Answer 2

Hypoxia, metabolic acidosis (blow off CO₂), hypotension/reduced C.O (causes stagnant hypoxia), pulmonary oedema (stimulates J receptors), obstruction of pulmonary artery, exercise, pregnancy (progesterone has direct effect on resp centre), anxiety and pain, anaemia

Type 1 can/will cause it via the peripheral chemoreceptors. Many causes of type 2 are due to hypoventilation and may not be associated with breathlessness.

NB: peripheral chemoreceptors affected by hypoxia, not central

Question 3

What are the 2 classification methods for conditions that cause breathlessness?

How do you assess breathlessness?

Answer 3

1) Surgical sieve (Very Early Man Did Not Talk IIIII)
2) Systems approach (ABCEHNAP)

History, associated features e.g. smoking, examination (resp and CDV), investigations (FBC (anaemia or infection), Us and Es, pulse oximetry, peak flow (obstructive vs restrictive), ABGs (acidosis, hypercapnia etc.), cardiac enzymes, ECGs (ST elevation/depression), CXR, echocardiogram (valve info too), cardiopulmonry exercise testing, VQ scan, holter monitoring (24h ECG)), treatment. Always give O₂ until pO₂/saturation known. Treat cause.