F2i / 22B04: Control of Ventilation Increase RR

22B04: Exam Report

List the physiological factors which increase respiratory rate and explain their mechanism

22% of candidates passed this question.

It was expected that candidates would provide not only a list of factors which increase respiratory rate but to give physiological reasoning behind each mechanism.

Providing a list of factors was not sufficient for a pass. Vague, imprecise answers attracted fewer marks.

A request to explain a mechanism requires the candidates to write a comprehensive physiological reasoning.

Many candidates did not demonstrate a comprehensive understanding of these mechanisms. Most answers failed to include all the stimulants of respiratory rate, especially the non-chemical controls.

Many answers were not structured or structured in a way that meant they missed many of the mechanisms or that they repeated the same information through the answer which used time but failed to gain additional marks.

F2i / 22B04: Control of Ventilation Increase RR

Respiratory Rate

  • Time taken for complete INSPIRATION, followed by EXPIRATION
  • Measured as no. of breaths / min
  • At rest 12 – 16bpm

Control of Ventilation

  • Respiratory centre in Medulla

Factors Altering to ↑RR

Send information to resp centre of Medulla

  • Chemoreceptors: ↑pCO2, ↓pO2, ↑H+
  • Higher centres: pain, fear, anxiety
  • Lung receptors: irritants, bronchoconstriction
  • Baroreceptors: ↓BP
  • Nociceptors: Pain
  • Thermoreceptors: ↑Temp
  • Joint/Muscle receptors: ↑Limb movement
  • Extremes: ↑[progesterone]


  • Detected by central (95%) & peripheral chemoR (5%) → response to ↑pCO2
  • Sensitive minute-by-minute detection
  • Peripheral work faster but greater overall response from Central ChemoR
  • Central chemoR detects Brain ECF [H+]
  • ↑CO­2 → ↑CO2 CSF → diffuses across BBB → converted
  • CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3- → ↑[H+] → ↑afferent output of central chemoR to resp centre → ↑MV
  • sensitive to ∆pCO2 because CSF has less buffering capacity cf. blood because ↓[protein] with ↑MV 2 – 3L/min for every 7mmHg ↑CO2

Peripheral chemoR

  • ↑pCO2 / ↑H+ → ↓intracellular ATP → ↑NT production & release → ↑firing afferent nerves via Vagus (X) & Glossopharyngeal (IX) → ↑MV
  • Response to ↑CO2 is linear ↑MV 2 – 3L / 1mmHg ↑CO2
  • Response is augmented by ↓PAO2


  • Peripheral chemoR = high rate of perfusion = small A-V difference → detected + rapidly respond to ∆pO2
  • Stimulated by O2 tension NOT CONTENT
  • ↓pO2 = ↓intracellular ATP = ↑intracellular Ca2+ = ↑firing T1 glomus cells = ↑firing Glossoph. + Vagus nerves → resp centre → ↑MV
  • Response to hypoxia augmented by hypercarbia
  • Non-linear response


  • Peripheral detected by peripheral ChemoR (CAROTID BODY)
  • pH sensitive K+ channels or peripheral chemoR
  • ↓intracellular ATP = ↑firing of afferents to resp C = ↑MV
  • Can also directly activate Resp Centre (Vagal input)e. DKA ↓pH, ↓pCO2, but ↑↑↑RR
  • If pH drops low enough, BBB will become permeable to H+ & central chemoR respond

Pain, fear, anxiety

  • Stimulate irritant receptors of upper airway = ↑RR

Toxins, mucous

  • Detected by bronchial C fibres = ↑RR


  • Detected by BaroR → ↑RR

Limb movement

  • Stimulates resp centre = ↑RR pre-emptively


  • ↑[Progesterone] = ↑MV


  • Detected by thermoreceptors = ↑RR