G5ii: What is the Valsalva manoeuvre? Explain the cardiovascular response & include graphs in your answer

Definitions

Valsalva = the action of forced expiration against a closed glottis after full inspiration

Aim: To Test Autonomic Function

  • Uses the CVS feedback loop (sensor → C → effector) known as the BaroReceptor
  • To cause maximal vagal outflow
  • To terminate AVNRTs

Phases:

  • 4 phases of P/Vol ∆ in Great Vessels
  • With resultant ∆ in SNS/PNS outflow from vasomotor centre
  • Named for Italian Anatomist who first used it to expel pus from middle ear

ITP = intrathoracic pressure, ITBV = intrathoracic blood volume, BP = blood pressure, BAROR = Baroreceptor, HR = heart rate

Phase 1: Onset of Straining

    • ITP – sharp ↑ITP
    • ITBV – expels blood from thoracic vessels = ↑CO
    • BP – ↑BP (BP = CO x SVR)
    • BAROR – Detect high P → inhibits symp. outflow & ↑parasymp. outflow
    • HR – ↓HR

Phase 2: Sustained Straining

  • ITP – remains high
  • ITBV – low (high ITP prevents blood returning to thorax)
  • BP – ↓BP
  • BAROR – ↓afferent d/c to vasomotor centre NTS releases symp. inhibition → ↑symp. outflow
    • H = ↑HR, ↑FoC
    • Resistance Vessels = VC = ↑SVR
    • Capacitance Vessels = VC = ↑VR
  • HR – ↑HR

Phase 3: Release of Glottic Pressure

    • ITP – pressure released → returns to normal
    • ITBV – venous blood pools in pulm. vessels ∴LV preL ↓ → by F-S → ↓CO → ↓BP
    • BP – ↓BP
    • BAROR – Cont to ↓afferent d/c
      • Vasomotor centre cont. ↑ symp. outflow to restore BP
    • HR – ↑HR

Phase 4: Overshoot

  • ITP – normal
  • ITBV – restored to R & L side of heart
  • BP – ↑BP
  • BAROR – Overshoot of BP (↑CO to VC peripheries)
    • Detected by BaroR
    • Vasomotor centre:

→ Inhibits symp. outflow

→ Profound vasal response

  • HR – ↓↓↓HR

AVNRT Termination

  • AVNRT caused by rapid depol. through AV Node
  • Vagal stimulus releases ACh at mAChR
  • ↓cAMP intracellularly
  • ↓Ca2+ release
  • ↓slope of Ph 0 cardiac cell (which is Ca2+ depolarisation)
  • Slows conduction
  • Prolongs refractory period
    • -VE DROMOTROPY
  • Hopefully interrupts re-entry circuit of AVNRT
AVNRT Termination
AVNRT Termination1

Abnormal Valsalva

Square Wave Response

    • Pericarditis, tamponade, CCF
    • AII ↑CVP
    • ∴BP remains high through manoeuvre & returns to normal at the end
Square Wave Response

Autonomic Dysfunction

  • BP falls & remains low until intrathoracic P is released
  • Absent ∆HR
Autonomic Dysfunction

Hypovolaemia/Ventilated

    • Changes are exaggerated