Valsalva manoeuvre

[Ref: PK1: p157-158; WG21:p611; KB2: p53-55]

 

 

Phase 1

(Straining starts)

BP increases, because

• Transient increase in return of blood to the left side of the heart
• Increased intrathoracic pressure transmitted directly onto the aorta

HR decreased due to increased BP

 

Phase 2

(Continued straining)

BP drops initially because of decreased cardiac output secondary to decreased venous return.

--> Stimulation of baroreceptors

--> Reflex compensation via sympathetic stimulation

Thus,

• HR increased
• Peripheral vasoconstriction

--> BP later restored (or even exceed baseline level)

Also,

• Pulse pressure decreased
• Cardiac output still decreased

 

Phase 3

(Release of straining)

BP decreases because (essentially reverse of phase 1)

• Transient decrease in return of blood due to removal of the squeeze on intrapulmonary vessels
• Removal of pressure on aorta

HR increased further [PK1:p157]

HR unchanged because the phase is very brief [KB2:p53]

 

Phase 4

(Continued relief)

Return of normal venous return to heart

--> Cardiac output returns to near normal

BP overshoots above the baseline initially because of vasoconstriction

--> Baroreceptor inhibited

--> Reflex vagal stimulation

Thus,

• HR decreased
• Peripheral vasodilation

--> BP later restored to normal

 

Abnormal responses

Diminished baroreceptor reflex

e.g. quadriplegia, diabetic autonomic neuropathy, elderly

Also in hyperaldosteronism, for unknow reason [WG21:p611]

• Excessive fall in BP in phase 2
  * Due to impaired tachycardiac and vasoconstriction response
• Absence of overshoot and bradycardia in phase 4

Congestive cardiac failure

Square-wave response seen

• Blood pressure is elevated throughout phase 2
• No overshoot in phase 4
• HR doesn't change much

May be due to increased pulmonary blood volume
--> LV filling maintained for extended periods

Beta-blocker

Less vasoconstriction/BP effect

Much smaller BP overshoot in phase 4

HR not changed much

Alpha-blocker

Lower BP during phase 2

Increased BP overshoot during phase 4

@@Why??

Use of Valsalva manoeuvre

• Assess autonomic function
• Supraventricular tachycardia
  * Increased vagal tone in phase 4 terminates SVT
• To assess certain heart murmurs
  * e.g. mitral valve prolapse

 

Valsalva ratio

• Minimum heart rate (longest R-R interval) in phase 4 divided by the maximum heart rate (longest R-R interval) in phase 2
  * In [PK1:p158], only phase 4 RR intervals are used (??print error)
• Valsalva ratio is normally greater than 1.5
• Impaired autonomic function: <1.5