Phases of the Valsalva Maneuver
The Valsalva maneuver consists of four distinct hemodynamic phases that occur during and after forced expiration against a closed glottis.
The Four Phases
Phase I: Onset of Strain
- Immediate increase in intrathoracic pressure when the patient begins bearing down
- Transient rise in systolic blood pressure (SBP) due to compression of the aorta and increased intrathoracic pressure
- Brief increase in venous return to the left ventricle
- This phase lasts only a few seconds at the initiation of the maneuver 1
Phase II: Continued Strain (Early and Late Components)
This phase has two distinct components:
Phase II Early (II_E):
- Decreased venous return due to sustained elevated intrathoracic pressure
- Progressive fall in cardiac output and blood pressure
- The magnitude of this decrease becomes more pronounced with age and higher baseline blood pressure 2
Phase II Late (II_L):
- Compensatory sympathetic activation occurs
- Reflex tachycardia and peripheral vasoconstriction attempt to maintain blood pressure
- Blood pressure begins to recover despite continued strain
- This compensatory response becomes attenuated with increasing age 2
Phase III: Release of Strain
- Abrupt drop in blood pressure immediately upon release of expiratory pressure
- Sudden decrease in intrathoracic pressure causes blood to pool in pulmonary vessels
- Transient reduction in left ventricular filling
- This is the briefest phase, lasting only 1-2 cardiac cycles 1
Phase IV: Recovery/Overshoot
- Marked overshoot of blood pressure above baseline (reactive hyperemia)
- Reflex bradycardia occurs due to baroreceptor activation
- Enhanced venous return combines with residual peripheral vasoconstriction from Phase II
- Represents the most profound hemodynamic change, with cerebral autoregulation being least effective during this phase 1
- Blood pressure and heart rate gradually return to baseline values
Clinical Relevance
The proper technique requires the patient to raise intrathoracic pressure by bearing down against a closed glottis for 10-30 seconds, equivalent to at least 30-40 mm Hg 3. The maneuver should be performed with the patient in the supine position for optimal effectiveness 3.
Key Hemodynamic Effects by Phase:
- Phases II and III: Decreased cerebral blood flow and oxygenation, with Phase III showing the greatest reduction (up to -19 cm/s in middle cerebral artery velocity during intense maneuvers) 1
- Phase IV: Reactive hyperemia with increased cerebral perfusion and the characteristic blood pressure overshoot that terminates supraventricular tachycardias 1
Important Technical Considerations:
- Lung volume matters: Maneuvers initiated from end-expiratory lung volume produce significantly greater blood pressure changes and decreased R-R intervals throughout all phases compared to those initiated from total lung capacity 4
- Reproducibility: The Valsalva ratio (Phase IV/Phase II blood pressure) and total recovery are highly reliable quantitative parameters (ICC >0.89) 5
- Age affects the response, with older patients showing progressively more negative Phase II_E and attenuated Phase II_L 2
The four-phase response forms the physiologic basis for using the Valsalva maneuver to terminate narrow-complex tachycardias, with success rates of 20-30% using standard technique and up to 50% with modified approaches 6.