Performing the valsalva maneuver tests the body’s ability to compensate for changes in the amount of blood that returns to the heart (preload). The changes in heart rate and blood pressure observed during this test are regulated by the autonomic nervous system. Patients with autonomic dysfunction will therefore have changes in heart rate and/or blood pressure that differ from those expected in healthy patients.
The test consists of blowing against resistance for several seconds, then relaxing. As soon as a person begins to blow, the sudden increase in chest and abdominal pressure forces blood out of the chest and down the arms. This increases blood pressure briefly (phase I). Soon afterwards, the amount of blood ejected by the heart with each beat (stroke volume) plummets, because the straining decreases entry of blood from the veins into the heart. Blood pressure progressively falls (phase II). The brain senses this fall and a rapid decrease in outflow in the parasympathetic nervous system to the heart. The increase in nerve traffic leads to more release of norepinephrine, which tightens blood vessels throughout the body. When the patient relaxes at the end of the maneuver (phase III), briefly, the blood pressure falls, but then blood rushes back into the chest and within a few heartbeats, the heart ejects this blood. The blood pressure increases (phase IV) and since the blood vessels are constricted, produces an overshoot of blood pressure, outflow to blood vessels falls and in response to this increase in blood pressure the heart rate falls. The pattern of these various perturbations gives physicians important information about both sympathetic and parasympathetic function.