Assessment of beat to beat changes in cardiac output during the Valsalva manoeuvre using electrical bioimpedance cardiography.

Beat to beat changes in cardiac output during standardized Valsalva's manoeuvres were recorded using electrical bioimpedance cardiography in 13 normal subjects. Cardiac output increased by 12 +/- 5% after 1 s of straining solely because of an increase in heart rate. Subsequently, cardiac stroke volume and cardiac output fell during the strain to lows of -40 +/- 6% and -21 +/- 3% respectively at 15 s. There was a sustained increased in cardiac output (maximum +17 +/- 4%) in the late post strain period. The mean coefficient of variation in impedance measurements of cardiac output was 6.8% during all parts of Valsalva's manoeuvre, with no single value exceeding 10%.