Impedance cardiographic measurement of the physiological response to the Valsalva manoeuvre

The Valsalva manoeuvre was performed, with airway pressures of 10, 20, 30, 40 and 50 mmHg, on 11 healthy male subjects in both the standing and supine positions, and was evaluated with impedance cardiography using the Minnesota impedance cardiograph. Along with the impedance waveform, the output of a finger photoplethysmograph was recorded. The ratios of the amplitude of the finger and impedance pulses at the end of a 10s strain phase during the Valsalva manoeuvre were compared with those of the control period. The results in the standing position showed the impedance ratio changed from 0.81 to 0.61 as the airway pressure increased from 10 to 50 mmHg, whereas, over the same pressure range, the finger pulse ratio changed from 0.44 to 0.21. In the supine position, the response was similar to that for standing for most pressures. Upon release of the pressure, the impedance showed an immediate, large decrease, which suggests a significant right-heart and vena cava component in the impedance cardiographic signal. The results show that the impedance signals responded similarly to those of previous studies of central arterial pressure during the Valsalva manoeuvre, whereas the finger pulse decrease was approximately twice as much.