5.2. Abnormal blood pressure pulse
It is interesting to know whether the changes in the shape of the pressure profile can be registered if the pressure pulse changes. These results are presented in the original paper III. To achieve an abnormal pressure pulse, the blood pressure is manipulated by performing the so-called Valsalva manoeuvre. The Valsalva manoeuvre is used in medical research to study autonomic regulation (Sovijärvi et al. 1994). In the Valsalva manoeuvre the volunteer exhales against a pressure of 40 mmHg for 10 seconds. This blocks the vein returning to the heart. The resulting reduced blood flow decreases the blood pressure, which stimulates the heart to work more actively to maintain normal blood pressure. Fig. 17 presents the RR interval, MAP and PTT between heart and wrist during this manoeuvre.
The exhalation phase is timed between 13–25 seconds. The MAP decreases due to the decreased vein return to the heart. The RR interval also decreases, reflecting the increased activity of the heart. The PTT between heart and wrist increases from 0.13 seconds at the beginning to 0.21 seconds at the end of the Valsalva manoeuvre. This can be explained by the elasticity changes in the arterial tree. When the MAP decreases the elasticity of the arterial tree increases. Thus, more of the energy of the pressure pulse can be stored in the arterial wall and this retards the velocity of the pressure pulse.
The blood pressure signal and the reconstructed Doppler spectrogram from the corresponding pulses during the exhalation phase of the Valsalva manoeuvre are shown in Fig. 18. The diastolic blood pressure decreases dramatically due to the reduced blood flow. In addition, the pulse pressure decreases to 20 mmHg and the shape of the pulsation is significantly altered from Fig. 16. However, the Doppler spectrogram follows the pressure variation exactly. The peaks in the Doppler spectrogram correspond to the maximums of the derivative of the blood pressure signal. The radial displacement is 25 m on the rising edge of the blood pressure pulse.
