Impact of Heart Rate on Ventilation and Pulmonary Perfusion Associated Impedance Changes

Abstract

The potential of electrical impedance tomography (EIT) to assess perfusion changes in the lung has already been demonstrated in several studies. Methods like frequency domain filtering, principal component analysis or breath holding have been introduced. Since EIT is noninvasive and radiation-free, it depicts a promising supplement to current methods such as single photon emission computed tomography. In our study we investigated ventilation and pulmonary perfusion associated impedance changes as a function of heart rate in four healthy spontaneously breathing subjects. EIT measurements were conducted during physical exercises on a bicycle ergometer to get various heart rates. EIT data were acquired at three to four different heart rates in the 3rd and 5th intercostal space (ICS), respectively. Spirometry was performed simultaneously to determine tidal ventilation. A Fast Fourier Transform and frequency domain filtering were applied to separate ventilation from pulmonary perfusion signals. Ratios of ventilation and pulmonary perfusion related impedance changes ∆IV/∆IQ were calculated in a predefined region of interest within the different thorax planes. All subjects showed a higher gain in ∆IV/∆IQ dependent on heart rate in the 3rd ICS than in the 5th ICS. It was observed that in all subjects pulmonary perfusion associated impedance amplitudes increased stronger in the 5th ICS compared to the 3rd ICS. Minute volumes determined by spirometry (MVspiro) featured similar trends like minute variations calculated with ventilation related impedance amplitudes (MVEIT). EIT measurements could reliable conducted on spontaneously breathing subjects during physical exercises. Separation of ventilation and pulmonary perfusion associated impedance changes was successfully achieved by frequency domain filtering within the different thorax planes for all subjects.