Ppa and flow signals were recorded after the pulmonary catheter was then carefully withdrawn to position its tip just above the pulmonary valve, as close as possible to the pulsed Doppler pulmonary artery flow-velocity sampling site. The signals were visually checked for quality, and then were synchronized by an ECG artifact and recorded on paper at a speed of 100 mm/s using the built-in printing system of the echocardiograph. Pressure and flow-velocity tracings were scanned (Scanjet 4470c; Hewlett Packard), digitized at a sampling rate of 200 Hz, and analyzed on a personal computer. Between three and five heartbeats were used for the analysis during each data collection period. For each patient, a series of thermodilution cardiac outputs and concomitant average Doppler flow velocities were used to calculate a conversion factor for the flow-velocity tracings into volume flow. Link
The PVZ spectrum was calculated from the Fourier series expressions for pressure and flow signals, as previously de-scribed. Zc was calculated as the average of the impedance wave reflection factor (RF) moduli between 2 and 15 Hz. A wave RF was calculated as (Z0 — Zc)/(Z0 + Zc), where Z0 is impedance at 0 Hz. First harmonic impedance (Z1), the first minimum frequency of the ratio of pressure and flow moduli (Fmin), and the frequency of the zero crossing of the impedance phase angle (F0 cross) were also determined.
A complete set of pulmonary hemodynamic measurements and sampling of the instantaneous pressure and flow signals was obtained at baseline, with the patients in a stable state, as assessed by unchanged HR and pulmonary vascular pressures for at least 15 min. The measurements were repeated in 17 patients after 10 min of breathing nitric oxide (NO) [10 to 20 ppm], and epoprostenol administration slowly increased until intolerance (ie, a fall in Psa, facial flush, headache, jaw pain) had occurred to an average of 8.5 ng/kg/min in 5 other patients. In addition, after a washout period of 20 min, and a return of Ppa, HR, and Psa values to baseline levels, a complete set of hemodynamic measurements, and a sampling of pressure and flow signals was obtained at the 15th min of an infusion of dobutamine at a dose of 8 ^g/kg/min.