DO CHANGES IN FRACTION OF INSPIRED OXYGEN AFFECT PULMONARY-ARTERY ACCELERATION TIME

Pulmonary artery (PA) pressure is difficult, but important, to estimate by noninvasive methods. Accordingly, numerous noninvasive methods have been used. Perhaps the most accurate noninvasive method is determination of tricuspid regurgitation velocity gradient, which estimates instantaneous difference between right atrial and ventricular systolic pressure. In the absence of pulmonary stenosis and with addition of right atrial pressure, the result can be used to approximate PA pressure.1 Reliable recording of tricuspid regurgitation in some individuals, however, has proven difficult. Accordingly, many centers have used the inverse relations between PA pressure and PA acceleration time to predict PA pressure.2 PA acceleration time is derived from Doppler PA velocities. Although PA acceleration time has been used to estimate PA pressure, full characterization of the measurement has yet to be determined. PA acceleration time has been reported to vary over a small range in adults (75 to 170 ms)2 and a smaller range in children (51 to 140 ms).3 Ranges are not truly continuous because the Doppler waveform is obtained by intermittent Fourier analysis, a method that depends on a time history of the waveform, especially for low velocities such as those inscribed at the very beginning of systole. Finally, information is unavailable to suggest whether PA acceleration time is variable for a given individual as the result of small changes in PA pressure. Alveolar oxygen partial pressure alteration inversely affects PA pressure and vascular resistance.4 Accordingly, increased fraction of inspired oxygen should decrease PA pressure and resistance and lengthen the PA acceleration time. Conversely, lowering inspiratory oxygen percentage below room air should increase PA pressure and resistance and shorten PA acceleration time. The hypothesis for this study is that PA acceleration time is variable for a given individual and that changes in fraction of inspired oxygen cause inverse changes in PA acceleration time. © 1990.