SPECTRAL-ANALYSIS OF BLOOD-PRESSURE VARIABILITY IN HEART-TRANSPLANT PATIENTS

The cardiac transplant patient provides a unique model for the study o f blood pressure variability in the absence of heart rate variability. We examined the harmonic and fractal components of blood pressure var iability in 14 heart transplant patients (12 men, 2 women; 21 to 62 ye ars of age) and in age-and sex-matched control subjects during seated rest, supine rest, and supine rest with fixed-pace breathing (12 respi rations per minute). Heart rate was faster in transplant patients than in control subjects, with much less heart rate variability (P < .0001 ). Spectral analysis of blood pressure variability revealed no differe nce in total power for either systolic or diastolic pressure, but tran splant patients had less low-frequency (0 to 0.15 Hz) harmonic spectra l power in both systolic (P < .01) and diastolic (P < .03) pressure an d more high-frequency power (0.15 to 0.5 Hz) in diastolic pressure tha n control subjects. The ratio of high-frequency power in diastolic rel ative to systolic pressure was consistently higher (P < .0001) in the transplant patients (0.29 to 0.51) than in control subjects (0.11 to 0 .13). The slope of the fractal component of systolic pressure was appr oximately 1.8 in both transplant patients and control subjects. This w as greater than the slope for heart rate variability (approximately 1. 1 in control subjects). These data provide clear evidence of independe nce of the fractal component of heart rate and blood pressure variabil ities in both transplant patients and control subjects. The heart rate component of the arterial baroreflex minimized high-frequency diastol ic pressure changes while contributing to low-frequency variations in both systolic and diastolic pressures.