Abnormal diurnal variation of blood pressure, cardiac output, and vascular resistance in cardiac transplant recipients.

BACKGROUND An attenuated or absent nocturnal decline in blood pressure has repeatedly been documented in cardiac transplant recipients. The present study was aimed at investigating the hemodynamic mechanism underlying this abnormality. METHODS AND RESULTS In 23 cardiac transplant recipients (11 to 36 months after transplantation) and in 23 control subjects matched for age and 24-hour mean arterial pressure, invasive 24-hour ambulatory blood pressure was measured by means of the Oxford technique. Beat-to-beat relative values of stroke volume were determined by means of a pulse-contour method, and relative changes of cardiac output (stroke volume x heart rate) and total peripheral vascular resistance (blood pressure/cardiac output) over the 24-hour period were calculated. The nocturnal decline in blood pressure was 20 +/- 8% (mean +/- SD) in control subjects but only 5 +/- 9% (P < .001) in cardiac transplant recipients. In control subjects, the nocturnal decline in blood pressure was associated with a nocturnal fall in cardiac output of 24 +/- 13%, whereas vascular resistance compared with daytime value did not change. The small nocturnal decline in blood pressure in cardiac transplant recipients was associated with an attenuated nocturnal fall in cardiac output of 14 +/- 12% (P < .05 versus control subjects). In addition, vascular resistance compared with daytime value was increased by 9 +/- 9% (P < .05) during the night. Both in cardiac transplant recipients and in control subjects, the nocturnal changes in blood pressure were correlated with the nocturnal changes in cardiac output but not with the nocturnal changes in total peripheral vascular resistance. CONCLUSIONS This study confirms the attenuated nocturnal fall in blood pressure in cardiac transplant recipients. Hemodynamically, this attenuated blood pressure decline is characterized by a reduced nocturnal fall in cardiac output, and it is associated with a nocturnal increase in vascular resistance.