title: Hemodynamic responses to head-up tilt in uremic patients.
abstract: The hemodynamic responses to 45 degrees C head-up tilt for 30 min were compared between a group of 13 normal healthy subjects, 16 patients with end-stage renal failure (Group 1) and 9 hypertensive patients (Group 2). In the normal subjects there was no change in systolic blood pressure (SBP), a significant increase in diastolic blood pressure (DBP) (9 +/- 1 mmHg, mean + SEM, p less than 0.01), heart rate (HR) (11 +/- 2 beats/min) and derived peripheral resistance (PR) (66 +/- 8%, p less than 0.001). Stroke volume (SV) and cardiac output (CO) fell significantly by 42 +/- 3% and 33 +/- 3%, respectively. The responses in Group 2 patients were similar to those of the controls. However in Group 1 patients, though there was a rise in heart rate (9 +/- 2, p less than 0.001), SBP fell significantly accompanied by no change in either DBP or PR. The decrease in SV was only 12 +/- 4% while there was no change in derived CO. The results suggest that there was a lack of vasoconstriction during postural stress in patients with endstage renal failure, which was probably due to a functional defect in the baroreceptor reflex. Concomitantly, the small decrease in SV suggests stiffness of the veins and/or active venoconstriction which may help to prevent a bigger fall in blood pressure.
authors.affiliation: Institute of Urology, London.
authors.forename: C H
authors.initials: CH
authors.lastname: Kong
authors.forename: F D
authors.initials: FD
authors.lastname: Thompson
mesh_terms: D000328:Adult; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D008297:Male; D011187:Posture / Q000502:physiology*; D013997:Time Factors; D014511:Uremia / Q000503:physiopathology*; D014661:Vasoconstriction / Q000502:physiology