title: Extended measurement of glomerular filtration rate and effective renal plasma flow in ambulatory patients.
abstract: We describe a standardized clearance method over 5 h (one hour equilibration followed by eight consecutive 30 min clearance periods [period 2-9]) for the estimation of GFR (iothalamate I125) and ERPF (hippuran I131) during water diuresis in ambulatory and exercising patients. Four groups were examined. In group I (normal controls, n = 15) there were no significant changes in GFR, ERPF and FF (P > 0.10) during repeated clearance periods (mean of period 2-5 versus period 6-9). The reproducibility of the method was studied at a mean interval of 3.7 weeks in a group of patients with stable reduction of GFR (group II, n = 7). The values for GFR, ERPF, FF and RVR did not change significantly in this group, and correlated significantly between repeated studies (r = 0.81 to r = 0.99). In group III (untreated hypertensive patients with reduced GFR, n = 13) there was a time dependent 7.2% decrease in GFR (P < 0.05), significantly different from group I (P < 0.02), a 10.0% decrease in ERPF (P < 0.01) and no significant change in FF (P = 0.08) when the mean of period 2-5 was compared with the mean of period 6-9. In healthy controls (group IV, n = 8) light sustained bicycle exercise (25 W) induced a 7.1% decline in GFR (P < 0.01), 17.4% decline in ERPF (P < 0.001) and a 13.6% increase in FF (P < 0.001). We conclude that ambulatory measurements of GFR and RPF can be carried out over a period of 5 h with satisfactory precision and repeatability. Ambulatory hypertensive patients with moderately reduced GFR showed the same degree of time dependent downward drift of GFR and ERPF without exercise as was seen in healthy individuals during light exercise. Accordingly, in these groups single clearance periods imply a risk for under or overestimation of renal function, and time controls are necessary during clearance studies.
authors.affiliation: Medical Department A, University of Bergen, Norway.
authors.forename: E
authors.initials: E
authors.lastname: Svarstad
authors.forename: B M
authors.initials: BM
authors.lastname: Iversen
authors.forename: J
authors.initials: J
authors.lastname: Ofstad
mesh_terms: D000328:Adult; D000368:Aged; D000553:Ambulatory Care; D001783:Blood Flow Velocity / Q000502:physiology; D002908:Chronic Disease; D005080:Exercise Test; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D005921:Glomerulonephritis / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D006973:Hypertension / Q000175:diagnosis / Q000503:physiopathology; D007465:Iodohippuric Acid; D007483:Iothalamic Acid; D007668:Kidney / Q000098:blood supply*; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009400:Nephrosclerosis / Q000175:diagnosis* / Q000503:physiopathology; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D007465:Iodohippuric Acid; D007483:Iothalamic Acid