In order to estimate ICF and ECF volumes 250mL of normal saline was delivered to a research subject via IV with 5 mg of inulin. Following ECF equilibration but prior to excretion, the following measurements were made [inulin]plasma = 0.0003 mg/mL.
(a) What is the estimated ECF volume based on the information given?
(b) What is the estimated ICF volume?
(c) If you were then told that the individual weighed 80 kg, how do the calculated estimates vary from the estimates you can make from body weight?
(d) The cardiac output of the subject is 4500 mL/min and the kidneys receive 20% of the cardiac output (i.e. Renal blood flow, RBF = 0.20*CO; Renal plasma flow (RPF) = RBF*hematocrit, Hct, fraction of blood that is cells). Hct=0.45. The subject urinates after 1 hour and it is found that Vurine=187 mL, [inulin]urine=0.012mg/mL. Calculate the filtration fraction.