Measurement of bone blood flow using the hydrogen washout technique-part II: Validation by comparison to microsphere entrapment.

Accurate and reproducible measurement of bone blood flow has important clinical and experimental applications. Hydrogen washout is simple, safe, and widely used, but its use in bone tissue has not been validated. To this end, we have compared cortical bone blood flow measurements obtained by radioactive-labeled microsphere entrapment with those from hydrogen washout. Blood flow was measured in tibial cortical bone of 12 New Zealand White rabbits by radioactive microsphere entrapment and by hydrogen washout. Besides a control group (n = 6), four animals were treated with systemic epinephrine (0.8 microg/kg/min) (group 2) and two with nitroprusside (100 microg/kg/min) (group 3). Furthermore, nine femora from seven rats were isolated on their vascular pedicles and repeated bone blood flow measurements were made at each location with the hydrogen washout method to confirm reproducibility of blood flow determinations by hydrogen washout. An average flow of 2.3 +/- 2.0 mL/min/100 g was obtained with the microsphere method and 2.0 +/- 0.5 mL/min/100 g with the hydrogen washout method. There was a significant correlation and agreement: R(2) = 0.97 (p < 0.01). No consistent flow variations were found with systemic vasoactive drug administration. Hydrogen washout provided reproducible results and showed high sensitivity to flow changes. Hydrogen washout is both sensitive and reproducible in measuring bone blood flow. Results agree well with flow values obtained by labeled microsphere entrapment.