Validation of transit-time flowmetry for chronic measurements of regional blood flow in resting and exercising rats

ABSTRACT

The objective of the present study was to validate the transit-time technique for long-term measurements of iliac and renal blood flow in rats. Flow measured with ultrasonic probes was confirmed ex vivo using excised arteries perfused at varying flow rates. An implanted 1-mm probe reproduced with accuracy different patterns of flow relative to pressure in freely moving rats and accurately quantitated the resting iliac flow value (on average 10.43 + 0.99 ml/min or 2.78 + 0.3 ml min(-1) 100 g body weight(-1)). The measurements were stable over an experimental period of one week but were affected by probe size (resting flows were underestimated by 57 per cent with a 2-mm probe when compared with a 1-mm probe) and by anesthesia (in the same rats, iliac flow was reduced by 50-60 per cent when compared to the conscious state). Instantaneous changes of iliac and renal flow during excercise and recovery were accurately measured by the transit-time technique. Iliac flow increased instantaneously at the beginning of mild exercise (from 12.03 + 1.06 to 22.55 + 3.89 ml/min at 15 s) and showed a smaller increase when exercise intensity increased further, reaching a plateau of 38.43 + 1.92 ml/min at the 4th min of moderate exercise intensity. In contrast, exercise-induced reduction of renal flow was smaller and slower, with 18 per cent and 25 per cent decreases at mild and moderate exercise intensities. Our data indicate that transit-time flowmetry is a reliable method for long-term and continuous measurementes of regional blood flow at rest and can be used to quantitate the dynamic flow changes that characterize exercise and recovery.