Real-time contrast imaging: a new method to monitor capillary recruitment in human forearm skeletal muscle.
OBJECTIVE
Muscle capillary perfusion can be measured by contrast-enhanced ultrasound. We examined whether a less time-consuming ultrasound technique, called "real-time imaging," could be used to measure capillary recruitment in human forearm skeletal muscle.


METHODS
We measured microvascular blood volume and microvascular flow velocity using bolus injections of contrast microbubbles after forearm muscle exercise and a two-hour infusion of insulin into the brachial artery (both associated with capillary recruitment) and after sodium nitroprusside infusion (no changes in flow distribution).


RESULTS
After an intravenous bolus injection of the contrast agent, the steady-state concentration of contrast agent in forearm muscle lasted long enough (approximately 190 seconds) for the duration of the measurements (which take 70-80 seconds), rendering the continuous infusion of microbubbles unnecessary. Microvascular blood-volume measurements showed a good short-time reproducibility and a good reproducibility after repositioning of the forearm. Reproducibility of microvascular flow velocity was too low. Exercise and insulin infusion both increased microvascular blood volume, consistent with capillary recruitment. Sodium nitroprusside had no effect.


CONCLUSIONS
Real-time contrast imaging, after bolus injections of an ultrasound contrast agent, provides reliable information about capillary recruitment in human forearm skeletal muscle, and may offer a valuable tool in studying human (patho)physiology.
Mulder
Alexandra H
AH
Departments of Medicine, Division of General Internal Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
van Dijk
Arie P J
AP
Smits
Paul
P
Tack
Cees J
CJ
D000328:Adult; D002196:Capillaries / Q000000981:diagnostic imaging / Q000502:physiology; D003287:Contrast Media; D015444:Exercise / Q000502:physiology; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage; D007328:Insulin / Q000008:administration & dosage; D008297:Male; D008955:Models, Cardiovascular; D018482:Muscle, Skeletal / Q000098:blood supply*; D009599:Nitroprusside / Q000008:administration & dosage; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology*; D015203:Reproducibility of Results; D013997:Time Factors; D014463:Ultrasonography / Q000295:instrumentation / Q000379:methods* / Q000592:standards*; D014665:Vasodilator Agents / Q000008:administration & dosage
D003287:Contrast Media; D007004:Hypoglycemic Agents; D007328:Insulin; D014665:Vasodilator Agents; D009599:Nitroprusside