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Non-invasive Flow

Non-invasive measurement of blood flow in humans is commonly made using techniques applicable to fore-arm blood flow. For a short discussion of techniques, please see our application note. Components shown here are for fore-arm flow measurement using strain-gauge plethysmography (SPG).

Strain Gauges

We supply strain gauges from Hokanson which are ideal for measuring the circumferential dilation of the limb after venous occlusion. The gauges simply loop around the limb and hook back onto a hook moulded into the cable connector. Gauges have a limited stretch and must be ordered to suit the limb circumference. Sets of gauges (in 2 cm increments) are available. Gauges are either mercury or gallium-indium - the latter are more expensive but have a longer life.

Strain Gauge Amplifier

It may be possible to connect a strain gauge to your data acquisition system using a standard acquisition system amplifier (it is possible with BIOPAC). If not, you may need a dedicated plethysmography amplifier to which to connect the gauge. The Hokanson EC6 is an accurate, easy to use strain gauge amplifier, and is the lowest cost strain gauge plethysmograph with in-situ electrical calibration. The EC6 will handle mercury strain gauges from 3 to 50 cm and Indium-Gallium gauges from 5 to 50 cm. A high-level output for your data acquisition system is available via a jack connector.

Occluding Cuffs

We can supply a variety of occluding cuffs from Hokanson, but the cuffs that we particularly recommend for fore-arm blood flow are the SC10D size. These are 11 x 85 cm overall, and are fitted with a very large bore tubing connector to allow for rapid inflation (and deflation) - especially important for finding the initial rate of limb swelling due to arterial inflow.

Narrow cuffs for a wrist tourniquet, and other cuffe sizes for the lower limb, are also available.

Cuff Inflator

For rapid and easy inflation of the occluding cuff, we recommend the E20 Rapid Cuff Inflator from Hokanson, together with the AG101 Air Source. The E20 inflates any cuff in 0.3 sec, holds the pressure indefinitely or for whatever time your protocol needs and then deflates the cuff in 0.3 sec. Works every time no matter the size of the cuff or leg. Simply dial in the pressure needed, and push the button for inflation and then push the button to deflate. A built-in cycle timer is available as an option.

The AG101 is a whisper-quiet matching air compressor, which is dependable and of adequate capacity to repetitively inflate an occlusion cuff.

Data Acquisition

To acquire the results of repeated limb occlusions and to actually measure the corresponding flow, we recommend a BIOPAC data aquisition system. This makes the analysis particularly easy - a cursor is dragged over the relevant period of the waveform and the resulting least-squares slope transferred to a journal (log) with a single keystroke. The BIOPAC system is available for either Windows or Macintosh, and can be expanded for a whole range of other physiological measurements.

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