Frequently Asked Questions
 

What physiological parameters does OxyFlo™ measure?

Our range of laser Doppler blood flow monitors are intended for the investigation of blood flow (also knows as blood perfusion or microvascular blood flow) in the microcirculation. The laser Doppler technique is well-established as the most convenient method for assessing tissue blood flow non-invasively and continuously. The technique allows continuous assessment of flow at one or more tissue sites via fibre-optic probes in contact with the tissue. The measurement of microvascular blood flow provides researchers with critical information in a number of research applications where blood supply has been disrupted (ischaemia). The technique is not intended for the measurement of blood flow rates in isolated blood vessels.

What makes the OxyFlo™ unique?

While substantially equivalent to other laser Doppler monitors on the market, our OxyFlo™ monitors offer a number of distinguishing key features. Most notable of these is their ability to operate in conjunction with our counterpart oxygen monitors for combined tissue oxygen, blood perfusion and temperature monitoring from a single sensor and therefore the same tissue micro-region. Furthermore, our multi-channel OxyFlo™ Pro models offer an industry-first touch-screen display and user interface as well as an advanced, intelligent signal noise suppression output (ART™).

What are the typical applications for your instruments?

Our instruments have proved popular in applications covering such disciplines as peripheral vascular disease, cerebral perfusion monitoring in models of stroke and brain injury, tumour perfusion monitoring / angiogenesis, blood flow in free flaps and pedicle flaps, wound healing, gastroenterology and more.

How do your blood perfusion instruments work?

Our blood perfusion monitors utilise the well-established method of laser-Doppler Flowmetry (LDF) to provide a continuous measure of tissue blood blow. LDF works by illuminating a small region of tissue under observation with low power laser light from a sensor containing optical fibre light guides. Laser light from one fibre is directed towards the tissue and is scattered within the tissue. Some of the scattered laser light is incident upon moving red blood cells within the tissue and this light becomes Doppler-frequency shifted as a result. A second optical fibre collects this backscattered, Doppler-shifted light from the tissue and returns it to the detector within the monitor. The photo-detected signal comprises a broad spectrum of Doppler frequency shifted signals generated as a result of the movement of red blood cells within the tissue. Microvascular blood flow is electronically calculated as the product of mean red blood cell velocity and mean red blood cell concentration in the volume of tissue under illumination from the sensor.

What are your blood flow probes made of and how large are they?

All our blood flow probes are constructed internally from glass or specialist plastic optical fibre light guides, terminating in needle, surface or other, specialist conformations designed to support the measurement of blood flow from almost any tissue. Probes are typically supplied in 3 m lengths and composed of specialist surgical steel, medical grade plastic and silicone materials. See here for a full list of available blood flow probe types.

Do your blood flow monitors support the use of multiple probes at the same time?

Yes, the OxyFlo™ Pro is a two-channel monitor, while the OxyFlo™ Pro XL is a four-channel monitor capable of simultaneously driving and reading from up to 4 blood flow probes simultaneously. This allows the simultaneous collection of physiological blood flow data from up to four separate tissue sites at the same time, which may for example be useful when comparing pathological versus control tissue sites (e.g. contralateral cerebral perfusion). The ability to monitor from more than one tissue site can also be useful in mitigating for natural site to site blood flow variability by allowing multi-site signal averaging.

Are your blood flow probes supplied sterile?

No. While we manufacture blood flow probes in a clean room environment, they are not supplied sterile. Our blood flow probes can however be disinfected using 70% IMS or ethanol, and can be sterilized using industry-standard liquid sterilizers (e.g. Cidex®) or the low-temperature ethylene oxide gas method. Note that neither our blood flow probes, nor our blood flow monitors possess CE or FDA regulatory approval for use in human subjects.

What is the sampling volume of your blood flow probes?

For most tissues the mean sampling depth is in the region of 0.5 – 1.5 mm with a typical sampling volume in the region of 1 mm3. These values could be higher in regions where reduced photon absorption would be expected due to depleted erythrocyte concentration. These values have been obtained heuristically through many years of experience and are based on both in vitro observations and mathematical modelling of photon diffusion through ‘imaginary tissues’ using Monte-Carlo techniques.

What are the units of blood flow measurement?

The laser-Doppler technique for tissue blood flow measurement provides arbitrary, non-absolute, units for blood perfusion since the actual sampling volume/depth can only be determined by identifying which erythrocytes have interacted with the light remitted from the tissue, which in turn, is principally dependant on two parameters; namely the optical scattering and the optical absorption coefficients of the tissue under observation. Since both of these coefficients are entirely dependent on the site of observation and perfusion of the microvasculature at the time of measurement, it is impossible to determine the actual sampling volume at any tissue site and thus to express the measured component in absolute terms. The strengths of the laser-Doppler technique lie in observing continuous and quantifiable changes relative to baseline (control) measurements.

Do your tissue blood flow monitors possess regulatory approval for clinical use?

No. At this time our blood flow monitors and probes do NOT possess CE or FDA regulatory approvals for use on human subjects.

Do you offer on-site demonstrations of your instruments?

Yes, depending on geographical location we will try to arrange for an on-site demonstration of our products by an experienced product specialist. Ideally this will involve a full simulation of your application in order to maximise the benefit of the demonstration. On-site demonstrations are usually free of charge and can typically be arranged at 2 – 8 weeks notice. Alternatively we can also arrange for a limited free trial of our monitors and sensors.