Applications

Intestinal And Gastric Mucosal Perfusion

The Gut includes all mucosal surfaces from oesophagus through the stomach, duodenum, intestines, colon and rectum. Laser Doppler has been used to assess mucosal blood flow and a range of functions at these sites.

Laser Doppler Montoring

Ohri et al, 1993, studied the effect of cardiopulmonary bypass (CPB) on the gastric mucosa of adults (GI damage occurs in up to 2% of patients on CPB with significant mortality). They used a wet-stick (P10e) probe, positioned in the gut following retrograde insertion in a naso-gastric tube. This enabled laser Doppler (LD) measurements to be taken with increased stability. Observations included profound reductions in mucosal blood flow during hypothermic phase of CPB despite maintenance of mean arterial pressure (MAP) and flow. A close relationship between core temperature and gastric mucosal blood flow (GMBF) was found, and also between MAP and GMBF.

The current equipment recommended by Moor Instruments for this type of study would be:

moorVMS-LDF with a VP10M200ST master probe and coupler connected to a P10k wet stick probe.

Booker et al, 1996, assessed the effect of CPB on neonatal gut mucosal blood flow at the rectum (Booker et al 1996a) and investigated the effect of hypothermia/re-warming (Booker et al 1996b); it was found that neonates requiring aortic arch surgery may be at particular risk of gut mucosal hypoxia before and after surgery; with regard to temperature, LDF was reduced during cooling but was lowest during the re-warming phase.

For these measurements a special, sprung probe was designed to keep the active area of the LD probe in contact with the rectal mucosa (VP6ds).

Emmanuelle et al, 1999, found LDF to be a highly reproducible and studied the effect on rectal mucosal blood flow of eating, smoking, body size, sex, ovulatory status and menstrual phase . Changes in mucosal blood flow induced by autonomically active drugs and nerve stimulation confirm the role of the mucosal microcirculation as a measure of extrinsic nerve activity. Emmanuelle et al (2000) used LDF in a similar way showed that patients with idiopathic constipation have impaired extrinsic gut nerve activity, particularly in those with slow transit. The influence of psychological factors was also investigated (Emmanuelle et al, 2001).

In these studies, patients were measured in a room maintained at 22°C after 15 minutes of acclimatisation, in the left lateral position. After digital examination and rigid sigmoidoscopy had confirmed the rectum to be empty, the laser Doppler probe was introduced via the sigmoidoscope. Recordings were made at 10 cm from the anal verge at four points circumferentially at 90° to each other, with results averaged to reduce variance. Readings were taken after the trace had stabilised for 30 seconds. A standard VP6a endoscopic probe was used.

Laser Doppler and Speckle Contrast Imaging

Hajivassiliou et al, 1998, assessed blood flow distributions in human colon during operations on six controls and six patients with inflammatory bowel disease undergoing colectomy. Ischaemia demarcation lines were identified before the onset of visible changes.

Boyle et al, 2000, compared results from LDF with results from LDI scans; they studied patients undergoing oesophageal resection. In each 6 measurements of gastric corporal serosal/muscularis were made over 30 seconds using LDF. A single 1 cm² LDI image was made of the same area prior to any vascular division. These measurements were repeated after partial gastric devascularisation and the two techniques' measurements then compared. Correlation between the 2 methods was good: coefficient of correlation was 0.955 (p<0.01).

The modern equivalent of equipment used in these studies would be the moorLDI2 but the moorLDLS2 and the moorFLPI should also be considered as suitable options. The moorLDI2 is able to scan large areas (up to 50cm x 50cm), the moorLDLS2 scans smaller areas but has the advantage of rapid scan times, and the moorFLPI images at video frame rate – up to 25 frames per second. If you are unsure which model is best suited to your individual study contact us for specialist advice.

References

For additional information on this Application or advice for tailoring Moor Instruments products to your specific application contact us for more information.