Research

Evaluating Medicinal Leeches

In our laboratories at the University of Wisconsin and the William S. Middleton Memorial Veterans Hospital, work toward the development of a mechanical device to replace the use of leeches in medicine began with a characterization of medicinal leech (Hirudo medicinalis) performance in decongesting a large tissue flap.

We found that in our model of total venous occlusion, the average bloodmeal volume for medicinal leeches was 2.45 mL. Average passive bleeding for the first 2 and 4 hours after leech detachment totaled 2.21 and 2.50 mL, respectively, with 90 percent of passive bleeding occurring within 5 hours after detachment.

Initial Experiments

We improved upon the passive bleeding component with our first mechanical device, which augmented passive blood retrieval after leech detachment. The results of our experiments indicated that use of the device resulted in significant increases in blood retrieval relative to reports of passive bleeding alone (141%, 156%, and 155% in hours 1, 2, and 3, respectively) and were an encouraging first step toward development of AutoFlow.

AutoFlow Prototypes

We then developed a series of mechanical models designed to completely replace the use of leeches.These models were adhered to the skin over a surgically created bleeding wound.

Each model was built as a clear outer shell (1.5 cm diameter, height varied) with inflow and outflow ports that allowed computer controlled irrigation/anticoagulation and suction. The three models differed in the characteristics of the surgically created bleeding wound and the method of delivering concentrated anticoagulant to the site.

Laboratory Results

We found that our models exceeded the blood removal ability of the medicinal leech (recorded in our prior study) by 490%, 643%, and 872%, under identical conditions. We extended the time period of device testing to 15 hours in our next study, and found that congested tissue flaps treated with up to 3 early AutoFlow prototypes were much healthier in terms of oxygen tension, blood perfusion, color, and underlying histology when compared to control flaps.

When directly compared with 75 medicinal leeches per congested flap over 15 hours of congestion, the use of 3 AutoFlow units resulted in equivalent volumes of blood removed, surface perfusion, and oxygen tension. Improved skin color was found in the AutoFlow treated flaps in comparison with the leech-treated flaps. Histological assessment showed mild congestion in 100% of the leech-treated flaps and on only 33% of the device-treated flaps. The significant differences in skin color change over time demonstrated that device therapy promoted more global decongestion versus leech therapy.

Accordingly, in our laboratory, we have developed working models of mechanical devices for treating venous congestion that have excellent clinical potential.

Published Studies

Russell JA, Conforti ML, Connor NP, Hartig GK. Cutaneous tissue flap viability following partial venous obstruction. Plastic & Reconstructive Surgery. 2006, 117: 2259-2266.

Hartig GK, Connor NP, Warner TF, Heisey DM, Sarmadi M, Conforti ML. Testing a device to replace the leech for treating venous congestion. Archives of Facial Plastic Surgery, 2003;5(1):70-77.

Hartig GK, Connor NP, Heisey DM, Conforti ML. Comparing a mechanical device to medicinal leeches for treating venous congestion. Otolaryngology-Head and Neck Surgery, 2003, 129: 556-564

Connor NP, Conforti MC, Heisey DM, Vanderby R, Kunz D, Hartig GK. Augmented blood removal after medicinal leech feeding in congested tissue flaps. Journal of Rehabilitation Research and Development, 2002; 39:509-512.

Conforti MC, Connor NP, Heisey DM, Vanderby R, Kunz D, Hartig GK. Development of a mechanical device to replace the medicinal leech (Hirudo medicinalis) for the treatment of venous congestion. Journal of Rehabilitation Research and Development, 2002; 39:497-504.