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Biomedical subjects

J G Thomson

Publications and source records attributed to J G Thomson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Timing, magnitude, and utility of surgical delay in the TRAM flap: I. Animal studies.

Surgical delay is an effective technique, but the precise timing of the delay effect and the required extent of the delay procedure are uncertain. We endeavored to study flap survival as a function of the duration of the delay period in a rat transverse rectus abdominis myocutaneous (TRAM) flap model. Two specific delay procedures (limited and extensive) were utilized, and flap survival was assessed after delay periods of 3, 7, 10, 14, 21, and 30 days (n > or = 7, all groups). A delay of 7 days or greater resulted in statistically significant improvement in flap survival in all groups. The delay effect appeared to be maximal at 14 days, and in the extensive delay group, a 14-day delay resulted in statistically greater flap survival than a 7-day delay. Improvement in flap survival was greater when an extensive delay procedure was used. Although the model system has limitations, the rat TRAM flap appears to be a suitable model for the study of the delay phenomenon. Possible clinical correlations are addressed in part II.

Analysis of Variance↗
PubMed1997

A new experimental model: the vascular pedicled cutaneous flap over the mid-dorsum of the rat.

The cutaneous vascular anatomy of the mid-dorsum in the rat and its role in flap design was studied in the rat. The investigation consisted of anatomic dissection, methylene blue injection into the axial artery, and flap harvesting in live animals. Dissection and injection revealed that the mid-dorsum of the rat derives its blood supply largely from the 10th intercostal artery, here referred to as the middle dorsal artery, which originates from the lateral aspect of the thoracic aorta. The cutaneous vascular territory of the middle dorsal artery was defined as follows: the medial border, midline of the dorsum; the lateral border, midaxillary line; the cephalic border, a line joining the medial and lateral borders midway between the level of the axilla proximally and 1 cm above the base of the rib cage distally; and the caudal border, a line drawn midway between the latter point proximally and the anterior superior iliac spine distally. Both unilateral and bilateral vascular pedicled island cutaneous flaps were harvested in living rats based on and exceeding the vascular territory delimited by methylene blue injection. Flaps limited to this territory with intact middle dorsal arteries showed total survival, while oversized flaps underwent partial necrosis peripherally. Because of its simplicity, reliability, and consistent vascularity, this flap has potential applications in the study of flap hemodynamics.

Animals↗
PubMed1996

The extended lateral arm free flap for head and neck reconstruction: the Yale experience.

The lateral arm free flap (LAFF) has been chosen by some head and neck reconstructive microsurgeons to be their fasciocutaneous free flap of choice. The qualities of this flap have been suggested to include its consistent vascular anatomy, its thin and pliable nature, and its reinnervation capabilities, as well as its low donor site morbidity and ease of closure. During the past year we have performed 14 head and neck reconstructions using the extended LAFF (ELAFF). We present our indications for its use and review its shortcomings. Although the ELAFF does have its limitations, including variability in its flap thickness and donor vessel size, it unquestionably is an important flap in head and neck reconstruction and is our flap of choice for soft tissue reconstruction.

Adult↗
PubMed1995

Use of vaccinia virus poly(A) polymerase for RNA 3'-end labeling with a chain-terminating nucleotide or a short 3' homopolymer tract.

Conditions are described for the 3'-end labeling of RNA with 32P 3'-dATP (3'-deoxyadenosine-5'-triphosphate), a chain-terminating nucleotide, using the poly(A) polymerase (PAP) encoded by vaccinia virus. Reaction time, divalent cation species and concentration, and the requirement for both subunits of the PAP were investigated. In the presence of Mn2+, vaccinia PAP is able to tail RNA primers with tracts of 3'-oligo(U), oligo(C) and oligo(G). Conditions for the addition of labeled 3'-homopolymer tracts were characterized. The use of low nucleotide concentrations in this study revealed an apparently fixed divalent cation concentration optimum of 0.1 mM, distinct from the previously noted requirement for a 1:1 divalent cation:NTP complex. This indicates a possible requirement for multiple divalent cations in nucleotidyl transfer by vaccinia PAP.

Cations, Divalent↗
PubMed1995

Microsurgery for cranial base tumors.

Local or regional flaps usually are sufficient for reconstruction of defects of the cranial base. In some cases, however, free-tissue transfer may be the best or the only choice. Reasons for choosing free-tissue transfer over other methods of reconstruction include previous radiation, previous surgery, limited arc of rotation of pedicle flaps, lower complication and failure rates of free flaps, and specific tissue requirements that only can be met with a free flap. The anatomy, available flap choices, indications, and technical considerations applicable to cranial base reconstruction with microvascular surgery are discussed.

Esthetics↗
PubMed1991

Effects of sodium pentobarbital anesthesia on blood flow in skin, myocutaneous, and fasciocutaneous flaps in swine.

Drug effect on flap blood flow is most commonly determined in anesthetized animals, yet the effect of the anesthetic is often poorly understood. Halothane and nitrous oxide cause profound changes in skin blood flow and thus provide an unsuitable anesthetic technique for use in measuring drug effects on skin and myocutaneous flaps in swine. The goal of this study was to determine the effects of sodium pentobarbital anesthesia on cardiovascular parameters and blood flow in skin, myocutaneous, and fasciocutaneous flaps in pigs. In seven pigs, 7 forelimb skin flaps, 7 forelimb fasciocutaneous flaps, 14 arterial buttock flaps, and 14 latissimus dorsi flaps were created. Blood flow was measured at 2-cm intervals along each flap while the animal was awake and anesthetized. A cardiac depressant effect of pentobarbital was observed, but no change in blood flow could be demonstrated in control skin or control muscle. However, pentobarbital did significantly increase blood flow in all viable portions of arterial and random skin flaps, fasciocutaneous flaps, and the cutaneous segments of the latissimus dorsi flap. These demonstrated effects of pentobarbital should be taken into consideration in designing and analyzing studies of flap blood flow in the acute postoperative phase.

Analysis of Variance↗
PubMed1991

Hydrogen clearance: assessment of technique for measurement of skin-flap blood flow in pigs.

The hydrogen clearance technique has been used for many years by investigators to determine brain blood flow and has been partially validated in this setting using other methods of blood flow measurement. The method has been modified to allow blood flow measurements in skin, but the accuracy of H2 clearance for measuring skin blood flow has not been determined. Multiple blood flow measurements were performed using H2 clearance and radioactive microspheres on skin flaps and control skin in pigs. On 12 pigs, a total of 117 flap and 42 control skin measurements were available for analysis. There was no significant difference between the two techniques in measuring mean control skin blood flow. In skin flaps, H2 clearance was significantly correlated to microsphere-measured blood flow, but it consistently gave an overestimate. Sources of error may include injury to the tissues by insertion of electrodes, consumption of H2 by the electrodes, or diffusion of H2 from the relatively ischemic flap to its well-vascularized bed. Further studies are necessary to determine the cause of this error and to measure the technique's accuracy in skeletal muscle and other flaps.

Animals↗
PubMed1990

Critical ischemia times and survival patterns of experimental pig flaps.

Previous work on critical ischemia time suggested (1) a greater susceptibility of myocutaneous flaps over skin flaps to the ischemia reperfusion injury and (2) that duration of ischemia may affect the survival area of a flap. Using a pig model, 55 animals were operated on and the critical ischemia times and survival patterns of the buttock skin (n = 85) and latissimus dorsi myocutaneous (n = 88) island flaps were determined after being submitted to 0, 2, 4, 6, 8, 10, 12, 14, and 16 hours of normothermic ischemia. The average critical ischemia times (CIT50) were determined to be 9 and 10 hours for the buttock skin and latissimus dorsi myocutaneous flaps, respectively. Percentage of total area surviving (%TAS) in those flaps which did survive was adversely affected by increases in the ischemic interval in both flap models. A statistically significant decrease in percentage of total area surviving was found after 6 and 8 hours of ischemia for the buttock skin and latissimus dorsi myocutaneous flaps, respectively.

Animals↗
PubMed1989

Dermofluorometry: thresholds for predicting flap survival.

The dye fluorescence index (DFI) has been cited as an accurate predictor of skin-flap survival. However, two thresholds, one each for flap survival and flap necrosis, have been advocated. A DFI of less than 15 to 20 percent predicts failure, and a DFI greater than 35 to 50 percent predicts survival. Values of 20 to 35 percent indicate an uncertain outcome. The present study was undertaken (1) to determine the optimum threshold for flap survival prediction in pigs, and (2) to compare dermofluorometry with flap blood flow as measured by radioactive microspheres. Dermofluorometry was found to be an accurate (90 percent) and repeatable predictor of skin and fasciocutaneous flap survival in pigs. At 2 and 5 hours after flap elevation, the optimum DFI thresholds are 7 and 27 percent, respectively. This reflects the dynamic nature of circulation in acute skin flaps and the increased dye delivery over time. Using these calculated thresholds, a high degree of correlation was found with survival estimated at 24 hours. Dermofluorometry also was correlated with the blood flow index. Thus not only is it an accurate flap monitor, but a quantitative estimate of flap blood flow can be obtained.

Animals↗
PubMed1989

Fasciocutaneous flaps: an experimental model in the pig.

No experimental studies have substantiated the claim that fasciocutaneous flaps are superior to skin flaps. Using fasciocutaneous flaps designed in the pig, both flap survival and blood flow were assessed. The forelimb and hindlimb fasciocutaneous flaps survived to 8.2 +/- 0.3 cm and 7.9 +/- 0.3 cm, respectively, compared with 7.3 +/- 0.3 cm and 6.7 +/- 0.3 cm for the comparable cutaneous flaps, a statistically significant finding (p less than 0.01). Random fasciocutaneous flaps survive 12 to 18 percent longer than skin flaps. Using the radioactive microsphere technique, blood flow was measured after flap elevation, and flap survival was estimated using fluorescein. Again, a significant difference in flap survival was found, but there was no significant difference in measured blood flow. This can be explained by the relatively large interval between blood flow measurements (2 cm) compared with the observed difference in survival length (1.0 +/- 0.3 cm).

Animals↗
PubMed1981

Observer variation in lower limb venography.

Three radiologists examined 34 venograms (68 limbs) performed supine without fluoroscopy for evidence of thrombosis. At 11 major veins in each limb they stated whether thrombus was "absent," "doubtful," "presumed" or "definite" or expressed " "no opinion." Data were analyzed by using the kappa statistic, which corrects for chance agreement. Results were compared with those from a previous study in which two of the observers assessed venograms performed under fluoroscopic control with the patient semi-erect. In the present study observers expressed "no opinion" much more often, particularly for anterior tibial and iliac veins. With these examinations excluded, the extent of observer variation was similar in the two studies, disagreement about the presence of thrombus occurring in about 10% of examinations. The frequency with which the diagnosis of thrombus remains in doubt severely limits the value of venography performed supine without fluoroscopy. Fluoroscopically-controlled examinations in the semi-erect position are preferable.

Humans↗
PubMed1979

Observer variation in the interpretation of lower limb venograms.

After agreeing on diagnostic criteria and after a pilot study, two experienced radiologists twice independently reviewed 40 lower limb venograms performed by a standard technique in patients suspected or known to have venous thrombosis. The observers reviewed 20 examinations at a time, their analysis requiring separate identification of 11 major veins. At each site observers stated whether thrombus was "absent," "doubtful," "presumed," or "definite," or declared "no opinion possible." They then rediscussed criteria of diagnosis and, using the same experimental design, examined another 40 venograms. To correct for agreement expected by chance, data were analyzed by using the kappa statistic. In general, levels of agreement were higher than those reported for many other clinical and radiologic investigations, probably because of refinement of criteria after the pilot study. Nonetheless, observers disagreed about the probable presence or absence of thrombus at some site in the limb in about 10% of examinations. Observer variation should be considered when venography is used as a reference standard to evaluate other methods of diagnosing thrombi.

Adult↗
PubMed1977

Rectal wall bleeding--an overlooked source of massive lower gastrointestinal hemorrhage.

Two cases of acute massive bleeding from the rectum are described. In both cases, the diagnosis was made angiographically. Some points of angiographic technique are discussed. In both cases, there had been previous negative sigmoidoscopy. Care must be taken to include the entire rectum on the films obtained during injection of the inferior mesenteric artery regardless of findings on sigmoidoscopy.

Adult↗