Danny O. Jacobs

Assessing burn wound depth using in vitro nuclear magnetic resonance (NMR)

There is no accurate noninvasive method for differentiating between partial-thickness and full-thickness cutaneous burn wounds. Full-thickness burns (FTB) result in slower resorption of wound edema than partial thickness burns (PTB). Since proton NMR parameters, particularly the T1 relaxation time, correlate with tissue water content (TWC), the present study determined whether proton NMR could distinguish PTB from FTB. An area of upper dorsum (approximately 15% BSA) of 35 adult rats was immersed in boiling water for either 3 sec (PTB) or 10 sec (FTB). In 10 control rats, the same area was immersed in room temperature water. Rats were sacrificed at either 3 or 48 hr after burn, and skin samples were analyzed to determine spin-lattice (T1) and spin-spin (T2) relaxation times. TWC was then measured gravimetrically by desiccation. Both T1 and T2 times significantly correlated with TWC (T1: r = 0.74, P less than 0.0001; T2: r = 0.75; P less than 0.0001). Both PTB and FTB resulted in significant elevations of T1, T2, and TWC 3 hr after injury (P less than 0.001). At 48 hr postburn the T1, T2, and TWC of the PTB group had decreased to control values (P less than 0.05), while all FTB parameters remained significantly elevated as compared to both the control and the 48-hr PTB parameters (P less than 0.001). In vitro NMR measurements distinguish PTB from FTB in this rat model within 48 hr. These data provide a basis for investigating in vitro NMR techniques for the noninvasive assessment of burn wound depth.

Impact of a nutritional support service on VA surgical patients

The impact of a multidisciplinary Nutritional Support Service (NSS) on the reduction of complication was evaluated in 78 consecutive patients who received total parenteral nutrition (TPN) on the same VA surgical service. Patients were placed into one of three groups (pre-NSS, transition-NSS, post-NSS) based on the evolution of the NSS. A significant reduction in catheter sepsis was observed and was attributable to the establishment of an NSS, specifically, a nurse specialist and protocols for catheter insertion and care.

The identification of experimentally induced appendicitis using in vitro nuclear magnetic resonance

Appendicitis was induced in six New Zealand white rabbits. The appendices from these animals had significantly higher spin-lattice relaxation times, T1, as determined in vitro by nuclear magnetic resonance (NMR) (10 controls vs 6 experimentals, 413 +/- 23 vs 455 +/- 41, X +/- SD, P less than (0.02). T1 correlated significantly with the water content of the appendiceal tissue (P less than 0.001). These findings suggest that in vivo NMR imaging techniques weighted on T1 might be able to identify human appendicitis noninvasively by detecting localized edema.

Detection of total parenteral nutrition-induced fatty liver infiltration in the rat by in vitro proton nuclear magnetic resonance.

In an effort to determine if NMR techniques might be used to detect TPN-induced hepatic steatosis, the NMR spin-lattice (T1) and spin-spin (T2) relaxation times were measured on liver tissue from rats who received one of five dietary regimens: (1) 100% of nonprotein calories as lipid (Fat); (2) a mixture of 50% lipid and 50% glucose nonprotein calories (50/50); (3) 100% of nonprotein calories as glucose (CHO); (4) intravenous saline and standard laboratory rat chow (Saline); and (5) rat chow alone (Oral). The parenteral diets were isonitrogenous and isocaloric. Serum liver function tests were also measured. Animals in the Fat and 50/50 groups had the greatest amounts of liver fat and significantly longer T1 and T2 times (p less than 0.01) than any other group. Furthermore, the correlation of T2 time with liver fat content (r = 0.82) was far superior (p less than 0.001) to that of serum SGPT (r = 0.48) which was the only liver function test which correlated significantly with liver fat content. In a multiple linear regression analysis, T1 and T2 predicted liver fat content with an r value of 0.84 (p less than 0.001). These data suggest that in vivo NMR imaging techniques might be used to detect TPN-induced fatty infiltration of the liver noninvasively.

Early diagnosis of experimental necrotizing enterocolitis using proton nuclear magnetic resonance

The purpose of this study was (1) to confirm an experimental model of aminophylline-induced necrotizing enterocolitis (NEC); and (2) to determine whether nuclear magnetic resonance (NMR) imaging, based upon proton relaxation values (T1, T2), could detect NEC during its early pathogenesis. Sixty male weanling Lewis rats (avg wt = 75 g) were randomly assigned to one of three experimental groups: (A) superior mesenteric artery (SMA) occlusion (1 min) + aminophylline treatment (40 mg/kg); (B) SMA occlusion; and (C) sham midline laparotomy (control). All surviving animals were sacrificed at 48 hr postoperation and a specimen of ileum was removed for light microscopy (LM), electron microscopy (EM), and NMR analysis. Percentage water content was determined for representative specimens. Mortality occurred only in experimental group A animals (18.2%; P less than 0.05), who had received aminophylline. Microscopy of ileum from sacrificed animals of this group showed changes ranging from mild cellular disruption to severe hemorrhagic necrosis. Early ultrastructural changes consistent with NEC were detectable with EM before LM. Proton relaxation results obtained with NMR showed significant prolongation of T1 (252.5 +/- 4.4 msecs; P less than 0.001) and T2 (69.3 +/- 1.4 msecs; P less than 0.025) during the first stages of NEC. NMR may indeed enable early, safe diagnostic imaging of NEC in infants receiving aminophylline, or those who are otherwise at increased risk for development of this disease.

Nitrogen Utilization from Elemental Diets

Repletion experiments were performed in malnourished, chair-adapted primates to explore recently reported differences in nitrogen utilization from elemental diets. Two elemental diets were fed consecutively for 8 days through a gastrostomy. Diet C (maltodextrins, peptides, crystalline amino acids) resulted in: larger weight gain (F1,6 = 17.93, p less than 0.01); smaller decrease of serum albumin (F1,5 = 11.2, p less than 0.015), larger increase in total iron binding capacity (F1,6 = 30.6, p less than 0.002), and a more positive nitrogen balance (F1,6 = 30.4, p less than 0.002) than diet V (glucose oligosaccharides, crystalline amino acids). Diet C was considered to be more effective in the nutritional repletion of the study animals. Additional experiments were performed in normal human volunteers to investigate the metabolic fate of ingested glutamine and whether the rapid catabolism and excretion of the amido nitrogen of this amino acid, which constitutes 11.56% of total nitrogen in diet V, could explain the differences observed in primates in our study and in human subjects by other authors. Six normal volunteers were fed 15N amino glutamine, 15N alanine, or 15N H4Cl. Similar amounts of 15N from Gln and Ala were excreted in 10 hr. The amido group of glutamine does not seem to be metabolized differently from the alpha-amino group of alanine under the conditions of the study. The marked differences in nitrogen utilization from the study diets could not be explained by the presence of relatively large amounts of glutamine in one of them.

Identification of human appendicitis by in vitro nuclear magnetic resonance

The spin-lattice relaxation time, T1 as determined by nuclear magnetic resonance techniques, correlates positively with tissue water content. The latter relationship has been observed in rabbits with experimentally induced appendicitis whose inflamed appendiceal tissues had significantly higher T1s and water contents than tissue from normal controls. The present experiment studied these relationships in humans. Tissue water content and T1 were measured on appendiceal tissue from 10 patients with documented appendicitis and from 6 controls without the disease. All T1s were determined within 30-60 min of removal of the appendix at operation. The mean in vitro T1 of appendiceal tissue from patients with appendicitis was significantly higher than that of controls (527 +/- 15 msec versus 430 +/- 17 msec, mean +/- SEM, P less than 0.002). In addition, a strong positive correlation was noted between T1 and tissue water content (r = 0.70, P less than 0.01). Based on these findings, the use of in vivo magnetic resonance imaging techniques to detect human appendicitis noninvasively warrants investigation.

In vitro detection of fatty liver infiltration in protein-depleted rats using proton nuclear magnetic resonance

To determine if NMR techniques might be used to detect hepatic steatosis secondary to protein malnutrition, the T1 and T2 relaxation times of liver tissue from rats subjected to long-term protein malnutrition were measured in vitro. The liver tissue from rats fed a protein-deficient rat chow (PD) for 37 days (N = 9) was characterized by increased proportion of fat (P less than 0.001) but decreased water and nitrogen contents (P less than 0.001) relative to controls (N = 9). Mean T1 times were significantly shorter and T2 times significantly longer in liver tissue from protein-depleted animals (P less than 0.001). There was no overlap of T2 times between the protein-depleted and control animals. The consistent changes in T2 that occur with fatty infiltration of the liver should be detectable by current NMR imagers.