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Biomedical subjects

C E Nichols

Publications and source records attributed to C E Nichols.

52 records · Page 3Linked to original sources
PubMed1984

Decreased insulin sensitivity and glucose tolerance in spontaneous canine hyperadrenocorticism.

Alterations in carbohydrate metabolism were evaluated in 60 dogs with untreated hyperadrenocorticism by measuring basal concentrations of plasma glucose and insulin and performing glucose and insulin tolerance tests. The 60 dogs could be divided into four groups based on paired glucose and insulin concentrations. Eight dogs had normal concentrations of both glucose and insulin. Twenty-four dogs (40 per cent) were euglycaemic with mild to moderate hyperinsulinaemia whereas 23 (38 per cent) had moderate hyperglycaemia with moderate to severe hyperinsulinaemia. The five dogs (8 per cent) with overt ketoacidotic diabetes mellitus had relative insulin deficiency. Of eight dogs tested, six had intravenous glucose intolerance; all of the dogs had increased total insulin secretion during glucose tolerance testing. Resistance to the hypoglycaemic effect of exogenous insulin was demonstrated in six of the seven dogs tested. In 20 dogs that had basal glucose and insulin again determined after correction of hyperadrenocorticism, mean concentrations of both glucose and insulin decreased into the normal range.

Adrenalectomy↗
PubMed1981

Low-dose intramuscular insulin therapy for diabetic ketoacidosis in dogs.

Seven dogs with diabetic ketoacidosis were treated initially with lactated Ringer's solution or 0.45% NaCl solution subcutaneously or intravenously and low doses of regular (crystalline) insulin administered intramuscularly every hour until the blood glucose concentration decreased to less than 250 mg/dl. For dogs weighing less than or equal to 10 kg, the initial dose was 2 units and the hourly doses were 1 unit. For dogs weighing greater than 10 kg, the initial dosage was 0.25 units/kg of body weight, and the dosage for hourly injections was 0.1 units/kg. The mean hourly decrease of the blood glucose concentration for all 7 dogs was 87.6 mg/dl. The mean period of treatment required was 4.1 hours. Late hypoglycemia did not develop in any dog, but the serum potassium concentration decreased 0.4 to 1.0 mEq/L. The results suggested that low-dose intramuscular regular insulin therapy for treatment of diabetic ketoacidosis is an effective alternative to conventional regular insulin therapy in dogs.

Animals↗
PubMed1981

Adrenocortical suppression in cats given megestrol acetate.

Megestrol acetate was given orally to 8 cats at a dose of 2.5 mg every other day for 2 weeks and to 8 cats at a dose of 5.0 mg every day for 2 weeks. Four cats were designated nontreated controls. Pre-ACTH-stimulated plasma concentrations of cortisol (hydrocortisone) and ACTH-stimulated cortisol and tolerance to large-dose glucose infusion (IV) were determined on each of the 20 cats given megestrol acetate. Cats were restrained with acepromazine maleate and ketamine hydrochloride during blood sample collection and large-dose glucose infusion. Adrenocortical function and tolerance to large-dose glucose infusion were reevaluated for 4 weeks--after 1st and 2nd weeks of megestrol acetate treatment of the treated groups, and after 1st and 2nd weeks when treatment was stopped (ie, experiment weeks 3 and 4). Each week a cat from the control group and 2 cats from the 2 treated groups were selected to determine the changes occurring during the experiment for that week; after collection of plasma samples, each week's 5 selected cats were euthanatized and necropsied. Significant impairment of adrenocortical function and alteration of adrenocortical morphology occurred with both treated groups. The most severe adrenocortical alterations occurred in the cats 1 week after megestrol acetate was no longer given (ie, experiment week 3). Megestrol acetate-induced adrenocortical suppression contributed to the death of 1 cat. It was concluded that if stress occurs to cats on treatment or soon after treatment with megestrol acetate, glucocorticoids should be supplemented. The effects of megestrol acetate on glucose tolerance were overshadowed by the unforeseen intolerance caused by chemical restraint with acepromazine maleate and ketamine hydrochloride.

Adrenal Cortex↗
PubMed1977

Spinal injury at the level of the third and fourth cervical vertebrae from football.

Acute traumatic lesions of the spine at the third and fourth cervical levels without associated fracture are not common. The eight lesions in this report occurred as a result of injuries sustained during tackle football. They included acute intervertebral disc herniation, anterior subluxation of the third cervical vertebra on the fourth, unilateral dislocation of the joint between the articular processes, and bilateral dislocation of the joints between the articular processes. The mechanism of injury was the use of the top or crown of the helmet as the primary point of contact in a high-impact collision when blocking, tackling, or head-butting. To avoid a seemingly inevitable increase in the incidence of these lesions occurring from tackle football, coaches and officials will have to modify the current techniques of blocking tackling, and head-butting.

Adolescent↗
PubMedDate not supplied

Normal kinematics of the unconstrained glenohumeral joint under coupled moment loads.

The glenohumeral joint presents difficult experimental challenges, large ranges of motion, coupled motions, and multi-planar motions. Many biomechanical tests performed on the glenohumeral joint constrain it or provide conditions that might not be reproducible within and among specimens or treatments. The goal of this study was to determine a means to test the glenohumeral joint in vitro with coupled moments applied to the unconstrained humerus and recording its "6 degrees of freedom" motion relative to the glenoid. This procedure was achieved with the development of a new testing apparatus. Kinematics were described in abduction-adduction, flexion-extension, and abduction, extension, and external rotation, simulating the cocked phase of throwing. The advantage of the techniques was that only the glenohumeral capsule and articular surface contact control the motion of the humerus in response to the applied loading pattern. Also, the motions were unconstrained by the loading apparatus, allowing coupling of rotations and translations and multiplanar motions. Rotations were found to be coupled with translations. For adduction-abduction and flexion-extension, the humeral head was found to translate first in 1 direction, opposite the direction of increasing rotation, at low moments. Then, with increasing moment and angle of rotation, translations changed direction and moved with the primary motion. This occurrence indicates the existence of a region of joint laxity or neutral zone. Rotations were found to be coupled during motion to the cocked position of throwing, as the humerus adducted with extension from full abduction and then adducted further and extends with external rotation. Changes in these motion patterns with pathologic conditions may provide useful information about the nature of shoulder dysfunction and provide insight into appropriate means of repair.

Adult↗
PubMedDate not supplied

Hypertension in cats with chronic renal failure or hyperthyroidism.

The Doppler ultrasonic recording technique was used to measure systolic and diastolic blood pressures indirectly in 28 cats with naturally occurring renal failure, 39 cats with hyperthyroidism, and 33 clinically normal cats. The mean systolic and diastolic blood pressures in the normal cats were 118.4 +/- 10.6 mm Hg and 83.8 +/- 12.2 mm Hg, respectively. In the cats with chronic renal failure, both the systolic (146.6 +/- 25.4 mm Hg) and diastolic (96.6 +/- 15.2 mm Hg) blood pressures were significantly higher (P less than 0.0001 and P less than 0.01, respectively) than in the normal cats. Elevations in systolic and/or diastolic blood pressure were recorded in 17 (61%) of the 28 cats with chronic renal failure. In the 39 untreated hyperthyroid cats, both the mean systolic (167.9 +/- 28.9 mm Hg) and diastolic (111.6 +/- 21.5 mm Hg) pressures also were significantly higher (P less than 0.0001) than normal. Increased systolic and/or diastolic blood pressure was recorded in 34 (87%) of the 39 hyperthyroid cats. In seven cats with hyperthyroidism that were reevaluated two to four months after successful treatment of the hyperthyroid state, there was a significant fall in mean systolic pressure (P less than 0.05) from a pretreatment value of 159.5 +/- 15.4 mm Hg to a posttreatment value of 132.0 +/- 1.62 mm Hg. Overall, the results of this study indicate that mild to moderate hypertension is common in cats with chronic renal failure and in cats with untreated hyperthyroidism. In addition, the hypertension appears to be reversible following successful treatment of the hyperthyroid state.

Animals↗
PubMedDate not supplied

The elongation behavior of the anterior cruciate ligament graft in vivo. A long-term follow-up study.

The relationship between the elongation values of an autogenous bone-patellar tendon-bone graft immediately after fixation and the anterior-posterior laxity of the knee 5 years later was studied in vivo. Immediately after fixation, the change in the graft midsubstance length during passive knee flexion-extension was measured using a Hall-effect transducer, and anterior-posterior knee laxity was measured with the KT-1000 arthrometer. Subjects were divided into group 1 (N = 6), with graft elongation values bounded by the 95% confidence intervals of the normal anterior cruciate ligament elongation values, and group 2 (N = 7), subjects with values outside these intervals. Immediately after reconstruction, the side-to-side difference in anterior-posterior laxity between the reconstructed and uninjured knees was not different between group 1 (-2.6 +/- 0.7 mm, mean +/- SEM) and group 2 (-1.7 +/- 1.0 mm) (P = 0.49). At 5-year follow-up, the difference was 1.2 +/- 0.7 mm for group 1, while for group 2 it was significantly greater at 4.7 +/- 0.6 mm (P = 0.004). At surgery, graft elongation values produced by flexion of the knee that are outside the limits of the anterior cruciate ligament result in significant increases in anterior knee laxity at long-term follow-up, while grafts with elongation values similar to the normal anterior cruciate ligament do not. Not only is restoration of anterior-posterior laxity values to within normal limits important, but the biomechanical behavior of the graft produced by flexion-extension of the knee should be appreciated.

Adult↗
PubMedDate not supplied

The axial load teardrop fracture. A biomechanical, clinical and roentgenographic analysis.

The anteroinferior cervical vertebral body corner fracture was originally described by Schneider and Cann as the "teardrop" fracture. This report analyzes the biomechanical, clinical, and roentgenographic features of 55 such fractures obtained from the National Football Head and Neck Injury Registry. Teardrop fractures resulting from tackle football characteristically occurred in players attempting to make a tackle in which initial contact was made with the top or crown of the helmet. There were two fracture patterns associated with the anteroinferior corner (teardrop) fracture fragment: 1) the isolated fracture, which is usually not associated with permanent neurologic sequelae; and 2) the three-part, two-plane fracture in which there is an associated sagittal vertebral body fracture as well as fracture of the posterior neural arch. This latter pattern was almost always associated with permanent neurologic sequelae, specifically quadriplegia. Axial loading of the cervical spine was clearly identified as a mechanism of injury for both fracture patterns. Roentgenographic examination must include both anteroposterior and lateral views with computed tomography or tomography as necessary to determine the presence of the sagittal vertebral body fracture and the integrity of the posterior neural arch.

Biomechanical Phenomena↗
PubMedDate not supplied

Anterior cruciate ligament strain behavior during rehabilitation exercises in vivo.

Before studying the biomechanical effects of rehabilitation exercises on the reconstructed knee, it is important to understand their effects on the normal anterior cruciate ligament. The objective of this investigation was to measure the strain behavior of this ligament during rehabilitation activities in vivo. Participants were patient volunteers with normal anterior cruciate ligaments instrumented with the Hall effect transducer. At 10 degrees and 20 degrees of flexion, ligament strain values for active extension of the knee with a weight of 45 N applied to a subject's lower leg were significantly greater than active motion without the weight. Isometric quadriceps muscle contraction at 15 degrees and 30 degrees also produced a significant increase in ligament strain, while at 60 degrees and 90 degrees of knee flexion there was no change in ligament strain relative to relaxed muscle condition. Simultaneous quadriceps and hamstrings muscles contraction at 15 degrees produced a significant increase in ligament strain compared with the relaxed state but did not strain the ligament at 30 degrees, 60 degrees, and 90 degrees of flexion. Isometric contraction of hamstrings muscles did not produce change in ligament strain at any flexion angle. Exercises that produce low or unstrained ligament values, and would not endanger a properly implanted graft, are either dominated by the hamstrings muscle (isometric hamstring), involve quadriceps muscle activity with the knee flexed at 60 degrees or greater (isometric quadriceps, simultaneous quadriceps and hamstrings contraction), or involve active knee motion between 35 degrees and 90 degrees of flexion.

Adult↗
PubMedDate not supplied

The effect of functional knee bracing on the anterior cruciate ligament in the weightbearing and nonweightbearing knee.

We investigated the effect of functional bracing on anterior cruciate ligament strain in humans by arthroscopic implantation of a differential variable reluctance transducer on the ligament and measurement of its strain behavior. Strains were measured while "injury mechanism" loads were applied to the weightbearing and nonweightbearing knees for both braced and unbraced conditions. For the unbraced knee, there was a significant increase in ligament strain values when subjects went from a seated position (minimal shear and compressive loads across the knee) to a standing posture (substantial shear and compressive loads across the knee). Similar strain values were found between these same seated and standing postures when a 140-N anterior-directed load was applied to the tibia. This indicates that the ligament is strained during weightbearing and demonstrates that the compressive load across the knee produced during weightbearing does not significantly reduce ligament strain values in comparison with the unweighted joint with relaxed muscles for the 140-N load limit of our anterior shear test. Bracing produced a protective effect on the ligament by significantly reducing the strain values for anterior-directed loading of the tibia up to 140 N with the knee in both weightbearing and nonweightbearing conditions. Likewise, bracing produced a protective effect on the ligament by significantly reducing strain values in response to internal-external torque of the tibia up to 6 N-m with the knee nonweightbearing. The brace strap that contacts the tibia just distal to the insertion of the patellar tendon was instrumented with a load sensor, allowing us to measure the posterior-directed loads applied by the brace to the tibia. Adjustment of strap tension between low and high settings did not modulate the protective effect of the brace on the ligament.

Adult↗
PubMedDate not supplied

The strain behavior of the anterior cruciate ligament during squatting and active flexion-extension. A comparison of an open and a closed kinetic chain exercise.

The effects of weightbearing (closed kinetic chain) and nonweightbearing (open kinetic chain) exercises on the biomechanical behavior of an injured anterior cruciate ligament or a healing anterior cruciate ligament graft are unknown. To understand the effects of these exercises on the healing graft, we measured the strain behavior of the normal anterior cruciate ligament in human subjects while they performed squatting, a closed kinetic chain exercise, and active flexion-extension of the leg, an open kinetic chain exercise. The maximum anterior cruciate ligament strain values obtained during squatting did not differ from those obtained during active flexion-extension. Also, anterior cruciate ligament strain values obtained during squatting were unaffected by the application of elastic resistance intended to increase muscle activity. These findings indicate that squatting, which produces a substantial compressive joint force, does not necessarily protect the anterior cruciate ligament more than active flexion-extension of the leg, which is characterized primarily by contraction of the dominant quadriceps muscle. These findings also demonstrate that increasing resistance during the squat exercise does not produce a significant increase in anterior cruciate ligament strain values, unlike increased resistance during active flexion-extension exercise.

Adult↗
PubMedDate not supplied

The strain behavior of the anterior cruciate ligament during bicycling. An in vivo study.

Stationary bicycling is commonly prescribed after anterior cruciate ligament injury or reconstruction; however, the strains on the ligament or ligament graft during stationary bicycling remain unknown. In this study we measured ligament strain on eight patients who were candidates for arthroscopic meniscectomy under local anesthesia. Six different riding conditions were evaluated: three power levels (75, 125, and 175 W), each of which was performed at two cadences (60 and 90 rpm). The peak ligament strain values ranged from 1.2% for the 175-W, 90-rpm, condition to 2.1% for the 125-W, 60-rpm, condition. No significant differences were found in peak strain values due to changes in power level or cadence. Thus, the strain values were pooled across the six riding conditions tested. The mean peak strain value was 1.7%, a value that is relatively low compared with other rehabilitation activities previously tested. These data suggest that knee rehabilitation programs can be designed to include this selection of power and cadence levels without significantly changing ligament strain values. Thus, stationary bicycling is a rehabilitation exercise that permits the patient to increase muscle activity by increasing the power level or decreasing the cadence without subjecting the ligament or ligament graft to higher strain values.

Adult↗