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Biomedical subjects

P J Knight

Publications and source records attributed to P J Knight.

At least 37 records · Page 2Linked to original sources
PubMed1986

Distribution of mass within native thick filaments of vertebrate skeletal muscle.

The distribution of mass within the vertebrate skeletal thick filament has been determined by scanning transmission electron microscopy. Thick and thin filaments from fresh rabbit muscle were mixed with tobacco mosaic virus (TMV), fixed with formaldehyde, dried onto thin carbon films and viewed in a computer-linked microscope. Electron scattering data from both TMV and thick filaments were analysed with reference to the long axis of the particles so that the distribution of mass within the particles could be determined. While TMV appeared to be a uniform rod at the resolution employed (4.3 nm), the thick filament was clearly differentiated along its length. M-line remnants at the centre of the filament were flanked by regions of low mass per unit length, corresponding to the bare zone of the filament, and then by the more massive cross-bridge regions. The mass per unit length was approximately constant through most of the cross-bridge zone and declined at the filament tips, in a manner consistent with a constant number of myosin molecules per 14.3 nm interval (crown) throughout the cross-bridge zone. Fourier analysis of the data failed to detect the expected 43 nm periodicity of C-protein. The total mass of the thick filament was 184 Mdalton (s.e.m., 1.6 X 10(6); n = 70). The mass of adhering M-line proteins was highly variable but, on average, was about 4 Mdalton. The total mass of the filament and the mass distribution in the cross-bridge zone are consistent with three myosin molecules per crown.

Actin Cytoskeleton↗
PubMed1986

The use of interstitial radiation therapy in the treatment of persistent, localized, and unresectable cancer in children.

Two children with cancer that persisted after multiple exploratory laparotomies, external beam radiation therapy, and multidrug chemotherapy had gold 198 (198Au) seeds implanted into their localized but unresectable tumor. Both children are alive, are receiving no therapy, and are disease-free more than 2 years later. These two cases indicate the value of interstitial implant therapy in the treatment of some children with cancer.

Abdominal Neoplasms↗
PubMed1984

The diagnosis and treatment of the acute scrotum in children and adolescents.

Diagnosing acute scrotal pain and swelling in children and adolescents is urgent and often difficult. A review of 395 boys hospitalized with acute scrotal pain and/or swelling shows that a useful approach is to divide these patients into four groups--those with intermittent but recurrent episodes of pain, those with pathognomonic physical findings, those with definite epididymitis, and a remaining group with nonspecific swelling and tenderness. Five per cent of boys in this series presented with recurring episodes of scrotal pain; these boys should undergo a simple scrotal operation that yields excellent results. Eight per cent had pathognomonic physical findings; treatment in these boys is straightforward. Eighteen per cent had a definite diagnosis of acute epididymitis (i.e., three nonpathognomonic but suggestive findings of acute epididymitis or two suggestive findings plus a radionuclide scan showing bilateral perfusion); nonoperative therapy is indicated in this group. In the remaining boys, scrotal exploration is the diagnostic (and usually therapeutic) procedure of choice.

Acute Disease↗
PubMed1983

The diagnosis and treatment of midline neck masses in children.

Frustration in differentiating before operation among the various causes of midline neck masses stimulated us to review the clinical, operative, and pathologic findings in 176 children hospitalized for a midline cervical lump. The preoperative diagnosis was correct in 61% of these cases, the surgeon's postoperative diagnosis was correct in 83%, and the pathologist's diagnosis was correct in 98%. Only recurrence following prior excision and persistent sinus following drainage of a midline cyst were pathognomonic preoperative indicators of a thyroglossal duct cyst; these findings were present in only 6% of the cases. The age of the child, a history of inflammation or of fluctuation in size, the dimensions of the mass, and the relationship of the mass to the hyoid were useful in differentiating among groups of children with a thyroglossal cyst, an epidermoid cyst, or an enlarged perihyoid lymph node. The duration of the presence of the mass and its movement with swallowing were not helpful. Using the preoperatively recorded historical and physical findings in these children with a known cause for their midline neck mass and applying Bayes' theorem, one can only achieve a correct preoperative diagnosis with an 80% accuracy based on the best available data. Consequently, additional information obtained at surgical exploration is needed to establish a secure diagnosis and to ensure appropriate treatment.

Adolescent↗
PubMed1983

Superficial lumps in children: what, when, and why?

Deciding whether a visible or palpable lump should be excised in a trivial problem if one believes that every unexplained mass in an infant or a child must be promptly removed. But with the present increased public awareness of cancer, this approach would unnecessarily raise parental anxiety. This review of superficial lumps excised in infants and children shows that approximately 1% are malignant. Although a precise diagnosis on the basis of clinical findings remains imperfect, four fifths of the malignant lesions can be recognized on the basis of five risk factors: onset in the neonatal period, a history of rapid or progressive growth, skin ulceration, fixation to or location deep to the fascia, and a firm mass greater than 3 cm in diameter. In the absence of any of these risk factors, parents can be reassured with a 99.7% accuracy about the benign nature of their child's lump at the initial consultation. Approximately 6% of these lumps will spontaneously regress and, therefore, do not require excision. However, more than 90% of superficial lumps will persist or slowly enlarge and should be electively excised for cosmetic reasons, to prevent late infection or inflammation, and to diagnose the remaining three malignant lesions per thousand lumps that would not be recognized using the above five risk factors.

Adolescent↗
PubMed1982

Screening for latent malformations: cost effectiveness in neonates with correctable anomalies.

A screening program for latent malformations in infants born with surgically correctable anomalies was reviewed to determine its cost effectiveness. Two hundred and seventy six infants with esophageal atresia, imperforate anus, omphalocele, gastroschisis, or diaphragmatic hernia were screened for latent congenital anomalies not detected by the routine history, physical examination, and roentgenograms. While additional malformations were detected, many congenital defects were missed only to become evident later in the infant's course. Routine screening for latent malformations is not cost effective in all infants with surgically correctable anomalies, but directed screening is indicated in selected neonates. Screening IVP's are indicated in patients with esophageal atresia, high pouch imperforate anus and possibly diaphragmatic hernia. Screening IVP's are not indicated in infants with gastroschisis, omphalocele, or females with low pouch imperforate anus who have normal sacral spine films.

Age Factors↗
PubMed1982

When is lymph node biopsy indicated in children with enlarged peripheral nodes?

To better define the indications for diagnostic biopsy, 239 children who underwent peripheral lymph node biopsy were reviewed. The duration of the lymph-adenopathy by history, the consistency of the lymph nodes, and the presence of more than one site of palpable adenopathy were not specific in differentiating serious diseases involving lymph nodes from reactive hyperplasia. The differential diagnosis of specific causes for lymph node enlargement is approached based on the child's age, the location of the adenopathy, and the presence or absence of lymph node fixation and tenderness. Most children with supraclavicular adenopathy, children sick with fever of one week's duration or with weight loss for which a specific diagnosis is not readily made, and some children with fixation of the lymph node to the overlying skin should undergo early biopsy. Excluding the above findings, when a specific diagnosis is not apparent, serial measurements with a ruler over several weeks appears to be the most reasonable method, at the present time, of discriminating hyperplastic lymph nodes from nodes that are involved by a progressive disease process.

Adolescent↗
PubMed1981

Specific diseases mimicking appendicitis in childhood.

Of 1,039 children who underwent exploratory surgery with a preoperative diagnosis of acute appendicitis, 112 (11%) did not have suppurative, gangrenous, or perforated appendices. A specific disease other than appendicitis was found in 43 of these 112 children. Three fourths of these children (32/43) had their pathologic process diagnosed at the time of operation: one fourth (11/43) had the diagnosis made postoperatively on the basis of culture, histologic examination, roentgenograms, laboratory studies, or repeated exploratory surgery. More than half (24/43) required operation to treat the disease encountered. Although most of these children had diseases of the adjacent ileum and cecum or the pelvic adnexae, a number had disease outside the immediate operative field. A nonindurated appendix encountered at the time of operation for childhood appendicitis requires a thorough intra-abdominal exploration to exclude another disease that requires operative therapy.

Abdomen↗
PubMed1981

Omphalocele: a prognostic classification.

A classification for infants born with an omphalocele is proposed that is based on the recognition of four syndromes and two common associated anomalies. The recognition of these syndromes and anomalies in our newborns with an omphalocele provided a better estimate of expected mortality and morbidity than the size of the omphalocele, preoperative rupture, delay in treatment, or low birth weight. This classification should aid the physician in determining priorities regarding the timing and type of treatment for the omphalocele itself.

Abnormalities, Multiple↗
PubMed1981

Omphalocele: treatment options.

The charts of 62 infants born with an omphalocele were reviewed to determine both the timing and type of treatment that yielded the most satisfactory result. Infants born with an omphalocele can be divided into prognostic groups based on physical examination and simple roentgenograms. No single treatment method is applicable to or optimal for all types of omphalocele. Treatment options can be selected based on the presence or absence of conditions requiring emergency operation, the presence of complicating anomalies, and the size of the omphalocele. Although urgent evaluation of all infants born with an omphalocele is essential, emergency operation should be avoided in selected cases.

Abnormalities, Multiple↗
PubMed1980

Studies on the role of sulfhydryls in the myosin ATPase. Characterization of the site of modification by the bifunctional sulfhydryl reagent p-N,N'-phenylenedimaleimide.

Myosin has been modified with near stoichiometric amounts of the bifunctional reagent [14C]p-N,N'-phenylenedimaleimide (pPDM) in the presence of MgADP under conditions which abolish its ATPase activity. Subsequent carboxymethylation and CNBr cleavage results in the 14C label being associated with a single polypeptide of Mr approximately 10,000. Amino acid composition and partial sequence analysis of this peptide showed that it corresponded to the peptide containing -SH1 and -SH2 sequenced by Elzinga and Collins (Elzinga, M., and Collins, J.H. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 4281-4284) and to the peptide labeled at -SH1 or -SH2 by N-ethylmaleimide by Kunz et al. (Kunz, P.A., Walser, J.T., Watterson, J.G., and Schaub, M.C. (1977) FEBS Lett. 83, 137-140). These data indicating that pPDM does label the -SH1- and -SH2-containing region in myosin by covalently bridging them and shows that in the presence of MgADP these thiols can approach to within 12 to 14 A.

Adenosine Triphosphatases↗
PubMed1980

Calcium and phosphate requirements of preterm infants who require prolonged hyperalimentation.

Preterm infants require large amounts of calcium and phosphate to maintain skeletal mineralization during prolonged hyperalimentation. It is impossible to supply the amount of calcium and phosphate normally acquired transplacentally (150 mg/kg/day of calcium and 80 mg/kg/day of phosphate) with reasonable volumes of a single hyperalimentation solution of a physiological pH. We recently encountered calcium phosphate precipitates plugging our hyperalimentation catheters as we tried to raise the calcium concentration above 20 mEq of calcium per liter of hyperalimentation solution. Such a solution supplies 50 mg/kg/day of calcium when run at 125 mL/kg/day. In an attempt to circumvent this problem, we are currently using two hyperalimentation solutions--one high in calcium and the other high in phosphates--run alternately for 12-hour periods. This regimen supplies 80 mg/kg/day of calcium.

Bone and Bones↗