Biomedical subjects

C R Parks

Publications and source records attributed to C R Parks.

17 recordsLinked to original sources

PubMed1984

Distorted segregation and linkage of alcohol dehydrogenase genes in Camellia japonica L. (Theaceae).

Alcohol dehydrogenase isozymes in Camellia japonica are encoded by two genes, Adh-1 and Adh-2. Both loci are expressed in seeds, and their products randomly associate into intragenic and intergenic dimers. Electrophoresis of leaf extracts reveals only the products of Adh-2. Formal genetic analysis indicated that the two Adh loci are tightly linked (combined estimate of r = 0.004). Most segregations fit expected Mendelian ratios, but in some families distorted segregation was observed at Adh-1, Adh-2, or both loci. The deficient progeny class varied across families, and in two apparent back-crosses three rather than two phenotypic classes were recovered. The mechanism underlying these distortions is not known, but evidence is presented that suggests that the phenomenon is genic or segmental in nature. Plausible hypotheses include linkage of the Adh structural genes with a gametophytic self-incompatibility locus, translocation heterozygosity involving the segment bearing Adh-1 and Adh-2, or a combination of these two mechanisms.

Alcohol Dehydrogenase↗

PubMed1979

Use of an inclined footrest for panoramic dental radiography.

An inclined footrest was evaluated as a positioning aid for dental panoramic radiography. Experimental and control groups of students were examined by a conventional panoramic technique, with and without the addition of an inclined footrest. All radiographs obtained were evaluated for six parameters in a single-blind fashion by three dentists. Results indicated that the inclined footrest reduced spinal-shadow artifacts and improved over-all image quality.

Adult↗

PubMed1978

Xeroradiography of dental structures. II. Image analysis.

Xeroradiography provides an attractive, convenient, low-radiation-dose alternative to conventional intraoral film radiography. In this study the image properties of the two techniques were compared quantitatively and qualitatively. Over all, image quality was very similar, but xeroradiography delivered radiation doses seven to fourteen times less than conventional film radiography.

Models, Anatomic↗

PubMed1978

Use of intraoral cassettes for dental xeroradiography.

Before clinical trials of intraoral xeroradiography are begun, we felt the need to evaluate the clinical acceptability of the thicker, more rigid xerographic cassettes. We stimulated these cassettes by fastening rigid acrylic plates of appropriate thickness to conventional film packets and then conducted parallel evaluations of simulated cassettes and conventional film packets, using thirty volunteer patients. We found no difference in anatomic placement, operator acceptance, and patient acceptance between the "cassettes" and film packets. The increased thickness and rigidity of intraoral xerographic cassettes should not prove disadvantageous to in vivo intraoral xeroradiography.

Adolescent↗

PubMed1977

Ventilatory response in the fetal lamb following peripheral chemodenervation.

Carotid infusions of sodium cyanide solution and perfusions of hypoxemic or hypercapnic fetal blood were done before and after peripheral chemoreceptor denervation. Step changes in PaO2 ranged from -11 to -22 Torr; step changes in PaCO2 ranged from +17 to +42 Torr. The cyanide dose was 0.2 mg/kg per loop system. Control perfusions consisted of 25 ml of fetal blood without changes in pH and blood gases. A ventilatory response occurred in the majority of all experimental perfusions regardless of innervation status of the peripheral chemoreceptors. No response occurred with control perfusions. There was a marked variability in the time of onset of ventilatory activity with a delay of greater than 10 s occurring following most perfusions. These studies demonstrate that the fetus has an attenuated ventilatory response to chemical stimuli and that hypoxia stimulates ventilation in the absence of peripheral chemoreceptors.

Animals↗

PubMed1974