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Biomedical subjects

J Horrocks

Publications and source records attributed to J Horrocks.

10 recordsLinked to original sources
PubMed2002

Optimization of scanning parameters for CT colonography.

To determine the optimal collimation, pitch and reconstruction interval for CT colonography, 10 spherical polyps between 1 mm and 10 mm diameter and made of tissue equivalent material with a CT number of 40 Hounsfield units (HU) were placed in the colon of an anthropomorphic phantom. The phantom was scanned at slice thicknesses of 3 mm, 5 mm and 7 mm and pitches of 1.0, 1.3, 1.5, 1.7 and 2.0 on an IGE Hispeed advantage system. Images were reconstructed for each scanning parameter at the minimum intervals allowed along the z-axis. The optimum scanning protocol was assessed by measuring maximum contrast between the polyp and air, sensitivity for detection of each polyp along the z-axis, and relative radiation dose. In addition, images were reviewed separately by two radiologists who graded polyp conspicuity as: 0, not seen; 1, faintly seen; 2, well seen. It was found that varying the scanning parameters caused a marked alteration in the maximum contrast between each polyp and air. For example, for the 5 mm polyp, the range of contrasts from best to worst case was 910-490 HU. It was noted that with contrasts of less than 500 HU, polyps were only faintly seen. A slice thickness of 3 mm with a pitch of 2 offers optimal polyp conspicuity with a relatively low radiation dose, we conclude that scanning parameters can be optimized for threshold contrast, radiation dose and subjective conspicuity. We propose an optimal parameter of 3 mm slice thickness and pitch 2.

Anthropometry↗
PubMed2000

Effects of digoxin on acute, atrial fibrillation-induced changes in atrial refractoriness.

BACKGROUND: Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The acute changes in atrial refractoriness may be related to tachycardia-induced intracellular calcium overload. The purpose of this study was to determine whether digoxin, which increases intracellular calcium, potentiates the acute effects of AF on atrial refractoriness in humans. METHODS AND RESULTS: In 38 healthy adults, atrial ERP was measured at basic drive cycle lengths (BDCLs) of 350 and 500 ms after autonomic blockade. Nineteen patients had been treated with digoxin for 2 weeks. After a several-minute episode of AF, atrial ERP was measured serially at alternating BDCLs. Compared with pre-AF ERPs, the first post-AF ERPs were significantly shorter in both the digoxin and the control groups (P:<0.001). The post-AF ERP at a BDCL of 350 ms shortened to a greater degree in the digoxin group (37+/-16 ms) than in the control group (20+/-13 ms, P:<0.001); similar changes occurred at a BDCL of 500 ms. During post-AF determinations of the atrial ERP, secondary AF episodes occurred significantly more often in the digoxin group (32% versus 16%; P:<0. 04). CONCLUSIONS: After a brief episode of AF, digoxin augments the shortening that occurs in atrial refractoriness and predisposes to the reinduction of AF. These effects occur in the setting of autonomic blockade and therefore are more likely to be due to the effects of digoxin on intracellular calcium than to its vagotonic effects.

Administration, Oral↗
PubMed2000

Comparative audit of tonsillectomy.

The Comparative Audit Service of the Royal College of Surgeons of England undertook an audit of tonsillectomy throughout England and Wales in 1997. There were three parts to the audit: a management questionnaire related to tonsillectomy and its indications; an inpatient questionnaire for patients undergoing tonsillectomy; and a postoperative patient questionnaire. One hundred and fourteen ENT consultants returned the management questionnaire, 2450 questionnaires on inpatient details were returned by 132 consultants, and 1408 patients returned postoperative questionnaires. Two-thirds of the patients underwent tonsillectomy for recurrent acute tonsillitis, and most stayed 1 night in hospital; only 3% were day cases. Postoperative haemorrhage necessitated return to theatre for 0.75% of patients. Almost 7% of patients had to be readmitted after discharge. Overall, 92% of patients felt that their throat was better than before the operation, but slightly less than this number (88%) were pleased that they had the operation. The results are further discussed in the paper. The ability to cross-reference each part of the audit for individual patients proved extremely useful.

Adolescent↗
PubMed1999

Attentional ability among survivors of leukaemia.

Attentional ability in 19 survivors of acute lymphoblastic leukaemia and 19 sibling controls was assessed using a neuropsychological model of attention. Analysis revealed that children who had received treatment for leukaemia exhibited significantly poorer performance on measures of the "focus encode" and "focus execute" elements of attention and on measures of the ability to respond to external cues and feedback. No significant differences in performance were found for measures of sustained attention and the ability to shift attention. These results indicate that children who have received treatment for leukaemia may experience highly specific attentional deficits that could have an impact on academic performance, particularly mathematical and reading skills. It is suggested that this underlying attentional deficit might be the source of the neuropsychological sequelae associated with the disease. Future attempts at remediation should incorporate activities specifically designed to ameliorate focusing difficulties.

Antineoplastic Agents↗
PubMed1996

Utilization of health care services in patients with severe obstructive sleep apnea.

We compared the health care utilization of 97 obese patients diagnosed with obstructive sleep apnea (OSA) and 97 matched control subjects. Over a 2-year period that ended 2 years prior to initial diagnosis, the OSA group had 251 nights in hospital, compared to 90 nights for the control group. During the same 2-year period, total expenditures from physician claims were $82,238 (Canadian dollars) in the OSA patients versus $41,018 in the control group (p < 0.01). Depending upon which assumptions one uses for the calculation of hospital costs, during the same 2-year period, the 97 OSA patients utilized between $100,000 and $200,000 more in services than their control counterparts. We conclude that sleep apnea patients are already heavy consumers of health care services prior to any specific evaluation and treatment for apnea.

Adult↗
PubMed1993

Ligand binding to the haem-copper binuclear catalytic site of cytochrome bo, a respiratory quinol oxidase from Escherichia coli.

The Escherichia coli quinol oxidase, cytochrome bo, is closely related to the cytochrome-c oxidase, cytochrome aa3 and reacts with ligands to the high-spin ferric haem or the high-spin ferric-cupric binuclear catalytic site in similar ways. Cyanide reacts with the isolated enzyme to give a low-spin complex, manifested by a red shift in the Soret band, the loss of an absorption band at 630 nm and the appearance of a low-spin ferric haem EPR resonance at g = 3.3. Sulphide also elicits a low-spin complex, whereas azide gives a mixture of low-spin and high-spin species. Formate and fluoride (and azide) give a blue shift in the Soret band and the development of a modified absorption band in the 600-650 nm range. These latter species are attributed to an integral spin compound involving the binuclear centre.

Anions↗