Biomedical subjects
S Dorrell
Publications and source records attributed to S Dorrell.
The conservative NHS vision. Interview by Norah Casey.
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Coming of age. Interview by Linda Steele.
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Lies, damn lies, and HNS funding figures. Interview by Pat Healy.
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Determined to replace a central pay system. Interview by Dina Leifer.
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The relationship between dialysis graft pressure and stenosis.
RATIONALE AND OBJECTIVES: Pressure measurements during dialysis have been used to screen for venous outlet stenosis, but the relationship between the degree of stenosis and pressure has not been defined. METHODS: To determine this relationship, failing or failed dialysis grafts (n = 34) were studied with angiography and pressure measurements from the segment of the graft near the arterial anastomosis. RESULTS: By linear regression, the relationship between the highest grade stenosis in or central to the graft and pressure was as follows: percent stenosis = 55 systolic graft pressure/systolic blood pressure+13 (r = 0.75). CONCLUSIONS: There is a positive correlation between the severity of stenosis and graft pressure, confirming the use of this measurement in screening for stenosis. It is hypothesized that this relationship is the result of progressive elimination of the normal pressure drop between the artery and arterial limb of the graft as the degree of stenosis increases.
Crime and mental illness.
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Venous access pressures and the detection of intra-access stenosis.
Venous pressure measured by the dialyzer is an unreliable measure of intra-access venous pressure. During dialysis and zero extracorporeal blood flow, intra-access venous limb pressure (VPd) was measured directly 401 times in 133 subjects using a high flow "in-line" three-way stopcock adjacent to the venous return needle. Subjects with systolic VPd/systolic blood pressure (BP) > or = 0.4, inadequate blood flow, or edema in the access extremity were referred for angiography. Percent diameter lumen reduction by a stenosis (%D) > 50% was considered hemodynamically significant. The authors did 138 angiograms. It was found that VPd/BP increased with %D in both ePTFE bridge grafts and native fistulae. Measurements of venous limb VP/BP taken at the time of dialysis and at the time of angiography did not differ (n = 55). On 80 occasions, accesses had significant stenoses. The overall sensitivity of VPd/BP in ePTFE bridge grafts was 91% and specificity 91%. False negative results occurred in seven of 24 native and eight of 114 ePTFE graft studies; 14 of 15 patients had arm swelling caused by central stenosis. Recirculation > 15% was more sensitive (71%) in detecting stenosis in native accesses than was intra-access pressure. It was concluded that VPd/BP > 0.4 is a useful, sensitive, and specific criteria for detecting synthetic bridge graft accesses at risk for thrombosis.
Determinants of measured dialysis venous pressure and its relationship to true intra-access venous pressure.
Venous pressure measured at the venous bubble trap (VPdm) is a complex function of true intra-access pressure (VP0), hematocrit, needle gauge, and blood flow. In a patient free circuit, needle gauge, hematocrit, and blood flow influenced the pressure drop through the venous return needle. Measured intra-access pressure (VPm) and VPdm also were determined 149 times in 83 subjects. The increase in VPdm above VP0 under conditions of flow through 16 gauge needles was affected by blood flow rate, hematocrit, and VP0 with coefficients similar to those found in vitro. Calculation of VP0 from VPdm produced an absolute difference greater than 20 mmHg in 35-40% of cases. Mean VP0 was significantly lower in subjects with native compared with expanded polytetrafluorethylene accesses. It was concluded that VP0 is influenced by access type and can be estimated but that direct measurement is preferred. Direct measurement of VP0 may be a sensitive test to screen for venous outlet stenosis because it should vary with access flow and outlet geometry.
Charter for care. Interview by Adam Legge.
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Evolving health care.
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Tory boy. Interview by Rebecca Coombes.
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