Biomedical subjects

T Lubkowski

Publications and source records attributed to T Lubkowski.

6 recordsLinked to original sources

PubMed1998

Simplified measurement of intra-access pressure.

The measurement of intra-access pressure (P[IA]) normalized by mean arterial BP (MAP) helps detect venous outlet stenosis and correlates with access blood flow. However, general use of P(IA)/MAP is limited by time and special equipment costs. Bernoulli's equation relates differences between P(IA) (recorded by an external transducer as PT) and the venous drip chamber pressure, PDC; at zero flow, the difference in height (deltaH) between the measuring sites and fluid density determines the pressure deltaPH = P(IA) - P(DC) Therefore, P(DC) and PT measurements were correlated at six different dialysis units, each using one of three different dialysis delivery systems machines. Both dynamic (i.e., with blood flow) and static pressures were measured. Changes in mean BP, zero calibration errors, and hydrostatic height between the transducer and drip chamber accounted for 90% of the variance in P(DC), with deltaPH = -1.6 + 0.74 deltaH (r = 0.88, P < 0.001). The major determinants of static P(IA)/MAP were access type and venous outflow abnormalities. In grafts, flow averaged 555 +/- 45 ml/min for P(IA)/MAP > 0.5 and 1229 +/- 112 ml/min for P(IA)/MAP < 0.5. DeltaPH varied from 9.4 to 17.4 mmHg among the six centers and was related to deltaH between the drip chamber and the armrest of the dialysis chair. Concordance between values of P(IA)/MAP calculated from PT and from P(DC) + deltaPH was excellent. It is concluded that static P(DC) measurements corrected by an appropriate deltaPH can be used to prospectively monitor hemodialysis access grafts for stenosis.

Arteriovenous Shunt, Surgical↗

PubMed1992

Improved nutritional follow-up of peritoneal dialysis patients with bioelectrical impedance.

A threat to survival in renal failure, malnutrition in continuous ambulatory peritoneal dialysis patients (CAPD) is often occult as CAPD patients often gain weight masking actual protein malnutrition. Bioelectrical impedance (BEI) accurately assesses body composition in CAPD patients and uncovers subtle changes in lean body mass (LBM) that escape indirect anthropometric detection. Segregating parameters of body composition is crucial to nutritional management of CAPD patients in whom fat may account for overall weight gain. While both skin-fold methods and BEI correctly distinguished thin and overweight patients in terms of fat mass, only BEI accurately segregated these patients by LBM (P = 0.007). Serial weights of 39 CAPD patients followed longitudinally for three or more months did not correlate with BEI-measured changes in LBM. LBM was lost in 49% of patients as determined by BEI, while serial weights detected a loss of LBM in 36% of these patients. Strikingly, by serial weights, 64% of patients demonstrated weight gain; however, in 24% of these an actual loss of LBM was demonstrated by BEI. BEI provides specific quantitation of LBM in CAPD patients with changing body habitus and unrecognized nutritional derangement.

Adult↗

PubMed1992

Use of bioelectrical impedance for the nutritional assessment of chronic hemodialysis patients.

Although malnutrition poses a significant risk to the well-being of chronic hemodialysis patients, their nutritional assessment is usually empirical. We studied body composition by bioelectrical impedance (BEI) prospectively in 39 patients followed for 5-12 months. BEI correctly discriminated between underweight and overweight patients in terms of fat mass (21 +/- 5 vs. 34 +/- 10%; p = 0.002), lean body mass (78 +/- 4 vs. 67 +/- 10%; p = 0.004) and total body water (57 +/- 3 vs. 49 +/- 7%; p = 0.002), respectively. Serial body weights did not correlate with changes in lean body mass (LBM) as measured by BEI. While 28% of patients lost weight, 41% lost LBM. Most striking is the contrast between the patients who showed no change in LBM by BEI and those whose body weight remained neutral (3 vs. 28%). BEI is a most sensitive clinical tool for assessing changes in LBM in hemodialysis patients.

Body Composition↗

PubMedDate not supplied

Simplified measurement of intra-access pressure.

Normalized intra-access pressure (PIA), expressed as the access pressure/systemic blood pressure, detects venous outlet stenosis and correlates with access blood flow. General use of (PIA) is limited by time, special equipment needs, and cost. We therefore correlated pressure measurements from the venous drip chamber (PDC of Fresenius H-machines and from an external transducer, P tau, for blood flows (BFR) of 0 to 400-500 ml/min. Measurements were conducted 2-3 weeks apart in a cohort of 33 patients. PDC = -21 + 1.28 P tau; PDC = P tau = 75 mmHg at BFR = 146 ml/min. The major determinant of P tau at BFR = 0 was access type and venous outflow problems. The difference between P tau and PDC (delta = offset) was 17 +/- 1 mmHg (range, 2-43); delta correlated with the height difference between the two sites. Differences in systemic blood pressure, zero calibration, and hydrostatic pressure accounted for 90% of the variance between replicate measurements of PDC. Detection of outlet stenosis was compared by using PIA calculated from P tau and from PDC + 17. Only three of 66 measurements using the latter produced misclassification, and never on replicate measurements. P tau and PDC measurements in 62 additional patients showed a persistent offset of 17 mmHg. The authors conclude that PDC at BFR = 0 can be used to monitor prospectively prosthetic bridge grafts for stenosis as long as the offset for a particular dialysis machine is determined.

Blood Pressure↗

PubMedDate not supplied

Detecting vascular access dysfunction.

Access flow (QACC) is a major determinant of patency. Access recirculation (AR > 2%), normalized venous intra-access pressure (vPIA/MAP), and QACC are used to detect access dysfunction. We compared these three measures of access function (ultrasound dilution to measure AR and QACC). A total of 779 measurements were performed on 58 arteriovenous fistulas (AVFs) and 114 polytetrafluoroethylene (PTFE) grafts (1-8/access) over 13 months, and the access parameters at the beginning of each period were related to access events within that period. Pump blood flow averaged > 420 ml/min. AR occurred uncommonly (3.8%), and in half the cases, resulted from technical error by staff. In accesses that thrombosed or underwent intervention for stenosis, AR was present in only 3 of 11 AVFs and 8 of 57 PTFE accesses. When AR was present in grafts, QACC averaged 270 +/- 23, and access thrombosis followed unless intervention occurred. In grafts, vPIA/MAP averaged 0.34 +/- 0.01 in those remaining patent, 0.52 +/- 0.08 in those that had undergone intervention, and 0.54 +/- 0.04 in those that had thrombosed. QACC averaged 1,121 +/- 26, 605 +/- 45, and 550 +/- 65 ml/min, respectively, in the three groups. By contrast, QACC differed significantly in patent AVFs (1,053 +/- 35) compared with failing AVFs (363 +/- 48), but vPIA/MAP did not. AR is thus a late manifestation of access failure. QACC is the best diagnostic test of access dysfunction in AVFs. Interpretation of vPIA/MAP in grafts is enhanced by periodic QACC measurements.

Arteriovenous Shunt, Surgical↗

PubMedDate not supplied

Detection of access strictures and outlet stenoses in vascular accesses. Which test is best?

The location of stenoses within an access may influence the diagnostic value of access monitoring tests. Whereas decreasing access flow (QACC) should occur with both venous outlet stenoses and strictures within the body of the access, normalized intra-access venous pressure (vPIA/MAP) depends on location of the venous needle relative to the lesion. The authors determined the value of vPIA/MAP and direct measurement of percent access recirculation (AR) and QACC in detecting venous outlet stenoses and strictures. Abnormal access studies were evaluated by Doppler ultrasound and fistulography. Well functioning grafts and arteriovenous fistulas (AVFs) have no AR; QACC averages 1,101 +/- 26 and 1,073 +/- 35 mL/min, and vPIA/MAP ratios are 0.34 and 0.16, respectively. Venous outlet stenoses (n = 36) or strictures (n = 32) were detected before thrombosis or intervention in 172 vascular accesses at risk. QACC in accesses with stricture was significantly lower than in those with venous outlet stenosis (361 +/- 11 vs 526 +/- 43 ml/min), as was less than prescribed blood flow (423 +/- 7 ml/min). AR was not detected in any access with stricture and in only 4 of 36 accesses with outlet stenosis. vPIA/MAP was elevated with venous outlet stenosis but not with strictures. The findings of QACC being less than blood pump flow without AR by dilution methods differentiated strictures from venous outlet stenoses.

Arteriovenous Shunt, Surgical↗