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Biomedical subjects

A B Campbell

Publications and source records attributed to A B Campbell.

12 recordsLinked to original sources
PubMed1984

Diastolic coronary artery pressure-flow velocity relationships in conscious man.

We characterised the diastolic pressure-flow velocity relationship in the normal left coronary artery of conscious man before and after vasodilatation with angiographic contrast medium. Phasic coronary artery pressure and flow velocity were measured in ten patients during individual diastoles (0.5 to 1.0 s) using a 20 MHz catheter-tipped, pulsed Doppler transducer. All pressure-flow velocity curves were linear over the diastolic pressure range of 110 +/- 15 (SD) mmHg to 71 +/- 7 mmHg (r = 0.97 +/- 0.01). In the basal state, values for slope and extrapolated zero flow pressure intercept averaged 0.35 +/- 0.12 cm X s-1 X mmHg-1 and 51.7 +/- 8.6 mmHg, respectively. Vasodilatation resulted in a 2.5 +/- 0.5 fold increase in mean flow velocity. The diastolic pressure-flow velocity relationship obtained during peak vasodilatation compared to that during basal conditions was characterised by a steeper slope (0.80 +/- 0.48 cm X s-1 X mmHg-1, p less than 0.001) and lower extrapolated zero flow pressure intercept (37.9 +/- 9.8 mmHg, p less than 0.05). Mean right atrial pressure for the group averaged 4.4 +/- 1.7 mmHg, while left ventricular end-diastolic pressure averaged 8.7 +/- 2.8 mmHg. These observations in man are similar to data reported in the canine coronary circulation which are consistent with a vascular waterfall model of diastolic flow regulation. In this model, coronary blood flow may be regulated by changes in diastolic zero flow pressure as well as in coronary resistance.

Adult↗
PubMed1984

Interpretation and physiological significance of diastolic coronary artery pressure-flow relationships in the canine coronary bed.

We analyzed the relationship between diastolic coronary artery pressure and flow in the canine coronary bed, using an electrical analog model of the coronary circulation based on the theory of critical closure. The model contains a voltage-dependent nonlinear resistance and capacitance. The behavior of the resistive element was described using experimental diastolic pressure-flow curves obtained in the absence of compliance effects. Compliance free zero flow pressure intercepts (Pf0) exceeded coronary venous pressure (Pv) by 2- to 5-fold and were related to initial diastolic coronary artery pressure Pa(0) and flow F(0), and Pv by: Pf0 = 14.3 [(Pa(0) - Pv)/F(0)] + Pv + 4.0 (r = 0.93). When coronary artery pressure was suddenly lowered to values less than or equal to the compliance-free Pf0, diastolic flow abruptly decreased and, after a transient reversal, remained at zero for up to 8 seconds. In the model, zero flow pressure represents critical closing pressure and the resistance regulating flow is the difference between coronary artery and venous pressure divided by flow. Theoretically predicted pressure-flow curves were in good agreement with existing experimental data, including the effects of elevating coronary venous pressure on zero flow pressure. Differences between compliance-free pressure-flow curves and those obtained with pressure gradually decreasing were explained by a coronary arterial compliance whose magnitude varies inversely with pressure and is dependent on vasomotor tone. In conclusion, the results of this study demonstrate the existence of a diastolic pressure gradient across the canine coronary bed at zero flow which is dependent on coronary vasomotor tone. A theoretical model of the coronary circulation based on the concept of critical closure describes the observed relationship between diastolic coronary artery pressure and flow during various experimental conditions.

Animals↗
PubMed1984

Recertification: toward the development of standards for assuring continued competence.

NCCPA, in collaboration with NBME, has begun an investigation that may lead to the development of standards for measuring continued competence. In 1981, the 1980 Primary Care Physician's Assistants Certification Examination was administered as a recertification examination to 1,166 PAs who were originally certified in 1975. The scores were standardized by using the standardization constants for the 1980 Certification Examination reference group. There was a difference between the performance of the certification examinees and the performance of the recertification examinees, with recertification examinees doing less well on all sections than the certification examinees. Correlations calculated between recertificants' performance on their original certification examination and their performance on the recertification examination showed a positive relationship between the two examinations. Their performance on a variety of biographical variables was also analyzed, and the only variable that significantly changed their performance was their current employment status. The validity of the test for making judgments about the competence of experienced practitioners was not addressed by the current study and is a crucial question in evaluating the test as a recertification instrument.

Certification↗
PubMed1983

Plasma platinum levels: relationship to cisplatin dose and nephrotoxicity.

Renal dysfunction is the dose-limiting toxic effect for many patients receiving cisplatin (CP). Despite hydration and/or forced diuresis, some patients develop nephrotoxicity, and patients at risk cannot be easily identified. We studied 77 patients with several types of carcinoma who received 115 cycles of CP, by 24-hour infusion, at doses of 40-100 mg/m2. Blood samples for platinum (Pt) analysis were obtained during and after CP infusion; plasma Pt levels were dose- and time-dependent. A significant rise in serum creatinine was seen after the first cycle and cumulatively over subsequent CP cycles. The largest subgroup of patients, those who received 80 mg/m2, was analyzed for predictors of nephrotoxicity. Twenty-five percent of patients exhibited nephrotoxicity (greater than 30% rise in serum creatinine or greater than 30% fall in creatinine clearance). These nephrotoxic patients had significantly higher plasma Pt levels during CP infusion than did nonnephrotoxic patients. Age, sex, cycle number, and pretreatment creatinine did not predict nephrotoxicity. Patients predisposed to nephrotoxicity with CP chemotherapy may be identifiable, on the basis of elevated plasma Pt, early in the course of CP infusion.

Cisplatin↗