What is a pressure–volume curve?

The pressure–volume (PV) curve is a physiological tool proposed for diagnostic or monitoring purposes during mechanical ventilation of acute respiratory distress syndrome. The reduction in compliance measured by the PV curve and the different inflection points on the curve are considered interesting markers of the severity of and the levels of opening and closing pressures. Tracing a curve, however, may in itself influence the degree of opening or distension of the lung, and interpretation of the curve has to take this effect into account. In some individuals tracing the curve may even have moderate hemodynamic effects. Fortunately, on average, most of these effects are transient or negligible and do not invalidate the PV curve measurement.     

Diagnosis of diffuse and localized arrhythmogenic right ventricular dysplasia by gated blood-pool SPECT.

This study aimed to assess the ability of global and local systolic parameters measured with gated blood-pool SPECT (GBPS) to diagnose and characterize the severity of diffuse or localized arrhythmogenic right ventricular dysplasia (ARVD). METHODS: Fifty-nine subjects with symptomatic ventricular arrhythmias were prospectively included in the study. With the International Society and Federation of Cardiology criteria for ARVD as a gold standard, these subjects were classified as subjects without ARVD (21 control subjects) and patients with localized ARVD (16 patients) or diffuse ARVD (22 patients). Right ventricular volumes, right ventricular ejection fractions (EF), the SD of local EF (sigma-EF), and the SD of the local times of end systole (sigma-TES) were computed from GBPS data and compared among the groups in the study population. RESULTS: sigma-EF did not differ between control subjects and patients with diffuse or localized ARVD. Right ventricular EF and volumes differed between patients with diffuse ARVD and control subjects, with similar areas under the receiver-operating-characteristic curves, but right ventricular EF and volumes failed to differentiate patients with localized ARVD. In contrast, sigma-TES differed between patients with diffuse or localized ARVD and control subjects. Regression analysis showed that the systolic parameter most strongly associated with the diagnosis of ARVD was sigma-TES. The probabilities of a randomly chosen patient in the diffuse ARVD group and of a randomly chosen patient in the localized ARVD group having sigma-TES values greater than that of a randomly chosen control subject were 98.5% and 96.7%, respectively. For the diagnosis of localized ARVD, a threshold of 80 ms for sigma-TES corresponded to sensitivity, specificity, and positive and negative predictive values of 100%, 81%, 80%, and 100%, respectively. CONCLUSION: With GBPS, both diffuse ARVD and localized ARVD can be accurately diagnosed by computing sigma-TES for all of the pixels on the surface of the right ventricle.     

Evaluation of a Bayesian method of amikacin dosing in intensive care unit patients with normal or impaired renal function

Our study was designed to determine the population pharmacokinetic parameters of amikacin in intensive care unit patients and to develop a Bayesian method allowing individual estimation of pharmacokinetic parameters. A two-stage method was used for estimating the population characteristics of the pharmacokinetic parameters. Calculations of optimum doses and dosing intervals were based on individual parameters. Our results indicate that the Bayesian method is capable of estimating the individual pharmacokinetic parameters with no significant bias and good precision. Individualization of amikacin dosage was assessed 70 times in 52 patients. To determine the predictive performance of the method, observed peak and trough levels were compared with predicted values by computing precision, bias, and correlation. The amikacin dosing method was unbiased and showed a high correlation coefficient (r = 0.962) between measured and predicted drug serum concentrations. No significant differences were found between the predicted and observed peak (17.3 +/- 3.5 and 17.3 +/- 3.8 micrograms/ml, respectively) and trough (2.86 +/- 0.93 and 3.08 +/- 1.41 micrograms/ml, respectively) amikacin serum concentrations. Among the 52 patients, wide variations were observed in the pharmacokinetic parameters (Vd = 0.21-0.50 L/kg; t 1/2 = 1.1-22 h) and the daily doses (2.8-42 mg/kg/day).