Bernard J. Rubal

Effect of Magnesium Sulfate on Ventricular Rate Control in Atrial Fibrillation

STUDY OBJECTIVES The objectives of this study were to assess the efficacy of parenteral magnesium sulfate (MgSO4), digoxin, and combined MgSO4-digoxin therapies in acutely lowering ventricular rates in patients with newly recognized atrial fibrillation. DESIGN A randomized, double-blinded, placebo-controlled clinical study. SETTING US Army tertiary care facility. PARTICIPANTS Fifteen adults (mean age, 62 +/- 19 years) presenting with newly recognized atrial fibrillation and rapid ventricular rate (more than 99). INTERVENTIONS Patients were given an initial parenteral MgSO4 bolus with continuous infusion or placebo. After 30 minutes, all patients were given 0.5 mg IV digoxin and followed for 3.5 hours. MEASUREMENTS AND MAIN RESULTS Ventricular rates were obtained at baseline, every 5 minutes for the first 30 minutes, and then every 30 minutes for 3.5 hours. At 5 minutes, ventricular rates decreased 16 +/- 7% (P < .02) with MgSO4; this was comparable with rate control with digoxin (18 +/- 9%) at 4 hours. Rate control tended (26 +/- 7%) to improve with combined therapy. CONCLUSION Parenteral MgSO4 may be useful in the acute management of rapid ventricular rates in patients with atrial fibrillation.

Isolated aorta setup for hemodynamic studies

A setup consisting of a high-performance hydraulic pump connected to the ascending part of an isolated aorta, including all major distal branches, each loaded with calibrated artificial resistors, was developed. The system was used to study total aortic compliance of the baboon as a function of mean aortic pressure (n=5). The aorta loaded with the resistors was mounted in a custom-designed sink table, such that it was submersed in physiological saline maintained at 37°C. Mean distending pressure in the entire aortic compliance from pressure and flow waves generated by the pump. Total aortic compliance as a function of mean pressure was fitted with a logarithmic function: Ln (Compliance)=A+B * P. The value of A(±SE) was: 1.565±0.319 and B: −0.020±0.003 (P<0.001). The results were compared with previously published results (also using the same three-element Windkessel fit) obtained in three of the same animalsin vivo. Thein vivo data were A: 1.095±0.235 and B: −0.019±0.003.In vitro data had a significantly higher value of A thanin vivo (P=0.017), implying a significantly higher aortic compliancein vitro thanin vivo.Occlusion of the proximal descending aorta was performed at a low distending pressure (55 mm Hg) to determine the proximal complicance. It was found (n=4) that 46±11% (SD) of the total arterial compliance is to be attributed to the ascending and proximal descending aorta.

Hemodynamic response to rapid pneumatic antishock garment deflation

Irreversible hypotension with subsequent cardiovascular collapse has been reported as a catastrophic complication of inappropriate pneumatic antishock garment (PASG) deflation. This study was undertaken to analyze the cardiodynamic response by which PASG deflation produces hypotension. Five normovolemic patients undergoing cardiac catheterization for atypical chest pain syndrome volunteered for this study. Serial measurements of right atrial, right ventricular, pulmonary artery, left ventricular, and aortic pressures were obtained with subjects supine at the following times: prior to inflation of the PASG; during PASG inflation at 100 mm Hg; and during rapid PASG deflation. Pulmonary and aortic flow velocities were recorded in two patients. The application of external pressure with PASG produced a significant increase in left and right heart pressures (P less than .05). Sudden PASG deflation produced significant transient hypotensive changes (P less than .01). When PASG deflation hemodynamics were compared to preinflation data, mean arterial pressure decreased 14 mm Hg (P less than .01); mean pulmonary pressure decreased 6 mm Hg (P less than .01); and mean right atrial and left ventricular end-diastolic pressures decreased 4 and 6 mm Hg, respectively (P less than .01). An analysis of right and left heart hemodynamic data suggests that the early hypotensive response associated with PASG deflation is consistent with a reduction in left ventricular afterload followed by a decrease in preload.

Comparison of binomial, ZAM and minimum cross-entropy time-frequency distributions of intracardiac heart sounds

One reason why automated heart sound analysis remains unfeasible may be the inadequacy of conventional spectral techniques in representing the nonstationary, multicomponent characteristics of phonocardiograms. This study compares several generalized time-frequency distributions (GTFDs) applied to intracardiac phonocardiograms (ICP) obtained at rest in six patients using catheter-mounted transducers. ICPs were bandpass filtered (50-500 Hz) and digitized at 4 kHz. The TFDs employed in this study were the binomial transform (BT), Zhao-Atlas-Marks (ZAM) distribution, minimum cross-entropy (MCE) distributions and the spectrogram. The BT and MCE representations in particular show improved concentration of ICP energy in time-frequency vs. the spectrogram. These findings suggest that several GTFDs may prove useful in the design of automated auscultation systems.<<ETX>>