Intra-arterial blood pressure measurement: sources of error and solutions.

Intra-arterial blood pressure measurement is the cornerstone of hemodynamic monitoring in intensive care units (ICU). Accuracy of the measurement is dependent on the dynamic response of the measuring system, defined by its natural frequency (fnatural) and damping coefficient (Zdamping). Gardner's plot (1981) has long been the only way to determine the accuracy of the pressure measurement. Specific objectives: (i) estimation of the amplitude of error in pressure measurement through simulations based on real-world data, (ii) a novel method to correct the error. Simulated blood pressure waveforms of various heart rates were passed through simulated measurement systems with varying fnatural and Zdamping. The numerical errors in systolic and diastolic pressures and mean error in the measured pressure were used to generate heat maps for the various recording conditions, in the same plot as that by Gardner (1981). fnatural and Zdamping from 121 patient recordings are plotted on these heat maps to demonstrate the fraction of unacceptable recordings. Performance of a tunable filter to correct the error is demonstrated. In many clinical settings, the measurement of intra-arterial pressure is prone to significant error. The proposed tunable filter is shown to improve the accuracy of intra-arterial pressure recording.

Elusive Toxin in Cleistanthus collinus Causing Vasoconstriction and Myocardial Depression: Detailed NMR Analyses and Biological Studies of Cleistanthoside A.

Cleistanthus collinus leaf extracts are consumed for suicidal purposes in southern India. The boiled decoction is known to be more toxic than the fresh leaf juice. Although several compounds have been isolated and their toxicity tested, controversy remains as to which compounds are responsible for the high level of toxicity of C. collinus. We report herein that cleistanthoside A is the major toxin in the boiled aqueous extract of fresh leaves and causes death in rats in small doses. The toxicity of the boiled extract prepared in the manner described can be attributed entirely to cleistanthoside A. Cleistanthin A could also be isolated from the boiled extract, albeit in trace amounts. As hypotension not responding to vasoconstrictors is the cause of death in patients who have consumed the boiled extract, effects of cleistanthoside A on the determinants of blood pressure, namely, force of cardiac contraction and vascular resistance, were tested in isolated organ experiments. Cleistanthoside A has a direct vasoconstrictor effect; however, it inhibits ventricular contractility. Therefore, the notion that the shock in C. collinus poisoning is of vascular origin must be considered carefully, and the possibility of cardiogenic shock must be studied. We present the crystal structure of cleistanthin A and show the potency of fast NMR methods (NOAH4-BSCN-NUS) in the full spectral assignment of cleistanthoside A as a real-world sample of a natural product. We also compare the results of the NOAH4-BSCN-NUS NMR experiments with conventional NMR methods.