Journal of clinical monitoring and computing
-
J Clin Monit Comput · Dec 2007
Effects of tissue outside of arterial blood vessels in pulse oximetry: a model of two-dimensional pulsation.
We describe a new model of pulse oximetry that addresses the disagreement between theoretical calibration curves based on Beer-Lambert's Law and test results based on human test subjects. Sources of this discrepancy include variability among human subjects, experimental conditions and the effect of optical radiation propagating in tissue surrounding arteries. Unlike the conventional model, our model considers the change in the relative proportion of light that does or does not pass through blood in pulsating vessels in addition to the change in the path length of optical radiation through the blood. Theoretical calibration curves based on this model agree with human test results and help to explain the variability between in vitro and in vivo test conditions.
-
J Clin Monit Comput · Dec 2007
A new paradigm for the design of audible alarms that convey urgency information.
The current international standard (IEC 60601-1-8) stipulates that medical device audible alarms should be priority-encoded and validated for efficacy. Evidence suggests that the melodic alarms described in the standard are not functioning as originally intended. We present a multi-disciplinary, human factors paradigm for audible alarm development whereby urgency information is encoded via modulation of the physical characteristics of sounds. We also test the feasibility of this approach using information measures. ⋯ The proposed paradigm is feasible, and it offers an evidence-based strategy for alarm sound design and testing. This approach would be performed before implementation of new alarm sounds in clinical settings, and should result in development of alarm sounds that satisfy the requirements of priority-encoding and validation.
-
The instability of cardiac output (CO) measured by PulseCO (LiDCO Ltd.) during cardiac surgery has been reported. In the present study, we investigated the effects of vasodilation by prostaglandin E1 (PGE1) on the relation between cardiac output measured by PulseCO and that by thermodilution. ⋯ PulseCO might underestimate CO compared to that by bolus thermodilution method when simply decreasing the SVR by infusion of PGE1. Therefore, PulseCO might be unsuitable in cardiac surgery.
-
J Clin Monit Comput · Dec 2007
The relationship between the photoplethysmographic waveform and systemic vascular resistance.
The objective of this study was to determine the relationship between systemic vascular resistance (SVR), finger & ear photoplethysmographic measurements in 14 adult patients undergoing coronary artery bypass grafting (CABG). ⋯ The data indicate that pulse width of finger and ear plethysmographic tracing are more sensitive to changes in SVR than the other indices. An appreciation of changes in pulse width may provide valuable evidence with respect to changes in peripheral vascular tone.
-
J Clin Monit Comput · Dec 2007
A system of classification for the clinical applications of capnography.
We have attempted to list all the clinical applications of capnography described to date and classify them into categories. From an extensive Pubmed search 46 clinical applications of capnography were listed. To classify these we used six categories- Airway, Breathing, Circulation, Anesthetic Delivery Apparatus, Homeostasis and Non-perioperative. This list collates the described uses of capnography and this system of classification provides an aide-de-memoir in anesthesia education and simulation.