Technology and health care : official journal of the European Society for Engineering and Medicine
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Technol Health Care · Jan 2004
Effect of strain rate on tensile properties of sheep disc anulus fibrosus.
We investigated the effect of loading rate on tensile properties of sheep bone-anulus-bone specimens in axial direction. Disc anulus Samples with adjacent bone attachments were prepared from lateral, posterior and anterior regions of sheep lumbar spinal segments. The specimens were then tested at different strain rates under non-destructive cyclic tensile loading followed by destructive tensile loading. ⋯ However, there was a significant increase in the modulus at linear region as strain rate increased. Two major modes of failure were observed; rupture in the anulus mid-substance and at the anulus-endplate junction. The former failure was more frequent with no clear pattern across strain rates and locations, while the latter failure at anulus-endplate junction occurred primarily at slow strain rates.
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Technol Health Care · Jan 2003
Continuous monitoring of tracheal pressure including spot-check of endotracheal tube resistance.
During mechanical ventilation, the resistance of the endotracheal and tracheostomy tube (ETT) highly influences analysis of respiratory system mechanics and imposes additional work of breathing for the spontaneously breathing patient which both can be circumvented by applying the automatic tube compensation (ATC) mode. In the ATC mode, tracheal pressure (ptrach) is continuously calculated on the basis of measured flow and airway pressure using predetermined tube specific coefficients. However, as during long-term ventilation the ETT might become partially obstructed by secretions or tube kinking, the predetermined coefficients are no longer valid rendering calculation of ptrach inaccurate. ⋯ Accuracy of the procedure was determined during artificial ETT obstruction by comparing calculated with measured ptrach. Correspondence between calculated and measured ptrach has been found excellent. We conclude that by adopting this bedside procedure periodically, accurate calculation of ptrach is guaranteed and the advantages of the ATC mode are ensured even in long-term ventilatory support.
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The quality of the notifications issued within the European Medical Device Vigilance system were retrospectively reviewed and the adequacy of the recommended guidelines evaluated. The study material comprised all 589 vigilance notifications the Finnish competent authority received from manufacturers and other national competent authorities during 1997, 1999, and 2001. The number of vigilance reports, particularly the reports issued by national competent authorities, has increased from 82 in 1997 up 166 in 2001 while the proportion of reports with demonstrated bearing on health risk has decreased from about 40% down to 20% during the last five years. ⋯ It is obvious that the present vigilance guidelines provide adequate guidance for both the manufacturers and competent authorities to manage vigilance cases efficiently and appropriately. It is crucial that all pertinent parties should adopt the recommended procedures and act accordingly. The vigilance system underpinned with high quality notifications only assures the continuous enhancement of patient safety, the bottom line.
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Technol Health Care · Jan 2001
Analysis of mechanical stresses within the alveolar septa leading to pulmonary edema.
Mechanical ventilation has been associated with pulmonary edema in the clinical setting, but the pathophysiological mechanisms of this process have not been clearly defined. Experimental studies have shown that high transpulmonary pressures resulting from ventilation may damage the capillary walls, thereby leading to edema. ⋯ Significant stress concentrations were shown to develop near highly curved regions (small local radii of less than 4 mum in a lung inflated to 80% could be as high as 25 times that of average septal stresses. The combination of elevated stress sites that are formed in the stiffer parenchyma of the aging lung, together with the cyclic loading of ventilation, may explain the gaps and breaks previously observed in pulmonary edema.
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We describe a model for simulating a spontaneous electroencephalogram (EEG) and for simulating the effects of anesthesia on the EEG, to allow anesthesiologists and EEG technicians to learn and practice intraoperative EEG monitoring. For this purpose, we developed a linear model to manipulate the amplitude of the activity in each of the traditional EEG frequency bands. ⋯ Using these estimates, EEG time signals were simulated for isoflurane at various partial pressures, and for bolus intravenous doses of thiopental. Comparison with actual recorded EEG signals showed that the changes produced by isoflurane and thiopental in the simulated signals are very similar to the changes in the actual signals, which was confirmed by two clinicians with experience and routine practice in intraoperative EEG monitoring.