Journal of clinical monitoring and computing
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J Clin Monit Comput · Jun 2006
Real-time computation of a patient's respiratory effort during ventilation.
In this paper, a new algorithm is proposed to compute the spontaneously generated respiratory effort during ventilation. ⋯ The respiratory effort increases over time until the patient is disconnected from the ventilator. We hope the maximum amplitude can be used as an indicator of the pressure the muscles of the patient are able to produce. This amplitude of the (mus)-signal in combination with the standard deviation (SD) may eventually lead to a new indicator to determine the moment that the patient can be weaned from the ventilator. This will have to be examined in the future.
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J Clin Monit Comput · Jun 2006
Using the morphology of photoplethysmogram peaks to detect changes in posture.
The morphology of the pulsatile component of the photoplethysmogram (PPG) has been shown to vary with physiology, but changes in the morphology caused by the baroreflex response to orthostatic stress have not been investigated. Using two FDA approved Nonin pulse oximeters placed on the finger and ear, we monitored 11 subjects, for three trials each, as they stood from a supine position. Each cardiac cycle was automatically extracted from the PPG waveform and characterized using statistics corresponding to normalized peak width, instantaneous heart rate, and amplitude of the pulsatile component of the ear PPG. ⋯ During standing, the pulse rate always increases, and then amplitude of the ear PPG constricts by a factor of two or more. We hypothesis that the baroreflex first reduces the percentage of time blood flow is stagnant during the cardiac cycle, then increases the hear rate, and finally vasoconstricts the peripheral tissue in order to reestablishing a nominal blood pressure. These three features therefore can be used as a detector of the baroreflex response to changes in posture or other forms of blood volume sequestration.
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J Clin Monit Comput · Apr 2006
Rapid measurement of blood propofol levels: a proof of concept study.
Despite many advantages over traditional volatile anaesthetic techniques, propofol total intravenous anaesthesia (TIVA) makes up a small percentage of general anaesthetics administered. One of the reasons for this is the absence of a clinically useful method for measuring blood propofol concentrations. We have designed and tested a prototype system for rapidly measuring blood plasma levels of propofol using solid phase extraction (SPE) methodology, coupled with colorimetric and spectrometric techniques. ⋯ The results show that this methodology may be suitable for rapid and accurate clinical monitoring of propofol levels during general anaesthesia.
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J Clin Monit Comput · Apr 2006
Ventilator Y-piece pressure compared with intratracheal airway pressure in healthy intubated children.
Compare airway pressure measurements at the ventilator Y-piece of the breathing circuit (P( Y )) to intratracheal pressure measured at the distal end (P( T )) of the endotracheal tube (ETT) during mechanical ventilation and spontaneous breathing of intubated children. ⋯ In healthy children P( Y ) significantly overestimates PIP in the trachea during positive pressure ventilation and underestimates the intratracheal airway pressure during spontaneous inhalation. During positive pressure ventilation P( T ) better assesses the pressure generated in the airways and lungs compared to P( Y ) because P( T ) also includes the difference in airway pressure across the ETT tube due to resistance. During spontaneous inhalation, P( T ) reflects the series resistance of the ETT and ventilator circuit, while P( Y ) reflects only the resistance of the ventilator circuit, accounting for the smaller decreases in pressure. Additionally, P( Y ) underestimates the total WOBi load on the respiratory muscles. Thus, P( T ) is a more accurate reflection of pulmonary airway pressures than P( Y ) and suggests that it should be incorporated into ventilator systems to more accurately trigger the ventilator and to reduce work of breathing.
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J Clin Monit Comput · Apr 2006
The use of joint time frequency analysis to quantify the effect of ventilation on the pulse oximeter waveform.
In the process of determining oxygen saturation, the pulse oximeter functions as a photoelectric plethysmograph. By analyzing how the frequency spectrum of the pulse oximeter waveform changes over time, new clinically relevant features can be extracted. ⋯ Joint time frequency analysis of the pulse oximeter waveform can be used to determine the respiratory rate of ventilated patients and to quantify the impact of ventilation on the waveform. In addition, when applied to the pulse oximeter waveform new clinically relevant features were observed.