Blood Pressure Monitoring with Improved Noise rejection

Blood Pressure Monitoring with Improved Noise rejection

US Patent No.  5,873,836  February 23, 1999

A method and apparatus is provided for distinguishing blood pressure sounds from noise in an automatic blood pressure monitoring system using the information contained in two microphone signals. Two microphones are placed on a patient along an axis of an artery to pick up blood pressure sounds. Pressure is applied to the artery such that the artery opens and closes during each heart cycle, the opening snap of the artery producing a blood pressure sound. The two microphone signals are sampled, filtered, and multiplied together to produce a microphone signal product. The microphone signal product is wave width filtered to remove therefrom portions of the signal having a wave width which is less than a selected minimum wave width value. A blood pressure sound is indicated as being detected when an amplitude of this wave width filtered microphone signal product exceeds a noise signal threshold level. The microphone signal product is also wave width filtered to remove therefrom portions of the signal having a wave width which is greater than a selected maximum wave width value. The amplitude of the resulting noise amplitude signal is used to adjust dynamically the noise signal threshold level in response to changing noise conditions. The detection of blood pressure sounds at a range of applied pressure levels is used to determine the systolic and diastolic blood pressure levels of the patient.

 

 

Method and Apparatus for Processing a Physiological Signal

Method and Apparatus for Processing a Physiological Signal

US Patent No.  6,339,715 B1  January 15, 2002

US Patent No. 6,647,280 B2  November 11, 2003

A signal processing method, preferably for extracting a fundamental period from a noisy, low-frequency signal, is disclosed. The signal processing method generally comp rises calculating a numerical transform for a number of selected periods by multiplying signal data by discrete points of a sine and a cosine wave of varying period and summing the results. The period of the sine and cosine waves are preferably selected to have a period substantially equivalent to the period of interest when performing the transform.

 

 

 

Epidural Intracranial Pressure Monitoring: A New Methodology

Epidural Intracranial Pressure Monitoring: A New Methodology

The new sensor is designed for easy placement in epidural space and acts as a pneumatic flow switch. Air enters plenum at 40 cc/mm. Outside pressure against membrane will close off exhaust. The pressure which builds up within the plenum to overcome pressure against the membrane and re-establish air flow represents the ICP. The sensor is injection molded and disposable.

Limited Use Medical Probe

Limited Use Medical Probe

US Patent N0.  US 6,308,089 B1   October 23, 2001

US Patent No.  US 7,048,687 B1  May 23, 2006

A limited use medical probe is disclosed including a memory for maintaining a use value. The medical probe is coupled to a medical device that inhibits its function when the use value reaches a predetermined threshold value, preventing improper use of the probe. The probe memory may also store identification, usage, and clinical data. A probe auto-identification function, a probe re-identification function and a probe functional test sequence are disclosed for the medical probe. After use, a reprocessing step may reset the probe memory, permitting further probe use.

Physiological Simulation

Physiological Simulation

Computer modeling of physiological systems typically requires some knowledge of computer programming. The ultimate goal is to provide computer programs which allow the users to simply insert the necessary equations so they can devote their full attention to the models they are simulating. By using a language such as BASIC, which is easily learned, even the non expert can solve complex mathematical problems with relative ease. While some authors have stressed the uses of modeling for teaching purposes, this paper will emphasize the research aspect.

 

Epidural Intracranial Pressure Monitoring: a New System

Epidural Intracranial Pressure Monitoring: a New System

An intracranial pressure (ICP) monitoring system has been developed, consisting of an epidural sensor acting as a pneumatic flow switch connected by tubing to a pneumatic system and microprocessor-based monitoring unit. The frequency response to the system is 8 Hz at 10 mmHg measured peak to peak. ICP and arterial pressure data are collected and maintained in memory. The ICP in memory can be scrolled across a 2-hour or 24-mm graphic and digital video display. When memory is not being recalled, the previous 2 hours or 24 mm of data are displayed on the screen in graphic form. High and low ICP, low cerebral perfusion pressure, and abnormal pressure waves trigger alarms. Calibration of the system is maintained automatically by periodic rezeroing of all transducers to air. Changes in volume within the pneumatic system indicate a leak, and airflow ceases. The software management and alarm systems, as well as available memory, represent the latest in computerized technology.

Accelerations Aboard the NASA KC-135

Accelerations Aboard the NASA KC-135

During the typical 30s microgravity flight maneuvers of the NASA KC-135 aircraft, it is essential that pitch and power requirements are strictly adhered to in order to provide a laboratory space within an aircraft that is free of inertial accelerations. Thrust must precisely offset drag, which at first diminishes, then increases with passage through the apex of the parabola. During the maneuver, the pitch angle of the aircraft changes from approximately +45 deg to a -45 deg, causing a torque at every station except at the aircraft’s center of mass.

Narrowband Auscultatory Blood Pressure Monitor

Narrowband Auscultatory Blood Pressure Monitor

Auscultatory blood pressure measurement uses the presence and absence of acoustic pulses generated by an artery (i.e., Korotkoff sound), detected with a stethoscope or a sensitive microphone, to noninvasively estimate systolic and diastolic pressures. Unfortunately, in high noise situations, such as ambulatory environments or when the patient moves moderately, the current auscultatory blood pressure method is unreliable, if at all possible.  Empirical evidence suggests that the pulse beneath an artery occlusion travels relatively slow compared with the speed of sound. By placing two microphones along the bicep muscle near the brachial artery under the occlusion cuff, a similar blood pressure pulse appears in the two microphones with a relative time delay. The acoustic noise, on the other hand, appears in both microphones simultaneously.  The contribution of this paper is to utilize this phenomenon by filtering the microphone waveforms to create spatially narrowband information signals. With a narrowband signal, the microphone signal phasing information is adequate for distinguishing between acoustic noise and the blood pressure pulse. By choosing the microphone spacing correctly, subtraction of the two signals will enhance the information signal and cancel the noise signal. The general spacing problem is also presented.

A miniature Skin-Attached Hot Flash Monitor

A miniature Skin-Attached Hot Flash Monitor

A skin conductance monitoring system was developed and shown to reliably acquire and record hot flash events in both supervised laboratory and unsupervised ambulatory conditions. The 7.2 × 3.8 × 1.2 cm3 monitor consists of a disposable adhesive patch supporting two hydrogel electrodes and a reusable, miniaturized, enclosed electronic circuit board that snaps onto the electrodes. The monitor measures and records the skin conductance for seven days without external wires or telemetry and has an event marker that the subject can press whenever a hot flash is experienced. The accuracy of the system was demonstrated by comparing the number of hot flashes detected by algorithms developed during this research with the number identified by experts in hot flash studies. Three methods of detecting hot flash events were evaluated, but only two were fully developed. The two that were developed were an artificial neural network and a matched filter technique with multiple kernels implemented as a sliding form of the Pearson product-moment correlation coefficient.  Both algorithms were trained on a ‘development’ cohort of 17 women and then validated using a second similar ‘validation’ cohort of 20. All subjects were between the ages of 40 and 60 and self-reported ten or more hot flashes per day over a three day period. The matched filter was the most accurate with a mean sensitivity of 0.92 and a mean specificity of 0.90 using the data from the development cohort and a mean sensitivity of 0.92 and a mean specificity of 0.87 using the data from the validation cohort. The matched filter was the method implemented in our processing software.

Period Domain Analysis in Fetal Pulse Oximetry

Period Domain Analysis in Fetal Pulse Oximetry

The photoplethysmographic signals acquired during pulse oximetry can be compromised in many ways.  Intrapartum fetal pulse oximetry in particular presents challenges to signal processing. Period domain analysis can overcome the low pulsatile amplitudes, noise, and maternal modulation found in these signals. The efficiency of an incremental algorithm reduces the processing requirements for period domain analysis, facilitating use in low-power and portable devices.