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Biomedical subjects

F E Block

Publications and source records attributed to F E Block.

At least 19 recordsLinked to original sources
PubMed1992

Can people hear the pitch change on a variable-pitch pulse oximeter?

The introduction of the variable-pitch feature on pulse oximeters in 1983 by the Nellcor Corporation (Hayward, CA) allowed users to rapidly detect changes in oxygen saturation by listening for changes in the pitch of the tones emitted by the pulse oximeter. A few individuals have reported that they have been unable to detect a change in pitch when oxygen saturation changes. To these individuals, the variable-pitch feature of these pulse oximeters has not been beneficial. Using the pitches from one manufacturer of oximeters, we created a computer program to simulate the pitches that accompanied various oxygen saturations. The pitches were recorded onto a tape player and played for 75 volunteer subjects unfamiliar with the pitches of a variable-pitch pulse oximeter. Of our sample, 67% were able to detect a single change in pitch corresponding to a 1% fall in oxygen saturation, and 11% of the population could not detect a change in pitch until there was a change in pitch with every beat. We suggested four alternative designs that may prove beneficial to this group of individuals.

Acoustic Stimulation↗
PubMed1992

The "Torrstick": a ruler calibrated in millimeters of mercury for measurement of hydrostatic pressure.

We have designed and constructed a ruler ("Torrstick") calibrated in millimeters of mercury for the measurement of hydrostatic pressure differences. Marks are placed on a measuring stick every 1.34 cm, to afford the best compromise between a column of 0.9% saline solution and a column of blood. Several uses for this ruler are proposed, including the measurement of central venous pressure.

Blood Pressure Determination↗
PubMed1992

Evaluation of users' abilities to recognize musical alarm tones.

The problem of accurate identification of alarm sounds in the operating room, recovery room, and intensive care environment has persisted for many years. Monitors made by different companies may have different alarm sounds for the same monitored variable, and similar alarm sounds for different variables. In an effort to illustrate universal alarms sounds, a system of six musical alarm tones was designed with musical themes from popular songs used for oxygenation, ventilation, cardiovascular monitoring, temperature monitoring, artificial perfusion, and drug administration systems. These melodies were played for a group of anesthesiologists and others, who were initially asked to guess the organ system for each melody. The answers were then given to the participants, and after a short delay the melodies were played again in a different order. Seventy-nine response sheets were collected. The expected random score was 1.0 +/- 1.0 SEM correct. The observed score on the first hearing was 1.5 +/- 1.6 SEM, p = 0.01 compared with the random score. The observed score on the second testing was 4.3 +/- 2.2 SEM, p = 0.001 compared with the first hearing. Indeed, 42 of 79 (53%) respondents got all six answers correct on the second testing, versus three respondents for the first testing. The implications of these findings are discussed in the context of integrated alarm systems used in complex medical environments such as the operating room.

Association Learning↗
PubMed1991

Normal fluctuation of physiologic cardiovascular variables during anesthesia and the phenomenon of "smoothing".

With the advent of automated anesthesia record keeping devices, concern has arisen that "abnormal" values will appear in the record and possibly lead to medicolegal compromise. A retrospective review of automated records from a series of anesthesia cases was undertaken to determine if abnormal values do occur, how frequent they are, and whether they cause problems. A total of 14,826 (4,942 each) noninvasive heart rate, systolic, and diastolic blood pressure readings from 118 case printouts generated by a Diatek Arkive Patient Information Management System (63 cases) or a Datascope Datatrac record keeper (55 cases) were recorded. The study sample covered a broad range of surgical operations, anesthetic procedures, and patient ages and medical histories. During these 118 anesthetics, the majority of readings of all three variables fell within normal ranges (defined for this study as 80 to 180 and 50 to 110 mm Hg for systolic and diastolic blood pressures, respectively, and 60 to 140 beats/min for heart rate). During the anesthetics, 3.6% of the systolic pressure readings, 13.25% of the diastolic readings, and 4.25% of the heart rate readings were recorded outside these ranges. No serious intraoperative or postoperative anesthesia complications were associated with these out-of-range readings, nor would they be expected in a sample of this size, since serious anesthetic complications are rare. This preliminary observation of one person's experience may help address the concern associated with allowing high and low blood pressure and heart rate readings to be automatically recorded "unsmoothed." In medicolegal situations, it should also begin to demonstrate that such fluctuations are neither uncommon nor abnormal, and that a true record of these readings should be neither a cause for concern nor an opportunity for medicolegal exploitation.

Adult↗
PubMed1991

A clinical evaluation of rapid automatic noninvasive blood pressure determination with the Ohmeda 2120 "return-to-flow" method.

Most commercial noninvasive blood pressure devices use the oscillometric method for determination of blood pressure. The Ohmeda 2120 noninvasive blood pressure monitor uses the oscillometric technique, but it also includes a "Sys Stat" mode for rapid determination of systolic blood pressure up to ten times per minute. This Sys Stat mode uses the "return-to-flow" method, in which the pressure on an upper arm cuff decreases in small steps until a finger sensor detects the first pulse of blood. Data from 16 patients monitored with the Ohmeda 2120 unit and with an arterial cannula were analyzed. The line of regression was Sys Stat = 0.85 (arterial) + 9.49. The Ohmeda 2120 monitor tended to underestimate the arterial pressure, particularly at higher pressures. Several factors could have contributed to this underestimation. Even so, the accuracy is sufficient for clinical use under most circumstances. More importantly, in an urgent situation, the Sys Stat mode can provide a reading of systolic blood pressure within seconds.

Blood Pressure Determination↗
PubMed1991

Evaluation of a single-room, dedicated mass spectrometer.

A single-room dedicated mass spectrometer can be used to measure carbon dioxide, halogenated anesthetic agents, nitrous oxide, nitrogen, and oxygen. This device challenges the multiplexed mass spectrometer, a current standard in measurement. This study compared the single-room dedicated mass spectrometer with a conventional mass spectrometer that is normally used in a multiplexed setting. In this study, a single-room dedicated Ohmeda 6000 Mini-Mass Spectrometer and the Perkin-Elmer MGA-1100 mass spectrometer were calibrated with the same reference gases and both devices sampled various concentrations of dry gases. Regression lines and intercepts were plotted and showed excellent correlation between the two devices. The intraclass correlation test of Lee, Koh, and Ong, showed the devices to be equivalent with regard to the ability to determine various gas concentrations. Various advantages of a single-room dedicated mass spectrometer are discussed.

Anesthesiology↗
PubMed1989

Delayed recognition of an oximeter malfunction.

Most anesthesiologists, relying upon sales presentations from salesmen from oximeter manufacturers, believe that if an oximeter produces a steady signal with a good pulse amplitude, the numbers are always believable in the absence of interference from external light sources or from intravenous dyes. Here I report a case in which an oximeter appeared to be working properly yet displayed values which were falsely low. Trust in the oximeter resulted in delayed identification of the problem.

Aged↗
PubMed1988

A carbon dioxide monitor that does not show the waveform is worthless.

The author suggests that the carbon dioxide waveform should be displayed, as are the electrocardiogram and arterial pressure waveforms. He argues that a carbon dioxide analyzer that does not provide a waveform is not of value, as subtle changes in the carbon dioxide waveform can reflect impending problems. Only when a plateau is present in the capnogram can one be certain that end-tidal gas is being measured, and the author asserts that the presence or absence of this plateau can be detected only by visually inspecting the waveform.

Carbon Dioxide↗
PubMed1987

Analog and digital computer theory.

Analog signals abound in the natural world. With appropriate transducers these signals can be converted to continuous voltages and can be displayed, transmitted, stored, or copied. They can be processed by analog computers, the simplest of which is an audio amplifier. With analog signals, however, there can be errors because of signals loss, interference, and noise. Binary digital signals permit only two values, either 0 ('off' or 'low') or 1 ('on' or 'high'). These signals are much less susceptible to transmission problems. Binary signals are commonly organized into 8-bit groups which can represent 256 different numbers or meanings. These data can be transmitted in either serial or parallel fashion at high rates of speed. Analog-to-digital converters permit analog signals to be transformed to digital signals. A computer consists of the memory, the processor, and the input/output devices. Memory includes the fastest registers, the very fast core memory, the peripheral storage devices such as diskettes and disks, and the very slow peripheral devices such as magnetic tape. The processor can only load and store numbers in memory, add two numbers, test a number, and provide input and output. The program counter indicates the next computer instruction to be performed. Input/output devices allow communication with the outside world and may assume many forms. A computer by itself can do nothing. A program or series of instructions is required. The most simplistic program language is assembler or machine language. Most programming is done in more sophisticated languages, however.(ABSTRACT TRUNCATED AT 250 WORDS)

Analog-Digital Conversion↗
PubMed1986

Minimizing interference and false alarms from electrocautery in the Nellcor N-100 pulse oximeter.

Because the Nellcor N-100 pulse oximeter is generally quite sensitive to electrocautery interference, erroneous oxygen saturation values may be displayed and an audible false alarm may sound. We have discovered, through trial and error, several techniques that may minimize both the interference and the false alarms. Keeping the pulse oximeter sensor and the oximeter unit as far as possible from the surgical site and the electrocautery grounding plate will usually decrease the interference. If this step is inadequate, the incidence of false alarms can be decreased by setting the high pulse rate alarm to approximately 160, operating the unit in mode 2 (the rapid-response mode), and setting the "alarm off" function to 120 seconds. These steps will usually markedly decrease the incidence of false alarms.

Electricity↗