Dynamics of invasive pressure monitoring systems: clinical and laboratory evaluation

Seven pressure monitoring systems were evaluated in the clinical setting and in the laboratory to assess their adequacy for recording invasive blood pressures. We found that a large number of systems used in the clinical setting gave erroneous pressure results because of inadequate dynamic response. Results of testing similar systems in the clinical setting and under optimal laboratory conditions differed greatly. Four major findings were made: (1) Air bubbles in the monitoring systems near the transducer accounted for most of the variability of the dynamic characteristics of systems in the clinical setting; (2) simple catheter transducer system setups performed better, suggesting that simple "kits" be used; (3) membrane domes perform adequately if they are attached with care and according to the manufacturer's specifications; and (4) extension tubing was detrimental to the dynamic response of all systems, especially for pulmonary artery catheters. Fast-flush testing of pressure monitoring systems is needed to ensure the adequacy of dynamic response characteristics in the clinical setting. If the fast-flush characteristics are inadequate, physicians and nurses have the opportunity to troubleshoot the system and remove air bubbles and excessive tubing and to properly attach the transducer domes until optimal characteristics are obtained.

Obesity and body image: an evaluation of sensory and non-sensory components

Body image in 38 obese and normal weight subjects was measured using a video TV monitor. Tasks included a continuous task where subjects manipulated the size of their body image on a TV screen, and a discrete task, where they judged the accuracy of their TV image which was presented as either too heavy or too thin. Subjects viewed their images in both regular street clothes and with minimal clothing. Results from the continuous task revealed that obese subjects overestimated body size. All subjects were more accurate on trials in which the initial image was adjusted in the heavier direction. On the discrete task, a signal detection analysis revealed sensory sensitivity differences between obese and normal weight subjects. Obese subjects were better at detecting distortion caused by a too thin image, but were inferior in detecting a too heavy distortion. No significant differences were obtained in response criteria or between clothing conditions.

Purification and characterization of an exo-beta-1,4-glucanase from Ruminococcus flavefaciens FD-1

An exo-beta-1,4-glucanase (Exo A) from Ruminococcus flavefaciens FD-1 was purified to homogeneity and characterized. Enzyme activity was monitored during purification by using the substrate p-nitrophenyl-beta-D-cellobioside (NPC). Over 85% of the NPC activity was found to be extracellular once the filter paper was degraded (7 days). Culture supernatant was harvested, and the protein was concentrated by ultrafiltration. The retentate (greater than or equal to 300,000 Mr), containing most of the activity against NPC, was then fractionated with a TSK DEAE-5PW column. This yielded a sharp major peak of NPC enzyme activity, followed by a broader, less active area that appeared to contain at least six minor peaks of lower enzymatic activity. Further purification was achieved by chromatography with a hydroxylapatite column. Finally, gel filtration chromatography yielded a homogeneous enzyme (Exo A) as determined by silver stains of both sodium dodecyl sulfate- and nondenaturing electrophoresis gels. Substrate specificity experiments and the products of cellulose digestion indicate that the enzyme was an exo-beta-1,4-glucanase. Exo A required Ca2+ for maximal activity and had an apparent Km of 3.08 mM for NPC, with a Vmax of 0.298 mumol/min per mg of protein. The enzyme had an Mr of 230,000, as determined by gel filtration chromatography, and was a dimer of 118,000-Mr subunits. The N-terminal amino acid sequence of the enzyme is presented.

Turbine flowmeter vs. Fleisch pneumotachometer: a comparative study for exercise testing

The purpose of this study was to investigate the characteristics of a newly developed turbine flowmeter (Alpha Technologies, model VMM-2) for use in an exercise testing system by comparing its measurement of expiratory flow (VE), O2 uptake (VO2), and CO2 output (VCO2) with the Fleisch pneumotachometer. An IBM PC/AT-based breath-by-breath system was developed, with turbine flowmeter and dual-Fleisch pneumotachometers connected in series. A normal subject was tested twice at rest, 100-W, and 175-W of exercise. Expired gas of 24-32 breaths was collected in a Douglas bag. VE was within 4% accuracy for both flowmeter systems. The Fleisch pneumotachometer system had 5% accuracy for VO2 and VCO2 at rest and exercise. The turbine flowmeter system had up to 20% error for VO2 and VCO2 at rest. Errors decreased as work load increased. Visual observations of the flow curves revealed the turbine signal always lagged the Fleisch signal at the beginning of inspiration or expiration. At the end of inspiration or expiration, the turbine signal continued after the Fleisch signal had returned to zero. The "lag-before-start" and "spin-after-stop" effects of the turbine flowmeter resulted in larger than acceptable error for the VO2 and VCO2 measurements at low flow rates.

Contractions of the isolated uterus stimulated by epidermal growth factor

Epidermal growth factor (EGF) produces uterine contractions in tissues removed from immature and adult rats. EGF produces both an increase in resting tone and the development of rhythmic contractions, and this effect is abolished by treatment with antibodies against EGF. The ED50 for this response is observed at an EGF concentration of 3.5 nM. This in vitro effect of EGF requires treatment of the animals in vivo with estradiol for 24 h before removal of uterine tissue. This effect of estradiol does not appear to be due solely to an induction of tissue EGF receptors. These results demonstrate a new activity of EGF and suggest a previously unrecognized function for this peptide growth factor.

Factors influencing production of 5(E)-19-nor-10-keto-vitamin D3 by rumen bacteria

Mixed populations of rumen bacteria or Clostridium hastiforme (a rumen isolate) catalyzed the oxidation of vitamin D3 to 5(E)-19-nor-10-keto-vitamin D3. The reaction depended upon small amounts of O2 (less than 0.1% dissolved O2); when O2 was available, supernatant obtained from heat-killed mixed cultures also produced 5(E)-19-nor-10-keto-vitamin D3. Results obtained by ultrafiltration indicated that at least two heat-stable factors of bacterial origin were involved. Lower rates of the same oxidation were observed when O2 was introduced to solutions containing vitamins D3 and L-cysteine. Oxygen radicals are known to be produced in such solutions and the involvement of such radicals in the D3 oxidation is probable since production in cysteine solutions was inhibited by superoxide dismutase and catalase.

Measurement of anaerobic threshold in chronic airflow obstruction

We compared determinations of anaerobic threshold (AT) made from measurements of arterial lactate concentration with AT determined from ventilatory response measurements of subjects with chronic airflow obstruction (CAO). Six untrained subjects with CAO performed incremental maximal cycle ergometer tests. Ventilation (VE); O2 uptake (VO2), CO2 output (VCO2); end-tidal CO2 fraction (FETCO2); and end-tidal O2 fraction (FETO2) were measured breath by breath. Arterial lactate concentration was sampled at rest and every 30 s during exercise from an indwelling arterial catheter. For three subjects with more severe airflow obstruction, plots of VE/VO2 and FETO2 failed to detect AT. In contrast, a systematic increase of the respiratory gas exchange ratio across the lung (R) accompanied increasing arterial lactate concentrations in all 6 subjects. We conclude that progressive increases of VE/VO2 and FETO2 cannot be relied upon for the measurement of AT in patients with severe CAO. Progressive increases of R unaccompanied by decreasing FETCO2 detect AT in CAO.

Interactions between estrogen and EGF in uterine growth and function

The rat uterus contains specific, high-affinity EGF receptors which possess a tyrosine kinase activity. As demonstrated autoradiographically, these receptors are present in the epithelial, stromal and myometrial cells of the uterus. Estrogen treatment in vivo produces a 2-3-fold increase in EGF receptor levels in the immature rat, the immature mouse and the ovariectomized adult rat; furthermore, EGF receptor levels vary throughout the estrus cycle in concert with levels of occupied nuclear estrogen receptor. This estrogen-induced increase in EGF receptor is preceded by an increase in the level of EGF receptor mRNA as judged by Northern blot analysis. In general, there is a good correlation between estrogen-induced DNA synthesis and EGF receptor levels in the uterus, although in certain situations EGF receptor levels are elevated without a subsequent increase in DNA synthesis. These observations suggest that an increase in tissue EGF receptor levels is important in estrogen-induced uterine growth, but that this increase in receptor levels alone is not sufficient to stimulate DNA synthesis. In addition to its possible role in tissue growth, we have shown very recently that EGF causes contraction of myometrial smooth muscle in a completely in vitro organ bath system. The qualitative nature of this contractile response is distinct from that produced by other classical uterotonic agents. The physiological significance of this uterine response to EGF remains to be elucidated.

Computer surveillance of hospital-acquired infections and antibiotic use

Surveillance of hospital-acquired infections and antibiotic use is required of US hospitals. The time and cost needed to actively perform this surveillance can be extensive. We developed a computerized infectious disease monitor that automatically generates four types of surveillance "alerts" for patients with hospital-acquired infections, not receiving antibiotics to which their pathogens are susceptible, who could be receiving less expensive antibiotics, or who are receiving prophylactic antibiotics too long. Surveillance personnel using computer screening for two months found more hospital-acquired infections when compared with our traditional surveillance methods, while requiring only 35% of the time. In addition, alerts from the computer identified 37 patients not receiving appropriate antibiotics, 31 patients who could have been receiving less expensive antibiotics, and 142 patients, during one month, receiving prolonged cephalosporin prophylaxis. Computer screening can help focus the activities and improve the efficiency of hospital surveillance personnel.

Signal-detection analysis of recognition memory of obese subjects

Obese and normal-weight subjects were run on a series of recognition-memory tasks with low and high meaningful CVC trigrams. Subjects received feedback or no feedback regarding the appropriateness of their answers during testing for recognition memory. A signal-detection analysis was used to examine a relatively pure index of memory (d') as compared to response-bias factors [Ln (beta)]. No significant main effect on memory of obese and control subjects was noted although a significant interaction indicated that obese subjects' memory increases over trials in a differential fashion from normal-weight individuals with poorer performance among the obese after 3 trials. Feedback facilitated memory for both groups. Analysis of response criteria [Ln (beta)] showed no significant difference between groups. Highly meaningful trigrams had a significantly lower response criterion than low meaningful trigrams and there was a significant interaction of meaningfulness by trials. An interaction of feedback by meaningfulness was also present. Advantages of using a signal-detection analysis in memory studies comparing obese and normal weight subjects are discussed. Ramifications of the present data for the internality/externality hypothesis of obesity are also discussed.

Optimizing the electrocardiogram and pressure monitoring

Monitoring the electrocardiogram and directly measuring BP provide current and important data for intraoperative and ICU patient management. However, these physiologic measurements are not infallible; their accuracy is largely dependent on the careful set-up and use of the measuring instruments. This report integrates practical clinical and engineering information to provide a basis for optimizing ECG and pressure monitoring in the clinical setting.

Classical conditioning of pupillary constriction

Previous attempts to condition classically the pupillary response have resulted in mixed outcome. Studies using light as the UCS have generally been unsuccessful while those studies using shock as the UCS have been more successful. In the present study six subjects were visually presented 15 CVC trigrams while their pupil sizes were monitored. Five of the CVCs had been previously presented, five had been previously presented while paired with shock, and five had not been previously presented. Analysis indicated that more pupillary constriction occurred to the five CVCs paired with shock than those presented without shock or those not previously presented. The resulting classically conditioned pupillary constriction is discussed in terms of the development of meaning through classical conditioning.

Effect of a diabetic state on myometrial ultrastructure and isolated uterine contractions in the rat

Alterations in rat myometrial ultrastructure and in vivo uterine contractile responses to oxytocin were examined in estradiol-treated (40 micrograms/kg) euglycemic and streptozotocin-induced (85 mg/kg) diabetic rats. Myometrial morphology was examined 18, 24, and 36 hr after estradiol administration. At the time points examined, nuclei of myometrial cells from euglycemic and diabetic rats were pleomorphic and contained large areas of heterochromatin dispersed throughout the nuclei. Mitochondria were round to oval in shape and contained a dense matrix with cristae that extended across the mitochondria. Myofilaments were found in both euglycemic and diabetic cells but the relative number of myofilaments in diabetic cells appeared to be less than the number found in myometrial cells removed from euglycemic animals. The number of free cytoplasmic ribosomes in diabetic cells also appeared to be less than those found in euglycemic cells. In order to determine if apparent differences in the number of myofilament found in diabetic myometrial cells could be correlated with changes in uterine contractile responses to hormones, oxytocin dose-response curves (10(-8) to 10(-5) M) were examined in isolated uteri removed from saline-injected and estradiol-injected (24-hr pretreatments) euglycemic and diabetic rats. The maximal contractile responses (milligrams tension developed per milligrams tissue) in saline-injected euglycemic and diabetic rats were 49 +/- 5 and 36 +/- 4, respectively, while maximal contractile responses in estradiol-injected euglycemic and diabetic rats were 68 +/- 7 and 45 +/- 5, respectively. Maximal contractile responses induced by oxytocin in estradiol-treated diabetic uteri were significantly smaller than the contractile responses measured in euglycemic estradiol-treated uteri. This study demonstrates that estradiol-induced changes in both myometrial cell morphology and in vitro uterine contractile responses to oxytocin are altered in diabetic rats.

Effects of distraction and task complexity on reaction time in obese persons

40 obese and 40 normal weight individuals were given a series of reaction time (RT) tasks in the presence or absence of a distracting 75-dB static noise under varying levels of task complexity. Both RT and movement time (MT) from a "home" button to a response button were recorded. There were no significant differences in RT between obese and normal subjects although a significant interaction between task complexity and subjects' weight showed that obese subjects had a faster mean RT on the 1-light task but slower RTs on the choice-discrimination tasks with 2, 4, or 8 lights. Obese subjects had a significantly faster mean MT at all levels of task complexity. The distracting stimulus had no differential effect on over-all RTs although an interaction of distraction X task complexity was obtained. The distractor significantly decreased MT for all subjects with no differential for the groups. The results are not in accordance with previous RT studies which supported the internality/externality hypothesis about obesity but rather support the view that obese subjects approach the experimental task with a differential level of motivation or response set.

Frequency of wedge pressure errors in the ICU

Using 94 flow-directed pulmonary artery catheters in 53 ICU patients, we obtained prospectively 282 pulmonary artery wedge pressure (WP) measurements from 286 attempts. After catheter manipulation, 96% of these WP measurements were ultimately free of technical problems, and 84% were confirmed by aspiration of pulmonary capillary blood from the wedge position. The 95% confidence interval for repeated measurements of WP in stable ICU patients was 4 mm Hg. The WP measurement error was defined as the difference between unconfirmed and confirmed WP pairs obtained from stable patients. The probability of encountering a WP measurement error of at least 4 mm Hg was 33% for the 93 WP measurements with technical problems, 5% for the 189 WP measurements without technical problems, and 14% for the entire set of 286 WP measurement attempts. Quality control procedures, including dynamic response testing, easily identified most errors.

Computer charting: an evaluation of a respiratory care computer system

A respiratory care computer-charting system was developed and implemented as an addition to our hospital's computerized information system. Medical personnel charted and reviewed respiratory care procedures at nursing station computer terminals instead of using the patient's traditional paper chart. The computer automatically performed billing and provided management as well as clinical information. In an attempt to isolate specific benefits or shortcomings, we evaluated charting systems both before and after computer implementation. Four assessments were made: (1) a survey of therapists' attitudes, (2) an observation of work patterns, (3) an audit of the content of charting, and (4) an analysis of productivity statistics. Computer charting was well accepted by therapists. Charge capture was reduced from a four-step manual process to a single-step computer documentation of the procedure. Computer charting was more complete and informative. Productivity increased 18%, although it remains unclear to what degree the computer was responsible. Computer charting streamlined the process of documentation and allowed more beneficial use of clinical information.

Computerized data management and decision making in critical care

Computers are being increasingly employed in all levels of society. Computer applications in clinical medicine have lagged behind administrative and billing functions. However, computers are now finding an increasingly useful place in critical care medicine. The complexity of the patients' conditions and the large amount of data generated by critically ill patients provide an ideal area of application for computers. The computer can assist in collecting data, calculating derived parameters, speeding data communications, record keeping, report generation, and decision making. This article has discussed and illustrated how the computer can aid in the care of the critically ill.

Exercise performance of subjects with ankylosing spondylitis and limited chest expansion

To examine the mechanism of exercise limitation associated with chest wall restriction (CWR), we compared the ramp (1 W/3 s) exercise performance of six untrained subjects with ankylosing spondylitis (AS) and six healthy subjects matched for age and body size. Subjects with AS had CWR (maximum rib cage expansion : 1.4 +/- 0.2 cm; means +/- sem). The maximum oxygen uptake (VO2max) of AS subjects (2.15 +/- 0.2 1-stpd) was less than their predicted VO2max (2.68 +/- 0.13 1-stpd; p less than 0.03) and the measured VO2max of matched healthy subjects (2.78 +/- 0.22 1-stpd; p less than 0.03). Subjects with AS achieved 95 percent of predicted maximum heart rate, and their maximum voluntary ventilation exceeded their maximum exercise ventilation by at least 15 l X min-1 unless parenchymal pulmonary disease was present. We conclude that maximum ramp exercise performance of AS subjects with CWR is decreased. Deconditioning or cardiovascular impairment rather than ventilatory impairment appears responsible for the observed reduction of VO2max.

Effects of mepacrine on uterine contractile responses

Mepacrine is a potent inhibitor of uterine contractile responses in vitro. Pretreatment of isolated rat uterine horns with mepacrine (1.3 X 10(-4)M) for periods of time ranging from 15 s to 5 min prior to the addition of carbachol (1.0 X 10(-4)M) showed that mepacrine could significantly reduce carbachol-induced uterine contractile responses within 15 s of exposure. The maximal inhibitory effects of mepacrine on uterine contractile responses were observed within 2 min of mepacrine treatment. A dose-response study related to the effect of increasing concentrations of mepacrine (7.5 X 10(-6) to 1.3 X 10(-4)M) on carbachol-induced (1 X 10(-4)M) uterine contractions revealed that a dose of 3.1 X 10(-5)M mepacrine reduced the carbachol-induced contraction by 50%. A dose of 7.8 X 10(-5)M mepacrine produced the maximal inhibitory effect on the carbachol-induced uterine contractions. Two doses of mepacrine (3.1 X 10(-5) and 1.3 X 10(-4)M) significantly reduced maximal contractile responses and shifted contractile dose-response curves of carbachol, oxytocin, prostaglandin F2 alpha, and BaCl2 to the right. Based on the nonselective inhibition by mepacrine of contractile responses induced by different uterotonic agents, these results suggest that mepacrine cannot be used to characterize the role of phospholipase in regulating the actions of hormones in uterine tissue.

Development of a computerized infectious disease monitor (CIDM)

At the LDS Hospital in Salt Lake City, an interface was developed between the microbiology laboratory computer system and the HELP integrated central hospital computer system. The HELP system includes medical information from most clinical care support areas. The microbiology data are translated from the laboratory computer file structure to a hierarchical data structure on the HELP system. A knowledge base was created with the help of infectious disease experts, and became part of a Computerized Infectious Disease Monitoring system (CIDM). The knowledge base is automatically activated when specific microbiology data are entered into a patient's computer file (data driven), thus decisions are made automatically with no additional effort required of medical personnel. The CIDM was designed to inform infectious disease personnel when a patient has one of the following conditions: a hospital-acquired infection, an infection at a normally sterile body site, an infection due to a bacteria with an unusual antibiotic sensitivity pattern, an infection for which the patient is not receiving an antibiotic to which the offending bacteria is sensitive, an infection that could be treated with a less expensive antibiotic, an infection which is required by law to be reported to state and national health authorities, and those patients receiving prophylactic antibiotics longer than is medically indicated. All of the microbiology data are now extensively reviewed by nurses and physicians from terminals at nursing stations or intensive care units. The CIDM is currently being used for hospital-acquired infection surveillance at LDS Hospital.

The reverse affect test: a new interference task

A new interference test requires subjects to read a list of 10 pairs of words with affective responses inappropriate to the terms listed. 80 adults were given the task with significant interference occurring which decreased speed and accuracy of performance. Significantly increased variability was also noted under the condition of interference. The source of interference is discussed and possible uses of this new task are described.

Effects of experimentally-induced diabetes on oestradiol-stimulated changes in the ultrastructure of the rat endometrium

Alterations in endometrial cell morphology following oestradiol treatment of ovariectomized animals were examined in euglycaemic and streptozotocin-induced diabetic rats. Endometrial morphology was examined 18, 24, 36 and 48 h after oestradiol administration. Nuclei of endometrial cells from saline injected euglycaemic and diabetic rats exhibited pleomorphic nuclei with areas of heterochromatin dispersed throughout the nucleus. Nucleoli were homogeneous in appearance and endometrial cells showed no mitotic chromosome function or cell division. The cytoplasm of euglycaemic and diabetic cells contained few mitochondria. The mitochondria that were present contained a uniformly dense matrix and cristae that extended across the mitochondria. The formation of round to oval shaped nuclei with diffuse euchromatin was observed at 18, 24 and 36 h following oestradiol administration in euglycaemic animals. Alterations in nuclear morphology and the formation of euchromatin were absent or reduced at the same time intervals examined in diabetic animals. Nucleoli in oestradiol-treated euglycaemic animals at 18, 24 and 36 h post-injections became very prominent and displayed easily visible granules and fibrillar material. Comparable changes in nucleolar morphology in oestradiol-treated diabetic rats were absent. The development of oval to round mitochondria containing short cristae and an electron-lucent matrix became apparent at 18 h post-injection of oestradiol in euglycaemic control animals. Alterations in mitochondrial morphology did not appear in endometrial cells of oestradiol-treated diabetic animals at any of the time points examined. At 24 and 36 h post-injection of oestradiol in euglycaemic animals, mitotic figures were observed in mitochondrial cells. Cell division and mitotic figures were not observed in oestradiol-treated diabetic animals.(ABSTRACT TRUNCATED AT 250 WORDS)

A prospective comparison of arterial catheter blood and catheter-tip cultures in critically ill patients

To determine if a culture of blood obtained through an arterial catheter reflects culture of the catheter's tip, we studied 68 arterial catheters removed from 65 patients with and without suspected catheter infections. Cultures of blood obtained before catheter removal were compared to catheter-tip cultures. The arterial catheter blood culture was neither sensitive nor highly predictive of positive catheter-tip cultures. Suspicion of catheter infection was not associated with a significantly higher rate of positive catheter-tip or blood cultures.

A computer system for analysis and transmission of spirometry waveforms using volume sampling

A microprocessor-controlled data gathering system for telemetry and analysis of spirometry waveforms was implemented using a completely digital design. Spirometry waveforms were obtained from an optical shaft encoder attached to a rolling seal spirometer. Time intervals between 10-ml volume changes (volume sampling) were stored. The digital design eliminated problems of analog signal sampling. The system measured flows up to 12 liters/sec with 5% accuracy and volumes up to 10 liters with 1% accuracy. Transmission of 10 waveforms took about 3 min. Error detection assured that no data were lost or distorted during transmission. A pulmonary physician at the central hospital reviewed the volume-time and flow-volume waveforms and interpretations generated by the central computer before forwarding the results and consulting with the rural physician. This system is suitable for use in a major hospital, rural hospital, or small clinic because of the system's simplicity and small size.

Physician decision-making--evaluation of data used in a computerized ICU

New instrumentation, techniques and computers have made such large amounts of information rapidly available to ICU clinicians that there is now a danger of information overload. To help with this problem at LDS Hospital, a computerized system was implemented in the Shock-Trauma ICU. This ICU is almost totally computerized with each patient's physiologic, laboratory, drug, demographic, fluid input/output and nutritional data integrated into the patient's computer record. In the ICU, physician decision-making takes place in two situations: during rounds and on-site. For this study, data usage in decision-making was evaluated in both of these environments. The items of data used in decision-making were tabulated into six categories: bedside monitor, laboratory, drugs, input/output and IV, blood gas laboratory, observations and other. Comparisons were made between the portion of the computerized database occupied by a category and its use in decision-making. Combined laboratory data (clinical, microbiology and blood gas) made up 38 to 41% of total patient data reviewed and occupied 16.3% of the database. Observations made up 21-22% of the data reviewed and occupied 6.8% of the database. Drugs, input/output and IV data usage ranged from 13% to 23%, but occupied 36% of the database. Bedside monitor data usage was 12.5% to 22% and occupied 32.5% of the database. The 'other' category, used 2.5% to 5% of the time, made up 8.4% of the database. These results indicate that patient data collection and storage must be evaluated and optimized. This evaluation, along with implementation of the computerized ICU Rounds Report developed for optimal data presentation, will help physicians to evaluate patient status and should facilitate effective decisions.

Effect of O2, N2, and CO2 composition on nonlinearity of Fleisch pneumotachograph characteristics

Although the Fleisch pneumotachograph has many advantages, its flow-conductance characteristics are nonlinear and sensitive to changes in gas composition. The purpose of this study was to assess the effect of different O2, N2, and CO2 compositions on the nonlinearity of the Fleisch pneumotachograph flow-conductance characteristics, by use of a recently developed computerized calibration method. Hospital-grade O2 was mixed with room air to obtain seven gas mixtures (containing O2 percentages of 20.9, 28.3, 38.7, 52.8, 66.7, 78.7, and 99.6%). Within the accuracy of the applied method, the measured flow-conductance curves of the pneumotachograph had the same shape. Relative flow resistance of gas mixtures to room air was directly proportional to their O2 composition. Two O2-N2-CO2 mixtures were also tested. Their relative flow resistance compared with room air was proportional to the viscosity ratios. We concluded that the change in O2, N2, and CO2 composition does not affect the nonlinearity of the Fleisch pneumotachograph flow-conductance characteristics. However, the relative flow resistance compared with room air does change in a predictable way.

Frequency of technical problems encountered in the measurement of pulmonary artery wedge pressure

A total of 2711 pulmonary artery wedge pressure (WP) measurement attempts were made prospectively from WP recordings in 44 (30 men) critically ill patients, using 77 flow-directed catheters. Of these, 322 (12%) failed to yield a WP measurement, and 521 (18%) were associated with technical problems. One half of these technical problems were due to poor dynamic response or damped pressure tracings; other problems included balloon overinflation, partial WP, and inability to aspirate blood from the pulmonary artery (PA) port. Only 50% of wedge blood sampled at the time of initial PA catheterization yielded capillary blood (PO2 greater than or equal to 10 torr higher than PaO2). In 12 stable patients in whom paired measurements were available, there were clinically important differences (-13 to +22 torr) between paired WP measurements made before and after rapid correction of technical problems. Technical problems are common and may be associated with clinically important errors. Those due to poor dynamic response are easily and rapidly detected at the bedside.

Sensitivity to proprioceptive feedback in obese subjects

40 subjects, 20 obese and 20 normal, were run on a weight-discrimination task requiring judgments dependent on proprioceptive feedback. A signal-detection analysis was used to separate sensory factors from non-sensory, response-bias factors in the analysis of the discriminations. Obese subjects were inferior to normals in ability to make sensory discriminations; the largest differences occurred between obese and normal males. Obese subjects also adopted a more strict criterion (beta); the largest differences again occurred for male subjects. Obese subjects showed more variability in their sensory judgments, although there was a significant difference on only one of the 5 discrimination tasks. Results are discussed in terms of the internal-external explanation of obesity.

"Anaerobic threshold": problems of determination and validation

Despite the popularity of the concept of "anaerobic threshold" (AT), the noninvasive detection criteria remain subjective, and invasive validations of AT have been based on lactate data of arterial, mixed venous, venous, and capillary blood samples without any concern for the possible lactate differences from these sources. Eight normal subjects underwent two exercise tests on a bicycle ergometer. The protocol consisted of 3 min of rest, 3 min of 0 work load, and a 20 W/min ramp (1 W/3 s) until exhaustion. Simultaneous arterial and venous blood samples were drawn during the second test. Noninvasive gas response data were measured using a computerized breath-by-breath stress test system. Threshold phenomenon of the lactate accumulation was not found. The arterial lactate levels increased continuously after the start of the exercise ramp. The rise in venous lactate lagged behind the rise of the arterial lactate by about 1.5 min, and therefore venous lactate was not considered suitable for AT detection. Four independent exercise physiologists determined AT from the gas response data. The reviewer variability (avg range 16%) of AT for a given subject was representative of AT values reported for untrained and trained individuals (40-70% maximum O2 consumption). We concluded that 1) AT is not detectable using invasive methods (arterial and venous lactates); and 2) the noninvasive gas response determination has such a large range of reviewer variability that it is unsuitable for clinical use.

The risk of infection related to radial vs femoral sites for arterial catheterization

To evaluate risk factors for infections associated with indwelling arterial catheters, 186 catheters were randomly allocated for either femoral or radial insertion in 155 critically ill patients. Femoral catheters were easier to insert and it was easier to obtain blood specimens from them. Rates of local infection at the insertion sites and rates of positive catheter-tip cultures were similar for femoral and radial catheters. Evidence of local infection was not predictive of a positive catheter-tip culture. Percutaneously inserted femoral and radial artery catheters had a similarly low incidence of catheter-associated infections. There was only one catheter-related infection, and no cultured catheter was judged the cause of bacteremia. Routine prophylactic replacement of arterial catheter systems may be unnecessary in critical care units where rates of arterial catheter-associated infections are low.

Spirometry: what paper speed?

Controversy still exists regarding the paper speed necessary for accurate measurements from records of maneuvers for forced vital capacity. Twenty-four spirometric wave forms of known characteristics were plotted by a computer at 1, 2, and 3 cm/sec and were measured in random order by 12 experienced readers. We found that all readers made a surprisingly large number of major errors. The speed of the paper was found to be an important determinant for accurately measuring the forced expiratory volume in one second and the mean forced expiratory flow during the middle half of the forced vital capacity. A minimum paper speed of at least 3 cm/sec is important if spirograms are to be accurately measured by hand. Human errors in measurement may be minimized by obtaining results from at least three acceptable curves, by making duplicate reading of curves, and by making use of validated computerized measurement systems.

Sensory and non-sensory factors and the concept of externality in obese subjects

9 obese and 9 normal subjects performed a psychophysical task in which food- or non-food-related stimuli were briefly flashed tachistoscopically at a speed and intensity near the visual threshold. A signal was presented on one-half the trials and noise only on the other one-half of the trials. Using signal detection theory methodology, separate measures of sensory sensitivity (d') and response bias (beta) were calculated. No differences were noted between obese and normal subjects on measures of sensory sensitivity but significant differences on response bias. Obese subjects had consistently lower response criteria than normal ones. Analysis for subjects categorized by whether they were restrained or unrestrained eaters gave findings identical to those for obese and normal. The importance of using a methodology that separates sensory and non-sensory factors in research on obesity is discussed.

The effect of ventilation on the accuracy of pulmonary artery and wedge pressure measurements

A comparison was made of automated versus manual measurement of pulmonary artery (PA) and wedge (WP) pressures. The manual pressure measurements were taken at end-expiration whereas the automated measurements were taken using existing monitor and computer algorithms. A total of 40 critical care patients were divided into groups according to the ventilatory mode used (spontaneous, intermittent mandatory ventilation [IMV], or assist/control). In patients who were breathing spontaneously, the automated method underestimated mean PA pressure (MPAP) (p less than 0.01), WP (p less than 0.001), and PA diastolic (p less than 0.001) pressure but not PA systolic pressure. In patients on IMV, the automated method underestimated MPAP (p less than 0.05), WP (p less than 0.001), and PA diastolic (p less than 0.001) pressure and overestimated PA systolic pressure (p less than 0.05). In patients on assist/control, the automated method overestimated WP (p less than 0.001) and PA systolic (p less than 0.005) pressure pressure, underestimated PA diastolic (p less than 0.001) pressure and did not affect MPAP. The error was not affected by respiratory rate, thoracic compliance, or level of PEEP. The errors in automated pressure measurements believed to be clinically important varied with the ventilatory mode used. Patients breathing spontaneously had the largest measurement error, with 42% of these patients having a clinically important error in WP and 99% having a clinically important error in PA diastolic pressure. Patients on assist/control had the fewest errors in automated pressure measurements. In all ventilatory modes used, automated measurement of PA diastolic pressure had the largest amount of error.

Reference values for pulmonary tissue volume, membrane diffusing capacity, and pulmonary capillary blood volume

Pulmonary tissue volume (Vti), carbon monoxide diffusing capacity, membrane diffusing capacity, pulmonary capillary blood flow and pulmonary capillary blood volume were measured in ninety (54 men and 36 women) healthy lifetime nonsmokers using an inert gas rebreathing technique. Prediction equations were generated using multiple linear regressions with height and age as the independent variables. Normalizing the data by dividing by functional residual capacity eliminated all sex differences. In contrast to the other variables, normalized pulmonary tissue volume did not correlate with any of the independent variables tested. Therefore, an average normalized Vti value can be recommended as a reference value

A portable volume/flow calibrating syringe

Two samples of a manual 3 L calibrating syringe which displays an electronically calculated FEF25-75% were evaluated to determine its suitability as a flow calibrator were evaluated. Room air was discharged into a manual spirometer system known to be accurate. The calibrator-determined values correlated very closely with the spirometer values over an FEF25-75% range of 0.4 to 9 L/sec. The differences between calibrator and spirometer FEF25-75% values were small (mean +/- 1 percent, greatest 3.7 percent) and of little importance clinically. This portable, simple to operate calibrating syringe provides accurate FEF25-75% and volume values. By adding flow calibrating capability to a recommended standard volume calibrating syringe, it will facilitate the routine calibration of spirometers in the laboratory and in the field. Since it uses displaced air, it can be used at altitude and with flow measuring instruments without the correction required for calibrators using CO2 cartridges.