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R O Crapo

Publications and source records attributed to R O Crapo.

At least 37 records · Page 2Linked to original sources
PubMed1995

Standard flow-time waveforms for testing of PEF meters.

The American Thoracic Society (ATS) has recommended the use of 24 volume-time waveforms for the testing of spirometers. Although these waveforms include values of peak expiratory flow (PEF), they were not originally intended to test PEF meters, but, rather, volume parameters for spirometers. In addition, the practice of using ATS volume-time Waveform 24 with varying multiplying factors does not provide the range of flow-time waveform shapes (rise times) needed to evaluate PEF meters. Accordingly, we have developed a set of 26 flow-time waveforms specifically selected to evaluate PEF meters. PEF and other flow parameters (rise time and time to PEF) can be directly measured from these flow-time waveforms. When PEF determined directly from the flow-time curve was compared with PEF determined indirectly from a volume-time curve (ATS-recommended algorithm with an 80 ms time segment), as much as a 10.7% difference between the two methods was observed using a waveform with a fast rise time. In contrast, there was very little difference between the various methods of deriving PEF for waveforms with slower rise times. These 26 flow-time waveforms provide a means of defining PEF for the testing of software algorithms and the testing of PEF meters with computer-driven mechanical pumps.

Algorithms↗
PubMed1995

Intraindividual peak flow variability.

OBJECTIVES: To quantify intraindividual variability in peak expiratory flow (PEF) measured with peak flow-meters and to define factors affecting PEF variability. METHODS: Three hundred one healthy subjects (aged 4 to 84 years) were recruited from sites at sea level (n = 220) and at 1,400 m altitude (n = 81). All testing was done with the same model peak flowmeter. Each subject was actively coached through five to eight successive PEF maneuvers. Three meters of the same model were tested using a mechanical waveform simulator at three different flows at both testing altitudes (sea level and at 1,400 m). RESULTS: Excluding outliers, the mean PEF was 523 L/min, mean standard deviation (SD) was 22 L/min, and mean coefficient of variation (CV) was 4.6%. The upper 95th percentile for CV was 8% for adults and 10% for youths. Analyzing only the three highest peak flows for each subject, the mean PEF was 539 L/min, mean SD was 12 L/min, and mean CV was 2.4%. The upper 95th percentile for CV was 6% for adults and 9% for youths. Linear regression analysis revealed a small but statistically significant correlation (p < 0.01) between mean peak flow and CV. In adults, SD correlated with sex (p < 0.01) but neither CV nor SD was correlated with age, height, weight, or altitude. Meter variability defined with the mechanical waveform simulator was small. Standard deviation varied from 1.5 to 4.2 L/min and CV from 0.4 to 1.6%. When the three largest peak flows for each subject were used, 5.5% of intraindividual variance was explained by meter variance. CONCLUSIONS: These estimates of intraindividual variability in healthy subjects are generally lower than those previously reported. Meter variability accounts for only a small part of total intraindividual variability. The 95th percentile data suggest that a fall in PEF of 6 to 8% in adults and 9 to 10% in youths would be statistically significant.

Adolescent↗
PubMed1993

Predicting the presence of pulmonary function impairment in adult respiratory distress syndrome survivors.

Varying degrees of impairment in pulmonary function in survivors of adult respiratory distress syndrome (ARDS) have been reported. Physiologic indices of the severity of disease have been associated with impaired pulmonary function after ARDS, including duration of exposure to FIO2 > 0.6, AaDO2, maximal mean pulmonary artery pressure, lowest total static thoracic compliance, and peak airway pressure. Prediction of impairment following ARDS is difficult because clinical observations may reflect reversible lung injury (e.g. lung edema) and clinical features of ARDS do not predict subsequent function reliably. We developed a severity score to predict the presence of impairment of pulmonary function in 51 ARDS survivors, by examining the following clinical variables: (1) predisposing factor for ARDS; (2) age; (3) sex; (4) severity of hypoxemia; (5) smoking history; (6) number of days of positive pressure ventilation; (7) lowest total static thoracic compliance; (8) maximal mean pulmonary artery pressure, and (9) presence of barotrauma. Pulmonary function studies were performed at least 1 year after ARDS onset. The ARDSscore developed required only two variables: ARDSscorce = duration of positive pressure ventilation (days) minus lowest static thoracic compliance (ml/cm H2O). Significant correlations (p < 0.001) were found between linear regressions of percent predicted FEV1, FVC, TLC and DLCO against ARDSscore. ARDSscore > +20 predicted an 82% probability of impaired FEV1, FVC or TLC and a 100% probability of an impaired DLCO. We conclude that a score based upon duration of positive pressure ventilation and lowest static thoracic compliance predicts impaired pulmonary function more than 1 year after ARDS.

Adult↗
PubMed1992

Evaluation of accuracy and reproducibility of peak flowmeters at 1,400 m.

Peak flow meters provide physicians and patients with objective measures about changes in pulmonary obstruction. We evaluated eight models of peak flowmeters and measured their accuracy and reproducibility with methods recently recommended by the National Asthma Education Program (NAEP). Waveforms from the American Thoracic Society's spirometer testing set were used to drive a computer-controlled syringe. Testing was done at Salt Lake City at an altitude 1,400 m. It appears that the original Wright peak flowmeter has been used as the "de facto" standard. We found that the original Wright peak flowmeter overestimated flows in its midrange; and, as a consequence, most of the other peak flowmeters also overestimated peak flows. The overestimation of peak flows may have been understated because of the 1,400-m altitude testing site. To the credit of the instrument manufacturers, we were pleasantly surprised with the quality, accuracy, and reproducibility of presently available peak flowmeters; however, as a result of our testing, we suspect that with little effort, manufacturers of peak flowmeters could improve the accuracy of their devices. Standardized testing methods and equipment should make the task of peak flowmeter design, manufacture, and testing even easier. We trust that manufacturers of peak flowmeters will respond appropriately and improve their instruments.

Adult↗
PubMed1990

Adjustment of DLCO for varying COHb, and alveolar PO2 using a theoretical adjustment equation.

The diffusing capacity of the lung for carbon monoxide (DL) is affected by changes in alveolar partial pressure of oxygen (PAO2), hemoglobin concentration (Hb), and carboxyhemoglobin concentration (COHb). A number of investigators have derived empiric adjustment equations to account for changes in these variables. We evaluated an adjustment of DL for changes in COHb and PAO2 using a single equation derived from Roughton and Forster's original definitions (J. Appl. Physiol., 1957). Unadjusted DL values declined significantly with rising COHb (-0.938%/percent COHb increase, P less than 0.0001) and rising PAO2 (-0.343%/mm Hg PAO2 increase, P less than 0.0001). Adjusted measured DL using the derived equation showed no significant change with changing COHb and PAO2 levels and provides an acceptable method for adjustment of DL for the effects of varying COHb and PAO2 levels from the standard conditions of COHb% = 0, and PAO2 = 110 mm Hg. Since a similar equation has previously been used to adjust for changes in DL due to anemia, we propose to use a single equation which is theoretically derived and empirically verified to adjust DL measurements for changes in COHb, PAO2 and hemoglobin.

Carbon Monoxide↗
PubMed1990

Perioperative warfarin therapy in combined abdominal lipectomy and intraabdominal gynecological surgical procedures.

The combination of multiple surgical procedures is attractive and convenient to the patient. Increased awareness of wound healing difficulties and pulmonary complications, however, suggest caution with this approach, particularly when combining abdominal lipectomy with intraabdominal procedures. This study confirms the high risk of pulmonary emboli in patients with combined abdominal lipectomy and intraabdominal gynecological procedures. The use of perioperative warfarin may reduce the incidence of pulmonary embolism in patients who have combined abdominal lipectomy and gynecological surgical procedures, and it is not associated with increased bleeding or other postoperative complications.

Adult↗
PubMed1990

Automated sulfur hexafluoride washout functional residual capacity measurement system for any mode of mechanical ventilation as well as spontaneous respiration.

A new sulfur hexafluoride (SF6) washout functional residual capacity (FRC) measurement system has been developed which will work with any mode of mechanical ventilation, as well as with spontaneous respiration. This system was evaluated in three different human studies. In the first two studies, the accuracy of the system was compared with He dilution and body plethysmography in 12 spontaneously breathing normal volunteers and in 12 spontaneously breathing chronic obstructive pulmonary disease (COPD) patients. In the third study, the reproducibility and efficacy of using the system in the ICU was tested in 12 adult respiratory distress syndrome (ARDS) patients who were mechanically ventilated with PEEP. In the normal volunteers, there was no significant difference between the three measurement techniques. In the COPD group, there was an overall significant difference between measurement techniques (F[2,28] = 17.18, p less than .0001) and the rank of the magnitude of the FRC measurements from lowest to highest was SF6 washout, He dilution, and body plethysmography. There was a significant difference in accuracy between the COPD and normal volunteer groups (F[2,28] = 12.24, p less than .0002). There were a total of 1,227 FRC measurements made on the 12 ARDS patients. The number of FRC measurements per patient was 102 +/- 13 (SEM). The "stable" periods were 14 +/- 2 h long and ranged from 60 min to 63.5 h. The reproducibility for all 12 patients was 188 +/- 17 ml or 11.7 +/- 0.7%. This automated SF6 washout system should make routine FRC measurements in patients who are being mechanically ventilated simple and easy to do.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Effectiveness of the kinetic treatment table for preventing and treating pulmonary complications in severely head-injured patients.

The efficacy of using the Kinetic Treatment Table (KTT) to prevent or reduce pulmonary complications in severely head-injured patients is unclear. This study is a prospective, randomized trial using the KTT vs. conventional bed care in severely head-injured patients. Outcome measures were hospital length of stay (LOS), mortality, CNS morbidity at hospital discharge, and rate of improvement of pulmonary status as gauged by chest radiograph, arterial/alveolar PO2 ratio, patient temperature, WBC count, suctioning frequency, sputum volume, and days on ventilator. The KTT group (n = 23) and conventional bed care group (n = 26) were well matched for age, sex, severity of injury, and pulmonary status. There was no significant difference in mortality, CNS morbidity, LOS in ICU or hospital, or rate of pulmonary improvement between the groups. The efficacy of the KTT in reducing pulmonary complications in head-injured patients remains unclear.

Acute Disease↗
PubMed1990

Small-sample reproducibility estimates: an example using rebreathing measurements.

We developed a statistical technique to estimate the reproducibility of a parameter from a population in which only two repeated measurements can be made in a single individual. The following data were analyzed: acetylene cardiac output (Qc), lung tissue volume (Vti), and carbon monoxide diffusing capacity (DLCO) measured by rebreathing techniques in a population of 86 healthy subjects (51 men and 35 women). Each subject was measured twice with a computerized rebreathing system using a test gas of 10% He-0.3% C18O-0.7% C2H2-25% O2-balance N2 while sitting at rest. The estimated coefficients of variation for repeated measurements were 6.8, 10.3, and 5.7% for Qc, Vti, and DLCO, respectively. Chebyshev's inequality was used to estimate the imprecision for a single measurement of these parameters and for averages of two or more repeated values. A single measurement of Qc would be within 14.2% of a "true" mean 90% of the time, whereas an average of three consecutive measurements would be within 8.2% of the true mean 90% of the time. Single measurements of Vti and DLCO were found to be within 21.7 and 12.0%, respectively, of the true mean 90% of the time. When three consecutive measurements are averaged, Vti is within 12.6% and DLCO is within 6.9% of the true mean 90% of the time. We conclude that 1) rebreathing Qc is as reproducible as other measurements of cardiac output, 2) rebreathing measurements of DLCO are as reproducible as those made by the single-breath technique, and 3) an average of two to three measurements of Vti should be made to obtain values with a reasonable degree of precision.

Acetylene↗
PubMed1990

Ventilatory control during exercise in calves with artificial hearts.

To determine the role of cardiac reflexes in mediating exercise hyperpnea, we investigated ventilatory responses to treadmill exercise in seven calves with artificial hearts and seven controls. In both groups, the ventilatory responses were adequate for the metabolic demands of the exercise; this resulted in regulation of arterial PCO2 and pH despite the absence of cardiac output increase in the implanted group. In this group, there was a small but significant reduction of arterial PO2 by 4 +/- 3 Torr and a rise of blood lactate by 1.1 +/- 1 mmol/l. When cardiac output was experimentally increased in the implanted calves to a level commensurate with that spontaneously occurring in the control calves, ventilation was not affected. However, experimental reductions of cardiac output led to an immediate augmentation of exercise hyperpnea by 4.56 +/- 4.3 l/min and a further significant lactate increase of 1.2 +/- 1.22 mmol/l that was associated with a significant decrease in the exercise O2 consumption (0.32 +/- 0.13 l/min). These observations indicate that neither cardiac nor hemodynamic effects of increased cardiac output constitute an obligatory cause of exercise hyperpnea in the calf.

Animals↗
PubMed1990

Assessing precision and accuracy in blood gas proficiency testing.

Blood gas proficiency testing has focused on assessing the accuracy of measurement of each analyte (pH, PCO2) independently of each other. Recently, the American Thoracic Society-California Thoracic Society Blood Gas Proficiency Testing Survey distributed the same lot of ampules of proficiency testing material (a buffered fluorocarbon-containing emulsion) on three occasions within a 1-yr period, allowing us to assess the precision (reproducibility) of measurement of each analyte. Comparing 580 instruments of 13 models, we found that the precision of measurement of each analyte was positively correlated with the precision of measurement of each other analyte, and the correlation of precision between models was much stronger than precision between the individual instruments. We also found correlation of precision of each analyte with two targets for accuracy: (1) the all-instrument mean and (2) the model-specific means. Correlations were higher with the model-specific means. These findings suggest: (1) that features unique to design of each model are important in the precision of measurement of these ampules, and (2) that it would be informative to include measurements of precision with linked and cumulative ratings of analyte accuracy in proficiency testing rating systems.

Blood Gas Analysis↗
PubMed1990

Performance evaluation of contemporary spirometers.

A comprehensive evaluation of 62 spirometers from 37 different sources was performed using a two-part protocol: calibrated syringe, and dynamic waveform testing. All testing was done with ambient air. Calibrated syringe testing examined the ability of the spirometers to accurately measure the output of a 3 L calibrating syringe under varying conditions. The accuracy, FVC volume linearity, and stability of each spirometer was determined from these data. All but five of 42 spirometers accurately measured a 3 L calibrating syringe to within +/- 3 percent. Dynamic waveform testing consisted of introducing 24 standard waveforms into the spirometer from a computer-controlled air pump. The values of FVC, FEV1, and FEF25-75% were compared to the actual values for each waveform to determine a performance rating. Only 35 (56.5 percent) of the spirometers performed acceptably when measuring the 24 standard waveforms. Nine (14.5 percent) were marginal and 18 (29.0 percent) were unacceptable. Fifty-nine (95 percent) of the 62 spirometers were computerized. Software errors were found in 25 percent of the computerized systems evaluated. Although using a 3 L syringe for quality control purposes is essential, simple testing of spirometers with a 3 L calibrating syringe for validation purposes was inadequate to assess spirometer performance when compared to dynamic waveform testing. Dynamic waveform testing is essential to accurately measure and validate acceptability of spirometer system performance.

Calibration↗
PubMed1990

Reference equations used to predict pulmonary function. Survey at institutions with respiratory disease training programs in the United States and Canada.

Adult respiratory disease training programs in the United States and Canada were surveyed to determine which reference equations were used to predict normal pulmonary function and how ethnic differences were approached. Replies from 139 of the 180 (77.2 percent) institutions surveyed were received and evaluated. Surprisingly few studies account for most of the equations in use: three studies account for 85 percent of the spirometric equations, two for 83 percent of the lung volume equations and five for 84 percent of the diffusing capacity equations. Although there are no definite data, the form of many of the replies suggests that equipment default settings may influence the selection process. Of those responding to the ethnic difference question, 53 percent of institutions applied no correction for ethnic differences. There was no consistent pattern to the method of correction among those who did.

Canada↗
PubMed1990

Normal spirometric values in healthy Hispanic Americans.

FVC, FEV1, FEV1/FVC, and FEF25-75% were measured in 259 (116 men and 143 women) healthy nonsmoking Hispanic American volunteers from Utah and California. Linear regression equations were created for women greater than or equal to age 20 years and men greater than or equal to age 25 years using height, age, and weight as independent variables and the spirometric indices as dependent variables. Weight was a significant predictor only for female FEV1. The raw data from this study were compared with data from our previous studies in North American Indians and Salt Lake City whites with Middle European ethnic backgrounds. No differences were found for any of the age and height coefficients. The only differences found were in the comparisons of the equation intercepts (bias) for male FVC and FEV1 between data for the Salt Lake City white subjects and both Hispanic American and North American Indian men. These small biases could be explained by technical or sampling biases or they may represent small ethnic differences. Although the differences from our Salt Lake City study are small, we recommend that ethnic-specific equations be used where they are available.

Adolescent↗