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Biomedical subjects

R W Gotshall

Publications and source records attributed to R W Gotshall.

At least 37 records · Page 2Linked to original sources
PubMed1994

Comparison of band and spot electrodes for the measurement of stroke volume by the bioelectric impedance technique.

OBJECTIVES: Conventional impedance cardiography uses a tetrapolar band electrode configuration to determine thoracic bioelectrical impedance changes and to quantify cardiovascular variables. The present study evaluated the effect of electrode type, band or electrocardiograph (spot), placed in the same anatomical location, on both the absolute value of cardiovascular variables and the percent change in the variable when the patient changed position from supine to standing. DESIGN: Prospective, randomized studies using repeated-measures design. SETTING: Research laboratory. PATIENTS: Twenty-one adult volunteer subjects. INTERVENTIONS: Subjects were studied while supine and again when standing, in random order as to first position. MEASUREMENTS AND MAIN RESULTS: Stroke volume and impedance-derived variables were measured. Values for stroke volume measured by the band electrode array were 85 +/- 7 and 49 +/- 3 mL for supine and standing, respectively. In contrast, stroke volume measured through the spot electrodes was 110 +/- 8 and 59 +/- 3 mL, respectively. These differences were due to a lower baseline thoracic bioelectrical impedance value measured through the spot electrodes. However, the percent changes for stroke volume with standing subjects were the same when measured through band (-41 +/- 3%) or spot (-44 +/- 3%) electrodes. CONCLUSIONS: The comparison of cardiovascular values obtained by impedance cardiography should be accomplished only when the values are obtained using similar electrode configuration and type. While there may be a variation in the absolute value of the variable, the direction and magnitude of the change in the variable is relatively unaffected by the electrode types as used in this study.

Adult↗
PubMed1994

Difference in the cardiovascular response to prolonged sitting in men and women.

Orthostatic stress, sitting, results in adjustments of cardiovascular variables to maintain blood pressure and is prominent in a variety of occupations. Sitting serves as the control position for head-out water immersion studies. This study addressed gender differences in the cardiovascular response to prolonged sitting. Ten men and 10 women had cardiovascular measurements in the supine position compared with measurements during 2 hours in the seated position (Sit). Supine cardiovascular measurements were similar for both sexes. Heart rate changed similarly for both sexes with Sit. With Sit, men had elevated mean arterial pressure (9 +/- 3%), total peripheral resistance (54 +/- 9%), and decreased cardiac index (-27 +/- 5%), while women had no change in mean arterial pressure, lesser elevations in total peripheral resistance (17 +/- 7%), and lesser decreases in cardiac index (-12 +/- 5%) than men. Thus men, compared to women, had an elevated mean arterial pressure response to prolonged orthostatic stress.

Adult↗
PubMed1993

Use of impedance cardiography for assessing cardiovascular control in humans: orthostatic and Valsalva tests.

The purpose of this paper is to review our experience with impedance cardiography when used to evaluate cardiovascular control mechanisms in humans. We used the Minnesota impedance cardiograph and the Kubicek stroke volume formula, modified by using spot electrodes instead of band electrodes, a constant rho of 135, and careful attention to standardized procedures. With this technique we focused on the changes in cardiovascular variables with postural stress and during the Valsalva maneuver. More complete definition of cardiovascular function can be obtained by the use of this technique. We describe novel cardiovascular data with the use of impedance cardiography in humans.

Adult↗
PubMed1993

Application of impedance cardiography during exercise.

Impedance cardiography has been used over the last 30 years to measure stroke volume on a beat-by-beat basis. Cardiac output has been successfully measured with either upper or lower body exercise during light or moderate workloads. With strenuous exercise, movement artifacts severely limit the acquisition of a quality impedance cardiogram. Advances in computer technology and signal conditioning techniques have created the next generation of impedance cardiograph systems. The purpose of this study was to evaluate such a system, the noninvasive continuous cardiac output monitor (NCCOM3-R7), at rest and during submaximal upright cycle exercise. In addition, the relationships between thoracic impedance (Z(o)), first derivative of the change in thoracic impedance (dZ/dt) and posture were evaluated using the NCCOM3-R7 and the Minnesota impedance cardiograph 304B (MIC). Twenty-eight healthy men and women participated. The Z(o) progressively increased when moving from the supine to seated to standing position with both instruments. However, the NCCOM3-R7 yielded lower Z(o) values and higher dZ/dt values compared with the MIC for all postures. Z(o) and dZ/dt values appear to be dependent upon factors such as posture, gender, electrical current, and characteristics of the instrumentation. Exercise cardiac output values seemed reasonable for most subjects, although population subsets exist where the accuracy must be questioned. The general consensus supported by the impedance literature and reaffirmed by the present observations is that impedance cardiography provides a reasonable estimate of the directional changes in stroke volume and cardiac output during exercise and can be used to monitor changes in thoracic fluid balance. As this technology evolves and is further refined, it will undoubtedly play an increasing role in environmental medicine, exercise stress testing, cardiac rehabilitation, and sports medicine.

Adult↗
PubMed1993

Validity and reliability of the Cosmed K2 instrument.

The purpose of this study was to measure the validity and reliability of a portable telemetry system (Cosmed K2) for measurement of oxygen consumption (VO2) during a laboratory exercise test at submaximum and maximum intensities. Twenty subjects performed three testing sessions on a treadmill on three consecutive days. Each testing session consisted of a submaximal and a maximal exercise test. On one day, VO2 was determined with the conventional Douglas bag method, and on the other two days, VO2 was determined using the Cosmed K2 system. Utilization of the Douglas bag method or the Cosmed K2 was randomly assigned. The results indicated that the Cosmed K2 instrument is reliable and valid (p > 0.05) for measurement of VO2 (l.min-1) during laboratory exercise testing at submaximum and maximum intensities. The assumption made by the K2 apparatus of a constant respiratory gas exchange ratio (R) of 1.00 did not have a significant influence on VO2 measurements.

Adult↗
PubMed1992

Cardiorespiratory effects of changing inspiratory to expiratory ratio during high-frequency oscillation in an animal model of respiratory failure.

To examine the effects of varying inspiratory/expiratory ratio (I/E) on cardiorespiratory function during high-frequency oscillation (HFO), 11 saline-lavaged rabbits were ventilated at I/E = 1:2, 1:1.5, 1.5:1, and 2:1 in a paired comparison to a baseline of I/E = 1:1. HFO was delivered by a SensorMedics model 3100 oscillator at a frequency of 10 Hz. Pressure amplitude and proximal mean airway pressure (PPaw) were held constant as I/E was varied from baseline to the experimental I/E. During each paired observation, PaO2, PaCO2, cardiac output, blood pressure, and distal mean airway pressure (DPaw) were measured. We found that as I/E was increased or decreased from 1:1, no significant changes in PaO2, PaCO2, blood pressure, or cardiac output occurred. We conclude that in this model, varying I/E has no significant effect on oxygenation, ventilation, or cardiovascular function.

Analysis of Variance↗
PubMed1991

Cardiothoracic variables measured by bioelectrical impedance in preterm and term neonates.

OBJECTIVE: To report the range of normal values for impedance-derived cardiac output, stroke volume, and the baseline transthoracic impedance in the healthy preterm and term neonate over the weight range generally found in the intensive care nursery. DESIGN: Prospective, case-referent study. SETTING: University medical center special care and term nurseries. PATIENTS: Twenty-seven preterm and 25 term newborns with no evidence of cardiovascular problems. INTERVENTIONS: We determined the values for impedance cardiac output and stroke volume to be used as reference values. Also measured was the baseline transthoracic impedance, a number that reflects the air/fluid ratio of the thorax. MEASUREMENTS AND MAIN RESULTS: Stroke volume and stroke volume index were, respectively, 2.0 +/- 0.8 (SD) mL and 1.4 +/- 0.5 mL/kg for preterm infants, and 5.0 +/- 2.0 mL and 1.6 +/- 0.7 mL/kg for term neonates. Cardiac output and cardiac index were, respectively, 304 +/- 114 mL/min and 214 +/- 68 mL/min.kg for preterm newborns, and 648 +/- 244 mL/min and 205 +/- 78 mL/min.kg in term newborns. These values compared favorably with published values utilizing other techniques for these populations. Both cardiac output and stroke volume were linearly correlated to body weight, being largest in the heavier neonates. Transthoracic impedance values were 42.7 +/- 9.0 ohms and 6.7 +/- 1.7 ohms/cm for preterm infants and 32.3 +/- 4.3 ohms and 3.9 +/- 0.6 ohms/cm for term infants. Transthoracic impedance and transthoracic impedance/cm values were correlated negatively to body weight and were curvilinearly related to body weight. CONCLUSIONS: These values for transthoracic impedance and transthoracic impedance/cm are the first reported using the standard electrode lead configuration in neonates.

Cardiac Output↗
PubMed1991

Acute recovery profile of lung volumes and function after running 5 miles.

The purpose of this study was to characterize the acute changes and recovery profile of lung volumes and function subsequent to strenuous aerobic exercise. Eight experienced runners (X age = 25 yrs; wt = 73 kg; ht = 181 cm) completed three identical 5 mile runs. Determinations were made of forced vital capacity (FVC), residual volume (RV), closing capacity (CC), and pulmonary diffusion capacity (DLCO). Measurement of cardiac output (Q) and stroke volume (SV) occurred simultaneously with the 10 second DLCO breathhold maneuver. Measurements were obtained before and 5, 15 and 25 minutes after each run. FVC was reduced (-4.5%) 5 min post-run with a return to pre-run values by 15 min. CC (+16%) and RV (+18%) remained elevated for at least 30 min post-run. DLCO did not appear to be effected by the run. However, the single-breath DLCO breathhold maneuver consistently caused a fall in SV at rest and during recovery. The hypothesis has been forwarded that an increase in central blood volume post-run accounted for the acute reduction in FVC. The sustained elevation in RV resulted from early closure of the small airways possibly due to an increase in extra-vascular lung water.

Adult↗
PubMed1991

Effect of the prelaunch position on the cardiovascular response to standing.

Astronauts spend a minimum of 2 h in the reclined seated position (prelaunch position) prior to the launch of the Space Shuttle. This position favors a cephalad shift of blood volume and subsequent loss of body fluid volume, a physiologic situation associated with cardiovascular deconditioning and orthostatic intolerance following spaceflight. It is not known if the prelaunch position results in cardiovascular deconditioning and, therefore, impaired cardiovascular performance during standing. If so, this might hinder the ability of the crewmember to make an emergency egress from the shuttle during the launch. The purpose of this study was to evaluate the cardiovascular responses of men and women to the stand test before and after 2 h in the prelaunch position. Nine men and nine women performed the stand test before and after 2 h in the seated position (SIT), the prelaunch position (PL), or seated immersed to the neck in water (WI). Heart rate, blood pressure, and cardiac output were measured. Men had higher blood pressures than women and demonstrated increases in blood pressure with standing. There were no other gender differences. SIT did not alter the cardiovascular response to standing, while PL and WI resulted in greater increases in heart rate after 2 h in the position. This increase was only 4 to 7 beats/min greater than after SIT, and was the same for PL and WI. Thus, a small, but significant, degree of cardiovascular deconditioning occurred during the minimum time astronauts spend in the prelaunch position.

Adult↗
PubMed1991

Gender-based differences in the cardiovascular response to standing.

Reduced tolerance to orthostatic stress is a recognized consequence of spaceflight. Both men and women serve as astronauts and are staying longer in space. While there are recognized cardiovascular differences in baseline function based on gender, little is known about any gender-based differences in cardiovascular responses to orthostatic stress. The purpose of this study was to compare the cardiovascular responses of men and women to the stand test. The subjects were 10 men and 10 women, 20-30 years of age. Heart rate, blood pressure, stroke volume, cardiac output, and total peripheral resistance were monitored during 5 min supine and 5 min standing. Men responded similarly in heart rate (39 vs. 35%); but had significantly greater decreases in stroke volume (-53 vs. -40%), cardiac output (-36 vs. -21%), and pulse pressure (-19 vs. -12%); and greater increases in blood pressure (11 vs. 6%) and total peripheral resistance (77 vs. 34%) than did the women. Men and women demonstrated fundamental differences in cardiovascular responses during standing. Differences in the height of the subjects did not account for these differing cardiovascular responses. The mechanisms for these differences are not yet clear. Men and women should be studied as separate groups until these differences are understood.

Adult↗
PubMed1990

Impedance cardiography fails to measure accurately left ventricular ejection fraction.

The purpose of this study was to describe the technique proposed to measure left ventricular ejection fraction (LVEF) with the impedance cardiogram and to compare these values with those measured by radionuclide angiocardiography. Characteristics (mean +/- SE) of the healthy control group were: age, 32 +/- 3 yr; weight, 75 +/- 6 kg; and height, 177 +/- 3 cm. Characteristics of the patient population of 46 men and 49 women were: age, 63 +/- 1 yr; weight 74 +/- 2 kg; and height, 170 +/- 1 cm. LVEF was measured by impedance (ZEF) and multiple-gated scans (MEF) while in the supine position. The control group ZEF averaged 72% (range 67% to 78%) and the MEF averaged 71% (range 65% to 77%). There were no differences between the average ZEF (56 +/- 1%) and MEF (53 +/- 2%) in the patients. Correlations, however, between ZEF and MEF were unacceptably low for the several clinical populations within this group (-0.17 to 0.16). Furthermore, MEF correlated well with regional wall motion (r = .84) while ZEF did not (r = .00). Subdividing the patients according to heart function as determined by regional wall motion failed to improve the correlation between MEF and ZEF. The use of a previously published regression equation to predict LVEF from the systolic time interval ratio of pre-ejection period/left ventricular ejection time derived from the impedance cardiogram also proved ineffective. These data suggest that the previously proposed analysis of the impedance cardiogram to measure LVEF should not be used to make a clinical diagnosis.

Adult↗
PubMed1990

Measurement of tidal volume using a pneumotachometer during high-frequency oscillation.

To assess the accuracy of a pneumotachometer (PN) for tidal volume (VT) measurements during high-frequency oscillation (HFO), we determined simultaneously VT using a PN and a full body plethysmograph (PL) in 12 rabbits. HFO was delivered with an oscillator at a frequency of 10 Hz, mean airway pressure of 8 cm H2O, and inspiratory time of 50%. Pressure amplitude (delta P) was varied as follows: 40, 60, 80, 20, 100, 40 cm H2O. Finally, in ten rabbits a spacer equal in deadspace (VD) to that of the PN (15 ml) was left in-line for 5 min. Blood gases were obtained before and after the spacer was added. We found that VT-PN correlates well with VT-PL (r = .92), although the difference between VT-PN and VT-PL is greater at large VT. Significant respiratory acidosis developed with the spacer in-line. PN may be used to trend VT during HFO but PN must not be left in-line, as increased VD seriously affects ventilation.

Animals↗
PubMed1989

Comparison of two impedance cardiographic techniques for measuring cardiac output.

The purpose of the present study was to compare cardiac outputs obtained by both the Kubicek (MIC) and Sramek (NCCOM3) impedance cardiographic techniques with thermodilution (TD) in critically ill patients. The two impedance techniques were also compared in normal subjects. Seven healthy subjects and ten patients in the intensive care unit were enlisted in the study. Only those subjects with successful measurements by all three methods were used in the data analysis. Three measurements of cardiac output were made in each subject. In patients, there were no significant differences in cardiac outputs as measured by TD (6.61/min), MIC (6.3 1/min), NCCOM3 (6.4 1/min). MIC and NCCOM3 cardiac outputs were correlated and approximated the line of identify when compared to TD. In normals, however, the NCCOM3 overestimated the cardiac output (NCCOM3, 9.2 1/min; MIC, 6.2 1/min). Because of these inconsistent results, caution is urged when interpreting the values obtained by the NCCOM3. In contrast, the use of the MIC in both populations has been reaffirmed.

Adolescent↗
PubMed1989

Noninvasive assessment of cardiac output by impedance cardiography in the newborn canine.

Currently, critical care monitoring of cardiac function in the newborn human consists mainly of measuring heart rate and BP. A noninvasive technique for assessing cardiac output routinely in the critically ill neonate would facilitate clinical management. Impedance cardiography (IC) is a noninvasive technique which measures stroke volume on a beat-by-beat basis. This study compared cardiac output as measured by thermodilution (TD) to that measured by IC in seven canine pups 6 to 7 days old weighing 0.66 to 0.86 kg. Cardiac output was altered by the withdrawal and reinfusion of blood. There were no significant differences between the two methods for either the absolute value of cardiac output (r = .96) or the percent change in cardiac output (r = .97). Coefficients of variation were 3.0% for TD and 3.6% for IC. These results indicate that IC can be used to assess serially cardiac function in the newborn.

Animals↗
PubMed1989

Comparison of two impedance cardiographic techniques for measuring cardiac output in critically ill patients.

The purpose of the present study was to compare cardiac output (Q) values obtained by both the Kubicek (MIC) and Sramek (NCCOM3) impedance cardiographic techniques with thermodilution (TD) in critically ill patients. The two impedance techniques were also compared in normal subjects. Seven healthy subjects and ten ICU patients were enlisted in the study. Three Q measurements were made in each subject. In the ICU patients, there were no significant differences in Q values as measured by TD (6.6 L/min), MIC (6.3 L/min), and NCCOM3 (6.4 L/min). Both MIC and NCCOM3 Q values were comparable to TD in patients. In normals, however, the NCCOM3 estimated larger values for Q than did the MIC (NCCOM3, 9.2 L/min; MIC, 6.2 L/min). Q values obtained with MIC in normals were comparable with published values for supine normals. Thus, the two techniques agreed in the patients but not in the normals. The reasons for these results are not obvious from the data, but are attributable to the measurements by the NCCOM3. Because of this, caution is suggested when interpreting absolute Q values obtained by the NCCOM3.

Adult↗
PubMed1989

Modified head-up tilt test for orthostatic challenge of critically ill patients.

The purpose of this study was to assess the cardiovascular response to a modified head-up tilt test for use with the bedridden, critically ill patient. The cardiovascular responses of seven normals and ten critically ill patients to 45 degrees head-up tilt with the legs horizontal (0 degrees) were analyzed. Stroke volume index (SI) and cardiac index (CI) were measured with thoracic electric bioimpedance (TEB). The baseline TEB (Z0) was measured to monitor fluid shift out of the thorax during tilt. BP was measured and systemic vascular resistance index (SVRI) was calculated. Normals responded to the modified head-up tilt with a decreased SI (59 to 44 ml/m2 and CI (3.7 to 2.8 L/min.m2), and an increased SVRI and Z0 (25.5 to 27.9). As a group, the patients showed no significant change with tilt. However, individual analysis revealed a heterogeneous response by the patients. Those patients who demonstrated a caudal shift of blood (increased Z0) had decreased SI. Those with no indication of a caudal shift of blood, presumably due to decreased venous compliance, did not change SI. Thus, this type of modified head-up tilt can be used in the ICU to study more intensely cardiovascular function and control in the bedridden subject.

Adult↗
PubMed1989

Cardiopulmonary effects of high frequency positive-pressure ventilation versus jet ventilation in respiratory failure.

Conventional ventilators are frequently used at high rates in the intensive care nursery to achieve adequate oxygenation and ventilation with reduced peak inspiratory pressure. The efficacy and limitations of high frequency positive-pressure ventilation (HFPPV) using a conventional ventilator were studied by comparing the cardiopulmonary effects of HFPPV with those of high frequency jet ventilation (HFJV) in an animal model of respiratory failure. Sixteen saline-lavaged rabbits were ventilated with either HFPPV or HFJV for 2 h using rates of 200 breaths/min, inspiratory to expiratory ratio of 1:2, and FIO2 of 1.0. As controls an additional eight lavaged rabbits were ventilated at conventional rates (40 to 60 breaths/min). Proximal peak inspiratory pressure as indicated on the ventilator manometer or drive pressure was adjusted to maintain acceptable blood gases. Cardiac output (CO) was measured by thermodilution. Although there was a significant decrease in cardiac function over time, there were no significant differences between the groups in CO or stroke volume. Satisfactory oxygenation and ventilation were maintained in all groups. Static respiratory system compliance and mean airway pressure were similar among the groups. Histologic examination of the lungs revealed no differences between the three ventilator groups. The results of this study indicate that both HFPPV and HFJV are effective in short-term maintenance of normal blood gases in respiratory failure without any discernable differences in their effects on cardiovascular function. At very high rates, however, increases in VT are not possible with HFPPV, which limits its usefulness and flexibility in respiratory failure.

Animals↗