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Bioimpedance-derived differences in cardiac physiology during exercise stress testing in low-risk chest pain patients.



Background: Little has been written about the utility of thoracic electrical bioimpedance (TEB TEB Test & Evaluation Board
TEB Third Eye Blind (band name)
TEB Thread Environment Block
TEB Turkiye Ekonomi Bankasi
TEB Triethylborane
TEB Technical Evaluation Board
TEB Traffic Engineering Bureau (Pakistan) 
)-derived cardiac physiologic variables in evaluating patients with low-risk chest pain syndromes. Noninvasive bioimpedance can monitor cardiac physiology while a patient is performing an exercise stress test. In addition, the demographics of patients with chest pain, the incidence of coronary artery disease coronary artery disease, condition that results when the coronary arteries are narrowed or occluded, most commonly by atherosclerotic deposits of fibrous and fatty tissue.  (CAD), and the methods used for evaluation have well-documented sex differences.

Objective: The objectives are to show that there are different cardiac physiologic responses to exercise stress test in Chest Pain Evaluation Unit patients with and without true CAD that could be used to stratify strat·i·fy  
v. strat·i·fied, strat·i·fy·ing, strat·i·fies

v.tr.
1. To form, arrange, or deposit in layers.

2.
 patients and that there is a sex difference in TEB results.

Methods: Patients 18 to 65 years of age with low-risk chest pain were eligible. Patients were attached to the TEB throughout the exercise stress test procedure. Heart rate (HR) was monitored. Primary dependent variables were TEB-measured cardiac output cardiac output
n. Abbr. CO
The volume of blood pumped from the right or left ventricle in one minute. It is equal to the stroke volume multiplied by the heart rate.
 (CO, L/min) and stroke volume (SV, ml) at peak exercise. Secondary variables were TEB-measured ejection fraction ejection fraction
n.
The blood present in the ventricle at the end of diastole and expelled during the contraction of the heart.


Ejection fraction 
 (%), end-diastolic volume end-diastolic volume
n.
The amount of blood in the ventricle immediately before a cardiac contraction begins; used as a measurement of diastolic function.
 (EDV EDV end-diastolic volume. , ml), ventricular ejection time (ms), and thoracic fluid index ([OMEGA]) at peak exercise. Outcome variables were either proved CAD or patient sex. CAD was proved by angiography angiography
 or arteriography

X-ray examination of arteries and veins with a contrast medium to differentiate them from surrounding organs. The contrast medium is introduced through a catheter to show the blood vessels and the structures they supply, including
, stress scintigraphy scintigraphy /scin·tig·ra·phy/ (sin-tig´rah-fe) the production of two-dimensional images of the distribution of radioactivity in tissues after the internal administration of a radiopharmaceutical imaging agent, the images being obtained , or stress echocardiogram ech·o·car·di·o·gram
n.
A visual record produced by echocardiography.


Echocardiogram
A non-invasive ultrasound test that shows an image of the inside of the heart.
. Results were compared using a Student's t test assuming equal variances, with significance considered at a P < 0.05, and 95% confidence intervals were calculated for significant results.

Results: Nine patients had proved CAD, 82 patients did not. Forty-three women and 48 men were included in the study. At peak exercise, patients with CAD had a significantly smaller increase in EDV than patients without CAD (32.8 [+ or -] 59.5 ml versus 89.3 [+ or -] 101.8 ml) without a significant change in CO, SV, or HR. At peak exercise, women had a significantly smaller increase in CO and SV without a significant change in HR. In addition, women had a significantly smaller increase in EDV.

Conclusion: When compared with patients without CAD, patients with CAD have a significantly smaller increase in EDV and a trend toward the same effect in CO and SV. Women have significantly smaller increases CO, SV, and EDV compared with men. Because there were no differences in HR, using HR as the sole end point would miss these differences. TEB is a practical means of measuring these variables.

Key Words: cardiac output, cardiography cardiography /car·di·og·ra·phy/ (kahr?de-og´rah-fe) the graphic recording of a physical or functional aspect of the heart, e.g. , impedance, monitoring

**********

Cardiac output (CO) measurement by thermodilution and dye-dilution is invasive, carries the potential for significant complications, and is not practical in the outpatient setting. In contrast, thoracic electrical bioimpedance (TEB) is simple, noninvasive, and without risk to the patient. Because it uses a hands-off approach, it has better intermeasurement and interobserver reliability than thermodilution. (1) As the reliability and validity become better defined, TEB is finding an expanded role in many areas of medicine. Among its uses are defining changes in seriously ill patients, (2-10) monitoring pregnancy, (11-18) evaluating the effects of environmental stressors on healthy individuals, (19-25) and assessing drug effects. (26), (27)

Sex-related differences in chest pain management have been well documented. Not only is there a documented sex difference in demographics of chest pain, but there is also a documented sex difference in chest pain detection and evaluation. This difference has led to underdiagnosis of heart disease in women when signs and symptoms alone are considered. The addition of cardiac physiologic information could increase the yield of true-positive stress test results in female patients. (28-38) There is a need to better identify women at high cardiac risk. (36)

The use of TEB in outpatients has only been evaluated in a few studies, (39-44) despite the fact that this would be an excellent modality for use in these environments. There is usually insufficient time to initiate invasive monitoring in outpatient cases, nurses often are not trained in the technique, and the equipment is not readily available. There is a strong body of literature emerging, which indicates that TEB may be an effective method of tracking cardiac physiologic changes during exercise testing.

The ability to recognize low-risk patients with chest pain has led to alternatives to conventional coronary care for this group, including reduced time in coronary care units, direct admission to a step-down unit, and management in short-stay observation units. We presently use a Chest Pain Evaluation Unit (CPEU) composed of a specialized physician-staffed unit, which provides care to patients with chest pain, whose electrocardiograms (ECGs) and initial cardiac injury markers are not diagnostic for ischemia. Our previous study demonstrated that nearly 90% of patients initially identified as low risk by clinical assessment can be safely discharged from the emergency department on the basis of the results of the exercise test. (45), (46)

In this study we evaluate chest pain patients who are at low risk for acute coronary syndromes. We searched for ischemia-and sex-related differences in TEB-obtained cardiac physiologic variables. The hypotheses for this study are the following: 1) There are different cardiac physiologic responses to exercise stress testing Determining the durability of a system by pushing it to its limits. Stress testing a network is performed by transmitting excessive numbers of packets or attempting to break in illegally.  (EST EST electroshock therapy.

EST
abbr.
electroshock therapy
) in CPEU patients with and without true coronary artery disease (CAD) that could be used to stratify patients, and 2) there are sex-related differences in cardiac physiologic responses to EST.

Methods

A convenience sample of patients 18 to 65 years of age undergoing EST was included. For the evaluation of chest pain patients we used our previously described eligibility criteria and exercise treadmill testing protocol. (45), (47) Patients underwent EST according to a Bruce or modified Bruce protocol Bruce protocol Cardiology A treadmill exercise protocol used to classify a Pt's functional–NYHA status. Cf Cornell protocol.  depending on physician discretion. We enrolled these patients during a 6-month period. Patients were simultaneously attached to the TEB monitor while being connected to the exercise ECG ECG electrocardiogram.

ECG
abbr.
1. electrocardiogram

2. electrocardiograph


ECG
Also called an electrocardiogram, it records the electrical activity of the heart.
 monitor. TEB monitoring did not preclude or interfere with the standard exercise ECG monitoring. Patients were included if data were obtained by TEB. Patients were excluded if they were unwilling or unable to consent, or if they were [beta]-blocked. End point measurements for EST were 85% maximum predicted heart rate (HR) or symptoms, such as shortness of breath Shortness of Breath Definition

Shortness of breath, or dyspnea, is a feeling of difficult or labored breathing that is out of proportion to the patient's level of physical activity.
 or chest pain. The study was approved by the institutional review board to conform to standard practice for research in humans. Written informed consent was obtained from all participants.

The primary dependent variables were TEB-derived CO and stroke volume (SV) at rest and the change in variables between rest and peak exercise. Secondary variables were thoracic fluid index, ventricular ejection time, ejection fraction (EF), and end-diastolic volume (EDV) as determined by TEB during EST. We monitored HR because this was used for end point decisions in EST testing. In addition we calculated cardiac index cardiac index
n.
The volume of blood pumped by the heart in a unit of time divided by the body surface area, usually expressed in liters per minute per square meter.
 as CO divided by weight, and systemic vascular resistance systemic vascular resistance
n.
An index of arteriolar constriction throughout the body, calculated by dividing the blood pressure by the cardiac output.
 with the formula CO times 80 divided by mean arterial pressure The mean arterial pressure (MAP) is a term used in medicine to describe a notional average blood pressure in an individual. It is defined as the average arterial pressure during a single cardiac cycle. Calculation .

The outcome variable was a true-positive CAD on the basis of one of the following; 1) coronary angiography coronary angiography Interventional cardiology A diagnostic technique in which a radiocontrast is injected directly into the coronary arteries, allowing visualization and quantification of stenosis and/or obstruction.  (positive is a >50% reduction in coronary artery coronary artery
n.
1. An artery with origin in the right aortic sinus; with distribution to the right side of the heart in the coronary sulcus, and with branches to the right atrium and ventricle, including the atrioventricular branches and
 lumen diameter), 2) myocardial myocardial /myo·car·di·al/ (-kahr´de-al) pertaining to the muscular tissue of the heart.

myocardial

pertaining to the muscular tissue of the heart (the myocardium).
 stress (exercise or pharmacologic) scintigraphy by single-photon emission computed tomography Computed tomography (CT scan)
X rays are aimed at slices of the body (by rotating equipment) and results are assembled with a computer to give a three-dimensional picture of a structure.
 (positive is stress-induced perfusion defect), or 3) stress (dobutamine or exercise) echocardiography Echocardiography Definition

Echocardiography is a diagnostic test that uses ultrasound waves to create an image of the heart muscle. Ultrasound waves that rebound or echo off the heart can show the size, shape, and movement of the heart's valves and
 (positive is stress-induced segmental wall motion abnormality).

Two subgroup analyses were also performed. A first subgroup analysis was performed looking for Looking for

In the context of general equities, this describing a buy interest in which a dealer is asked to offer stock, often involving a capital commitment. Antithesis of in touch with.
 sex-related differences. A second subgroup analysis looked at only nonnegative EST using a decision tree analysis to determine cutoff points that could be used to stratify patients.

The NCCOM3-R7 (Bomed Corp., Irving, CA) monitor was used to obtain the impedance data. The electrodes are applied on the lateral neck and flank bilaterally. Two leads generate a low electrical field across the thorax thorax, body division found in certain animals. In humans and other mammals it lies between the neck and abdomen and is also called the chest. The skeletal frame of the thorax is formed by the sternum (breastbone) and ribs in front and the dorsal vertebrae in back.  using 2.5 mA alternating current at 70 KHz while the other two sensing leads measure changes in voltage. These sensing electrodes reflect changes in impedance and also function as ECG leads to enable the machine to monitor HR (needed to express the SV as CO).

Sex, body weight (kg), and height (cm) are entered into the TEB monitor. Derived cardiac variables are then displayed on the monitor. These include SV, CO, HR, EF, left ventricular ejection fraction, and EDV. Data were collected with the monitor in slow mode, during which the device provides an average result for the six variables on 16 consecutive accepted beats.

An a priori a priori

In epistemology, knowledge that is independent of all particular experiences, as opposed to a posteriori (or empirical) knowledge, which derives from experience.
 power calculation showed that 15 patients per group were needed to show a difference of 50% in primary physiologic variables with a power of 80%. Results were downloaded from the TEB monitor into a palmtop palmtop or hand-held personal computer, lightweight, small, battery-powered, general-purpose programmable computer. It typically has a miniaturized full-function, typewriterlike keyboard for input and a small, full color, liquid-crystal display  computer, transferred into an Excel database (Microsoft Corp., Redmond, WA), and analyzed with the use of the SPSS A statistical package from SPSS, Inc., Chicago (www.spss.com) that runs on PCs, most mainframes and minis and is used extensively in marketing research. It provides over 50 statistical processes, including regression analysis, correlation and analysis of variance.  9.0 statistical software package (SPSS, Inc., Chicago, IL). A P < 0.05 was considered significant, and 95% confidence intervals were calculated on all significant differences. Answer Tree software (SPSS, Inc.) was used to create a decision tree based on the data.

Results

One hundred twenty-eight patients were tested. Data were obtainable in 94 of these patients. Thirty-four had the device applied but did not produce acceptable readings. No patients with initial TEB readings needed to be excluded later because of motion artifact. Three patients were excluded because of their use of [beta]-blockers, leaving 91 people who were entered in the study.

Normal values normal values
pl.n.
A set of laboratory test values used to characterize apparently healthy individuals, now replaced by reference values.
, baseline values, and increases from baseline are outlined in Table 1. Twenty-one patients had non-negative EST results. Nine patients (10%) had proved CAD and nonnegative EST results. Forty-three women and 48 men were entered in the study. At peak exercise the CAD-positive patients had no significant changes over baseline for the primary variables CO and SV, although there was a trend toward a smaller increase in those variables. Among the secondary variables, CAD-positive patients had a significantly smaller increase in EDV. These results are summarized in Table 2.

Figure 1 shows the results of the decision tree analysis on the data for patients with nonnegative EST, indicating that either CO or EDV could effectively stratify all but one of the CAD-positive patients. At peak exercise, women had significantly smaller increases in CO and SV. Among the secondary variables, women had significantly smaller increases in EDV and cardiac index. They also had a significantly smaller decrease in systemic vascular resistance. These results are also summarized in Table 2. No significant results were found when both sex and pressure of CAD were taken into account. Figure 1 illustrates a decision tree analysis of the data using an increase in CO of less than 12.0 L/min or an increase in EDV of less than 55 ml as the decision variables. As can be seen, the negative group contained 1 (11%) of 9 positives while the positive group was 8 (67%) of 12 positives. The positive predictive value Positive predictive value (PPV)
The probability that a person with a positive test result has, or will get, the disease.

Mentioned in: Genetic Testing

positive predictive value 
 and sensitivity of this rule is 89% (8 of 9; Fig. 1). Figure 2 illustrates a typical curve of CO and HR as collected over time from the TEB monitor during an EST. The x axis represents time, and the y axis Y axis,
n See axis, Y.
 represents the measured HR or CO, respectively.

Discussion

The first important finding in this study was that reproducible TEB results were obtained despite the motion artifact that occurred during an EST. In fact, there was little effect of motion on the results. Significant, important differences were observed between both the CAD and the sex subgroups. Between the CAD-positive and CAD-negative patients, only the change in EDV was significantly different. However, between men and women there were more significant differences, including the primary variables (CO and SV), one of the secondary variables (EDV), and the calculated variables (systemic vascular resistance and cardiac index). Of note, there were no significant differences in either subgroup in the change in HR, which is in agreement with the fact that the HR was used (as was expected) as the primary end point for the

Key Points

* When patients with known coronary artery disease are compared with those without disease, exercise stress testing increases all variables to the same degree at peak exercise except end-diastolic volume.

* When women are compared with men, the increase in heart rate at peak exercise is the same.

* Women have significantly smaller increases in cardiac output and stroke volume at peak exercise.

* Heart rate may lead to unequal end points in women and men during exercise stress testing and may therefore lead to incorrect conclusions. EST. EDV proved to be one of the best variables (followed closely by CO) for differentiating these groups as shown in the decision tree analysis. The fact that there was a significant sex difference in changes in CO suggests that HR may not be the best end point to use for an EST. The increase in CO during the EST in men was almost twice that seen in women and may account for the lower published rates of positive testing in women when HR is used as the end point.

Sex-related differences in the management of patients with chest pain have been well documented. Not only is there a clear sex difference in the demographics of these patients, but also there is a sex-related difference in the sensitivity and specificity of the diagnostic tests used in their evaluation. This difference has led to underdiagnosis of heart disease in women when signs and symptoms alone are considered. An unacceptably high rate of false positives occurs if only the results of EST are used. The addition of cardiac physiologic information could increase the positive predictive value of the test, particularly in female patients. (28-38)

[FIGURE 1 OMITTED]

No previous study has attempted to stratify TEB results by sex. Previous studies have looked at the use of TEB during exercise in normal volunteers and in patients with ischemic heart disease Ischemic heart disease
Insufficient blood supply to the heart muscle (myocardium).

Mentioned in: Myocarditis

ischemic heart disease 
. (48), (49) Measurements were made by TEB during exercise (21), (48-57) and during postural stress. (24), (25), (58) When these studies compared the TEB results with those of other standard measurements, there were high correlation coefficients (for CO, r = 0.96 and 0.90, respectively). The conclusion is that the value of TEB was in evaluating trends in results, and changes with exercise or position rather than the absolute values of cardiac variables. Although CO, thoracic fluid index, and ventricular ejection time have all been suggested in the past as correlating with true ischemic heart disease, no previous study has evaluated the role of these markers in a prospective manner.

[FIGURE 2 OMITTED]

Our chest pain service evaluates 1,100 people per year, of which half qualify for EST. The positive stress test rate of this population is 15%; however, false-positives account for half of these, which can lead to additional testing and higher costs. (47) The addition of TEB may result in better recognition of true-positive ESTs and lead to a decrease in cost and fewer follow-up tests. (45) This is the first report looking at the use of this modality in emergency department patients.

We were able to show that TEB is a good noninvasive method of monitoring cardiac physiologic variables. There are numerous reasons a good noninvasive tool for the measurement of CO is desirable for use with chest pain patients undergoing EST. It provides moment-to-moment physiologic information about the patient and clarifies patient status changes that may not be apparent using other monitoring techniques. CO measurement by thermodilution or dye dilution is not practical in this setting. (55), (56) Also, because TEB uses a hands-off approach, it has better intermeasurement and interobserver reliability than the invasive monitoring techniques. The ability to further stratify the nonnegative EST results was of particular importance to us in the practical management of these patients. Because false-negative results are so rare, only the nonnegative results need to be stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers.

strat·i·fied
adj.
Arranged in the form of layers or strata.
. As can be seen from our results, there were small differences between the groups. When dichotomous di·chot·o·mous  
adj.
1. Divided or dividing into two parts or classifications.

2. Characterized by dichotomy.



di·chot
 statistical methods were used, it was possible to separate the two groups to a reasonable extent on the basis of CO alone. This method needs to be applied in the context of a much larger test group.

Previous studies have suggested that TEB monitoring was useful in quantifying changes in cardiac variables during early treatment of congestive heart failure congestive heart failure, inability of the heart to expel sufficient blood to keep pace with the metabolic demands of the body. In the healthy individual the heart can tolerate large increases of workload for a considerable length of time. , trauma, and neurologic problems. (39), (40), (43), (59), (60) We think that the addition of TEB monitoring may help clarify the results of routine exercise electrocardiography electrocardiography (ĭlĕk'trōkärdēŏg`rəfē), science of recording and interpreting the electrical activity that precedes and is a measure of the action of heart muscles.  and direct the clinician in the management of patients with chest pain suggestive of suggestive of Decision making adjective Referring to a pattern by LM or imaging, that the interpreter associates with a particular–usually malignant lesion. See Aunt Millie approach, Defensive medicine.  myocardial ischemia myocardial ischemia,
n a loss of oxygen to the heart muscle caused by blockage of the coronary arteries or their branches.

myocardial ischemia 
.

Limitations of the Study and Future Research Directions

This study has limitations. First, the patients were entered as a convenience sampling. This may have led to a selection bias on the basis of times of the day that the investigator was available. Thirty-four patients had no data recorded. Some reasons were because the body habitus habitus /hab·i·tus/ (hab´i-tus) [L.]
1. attitude (2).

2. physique.


hab·i·tus
n. pl.
 prevented proper application of the leads, the process of applying electrodes interfered with standard patient care, or the monitor did not record any data. This suggests that approximately 27% of patients will not produce adequate data for TEB analysis. We found, however, that many of the patients with large body habitus were able to have the pads applied and had appropriate information recorded. We could not predict ahead of time which patients would or would not be candidates for monitoring.

The monitor that we used was an older model. The NCCOM-R7 has been under continuous improvement and is presently available under a different name from a different company. The newer machines use algorithms that are reported by the companies as more accurate although there is no present literature to support this claim. Use of this machine, however, demonstrates its usefulness in this setting. This is not an outcome study. We were able to determine that all patients survived at 3 months; however, future studies need to focus not only on this sex difference but also on the sex differences among patients with positive stress test results.

Future direction for the use of TEB in a research capacity would be to evaluate EST results in light of long-term follow-up information regarding morbidity and mortality Morbidity and Mortality can refer to:
  • Morbidity & Mortality, a term used in medicine
  • Morbidity and Mortality Weekly Report, a medical publication
See also
  • Morbidity, a medical term
  • Mortality, a medical term
 in patients with an initial presentation of chest pain. It would also be of value in double-blind evaluations of early management approaches to other medical and surgical patients.

God has not called me to be successful; God has called me to be faithful.

-Mother Teresa
Table 1. Results at baseline and increases over baseline for all
variables measured (a)

                                         Normal mean
                                      baseline values

Primary outcome variables

  CO (L/min)                           6.0 [+ or -] 2.0
  SV (ml/min)                           80 [+ or -] 16

Secondary outcome variables

  EDV (ml)                             120 [+ or -] 50
  EF (%)                                45 [+ or -] 10
  TFI (Ohms)                            29 [+ or -] 9

Information for calculated variables

  MAP (mm Hg)                           90 [+ or -] 20
  HR (beats/min)                        80 [+ or -] 20

Calculated variables

  SVR (dynes*sec/c[m.sup.3])          1,600 [+ or -] 400
  CI (L/min/kg)                         95 [+ or -] 19


                                         Mean baseline

Primary outcome variables

  CO (L/min)                              6.6 [+ or -] 2.2
  SV (ml/min)                            80.0 [+ or -] 25.4

Secondary outcome variables
  EDV (ml)                              159.4 [+ or -] 56.2
  EF (%)                                 50.2 [+ or -] 7.4
  TFI (Ohms)                             35.2 [+ or -] 6.7

Information for calculated variables

  MAP (mm Hg)                            95.9 [+ or -] 2.4
  HR (beats/min)                         79.7 [+ or -] 2.9

Calculated variables

  SVR (dynes*sec/c[m.sup.3])          1,257.6 [+ or -] 370.6
  CI (L/min/kg)                          81.9 [+ or -] 28.7


                                      Increase over baseline
                                       at peak exercise (%)

Primary outcome variables

  CO (L/min)                            12.7 [+ or -] 9.4
  SV (ml/min)                           56.7 [+ or -] 50.1

Secondary outcome variables

  EDV (ml)                              83.7 [+ or -] 99.7
  EF (%)                                 7.6 [+ or -] 9.0
  TFI (Ohms)                            -0.4 [+ or -] 2.1

Information for calculated variables

  MAP (mm Hg)                           10.7 [+ or -] 13.4
  HR (beats/min)                        60.4 [+ or -] 21.3

Calculated variables

  SVR (dynes*sec/c[m.sup.3])          -686.9 [+ or -] 372.2
  CI (L/min/kg)                        153.0 [+ or -] 102.1

(a) CO, cardiac output; SV, stroke volume; EDV, end-diastolic volume;
EF, ejection fraction; TFI, thoracic fluid index; MAP, mean arterial
pressure; HR, heart rate; SVR, systemic vascular resistance; CI,
cardiac index.

Table 2. Increases over baseline for subgroup analysis of confirmed
coronary artery disease-positive versus coronary artery
disease-negative patients and females versus males (a)

                                      CAD-negative
                                       (n = 82)

Primary outcome variables

  CO                                    13.1 [+ or -]   9.4

  SV                                    59.3 [+ or -]  50.3

Secondary outcome variables

  EDV                                   89.3 [+ or -] 101.8

  EF                                     7.6 [+ or -]   9.2

  TFI                                   -0.4 [+ or -]   2.2

Information for calculated variables

  MAP                                   10.9 [+ or -]  13.8

  HR                                    60.0 [+ or -]  21.5

Calculated variables

  SVR                                 -709.4 [+ or -] 335.0

  Cardiac index                        158.3 [+ or -] 103.0

                             CAD-positive         P difference
                              (n = 9)              (95% CI)

Primary outcome variables

  CO                           9.1 [+ or -]   9.3        0.26

  SV                          33.3 [+ or -]  44.6        0.13

Secondary outcome variables

  EDV                         32.8 [+ or -]  59.5        0.03

                                                   56.5 (7.6-105.5) (b)

  EF                           7.7 [+ or -]   7.5        0.96

  TFI                         -0.6 [+ or -]   0.8        0.58

Information for calculated
variables

  MAP                          9.3 [+ or -]   8.9        0.63

  HR                          63.4 [+ or -]  20.1        0.65

Calculated variables

  SVR                       -482.0 [+ or -] 608.5        0.30

  Cardiac index              104.1 [+ or -]  82.4        0.10

                                        Mean increase over baseline
                                        Females (n = 43)

Primary outcome variables

  CO                                    8.4 [+ or -]   4.7

  SV                                   33.4 [+ or -]  24.7

Secondary outcome variables

  EDV                                  40.8 [+ or -]  50.5

  EF                                    8.8 [+ or -]   0.0

  TFI                                  -0.6 [+ or -]   2.2

Information for calculated variables

  MAP                                  10.1 [+ or -]  12.0

  HR                                   56.8 [+ or -]  22.5

Calculated variables

  SVR                                -595.3 [+ or -] 394.0

  Cardiac index                       114.6 [+ or -]  68.6

                                        Mean increase over baseline
                                        Males (n = 48)

Primary outcome variables

  CO                                    16.5 [+ or -]  14.7

  SV                                    77.7 [+ or -]  57.6

Secondary outcome variables

  EDV                                  122.2 [+ or -] 116.4

  EF                                     6.5 [+ or -]   8.0

  TFI                                   -0.3 [+ or -]   2.0

Information for calculated variables

  MAP                                   11.3 [+ or -]  14.7

  HR                                    63.5 [+ or -]  19.8

Calculated variables

  SVR                                 -769.0 [+ or -] 334.7

  Cardiac index                        187.3 [+ or -] 114.9

                                       P difference (95% CI)

Primary outcome variables

  CO                                         <0.01

                                         8.1 (4.5-11.6) (b)

  SV                                         <0.01

                                       44.3 (25.4-63.1) (b)

Secondary outcome variables

  EDV                                        <0.01

                                       81.4 (43.3-119.5) (b)

  EF                                          0.22

  TFI                                         0.48

Information for calculated variables

  MAP                                         0.69

  HR                                          0.14

Calculated variables

  SVR                                         0.03

                                      173.6 (21.8-325.5) (b)

  Cardiac index                              <0.01

                                       72.7 (32.7-112.7) (b)

(a) CAD, coronary artery disease; CI, confidence interval; CO, cardiac
output; SV, stroke volume; EDV, end-diastolic volume; EF, ejection
fraction; TFI, thoracic fluid index; MAP, mean arterial pressure; HR,
heart rate; SVR, systemic vascular resistance.
(b) Significant difference.


From the Division of Emergency Medicine, Department of Internal Medicine, School of Medicine, University of California, Davis The University of California, Davis, commonly known as UC Davis, is one of the ten campuses of the University of California, and was established as the University Farm in 1905. , and UC Davis Medical Center The UC Davis Medical Center is a major research hospital located in Sacramento, California and is the primary teaching hospital of UC Davis School of Medicine. Researchers and specialists at the 577 licensed bed medical center work in over 150 areas of specialty. , Sacramento, CA.

This study was supported by a grant from the UC Davis Research Committee.

Reprint requests to Steven J. Weiss, MD, Division of Emergency Medicine, Department of Internal Medicine, University of California, Davis, 2315 Stockton Blvd., PSSB PSSB Peoples State Savings Bank  2100, Sacramento, CA 95817. Email: sweiss52@aol.com

Accepted October 28, 2002.

Copyright [c] 2003 by The Southern Medical Association 0038-4348/03/9611-1121

References

1. Bernstein DP. Noninvasive cardiac output measurement, in Grenvik A, Ayres SM, Holbrook PR, Shoemaker WC (eds): Textbook of Critical Care. Philadelphia, W.B. Saunders Co., 1989, ed 2, pp 159-185.

2. Thangathurai D, Charbonnet C, Roessler P, Wo CC, Mikhail M, Yoahida R, et al. Continuous intraoperative noninvasive cardiac output monitoring using a new thoracic bioimpedance device. J Cardiothorac Vasc Anesth 1997;11:440-444.

3. Weiss S, Calloway E, Cairo J, Granger W, Winslow J. Comparison of cardiac output measurements by thermodilution and thoracic electrical bioimpedance in critically ill versus non-critically ill patients. Am J Emerg Med 1995;13:626-631.

4. Young JD, McQuillan P. Comparison of thoracic electrical bioimpedance and thermodilution for the measurement of cardiac index in patients with severe sepsis severe sepsis A condition defined clinically as 'Sepsis associated with organ dysfunction, hypotension, or hypoperfusion abnormalities (which include) …lactic acidosis, oliguria, or an acute alteration in mental status . Br J Anaesth 1993;70:58-62.

5. Nakatsuka M, MacLeod AD. Hemodynamic he·mo·dy·nam·ics  
n. (used with a sing. verb)
The study of the forces involved in the circulation of blood.



he
 and respiratory effects of transtracheal high-frequency jet ventilation jet ventilation Thoracic surgery A technique used during tracheal reconstructive surgery, in which a catheter is passed through the endotracheal tube into the distal main stem bronchus; a small tidal volume is delivered through the catheter at a high–60-150  during difficult intubation intubation /in·tu·ba·tion/ (in?too-ba´shun) the insertion of a tube into a body canal or hollow organ, as into the trachea.

endotracheal intubation
. J Clin Anesth 1992;4:321-324.

6. Mattar JA, Shoemaker WC, Diament D, Lomar A, Lopes AC, De Freitas E, et al. Systolic Systolic
The phase of blood circulation in which the heart's pumping chambers (ventricles) are actively pumping blood. The ventricles are squeezing (contracting) forcefully, and the pressure against the walls of the arteries is at its highest.
 and diastolic Diastolic
The phase of blood circulation in which the heart's pumping chambers (ventricles) are being filled with blood. During this phase, the ventricles are at their most relaxed, and the pressure against the walls of the arteries is at its lowest.
 time intervals in the critically ill patient. Crit Care Med 1991;19:1382-1386.

7. Castor G, Molter molt  
v. molt·ed, molt·ing, molts

v.intr.
To shed periodically part or all of a coat or an outer covering, such as feathers, cuticle, or skin, which is then replaced by a new growth.

v.tr.
 G, Helms J, Niedermark I, Altmayer P. Determination of cardiac output during positive end-expiratory pressure positive end-expiratory pressure
n. Abbr. PEEP
A technique used in respiratory therapy in which pressure is maintained in the airway so that the lungs empty less completely in expiration.
: Noninvasive electrical bioimpedance compared with standard thermodilution. Crit Care Med 1990;18:544-546.

8. Gotshall RW, Wood VC, Miles DS. Modified head-up tilt test tilt test Upright tilt test Cardiology A clinical maneuver in which a person is placed in a head-up position on a tilt table at a 40º to 80º from horizontal and maintained in a motionless upright position for ≥ 10-15 mins, the intent being to provoke  for orthostatic orthostatic /or·tho·stat·ic/ (or?tho-stat´ik) pertaining to or caused by standing erect.

or·tho·stat·ic
adj.
Relating to or caused by standing upright, as hypertension.
 challenge of critically ill patients. Crit Care Med 1989;17:1156-1158.

9. Preiser JC, Daper A, Parquier JN, Contempre B, Vincent JL. Transthoracic transthoracic /trans·tho·rac·ic/ (-thah-ras´ik) through the thoracic cavity or across the chest wall.

trans·tho·rac·ic
adj.
Across or through the thoracic cavity or chest wall.
 electrical bioimpedance versus thermodilution technique for cardiac output measurement during mechanical ventilation mechanical ventilation
n.
A mode of assisted or controlled ventilation using mechanical devices that cycle automatically to generate airway pressure.
. Intensive Care Med 1989;15:221-223.

10. Appel PL, Kram HB, Mackabee J, Fleming AW, Shoemaker WC. Comparison of measurements of cardiac output by bioimpedance and thermodilution in severely ill surgical patients. Crit Care Med 1986;14:933-935.

11. Scardo J, Kiser R, Dillon A, Brost B, Newman R. Hemodynamic comparison of mild and severe preeclampsia preeclampsia /pre·eclamp·sia/ (pre?e-klamp´se-ah) a toxemia of late pregnancy, characterized by hypertension, proteinuria, and edema.

pre·e·clamp·si·a
n.
: Concept of stroke systemic vascular resistance index. J Matern Fetal Med 1996;5:268-272.

12. Scardo JA, Vermillion ST, Hogg BB, Newman RB. Hemodynamic effects of oral nifedipine nifedipine /ni·fed·i·pine/ (ni-fed´i-pen) a calcium channel blocking agent used as a coronary vasodilator in the treatment of coronary insufficiency and angina pectoris; also used in the treatment of hypertension.  in preeclamptic hypertensive emergencies. Am J Obstet Gynecol 1996;175:336-340.

13. van Oppen AC, van der Tweel I, Alsbach GP, Heethaar RM, Bruinse HW. A longitudinal study longitudinal study

a chronological study in epidemiology which attempts to establish a relationship between an antecedent cause and a subsequent effect. See also cohort study.
 of maternal hemodynamics hemodynamics /he·mo·dy·nam·ics/ (-di-nam´iks) the study of the movements of blood and of the forces concerned.hemodynam´ic

he·mo·dy·nam·ics
n.
 during normal pregnancy. Obstet Gynecol 1996;88:40-46.

14. Hobel CJ, Castro L, Rosen D, Greenspoon JS, Nessim S. The effect of thigh-length support stockings on the hemodynamic response hemodynamic response Cardiology Response of the circulatory system to stimuli such as exercise, emotional stress, etc  to ambulation am·bu·late  
intr.v. am·bu·lat·ed, am·bu·lat·ing, am·bu·lates
To walk from place to place; move about.



[Latin ambul
 in pregnancy. Am J Obstet Gynecol 1996;174:1734-1741.

15. Ouzounian JG, Masaki DI, Abboud TK, Greenspoon JS. Systemic vascular resistance index determined by thoracic electrical bioimpedance predicts the risk for maternal hypotension hypotension
 or low blood pressure

Condition in which blood pressure is abnormally low. It may result from reduced blood volume (e.g., from heavy bleeding or plasma loss after severe burns) or increased blood-vessel capacity (e.g., in syncope).
 during regional anesthesia regional anesthesia
n.
Anesthesia characterized by the loss of sensation in a circumscribed region of the body, produced by the application of a regional anesthetic, usually by injection.
 for cesarean cesarean /ce·sar·e·an/ (se-zar´e-an) see under section.

ce·sar·e·an or cae·sar·e·an or cae·sar·i·an or ce·sar·i·an
adj.
Of or relating to a cesarean section.
 delivery. Am J Obstet Gynecol 1996;174:1019-1025.

16. Scardo JA, Hogg BB, Newman RB. Favorable hemodynamic effects of magnesium sulfate magnesium sulfate
n.
A colorless crystalline compound used as a cathartic and applied locally as an anti-inflammatory agent.


magnesium sulfate Warning - High-alert drug! 
 in preeclampsia. Am J Obstet Gynecol 1995;173:1249-1253.

17. van Oppen AC, van der Tweel I, Duvekot JJ, Bruinse HW. Use of cardiac index in pregnancy: Is it justified? Am J Obstet Gynecol 1995;173:923-928.

18. Heethaar RM, van Oppen AC, Ottenhoff FA, Brouwer FA, Bruinse HW. Thoracic electrical bioimpedance: Suitable for monitoring stroke volume during pregnancy? Eur J Obstet Gynecol Reprod Biol 1995;58:183-190.

19. Metry G, Wikstrom B, Linde T, Danielson BG. Gender and age differences in transthoracic bioimpedance. Acta Physiol Scand 1997;161:171-175.

20. van Oppen AC, van der Tweel I, Bruinse HW. Reproducibility of estimated cardiovascular function by transthoracic bioimpedance cardiography in healthy volunteers. Int J Biomed Comput 1994;37:15-18.

21. Moore R, Sansores R, Guimond V, Abboud R. Evaluation of cardiac output by thoracic electrical bioimpedance during exercise in normal subjects. Chest 1992;102:448-455.

22. Huang KC, Stoddard M, Tsueda KA, Heine MF, Thomas MH, White M, et al. Stroke volume measurements by electrical bioimpedance and echocardiography in healthy volunteers. Crit Care Med 1990;18:1274-1278.

23. Concu A, Scorcu M, Marcello C, Rocchitta A, Molari A, Esposito A, et al. Unchanging cardiac activity while increasing respiratory activity at the start of exercise in man: A beat-by-beat analysis by means of the impedance cardiography method. Cardiologia 1990;35:845-850.

24. Wong DH, O'Connor D, Tremper KK, Zaccari J, Thompson P, Hill D, Changes in cardiac output after acute blood loss and position change in man. Crit Care Med 1989;17:979-983.

25. Wong DH, Tremper KK, Zaccari J, Hajduczek J, Konchigeri HN, Hufstedler SM. Acute cardiovascular response to passive leg raising. Crit Care Med 1988;16:123-125.

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27. Massidda B, Fenu MA, Ionta MT, Tronci M, Foddi MR, Montaldo C, et al. Early detection of the anthracycline-induced cardiotoxicity: A non-invasive haemodynamic study. Anticancer Res 1997;17:663-668.

28. Raine RA, Crayford TJ, Chan KL, Chambers JB. Gender differences in the treatment of patients with acute myocardial ischemia and infarction in England. Int J Technol Assess Health Care 1999;15:136-146.

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coronary heart disease
 or ischemic heart disease

Progressive reduction of blood supply to the heart muscle due to narrowing or blocking of a coronary artery (see atherosclerosis).
 mortality: A population-based study in Olmsted County, Minnesota Olmsted County is a county located in the U.S. state of Minnesota, founded in 1855. As of 2000, the population was 124,277. Its county seat is Rochester6. Geography
According to the U.S.
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30. Frishman WH, Gomberg-Maitland M, Hirsch H, Catanese J, FuriaPalazzo S, Mueller H, et al. Differences between male and female patients with regard to baseline demographics and clinical outcomes in the Asymptomatic Cardiac Ischemia Pilot (ACIP ACIP Cardiology A clinical trial–Asymptomatic Cardiac Ischemia Pilot Study that evaluated 3 therapeutic strategies2 for ↓ myocardial ischemia during exercise testing. ) Trial. Clin Cardiol 1998;21:184-190.

31. Kosmas CE, Mallozzi M, Moten M, Banka VS. Clinical symptomatology symptomatology /symp·to·ma·tol·o·gy/ (simp?to-mah-tol´ah-je)
1. the branch of medicine dealing with symptoms.

2. the combined symptoms of a disease.


symp·to·ma·tol·o·gy
n.
 of coronary artery disease and results of exercise thallium thallium (thăl`ēəm), metallic chemical element; symbol Tl; at. no. 81; at. wt. 204.383; m.p. 303.5°C;; b.p. about 1,457°C;; sp. gr. 11.85 at 20°C;; valence +1 or +3.  scintigraphy: Gender-related differences. Indian Heart J 1997;49:497-501.

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34. Merz CN, Moriel M, Rozanski A, Klein J, Berman DS. Gender-related differences in exercise ventricular function ventricular function,
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35. Bergelson BA, Tommaso CL. Gender differences in clinical evaluation clinical evaluation Medtalk An evaluation of whether a Pt has symptoms of a disease, is responding to treatment, or is having adverse reactions to therapy  and triage triage

Division of patients for priority of care, usually into three categories: those who will not survive even with treatment; those who will survive without treatment; and those whose survival depends on treatment.
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36. Hachamovitch R, Berman DS, Kiat H, Bairey-Merz N, Cohen cohen
 or kohen

(Hebrew: “priest”) Jewish priest descended from Zadok (a descendant of Aaron), priest at the First Temple of Jerusalem. The biblical priesthood was hereditary and male.
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43. Bishop MH, Shoemaker WC, Shuleshko J, Wo CC. Noninvasive cardiac index monitoring in gunshot wound victims. Acad Emerg Med 1996;3:682-688.

44. Saunders CE. The use of transthoracic electrical bioimpedance in assessing thoracic fluid status in emergency department patients. Am J Emerg Med 1988;6:337-340.

45. Kirk JD, Turnipseed S, Lewis WR, Amsterdam EA. Evaluation of chest pain in low-risk patients presenting to the emergency department: The role of immediate exercise testing. Ann Emerg Med 1998;32:1-7.

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49. Sheps DS, Petrovick ML, Kizakevich PN, Wolfe C, Craige E. Continuous noninvasive monitoring of left ventricular function during exercise by thoracic impedance cardiography-automated derivation of systolic time intervals. Am Heart J 1982;103:519-524.

50. Wilson MF, Sung BH, Pincomb GA, Lovallo WR. Simultaneous measurement of stroke volume by impedance cardiography and nuclear ventriculography ventriculography /ven·tric·u·log·ra·phy/ (ven-trik?u-log´rah-fe)
1. radiography of the cerebral ventricles after introduction of air or other contrast medium.

2.
: Comparisons at rest and exercise. Ann Biomed Eng 1989;17:475-482.

51. Denniston JC, Maher JT, Reeves JT, Cruz JC, Cymerman A, Grover RF. Measurement of cardiac output by electrical impedance at rest and during exercise. J Appl Physiol 1976;40:91-95.

52. Hanel B, Teunissen I, Rabol A. Warberg J, Secher NH. Restricted post-exercise pulmonary diffusion capacity and central blood volume depletion. J Appl Physiol 1997;83:11-17.

53. Kim SY, Hinkamp TJ, Jacobs WR, Lichtenberg RC, Posniak H, Pifarre R. Effect of an inelastic inelastic

Of or relating to the demand for a good or service when quantity purchased varies little in response to price changes in the good or service.
 aortic aortic

pertaining to or emanating from the aorta. See also aortic arch.


aortic aneurysm
occurs most often in dogs, where it is caused by Spirocerca lupi larvae, turkeys and primates, causing dyspnea, cyanosis and coughing.
 synthetic vascular graft on exercise hemodynamics. Ann Thorac Surg 1995;59:981-989.

54. Kizakevich PN, Teague SM, Nissman DB, Jochem WJ, Niclou R, Sharma MK. Comparative measures of systolic ejection during treadmill exercise by impedance cardiography and Doppler echocardiography. Biol Psychol 1993;36:51-61.

55. Smith JJ, Muzi M, Barney JA, Ceschi J, Hayes J, Ebert TJ. Impedance-derived cardiac indices in supine and upright exercise. Ann Biomed Eng 1989;17:507-515.

56. Balasubramanian V, Hoon hoon Austral & NZ slang
Noun

a loutish youth who drives irresponsibly

Verb

to drive irresponsibly
 RS. Changes in transthoracic electrical impedance during submaximal treadmill exercise in patients with ischemic heart disease: A preliminary report. Am Heart J 1976;91:43-49.

57. Seguro C, Sau F, Zedda N, Mura O, Montaldo C, Scano G, et al. Hemodynamic assessment at rest and during dynamic physical exercise in young subjects with and without hypertensive hypertensive /hy·per·ten·sive/ (-ten´siv)
1. characterized by increased tension or pressure.

2. an agent that causes hypertension.

3. a person with hypertension.
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58. Smith JJ, Bush JE, Wiedmeier VT, Tristani FE. Application of impedance cardiography to study of postural stress. J Appl Physiol 1970;29:133-137.

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60. Velmahos GC, Wo CC, Demetriades D, Shoemaker WC. Early continuous noninvasive haemodynamic monitoring after severe blunt trauma. Injury 1999;30:209-214.

Steven J. Weiss, MD, Amy A. Ernst, MD, Gary Godorov, MD, Deborah B. Diercks, MD, Josh Jergenson, BS, and J. Douglas Kirk, MD
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Title Annotation:Original Article
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