Continuous measurement of hemodynamic alterations during pharmacologic cardiovascular stress using automated impedance cardiography

Assessment of the arterial input function for estimation of coronary flow reserve by single photon emission computed tomography: comparison of two different approaches

PURPOSE

Attempts to estimate coronary flow reserve (CFR) with single photon emission computed tomography (SPECT) tracers have been recently made. We compared two different methods for the estimation of CFR by SPECT imaging.

METHODS

Fourteen patients with coronary artery disease underwent dipyridamole 99mTc-sestamibi SPECT and intracoronary Doppler within 5 days. Myocardial blood flow (MBF) was estimated by measurement of first transit counts in the right pulmonary artery (PA) and left ventricular (LV) chamber, and myocardial counts from SPECT images. Estimated CFR was expressed as the ratio of stress MBF to rest MBF.

RESULTS

Rest and stress MBF obtained using first transit counts from PA were higher compared to that from LV chamber (rest: 1.05 ± 0.38 vs 0.87 ± 0.34 counts/pixel per s, respectively, p < 0.01 and stress: 1.34 ± 0.45 vs 0.91 ± 0.20 counts/pixel per s, respectively, p < 0.05). In the study vessels, CFR by Doppler was 1.39 ± 0.42, and SPECT CFR obtained using first transit counts from PA and LV chamber were 1.36 ± 0.43 and 1.16 ± 0.39, respectively (p across categories NS). A significant relationship between SPECT CFR obtained using first transit counts from PA and CFR by Doppler was found (r = 0.85, p < 0.001). No relationship between SPECT CFR obtained using first transit counts from LV chamber and CFR by intracoronary Doppler was OBSERVED (R = 0.43, P = NS).

CONCLUSION

SPECT-estimated CFR obtained using first transit counts from right PA is more accurate and correlates better with the results of intracoronary Doppler than estimated CFR obtained using arterial input function from LV chamber.

Interoceptive sensitivity and physical effort: Implications for the self-control of physical load in everyday life

This study examined the relationship between interoceptive sensitivity and the behavioral self-regulation of physical load. According to their performance in a heartbeat detection task, 34 participants were classified as good or poor heartbeat perceivers. Participants pedaled on a bicycle ergometer for 15 min and were free to choose the tempo of their cycling. Good heartbeat perceivers covered a significantly shorter distance and showed a significantly smaller increase in mean heart rate, stroke volume, and cardiac output. There were significant negative correlations between heartbeat perception score and covered distance, changes in heart rate, changes in stroke volume, and changes in cardiac output. These results were not explained by differences in physical fitness level (PWC150). The findings suggest that good heartbeat perceivers show a more finely tuned behavioral self-regulation of physical load than poor heartbeat perceivers.

Comparison of Impedance Cardiography and Thermodilution-Derived Measurements of Stroke Volume and Cardiac Output at Rest and During Exercise Testing

BACKGROUND

Non-invasive evaluation of haemodynamic variables remains a preferable and attractive option in both pharmacologic research and clinical cardiology.

OBJECTIVES

The objective of this study was to evaluate the correlation, feasibility and diagnostic value of haemodynamic measurements by ICG with the thermodilution (TD) method at rest and during exercise testing.

METHODS

We measured stroke volume (SV) and cardiac output (CO) with both methods in 20 patients with suspected coronary artery disease (CAD). All measurements were performed simultaneously at rest and during bicycle exercise.

RESULTS

There was a highly significant correlation (p < 0.001) for measurements of SV between both methods at rest (r = 0.83) and during exercise (r = 0.85-0.87) with 50-100 watts. For measurements of CO, the respective correlations were r = 0.85 at rest and r = 0.92-0.94 during exercise. The mean difference for measurements of SV were 3.8 +/- 12.6 ml at rest and 6.5+/- 11.4 ml during exercise. For measurements of CO, the mean difference between both methods was 0.9 +/- 1.0 l/min at rest and 1.0+/- 0.8 l/min during exercise. Compared to TD measurements, ICG had a bias to overestimate SV and CO of approximately by 5-10%. One patient had to be excluded because of inappropriate quality of the ICG signals during exercise.

CONCLUSIONS

ICG is a feasible and accurate method for non-invasive measurements of SV and CO. Haemodynamic measurements by ICG were correlated highly significant to simultaneous measurements by the TD method.

Stroke volume and systolic time intervals: beat-to-beat comparison between echocardiography and ambulatory impedance cardiography in supine and tilted positions

The aim of the study was to compare stroke volume (SV), ejection time (ET) and pre-ejection period (PEP) measurements obtained using a central haemodynamics ambulatory monitoring device based on impedance cardiography (ICG), in supine and tilted positions (60 degrees), with pulsed Doppler echocardiography as a non-invasive reference method. The Holter-type ICG device was used for off-line, beat-to-beat, automatic determination of SV, ET and PEP. ICG data were compared with those obtained simultaneously using pulsed Doppler echocardiography in the ascending aorta from a suprasternal projection, 1 min before and 10 min after tilting. The tests were performed in 13 young, healthy subjects (six men and seven women, aged 23-33 years). Linear regression between the measured values obtained for all subjects was described by the following formulas: SVicg= 13.9 + 0.813 x SVecho (r = 0.857, SEE = 9.03, n = 496), ETicg = 16.8 + 0.987 x ETecho (r = 0.841, SEE=21.3, n = 496), PEPicg= 22.8 + 0.890 x PEPecho (r = 0.727, SEE = 14.6, n = 496). The data showed that ambulatory impedance cardiography gives useful absolute values of SV and systolic time intervals measured in supine and tilted positions.

Acculturation and cardiovascular reactivity of second-generation Turkish migrants in Germany

OBJECTIVE

Previous studies have shown that migration and acculturation lead to higher blood pressures and a higher prevalence of cardiovascular diseases. Heightened cardiovascular reactivity is considered as a risk factor for cardiovascular diseases. Therefore, the purpose of the present study was to examine cardiovascular reactivity in young and healthy second-generation Turkish migrants to Germany.

METHOD

Forty-one Turkish and 20 German male students worked on a mental arithmetic task for 6 min and underwent the cold pressor test for 90 s. Heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were taken in intervals of 2 min at baseline and during task periods. Stroke volume (SV), cardiac output (CO), preejection period (PEP), and total peripheral resistance (TPR) were registered continuously by impedance cardiography. The Turkish volunteers were divided into weak and advanced acculturated migrants based on self-ratings given in a questionnaire.

RESULTS

Advanced acculturated Turkish students showed greater HR and CO increases and greater PEP and TPR decreases to the mental arithmetic task than Germans or weak acculturated Turkish students. No group differences were found for the cold pressor test.

CONCLUSION

Migrants' acculturation is associated with an enhanced beta-adrenergic activation pattern of the sympathetic nervous system that might put them at greater risk with regards to essential hypertension and coronary heart disease.

Nongenomic cardiovascular effects of triiodothyronine in euthyroid male volunteers

T(3) has been shown to exert cardiovascular effects. These effects have not yet been defined with regard to the mode of action (nongenomic vs. genomic) and with regard to an interaction with the adrenergic system in humans. To address these issues we conducted a randomized, double blind, 6-fold cross-over trial in 18 healthy male volunteers. After pretreatment with the beta-agonist dobutamine, the beta-blocking agent esmolol, or placebo (0.9% NaCl), 100 microg T(3) or placebo were injected. Primary target variables were systemic vascular resistance (SVR) and cardiac output (CO) within 45 min after injection of T(3) vs. placebo after placebo pretreatment. Sympatho-vagal balance was assessed by measurement of heart rate variability. T(3) caused a lower SVR and a higher CO than placebo (P < 0.001) after pretreatment with placebo. An increased low frequency (LF)/high frequency (HF) ratio (power in LF/power in HF band) after T(3) compared with placebo (P = 0.004) suggests an increase in sympathetic tone. After pretreatment with dobutamine, the effects of T(3) on SVR and CO were abolished, and the effect on LF/HF ratio was reversed. After pretreatment with esmolol, the effects on SVR and LF/HF ratio were reversed. Our data show, for the first time, nongenomic cardiovascular effects of T(3) in humans.

Estimation of coronary flow reserve with the use of dynamic planar and SPECT images of Tc-99m tetrofosmin

BACKGROUND

We developed a noninvasive method to examine coronary flow reserve with technetium 99m tetrofosmin based on the microsphere model. According to the microsphere model, myocardial blood flow (MBF) can be calculated by MBF = q / integral C(t)dt, where q is myocardial activity and C(t) is tracer concentration in blood. Because the ratio of integral C(t)dt at stress to rest is equal to the ratio of the first transit count in the pulmonary artery (PA) and attenuation factors were canceled out, we calculated the increase ratio of MBF (MBF(IR)).

METHODS AND RESULTS

After injection of dipyridamole, tetrofosmin was injected as a bolus and serial dynamic planar images were obtained to measure the first transit count in PA (PAC). Myocardial single photon emission computed tomography was performed to measure the regional myocardial count (RMC). MBF(IR) was calculated as [(RMCs x PACr)/(RMCr x PACs) - 1] x 100, where r and s denote resting and stress conditions, respectively. In contrast, the increase in the myocardial uptake ratio (MUR(IR)) was defined as (RMCs x SCr/RMCr x SCs - 1) x 100, where SC is syringe count of tracer. The results were as follows: (1) The mean MBF of healthy subjects was 46.9% +/- 22.8%. (2) MBF(IR) of the infarcted region and ischemic region was significantly decreased (8.3% +/- 12.2% and 11.2% +/- 11.9%, respectively; P <.001). (3) MUR(IR) was significantly lower than MBF(IR) (14.1% +/- 21.2%; P <.001). (4) MBF(IR) decreased according to the heart rate at rest (r = 0.47; P <.05).

CONCLUSIONS

MBF(IR) is a potential parameter with which to evaluate coronary flow reserve when the changes of arterial input function during stress are considered.

Short term cardiovascular effects of aldosterone in healthy male volunteers

Clinical evidence of rapid, nongenomic aldosterone effects in the cardiovascular system has been provided by clinical studies; an increase in systemic vascular resistance (SVR) was shown by invasive techniques within 3 min after injection of aldosterone. Here, we study the dose dependency and the later course of the rapid aldosterone effects by noninvasive techniques. In 12 healthy male volunteers, SVR and heart rate variability were determined by impedance cardiography and digital electrocardiography, respectively, for 8 h after the injection of 0.05 or 0.5 mg aldosterone in a double blind, placebo-controlled, 3-fold cross-over study. No significant differences were observed for baseline values among the three treatments. The area under the curve of SVR during the first 45 min after injection was significantly different between the periods with the highest areas under the curve seen after the injection of 0.5 mg aldosterone (mean +/- SD, 40.4 +/- 12.8 vs. 36.8 +/- 10.3 for 0.05 mg aldosterone and 36.8 +/- 10.4 for placebo; P = 0.05). Individual comparisons showed significant differences at 6 and 30 min between placebo and the 0.5 mg aldosterone period (P < 0.05), with values for the 0.05 mg aldosterone period similar to those for the placebo period. From 330-390 min, opposite changes occurred; SVR was depressed during the 0.05 mg (P < 0.05) and 0.5 mg aldosterone periods compared with that during the placebo period. These delayed effects may reflect an increased vagal tone in the aldosterone groups, as demonstrated by higher values of the time domain parameter of heart rate variability pNN50. This study provides further evidence for clinically detectable rapid cardiovascular aldosterone effects in vivo obtained by noninvasive techniques. The data are consistent with the view of aldosterone as a rapid modulator of cardiovascular responses acting through nongenomic mechanisms.

Evaluation of systolic performance by automated impedance cardiography

Impedance cardiography (ICG) is a noninvasive method for evaluating cardiac function. Left ventricular stroke volume (SV) is the basic hemodynamic parameter derived from thoracic bioimpedance curves. Issues of our study were to investigate the diagnostic value of other indices of left ventricular systolic performance, such as ejection fraction (EF), index of contractility (IC), peak flow index (PFI), and acceleration index (ACI), which can also be calculated by ICG. Forty patients (PTS) with suspected coronary artery disease (CAD) were monitored by automated ICG during pharmacologic stress testing with dobutamine. All PTS underwent subsequent cardiac catheterization. In PTS with single vessel disease, the dobutamine-induced changes of SV, EF, IC, PFI, and ACI were comparable to those of PTS without CAD. In PTS with multivessel disease, the impaired systolic performance during dobutamine stimulation could be clearly demonstrated. We conclude that automated ICG is a useful method for monitoring SV and other indices of left ventricular systolic performance for detecting PTS with ischemic left ventricular dysfunction during cardiovascular stress.