Comparison and reproducibility of transthoracic bioimpedance and dual beam Doppler ultrasound measurement of cardiac function in healthy volunteers

Comparison of pulse contour, aortic Doppler ultrasound and bioelectrical impedance estimates of stroke volume during rapid changes in blood pressure

NEW FINDINGS

What is the central question of this study? Pulse contour analysis of the finger arterial pressure by Windkessel modelling is commonly used to estimate stroke volume continuously. But is it valid during dynamic changes in blood pressure? What is the main finding and its importance? Second-by-second analysis revealed that pulse contour analysis underestimated stroke volume by up to 25% after standing from a squat, and 16% after standing thigh-cuff release, when compared with aortic Doppler ultrasound estimates. These results reveal that pulse contour analysis of stroke volume should be interpreted with caution during rapid changes in physiological state.

ABSTRACT

Dynamic measurements of stroke volume (SV) and cardiac output provide an index of central haemodynamics during transitional states, such as postural changes and onset of exercise. The most widely used method to assess dynamic fluctuations in SV is the Modelflow method, which uses the arterial blood pressure waveform along with age- and sex-specific aortic properties to compute beat-to-beat estimates of aortic flow. Modelflow has been validated against more direct methods in steady-state conditions, but not during dynamic changes in physiological state, such as active orthostatic stress testing. In the present study, we compared the dynamic SV responses from Modelflow (SV_MF ), aortic Doppler ultrasound (SV_U/S ) and bioelectrical impedance analysis (SV_BIA ) during two different orthostatic stress tests, a squat-to-stand (S-S) transition and a standing bilateral thigh-cuff release (TCR), in 15 adults (six females). Second-by-second analysis revealed that when compared with estimates of SV by aortic Doppler ultrasound, Modelflow underestimated SV by up to 25% from 3 to 11 s after standing from the squat position and by up to 16% from 3 to 7 s after TCR (P < 0.05). The SV_MF and SV_BIA were similar during the first minute of the S-S transition, but were different 3 s after TCR and at intermittent time points between 34 and 44 s (P < 0.05). These findings indicate that the physiological conditions elicited by orthostatic stress testing violate some of the inherent assumptions of Modelflow and challenge models used to interpret bioelectrical impedance responses, resulting in an underestimation in SV during rapid changes in physiological state.

Central Hemodynamics Measured During 5 Repetition Maximum Free Weight Resistance Exercise

The PhysioFlow™ is a piece of equipment that uses bioimpedance cardiography to measure central hemodynamics. The purpose of this research was to explore the novel approach of monitoring central hemodynamics during free weight resistance exercise using bioimpedance cardiography throughout a 5 repetition maximum (5RM). Thirty participants ranging from beginner to advanced lifters (16 males and 14 females) completed a 5RM for back squat, seated push press, and bicep curl while connected to the PhysioFlow™ to assess the response of heart rate (HR), stroke volume (SV), cardiac output (Q), and ejection fraction (EF). Participants were cued for form and to breathe normally throughout the lifts. The PhysioFlow™ detected an increase in HR and Q for all lifts between rest and each repetition (p < 0.05). There was also an increase in HR and Q from repetition 1 to repetition 5 for all lifts (p < 0.05). No changes in EF or SV were detected between resting measurements and each repetition for all lifts (p > 0.05) and no changes in EF or SV were detected when all repetitions were compared to each other for all lifts (p > 0.05). In conclusion, the PhysioFlow™ was able to detect changes in HR and Q during dynamic free weight resistance exercise. This novel approach may provide a mechanism for monitoring central hemodynamics during free weight resistance training. However, more research needs to be conducted as the exercise protocol for this investigation did not allow for a comparison to a reference method.

Systemic hemodynamic effects of sequential pneumatic compression of the lower limbs: a prospective study in healthy volunteers

STUDY OBJECTIVE

To evaluate the effects on systemic hemodynamics of sequential pneumatic compression of the lower limbs in healthy volunteers.

DESIGN

Prospective, self-controlled, volunteer study.

SETTING

University teaching hospital.

PATIENTS

11 healthy volunteers, aged 25 +/- 1.3 years.

INTERVENTIONS AND MEASUREMENTS

After volunteers underwent a 6-hour period of fasting and 15 minutes of rest in the supine position, baseline systemic hemodynamics were assessed using transthoracic electrical bioimpedance. Peripheral venous pressure was measured using a 16-gauge intravenous cannula inserted in the forearm and connected to a pressure monitor. Then sequential pneumatic compression of the lower limbs was activated for a 30-minute period, and systemic hemodynamic measurements were repeated. In each volunteer, measurements were repeated twice in two consecutive days, and average values were calculated for each volunteer.

MAIN RESULTS

After activation of sequential pneumatic compression of the lower limbs, mean arterial blood pressure increased from 90 mmHg (79-107 mmHg) to 95 mmHg (79-129 mmHg) (P = 0.02), whereas heart rate decreased from 79 bpm (51-94 bpm) to 75 bpm (53-90 bpm) (P = 0.02). This was associated with a significant increase in peripheral vascular resistance index (from 545 [440-1066] to 613 [369-1280] dynes s cm(-5) m(-2) [P = 0.013]) and reduction in cardiac index (from 3.4 [2.7- 4.5] to 3.2 [2.5-4.0] L/min per m2 [P = 0.034]).

CONCLUSIONS

The application of sequential pneumatic compression to the lower limbs is associated with minor increases in mean arterial blood pressure, with moderate reduction of cardiac output and heart rate.

Acute systemic, splanchnic and renal haemodynamic changes induced by molecular adsorbent recirculating system (MARS) treatment in patients with end-stage cirrhosis

AIM

To evaluate the acute effect of treatment with the molecular adsorbent recirculating system (MARS) on splanchnic, renal and systemic haemodynamics in patients with end-stage cirrhosis.

METHODS

Twelve patients with end-stage cirrhosis, undergoing MARS treatment, were enrolled. The following haemodynamic parameters were measured by means of Doppler ultrasonography and thoracic electrical bioimpedance, before and after each session: portal velocity, renal and splenic resistance indices, cardiac output, cardiac stroke volume, heart rate, mean arterial pressure, systemic vascular resistance.

RESULTS

Median portal velocity increased significantly after treatment (23.7 vs. 20.3 cm/s, P < 0.05) while renal resistance index (0.72 vs. 0.75, P < 0.05) and splenic resistance index (0.60 vs. 0.65, P < 0.05) decreased significantly. Mean arterial pressure (83 vs. 81 mmHg, P < 0.05) and vascular resistance (899 vs. 749 dyne. s/cm5, P < 0.05) increased significantly, while cardiac output and stroke volume showed no significant changes.

CONCLUSIONS

Data emerging from this investigation suggest that MARS treatment improves significantly various haemodynamic alterations in cirrhotic patients in the short term. The observed decrease in renal vascular resistance and improvement in splenic resistance index, a parameter related to portal resistance, which leads us to hypothesize that these haemodynamic effects are probably mediated by clearance of vasoactive substances during MARS treatment.

Comparative effects of ivabradine, a selective heart rate-lowering agent, and propranolol on systemic and cardiac haemodynamics at rest and during exercise

AIM

To compare in humans the effects of ivabradine and propranolol on cardiac and systemic haemodynamics at rest, during tilt and exercise.

METHODS

Nine healthy volunteers randomly received single oral doses of ivabradine (Iva, 30 mg), propranolol (Propra, 40 mg) or placebo (Plac) during a double-blind cross-over study. Doses were selected to be equipotent in heart rate (HR) reduction. HR, systolic and diastolic blood pressure (SBP, DBP), cardiac index (CI, bioimpedance), rate pressure product (RPP), plasma epinephrine (E) and norepinephrine (NE), were measured at rest at baseline, before and after two tilt and exercise tests, started 2 and 5 h after drug intake. Heart rate variability (low to high frequency ratio LF/HF) was evaluated at rest and at 5 th minute of tilt.

RESULTS

At rest, HR and RPP decreased similarly with Iva and Propra (both P < 0.01). During tilt, HR increased less with Iva than Propra (P < 0.01), LF/HF decreased after Iva (P < 0.03), SBP and mean blood pressure decreased after Propra (both P < 0.01), RPP decreased similarly after Iva and Propra (both P < 0.01) and CI decreased to a greater extent with Propra than with Iva or Plac (both P < 0.04). During exercise, Iva and Propra similarly decreased HR (both P < 0.01) and RPP (P < 0.01).

CONCLUSIONS

These results demonstrate that for a similar decrease in HR at rest and during sympathetic stimulation, acute administration of ivabradine, a selective heart rate-lowering agent, decreased myocardial oxygen demand to the same extent as a reference beta-blocker, propranolol, but without evidence of depressant effect on cardiac function.

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.

Short-term postural reflexes in diabetic patients with autonomic dysfunction

AIMS/HYPOTHESIS

Assessment of autonomic dysfunction provides prognostic data in diabetic patients. Clinical tests are limited to heart rate variability and blood pressure measurements. We investigated whether a detailed analysis of postural reflexes of patients during short-term head-up tilting and standing erect (both for 3 min) would provide useful clinical data.

METHODS

We studied 14 control subjects and 56 patients with Type 2 diabetes, stratified into four matched groups: uncomplicated, micro-albuminuria, macro-albuminuria and autonomic neuropathy, who were tilted 55 degrees three times and were standing erect. Non-invasive finger plethysmography blood pressure measurements, using the Portapres, and impedance cardiac output measurements, using the RheoCardioMonitor, were continuously recorded throughout the study. Wavelets of the response to tilting and standing were drawn. The wavelets for the three tilts were combined to improve definition. The degree of autonomic dysfunction was quantified by calculating the baroreflex sensitivity index from the heart-rate and blood-pressure variability data.

RESULTS

Baroreflex sensitivity data confirmed that autonomic dysfunction increased as diabetic complications worsened (p<0.001). Both standing and tilting resulted in an initial decrease in blood pressure followed by recovery, an increase in heart rate which was more pronounced with standing and a decrease in stroke volume. Characteristic and incremental changes in these responses were noted as the complications of diabetes worsened (p<0.001). These were a greater decrease in blood pressure with loss of the recovery phase, a reduced heart-rate response and paradoxically an increase in stroke volume.

CONCLUSION/INTERPRETATION

Non-invasive blood-pressure and stroke-volume measurements recorded during short-term tilting and standing promises to be useful in assessing diabetic autonomic dysfunction.

Systemic and splanchnic hemodynamic changes after liver transplantation for cirrhosis: a long-term prospective study

The effect of orthotopic liver transplantation (OLT) on the systemic and splanchnic hemodynamic alterations of cirrhosis is still largely unknown. The aim of this study was to prospectively investigate the long-term changes induced by OLT on several hemodynamic parameters. In 28 patients undergoing OLT for cirrhosis, the following parameters were measured before surgery and subsequently at 6-month intervals (mean follow-up period, 17 months): cardiac index, mean arterial pressure (MAP), heart rate, total peripheral resistance (TPR), portal vein flow velocity and flow volume, spleen size, and Doppler ultrasound resistance or pulsatility indexes (RI or PI) in the: 1) interlobular renal, 2) superior mesenteric, 3) splenic, and 4) hepatic arteries. The same parameters were measured in 10 healthy controls. After OLT, cardiac index and heart rate significantly decreased (P <.01), while MAP and TPR increased (P <.001), so that any significant difference from controls disappeared. Renal RI progressively decreased, achieving a significant reduction (P <.05) to normal values at the 12th month of follow-up. Portal flow velocity and hepatic and splenic RI returned to values not significantly different from controls. Portal flow volume increased over normal values after OLT (P <.001), and SMA PI, lower than normal before OLT, did not show any statistically significant increase thereafter. Spleen size decreased significantly, but persisted to be larger than in controls. In conclusion, systemic, renal, and most, but interestingly not all, splanchnic circulatory alterations of cirrhosis are restored to normal after OLT.

A meta-analysis of three decades of validating thoracic impedance cardiography

OBJECTIVE

To provide a meta-analysis of current literature concerning the validation of thoracic impedance cardiography (TIC) and to explain the variations in the reported results from the differences in the studies.

DATA SOURCES

A computer-assisted search of English-language, German, and Dutch literature was performed for the period January 1966 to April 1997. Moreover, references from review articles were obtained.

STUDY SELECTION

A total of 154 studies comparing measurements of cardiac output or related variables obtained from TIC and a reference method were analyzed.

DATA EXTRACTION

Articles were classified by differences in TIC methodology, reference method, and subject characteristics. Fisher's Zf transformed correlation coefficients were used to compare results. Data were pooled using the random-effects method.

DATA SYNTHESIS

An overall pooled r2 value of .67 (95% confidence interval, 0.64-0.71) was found. However, the correlation was higher in repeated-measurement designs than in single-measurement designs (r2 = .53; 95% confidence interval, 0.43-0.62). Further research using analysis of variance revealed a significant influence of the reference method and the subject characteristics on the correlation coefficient. The correlation was significantly better in animals than in cardiac patients. Subgroup analysis revealed that TIC correlated significantly better to the indirect Fick method than to echocardiography in healthy subjects. No significant influence of the applied TIC methodology was found.

DISCUSSION

The overall r2 value of .67 indicates that TIC might be useful for trend analysis of different groups of patients. However, for diagnostic interpretation, a r2 value of .53 might not meet the required accuracy of the study. Great care should be taken when TIC is applied to the cardiac patient. However, because the applied reference method was of significant influence, differences between TIC and the reference method are incorrectly attributed to errors in TIC alone.

Haemodynamic effects of inhibition of nitric oxide synthase and of L-arginine at rest and during exercise

OBJECTIVE

To compare effects of N(G)-monomethyl-L-arginine (L-NMMA; a NO synthase inhibitor) and L-arginine (a NO synthase substrate) on haemodynamics in healthy men at rest and during exercise.

METHODS

We infused L-NMMA and saline placebo intravenously in two groups of eight healthy men. Each group underwent a two-phase, randomized, single-blind crossover study. Men in one group received 3 mg/kg L-NMMA and men in the other group received 6 mg/kg L-NMMA. Haemodynamic measurements were performed before, during and after a 12 min stepped exercise protocol starting 6 min after the intravenous infusion. A further six men received, according to the same study design, 30 g L-arginine over 30 min and saline placebo before exercise. Blood pressure was measured by sphygmomanometry and cardiac output by bioimpedance, allowing computation of total systemic vascular resistance index (SVRI).

RESULTS

Infusion of 6 mg/kg L-NMMA into men at rest produced modest increases (compared with effect of saline placebo) in systolic and diastolic blood pressures of 4.1 +/- 1.1 and 12.6 +/- 3.5%, respectively (means +/- SEM, P < 0.01 for both comparisons) and a marked increase in SVRI of 39.2 +/- 5.2% (P < 0.01). Cardiac index and heart rate were 22.0 +/- 3.3 and 17.0 +/- 4.4% lower after administration of L-NMMA (P < 0.01 for each comparison) than after infusion of saline placebo. During exercise there was no significant difference between total SVRI after infusions of L-NMMA and saline (difference not significant, diminished with increasing exercise). Six minutes into recovery the difference between total SVRI after infusions of L-NMMA and saline reappeared with SVRI 25 +/- 6.9% higher after infusion of L-NMMA than after infusion of saline (P < 0.01). Administration of L-arginine had no significant effect on haemodynamics in men at rest, during exercise and during recovery.

CONCLUSIONS

Effects of L-NMMA on total systemic vascular resistance during exercise are less marked than are those on subjects at rest, probably because vasodilatation of resistance vessels of skeletal muscle during exercise is mediated mainly by factors other than NO. Our results also suggest that NO synthesis in healthy men is not substrate limited either at rest or during exercise.

Usefulness, usability, and quality criteria for noninvasive methods in cardiovascular clinical pharmacology

Validation of study methods is a prerequisite for their usability. Empirical quality criteria based on test-theoretical principles are useful for this purpose. These criteria are discussed for several noninvasive methods used in cardiovascular clinical pharmacology: electrocardiography, systolic time intervals, blood pressure, and estimates of stroke volume. Several of these methods are highly reliable and sensitive to drug effects. However, they are inherently low in validity because they are based on oversimplified algorithms and yield estimates rather than measurements of function and changes therein. These estimates are method-specific and are likely to be subject to method*subject*effect interaction. Highlighting these constraints and the limitations of these methods need not preclude their useful contribution to the early evaluation of drug action in humans.

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

The contribution of computerized impedance cardiography in monitoring and differentiating cardiovascular responses to pharmacologic stress after the administration of dipyridamole (group 1, n = 24) or dobutamine (group 2, n = 26) was investigated during stress echocardiography. Heart rate, stroke volume index, cardiac index and systemic vascular resistance index were evaluated continuously with an automated, computerized, signal-averaged impedance cardiography system. Dipyridamole had little average effect on heart rate, stroke volume index, and cardiac index. The responses were similar in patients with positive (n = 9) or negative (n = 15) stress echocardiography test results (as characterized by echocardiographic wall-motion abnormalities). Dobutamine induced a similar mean increase in heart rate in patients with negative (n = 13) or positive (n = 13) results on stress echocardiography. The mean increase in stroke volume index induced by dobutamine was greater in patients with negative stress echocardiography test results than in patients with stress-induced wall-motion abnormalities. This distinction was also seen in the cardiac index; the mean change in patients with negative stress echocardiography test results was larger than in patients with positive results. It is concluded that automated computerized impedance cardiography not only allows surveying and monitoring hemodynamic changes during pharmacologic stress echocardiography but also contributes to differentiation of pathologic stress responses.

Do changes in cardiac output affect the inspiratory to end-trial oxygen difference?

BACKGROUND

The paramagnetic technique has made it possible to monitor the end-tidal oxygen concentration and P(1-ET)O2, i.e. inspiratory to end-tidal oxygen difference, breath-by-breath. Little is known about the implications of a changing P(1-ET)O2, but so far studies have shown it to be a quick and sensitive variable to detect hypoventilation. This study was designed to observe the circulatory effects on P(1-ET)O2 in an experimental setting but monitored as in a clinical situation.

METHODS

We assessed the oxygen difference during changes in cardiac output induced by intravenous ephedrine-hydrochloride in 12 healthy male volunteers. P(1-ET)O2 was measured with a fast-response paramagnetic differential oxygen sensor. Cardiac output was measured with non-invasive transthoracic electrical bioimpedance. As simultaneous changes in metabolism and ventilation will also influence P(1-ET)O2 oxygen uptake and expired minute volume were monitored. After a rest period, the subjects had an intravenous injection of ephedrine-hydrochloride 0.1 mg.kg-1 followed by a 30-min observation period.

RESULTS

Cardiac output increased significantly as did the oxygen uptake and the ventilation. We found no biological significant correlation between cardiac output and P(1-ET)O2. The P(1-ET)O2 was influenced by ventilation and metabolism.

Comparison of cardiac output measurements by thermodilution and thoracic electrical bioimpedance in critically ill versus non-critically ill patients

Thoracic electrical bioimpedance (TEB) has been proposed as an alternative to thermodilution (TD) for the measurement of cardiac output in settings such as the Emergency Department where invasive monitoring is not available. Validation studies comparing TEB with TD suggest a wide range of variability in the agreement between the two methods. This prospective study tests the hypothesis that this variability may be related to the severity of patient illness. Fifteen non-critically ill patients undergoing cardiac catheterization and 13 critically ill patients who underwent Swan-Ganz catheterization in the medical intensive care unit (MICU) were enrolled. Fifty-one pairs of data from the catheterization laboratory and 49 pairs of data from the MICU were obtained. The patients were graded retrospectively according to the APACHE II scoring system. The mean difference (bias) between TEB and TD results was calculated for each patient using the method suggested by Bland and Altman. A pooled t-test was performed to determine whether there was any significant difference between the APACHE II scores or cardiac output measurements obtained by TEB and TD in the two groups. APACHE II scores were 4.7 +/- 1.2 for the catheterization laboratory and 14.2 +/- 5.0 for the intensive care unit patients (P < .001). The catheterization laboratory (cath lab) group bias was 0.23 +/- 2.19, whereas the MICU bias was .002 +/- 2.33. There was no significant difference in the bias between the two groups despite significant differences in the APACHE II scores. Standard deviations of the bias were less than 15% different from each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and neurohumoral effects of levosimendan, a new calcium sensitizer, at rest and during exercise in healthy men

Levosimendan is a novel inodilator that increases the calcium sensitivity of troponin C in a calcium-dependent way. Cardiac function (impedance cardiography, systolic time intervals), neurohumoral responses at rest and during exercise at 2 workloads, and peripheral blood flow (plethysmography) were studied in 14 healthy young men. Vehicle and 2 doses of levosimendan (6.5 micrograms/kg, low dose [LD]; and 25 micrograms/kg, high dose [HD]) were given intravenously in a crossover study. Measurements taken 15 minutes after a supine rest showed HD levosimendan shortened electromechanical systole (QS2i) by 16 ms maximally (p < 0.001), and decreased systemic vascular resistance by 25% (p < 0.001), compared with baseline values. Diastolic blood pressure fell by 9 mm Hg (p < 0.01). When the changes after vehicle were compared with the changes after HD levosimendan, the difference was 2.1 L/min after 25 micrograms/kg (p < 0.001), caused by an increase in stroke volume, with the heart rate being unaffected. Leg blood flow increased by 35% (p < 0.001). During exercise at the lower workload, HD levosimendan increased cardiac output by 1.5 L/min (p < 0.05), compared with that caused by vehicle, by an increase in heart rate, with the stroke volume being unchanged. Electromechanical systole was shortened significantly (20 ms, p < 0.001 after HD; 12 ms, p < 0.01 after LD). At the higher workload, no effects on electromechanical systole or cardiac output compared with that associated with administration of vehicle were seen, but the mean heart rate increased (p < 0.001, LD and HD) and mean diastolic blood pressure decreased (p < 0.01, HD).(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of estimated cardiovascular function by transthoracic bioimpedance cardiography in healthy volunteers

In ten healthy volunteers, stroke index (SI), heart rate (HR), thoracic fluid conductivity (TFC) and index of contractility (IC) were estimated by transthoracic bioimpedance measurements (BoMed Noninvasive Continuous Cardiac Output Monitor, model 3, Revision 7 (NCCOM3-R7)). Intra- and inter-observer variability and the influence of time of day (morning or afternoon) were determined. The intra-observer variability was significantly smaller during the morning than during the afternoon. The mean differences +/- standard error between consecutive measurements for morning versus afternoon measurements were, respectively: SI, 0.8 +/- 1.2 vs. 4.6 +/- 1.2 ml/m2 (P = 0.057); HR, -1.0 +/- 0.6 versus -0.9 +/- 0.6 beats/min; TFC, -0.0 +/- 0.3 vs. 1.0 +/- 0.3 (= TFC x 1000.omega-1) (P = 0.031) and IC, -0.6 +/- 0.9 vs. 5.6 +/- 0.9 (= IC x 1000.s-1) (P = 0.001). The inter-observer variability for SI, HR, TFC and IC did not reach statistical significance. These data suggest that reproducible measurements can be obtained provided that only morning or afternoon measurements are compared. Since the reproducibility of measurements was better during the morning than during the afternoon, we recommend that measurements are performed in the morning.

Lack of pharmacodynamic interactions between acute dose flosequinan and xamoterol. A pilot study in healthy subjects

The possible cardiovascular pharmacodynamic interactions at rest and during exercise of combining oral flosequinan (100 mg) with xamoterol (200 mg) was investigated in a four-way randomised double-blind placebo-controlled crossover trial in eight healthy male volunteers. Xamoterol was better tolerated than flosequinan. The most common adverse events were mild to moderate headache and facial flushing. One volunteer developed headache and vomiting following flosequinan treatment and was replaced. Compared to placebo, at supine rest, flosequinan significantly increased heart rate (HR) by 5 beats.min-1, but had no effect on cardiac output (CO), stroke volume (SV) and mean blood pressure (MBP). Xamoterol significantly increased CO by 1.5 l.min-1, HR (5 beats.min-1) and MBP (6 mmHg) but not SV. The combined treatment (flosequinan + xamoterol) significantly increased CO (1.7 l.min-1) and HR (10 beats.min-1), but had no effect on SV and MBP. During exercise, flosequinan had no significant effect on any variable compared to placebo. Both xamoterol and combined treatment reduced the increase in CO (-4.6 l.min-1 after xamoterol and -3.4 l.min-1 after combined treatment vs. 0.1 l.min-1 after placebo), but had no effect on other variables. The effect of the combined treatment on each haemodynamic variable were no more than the anticipated additive effects of the two drugs. Thus, no cardiovascular pharmacodynamic interaction was found between flosequinan and xamoterol in healthy volunteers.

Haemodynamic comparison of amlodipine and atenolol in essential hypertension using the quantascope

1 We have utilised a non-imaging echo-Doppler cardiac output device, using the principle of attenuated compensation volume flow (ACVF), to assess the cardiovascular effects of amlodipine and atenolol over 3 months in 24 patients with essential hypertension. 2 Both amlodipine and atenolol, at 4 and 12 weeks, similarly reduced mean arterial pressure (12 weeks amlodipine -12.6 mmHg, atenolol -14.9 mmHg; P < 0.01 for each vs baseline). 3 The heart rate fell on atenolol, both at 4 weeks (amlodipine -3 vs atenolol -12 beats min(-1); P < 0.05) and 12 weeks (-1 vs -11 beats min(-1); P < 0.05), without change on amlodipine. 4 Stroke volume initially rose on atenolol without change on amlodipine (4 weeks amlodipine -1.3 ml vs atenolol +10.1 ml; P = 0.05) but between drug effects were not different at 12 weeks. 5 The systemic vascular resistance was reduced on amlodipine (12 weeks: amlodipine -176 dyn s cm(-5): P < 0.05) without change on atenolol (atenolol -48 dyn s cm(-5): NS). 6 The cardiac stroke work was lowered on amlodipine both at 4 weeks (P < 0.01) and 12 weeks (P < 0.05) and statistically different from the unaltered atenolol values at both time points. 7 Skin nutrient flow or fingertip temperature was not altered by either treatment. 8 These results are consistent with contrasting mechanisms of action--vasodilator for amlodipine and decreased cardiac pumping for atenolol. The greater reduction in cardiac stroke work on amlodipine compared with atenolol warrants further investigation during longer-term studies.

Dose-dependent heart rate reducing effect of nizatidine, a histamine H2-receptor antagonist

1. Twelve healthy subjects were treated in a randomised placebo-controlled crossover study with placebo, 150 mg, 300 mg, and 600 mg nizatidine, 100 mg pirenzepine, and 300 mg nizatidine plus 100 mg pirenzepine for 1 week each. 2. On the seventh treatment day, heart rate, blood pressure, systolic time intervals, impedance cardiographic and Doppler ultrasound variables were measured. 3. Stroke volume and blood pressure were not altered by nizatidine and/or pirenzepine. By contrast, heart rate and cardiac output significantly (P < 0.05) decreased in a dose-dependent manner 1.5 and 3 h after administration of 300 and 600 mg nizatidine. Treatment with 150 mg nizatidine led to similar though non-significant trends. 4. While a slightly insignificant rise in heart rate was detected with pirenzepine alone, heart rate and cardiac output remained unchanged upon combined nizatidine and pirenzepine treatment as compared with placebo and baseline values. 5. In conclusion, nizatidine reduced heart rate and cardiac output in a dose-dependent manner, whereas this negative chronotropic effect was counteracted by concurrent administration of the anti-cholinergic drug pirenzepine.

Disagreement between standard transthoracic impedance cardiography and the automated transthoracic electrical bioimpedance method in estimating the cardiovascular responses to phenylephrine and isoprenaline in healthy man

1. Impedance cardiography is a well-established noninvasive method to assess within-subject changes of cardiovascular function. We compared the standard approach (ZCG) which requires tedious signal analysis with an automated approach (TEB: NCCOM 3) with its own specific equipment, algorithms and equations in order to assess agreement of the method-specific measurements and calculations. 2. Ten healthy men were studied on two occasions with either ZCG or TEB, at rest and at the end of 5 min i.v.-infusions with 1 microgram min-1 isoprenaline and 100 micrograms min-1 phenylephrine. 3. There was good agreement for the method-independent changes (HR, SBP/DBP), but there were large differences for method-specific measurements: dZ/dtmax [TEB-ZCG] = -0.68, CI: -0.83 to -0.53 ohm s-1, PEP [TEB-ZCG] = -22.1, CI: -35.0 to -9.2 ms and QS2c [TEB-ZCG] = -16.5, CI: -32.4 to -0.6 ms and for the calculated stroke volume SV [TEB-ZCG] = 30.3, CI: 15.5 to 45.2 ml. The responses of dZ/dtmax and SV to isoprenaline and phenylephrine, although qualitatively similar, reached no quantitative agreement either. A substantial disagreement was evident for the STI responses to isoprenaline where TEB failed to detect the expected reduction of VETc and thus grossly underestimated the shortening of QS2c. 4. It is concluded that TEB-measurements and -calculations did not agree with standard ZCG, that the methods, albeit related, cannot be considered as interchangeable and that suspicion is justified that TEB might yield erroneous results under specific circumstances.

Agreement and reproducibility of the estimates of cardiovascular function by impedance cardiography and M-mode echocardiography in healthy subjects

The reproducibility and agreement of the estimates of stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) by transthoracic impedance cardiography (ZCG) and M-mode echocardiography (ECHO) were analyzed before and after the placebo-controlled administration of ascending doses of isosorbide dinitrate and nicorandil in 12 healthy subjects. There was no biostatistical agreement between the two methods in estimating cardiovascular function either before or after dosing (ZCG estimated substantially larger SV, CO and lower TPR). But, ZCG and ECHO estimated about similar overall treatment related changes (across treatments and periods) and reached substantially better agreement when the values were expressed as ratio of the baseline before dosing. Such improvement did not occur when the data were expressed as arithmetic difference from baseline. In spite of the improvement of agreement by expressing the data as ratio of baseline, the coefficients of reproducibility between the two methods (circa 25% of baseline) remained too large to judge the methods interchangeable.