Impedance cardiography derived cardiac output in hemodialysis patients: a study of reproducibility and comparison with echocardiography.

BACKGROUND: Hemodialysis patients experience a variety of hemodynamic abnormalities that contribute to cardiovascular disease mortality which is the leading cause of death in these patients. Impedance cardiography has been utilized in order to monitor cardiac hemodynamics with lower cost and inconvenience, but it has not been appropriately validated in the hemodialysis population. AIM: We repeatedly used impedance cardiography to assess short- (48 hours) and long-term (15 days) reproducibility of cardiac output measurements and we compared baseline impedance cardiography measurements with echocardiographic measurements. PATIENTS AND METHODS: We studied 109 stable hemodialysis patients, aged 59.70 +/- 11.97 years being on hemodialysis for 67.59 +/- 40.15 months, on a non-dialysis day. Cardiac output was obtained with the BioZ impedance cardiography system (Cardiodynamics, San Diego, Ca, USA). Baseline echocardiography was performed using a Hewlett-Packard Sonos 2500 (Andover, Mass., USA). RESULTS: The values of impedance cardiography derived cardiac output were 5.28 +/- 0.79, 5.27 +/- 0.75 and 5.25 +/- 0.74 l/min at baseline (107 patients), 48 hours (107 patients) and 15 days (98 patients) respectively, showing high reproducibility. Bland and Altman analysis estimated that bias at 48 hours and at 15 days were: -0.013 (95% confidence intervals = -0.045 to 0.019) and 0.028, (95% confidence intervals = -0.044 to 0.101), respectively. In addition baseline impedance cardiography derived cardiac output was significantly correlated with the echocardiographic derived cardiac output (r = 0.9, p < 0.0001). CONCLUSION: Impedance cardiography is a simple non invasive technique for cardiac output estimation in hemodialysis patients which has high reproducibility when performed under controlled conditions, and is closely correlated with echocardiographic measurements of cardiac output.

Alteration of proximal aorta biophysical properties in patients with end stage renal disease.

OBJECTIVE: To present a novel, non-invasive echocardiographic application to assess the structural and functional properties of the complex composition of the proximal aorta in patients with end stage renal disease (ESRD). METHODS: 71 haemodialysis patients (mean (SD) age 61.3 (9.3) years, dialysis duration 79.2 (51.6) months) and 62 age matched controls were studied. From the suprasternal view, the distance between ascending and descending aorta was measured with two dimensional ultrasound. The aortic flow wave transit time was measured with pulsed wave Doppler. M mode echocardiography, with simultaneous blood pressure estimates, was used to assess the diameters of the aortic annulus and of the ascending aorta. Pulse pressure, pulse wave velocity (PWV), pressure strain elastic modulus, characteristic impedance, and beta index were calculated. RESULTS: Patients had increased pulse pressure (68.0 (7.2) v 51.4 (5.0) mm Hg, p < 0.001), PWV (6.1 (1.1) v 3.9 (0.6) m/s, p < 0.001), characteristic impedance (174 (58) v 111 (31) m/s.cm2, p < 0.001), pressure strain elastic modulus (872 (254) v 541 (140) mm Hg, p < 0.001), and beta index (8.9 (3.4) v 5.5 (1.4), p < 0.001) compared with controls. In patients PWV was correlated with age and time on haemodialysis (r = 0.44, p < 0.001, and r = 0.51, p < 0.001, respectively). CONCLUSION: A novel application of duplex ultrasound of the proximal aorta showed that patients with ESRD have impaired proximal aortic function compared with controls. The data indicate that these non-invasive measurements can be used to describe status and change in aortic biophysical properties and may be used as a marker for cardiovascular disease risk.