Thoracic Impedance Measurements Research Articles

Pacemaker Auto‐Interference by Thoracic Impedance Measurement for the Rate Response Function

This report describes two cases of pacemaker auto-interference caused by thoracic impedance measurements for the rate response function of a dual chamber pacemaker. Mechanisms of this phenomenon and reprogramming strategies are discussed.

Use of thoracic impedance measurements for the surveilllance of heart failure patients under resynchronization therapy

Early detection of volume overload prior to clinical decompensationis crucial in the management of the heart failure patients. To reach this goal tho-racic impedance measurements generating an index with alarming functions(Optivol) are integrated in a newly released defibrillator for cardiac resynchro-nization therapy (Sentry, Medtronic Inc). Up to now there are no data on the clin-ical usefulness of these measurements. From August 2004 to January 2005 Sentry devices were implanted in18 patients in our center. There were 13 man and 5 women (mean age 61±17years, mean LVEF 23±8%). Data of the Optivol-Index were interrogated from thedevices in approximately 4 week intervals and correlated to the clinical course ofthe patients. There were 2 patients alarms in our group. One alarm could be relatedto impending cardiac decompensation and weight gain (consequence: increase ofdiuretics), the other alarm could be related to technical reasons (change of thepace sense lead due to oversensing). Furthermore we detected four increases in the index, which could be correlated toworsening symptoms, and in one case prior to sudden death of a patient due toelectro-mechanical dissociation. In the other 12 cases stable or decreasing indexesreflected a clinical course without cardiac events. Our first preliminary results with the Optivol index showed a goodcorrelation to clinical data in patients with severe heart failure. Changes in thelead system can be one reason of non-specific alarms.

Thoracic Impedance Measurements During Orthostatic Change Test and During Hemodialysis in Hemodialyzed Patients

Measurements were performed before and after hemodialysis (HD) in the supine and upright positions (orthostatic change test) and during HD session every 30 minutes in recumbent position on 11 HD patients. Two hydration states were compared: hyperhydration and normal hydration. Each patient served as his own control. Blood pressure and total body bioimpedance were obtained simultaneously. Thoracic impedance values (Zo) obtained during HD were significantly greater in the normal hydration state. There was strong correlation between Zo gain and total ultrafiltration; however, Zo gain divided through total ultrafiltration (calculated for every 100 ml) was also higher in this state. The ratio Zo/R (where R is resistance of total body bioimpedance) was stable during HD but was significantly higher in the normal hydration state. Zo gain during the orthostatic change test was significantly higher after HD than before HD in both hydration states. The anticipated difference in Zo gains between both hydration states was not significant. After echocardiographic analysis of patients, we determined that cardiac dysfunction or valvular defects in four patients were likely responsible for opposite reaction on orthostatic change test. During our measurements, we observed the influence of Zo changes on episodes such as intradialytic hypotension or acute atrial fibrillation. Thoracic impedance is an intriguing method for controlling pathophysiology of fluid distribution, but it requires the accurate definition of a patient's hemodynamics and strong conditions during measurement. During our measurements, we observed the influence of such episodes as intradialytic hypotension or acute atrial fibrillation on Zo changes.

Thoracic impedance used for measuring chest wall movement in postoperative patients

Thoracic impedance (TTI) and rib cage inductance band (IB) signals were measured in 10 patients during the first night after abdominal surgery, and compared by successive correlation of the change in each signal. Poor matching of the signals occurred, on average, for 94 min either because of movement of differences in the waveform. There were frequent episodes of transient poor correlation, generally associated with transient respiratory disturbance, predominantly airway obstruction (58%). Thoracic impedance measurements are simpler than inductance band methods for detecting rib cage movement and may be useful for large studies of respiratory abnormalities in patients after operation.

From in vitro to in vivo monitoring

In vitro monitoring is inherently invasive with discrete measurements on blood samples and the results are often delayed an hour or more when the analyses are performed in the central laboratory. The delay may be greatly reduced if the analyses are performed near the patient. In vivo monitoring may be non‐invasive and may provide continuous real‐time data but the accuracy usually does not match that of in vitro measurements. In vivo monitoring therefore finds its application in the detection of trends of change, and it is needed only for quantities that change rapidly and unpredictably and where a suitable therapeutic action is available. In critically ill patients, this applies to the arterial pO2, pCO2, and pH, and the mixed venous pO2. Ideal in vivo monitoring techniques are not available for all these quantities. In the newborn, the arterial pO2 may be monitored with a transcutaneous pO2 electrode. In the adult, the arterial pO2 may be monitored indirectly by monitoring the arterial oxygen saturation with a pulse oximeter and the mixed venous pO2 by monitoring the mixed venous oxygen saturation with a catheter tip sensor. The arterial pCO2 may be monitored with a transcutaneous pCO2 electrode or by capnography, i. e., by monitoring the end‐expiratory pCO2. Other in vivo monitoring techniques such as gastric tonometry for the gastric mucosal pH and thoracic impedance measurement have found some routine application, whereas near‐infrared spectrometry for oxy‐ and deoxyhaemoglobin in the brain, and magnetic resonance spectroscopy for tissue ATP are at the stage of research and development.

Single-chamber Cardiac Pacing with Two Forms of Respiration-controlled Rate-responsive Pacemaker

Ventilatory changes correlate with the heart rate response during exercise, and such changes have been used to determine an appropriate chronotropic response in the Biorate (RDP3 and MB-1) and Meta pacemakers, both of which use a thoracic impedance measurement principle. Ten patients with the Biorate and 11 patients with the Meta were studied. In both groups, significant rate response and improvement in exercise duration compared with fixed rate ventricular pacing were achieved during symptom-limited treadmill exercise tests, with good correlations between the pacing rate and estimated oxygen consumption. Motion artefacts affected the measured impedance of both pacemakers, with rate response occurring during arm movements in the absence of respiratory activity. This observation suggested that both pacemakers have the potential of activity sensing. The earlier version of the Biorate (RDP3) was limited by myopotential interference, and erosion of the auxiliary lead can be problematic in some patients.

The Synchronometer: A Prototype Device to Measure Infant/Ventilator Synchrony

Publisher Summary This chapter describes a prototype device to measure infant/respirator synchrony. To detect breath-by-breath chest expansion, a thoracic impedance measurement from bilateral mid-axillary line electrodes is used. This gives a distinction between inspiration and expiration. This lead position was chosen since it is most commonly used in the clinical setting. To detect the respiratory cycle generated by the ventilator, pressure changes at the exhalation port in a Bournes BP 200 ventilator are used. Certainly, some noninvasive breath-by-breath measurement of alveolar ventilation would be best. Breath-by-breath alveolar-air equations could possibly be calculated by computer from relatively noninvasive measurements and used to assure proper ventilation. Esophageal pressure could be used to give another indication of alveolar inflation, but it has been experience that actual ventilation in severe respiratory distress syndrome is poorly reflected in esophageal pressures. Another aspect of thoracic impedance is electrode position. It is suggested to consider chest expansion in ventilated infants by reviewing video tapes of their chest from different perspectives.

Treatment of Prostatic Cancer: Effects on Serum Lipoproteins and the Cardiovascular System

We studied 32 patients with prostatic cancer before, and after 1 and 6 months of treatment with orchiectomy, estramustine phosphate or conventional estrogens (polyestradiol phosphate plus ethinyl estradiol). Lipid metabolism was evaluated by lipoprotein analysis and the intravenous fat tolerance test. Effects on the cardiovascular system were studied by exercise electrocardiography, blood volume estimation and thoracic electrical impedance measurement, a sensitive method to detect early signs of fluid retention.Present treatment programs for prostatic cancer seem to result in effects on lipoprotein metabolism that probably are of minor importance for the development of atherosclerotic manifestations. Measurement of thoracic impedance may be of value to detect fluid retention in individual patients.

Decreases in Electric Thoracic Impedance During transurethral Resection of the Prostate: an Index of Early Water Intoxication

Toracic impedance of 18 patiennts undergoing transurethral resection of the prostate was measured 15 minutes preoperatively, and 30 and 60 minutes after the start of the operation. Impedance variations were compared to variation in 1) cardiac output, 2) serum sodium osmolality and 3) alveolar-arterial oxygen tension difference. Thoracic impedance, initially 24.6 plus or minus 0.3, decreased to 23.8 plus or minus 0.5, 30 minutes after the onset of the operation (p less than 0.0005) and 22.9 plus or minus 0.5, 30 minutes later (p less than 0.01 from previous reading and 0.0005 from control). Patients in whom impedance had decreased 10 per cent or more from control values received 10mg. furosemide intravenously 60 minutes after the onset of the operation. This therapy permitted the restoration of impedance values, cardiac output, alveolar-arterial oxygen tension difference and serum sodium osmolality to values statistically similar to those found in the 10 patients who had not sustained such precipitous decreases in impedance within 60 minutes. We believe that the measurement of thoracic impedance during transurethral prostatic surgery offers the most sensitive index of early water intoxication. Measurements can be obtained without delay in the operating room and, thus, permit immediate correction of the condition.

SERIAL MEASUREMENTS OF THORACIC IMPEDANCE AND CARDIAC OUTPUT IN HEALTHY NEONATES AFTER NORMAL DELIVERY AND CAESAREAN SECTION

Thoracic electrical impedance measurements were serially performed during the 1st, 2nd, 8th and up to the 32nd hour of life in two groups (V and S) of healthy infants. In group V, all 24 infants were delivered vaginally, in group S, all 24 infants were delivered by caesarean section for obstetrical reasons. Basal thoracic impedance (Zo), heart rate (HR), stroke volume (SV) and cardiac output (Q) were determined on each examination. In group V, Zo increased from 31.9 to 34.0 ohm between 2 hours and the last recording between 8 and 32 hours. SV decreased from 4.1 to 3.4 ml between 2 and 4 hours and was accompanied by a decrease of Q from 560 to 450 ml/min. Heart rate slowed from 129 to 115 beats/min between 2 hours and the last recording at greater than or equal to 8 hours. In group S, Zo increased from 32.2 to 35.9 ohm between 2 and 8 hours. Mean SV increased from 3.6 to 4.4 ml between 8 and 32 hours and heart rate slowed from 131 to 113 beats/min between 1 and 8 hours. No significant differences were observed between the groups. The accuracy of the impedance--SV and Q data cannot be validated. For the most part they compare favourably with values previously obtained by soluble gas methods. Serial changes may reflect not only decreasing shunts and/or increasing aeration but also changes in total fluid volume of the lungs, intra- or extravascular. The precision of the measurements is good since reproducibility of single SV and Q determinations is higher than with standard dilution techniques. The data obtained may serve as baseline values for comparison with data in infants of the same age with various anomalies.