Bo Tedner

Evaluation of impedance technique for fluid-volume monitoring during hemodialysis

Fluid-volume changes during hemodialysis were studied in 30 patients at four separate treatments in each patient. Readings of fluid-volume changes obtained by a fluid-balance monitor with non-invasive tetrapolar impedance technique were compared to changes in weight caused by the treatment. A correlation coefficient of r=0.90 (p<0.001) was found. A survey of papers describing impedance measurements during hemodialysis or diuresis is also presented.

Short-term cardiovascular responses to rapid whole-body tilting during exercise

Abstract Our objective was to characterize the responses of heart rate (HR) and arterial blood pressure (BP) to changes in posture during concomitant dynamic leg exercise. Ten men performed dynamic leg exercise at 50, 100, and 150 W and were rapidly and repeatedly tilted between supine (0°) and upright (80°) positions at 2-min intervals. Continuous recordings of BP and HR were made, and changes in central blood volume were estimated from transthoracic impedance. Short-lasting increases in BP were observed immediately upon tilting from the upright to the supine position (down-tilt), averaging +18 mmHg (50 W) to +31 mmHg (150 W), and there were equally short-lasting decreases in BP, ranging from −26 to −38 mmHg upon tilting from supine to upright (up-tilt). These components occurred for all pressure parameters (systolic, mean, diastolic, and pulse pressures). We propose that these transients reflect mainly tilt-induced changes in total peripheral resistance resulting from decreases and increases of the efficiency of the venous muscle pump. After 3–4 s (down-tilt) and 7–11 s (up-tilt) there were large HR transients in a direction opposite to the pressure transients. These HR transients were larger during the down-tilt (−15 to −26 beats · min−1) than during the up-tilt (+13 to +17 beats · min−1), and increased in amplitude with work intensity during the down-tilt. The tilt-induced HR fluctuations could be modelled as a basically linear function of an arterial baroreflex input from a site half-way between the heart and the carotid sinus, and with varying contributions of fast vagal and slow sympathetic HR responses resulting in attenuated tachycardic responses to hypotensive stimuli during exercise.

Whole body impedance measurements reflect total body water changes. A study in hemodialysis patients

Fluid volume changes during hemodialysis was monitored by continuous whole body impedance measurements. The fluid changes recorded using this method was compared to fluid volume changes measured in plasma water (PV) using125I-albumin, and extracellular volume (ECV) using51Cr-EDTA before and after treatment, and total body water (TBW) changes reflected by continuous bed scale monitoring. Changes in impedance correlated to TBW changes, r=0.80, p<0.001, while correlations to changes in ECV and PV were: r=0.57 and r=0.55, respectively, p<0.05. Alterations in body fluid volumes recorded with whole body impedance is best correlated to total body water changes.The use of continuous whole body impedance monitoring has been shown to offer a simple non-invasive method for recording total body water changes during hemodialysis.

Study of the electrical impedance of blood from house painters.

SummaryUsing a four-electrode technique the electrical impedance was measured at 150 kHz (100 μA) on whole blood samples from 13 male house painters (age 19–49 years; median 35 years) exposed occupationally to vapors from alkyd paints containing organic solvents and from a control group of 7 healthy unexposed men (age 27–53 years; median 37 years). The blood impedance of the two groups was monitored prior to and 9 days after an initial administration of acetylsalicylic (600 mg). The resistivity calculated from the impedance of whole blood from the painters remained significantly higher than the corresponding values for the controls. The hematological values for the two groups were within normal ranges, although the painters had significantly higher platelet counts than the controls. Effects of long-term exposure of the painters to volatile solvents are discussed.

Lower leg fluid displacement during a simulated space shuttle launch.

Abstract Reductions in leg fluid volume of about 1 l per leg or 10% of total leg volume have been reported during space flight. We wanted to test the hypothesis that a significant portion of these changes occur during the prelaunch and launch periods. Fluid volume changes in the lower leg were estimated in six men during a simulated Space Shuttle launch. After 2 h in the launch position, i.e. supine with elevated legs, the subjects were exposed to 500 s of two to three times increased g force in the anterio-posterior direction in a human centrifuge. During the prelaunch period one lower leg lost a mean of (113 SD 53) ml of fluid and there was little or no additional fluid reduction during the period of increased g force. This compares with the 178-ml reduction of lower leg volume that has been reported during the 1st day of Shuttle missions. We concluded that a significant portion of the fluid reduction observed in the lower leg during the early stages of space flight had already occurred before the launch.