Pulmonary edema in man: comparison of capillary filtration pressure, quantification by means of the double indicator-dilution method, and clinical observations

Transthoracic electrical impedance at 1 and 100 kHz--a means for separating thoracic fluid compartments?

The electrical impedance of biological tissues varies with their water and electrolyte contents. Alternating current above 5-10 kHz passes both intra- and extracellular fluid, and lower frequency current preferentially extracellular fluid. In an attempt to evaluate thoracic fluid in different compartments, transthoracic electrical impedance (TEI) was measured at 1 and 100 kHz in 15 consecutive patients, without overt left heart failure and under haemodynamic surveillance, during the first two days of myocardial infarction. To achieve different states of hydration the patients were given i.v. furosemide, either 40 mg t.i.d. (high dose group--HDG) or 20 mg once daily (low dose group--LDG). Effects of altered body position and the respective furosemide injections, were evaluated on both days. Mean 24-h-diuresis was 3.9 l in the HDG and 2.5 l in the LDG. After 24 h mean pulmonary arterial diastolic pressure had decreased by 30% in the HDG but remained almost unchanged in the LDG. By then mean basal TEI was increased only in the HDG, by 17% at 1 kHz and 13% at 100 kHz. On Day 1, within one hour after furosemide, TEI increased temporarily by 3-5%, at both frequencies and in both groups. On Day 2, this short-term increase was similar in the LDG at both frequencies and in the HDG at 100 kHz, but not at 1 kHz, consistent with a major extracellular fluid loss in the HDG. TEI at 1 and 100 kHz may thus reflect extracellular and total thoracic fluid, respectively.

Influence of furosemide and body posture on transthoracic electrical impedance in AMI

Transthoracic electrical impedance (TEI) is related to thoracic fluid content. In order to analyze this relation, we studied the acute effects of changes in body posture and of intravenous administration of furosemide on TEI in patients with different diuretic regimens. The TEI was measured using a tetrapolar electrode system, and a 100 microA constant current at 100 kHz. The measurements were performed repeatedly during the first two days in 15 consecutive patients with acute myocardial infarction (AMI) and without overt left heart failure, as evaluated from clinical data and bedside catheterization. It was concluded that TEI appears to be a sensitive, noninvasive means of evaluating changes in thoracic fluid content in AMI.

Pharmacologic therapy of low output syndromes after cardiac surgery

With the advancement of surgical techniques and myocardial protection we can expect that patients previously felt to be inoperable because of poor ventricular function will be surgical candidates. This group of patients will on occasion develop severe left ventricular dysfunction in the peri-operative period. Optimum management in this setting will require acquisition of haemodynamic data, assessment of ventricular loading conditions and inotropic state and the selection of appropriate drug therapy. Drugs are available with specific haemodynamic profiles and therapy is enhanced by matching the abnormal haemodynamics of patients with an appropriate therapeutic agent. If the patient fails to respond quickly to pharmacotherapy, consideration should be directed toward use of an intra-aortic balloon pump.

Physiological interpretation of the skewness of indicator-dilution curves; theoretical considerations and a practical application

Indicator-dilution curves can be interpreted and analysed by describing the system between injection- and sampling site with a physical model. Till now mainly compartmental and distributed models have been investigated. One feature of distributed models is the possibility to interpret skewness or asymmetry of the curve in terms of a parameter, proportional with the Peclet number, which is a measure of the relative contribution between convection and diffusion in indicator transport. In patients with and without pulmonary edema, we analyzed a number of curves obtained with an intravascular indicator (131I radioiodinated serum albumin, RISA) and a diffusing indicator (tritiated water, THO) over the pulmonary vascular bed. Edema was measured by indexed extravascular lung water and by critical pressure, defined as the difference between pulmonary capillary wedge pressure and plasma colloid osmotic pressure. The significant decrease of the symmetry of the RISA curves with increasing cardiac output we explained by an increasing labyrinth dispersion and increasing turbulence at higher flows. For normals we found all THO curves to be less skew than albumin curves. This difference diminished and even reversed when the degree of pulmonary edema increased. We suggest a hypothesis for this phenomenon by considering various mechanisms responsible for dispersion and capillary exchange of the indicator during transport from injection to sampling site. In normals the contribution of Taylor diffusion during laminar flow in parts of the circulatory system may be responsible for the greater symmetry of THO curves; with increasing pulmonary edema, transcapillary diffusion of THO causes THO curves to become more skew and even more asymmetric when compared with albumin curves.