Abstract: A method for measuring plasma levels of an inhibitor of (Na.sup.+ +K.sup.+)ATPase associated with hypertension comprising:(1) incubating deproteinized plasma of a patient suspected of being hypertensive in a (Na.sup.+ +K.sup.+)ATPase assay solution comprising (a) (Na.sup.+ +K.sup.+)ATPase; and(2) following the activity of the (Na.sup.+ +K.sup.+)ATPase over the course of time, and use of the method in diagnosing hypertension and in monitoring anti-hypertensive therapy.

Abstract: A small, portable, constant withdrawal device is connected to tubing, including a catheter, whose internal walls are coated with heparin. The catheter is inserted intravenously through a disposable needle into a subject such as a human being. The subject may then move about for a selected period when blood is being slowly withdrawn at a prescribed rate and collected in a container within a housing supporting the device. The collected blood may then be analyzed to permit the measurement of the integrated concentration of growth hormone or any substance whose concentration in blood fluctuates widely.In addition, a portable microdiffusion chamber is incorporated between the indwelling catheter and the extra corporal tubing and is electrically connected through a sensing probe to an associated portable sensory responsive device. This permits analyzation of the extracted blood to determine the in vivo concentration of circulating concentrations of the diffusable fraction of biological materials in the blood.

Abstract: A method of evaporating liquids to separate solid substances contained therein to form a residue of the substances characterized by applying subatmospheric pressure to at least one discrete portion of the liquid at a first pressure level and subsequently applying subatmospheric pressure to the discrete portion at a second pressure level lower than the first level to gradually evaporate the liquid from the discrete portion thereby leaving a residue of solid substances. Apparatus for performing the foregoing method preferably comprises an enclosure within which a support means is used for supporting at least one discrete portion of the liquid to be separated, a vacuum pump connected to the enclosure for evacuating atmosphere from within the enclosure, and a valve means between the pump and enclosure operable automatically to apply first and second subatmospheric pressure levels to within the enclosure.