A plethysmograph for the kidney

Summary The renal plethysmograph consists of two separate kidney-like half-molds. The surface of these halfmolds is covered with thin rubber of a special shape. The rubber is attached with the aid of a ligature at the edge furrow. The ligature around the portals of the plethysmograph is placed along the figured furrow and is held in place by means of miniature bitts. This instrument may be employed both in air and water plethysmography.Presented by Active Member AMN SSSR V. V. Parin     

A direct reading capacitance plethysmograph

An improved capacitance system for blood flow measurement by venous occlusion plethysmography is described. It is shown both theoretically and experimentally, that the change in the capacitance between the surface of the segment and an encircling flexible screen cuff at a fixed distance from the skin is related to the fractional change in volume of the part by a simple constant which can be determined from the initial capacitance. Thus, neither calibration nor measurement of segment volume is needed. Practical, sensitive systems for measurement of initial capacitance between the screen and the skin as well as the change in capacitance are described. Analogue circuits by which the progressive increase in capacitance after venous occlusion is filtered, differentiated and surveyed for the most consistent part of the curve are outlined. The final digital read-out is in units of perfusion, i.e. ml/100 ml tissue/min.     

Automated strain-gauge plethysmograph

An automatic 2-channel strain-gauge plethysmograph, based on an absolute resistance measurement technique, will be described in the paper. This device is compact, easy to use, provides inherent self-calibration for any gauge and any length of that gauge, automatically performs the measured cycle, and generates annotated graphical printouts of the measurement data, along with the results which it computes from that data.     

A plethysmograph for the measurement of digital blood flow

Venous occlusion plethysmography using a water-filled plethysmograph is an accurate and reliable method for the measurement of limb flow which has been used for many years. The technique has been adapted to produce a plethysmograph for the measurement of digital blood flow. The device is small, light, cheap, simple to use, and can be calibrated directly with the digit 'in situ'. It is especially suitable for the assessment of digital blood flow, since flow through a large portion of the whole digit is measured and the local temperature of the digit is accurately controlled.     

Automated venous occlusion plethysmograph

A self-contained automated system for venous occlusion plethysmography is described. The system is microprocessor controlled and performs the complete venous occlusion plethysmographic process of measurement, analysis and printout of results at the command of two keypresses on a keypad. Limb circulation is modelled by a linear model. Limb volume change is measured by electrical impedance plethysmography. The system is convenient to use clinically, either for the measurement of blood flow in the legs or for the diagnosis of venous thromboembolic disease. The hardware and data processing software of the system are described and examples from clinical use of the system are presented.     

Two-frequency impedance plethysmograph: real and imaginary parts

A four-channel impedance plethysmograph has been designed. Impedance signals are obtained at two frequencies by measuring both real and imaginary parts. Particular attention has been paid to the sine wave generation circuits that provide system versatility. The required phase-sensitive demodulation is achieved by means of analogue multiplexers. Results show that there are significant variations in the thoracic equivalent capacitance related to respiration and that there is an increased sensitivity to cardiac activity at low frequencies.     

A critical review of the theory of the mercury strain-gauge plethysmograph

A short introductory treatment of the basic theory of the mercury strain-gauge plethysmograph is presented. Some physiological aspects of this type of plethysmography are then discussed which, among other things, illuminate the difficulty in discriminating between skin-flow and muscular flow. A detailed calculation of the elastic influences follows and shows that one cannot generally expect a cancellation of these influences when comparing measurements with the calibration. This part illuminates further the difficulties in discriminating between skin-flow and muscular flow. As a result, such discrimination should be regarded as dubious. Some other sources of error are also discussed briefly. Two proposals for a new design are given. Finally, the Appendix shows the values of the gauge stretch which will give cancellation of the elastic errors in a simple model. The actual values cannot be used in practice but they indicate that the amount of stretch is quite critical.     

A multiplex cathode-ray-tube display with digital readout for a body plethysmograph

The cathode-ray-tube display of a body plethysmograph is enhanced by a composite switching circuit, which displays an electronically generated angle cursor and plethysmograph parameters simultaneously on an accurate single beam oscilloscope. A direct readout of the angle is obtained by means of a panel-mounted digital voltmeter together with facilities for operating a printer to provide permanent records. Additional circuits provide controllable antidrift voltages to the oscilloscope that counteract the drift of the plethysmograph and improve the stability of the display.     

Simple design for an impedance plethysmograph

A simple and inexpensive impedance plethysmography has been designed. Complete circuit diagrams are provided to facilitate system replication. The operation of each functional unit in the measurement system is described. Particular attention is given to the demodulation chip, which simplifies circuit design and increases measurement performance.     

Dual-channel self-balancing impedance plethysmograph for vascular studies

A self-balancing two-channel electrical impedance plethysmograph is described. It uses a phasesensitive detector and incorporates both fine and coarse feedback loops to achieve rapid, automatic balancing of the resistive component of the tissue impedance. A calibrated output is produced which is proportional to the tissue resistance and is independent of the exciting current amplitude. The system has a bandwidth from 0–30 Hz and a resolution of 0·002 ω. Results of preliminary investigations are presented illustrating its application for the measurement of arterial pulse-wave velocity, the diagnosis of deep-vein thrombosis and the measurement of systolic blood pressure.