Showing papers in "Medical & Biological Engineering & Computing in 1978"
TL;DR: The spatial selectivity of bipolar electrodes, and its possible enhancement by linear filtering techniques, are discussed, and predicted e.m. power spectra are compared with some practical measurements on biceps brachii muscle in normal subjects.
Abstract: A 2-dimensional conducting-paper analogue and a 3-dimensional field-theory model are used to investigate the influence of electrode spacing and size on the waveshape and frequency spectrum of the signal detected by bipolar surface electrodes, when an action potential propagates in a muscle fibre below the skin surfce. The spatial selectivity of bipolar electrodes, and its possible enhancement by linear filtering techniques, are then discussed. Finally, predicted e.m.g power spectra are compared with some practical measurements on biceps brachii muscle in normal subjects.
144 citations
TL;DR: Clinically, the system has been used for the recording of ambulatory blood pressures in 110 patients for periods up to 72 h with satisfactory results, and appears to be fully satisfactory and considerably more reliable than the earlier designs.
Abstract: A new perfusion and transducer unit for ambulatory blood-pressure recording is described, followed by reports of both the laboratory evaluation of the unit and experience with its clinical use. The major change from earlier systems is the perfusion system, now based on an electrically driven ‘delta’ pump. Pressure is measured by a semiconductor strain-gauge pressure transducer. Laboratory evaluation has shown that the transducer with associated tubing and cannulae has a satisfactory frequency response, considerably better than that of the recording system normally used. Both quantitatively and qualitatively there was a very close correspondence between signals obtained from the entire Oxford system (including recording and replay) and signals obtained directly by means of a catheter-tip transducer. Small, but consistent, signal drifts attributable to battery behaviour are described. The system appears remarkably insensitive to temperature variations within the range of expected ambient temperatures. Delta pump performance is satisfactory, producing essentially constant perfusion rates. Clinically, the system has been used for the recording of ambulatory blood pressures in 110 patients for periods up to 72 h with satisfactory results. Reliability appears good, with minimal artefacts atributable to the equipment. This transducer and perfusion system appears to be fully satisfactory and considerably more reliable than the earlier designs.
127 citations
TL;DR: A needle-puncture method for producing the minimum amount of skin abrasion required to eliminate stretch artefact, and recommends puncture in clinical recording where motion artefact is a problem.
Abstract: Artefacts arising from variations in potential across the skin pose the greatest artefact problem remaining in a well designed biopotential recording system. We examined the nature of skin potential artefacts caused by stretch deformation, often called ‘motion artefacts’, and the manner by which skin abrasion reduces these artefacts, using a simultaneous skin-potential and impedence-measuring device to verify a simple d.c. electrical model of the skin. We found that abrasion reduces artefacts by resistively loading the high-impedance transcutaneous potential generator within the epidermis. We devised a needle-puncture method for producing the minimum amount of skin abrasion required to eliminate stretch artefact. We found that 10 0·5-mm skin punctures reduced the artefact from 5–10 mV to less than 0·2 mV. Skin irritation and redness are absent in the majority of cases, but cause a slight reddening in some cases. In contrast, sandpaper abrasion by an inexperienced operator often results in large welts and scabbing. We recommend puncture in clinical recording where motion artefact is a problem.
113 citations
TL;DR: In this paper, the impedance of small platinum electrodes has been measured as a function of frequency in the range of 0·1 Hz to 10 kHz, and the value of K is about 2·5 Mω for a surface are of 0.05 mm2.
Abstract: The impedance of small platinum electrodes has been measured as a function of frequency. In the range of 0·1 Hz to 10 kHz, this impedance Z can be described accurately as K/(i2πf)m. The value of K is about 2·5 Mω for a surface are of 0·05 mm2. The values for m are in the order of 0·75. Various step responses are computed based on this expression and are compared to recorded wave forms. All step responses are shown to result directly and consistently from the same expression. The consequences of these results for various models and equivalent circuits of the electrode-medium interface are discussed.
107 citations
TL;DR: A computer-controlled stimulator and special electrode array are described which can control the pattern of motor-unit recruitment during electrical stimulation of the lower leg of the cat and is able to sustain isometric muscular contractions to fatigue at a variety of tensions with almost identical endurance times.
Abstract: Although the order by which motor units are recruited, and the frequencies at which they fire, vary during different types of exercise, laboratory studies involving the electrical stimulation of muscle have never examined the effect of different orders of recruitment on muscular function. This has been due, principally, to the lack of an adequate technique capable of selectively stimulating discrete populations of motor units in a muscle having a mixed population of fibres. The paper describes a computer-controlled stimulator and special electrode array which can control the pattern of motor-unit recruitment during electrical stimulation of the lower leg of the cat. In addition, following a program of recruitment analogous to that which is believed to normally occur during voluntary isometric exercise, the computer was able to sustain isometric muscular contractions to fatigue at a variety of tensions with almost identical endurance times. as are found in man.
72 citations
TL;DR: In this paper, a model of the passive properties of the urinary bladder in the collection phase is presented, which is defined in terms of a pressure-volume relationship, and is divided into four subsystems or blocks, namely two geometry blocks, a block describing the time-dependent property of the bladder wall, and a block representing its length-dependent properties.
Abstract: A model is presented that describes the passive properties of the urinary bladder in the collection phase. A black-box approach is used. The system under investigation, which is defined in terms of a pressure-volume relationship, is divided into four subsystems or blocks, namely two geometry blocks, a block describing the time-dependent properties of the bladder wall, and a block describing its length-dependent properties. Models have been developed and tested for each block separately. With regard to geometry, the bladder is described as a thick-walled sphere of constant tissue volume. The time-dependence of the properties of the wall can be explained using a visco-elastic model, and the length dependence of the wall properties is shown to yield elastic moduli which depend biexponentially on strain. Estimates of the value of the parameters involved were obtained from experiments on strips of urinary bladder, obtained from the local slaughterhouse. Combination of the blocks yielded an overall model of the passive properties of the urinary bladder in the collection phase. The model contains 14 parameters. The classical way of investigating the urinary bladder, by filling it slowly and measuring the pressure produced, yields a pseudostatic pressure-volume relationship called a cystometrogram. The model predicts the form of the cystometrogram accurately. However, analysis of a classical cystometrogram enables us to determine only three parameters of our model. A better measurement method is based on stepwise (or almost stepwise) straining of the urinary bladder. One stepwise straining yields eight parameters, provided the initial volume of the bladder is known, and several measurements on one bladder at different strains enable us to determine ten parameters. The results obtained with stepwise straining are compatible with the model.
67 citations
TL;DR: A noninvasive electroacoustical technique was developed which gives an objective measure of the degree of cartilage damage through the measurement of knee emitted acoustic power and the reliability of the procedure was verified throughin vivo modelling of the disease using animals.
Abstract: The arthritides continue to be the most common cause of non-fatal, crippling disorders. They account for many hours of lost work time. Because of the preference for some forms of arthritis for the older age groups and the increasing longevity of our society, the need to develop tools for early detection and monitoring are becoming more urgent. However, at present there are no noninvasive, clinical tools available that would provide an objective evaluation of the condition of the articular cartilage during the progress of the disease. Unfortunately, articular cartilage is radiolucent and X-ray gives onlypost facto information. Recently, a noninvasive electroacoustical technique was developed which gives an objective measure of the degree of cartilage damage through the measurement of knee emitted acoustic power. The reliability of the procedure was verified throughin vivo modelling of the disease using animals. This technique is of immediate interest to clinicians who urgently need a more objective ‘tool’ in the determination of the efficacy of certain drugs and/or treatment programmes during the course of the disease.
64 citations
TL;DR: The effect of the electrode configuration (unipolar against bipolar), the electrode separation, the electrode position and the electrode contact area on the bandwidth of the power density spectrum of the surface e.m.g. has been studied.
Abstract: The effect of the electrode configuration (unipolar against bipolar), the electrode separation, the electrode position and the electrode contact area on the bandwidth of the power density spectrum of the surface e.m.g. has been studied. The dependence of the half-power point bandwidthB on the interelectrode distanced can be described by the regression function BHz=810/dmm+58. The unipolar electrode configuration yields an e.m.g. signal with the smallest bandwidth. Neither a variation of the electrode position nor a variation of the electrode contact area has a significant effect on the bandwidth of the e.m.g.
57 citations
TL;DR: A portable device has been designed, constructed and tested which measures continuously the vertical component of the forces exerted by the foot during walking and is found to be accurate enough for its intended use for the clinical assessment of pathological gait.
Abstract: A portable device has been designed, constructed and tested which measures continuously the vertical component of the forces exerted by the foot during walking. The device consists of two pairs of force transducers, an amplifier-transmitter unit, and a receiver-processing unit. A pair of force transducers are attached to the soles of a pair of sports shoes at the metatarsal region of the heel. The transducers are relatively thin (6 mm) and light (65g) so that they hardly interfere with the patient's customary walking style. The signals detected by the transducers are amplified, f.m. telemetered, and summed to give the total force acting on each foot. The amplifier-transmitter unit worn by the patient weighs about 180 g and measures 105×80×23 mm. The performance of the device is tested by comparing the output of the device with that of a conventional force plate. The device is found to be accurate enough for its intended use for the clinical assessment of pathological gait.
54 citations
TL;DR: Electromyographic patterns of selected lower-limb muscles were investigated in highly-trained male athletes and nonathletes during ascending and descending stairs and level walking and some general biomechanical observations are presented.
Abstract: Electromyographic patterns of selected lower-limb muscles were investigated in highly-trained male athletes and nonathletes during ascending and descending stairs and level walking. Significant variability is found between the individual patterns for ascending and descending, although primary patterns can be identified. Some of the primary patterns found are different from those previously reported. The atypicalities are not related to athletic training nor to the incidence of knee injury/surgery among the athletes. All gaits appeared kinematically similar and some general biomechanical observations are presented.
43 citations
TL;DR: The present study was designed to indicate the relative contributions made by blood volume changes and blood flow changes to the impedance signal in an in vitro flow system containing a pulsatile pump, a bovine carotid artery, a rigid tube, and a terminal resis tance.
Abstract: Impedance plethysmography has been widely used clinically. However, uncertainty exists concerning the source of the impedance signal. The present study was designed to indicate the relative contributions made by blood volume changes and blood flow changes. Anin vitro flow system containing a pulsatile pump, a bovine carotid artery, a rigid tube, and a terminal resis tance was assembled. Impedance recordings were made on both the expansile artery and the rigid tube. The impedance signal from the rigid tube was taken as the flow-related component. The signal from the expansile artery represented the combined effects of volume changes and flow changes. The recordings were made over the full physiological range of pulse pressures and peak flow values, using both normal saline and blood (haematocrit =26±4%). No impedance change was detected in the rigid vessel using saline as the perfusate. When blood was used, the impedance signal from the rigid tube averaged about 10% of that from the expansile vessel and its morphology was different. Changes in erthrocyte velocity produced a small but definite change in the impedance signal recorded from the artery.
TL;DR: A method of determining the periodicities of gastrointestinal data using an autoregressive modelling technique is presented and is both automatic and capable of yielding frequency estimates on as little as 5 cycles of data corrupted with noise.
Abstract: A method of determining the periodicities of gastrointestinal data using an autoregressive modelling technique is presented. The method has been applied both to simulated sinusoidal data and to gastrointestinal and colonic data. Unlike the fast Fourier transforms, the method presented is both automatic and capable of yielding frequency estimates on as little as 5 cycles of data corrupted with noise.
TL;DR: The surface e.m.g. from human triceps muscle during isometric contractions was obtained, filtered and rectified, and convolved with the impulse response of an overdamped 2nd-order system, and a good fit was found.
Abstract: The response of muscle to an impulse of stimulus is called a twitch. For a linear system, the convolution of an input to the system with the system's impulse response yields the output of the system. Experiments were performed to obtain the surface e.m.g. from human triceps muscle during isometric contractions. This e.m.g. was filtered and rectified, and convolved with the impulse response of an overdamped 2nd-order system. The resulting signal was fitted to the measured force by linear regression, and a good fit was found. The information content of surface e.m.g. when used as a force predictor is confined to a small range of frequencies: d.c.-30Hz.
TL;DR: The purpose of the investigation has been to gain some information on the electrode processes, which govern the electrode response, and to use this information to synthesise more stable and reproducible electrodes than those presently existing.
Abstract: In routine clinical care rapid results from pH determinations are often desired. This calls for continuousin vivo measurements. Today only intermittentin vitro pH analysis is routinely performed, as the existing transducers do not meet the clinical demands on dimensions, stability, stabilisation time, resolution and ruggedness. Here, some results from a basic experimental study on antimony-antimonyoxide pH electrodes are presented. The purpose of the investigation has been to gain some information on the electrode processes, which govern the electrode response, and to use this information to synthesise more stable and reproducible electrodes than those presently existing. These electrodes are intended, in an appropriate miniaturised form, forin vivo routine pH determinations on homo, e.g in a continuous acid-base balance surveillance application.
TL;DR: The skin impedance can be expressed with an equivalent circuit as reported in a previous paper and this necessitated the three independent parameters for a perfect description: dispersion and correlation of these parameters are described.
Abstract: ] I n t r o d u c t i o n IT is well known that the skin impedance undergoes dispersion due to various factors inside and outside the body. A few precise analyses of the dispersion of the skin impedance have been carried out in the past, but only ALMASI and Scm~lxr (1970) reported on the dispersion of the absolute value of the impedance at 10 Hz. However, the skin impedance can be expressed with an equivalent circuit as reported in a previous paper (YAMAMOTO and YAMAMOTO, 1977), and this necessitated the three independent parameters for a perfect description: Accordingly, dispersion and correlation of these parameters are described.
TL;DR: It has been demonstrated that, under normal circumstances, the drag caused by fluid, set in motion by wall peristalsis, is the primary propelling force.
Abstract: Although the forces leading to ovum transport in the oviduct cannot be measured experimentally, their magnitudes can be estimated analytically. Using anatomical and physiological data, with biomechanical tools, it has been demonstrated that, under normal circumstances, the drag caused by fluid, set in motion by wall peristalsis, is the primary propelling force. This force may lead to back-and-forth motion, but the net movement is in the forward direction. Segmental contraction, fluid circulations due to ciliary beat and the force due to brushing action of cilia on the ovum, are of minor significance. When wall peristalsis is inhibited, cilia activity may lead to ovum movement at near normal rates.
TL;DR: Catheter-tip devices of this design have operated stably in saline giving outputs for pO2 and pCO2 correct to +5 mm Hg for up to 12 days.
Abstract: Medical & Biological Engineering & Computing (a) pH-sensitive glass bulb at the tip of the catheter for measuring changes in pH and hence pCO2 according to the method of STOW et al. and SEVERINGHAUS et al. (b) 180 t~m diameter silver cathode for measuring pO2 (c) silver/silver chloride electrode used as a common reference electrode (at) semisolid electrolyte which is common for both the pO2 and pCO2 electrodes (e) common gas-permeable diffusion membrane applied by a dip-coating technique. After assembling the device, the tip is dipped in hydrogel (Hydron Copolymer) which is allowed to dry. The tip is then soaked in an electrolyte containing NaHCOa (0.005M) and NaC1 (0.02M). After drying the tip in air, the electrodes are dip-coated with a thin polystyrene diffusion membrane. When the device is placed in saline or blood, water vapour diffuses through the membrane and, together with the NaHCO3 and NaC1 crystals deposited in the hydrogel film, constitutes the electrolyte normally used with pCO2 electrodes. At this stage an output signal from both the pO2 and pCO2 electrodes~ is obtained. The time required for the electrodes to stabilise during this hydration process is approximately 40 min. The response of the electrodes to changes in PO2 and pCO2 in saline at 37~ is shown in Fig. 2. The current output (expressed in nanoaml~res) from the pO2 electrode is seen to be proportional to pO2 while the pCO2 electrode output (expressed in millivolts) can be shown to be proportional to log (pCO2), as expected. Further, it can be seen that the pO2 electrode output is unaffected by changes in pCO2 and vice versa. The response time of the pO2 and pCO2 electrodes for a 90 % change in gas tensions is seen to be about 2 min. Catheter-tip devices of this design have operated stably in saline giving outputs for pO2 and pCO2 correct to +5 mm Hg for up to 12 days. However, as can be seen from Fig. 2, the time for 100 % stabilisation of the outputs for pO2 and pCO2 after a 'step-change' in pO2 and pCO2 in solution is long. The drift figures quoted were derived
TL;DR: A low-compliance perfusion pump has been constructed to increase the bandwidth of perfused measurement systems in oesophageal manometry by giving a constant flow at a high mechanical impedance by forcing the perfusion fluid through a steel capillary.
Abstract: A low-compliance perfusion pump has been constructed to increase the bandwidth of perfused measurement systems in oesophageal manometry. This pump gives a constant flow at a high mechanical impedance by forcing the perfusion fluid through a steel capillary. With this low-compliance perfusion pump a wide bandwidth was obtained for the catheter types and perfusion flows investigated. The pump improves the accuracy of oesophageal manometry.
TL;DR: A homologous series of bile salts were used as marker compounds to quantify the importance of protein binding in the equilibrium properties of a range of activated charcoals and polymeric resins.
Abstract: The equilibrium adsorption properties of a range of activated charcoals and polymeric resins have been measured with respect to their ability to adsorb protein-bound metabolites whose presence in the blood has been implicated in hepatic failure. Some possible reasons for the low clearances of bilirubin observed clinically are discussed. A homologous series of bile salts, differing only in their degree of protein binding, were used as marker compounds to quantify the importance of protein binding in the equilibrium properties.
TL;DR: The results show that the impedance sensitivities to volume changes in the atria and aorta are similar, whereas the volume changes of the ventricles showed a significantly smaller effect, indicating that changes in volume of several of the intrathoracic cardiovascular structures are likely to be involved in the generation of a composite cardiogenic electrical impedance change.
Abstract: The purpose of this study was to determine the sensitivity of the thoracic electrical impedance change to blood-volume changes in various regions of the thorax. Using recently euthanatised dogs blood was infused in both a stepwise and a continuously varying manner into the ventricles, atria, lungs and isolated segments of the aorta. The results show that the impedance sensitivities to volume changes in the atria and aorta are similar, whereas the volume changes of the ventricles showed a significantly smaller effect. Equal blood-volume pulses into the lungs or aorta cause an impedance change of a similar magnitude, but estimates based on control-pressure changes indicate the effect of aorta volume change on the impedance to be less than 30%. The data, therefore, indicate that changes in volume of several of the intrathoracic cardiovascular structures are likely to be involved in the generation of a composite cardiogenic electrical impedance change.
TL;DR: An implantable electro-osmotic valve for the controlled and continuous administration of medication is under development and the objective is to regulate the amount of drug to be released.
Abstract: An implantable electro-osmotic valve for the controlled and continuous administration of medication is under development. The objective is to regulate the amount of drug to be released. The driving force behind this valve is a liquid with a vapour pressure above 1 bar (100 kPa) which presses the solution under question through the membrane. The rate of flow is additionally controlled by the current passing through the membrane. In a typical example the performance characteristics of this electro-osmotic valve are: 0·4 μW/cm2 at 40 μA/cm2 for a flow rate of 0·025 cm3/d.cm2 under a pressure of 1·5 bar (150 kPa). Thus in a system with a membrane area of 5 cm2, the rate of release is 0·125 cm3/day. The aim is to store about 10 to 50 ml of the drug solution within the body and to release it at a rate of 0·1 cm3 to 1 cm3 per day. It is also planned to refill the delivering system after the drug is discharged.
TL;DR: A method for visualising and mapping the chest-surface movements induced by heart action and the localisation of motion maxima and their distribution contain valuable clinical information is initiated.
Abstract: Phonocardiograms and external pulse recordings are mainly analysed in the time and frequency domains because of the inherent limitations of the spatial resolution of these techniques. Therefore a study has been initiated which aims at a method for visualising and mapping the chest-surface movements induced by heart action. It is believed that the localisation of motion maxima and their distribution contain valuable clinical information. In the paper experimental results obtained with holographic interferometry are presented. The method provides an image of the object with a superimposed fringe pattern which shows the movement of each part of the object between two instants of time. The resulting picture on a healthy subject shows distinct motion maxima at the apex region and intercostal spaces in early systole, whereas the patterns obtained from a patient with a right-sided heart failure are totally different. Continuing development is directed towards a technique suitable for clinical evaluation.
TL;DR: A comaprison is made of three techniques for processing evoked potentials, conventional signal averaging, crosscorrelation averaging and latency corrected averaging.
Abstract: A comaprison is made of three techniques for processing evoked potentials. These techniques are conventional signal averaging, crosscorrelation averaging and latency corrected averaging. Results obtained for 20 subjects are shown in the Appendix and the results for two of the subjects are analysed in detail.
TL;DR: A method for setting a reference level based on identity transformation of skin impedance, linear-transformation theory for data analysis, and rate of change triangle expression of the results obtained, are proposed, and a basic principle of measurement has been established.
Abstract: Numerous studies have been carried out on the application of skin impedance to biological measurement. Measurement is possible because a difference will result due to the objective factor of the impedance, and the reference impedance (which does contain the objective factor). Emphasis has been placed, in the past, on the relationship between the change in skin impedance and objective factors such as disease, and there are only a few studies on the principle of measurement as the establishment of a reference impedance and a data-analysis method. (a) A method for setting a reference level based on identity transformation of skin impedance, (b) linear-transformation theory for data analysis, and (c) rate of change triangle expression of the results obtained, are proposed, and a basic principle of measurement has been established. Performance evaluation of cosmetics was carried out as an example of the application of this principle.
TL;DR: A means for the measurement of the thoracic impedance of human subjects is described, and some account is given of its application under conditions of emergency in a hospital.
Abstract: A means for the measurement of the thoracic impedance of human subjects is described, and some account is given of its application under conditions of emergency in a hospital. The results obtained are presented in various ways, and some inferences are drawn regarding the inter-relation of the various parameters and quantities involved.
TL;DR: A selfcontained electronic device is described for controlling the limb load exerted by a patient in a partial-weight-bearing walking exercise, which has an accuracy of ±10% in all stages of the stance phase.
Abstract: A selfcontained electronic device is described for controlling the limb load exerted by a patient in a partial-weight-bearing walking exercise. The device measures the limb load with two removable load transducers attached to the sole of the patient's shoe, compares the load with two preset thresholds and emits audible biofeedback tones. A low-frequency tone is emitted when the load falls in the desired range and a high-frequency tone is activated when the load exceeds the maximum load allowable for the patient. The device has an accuracy of ±10% in all stages of the stance phase. Experimental results that demonstrate the effectiveness of the device in controlling the limb load are also presented.
TL;DR: The application of a phaselock system, using a smaller number of readily available integrated circuits, to this problem of poor signal/noise ratio with surface electrode recordings, is described in the paper.
Abstract: The 0·05 Hz (3 cycle/min) electrical activity from the human stomach was first recorded in 1922, by Alvarez, using electrodes placed on the skin. The major problem with surface electrode recordings is the poor signal/noise ratio. The application of a phaselock system, using a smaller number of readily available integrated circuits, to this problem is described in the paper.
TL;DR: The electronic model is capable of reproducing physiological phenomena such as ‘waxing and waning’ and frequency entrainment which have been observed in electrical recordings from the mammalian digestive tract and the advantages of this approach over simpler coupled van der Pol oscillators are discussed.
Abstract: An electronic model comprising a number of coupled Hodgkin-Huxley type nonlinear oscillators is described. The individual oscillator units are based on a simplified version of an analogue of the Hodgkin-Huxley squid axon membrane due to Roy (1972). The electronic model is capable of reproducing physiological phenomena such as ‘waxing and waning’ and frequency entrainment which have been observed in electrical recordings from the mammalian digestive tract. With reactive intercoupling components the model is shown to produce inphase and antiphase entrainment together with nonresonant dual mode oscillations. A number of results from this model are presented and the advantages of this approach over simpler coupled van der Pol oscillator models are discussed.
TL;DR: It is concluded that electrolytic degradation of waste metabolites shows promise in development of a recycle dialysis scheme and further investigations of this technique are warranted.
Abstract: Experiments are described on the decomposition of urea in an electrolytic cell. Results show that urea decomposition rate increases as the power to the cell is increased and rates up to 0·8 mg/h/mm2 of electrode area were observed. Current efficiency decreases as the power input to the cell is increased, and the pH tends to drop about one unit as the urea is decomposed. It is concluded that electrolytic degradation of waste metabolites shows promise in development of a recycle dialysis scheme and further investigations of this technique are warranted.
TL;DR: Evidence that the conditions downstream of an elastic constriction can strongly influence the frequency and existence of oscillations in collapsible tubes is presented and an extension of the existing theory which takes into account the influence of distributed loads on the collapsible tube.
Abstract: Evidence that the conditions downstream of an elastic constriction can strongly influence the frequency and existence of oscillations in collapsible tubes is presented. A lumped negative resistance model is used to describe oscillations in collapsible tubes. An extension of the existing theory is presented which takes into account the influence of distributed loads on the collapsible tube.