Total Compliances Research Articles

Assessing Crack‐Induced Compliance in Low Porosity Rocks Damaged by Thermo‐Hydro‐Chemo‐Mechanical Processes

AbstractFracture geometry, density, and distribution control fluid and thermal transport in low porosity rocks, as well as their seismic attributes. The creation of cracks throughout the matrix can result in large and disparate reductions in P and S wave velocities with negligible porosity development, which breaks the classic velocity‐porosity relationship. Properly interpreting these signatures in seismic surveys from stimulated geothermal, oil, and gas reservoirs or seismogenic areas requires a rock physics model that uses realistic elastic properties of fractures. Conventional models for cracked rocks employ specific inclusion shapes such as spheroids with small aspect ratios. However, all these exhibit the same normal‐to‐shear compliance ratio—regardless of aspect ratio—and therefore impact the bulk and shear moduli in the same qualitative way. As such they are inadequate for describing many of the complementary evolutions of P and S wave velocities that transpire with the generation of cracks. Using a differential model of dimensionless compliances, we analyze published velocities for granite, basalt, and limestone to quantify typical compliance ratios and find that they are often different from those assumed in conventional crack models, which then affects crack density estimates. We also investigate how the total normal and shear compliances change due to certain thermo‐hydro‐chemo‐mechanical processes that generate large crack densities, and conclude that the final ratios often still deviate from that of conventional models. Finally, we demonstrate how the model can be used to describe scatter in both P and S wave velocity‐porosity trends. Implications for energy extraction and seismic monitoring are discussed.

Pareto Optimal Design of Non‐Homogeneous Isotropic Material Properties for the Multiple Loading Conditions

The present paper concerns two methods: IMD (isotropic material design) and YMD (Young modulus material design) concerning Pareto optimal distributions of the material and its isotropic properties. The merit function is the weighted sum of compliances corresponding to n independent loading conditions. The unit cost of the design is assumed as equal to the trace of the elastic moduli tensor C. In the IMD method, the design variables are the bulk and shear moduli. In the YMD method, the Poisson ratio is assumed as given, possibly non‐uniformly distributed in the design domain, the Young modulus being the only design variable. Both the methods reduce to the auxiliary minimization problem involving statically admissible stress fields corresponding to the subsequent loading conditions. The integrand is expressed by a norm of the collection of these stresses, hence has linear growth. The numerical method proposed refers to the primal formulation: it is based on piece‐wise polynomial approximation of the set of statically admissible stresses. The exemplary Pareto optimal solutions show that admitting negative values of Poisson's ratio may contribute to a decrease of the total compliances.

STABILITY AND RESPONSIVENESS OF THE CARDIOVASCULAR SYSTEM UNDER A PHYSIOLOGICALLY INSPIRED BAROREFLEX MODEL

We investigate the Seidel–Herzel model of the human baroreflex feedback control mechanism in terms of parameter choices and its ability to mimic heart rate physiology. We show that this model has the potential to be re-parameterized to better mimic features commonly observed in human physiology. We investigate the modification of the RR return maps as a function of parameter values and show that the model exhibits chaotic behavior. Extensive simulations are performed to establish which parameters mostly contribute to model flexibility in terms of observable output, and critical considerations are cast about potential pitfalls in model re-parameterization to mimic health and pathological behaviors. The Seidel–Herzel model is then merged with a detailed 21-compartment model for the vascular bed in order to examine sensitivity of RR dynamics to whole body simulation parameters. Pathological situations are simulated by altering total blood volume, ventricular compliances and baroreflex gains. The RR solutions show bifurcation diagrams typical of chaotic behavior, where the extension of the chaotic regions is in general smaller in simulated pathological states when compared to baseline (healthy) situations. We speculate that, despite the limits of the model and the limitations of the physiological parameterization, a loss of chaotic behavior correlates with the presence of disease-related aberrations.

Kinetics of structure build-up in self-bodied emulsions stabilized by mixed emulsifers.

Journal Article Kinetics of structure build-up in self-bodied emulsions stabilized by mixed emulsifiers Get access B W BARRY, B W BARRY School of Pharmacy, Portsmouth Polytechnic, Park Road, Portsmouth, PO1 2QQ, UK Search for other works by this author on: Oxford Academic Google Scholar G M SAUNDERS G M SAUNDERS School of Pharmacy, Portsmouth Polytechnic, Park Road, Portsmouth, PO1 2QQ, UK Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 23, Issue Supplement_1, December 1971, Page 240S, https://doi.org/10.1111/j.2042-7158.1971.tb08827.x Published: 12 April 2011

RC time constant of single lung equals that of both lungs together: a study in chronic thromboembolic pulmonary hypertension

The product of resistance, R, and compliance, C (RC time), of the entire pulmonary circulation is constant. It is unknown if this constancy holds for individual lungs. We determined R and C in individual lungs in chronic thromboembolic pulmonary hypertension (CTEPH) patients where resistances differ between both lungs. Also, the contribution of the proximal pulmonary arteries (PA) to total lung compliance was assessed. Patients (n=23) were referred for the evaluation of CTEPH. Pressure was measured by right heart catheterization and flows in the main, left, and right PA by magnetic resonance imaging. Total, left, and right lung resistances were calculated as mean pressure divided by mean flow. Total, left, and right lung compliances were assessed by the pulse pressure method. Proximal compliances were derived from cross-sectional area change DeltaA and systolic-diastolic pressure difference DeltaP (DeltaA/DeltaP) in main, left, and right PA, multiplied by vessel length. The lung with the lowest blood flow was defined "low flow" (LF), the contralateral lung "high flow" (HF). Total resistance was 0.57+/-0.28 mmHg.s(-1).ml(-1), and resistances of LF and HF lungs were 1.57+/-0.2 vs. 1.00+/-0.1 mmHg.s(-1).ml(-1), respectively, P<0.0001. Total compliance was 1.22+/-1.1 ml/mmHg, and compliances of LF and HF lung were 0.47+/-0.11 and 0.62+/-0.12 ml/mmHg, respectively, P=0.01. Total RC time was 0.49+/-0.2 s, and RC times for the LF and HF lung were 0.45+/-0.2 and 0.45+/-0.1 s, respectively, not different. Proximal arterial compliance, given by the sum of main, right, and left PA compliances, was only 19% of total lung compliance. The RC time of a single lung equals that of both lungs together, and pulmonary arterial compliance comes largely from the distal vasculature.

Hemodynamic effects of medical antishock trousers during mechanical ventilation.

To compare the hemodynamic effects of medical antishock trousers (MAST) inflation in mechanically ventilated patients with normal and poor left ventricular function. Twelve patients requiring respiratory support were divided into two groups according to baseline transesophageal echocardiography (TEE) measurements: normal left ventricular dimensions and fractional area of contraction (FAC=61 +/- 5%) (n=7) and dilated cardiomyopathy with reduced FAC (21 +/- 1%) (n=5). All patients were studied when two successive levels of load (mild load by inflation of the leg compartment of MAST at 50 cmH2O and high load by adding the abdominal compartment of MAST inflated at 30 cmH2O) were applied. Global left ventricular systolic function was assessed on the TEE transgastric short-axis view. End-systolic wall stress (ESWS) was used as an indicator of left ventricular afterload. Total respiratory, lung and chest wall compliances were reduced by 48%, 51% and 27% respectively at the high load level (P < 0.05). Whereas no hemodynamic changes occurred at mild load, the high load level produced an increase in left ventricular afterload as evidenced by concomitant increases in diastolic arterial blood pressure (66 +/- 6 to 79 +/- 6 mmHg, P < 0.05) and ESWS (69 +/- 12 to 74 +/- 12 Kdyn x cm(-2) x m(-2), P < 0.05). In patients with dilated cardiomyopathy, this increase in afterload impaired the left ventricular systolic function and end-systolic area increased (19.0 +/- 2.5 to 21.4 +/- 2.9 cm2 x m(-2), P < 0.05) while FAC decreased (22 +/- 2 to 16 +/- 2%, P < 0.05). Left ventricular end-diastolic area remained unchanged during the study in both groups. MAST inflation impairs respiratory mechanics and global left ventricular systolic function in cardiac patients without changes in left ventricular preload.

A scanographic assessment of pulmonary morphology in acute lung injury. Significance of the lower inflection point detected on the lung pressure-volume curve.

The goal of this study was to assess lung morphology in patients with acute lung injury according to the presence or the absence of a lower inflection point (LIP) on the lung pressure-volume (P-V) curve and to compare the effects of positive end-expiratory pressure (PEEP). Eight patients with and six without an LIP underwent a spiral thoracic CT scan performed at zero end-expiratory pressure (ZEEP) and at two levels of PEEP: PEEP1 = LIP + 2 cm H2O and PEEP2 = LIP + 7 cm H2O, or PEEP1 = 10 cm H2O and PEEP2 = 15 cm H2O in the absence of an LIP. The volumes of air and tissue within the lungs were measured from the gas-tissue ratio and the volumes of overdistended and normally, poorly, and nonaerated lung areas were determined by the analysis of the frequency histogram distribution. In the ZEEP condition, although total lung volume, volume of gas, and volume of tissue were similar in both groups, the percentage of normally aerated lung was lower (24 +/- 22% versus 55 +/- 12%, p < 0.05) and the percentage of poorly aerated lung was greater (40 +/- 12% versus 23 +/- 8%, p < 0.05) in patients with an LIP than in patients without an LIP. Lung density histograms of patients with an LIP showed a unimodal distribution with a peak at 7 Hounsfield units (HU). Lung density histograms of patients without an LIP had a bimodal distribution, with a first peak at -727 HU and a second peak at 27 HU. Total respiratory system and lung compliances were lower in patients with an LIP whereas all other cardiorespiratory parameters were similar in the two groups. In both groups, PEEP induced an alveolar recruitment that was associated with lung overdistension only in patients without an LIP. The amount of lung overdistension was related to the volume of lung parenchyma, characterized by a CT number less than -800 HU before PEEP implementation (y = 0.52x + 4, R = 0.87, and p < 0.0001). This study shows that the presence or the absence of an LIP on the lung P-V curve is associated with differences in lung morphology. In patients without an LIP on the lung P-V curve, normally aerated lung areas coexist with nonaerated lung areas and increasing levels of PEEP result in lung overdistension rather than in additional alveolar recruitment. In patients with an LIP, air and tissue are more homogeneously distributed within the lungs and increasing levels of PEEP result in additional alveolar recruitment without lung overdistention.

Effect of neuromuscular blockade on the elastic properties of the lungs, thorax, and total respiratory system in anesthetized pigs

Objective: To evaluate the effect of neuromuscular blockade on the elastic properties of the lungs, thorax, and total respiratory system in pigs anesthetized to suppress spontaneous breathing. Design: Prospective, randomized, experimental study. Setting: A research laboratory at a university medical center. Subjects: Eight healthy, anesthetized pigs, weighing 22 to 25 kg. Interventions: Pigs, with and without muscular blockade, were mechanically ventilated during an infusion of sodium pentobarbital that was titrated to suppress spontaneous breathing activity. Measurements and Main Results: No significant differences were observed between pressure/volume curves of the lungs, the chest wall, and the total respiratory system, as determined by inflating and deflating the lungs during anesthesia, with or without neuromuscular blockade, in random order. Functional residual capacity was 985 ± 87 mL with neuromuscular blockade and 997 ± 78 mL without neuromuscular blockade (NS). A comparison of the total respiratory system, lung, and chest wall compliances obtained with and without neuromuscular blockade showed high correlations (total respiratory system compliance [r2 = .86]; chest wall compliance [r2 = .83]). Conclusion: Neuromuscular blockade does not alter the elastic properties of the lungs, chest wall, or total respiratory system in mechanically ventilated pigs receiving sodium pentobarbital anesthesia to suppress spontaneous breathing efforts. (Crit Care Med 1994; 22:1976-1980)

Effect of neuromuscular blockade on the elastic properties of the lungs, thorax, and total respiratory system in anesthetized pigs

To evaluate the effect of neuromuscular blockade on the elastic properties of the lungs, thorax, and total respiratory system in pigs anesthetized to suppress spontaneous breathing. Prospective, randomized, experimental study. A research laboratory at a university medical center. Eight healthy, anesthetized pigs, weighing 22 to 25 kg. Pigs, with and without muscular blockade, were mechanically ventilated during an infusion of sodium pentobarbital that was titrated to suppress spontaneous breathing activity. No significant differences were observed between pressure/volume curves of the lungs, the chest wall, and the total respiratory system, as determined by inflating and deflating the lungs during anesthesia, with or without neuromuscular blockade, in random order. Functional residual capacity was 985 +/- 87 mL with neuromuscular blockade and 997 +/- 78 mL without neuromuscular blockade (NS). A comparison of the total respiratory system, lung, and chest wall compliances obtained with and without neuromuscular blockade showed high correlations (total respiratory system compliance [r2 = .86]; chest wall compliance [r2 = .83]). Neuromuscular blockade does not alter the elastic properties of the lungs, chest wall, or total respiratory system in mechanically ventilated pigs receiving sodium pentobarbital anesthesia to suppress spontaneous breathing efforts.

Baroreflex control of arterial and venous compliances and vascular capacity in hypertensive dogs

The ability of the carotid sinus baroreflex to elicit reflex changes in vascular capacity was studied in chronically hypertensive (one-kidney, one-clip) and sham-operated normotensive dogs under pentobarbital sodium anesthesia. Vascular compliances and reflex-induced changes in external reservoir volume were measured in response to changes in isolated carotid sinus pressure (CSP). The mean arterial pressure-CSP reflex characteristic curve was shifted to a higher arterial pressure with hypertension with no change in maximum reflex gains. Arterial compliance in both groups increased significantly (P < 0.01) when CSP was increased from 50 to 200 mmHg. Total, arterial, and venous vascular compliances were not different in normotensive and hypertensive groups. Changes in CSP caused no significant changes in either total systemic vascular or calculated venous compliances. A decrease in CSP from 250 to 50 mmHg resulted in an increase in external reservoir volume of 8.02 +/- 1.03 and 7.44 +/- 1.33 ml/kg in normotensive and hypertensive groups, respectively, with changes in venous volume of 11.99 +/- 1.39 and 12.58 +/- 1.52 ml/kg (NS). We conclude that despite the increase in arterial resistance, Goldblatt hypertensive dogs retain the ability to make short-term reflex adjustments in both arterial pressure and venous blood volume.

Ventilatory Compliance after Three Sufentanil–Pancuronium Induction Sequences

Poor ventilatory compliance, a predictable side effect of high-dose opioid induction techniques, is purportedly blunted by pretreatment with nondepolarizing muscle relaxant. This study used both total compliance and a subjective compliance score to compare three different sequences of opioid induction using a 2-min infusion of sufentanil 3 micrograms.kg-1. Nineteen patients in each of three groups received a total of 100 micrograms.kg-1 of pancuronium, in the following randomized double-blinded fashion: control, all pancuronium 1 min after sufentanil; pretreated, 1 mg pancuronium 1 min before sufentanil and the balance of pancuronium 1 min after sufentanil; and mixed, all pancuronium mixed with sufentanil. Topical lidocaine prior to induction permitted early oral airway insertion midway through the sufentanil infusion. Immediately at the conclusion of sufentanil infusion, a tightly fitted mask, anterior jaw thrust, and mechanical ventilator permitted measurement of plateau airway pressure and exhaled volume in five replicates. Pressure and volume measurements were repeated 5 min later. Total compliance was calculated as the median plateau airway pressure divided into its associated exhaled volume. Groups did not differ in demographics. In one control patient and two pretreated patients hemoglobin oxygen saturation as measured by pulse oximetry decreased below 90%. Immediately after sufentanil infusion, the total compliance for control patients of 4.1 ml.cmH2O-1 (mean [2.6-6.5, 95% confidence interval] ) did not differ from that of the pretreated group (6.3 [3.5-11.4] ml.cmH2O-1), but the mixed group exhibited higher compliance (40.3 [33.8-47.9] ml.cmH2O-1) than the other groups (P less than 10(-8]. All groups achieved similar total compliances several minutes after a total of 100 micrograms.kg-1 pancuronium had been administered.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bovine surfactant in premature lambs after intra-tracheal application

Twenty-two premature lambs (gestational age 124-125 days, term 144-160 days) were intubated and supported by infant ventilators immediately after delivery. Respiratory rate was 60/min, inspiratory time 0.4 s, peak inspiratory pressure (PIP) 35 cm H2O, positive endexpiratory pressure (PEEP) 2 cm H2O, FiO2 1.0. 15 min after delivery 10 lambs (group 1) were treated with 35 mg/kg body weight bovine surfactant (SF-RI 1), whereas 1 ml/kg body weight saline was instilled in 12 lambs as controls (group 2). Sequential measurements of blood gases and acid base status (every 30 min) as well as continuous registration of PIP, PEEP, respiratory rate and tidal volume (TV) were performed in all lambs for 300 min. PIP was varied between 20 and 40 cm H2O in order to attain paCO2 values between 35 and 50 mm Hg. Significantly improved oxygenation was observed in group 1 lambs with maximum differences 30 min after delivery for 2 h. Ventilation was likewise affected: paCO2 and PIP values were significantly lower in the surfactant-treated animals (group 1). Total lung-thorax compliances (calculated from TV and delta P, i.e. PIP-PEEP) per kg body weight also significantly reflected the improvement of pulmonary function in group 1 compared to group 2 lambs. Intratracheal instillation of SF-RI 1 improved gas exchange in premature lambs, whereas control animals exhibited severe respiratory failure characteristic of respiratory distress syndrome (RDS).

Histamine's effect on pulmonary vascular resistance and compliance at elevated tone

Histamine's effect on the longitudinal resistance and compliance distribution in the canine pulmonary circulation was determined under control and elevated vascular tone using the thromboxane analogue U46619. The arterial-, venous-, and double-occlusion techniques were used in isolated blood-perfused dog lungs at both constant flow and constant pressure. Large and small blood vessel resistances and compliances were studied in lungs given the following treatments: 1) histamine; 2) histamine in lungs pretreated with the H1-receptor antagonist diphenhydramine, and 3) histamine in lungs pretreated with the H2-receptor antagonist cimetidine. The results of this study indicate that histamine constricts small and large veins through H1-receptor mediation at both normal and elevated vascular tone. When vascular tone was elevated, H2-receptor vasodilatation was also apparent in all blood vessel segments. Histamine decreased total, middle compartment, and large vessel vascular compliances by an H1-receptor effect. When vascular tone was elevated, histamine's H1-receptor-mediated vasoconstrictor effect on compliance vessels was less due to the presence of an H2-receptor-mediated vasodilatory system.

Beat-to-beat estimation of peripheral resistance and arterial compliance during pressure transients.

We have used a computer-based parameter estimation method to obtain peripheral resistance, total arterial compliance, and characteristic resistance from the measurement of aortic pressure and flow in the open-thorax cat, assuming the three-element windkessel as a model of the systemic arterial tree. The method can be applied on a beat-to-beat basis in the steady state and in transients. We have validated this method by analyzing nonsteady-state data obtained from an electrical analog with fixed values of the resistances and compliance and by showing that the values obtained by this procedure were within 5% of the fixed values of the circuit. Changes in total peripheral resistance and arterial compliance were studied before, during, and after acute heart rate changes in five open-thorax cats with blocked autonomous nervous system. As expected, the peripheral resistance, estimated during the heart rate transient [3.93 +/- 0.94 (SE) kPa X ml-1 X s] was the same as before the transient (3.53 +/- 0.83 kPa X ml-1 X s); total arterial compliances were also identical (0.28 +/- 0.04 vs. 0.27 +/- 0.03 ml/kPa). In six cats without nervous blockade we obtained similar results. Calculation of peripheral resistance during transients from the mean pressure-to-mean flow ratio, i.e., without correction for arterial compliance, suggested changes in resistance values of less than or equal to 57%, which shows that correction is necessary. The findings indicate that peripheral resistance and total arterial compliance can be estimated in vivo on a beat-to-beat basis, even during hemodynamic transients.

Decelerating inspiratory flow waveform improves lung mechanics and gas exchange in patients on intermittent positive-pressure ventilation.

The effects of two inspiratory flow waveforms (WFs), decelerating and constant have been studied in 14 patients undergoing intermittent positive-pressure ventilation (IPPV). With tidal volume (VT), inspiratory time, inspiratory-expiratory (I/E) ratio and frequency being kept constant, the decelerating waveform produced statistically significant reduction of peak pressure, total respiratory resistance, work of inspiration, ratio of dead space to tidal volume (VD/VT) and alveolar-arterial gradient for oxygen (A-a)PO2. There was significant increase in total static and kinetic compliances and PaO2, with no significant changes in PaCO2, in cardiac output (CO) and in other haemodynamic measurements.

Total, peripheral and intrathoracic effective compliances of the vascular bed in normotensive and hypertensive patients.

Total, peripheral and intrathoracic effective compliances of the vascular bed in normotensive and hypertensive patients.

Effects of fentanyl on respiratory pressure-volume relationship in supine anesthetized children.

The effects of fentanyl on total respiratory pressure-volume relationship were studied in 12 supine, anesthetized (thiopental, succinylcholine, halothane, N2O/O2) children, 5, 10 and 15 min after administration of fentanyl, 3 micrograms/kg (Group F) and at similar intervals in 11 control, anesthetized children who did not receive fentanyl (Group C). Lung and chest wall pressure-volume relationships were measured in five children from Group F and in six from Group C. Compliance values were estimated from the linear part of PVR curves. In Group F, a significant decrease was observed at 5, 10 and 15 min (maximum 29%) for total compliance and at 15 min (maximum 26%) for lung compliance. Chest wall compliance was reduced (maximum 45%) at 15 min, but not significantly. In Group C, no change in compliances was noted. The comparison between the two groups for total, chest wall and lung compliances showed a significant decrease in these three parameters at 15 min in children receiving fentanyl. The decrease of chest wall compliance can be explained by increased muscle tone, but the mechanism of decreased lung compliance awaits further study.

Halothane anesthesia and respiratory mechanics in dogs lying supine.

Functional residual capacity (FRC) and quasi-static deflation pressure-volume (PV) curves of the total respiratory system, lung, and chest wall were measured in eight trained dogs lying supine, first awake and then anesthetized with halothane. Two of the eight dogs were repetitively examined 10 times during a 15-mo period. FRC decreased with anesthesia in six of the eight dogs and incresed with anesthesia in the remaining two dogs. There was a significant mean anesthesia-induced reduction in FRC of 16.9% (P < 0.05). FRC change with anesthesia varied between studies in one of the two dogs repetitively examined. Mean PV curves of the total system, lung, and chest wall of the six dogs whose FRC decreased with anesthesia were shifted to the right by anesthesia. PV curves from the two dogs whose FRC increased with anesthesia were shifted to the left. Anesthesia produced a significant reduction (P < 0.05) in mean lung compliance and significant increases (P < 0.05) in mean chest wall and total system compliances.

Control of Total Systemic Vascular Capacity by the Carotid Sinus Baroreceptor Reflex

To attain a quantitative understanding of carotid sinus baroreceptor reflex control of cardiac output, we studied the reflex control of total systemic vascular capacity in vagotomized dogs. In experiments measuring blood volume shifts caused by the carotid sinus reflex (series 1), venous return was diverted into a reservoir while cardiac output and central venous pressure were maintained at constant levels. The pressure in the isolated carotid sinuses (ISP) was lowered or raised in 25-mm Hg steps between 75 and 200 mm Hg. This procedure mobilized blood into or out of the reservoir, indicating a decrease or an increase in total vascular capacity, respectively. The mean maximum volume shift, 3.6 ml/kg body weight, occurred in the same ISP region, 135 ± 12.5 mm Hg, where reflex control of total peripheral resistance was strongest. The total volume shift was approximately 7.5 ml/kg for ISP changes from 75 to 200 mm Hg. When mean arterial blood pressure was maintained constant during the ISP step changes, the volume shift almost doubled. In experiments measuring the reflex effect on total systemic vascular compliance (series 2) and in experiments determining the reflex control of arterial compliance (series 3), total systemic vascular and lumped arterial compliances were measured in the same dogs that were used in series 1 experiments. The total systemic vascular and arterial compliances were approximately 2.0 ml/mm Hg kg -1 and 0.0677 ml/mm Hg kg -1 , respectively. The reflex did not affect these compliances. We concluded that the reflex controls the total systemic venous capacity to a degree that changes cardiac output potentially by 30-10% per 25-mm Hg change in ISP.

Kinetics of structure build-up in self bodied emulsions stabilized by mixed emulsifiers

Ternary systems and emulsions prepared with anionic (sodium dodecyl sulfate), cationic (cetrimide), or nonionic (cetomacrogol) surfactants and cetostearyl alcohol were examined in creep and in continuous shear rheometry at the storage temperature of 25°C. Systems were tested frequently during the first 24 hr after preparation, and then regularly for 3 months. Creep tests were of short duration and the curves were analyzed to derive continuous spectra of retardation times. For each surfactant, the results obtained were correlated with the mechanisms by which gel networks formed. With age, anionic and cationic ternary systems and emulsions behaved similarly with respect to total compliances, retardation spectra, and continuous shear parameters. Additional structure, although not extensive, formed within the first 2 hr storage. This was indicated in creep by initial falls in total compliance values and decreases in the heights of retardation spectra, and in continuous shear by corresponding increases in apparent viscosities and hysteresis loop areas. Thereafter negligible new structure formed, and thus retardation spectra for systems tested after 2.5 and 24 hr storage were similar, and there was little variation in total compliance, apparent viscosity, and loop area values. The essentially constant position of maxima in the retardation spectra indicated that the high temperature interaction which occurred during the preparation of ionic systems was the major mechanism which operated to form gel networks. The low temperature interaction occurring during the first 2 hr storage was insignificant. Cetomacrogol ternary system and emulsion behaved differently to the ionic systems. Structure built up rapidly during the first 24 hr storage. This was shown in creep by marked reductions in total compliances and retardation spectral values and in continuous shear by changing complex flow properties. The movement of maxima in the retardation spectra to longer times indicated that the mechanisms which operated to form gel networks at the storage temperature produced structures which differed at a molecular level to those formed at high temperatures.