Regulation of canine jejunal transit

1990 ◽  
Vol 259 (6) ◽  
pp. G928-G933
Author(s):  
N. J. Soper ◽  
K. L. Geisler ◽  
M. G. Sarr ◽  
K. A. Kelly ◽  
A. R. Zinsmeister
Keyword(s):  
Mean Transit Time ◽  
Intraluminal Pressure ◽  
Reversed Flow ◽  
Forward Flow ◽  
Pacesetter Potentials ◽  
Direction Of Movement ◽  
Loop Volume ◽  
The Mean ◽  
Pacesetter Potential ◽  
Recording Electrodes

The aim of this study was to determine what factors influence the direction of movement of canine jejunal chyme. In four dogs, pacing electrodes were implanted near each end of a 50-cm jejunal Vella loop, while recording electrodes and intraluminal pressure catheters were spaced along the loop. After recovery, the loop was perfused from either the proximal stoma (forward flow) or the distal stoma (reversed flow), and effluent was collected from the nonperfused stoma. The pacesetter potentials were paced electrically in a forward (aborad) or a reverse (orad) direction. During control conditions (forward flow-forward pacing), the mean transit time of liquids was 2.6 +/- 0.1 min (mean +/- SE) and the static volume of the loop was 8.8 +/- 0.3 ml. Reversing both direction of flow and direction of pacesetter potential propagation slowed transit (4.4 +/- 0.4 min; P less than 0.05) and increased loop volume (16.0 +/- 1.0 ml; P less than 0.01). Reversing flow with forward pacing resulted in even slower transit (7.5 +/- 1.2 min; P less than 0.05), maintained a large volume (33 +/- 10 ml), and increased basal pressure in the loop from -1.2 +/- 1.7 (control) to 2.3 +/- 1.6 mmHg (P less than 0.05). These observations suggest that the direction of propagation of jejunal pacesetter potentials influences the direction of movement of jejunal chyme but that other factors have a role as well.

Electrical control of canine jejunal propulsion

1981 ◽  
Vol 240 (5) ◽  
pp. G355-G360 ◽  
Author(s):  
M. G. Sarr ◽  
K. A. Kelly ◽  
H. E. Gladen
Keyword(s):  
Action Potentials ◽  
Intestinal Content ◽  
Jejunal Loop ◽  
Electrical Control ◽  
Pacesetter Potentials ◽  
Direction Of Movement ◽  
Pacesetter Potential

We wondered whether the direction of propagation of intestinal pacesetter potentials determines the direction of movement of intestinal content. In six dogs, electrodes for pacing were implanted near each end of an 80-cm isolated jejunal loop, and a cannula was positioned at the middle of the loop for intraluminal insertion of solids and/or liquids. After recovery and during fasting, 50 nylon spheres (2 mm diam) always emptied from the distal stoma regardless of the direction of pacing. In contrast, 150 mM NaCl, given alone at 2.8 ml/min or with spheres, emptied from the distal stoma during forward pacing and from the proximal stoma during backward pacing. Spheres given with the liquid emptied from the distal stoma during forward pacing, but during backward pacing, the site of emptying varied among dogs. Neither pacing nor spheres altered jejunal interdigestive myoelectric cycles, but the perfusate abolished the cycles and resulted in a noncyclic pattern of jejunal action potentials. We concluded that the direction of pacesetter potential propagation determined the direction of liquid transit. Direction of solid transit depended, in part, on other mechanisms.

scholarly journals The implications of lag times between nitrate leaching losses and riverine loads for water quality policy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
R. W. McDowell ◽  
Z. P. Simpson ◽  
A. G. Ausseil ◽  
Z. Etheridge ◽  
R. Law
Keyword(s):  
Water Quality ◽  
Mean Transit Time ◽  
Lag Time ◽  
Practice Change ◽  
N Leaching ◽  
N Losses ◽  
Leaching Losses ◽  
Nitrate N ◽  
The Mean ◽  
Lag Times

AbstractUnderstanding the lag time between land management and impacts on riverine nitrate–nitrogen (N) loads is critical to understand when action to mitigate nitrate–N leaching losses from the soil profile may start improving water quality. These lags occur due to leaching of nitrate–N through the subsurface (soil and groundwater). Actions to mitigate nitrate–N losses have been mandated in New Zealand policy to start showing improvements in water quality within five years. We estimated annual rates of nitrate–N leaching and annual nitrate–N loads for 77 river catchments from 1990 to 2018. Lag times between these losses and riverine loads were determined for 34 catchments but could not be determined in other catchments because they exhibited little change in nitrate–N leaching losses or loads. Lag times varied from 1 to 12 years according to factors like catchment size (Strahler stream order and altitude) and slope. For eight catchments where additional isotope and modelling data were available, the mean transit time for surface water at baseflow to pass through the catchment was on average 2.1 years less than, and never greater than, the mean lag time for nitrate–N, inferring our lag time estimates were robust. The median lag time for nitrate–N across the 34 catchments was 4.5 years, meaning that nearly half of these catchments wouldn’t exhibit decreases in nitrate–N because of practice change within the five years outlined in policy.

Dynamic computed tomography with low- and high-molecular-mass contrast agents to assess microvascular permeability modifications in a model of liver fibrosis

2002 ◽  
Vol 103 (2) ◽  
pp. 213-216 ◽  
Author(s):  
Roland MATERNE ◽  
Laurence ANNET ◽  
Stéphane DECHAMBRE ◽  
Christine SEMPOUX ◽  
Anne M. SMITH ◽  
...  
Keyword(s):  
Liver Fibrosis ◽  
Contrast Agents ◽  
Molecular Mass ◽  
Hepatic Fibrosis ◽  
Mean Transit Time ◽  
Distribution Volume ◽  
High Molecular Mass ◽  
Permeability Changes ◽  
Molecular Masses ◽  
The Mean

Interstitial collagen formation and transformation of the fenestrated hepatic sinusoids into continuous capillaries are major ultrastructural changes that occur in liver cirrhosis and fibrosis. These modifications lead to progressive restriction of blood–liver exchanges. The purpose of our study was to evaluate the permeability changes in a model of hepatic fibrosis by using dynamic computed tomography (CT) enhanced with contrast agents of different molecular masses. Dynamic single-section CT of the liver was performed after intravenous bolus administration of a low-molecular-mass contrast agent (iobitridol) and an experimental high-molecular-mass agent (P840) in normal control rabbits and in rabbits with hepatic fibrosis. Hepatic, aortic and portal venous time–density curves were fitted with a dual-input one-compartmental model to calculate the hepatic mean transit time and distribution volume of the contrast agents. In the rabbits with liver fibrosis, the mean transit time of the high-molecular-mass agent was shorter than that of the low-molecular-mass agent (10.0±1.8s and 12.0±1.2s respectively; P<0.05). The distribution volume accessible to the high-molecular-mass agent was also smaller (22.2±4.8% compared with 32.0±6.7%; P<0.01). In the normal rabbits, the mean transit times of the high- and low-molecular-mass agents did not differ significantly, and nor did their distribution volumes. Our results demonstrate decreased sinusoidal permeability for the high-molecular-mass agent P840 in a model of hepatic fibrosis. Non-invasive assessment of permeability changes in liver fibrosis can be performed with dynamic CT and contrast agents of different molecular masses.

Reabsorption kinetics of albumin from pleural space of dogs

1988 ◽  
Vol 255 (2) ◽  
pp. H375-H385 ◽  
Author(s):  
M. Miniati ◽  
J. C. Parker ◽  
M. Pistolesi ◽  
J. T. Cartledge ◽  
D. J. Martin ◽  
...  
Keyword(s):  
Control Mechanism ◽  
Mean Transit Time ◽  
Input Function ◽  
Pleural Space ◽  
Frequency Function ◽  
Liquid Pressure ◽  
Physiological Conditions ◽  
Transit Times ◽  
The Mean ◽  
Kinetics Of

The reabsorption of albumin from the pleural space was measured in eight dogs receiving 0.5 ml intrapleural injection of 131I-labeled albumin and a simultaneous intravenous injection of 125I-labeled albumin. Plasma curves for both tracers were obtained over 24 h. The 125I-albumin curve served as input function of albumin for interstitial spaces, including pleura, whereas the 131I-albumin curve represented the output function from pleural space. The frequency function of albumin transit times from pleural space to plasma was obtained by deconvolution of input-output plasma curves. Plasma recovery of 131I-albumin was complete by 24 h, and the mean transit time from pleura to plasma averaged 7.95 +/- 1.57 (SD) h. Albumin reabsorption occurred mainly via lymphatics as indicated by experiments in 16 additional dogs in which their right lymph ducts or thoracic ducts were ligated before intrapleural injection. A pleural lymph flow of 0.020 +/- 0.003 (SD) ml.kg-1.h-1 was estimated, which is balanced by a comparable filtration of fluid into the pleural space. This suggests that, under physiological conditions, the subpleural lymphatics represent an important control mechanism of pleural liquid pressure.

scholarly journals Use of the mean transit time of an intravascular contrast agent as an exchange-insensitive index of myocardial perfusion

1999 ◽  
Vol 9 (3) ◽  
pp. 402-408 ◽  
Author(s):  
Massimo Lombardi ◽  
Richard A. Jones ◽  
J�rgen Westby ◽  
Geir Torheim ◽  
Timothy E. Southon ◽  
...  
Keyword(s):  
Myocardial Perfusion ◽  
Contrast Agent ◽  
Transit Time ◽  
Mean Transit Time ◽  
Intravascular Contrast Agent ◽  
The Mean

Lung water measurements with the mean transit time approach

1985 ◽  
Vol 59 (3) ◽  
pp. 673-683 ◽  
Author(s):  
R. M. Effros
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Tissue Perfusion ◽  
Time Data ◽  
Lung Water ◽  
Thermal Signal ◽  
The Mean ◽  
Points Of View ◽  
Vascular Obstruction ◽  
Pulmonary Vascular Obstruction

The potential usefulness and limitations of the double-indicator mean transit time approach for measuring lung water are evaluated from both theoretical and empirical points of view. It is concluded that poor tissue perfusion is the most serious factor that can compromise the reliability of this approach. Replacement of the conventional water isotopes with a thermal signal enhances indicator delivery to ischemic areas but the diffusion of heat is not sufficiently rapid to permit measurements of water in macroscopic collections of fluid which remain unperfused. The frequency of pulmonary vascular obstruction in patients with pulmonary edema related to lung injury suggests that interpretation of transit time data will be complicated by uncertainties concerning perfusion. Thermal-dye measurements of lung water may prove more helpful in situations where pulmonary blood flow remains relatively uniform.

Comparison of measures of forced expiration

1977 ◽  
Vol 42 (4) ◽  
pp. 607-613 ◽  
Author(s):  
J. R. Ligas ◽  
F. P. Primiano ◽  
G. M. Saidel ◽  
C. F. Doershuk
Keyword(s):  
Obstructive Lung Disease ◽  
Vital Capacity ◽  
Mean Transit Time ◽  
Forced Expiration ◽  
Flow Volume ◽  
Minimal Set ◽  
Average Flow ◽  
Maximal Expiratory Flow ◽  
The Mean ◽  
Independent Parameters

Theoretical relationships among a number of parameters were derived for idealized timed vital capacity (TVC) and maximal expiratory flow-volume (MEFV) curves to determine a minimal set of independent parameters. Normal pediatric subjects and those with cystic fibrosis were studied to verify these relationships experimentally. The average flow over the middle half (FEF25–75%) of the forced vital capacity (FVC) and flows at various exhaled percentages of the FVC (FEF50%, FEF75%), as well as moments of the TVC and MEFV curves were computed. From the TVC moments, a mean transit time (MTT) and an index of dispersion (ID) were also calculated. The minimum information needed to detect pulmonary mechanical changes associated with obstructive lung disease requires at least two reproducible measures: one related to the mean slope (e.g., FEF25–75%/FVC or MTT) and the other to the shape (e.g;, ID) of the effort-independent portion of the MEFV curve.

Effect of edema and hemodynamic changes on extravascular thermal volume of the lung

1984 ◽  
Vol 56 (4) ◽  
pp. 878-890 ◽  
Author(s):  
B. A. Gray ◽  
R. C. Beckett ◽  
R. C. Allison ◽  
D. R. McCaffree ◽  
R. M. Smith ◽  
...  
Keyword(s):  
Pulmonary Edema ◽  
Mean Transit Time ◽  
Hemodynamic Changes ◽  
Pulmonary Hemodynamics ◽  
Indocyanine Green Dye ◽  
Pulmonary Arterial ◽  
The Mean ◽  
The Difference ◽  
Acute Changes ◽  
Thermal Dilution

The extravascular thermal volume of the lung (ETV) has been measured in dogs as the difference between mean transit time (t) volumes for heat and indocyanine green dye across the pulmonary circulation, calculated as the product of thermal dilution cardiac output (CO) and the difference in t for aortic indicator-dilution curves generated by right and left atrial injections. ETV measurements were compared with the extravascular lung mass (ELM): in 21 normal dogs, ETV/ELM = 1.11 +/- 0.14 (SD); in 17 dogs with hydrostatic pulmonary edema (up to 21 g/kg), ETV/ELM = 0.90 +/- 0.11; and in 27 dogs with alloxan pulmonary edema (up to 51 g/kg); ETV/ELM = 0.93 +/- 0.13. For all 65 dogs the mean ETVELM was 0.98 +/- 0.15, and the liner regression was ETV (ml/kg) = 0.90 ELM (g/kg) + 0.86 +/- 2.25 (SEE; r = 0.96). Calculations based on measurements of lung specific heat predict that ETV/ELM should equal 0.984. With acute changes in pulmonary hemodynamics, ETV was reduced by reductions in pulmonary arterial pressure (Ppa) sufficient to produce zone 1 conditions at the top of the lung. However, ETV was not affected by increases in CO (mean = 50%) produced by nitroprusside or by increases in Ppa and pulmonary blood volume (mean = 27%) produced by partial mitral valve obstruction. Distortion of the thermal dilution curve due to position of the arterial thermistor appears to be the greatest source of variability and overestimation. Simultaneous measurements from pairs of thermistors differed by 14% (range 0.4–50%).

Response time of cardiac mitochondrial oxygen consumption to heart rate steps

1991 ◽  
Vol 260 (2) ◽  
pp. H613-H625 ◽  
Author(s):  
J. H. Van Beek ◽  
N. Westerhof
Keyword(s):  
Heart Rate ◽  
Response Time ◽  
Time Course ◽  
Mean Transit Time ◽  
Impulse Response Function ◽  
Heart Tissue ◽  
Experimental Information ◽  
O2 Consumption ◽  
Mean Response Time ◽  
The Mean

We investigated the time course of cardiac mitochondrial O2 consumption following steps in heart rate in 16 isolated rabbit hearts perfused with Tyrode solution. The time course was characterized by the mean response time, i.e., the first statistical moment (mean time) of the impulse response function. Like the mean transit time for an indicator, it provides an important characteristic of the response time course. The venous O2 content transients during steps in heart rate were measured and corrected for O2 diffusion and vascular transport using a mathematical model with experimental information derived from O2 washout following steps in arterial O2 concentration or perfusion flow. We deduce from these washout experiments that the effective O2 solubility in heart tissue is 86 +/- 13% (mean +/- SE) of solubility in water. The measured venous mean response time following a step in heart rate at 37 degrees C was 17.6 +/- 1.1 s. The mean response time of cardiac mitochondrial O2 consumption to changes in heart rate after correction for O2 transport was 7.7 +/- 0.7 s.

Dynamical Organization of Directional Tuning in the Primate Premotor and Primary Motor Cortex

2003 ◽  
Vol 89 (2) ◽  
pp. 1136-1142 ◽  
Author(s):  
Yoram Ben-Shaul ◽  
Eran Stark ◽  
Itay Asher ◽  
Rotem Drori ◽  
Zoltan Nadasdy ◽  
...  
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Hand Movement ◽  
Movement Direction ◽  
Cortical Surface ◽  
Preferred Direction ◽  
Preparation Period ◽  
Direction Of Movement ◽  
The Mean ◽  
Movement Parameters

Although previous studies have shown that activity of neurons in the motor cortex is related to various movement parameters, including the direction of movement, the spatial pattern by which these parameters are represented is still unresolved. The current work was designed to study the pattern of representation of the preferred direction (PD) of hand movement over the cortical surface. By studying pairwise PD differences, and by applying a novel implementation of the circular variance during preparation and movement periods in the context of a center-out task, we demonstrate a nonrandom distribution of PDs over the premotor and motor cortical surface of two monkeys. Our analysis shows that, whereas PDs of units recorded by nonadjacent electrodes are not more similar than expected by chance, PDs of units recorded by adjacent electrodes are. PDs of units recorded by a single electrode display the greatest similarity. Comparison of PD distributions during preparation and movement reveals that PDs of nearby units tend to be more similar during the preparation period. However, even for pairs of units recorded by a single electrode, the mean PD difference is typically large (45° and 75° during preparation and movement, respectively), so that a strictly modular representation of hand movement direction over the cortical surface is not supported by our data.

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