| 1. |
- Ask, Per, et al.
(författare)
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Effect of time interval between swallows on esophageal peristalsis.
- 1980
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 238:6, s. G485-90
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Tidskriftsartikel (refereegranskat)abstract
- Esophageal peristaltic pressure amplitude, peristaltic incidence, speed of peristalsis, and wave duration were investigated as a function of swallow interval. In the distal half of the esophagus, the amplitude decreased at swallow intervals of 8 s and shorter. At intervals of 8 and 4 s, dropouts of contractions that were obtained were most frequent in the distal esophagus and for the 4-s interval. At continuous swallows no contractions were obtained below the upper esophageal sphincter until the end of the swallow sequence, after which a peristaltic wave of high amplitude propagated along the esophagus. The peristaltic speed increased toward a level 5 cm above the lower esophageal sphincter. The peristaltic wave duration was approximately the same in different parts of the esophagus and at different swallow intervals. The findings indicate an impairment of esophageal transport function by short swallow intervals.
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| 2. |
- Ask, Per, et al.
(författare)
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Frequency content of esophageal peristaltic pressure.
- 1979
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 236:3, s. E296-300
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Tidskriftsartikel (refereegranskat)abstract
- Fourier analysis of esophageal peristaltic pressure waves was performed by computer fast Fourier transform. The highest power spectral density was obtained in the frequency range below 1 Hz. The Fourier analysis showed spectral components up to about 12 Hz in the upper esophageal sphincter (UES). The significance of different frequency components was investigated by low-pass filtering at different cut-off frequencies. A reduction in the amplitude of UES contractions was obtained at a cut-off frequency of 4 Hz, whereas the cut-off frequency of 8 Hz did not show any distortion. For perfused manometry systems, only a low-compliance perfusion pump will have sufficient bandwidth for accurate recording of esophageal peristaltic pressures.
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| 3. |
- Ask, Per, et al.
(författare)
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Peripheral nerve as an osmometer : role of the perineurium in frog sciatic nerve.
- 1983
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 244:1, s. C75-81
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of volume and hydrostatic pressure in the frog sciatic nerve in vitro demonstrate that the nerve acts as an osmometer, in large part because the perineurium is a semipermeable membrane for water flow. Endoneurial hydrostatic pressure in nerves in isotonic Ringer exceeds bath pressure by about 7 mmHg. In Ringer made hypertonic by addition of sucrose, nerve volume and endoneurial pressure fall linearly in relation to 1/osmolality. The slope of the plot of pressure against volume provides a value for nerve compliance equal to 0.006 mm2/mmHg. Calculations based on the model of the nerve as an osmometer indicate that the nerve has an osmotically "inactive" volume equal to 0.19 mm3/mm, which is about 75% of the total volume of a nerve segment of unit length in normal Ringer. Perineurial hydraulic conductivity (Lp) equals 7.5 x 10(-13) cm3.s-1.dyn-1, a value characteristic of nonleaky epithelia. The perineurium is an elastic tissue with a constant modulus of elasticity equal to 3 x 10(6) dyn/cm2 when not markedly stretched and may limit nerve swelling under pathological conditions of nerve edema.
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| 4. |
- Ask, Per, et al.
(författare)
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Static and dynamic characteristics of fluid-filled esophageal manometry systems
- 1977
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Ingår i: American Journal of Physiology. - 0002-9513. ; 233:5, s. E389-E396
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Tidskriftsartikel (refereegranskat)abstract
- Esophageal manometric systems with water-filled catheters have been characterized by the use of model experiments. The examined parameters have been: catheter dimension, catheter compliance, catheter resistance, pump type, pump compliance, and perfusion flow. Accurate static pressure measurements have been obtained for perfused systems independently of the investigated parameters. The dynamic characteristics vary with catheter diameter and perfusion flow. For catheters with low diameter, a narrow bandwidth is obtained for the investigated perfusion flows. The results have been expressed in terms of an electric model of the measurement system. Perfusion pumps with low compliance are recommended to improve the dynamic properties of the measurement system.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Rundquist, I, et al.
(författare)
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Sciatic nerve blood flow measured by laser Doppler flowmetry and [14C]iodoantipyrine.
- 1985
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 248:3 Pt 2, s. H311-317
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Tidskriftsartikel (refereegranskat)abstract
- Blood flow was examined in sciatic nerves of pentobarbital-anesthetized rats by means of laser Doppler flowmetry (LDF) and intravenous [14C]iodoantipyrine infusion. Continuous LDF signals demonstrated slow oscillations and acute, pressure-related changes in flow. The steady-state LDF signal was related linearly to nerve blood flow, as measured with [14C]iodoantipyrine, in intact nerves and nerves stripped of the epineurium. In 14 intact nerves, nerve blood flow averaged 0.27 +/- 0.03 (SE) ml X min-1 X g-1, whereas it averaged 0.13 +/- 0.01 in 5 stripped nerves. Autoradiographs of [3H]-nicotine-infused nerves and intra-arterial injection of 57Co-labeled microspheres demonstrated that flow was not uniform throughout the nerve cross section. The results indicate that LDF can be used to examine nerve blood flow in vivo, demonstrate a linear relation between the LDF signal and flow, and establish absolute values for blood flow in intact and stripped nerves of the anesthetized rat.
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| 9. |
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| 10. |
- Sun, Y, et al.
(författare)
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Mathematical model that characterizes transmitral and pulmonary venous flow velocity patterns.
- 1995
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 268:1 Pt 2, s. H476-89
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Tidskriftsartikel (refereegranskat)abstract
- The transmitral and pulmonary venous flow velocity (TMFV and PVFV, respectively) patterns are related to the physiological state of the left heart by use of an electrical analog model. Filling of left ventricle (LV) through the mitral valve is characterized by a quadratic Bernoulli's resistance in series with an inertance. Filling of the left atrium (LA) through the pulmonary veins is represented by a lumped network of linear resistance, capacitance, and inertance. LV and LA are each represented by a time-varying elastance. A volume dependency is incorporated into the LV model to produce physiological pressure-volume loops and Starling curves. The state-space representation of the analog model consists of 10 simultaneous differential equations, which are solved by numerical integration. Model validity is supported by the following. First, the expected effects of aging and decreasing LV compliance on TMFV and PVFV are accurately represented by the model. Second, the model-generated TMFV and PVFV waveforms fit well to pulsed-Doppler recordings in normal and postinfarct patients. It is shown that the TMFV deceleration time is prolonged by the increase in LV compliance and, to a lesser extent, by the increase in LA compliance. A shift from diastolic dominance to systolic dominance in PVFV occurs when LA compliance or pulmonary perfusion pressure increases or when LV compliance or mitral valve area decreases. The present model should serve as a useful theoretical basis for echocardiographic evaluation of LV and LA functions.
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