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  • 1.
    Ask, Per
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Levitan, H
    Robinson, P J
    Rapoport, S I
    Peripheral nerve as an osmometer: role of the perineurium in frog sciatic nerve.1983In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 244, no 1, p. C75-81Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Ask, Per
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Tibbling, Lita
    Effect of time interval between swallows on esophageal peristalsis.1980In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 238, no 6, p. G485-90Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Ask, Per
    et al.
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Öberg, Åke
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Tibbling, Lita
    Frequency content of esophageal peristaltic pressure.1979In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 236, no 3, p. E296-300Article in journal (Refereed)
    Abstract [en]

    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.

  • 4. Rundquist, I
    et al.
    Smith, Q R
    Michel, M E
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Öberg, Åke
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Rapoport, S I
    Sciatic nerve blood flow measured by laser Doppler flowmetry and [14C]iodoantipyrine.1985In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 248, no 3 Pt 2, p. H311-317Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Sun, Y
    et al.
    Sjöberg, Birgitta Janero
    Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV). Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wranne, Bengt
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Mathematical model that characterizes transmitral and pulmonary venous flow velocity patterns.1995In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 268, no 1 Pt 2, p. H476-89Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Swanson, Julia C.
    et al.
    Stanford University School of Medicine, USA.
    Krishnamurthy, Gaurav
    Stanford University School of Medicine, USA.
    Kvitting, John-Peder Escobar
    Stanford University School of Medicine, USA.
    Miller, D. Craig
    Stanford University School of Medicine, USA.
    Ingels Jr, Neil B.
    Stanford University School of Medicine, USA.
    Electro-Mechanical coupling between the atria and the mitral valve2011In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 300, no 4, p. H1267-H1273Article in journal (Refereed)
    Abstract [en]

    Anterior leaflet (AL) stiffening during isovolumic contraction (IVC) may aid mitral valve closure. We tested the hypothesis that AL stiffening requires atrial depolarization. Ten sheep had radioopaque-marker arrays implanted in the left ventricle, mitral annulus, AL, and papillary muscle tips. Four-dimensional marker coordinates (x, y, z, and t) were obtained from biplane videofluoroscopy at baseline (control, CTRL) and during basal interventricular-septal pacing (no atrial contraction, NAC; 110-117 beats/min) to generate ventricular depolarization not preceded by atrial depolarization. Circumferential and radial stiffness values, reflecting force generation in three leaflet regions (annular, belly, and free-edge), were obtained from finite-element analysis of AL displacements in response to transleaflet pressure changes during both IVC and isovolumic relaxation (IVR). In CTRL, IVC circumferential and radial stiffness was 46 ± 6% greater than IVR stiffness in all regions (P < 0.001). In NAC, AL annular IVC stiffness decreased by 25% (P = 0.004) in the circumferential and 31% (P = 0.005) in the radial directions relative to CTRL, without affecting edge stiffness. Thus AL annular stiffening during IVC was abolished when atrial depolarization did not precede ventricular systole, in support of the hypothesis. The likely mechanism underlying AL annular stiffening during IVC is contraction of cardiac muscle that extends into the leaflet and requires atrial excitation. The AL edge has no cardiac muscle, and thus IVC AL edge stiffness was not affected by loss of atrial depolarization. These findings suggest one reason why heart block, atrial dysrhythmias, or ventricular pacing may be accompanied by mitral regurgitation or may worsen regurgitation when already present.

  • 7. Ödman, Svante
    et al.
    Levitan, Herbert
    Robinson, Peter J
    Michel, Mary Ellen
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Rapoport, Santley I
    Peripheral nerve as an osmometer: role of endoneurial capillaries in frog sciatic nerve.1987In: American Journal of Physiology, ISSN 0002-9513, E-ISSN 2163-5773, Vol. 252, no 3 Pt 1, p. C335-41Article in journal (Refereed)
    Abstract [en]

    The sciatic nerve of the frog was perfused in vivo with isotonic Ringer solution followed by Ringer made hypertonic by addition of sucrose or of NaCl. Nerve diameter and endoneurial hydrostatic pressure fell during hypertonic Ringer perfusion. Using a model that describes the elastic and osmotic properties of the nerve, sigma sLp, the product of the osmotic reflection coefficient at endoneurial capillaries for s equals sucrose or NaCl (which approximates 1), and of capillary hydraulic conductivity, was found to equal 73 X 10(-13) cm3 X s-1 X dyn-1. The nerve is elastic. It has a compliance K of 3.7 X 10(-5) cm2 X mmHg-1, corresponding to a modulus of elasticity E of the perineurium equal to 1.2 X 10(6) dyn X cm-2. The results indicate that the nerve behaves as an osmometer during vascular perfusion, due to the low permeability of endoneurial capillaries to small solutes such as NaCl and sucrose. A low capillary hydraulic conductivity limits bulk water flow between blood and nerve, and a low compliance limits nerve swelling and edema.

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