共查询到20条相似文献,搜索用时 31 毫秒
1.
OP Timopheeva ND Vdovichenko SV Kuznetsov 《Bulletin of experimental biology and medicine》2012,152(4):397-401
The development of heart activity and its relationship with respiratory and motor activities were studied in rat fetuses with
preserved placental circulation on gestation days 15-20 (E15-20) and in newborn rats (P0). During the studied period, the
heart rate in fetuses increased from 175.93 ± 6.10 bpm (E15) to 271.82 ± 5.93 bpm (E20). After birth, the heart rate decreased
to 220.94 ± 8.73 bpm. Heart rate variability in the decasecond and near-minute ranges was detected. At E16 stage it is presented
by slow regular oscillations lasting for 20-35 sec with an amplitude of 10-45 msec. Comparison of functional activities of
the cardiac and somatic motor systems showed that at E16, fl uctuations in heart rate are independent of the bouts of motor
excitation. During growing, the degree of synchronization of heart rate variability with physical activity increased. E17-18
stage is characterized by short-term episodes of heart rate deceleration associated with motor activity; their duration and
amplitude did not depend much on the force of movement. At E19-20, decelerations typical of early gestation terms were replaced
by acceleration-type reactions typical for mature organism, which is related to maturation of coordination function of the
nervous system. In the heart rhythm, respiratory arrhythmia appears during episodes of rhythmic breathing. Newborn rats demonstrated
acceleration episodes; their parameters depend on the force of motor bouts; respiratory arrhythmia was not observed. 相似文献
2.
Closed-chest cardiac stimulation with a pulsed magnetic field 总被引:5,自引:0,他引:5
G. A. Mouchawar Dr J. D. Bourland J. A. Nyenhuis L. A. Geddes K. S. Foster J. T. Jones G. P. Graber 《Medical & biological engineering & computing》1992,30(2):162-168
Magnetic stimulators, used medically, generate intense rapidly changing magnetic fields, capable of stimulating nerves. Advanced
magnetic resonance imaging systems employ stronger and more rapidly changing gradient fields thant those used previously.
The risk of provoking cardiac arrhythmias by these new devices is of concern. In the paper, the threshold for cardiac stimulation
by an externally-applied magnetic field is determined for 11 anaesthetised dogs. Two coplanar coils provide the pulsed magnetic
field. An average energy of approximately 12kJ is required to achieve closed-chest magnetically induced ectopic beats in the
17–26kg dogs. The mean peak induced electric field for threshold stimulation is 213 Vm
−1
for a 571 μs damped sine wave pulse. Accounting for waveform efficacy and extrapolating to long-duration pulses, a threshold
induced electric field strength of approximately 30 Vm
−1
for the rectangular pulse is predicted. It is now possible to establish the margin of safety for devices that use pulsed
magnetic fields and to design therapeutic devices employing magnetic fields to stimulate the heart. 相似文献
3.
Novel maglev pump with a combined magnetic bearing 总被引:1,自引:0,他引:1
Onuma H Murakami M Masuzawa T 《ASAIO journal (American Society for Artificial Internal Organs : 1992)》2005,51(1):50-55
The newly developed pump is a magnetically levitated centrifugal blood pump in which active and passive magnetic bearings are integrated to construct a durable ventricular assist device. The developed maglev centrifugal pump consists of an active magnetic bearing, a passive magnetic bearing, a levitated impeller, and a motor stator. The impeller is set between the active magnetic bearing and the motor stator. The active magnetic bearing uses four electromagnets to control the tilt and the axial position of the impeller. The radial movement of the levitated impeller is restricted with the passive stability dependent upon the top stator and the passive permanent magnetic bearing to reduce the energy consumption and the control system complexity. The top stator was designed based upon a magnetic field analysis to develop the maglev pump with sufficient passive stability in the radial direction. By implementing this analysis design, the oscillating amplitude of the impeller in the radial direction was cut in half when compared with the simple shape stator. This study concluded that the newly developed maglev centrifugal pump displayed excellent levitation performance and sufficient pump performance as a ventricular assist device. 相似文献
4.
Eiji Okamoto PhD Tsutomu Makino PhD Shuji Tanaka MS Takahiko Yasuda MS Yuta Akasaka BS Makiko Tani BS Yusuke Inoue MS Ayumu Mitoh PhD Yoshinori Mitamura PhD 《Journal of artificial organs》2007,10(3):158-164
We have been developing a small, lightweight motor-driven pulsatile left ventricular assist device (LVAD) with a ball screw.
The motor-driven LVAD consists of a brushless DC motor and a ball screw. The attractive magnetic force between Nd–Fe–B magnets
(with a diameter of 5 mm and a thickness of 1.5 mm) mounted in holes in a silicone rubber sheet (thickness 2 mm) and an iron
plate adhered onto the a diaphragm of the blood pump can provide optimum active blood filling during the pump filling phase.
The LVAD has a stroke volume of 55 ml and an overall volume of 285 ml; it weighs 360 g. The controller mainly consists of
a fuzzy logic position and velocity controller to apply doctors' and engineers' knowledge to control the LVAD. Each unit of
the controller consists of a functionally independent program module for easy improvement of the controller's performance.
The LVAD was evaluated in in vitro experiments using a mock circulation. A maximum pump outflow of 5.1 l/min was obtained
at a drive rate of 95 bpm against an afterload of 95 mmHg, and active filling using the attractive magnetic force provided
a pump output of 3.6 l/min at a drive rate of 75 bpm under a preload of 0 mmHg. The operating efficiency of the LVAD was measured
at between 8% and 10.5%. While the LVAD can provide adequate pump outflow for cardiac assistance, further upgrading of the
software and improvement of the blood pump are required to improve pump performance and efficiency. 相似文献
5.
Jesus A. Tapia Agustin L. Herrera-May Pedro J. García-Ramírez Jaime Martinez-Castillo Eduard Figueras Amira Flores Elías Manjarrez 《Biomedical microdevices》2011,13(2):303-313
We describe a simple procedure to characterize a magnetic field sensor based on microelectromechanical systems (MEMS) technology,
which exploits the Lorentz force principle. This sensor is designed to detect, in future applications, the spiking activity
of neurons or muscle cells. This procedure is based on the well-known capability that a magnetic MEMS device can be used to
sense a small magnetic flux density. In this work, an electronic neuron (FitzHugh–Nagumo) is used to generate controlled spike-like
magnetic fields. We show that the magnetic flux density generated by the hardware of this neuron can be detected with a new
MEMS magnetic field sensor. This microdevice has a compact resonant structure (700 × 600 × 5 μm) integrated by an array of
silicon beams and p-type piezoresistive sensing elements, which need an easy fabrication process. The proposed microsensor
has a resolution of 80 nT, a sensitivity of 1.2 V⋅T−1, a resonant frequency of 13.87 kHz, low power consumption (2.05 mW), quality factor of 93 at atmospheric pressure, and requires
a simple signal processing circuit. The importance of our study is twofold. First, because the artificial neuron can generate
well-controlled magnetic flux density, we suggest it could be used to analyze the resolution and performance of different
magnetic field sensors intended for neurobiological applications. Second, the introduced MEMS magnetic field sensor may be
used as a prototype to develop new high-resolution biomedical microdevices to sense magnetic fields from cardiac tissue, nerves,
spinal cord, or the brain. 相似文献
6.
The use of the 2-point seat belt or lap belt in motor vehicles, particularly to restrain young rear seat passengers, remains an issue of some concern. The occurrence of lumbar spinal flexion-distraction injuries in lap belt restrained children and adolescents during road traffic accidents is a well known phenomenon, but is still occurring. High velocity paediatric Chance fractures are frequently associated with significant intra-abdominal trauma. We present the case of a Chance fracture sustained by a 15 year old girl, involved in a motor vehicle collision, while wearing a lap belt. We emphasise the need to develop safer seat belt designs for juvenile car passengers. 相似文献
7.
Cell loss during sample transporting from macro-components to micro-components in integrated microfluidic devices can considerably
deteriorate cell detection sensitivity. This intrinsic cell loss was studied and effectively minimized through (a) increasing
the tubing diameter connecting the sample storage and the micro-device, (b) applying a hydrodynamic focusing approach for
sample delivering to reduce cells contacting and adhesion on the walls of micro-channel and chip inlet; (c) optimizing the
filter design with a zigzag arrangement of pillars (13 μm in chamber depth and 0.8 μm in gap) to prolong the effective filter
length, and iv) the use of diamond shaped pillar instead of normally used rectangular shape to reduce the gap length between
any two given pillar (i.e. pressure drop) at the filter region. Cell trapping and immunofluorescent detection of 12 Giardia lamblia and 12 Cryptosporidium parvum cells in 150 μl solution and 50 MCF-7 breast cancer cells in 150 μl solution was completed within 15 min with trapping efficiencies
improved from 79 ± 11%, 50.8 ± 5.5% and 41.3 ± 3.6% without hydrodynamic focusing, respectively, to 90.8 ± 5.8%, 89.8 ± 16.6%
and 77.0 ± 9.2% with hydrodynamic focusing. 相似文献
8.
Micromachined optical fiber enclosed 4-electrode IPMC actuator with multidirectional control ability for biomedical application 总被引:1,自引:0,他引:1
The present paper examined a novel micromachined column structured Ion Polymer Metal Composite (IPMC) actuator with multidirectional
control capability. The developed 4-electrode transducer enclosed a section of optical fiber, thereby allowing electronic
directional control of conducted laser light. The fabricated device with IPMC actuator dimensions of 5 mm × 2 mm × 1 mm reached
a maximum displacement of 400 μm when a square wave of 9 V was applied to the top-bottom electrode pair. Displacements in
different directions and moving angles were characterized with side-side and top-right electrode pairs connected to the actuating
signals. Furthermore, the generating moment per volt per second by the transducer was analyzed. The maximum value of approximately
200 μN*m/V/s was displayed when the device actuated with the side-side electrode pair. Controlling the developed IPMC actuator
moved the laser beam in multiple directions. This device could be promising for biomedical applications such as microendoscopic
ocular surgery. 相似文献
9.
Alter P Rupp H Rominger MB Klose KJ Maisch B 《Pflügers Archiv : European journal of physiology》2008,455(4):627-636
In experimental animals, cardiac work is derived from pressure–volume area and analyzed further using stress–length relations.
Lack of methods for determining accurately myocardial mass has until now prevented the use of stress–length relations in patients.
We hypothesized, therefore, that not only pressure–volume loops but also stress–length diagrams can be derived from cardiac
volume and cardiac mass as assessed by cardiac magnetic resonance imaging (CMR) and invasively measured pressure. Left ventricular
(LV) volume and myocardial mass were assessed in seven patients with aortic valve stenosis (AS), eight with dilated cardiomyopathy
(DCM), and eight controls using electrocardiogram (ECG)-gated CMR. LV pressure was measured invasively. Pressure–volume curves
were calculated based on ECG triggering. Stroke work was assessed as area within the pressure–volume loop. LV wall stress
was calculated using a thick-wall sphere model. Similarly, stress–length loops were calculated to quantify stress–length-based
work. Taking the LV geometry into account, the normalization with regard to ventricular circumference resulted in “myocardial
work.” Patients with AS (valve area 0.73 ± 0.18 cm2) exhibited an increased LV myocardial mass when compared with controls (P < 0.05). LV wall stress was increased in DCM but not in AS. Stroke work of AS was unchanged when compared with controls (0.539 ± 0.272
vs 0.621 ± 0.138 Nm, not significant), whereas DCM exhibited a significant depression (0.367 ± 0.157 Nm, P < 0.05). Myocardial work was significantly reduced in both AS and DCM when compared with controls (129.8 ± 69.6, 200.6 ± 80.1,
332.2 ± 89.6 Nm/m2, P < 0.05), also after normalization (7.40 ± 5.07, 6.27 ± 3.20, 14.6 ± 4.07 Nm/m2, P < 0.001). It is feasible to obtain LV pressure–volume and stress–length diagrams in patients based on the present novel methodological
approach of using CMR and invasive pressure measurement. Myocardial work was reduced in patients with DCM and noteworthy also
in AS, while stroke work was reduced in DCM only. Most likely, deterioration of myocardial work is crucial for the prognosis.
It is suggested to include these basic physiological procedures in the clinical assessment of the pump function of the heart. 相似文献
10.
Saeko Yoshida Kousaku Fujiwara Satoshi Kohira Minoru Hirose 《Journal of artificial organs》2014,17(3):243-249
Shoulder massage machines have two pads that are driven by solenoid coils to perform a per cussive massage on the shoulders. There have been concerns that such machines might create electromagnetic interference (EMI) in implantable cardiac devices because of the time-varying magnetic fields produced by the alternating current in the solenoid coils. The objective of this study was to investigate the potential EMI from one such shoulder massage machine on implantable cardiac devices. We measured the distribution profile of the magnetic field intensity around the massage machine. Furthermore, we performed an inhibition test and an asynchronous test on an implantable cardiac pacemaker using the standardized Irnich human body model. We examined the events on an implantable cardioverter–defibrillator (ICD) using a pacemaker programmer while the massage machine was in operation. The magnetic field distribution profile exhibited a peak intensity of 212 (A/m) in one of the solenoid coils. The maximal interference distance between the massage machine and the implantable cardiac pacemaker was 28 cm. Ventricular fibrillation was induced when the massage machine was brought near the electrode of the ICD and touched the Irnich human body model. It is necessary to provide a “don’t use” warning on the box or the exterior of the massage machines or in the user manuals and to caution patients with implanted pacemakers about the dangers and appropriate usage of massage machines. 相似文献
11.
Our interest is in the development of engineered microdevices for continuous remote monitoring of intramuscular lactate, glucose,
pH and temperature during post-traumatic hemorrhaging. Two important design considerations in the development of such devices
for in vivo diagnostics are discussed; the utility of micro-disc electrode arrays (MDEAs) for electrochemical biosensing and
the application of biomimetic, bioactive poly(HEMA)-based hydrogel composites for implant biocompatibility. A poly(HEMA)-based
hydrogel membrane containing polyethylene glycol (PEG) was UV cross-linked with tetraethyleneglycol diacrylate following application
to MDEAs (50 μm discs) and to 250 μm diameter gold electrodes within 8-well culture ware. Cyclic voltammetry (CV) of the MDEAs
revealed a reduction in the apparent diffusion coefficient of ferrocenemonocarboxylic acid (FcCO2H), from 6.68 × 10−5 to 6.74 × 10−6 cm2/s for the uncoated and 6 μm thick hydrogel coated devices, respectively. Single frequency (4 kHz) temporal impedance measurements
of the hydrogels in the 8-well culture ware showed a reversible 5% change in the absolute impedance of the hydrogels when
exposed to a pH change between 6.1 to 7.2 and a 20% drop between pH 6.1 and 8.8. 相似文献
12.
Fifty-seven Hirundo rubicola savignii swallows were collected from Damietta, Tanta, Dakahlyia and Sharkia Provinces, Egypt. They were examined for coccidian parasites.
The percentage of infection with Isospora stages was 12.3%. After diagnosis it was noted that the parasites belong to a new species. The unsporulated oocysts were
spherical, measuring 25.7–31.9 μm in diameter with a mean of 28.3 μm. A micropyle, polar granule and oocyst residuum were
absent. Sporocysts appeared lemon-shaped and measured 19.6–24.5 μm × 12.5–17.5 μm with a mean of 22.9 × 14.4 μm. Stieda body
and the sporocyst's residual body were clearly visible. Sporozoites measured 11–14.2 × 4.4–5.1 μm with a mean of 11.4 × 4.7 μm.
Sporulation time was 72 h at room temperature (25 °C). Endogenous stages including schizogony and gamogony were detected in
epithelial cells of the duodenum, jejunum and ileum of the host. Schizogony consisted of two generations. Mature first generation
schizonts reached up to 11 μm in diameter and produced merozoites measuring 3.5 × 1.7 μm. Mature second generation schizonts
measured 17.2 × 12.3 μm and produced merozoites measuring 11.8 × 2.2 μm. Gamogonic stages were differentiated into microgamonts
and macrogamonts. Mature microgamonts were spherical and measured 23.2 μm in diameter, producing curved microgametes measuring
4.5 × 0.7 μm. The ovoid macrogametes measured 19.6 × 14.7 μm and were characterized by a large nucleus and nucleolus. Early,
more or less spherical, oocysts were detected inside the intestinal epithelial cells and in the intestinal lumen. They measured
19.6 μm in diameter. The sporont measured 17.2 μm in diameter. Cytochemical studies on schizogony, gamogony and oocysts were
accomplished and showed distribution of polysaccharides and composition of the oocyst wall.
Received: 15 May 1999 / Accepted: 25 June 1999 相似文献
13.
Jun Horiguchi Hideya Yamamoto Ryuichi Arie Masao Kiguchi Chikako Fujioka Megu Ohtaki Yasuki Kihara Kazuo Awai 《Journal of digital imaging》2011,24(4):688-693
The effect of heart rate and variation during cardiac computed tomography (CT) on the examination quality. The purpose of
this study is to investigate whether it is possible to predict heart rate and range during enhanced cardiac computed CT scan
from previous non-enhanced cardiac CT scan. Electrocardiograph (ECG) files from 112 patients on three types of cardiac 64-slice
CT (non-enhanced, prospective ECG-triggered and retrospective ECG-gated enhanced scans) were recorded. The mean heart rate,
range (defined as difference between maximal and minimal heart rates) and the range ratio (defined as maximal heart rate divided
by minimal heart rate) during the scans were compared. Scan time was 4.8, 4.6, and 7.3 s on non-enhanced, prospective ECG-triggered
and retrospective ECG-gated scans, respectively (p < 0.0001). The heart rates were not significantly different (60 ± 9 beats per minute (bpm), 60 ± 9 and 61 ± 10 bpm; p = 0.64). Heart rate on the enhanced scan markedly correlated with that of the non-enhanced scan (r = 0.78 and 0.74). In contrast, the ranges of heart rate were 2 ± 5, 4 ± 8, and 8 ± 21 bpm, with different range ratios (1.04,
1.07, and 1.14; p < 0.0001). Correlation of heart rate ranges between non-enhanced scan versus prospective ECG-triggered scan was low (r = 0.27) and that between non-enhanced scan versus retrospective ECG-gated scan negligible (r = −0.027).Heart rate on enhanced cardiac CT, in most cases, can be predicted from a non-enhanced scan. Heart rate range on
enhanced cardiac CT, however, is hard to predict from the non-enhanced scan. 相似文献
14.
A novel glaucoma drainage device (GDD) using a polymeric micro check valve with no reverse flow is presented for the effective
regulation of intraocular pressure (IOP). A significant functional improvement was achieved by reducing the possible incidence
of hypotony, as the proposed GDD only drains aqueous humor at a certain cracking pressure or higher. The device consists of
three biocompatible polymer layers: a top layer (cover), an intermediate layer (membrane), and a bottom layer (base plate
with a cannula). All three layers, made of soft polydimethylsiloxane (PDMS), were bonded together to realize the thin GDDs.
The bottom layer was selectively coated with chromium (Cr)/gold (Au) to prevent stiction between the valve seat and the valve
orifice so that the device could show enhanced reliability in operation and high yield in production. Two types of polymeric
devices were fabricated; one was a glaucoma drainage device for humans (GDDH) and the other was a glaucoma drainage device
for animals (GDDA). From subsequent in vitro tests, the cracking pressures were 18.33 ± 0.66 mmHg (mean ± standard deviation) for GDDH and 12.42 mmHg for GDDA, both of
which were very close to the corresponding normal IOPs. From in vivo tests of GDDA, the IOP of all implanted devices was properly regulated within the target pressure (10–15 mmHg). The experimental
results showed that the proposed polymeric GDD has high potential for use in the treatment of glaucoma disease in terms of
its repeatability of the cracking pressure and patients’ relief from post-operative discomfort. 相似文献
15.
Nuclear transfer (NT) cloning involves manual positioning of individual donor-recipient cell couplets for electrofusion. This
is time-consuming and introduces operator-dependent variation as a confounding parameter in cloning trials. In order to automate
the NT procedure, we developed a micro-fluidic device that integrates automated cell positioning and electrofusion of isolated
cell couplets. A simple two layer micro-fluidic device was fabricated. Thin film interdigitated titanium electrodes (300 nm
thick, 250 μm wide and 250 μm apart) were deposited on a solid borosilicate glass substrate. They were coated with a film
of electrically insulating photosensitive epoxy polymer (SU-8) of either 4 or 22 μm thickness. Circular holes (“micropits”)
measuring 10, 20, 30, 40 or 80 μm in diameter were fabricated above the electrodes. The device was immersed in hypo-osmolar
fusion buffer and manually loaded with somatic donor cells and recipient oocytes. Dielectrophoresis (DEP) was used to attract
cells towards the micropit and form couplets on the same side of the insulating film. Fusion pulses between 80 V and 120 V
were applied to each couplet and fusion scored under a stereomicroscope. Automated couplet formation between oocytes and somatic
cells was achieved using DEP. Bovine oocyte-oocyte, oocyte-follicular cells and oocyte-fibroblast couplets fused with up to
69% (n = 13), 50% (n = 30) and 78% (n = 9) efficiency, respectively. Fusion rates were comparable to parallel plate or film electrodes that are conventionally
used for bovine NT. This demonstrates proof-of-principle that a micropit device is capable of both rapid cell positioning
and fusion. 相似文献
16.
Restitution analysis of alternans and its relationship to arrhythmogenicity in hypokalaemic Langendorff-perfused murine hearts 总被引:1,自引:1,他引:0
Sabir IN Li LM Grace AA Huang CL 《Pflügers Archiv : European journal of physiology》2008,455(4):653-666
Alternans and arrhythmogenicity were studied in hypokalaemic (3.0 mM K+) Langendorff-perfused murine hearts paced at high rates. Epicardial and endocardial monophasic action potentials were recorded
and durations quantified at 90% repolarization. Alternans and arrhythmia occurred in hypokalaemic, but not normokalaemic (5.2 mM
K+) hearts (P < 0.01): this was prevented by treatment with lidocaine (10 μM, P < 0.01). Fourier analysis then confirmed transition from monomorphic to polymorphic waveforms for the first time in the murine
heart. Alternans and arrhythmia were associated with increases in the slopes of restitution curves, obtained for the first
time in the murine heart, while the anti-arrhythmic effect of lidocaine was associated with decreased slopes. Thus, hypokalaemia
significantly increased (P < 0.05) maximal gradients (from 0.55 ± 0.14 to 2.35 ± 0.67 in the epicardium and from 0.67 ± 0.13 to 1.87 ± 0.28 in the endocardium)
and critical diastolic intervals (DIs) at which gradients equalled unity (from −2.14 ± 0.52 ms to 50.93 ± 14.45 ms in the
epicardium and from 8.14 ± 1.49 ms to 44.64 ± 5 ms in the endocardium). While treatment of normokalaemic hearts with lidocaine
had no significant effect (P > 0.05) on either maximal gradients (0.78 ± 0.27 in the epicardium and 0.83 ± 0.45 in the endocardium) or critical DIs (6.06 ± 2.10 ms
and 7.04 ± 3.82 ms in the endocardium), treatment of hypokalaemic hearts with lidocaine reduced (P < 0.05) both these parameters (1.05 ± 0.30 in the epicardium and 0.89 ± 0.36 in the endocardium and 30.38 ± 8.88 ms in the
epicardium and 31.65 ± 4.78 ms in the endocardium, respectively). We thus demonstrate that alternans contributes a dynamic
component to arrhythmic substrate during hypokalaemia, that restitution may furnish an underlying mechanism and that these
phenomena are abolished by lidocaine, both recapitulating and clarifying clinical findings. 相似文献
17.
Haematological data from 12 western ringtail possums with tissue trauma resulting from motor vehicle impact or dog bite wounds
were analysed. The greatest concentration of neutrophils observed was 7.22 × 109/l. Morphological atypia of neutrophils was evident in four animals. Four animals had significant anaemia, and three animals
exhibited increased erythropoiesis (6–17.2% polychromatophilic erythrocytes). The study illustrates that marked neutrophilia
is unlikely to occur in response to trauma-induced tissue inflammation in this species. However, marked increases in immature
erythrocytes may be observed in the peripheral blood in response to anaemia. 相似文献
18.
Keyl C Schneider A Greene RE Passino C Spadacini G Bandinelli G Bonfichi M Arcaini L Malcovati L Bernardi L 《European journal of applied physiology》2000,83(6):481-486
This study was performed to investigate the influence of breathing control on the autonomic cardiac regulation at high altitude
in adapted and non-adapted awake subjects. We recorded electrocardiogram and pulse oximetry in 14 short-term acclimatized
lowlanders and 14 Himalayan Sherpas during resting conditions at an altitude of 5,050 m. Spectrum analysis was performed on
synchronized 15 min periods of R-R intervals and the oxygen saturation of arterial blood (SaO2). Despite mean SaO2 being similar in lowlanders and Himalayan Sherpas [78.5 (SD 7.0)% compared to 79.4 (SD5.8)%, respectively], fluctuations
in SaO2 were significantly increased in lowlanders compared to Sherpas, thus indicating an unstable regulation of respiration control
in lowlanders. Regression analysis demonstrated a significant relationship between spectrum power of SaO2 and the relative power of R-R intervals in the frequency band between 0.01 and 0.08 Hz in lowlanders, but not in Sherpas.
Our results demonstrate differences in respiratory and autonomic cardiac control between non-adapted lowlanders and Himalayan
high-altitude residents and indicate that unstable breathing control during chronic hypobaric hypoxia is significantly correlated
with the autonomic cardiocirculatory regulation.
Accepted: 11 September 2000 相似文献
19.
Sakran TF 《Parasitology research》2000,86(9):729-732
Macroscopically visible sarcocysts were observed in the skeletal muscles of naturally infected skinks of the genus Agama (infection rate 11.3%). Sarcocysts were described by means of transmission electron microscopy. These cysts measured 0.03–0.25 × 0.38–1.7 mm
(mean 0.12 × 1.1 mm). Typical mature cysts were bordered by a primary cyst wall that measured 2.4–5.3 μm (mean 3.9 μm) and
was folded into a few nonbranched finger-like protrusions measuring 0.7–1.5 × 1.0–2.5 μm (mean 1.2 × 1.5 μm). These protrusions
contained granular elements, but filaments and tubular elements were not observed. A relatively thick, homogeneous tape was
observed just underneath the primary cyst wall, measuring 0.5–1.0 μm (mean 0.8 μm) and containing a granulated ground substance
in which filaments and tubular elements were not observed. Metrocytes measured 3.1–5.5 × 4.2–7.2 μm (mean 4.0 × 5.8 μm) and
merozoites measured 1.2–3.3 × 4.4–8.6 μm (mean 2.6 × 7.5 μm). The fine ultrastructural characteristics of both metrocytes
and merozoites were similar to those described for many Sarcocystis species and were generally nonspecific.
Received: 21 February 2000 / Accepted: 1 March 2000 相似文献
20.
Matthew W. Curtis Sadhana Sharma Tejal A. Desai Brenda Russell 《Biomedical microdevices》2010,12(6):1073-1085
Cardiac myocytes are known to be influenced by the rigidity and topography of their physical microenvironment. It was hypothesized
that 3D heterogeneity introduced by purely physical microdomains regulates cardiac myocyte size and contraction. This was
tested in vitro using polymeric microstructures (G′ = 1.66 GPa) suspended with random orientation in 3D by a soft Matrigel matrix (G′ = 22.9 Pa).
After 10 days of culture, the presence of 100 μm-long microstructures in 3D gels induced fold increases in neonatal rat ventricular
myocyte size (1.61 ± 0.06, p < 0.01) and total protein/cell ratios (1.43 ± 0.08, p < 0.05) that were comparable to those induced chemically by 50 μM phenylephrine treatment. Upon attachment to microstructures,
individual myocytes also had larger cross-sectional areas (1.57 ± 0.05, p < 0.01) and higher average rates of spontaneous contraction (2.01 ± 0.08, p < 0.01) than unattached myocytes. Furthermore, the inclusion of microstructures in myocyte-seeded gels caused significant
increases in the expression of beta-1 adrenergic receptor (β1-AR, 1.19 ± 0.01), cardiac ankyrin repeat protein (CARP, 1.26 ± 0.02),
and sarcoplasmic reticulum calcium-ATPase (SERCA2, 1.59 ± 0.12, p < 0.05), genes implicated in hypertrophy and contractile activity. Together, the results demonstrate that cardiac myocyte
behavior can be controlled through local 3D microdomains alone. This approach of defining physical cues as independent features
may help to advance the elemental design considerations for scaffolds in cardiac tissue engineering and therapeutic microdevices. 相似文献