应用植入式遥测技术观察自发性高血压大鼠血压的昼夜波动

目的应用植入式遥测技术观察自发性高血压大鼠在清醒无束缚状态下血压昼夜波动变化。方法取8只SPF级3月龄雄性SHR大鼠,进行C50-PXT植入子植入手术,恢复7 d后,用遥测系统进行24 h连续清醒无束缚的血压监测,并用EMKA分析软件对动态血压心率均值、24 h血压心率趋势等指标进行分析。结果 3月龄的SHR大鼠血压和心律呈昼夜节律性变化,白昼阶段血压明显低于夜间阶段(P<0.01),血压在1∶30～2∶30和20∶30～21∶30时出现两个高峰期,14∶00～14∶30时出现一低谷期。其中夜间阶段平均收缩压为166.02 mmHg,两个收缩压峰值分别为172.13 mmHg和171.38 mmHg;白昼平均收缩压是162.73 mmHg,收缩压谷底值为155.73mmHg。而心率两个高峰期出现在1∶30～2∶00和20∶00～21∶00,高峰值分别为375.00次/分和373.26次/分;心率低谷出现在11∶00左右,谷底值为310.91次/分,白昼和夜间的平均心率分别为328.85次/分和346.05次/分。结论 3月龄的SHR大鼠血压和心律呈昼夜节律性变化,血压和心率在夜间出现两个高峰,白昼出现一个低谷,且夜间的平均血压和心率要高于白昼,SHR大鼠的血压和心率的节律变化与其活动有关。植入式遥测技术可准确反映SHR大鼠血压昼夜的节律性变化,有助于正确评价抗高血压药物的作用和高血压的生理机制研究。     

Measurement of the common carotid arterial flow during parabolic flight in the anesthetized rat]

To measure the blood flow of a common carotid artery (CCA) during parabolic flight in the rat, we developed an animal double hold box (ADHB) made of styrene expanded form for the anesthetized rat to keep the animal at a proper posture in an aircaft. Twelve anesthetized rats weighing 291-342 g were surgically operated to mount a ultrasound flowmeter probe (1 mm size,1RS:Transonic Systems Inc.) around the right CCA and to insert a catheter into the right axillar artery for blood pressure measurement. These animals were held comfortably in ADHBs which were placed on the rack installed in the aircraft (MU-300). A total of 27 parabolic flights was performed and the blood flow was measured accurately in 9 rats. This special animal holding facility is useful for various types of animal experiments in an aircraft.     

Effects of parabolic flight on abdominal arterial pressure in conscious rats.

Abdominal arterial pressure during parabolic flight was measured using a telemetry system to clarify the acute effect of microgravity on hemodynamics in conscious rats. The microgravity condition was elicited by three different levels of entry gravity, i.e. 2 G, 1.5 G and 1 G. On exposure to 2 G, mean aortic pressure (MBP) increased up to 118.7 mm Hg +/- 7.3 compared with the value at 1 G (107.0 +/- 6.3 mm Hg, n=6). The value at microgravity preceded by 2 G was 118.0 mmHg +/- 5.2 mm HG and it was still higher than at 1 G. When 1.5 G was elicited before microgravity exposure, MBP also increased (1.5 G: 114.9 +/- 5.3 vs 1 G: 105.8+/-5.0 mm Hg) and the value at microgravity was 117.3 + /- 5.3 mmHg. During pre-microgravity maneuver with 1 G, no changes were observed compared with the control level at 1 G (pre-microgravity: 105.0 +/- 5.0 vs 1G: 104.8 +/- 5.1 mm Hg ), whereas the MBP increased up to 117.0 +/- 6.5 mm Hg on exposure to microgravity. From these results, we found that in conscious rat MBP increase during acute microgravity exposure with either 1 G or hyper-G entry.     

Regional difference of blood flow in anesthetized rats during reduced gravity induced by parabolic flight.

To examine a hypothesis that change in regional blood flow due to decreased hydrostatic pressure gradient and redistribution of blood during reduced gravity (rG) is different between organs, changes in cerebrocortical blood flow (CBF) and blood flow in the temporal muscle (MBF) with exposure to rG were measured in anesthetized rats in head-up tilt and flat positions during parabolic flight. Carotid arterial pressure (CAP), jugular venous pressure (JVP), and abdominal aortic pressure were also measured simultaneously. In the head-up tilt group, CBF increased by 15 +/- 3% within 3 s of entry into rG and rapidly recovered during rG. MBF also increased, but the change was significantly greater than that of CBF. JVP increased by 1.8 +/- 0.5 mmHg, probably due to loss of hydrostatic pressure gradient, since the measuring point of JVP was 2-3 cm above the hydrostatic indifference point. CAP and abdominal aortic pressure increased by 16.7 +/- 2 and 7.7 +/- 2 mmHg, respectively, compared with the 1-G condition. Muscle vascular resistance [(CAP-JVP)/MBF] decreased on entry into rG, but no significant change was observed in cerebrocortical vascular resistance [(CAP-JVP)/CBF]. In the flat group, no significant change was observed in all the variables. The results indicate that arteriolar vasodilatation occurs in the temporal muscle but not in the cerebral cortex. Thus the blood flow control mechanism at the onset of rG is different between intra- and extracranial organs.     

Recording of blood pressure,heart rate and aortic nerve activity during parabolic flight in the rat via radio-telemetry

Exposure to microgravity induces cardiovascular deconditioning characterized by orthostatic hypotension when astronauts return to the earth. In order to understand the mechanism of cardiovascular deconditioning, it is necessary to clarify the changes in hemodynamics and the cardiovascular regulation system over the period of space flight. The telemetry system applied to freely moving animals will be a useful and appropriate technique for this kind of long term study of the cardiovascular system in the conscious animal during space flight. The purpose of the present study is twofold: firstly, to observe the detailed changes of arterial pressure and heart rate (HR) during microgravity elicited by the parabolic flight in order to study the acute effect of microgravity exposure on the cardiovascular system; and secondly, to test the feasibility of the telemetry system for recording blood pressure, HR and autonomic nervous activities continuously during space flight.     

Noninvasive beat-to-beat stroke volume computation during acute hydrostatic pressure changes in parabolic flight

A three-element model of the cardiovascular system was used to monitor stroke volume (SV) changes during parabolic flight. Aortic blood flow was estimated from continuous arterial finger pressure and SV computed by integrating simulated aortic flow during each systole. SV was significantly higher in microgravity (microgravity) compared to 1 G whereas in hypergravity (hG), SV was significantly lower. Exponential SV transients were observed after the transitions to and from microgravity and the succeeding or preceeding hG phases. These SV transients present different time constants, which reflect two different mechanisms of cardiovascular adaptation to sudden gravitational changes. These results show that beat-to-beat computation of SV provides noninvasive information on circulatory adaptation to acute hydrostatic pressure changes.     

A multichannel telemetry system for autonomic neural signals, blood flow velocity, blood pressure, and ECG measurements]

A radio multichannel telemetry system has been developed for use with chronically instrumented, unrestrained, small animals. The system can simultaneously record autonomic neural signals, blood flow velocity, blood pressure, and ECG. The system is time-multiplexed and pulse width modulation (PWM)/FM device, which employs two sampling frequencies. The system is designed with 10 standard low power integrated circuits, a 3 terminal voltage regulator, and a transistor. The size is 53 x 42 x 20 mm, and the weight, including two batteries is 40 grams. The system is powered by two lithium cells, which provide 60 hours of continuous operation.     

Dynamics of blood pressure, pulse wave transit time and systolic timei intervals during acute gravity changes induced by parabolic flight

To investigate cardiovascular adaptation to transient microgravity (Microgravity), we measured RR intervals (RRI), arterial blood pressure (BP), pulse wave transit time (PTT) and systolic time intervals (STI) during parabolic flight. Our results demonstrate that during microgram RRI, BP and PTT are subject to a rapid adaptation likely mediated by the baroreflex whereas STI changes with microgravity but does not present further adaptation.     

Effects of microgravity elicited by parabolic flight on abdominal aortic pressure and heart rate in rats.

Abdominal aortic pressure (AAP), heart rate (HR), and aortic nerve activity (ANA) during parabolic flight were measured by using a telemetry system to clarify the acute effect of microgravity (microG) on hemodynamics in rats. While the animals were conscious, AAP increased up to 119 +/- 3 mmHg on exposure to microG compared with the value at 1 G (95 +/- 3 mmHg; P < 0.001), whereas AAP decreased immediately on exposure to microG under urethane anesthesia (microG: 72 +/- 9 mmHg vs. 1 G: 78 +/- 8 mmHg; P < 0.05). HR also increased during microG in conscious animals (microG: 349 +/- 12 beats/min vs. 1 G: 324+9 beats/min; P < 0.01), although no change was observed under anesthesia. ANA, which was measured under anesthesia, decreased in response to acute microG exposure (microG: 33 +/- 7 counts/s vs. 1 G: 49 +/- 5 counts/s; P < 0.01). These results suggest that microG essentially induces a decrease of arterial pressure; however, emotional stress and body movements affect the responses of arterial pressure and HR during exposure to acute microG.     

Changes in Doppler mitral inflow patterns during parabolic flight

Aim of the study was to evaluate by transthoracic Doppler the alterations in mitral inflow velocity pattern caused by acute changes in loading conditions occurring during parabolic flights. Each parabola included normogravity (1 Gz, 1 min), mild hypergravity (1.8 Gz, 20 sec), microgravity (0 Gz, 24 sec) and mild hypergravity (1.8 Gz, 20 sec) phases. Pulsed-Doppler images were digitally acquired in 11 unmedicated subjects (46 +/- 5 years), in standing upright position and supine resting. Doppler profiles were semi-automatically traced and inflow parameters extracted and averaged onto three consecutive beats. Only in standing position, significant alterations during microgravity (p<0.05) were noted in several parameters.     

Changes in lower limb volume in humans during parabolic flight

Variations in gravity [head-to-footacceleration (G_z)] inducehemodynamic alterations as a consequence of changes in hydrostatic pressure gradients. To estimate the contribution of the lower limbs toblood pooling or shifting during the different gravity phases of aparabolic flight, we measured instantaneous thigh and calf girths byusing strain-gauge plethysmography in five healthy volunteers. Fromthese circumferential measurements, segmental leg volumes werecalculated at 1, 1.7, and 0 G_z.During hypergravity, leg segment volumes increased by 0.9% for thethigh (P < 0.001) and 0.5% for thecalf (P < 0.001) relative to1-G_z conditions. After suddenexposure to microgravity following hypergravity, leg segment volumeswere reduced by 3.5% for the thigh (P < 0.001) and 2.5% for the calf (P < 0.001) relative to 1.7-G_zconditions. Changes were more pronounced at the upper part of the leg.Extrapolation to the whole lower limb yielded an estimated 60-mlincrease in leg volume at the end of the hypergravity phase and asubsequent 225-ml decrease during microgravity. Although quantitativelyless than previous estimations, these blood shifts may participate inthe hemodynamic alterations observed during hypergravity and weightlessness.