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.     

Influence of gravity changes induced by parabolic flight on cytokine production in mouse spleen

Dysregulation of the immune system has been a well-documented effect of human exposure to a microgravity environment during space flight. These effects have included altered cytokine production, reduced proliferative responses, altered signal transduction pathways and altered distribution of peripheral immune cells. Recent reports have documented immunologic studies performed in-flight. When tested during space flight, delayed-type hypersensitivity was reduced, indicating a dysregulation of cell-mediated immune function. However, the mechanisms by which this occurs remain unclear. The production of cytokines plays a critical role in the ability of a host to mount an immune response against an invading microorganism. In this study, the alteration of cytokine responses in mice following parabolic flight (PF) was investigated.     

Shift in arm-pointing movements during gravity changes produced by aircraft parabolic flight.

It has been shown that target-pointing arm movements without visual feedback shift downward in space microgravity and upward in centrifuge hypergravity. Under gravity changes in aircraft parabolic flight, however, arm movements have been reported shifting upward in hypergravity as well, but a downward shift under microgravity is contradicted. In order to explain this discrepancy, we reexamined the pointing movements using an experimental design which was different from prior ones. Arm-pointing movements were measured by goniometry around the shoulder joint of subjects with and without eyes closed or with a weight in the hand, during hyper- and microgravity in parabolic flight. Subjects were fastened securely to the seat with the neck fixed and the elbow maintained in an extended position, and the eyes were kept closed for a period of time before each episode of parabolic flight. Under these new conditions, the arm consistently shifted downward during microgravity and mostly upward during hypergravity, as expected. We concluded that arm-pointing deviation induced by parabolic flight could be also be valid for studying the mechanism underlying disorientation under varying gravity conditions.     

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.     

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.     

Cerebral cortical blood flow in rabbits during parabolic flights (hypergravity and microgravity)

We studied the effect of gravity on cerebral cortical blood flow (CBF), mean arterial blood pressure () and heart rate in six rabbits exposed to parabolic flights. The CBF was obtained using a laser-Doppler probe fixed on to a cranial window. Before weightlessness, the animals were exposed to chest-to-back directed acceleration (1.8–2.0 g). The CBF values were expressed as a percentage of CBF_o (mean CBF during 60 s before the 1st parabola). Propranolol (1 mg · kg⁻¹ IV) was given after the 11th parabola and pentobarbital (12–15 mg · kg⁻¹ IV) after the 16th parabola. Before the administration of the drugs, CBF increased (P < 0.01) during hypergravity [i.e. maximal CBF 151 (SD 64)% CBF_o. Simultaneously increased [maximal , 119 (SD 11) mmHg (P < 0.01)]. At the onset of weightlessness, CBF and reached maximal values [194 (SD 96)% CBF_o (P < 0.01) and 127 (SD 19) mmHg, (P < 0.01) respectively]. The microgravity-induced increase in CBF was transient since CBF returned to its baseline value after 8 (SD 2) s of microgravity. After propranolol administration, CBF was not statistically different during hypergravity but an elevation of CBF was still observed in weightlessness. The increases in CBF and also persisted during weightlessness after pentobarbital administration. These data would indicate that CBF of nonanesthetized rabbits increases during the first seconds of weightlessness and demonstrate the involvement of rapid active regulatory mechanisms since CBF returned to control values within 8 (SD 2) s. We concluded that this elevation in blood flow was not related to stress because it persisted after the administration of propranolol and pentobarbital. Accepted: 6 November 1997     

Rapid changes in tubulin RNA synthesis and stability induced by deflagellation in Chlamydomonas

Detachment of the flagella of Chlamydomonas induces a rapid accumulation of mRNAs for tubulin and other flagellar proteins. Measurement of the rate of alpha and beta tubulin RNA synthesis during flagellar regeneration shows that deflagellation elicits a rapid, 4-7- fold burst in tubulin RNA synthesis. The synthesis rate peaks within 10- 15 min, then declines back to the predeflagellation rate. Redeflagellation of cells at times before the first flagellar regeneration is completed (and when cells have already accumulated elevated levels of tubulin RNA) induces another burst in tubulin RNA synthesis which is identical to the first in magnitude and duration. This finding indicates that the induction signal may act to simply reprogram the tubulin genes for a transient burst of maximal synthesis. Evidence is presented that the stability of the tubulin RNAs changes during regeneration. Stability changes include both an apparent stabilization during regeneration and accelerated decay following regeneration.     

Atrial distension in humans during weightlessness induced by parabolic flights

Central venous pressure, esophageal pressure, and left atrial diameter were measured in individuals during each stage of parabolic flight, with emphasis on weightlessness. Results indicated that short periods of weightlessness lead to an increase in transmural central venous pressure and left atrial diameter, although there is a decrease in central venous pressure.     

Atrial distension in humans during microgravity induced by parabolic flights

Videbaek, Regitze, and Peter Norsk. Atrialdistension in humans during microgravity induced by parabolic flights.J. Appl. Physiol. 83(6):1862-1866, 1997.The hypothesis was tested that human cardiacfilling pressures increase and the left atrium is distended during 20-speriods of microgravity (µG) created by parabolic flights, comparedwith values of the 1-G supine position. Left atrial diameter(n = 8, echocardiography) increasedsignificantly during µG from 26.8 ± 1.2 to 30.4 ± 0.7 mm(P < 0.05). Simultaneously, centralvenous pressure (CVP; n = 6, transducer-tipped catheter) decreased from 5.8 ± 1.5 to 4.5 ± 1.1 mmHg (P < 0.05), and esophageal pressure (EP; n = 6) decreased from1.5 ± 1.6 to 4.1 ± 1.7 mmHg (P < 0.05). Thus transmural CVP(TCVP = CVP  EP; n = 4)increased during µG from 6.1 ± 3.2 to 10.4 ± 2.7 mmHg(P < 0.05). It is concluded thatshort periods of µG during parabolic flights induce an increase inTCVP and left atrial diameter in humans, compared with the resultsobtained in the 1-G horizontal supine position, despite a decrease inCVP.

     

Arterial pressure in humans during weightlessness induced by parabolic flights.

Results from our laboratory have indicated that, compared with those of the 1-G supine (Sup) position, left atrial diameter (LAD) and transmural central venous pressure increase in humans during weightlessness (0 G) induced by parabolic flights (R. Videbaek and P. Norsk. J. Appl. Physiol. 83: 1862-1866, 1997). Therefore, because cardiopulmonary low-pressure receptors are stimulated during 0 G, the hypothesis was tested that mean arterial pressure (MAP) in humans decreases during 0 G to values below those of the 1-G Sup condition. When the subjects were Sup, 0 G induced a decrease in MAP from 93 +/- 4 to 88 +/- 4 mmHg (P < 0.001), and LAD increased from 30 +/- 1 to 33 +/- 1 mm (P < 0.001). In the seated position, MAP also decreased from 93 +/- 6 to 87 +/- 5 mmHg (P < 0.01) and LAD increased from 28 +/- 1 to 32 +/- 1 mm (P < 0.001). During 1-G conditions with subjects in the horizontal left lateral position, LAD increased compared with that of Sup (P < 0.001) with no further effects of 0 G. In conclusion, MAP decreases during short-term weightlessness to below that of 1-G Sup simultaneously with an increase in LAD. Therefore, distension of the heart and associated central vessels during 0 G might induce the hypotensive effects through peripheral vasodilatation. Furthermore, the left lateral position in humans could constitute a simulation model of weightlessness.     

Dipteran flight motor pattern: Invariabilities and changes during postlarval development

For Calliphora the wingbeat frequency and the underlying motoneuronal activity were recorded during adult life. Wingbeat frequency increases during the ten days following last molt. The activity of motoneurons serving four selected flight muscles (nonfibrillar and fibrillar ones) also increases with age. The motoneuronal activity of young and old flies was analyzed statistically (serial and cross-correlograms, latency and phase histograms). In addition, several wing manipulations were carried out to evaluate the significance of sensory feedback on pattern generation during maturation. These ontogenetic studies suggest a centrally generated motor pattern that (1) is essentially complete with the molt to adulthood, (2) shows a progressive increase in intrinsic activity, and (3) is modulated by sensory feedback from the wing region by the same amount irrespective of age. Similarities in the postlarval development of the flight pattern of neurogenic and myogenic flyers are discussed.     

Time-variant spectral analysis of heart rate variability during parabolic flight with and without LBNP

Modifications of autonomic activity during parabolic flight were studied by a time-variant model able to estimate low (LF, 0.04-0.14 Hz) and high (HF, 0.14-0.35 Hz) frequency spectral components on a beat-to-beat basis. Ten subjects were studied with and without lower body negative pressure (LBNP). ECG and Gz load were digitized (500 Hz) and RR interval variability series extracted. Beat-to-beat mean RR, variance, LF and HF power were obtained. One-way ANOVA (p<0.01) was used to compare values obtained during starting 1Gz (I), first 1.8Gz (II), 0Gz (III), second 1.8Gz (IV), ending 1Gz (V). Without LBNP, total and LF power increased during 0Gz to 1.69 +/- 1.41 and 2.87 +/- 4.66 respectively (mean +/- SD, normalized by phase I value). With LBNP, their change during 0Gz (1.38 +/- 1.37 and 1.54 +/- l.04 respectively) reached significance only with phase II and phase V. Phase I HF power was higher than in the other phases, both without and with LBNP.