Effects of simulated

microgravity

(HDT)

on blood fluidity

L. LAMPE, K. WIENHOLD, G. MEYER, F. BAISCH, H. MAASS, W. HOLLMANN, Institute for Cardiology and Sports Medicine, German Sports Uniuersity, and Institute for Aerospace Medicine, D-5000 Cologne, Federal Republic of Germany

LAMPE, L.,K. WIENHOLD,G.MEYER, F. BAISCH,H. MAASS, W. HOLLMANN,ANDR. ROST.Effects of simulated microgravity (HDT) on blood fluidity. J. Appl. Physiol. 73(4): 1366-1369, 1992.-Exposures to microgravity and head-down tilt (HDT) produce similar changes in body fluid. This causes an increase in hematocrit that significantly affects hemorheological values. Lack of physical stimulation under bed rest conditions and the relative immobility of the crew during spaceflight also affects the blood fluidity. A group of six healthy male subjects participated as volunteers, and blood samples were collected 10 days before, on day 2 and day 9, and 2 days after the HDT phase. Blood rheology was quantified by plasma viscometry, red cell aggregability, and red cell deformability. A reduced red cell deformability, an indication of the diminished quality of the red blood cells, was measured under HDT conditions that finally led to the so-called “space flight anemia.” Enhanced red cell membrane fragility induced by diminished physical activity and an increase in hemoglobin concentration are responsible for this effect. Plasma viscosity is reduced as a result of diminished plasma proteins. However, despite the reduction in plasma proteins, including fibrinogen, cw,-macroglobulin, and immunoglobulin M, red cell aggregation was enhanced, principally because of the increase in hematocrit. Our results of hemorheological alterations under HDT conditions may help to elucidate the formerly documented hematologic changes during spaceflight.

OVER THE PAST 15 years space medicine has become increasingly concerned with the effects of spaceflight on hematologic processes. These hematologic changes which have been found to occur during spaceflight are expressed as a loss of red cell mass, presumably as a result of suppressed erythropoietic activity on the one hand and because of an increased destruction of red blood cells on the other (15). In the microgravitational environment during orbital flight or when a subject moves from an erect to a recumbent position, the cardiovascular system and the blood inside is altered. A known pathophysiological effect of spaceflight is a reduction in blood volume, and it has been proved that in both conditions the cumulative water balance reveals a body water loss of -1.5 liters. That is why a recumbent position or, even more so, a slight headdown tilt (HDT) affects some of the body’s systems involved in space adaption in a similar way (2). Hemorheologic variabilities such as plasma viscosity, red cell aggregability, and red cell deformability are of great importance for the passage of blood cells through 1366

0161-7567/92

$2.00

Copyright

R. ROST

the microcirculation where cellular diameter is normally larger than luminal diameter (23). A survey of experimental results obtained under HDT conditions gives reasons for one to assume that similar changes would occur under spaceflight conditions and would have a substantial influence on the 0, supply and tissue oxygenation of the organism. The evaluation of determinants of blood fluidity contributes a possible explanation for the well-documented phenomenon of “space anemia,” and also explains the specific perfusion conditions in microcirculation. Previous studies (5, 12, 17-19) also may explain that high levels of physical activity improve blood fluidity. The present study also tested the hypothesis that inactivity induces changes to the contrary namely a decreased level of blood fluidity. Because these issues are of considerable significance with regard to the conditions of spaceflight, we performed the present study on blood fluidity during zero-gravity situation in the form of a 6” HDT. MATERIAL AND METHODS The study group consisted of six healthy male subjects with a mean age of 26 yr and a mean value for maximal oxygen intake values of 42.5 ml min-l kg body wt-? They all participated as volunteers and signed an informed consent form. The study plan was approved by the D-Z Medical Board in accordance with the rules of the National Aeronautics and Space Administration Human Research Policy and Procedure Committee. A 6* HDT was chosen to produce redistributions of body fluids and the necessary adaptations in many organ systems similar to the phenomena that can be expected to occur in microgravity (2). After an initial data collection period, a lo-day period of continuous head-down tilt and 6 days of recovery followed. All blood samples were collected at the same time and anticoagulated with EDTA 10 days before the test period (pre), on day 2 (HDT,) and day 9 (HDT,) of HDT phase and 2 days after the HDT phase (post). Hematological parameters were determined by a hemogram, which evaluated red blood cells, hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) (Coulter Counter). Blood rheology was quantified using the following methods. 1) Plasmaviscometry: after centrifugation of the whole blood plasmaviscosity was quantified at 37°C (Luckham Capillary Viscometer). In this way the ease of the plasma flow proceeding through a capillary of a fixed l

anemia of spaceflight; membrane fragility; hemoconcentration; plasma viscosity; red cell deformeability; red cell aggregability

AND

@I 1992 the American

Physiological

l

Society

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.252.067.066) on September 18, 2018. Copyright © 1992 American Physiological Society. All rights reserved.

EFFECTS

TABLE

OF

HEAD-DOWN

TILT

ON

BLOOD

1. Erythrocytes, hemoglobin, and hematocrit under the influence of head down tilt Ery,

Pre

1012/1

Hb, g/d1

4.73kO.39

Hct,

14.5-+1.10 i

HDT,

5.1520.35

HDT,

5.11+0.31

-

Post

4.62kO.21

- +J

Values are means k SD. Ery, of HDT; HDT,, day 9 of HDT;

I+

corpuscular values influenced by

10 days head down tilt fl

MCH,

Pre

90.5k2.06

HDT,

9O.lk2.62

1*

31.4k1.571

HDT,

89.6k2.30

-I

31.7kO.96

Post

93.3k6.10

-

15.7k1.10

- +-l

erythrocytes; Hb, hemoglobin; Hct, hematocrit. post, 2 days after HDT. * P 5 0.5; t P 5 0.01.

The hematologic data indicated that HDT induced increases in red cell counts (P 5 0.01) and hematocrit (P 5 0.01). The increase in hemoglobin concentration was not statistically significant. During the HDT phase (HDT, HDT,) a decrease of hemoglobin (P 5 0.01) could be measured, but there were no significant variations in the red cells and hematocrit. Apart from MCV a decrease to the initial level of the hematologic data was observed after HDT (Table 1). Regarding the corpuscular values, HDT induced a reduction of the MCV (P 5 0.05) but an increase of both the MCH (P < 0.05) and the MCHC (P 5 0.01) (Table 2). The hemorheological data indicated a less homoge-

MCV,

31.9d.33

MCHC,

pg

* A

-

35.4t0.94

-

34.5k0.62

1

t

1

2

*

31.2k1.09

*

47.8k3.06

J -

t

1*

Pre, 10 days before

head-down

tilt

(HDT)

test period;

HDT,

day 2

neous development. Plasma viscosity showed an initial reduction at first (P 5 0.05) but no further change during the remaining HDT phase. The measurement taken 2 days after HDT revealed a distinct decrease of the plasma viscosity (P 5 0.01) (Fig. 1). Because of HDT a reduction of red cell flexibility was induced, which was indicated by a diminuation of red cell filterability throughout the whole HDT phase and was intensified after HDT (P 5 0.01) (Fig. 2). Concerning the question of red cell aggregation, we found a small and not statistically significant increase initiated by HDT. Two days after the HDT phase, red cell aggregation decreased to below the initial level (P 5 0.01) (Fig. 3). DISCUSSION

Exposure to microgravity and to HDT appears to produce similar changes in body fluid. It has been proved that under both conditions the cumulative water balance reveals a body water loss of -1.5 liters (6). This effects the composition and the quality of the blood to some extent. In our investigations an increase in erythrocytes, hemoglobin, hematocrit, MCH, and MCHC at the beginning of the experiment and a decrease of these values after HDT in combination with a continuous reduction in the MCV (Table 1) quite obviously indicates a hemoconcentration. Former investigations, either during spaceflight or in simulation studies, have always pointed to typical hematologic variations in the form of space-induced hemocon1.307

y* n

I

2

1.25-

r I

k

*

*

* *

*--1 1 0

*-

x 1.20.--t, ul 8 -2 1.15-

g/d1

34.6k1.07

37.3kO.55

-

14.4k0.21

RESULTS

2. Erythrocyte

16.2kl.20

%

42.3k3.46 1

length was measured (14, 16). 2) Red cell deformability: the principle is an automatic measurement of the initial flow rate of a diluted red cell suspension (hematocrit 10%) through 5-pm-diam pores (nuclepore filter). Because there is a correlation between red cell “mechanical behavior” and red cell velocity (i.e., transit time) flowing through small pores, deformability is described as the relationship between suspension passage time and the passage time of the buffer solution in which the erythrocytes were suspended so that high reading implicates reduced deformability (4,16,20) (St. George’s Filtrometer, Fa Carrymed, Dorking, UK). 3) Red cell aggregation: in a semiautomatic transparent cone plate viscometer a blood sample was exposed at a shear rate of 3 s-l for 10 s. Aggregation occurred after stopping the shear stress procedure and was quantified by an increase of light transmission through the blood sample (16, 25, 26). All variables were analyzed using a Wilcoxon signedrank test with contrasts for each hypothesis between the control and each experimental day (highly significant, P 5 0.01; significant, P 5 0.05).

TABLE

1367

FLUIDITY

"E i$ l.lOa, 1.05-

t

A -

Values are means + SD. MCV, mean corpuscular volume; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration. * P 5 0.5; t P I 0.01.

I PRE

I HDTl

I HDT2

1 POST

FIG. 1. Plasma viscosity influenced by head downtilt (HDT). Pre, 10 days before HDT; Post, 2 days after HDT; HDT,, day 2 of HDT period; HDT,, day 9 of HDT period. * P s 0.05; ** P 5 0.01.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.252.067.066) on September 18, 2018. Copyright © 1992 American Physiological Society. All rights reserved.

1368

EFFECTS

OF

*

I

7*

9.20-

I

HEAD-DOWN *

--

TILT 1

I * *

9.00z

8.80x 2 8.60n.-\cz 8.40-

-

a, 8.200 -73 a~ 8.00E

I

7.807.60-

I PRE

I HOT1

FIG. 2. Red cell flexibility (ratio of suspension sage time of buffer solution in which red blood under influence of HDT. High reading implicates ity. * P I 0.05; ** P I 0.01.

I HOT2

I POST

passage time to pascells were suspended) reduced deformabil-

centration and an increase in cell membrane fragility (6, 15). The consequence of these facts may be an enhanced frequency of thrombosis on the one hand and a reduced red cell life span on the other, probably responsible for the so-called “spaceflight anemia”also observed during earlier spaceflights (6, 11, 15). This specific kind of anemia has been variously ascribed to the conditions of weightlessness and the relative immobility of the crew (15). Hemorheological knowledge and its specific methods are perhaps able to explain these hematological changes. Red cell flexibility is a widely accepted term to indicate the property of red blood cells to adapt their shape to the forces acting in blood circulation. The enhanced red cell membrane fragility becomes apparent in diminished red cell flexibility, possibly a prestate of this condition. Similar conditions are known to occur elsewhere, more specificially in long-distance running where mechanical alterations induce a red cell sequestration with a subsequent tendency toward a reduced red cell life span and resulting in anemia (running anemia) (7). In our study a higher rigidity of the red blood cells can also be observed. Thus the reduced red cell deformability, which was measured during HDT, can also be assumed to be an indication of a diminished quality of the red blood cells and their easier destructibility, finally effecting a greater risk of anemia. Diminished physical activity because of the relative immobility of the crew under the conditions of weightlessness, just as the volunteers during HDT had, has also been held responsible for these effects (15). Hemorheological studies show that enhanced physical stimulation leads to an improvement of the red cell deformability (17) so that the opposite reduced physical activity below the standard conditions of everyday life during weightlessnessand bed rest would thus cause reduced deformability (5, 8, 9, 21). Assessing the factor “immobility” with regard to rheological variations allows for only an indirect relationship, but all observations point to a connection between these factors.

ON

BLOOD

FLUIDITY

A further reason for the diminished red cell flexibility is caused by the loss of extracellular and, in consequence, intracellular fluids. Not only the red cell membrane but also the composition and concentration of the cytoplasma are responsible for the rheological quality of the red blood cells (23). An increased cytoplasmatic concentration, as evidenced by an increased MCHC, leads to a reduced red cell deformability (3). The significant differences between the MCV and MCHC values induced by HDT in comparison to the initial levels suggest that the properties of individual erythrocytes were also affected by a simulated microgravity; these changes in red cell structure could explain the impaired deformability (13). Plasma viscosity, a far more important factor for hemodynamics than originally assumed, particularly in microcirculation, showed only an initial yet significant reduction under the influence of HDT. In previous reported studies plasma viscosity in the resting state depended largely on fibrinogen, total globulin, and hence, total protein concentrations, especially +-macroglobulin, whereas albumin concentration was not a significant determinant (1, 3, 6). Former HDT studies measured a reduction in total plasma protein of -20% during HDT (11). This is one and probably the main factor for the decrease of plasma viscosity we detected under HDT conditions. The additional distinct deterioration of plasma viscosity after the HDT phase was caused by a general dilution of the blood in the period of rehydration after HDT. Red cell aggregation, in comparison to plasma viscosity, shows an increase induced by HDT, a reaction that was not expected, and a reduction to below the initial level in the post-HDT phase. The reversible aggregation of red blood cells continues to be a central issue in hemorheology, in that red cell aggregation is a primary determinant for the rheological behavior of blood at low shear conditions. At low shear rates, red cell aggregation is the major cause of the nonNewtonian flow properties of normal blood (23, 24). As with plasma viscosity, red cell aggregation is also caused by fibrinogen, cu,-macroglobulin, and immunoglobulin M (23). In general, however, the aggregation pro-

I ** **‘“*oo~ r 7*

+------1

9.50

7

I

9.00

-

8.50

.s5

8.00

g

7.50

al

& 7.00 m o 6.50 T

6.00

;

5.50

g

5.00 4.50

i 1

4.00 I PkE FIG.

3. Changes

HD/Tl

of red cell aggregability

HdT2

according

P&T

to HDT.

**

P5

0.01.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.252.067.066) on September 18, 2018. Copyright © 1992 American Physiological Society. All rights reserved.

EFFECTS

OF

HEAD-DOWN

cess depends on the properties of the red blood cells and not only on the physiochemical characteristics of their environment (22). The enhanced aggregation under HDT is probably attributable to the elevated hematocrit (27). During spaceflight well-documented hematologic changes occur that can similarly be observed under the conditions of a 6’ HDT. As our results demonstrate, hemorheological parameters could well allow for an estimation of those abnormalities in advance and also offer possible explanations for the observed phenomena. Address for reprint chung und Sportmedizin, Received

16 May

requests: L. Lampe, Institut fur KreislaufforsCarl Diem Weg 6, 5000 Koln 41, FRG.

1991; accepted

in final

form

10 March

1992.

TILT

12. 13.

14. 15.

16. 17.

18.

REFERENCES 1. ANGELKORT, B., H. KIESEWETTER, AND H. GERLACH. Htt’morheologie und Hamostase Tagungsbericht der DGKH. Munich, FRG: 1982. 2. BLOMQVIST, C. G., AND H. L. STONE. Cardiovascular adjustments to gravital stress. In: Handbook of Physiology. The Cardiovascular Systems. Peripheral Circulation and Organ Blood Flow. Bethesda, MD: Am. Physiol. Sot., 1983, sect. 2, vol. III, pt. 2, chapt. 28, p. 1025-1063. 3. CHIEN, S. Present state of blood rheology. In: Hemodilution, Theoretical Basis and Clinical Application, edited by K. Messmer and H. Schmid-Schonbein. Basel: Karger, 1972. 4. DORMANDY, J. Red Cell Deformability and Filterability, Boston, MA: Nighoff, 1983. 5. ERNST, E., AND M. SCHMID. Verbesserung der Blutfluiditat durch intensives korperliches Training. Fortschr. Med. 102: 1097-1099, 1984. 6. FISCHER, C. L., P. C. JOHNSON, AND C. A. BERRY. Red blood cell mass and plasma volume changes in manned space flight. J. Am. Med. Assoc. 200: 99-103, 1967. 7. GALEA, G., AND R. J. L. DAVIDSON. Hemorheology of marathon running. Int. J. Sports Med. 25: 207-210, 1985. 8. HARALAMBIE, G. Serum glycoproteins and physical exercise. J. Appl. Physiol. 27: 669-672, 1969. 9. HARALAMBIE, G. Changes of serum glycoprotein level after longlasting physical exercise. Clin. Chim. Acta 27: 475-479, 1970. 10. HINGHOFER-SKALKAY, H. Continuous blood densitometry: fluid shifts after graded hemorrhage in animals. Am. J. Physiol. 250 (Heart Circ. Physiol. 19): H342-H350, 1986. 11. HINGHOFER-SKALKAY. H. Method of high-nrecision microsamnle

19.

20.

21.

22.

23.

24. 25.

26.

27.

ON

BLOOD

FLUIDITY

1369

blood and plasma mass densitometry. J. Appl. Physiol. 60: 10821088, 1986. HOLLMANN, W., AND T. HETTINGER. Sportmedizin-Arbeitsund Trainingsgrundlagen. Stuttgart, FRG: Schattauer, 1980. INTERNATIONAL COMMITTEE FOR STANDARDIZATION IN HEMATOLOGY. (ICSH). Guidelines for measurement of blood viscosity and erythrocyte deformability. Clin. Hemorheol. 6: 439-453, 1986. JANSON, J., AND D. E. BROOKS. Do plasma proteins adsorb to red cells? Clin. HemorheoZ. 9: 695, 1989. JOEL, I. A System Analysis of the Erythropoetic Responses to Weightlessness. Mathematical Model Simulation of the Erythropoietic Responses to Weightlessness. Houston, TX: NASA, 1985, vol. I. (NASA-CR-171890) KIESEWETTER, H., A. M. EHRLY, AND F. JUNG. Hemorheologische Messmethoden: 3. Kongress DGKH. Homburg, FRG, 1984. LAMPE, L., K. WIENHOLD, G. MEYER, AND W. HOLLMANN. Einfluss unterschiedlicher Trainingsqualita’auten auf die Blutfluidita’aut. Dtsch. 2. Sportned. 40: 3, 1990. LETCHER, R. L., T. G. PICKERING, S. CHIEN, AND J. H. LAREGH. Effect of exercise on plasma viscosity in athletes and sedentary normal subjects. Clin. Cardiol. 4: 174-179, 1981. LIESEN, H., B. DUFAUX, AND W. HOLLMANN. Ausdauertraining und natiirliche Proteinaseininhbitoren: Der Einfluss auf die Plasmavolumenregulation in Ruhe und bei dosierter korperlicher Belastung. Dtsch. 2’. Sportned. 29: 37-44, 1978. MATRAI, A., E. ERNST, AND J. A. DORMANDY. Erythrozytenfiltrabilittit: Unterscheidung zwischen Filterokklusion und Erythrozytenpossagezeit. 2. Phys. Med 15: 117-120, 1985. MATRAI, A., S. ST~HR, S. PAULSEN, AND E. ERNST. Zur Beziehung zwischen Hamorheologie und kijrperlicher Leistungfahigkeit bei untrainerten Freiwilligen. Ztschr. Phys. Med. 15: 424-426, 1986. NASH, G. B., R. B. WENBY, S. 0. SOWEMIMO-COHER, AND H. J. MEISELMAN. Influence of cellular properties on red cell aggregation. Clin. Hemorheol. 7: 93-108, 1987. SCHMID-SCH~NBEIN, G. W., R. SHALAK, R. USAMI, AND S. CHIEN. The interaction of leucocytes and erythrocytes in capillary and postcapillary vessels. Microvasc. Res. 19: 45, 1980 SCHMID-SCH~NBEIN, H., K. MESSMER, AND H. RIEGER. Hemodilution and Flow. Basel: Karger, 1981. SCHMID-SCH~NBEIN, H., E. VOLGER, P. TEITEL, H. KIESEWETTER, U. DAUER, AND L. HEILMANN. New hemorheological technics for the routine laboratory. Clin. Hemorheol. 2: 93-105, 1982. SCHMID-SCH~NBEIN, H., J. VON GOSEN, L. HEINRICH, H. J. KLOSE, AND E. VOGLER. A counter-rotating “rheoscope chamber” for the study of the microrheology of blood cell aggregation by microscopic observation and microphotometry. Microvasc. Res. 6: 366, 1973. SCHWEIGER, B., J. POHL, G. DRIESSEN, H. HEIDTMANN, AND H. SCHMID-SCH~NBEIN. Influence of fibrinogen concentration on flow velocitv of RBC’s in rat mesenterv. B&Z. Anat. 20: 230. 1981.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (128.252.067.066) on September 18, 2018. Copyright © 1992 American Physiological Society. All rights reserved.