Microcirculation and blood rheology abnormalities in chronic heart failure

Abstract

BACKGROUND: Generalized restricted blood flow is hallmark of CHF of any etiology, but the extent of microcirculation restriction and the role of intrinsic blood properties in heart failure remains unknown.

OBJECTIVE: The aim of this study was to estimate the microvascular blood flow and hemorheological properties in chronic heart failure to test the hypothesis that CHF patients have altered peripheral blood flow which contributes to the tissue perfusion disturbances.

METHODS: Cutaneous microvascular blood flow was estimated by Laser Doppler and Optical Tissue Oximetry techniques. Whole blood and plasma viscosity were measured by capillary viscometer, red blood cell aggregation was evaluated by direct microscopic method, erythrocyte deformability was assessed as elongation index in flow microchamber. Hematocrit-to-viscosity ratio was used as index of oxygen transport efficacy.

RESULTS: Depression of the regulatory mechanisms of microvascular blood flow as well as decreased tissue perfusion indicated the restricted blood flow in microcirculatory network in CHF. Increased blood and plasma viscosity, enhanced red blood cell aggregation and decreased erythrocyte deformability were registered in CHF.

CONCLUSIONS: Complex impairment of peripheral blood flow in CHF including restricted microcirculation, attenuated regulatory mechanisms and impaired hemorheological properties caused the reduced oxygen utilization contributing to symptoms and advance of heart failure.

1 Introduction

Chronic heart failure (CHF) is one of the leading causes of morbidity and mortality worldwide. The reduction in work capacity in patients with CHF was originally linked solely to central limitations associated with a malfunctioning cardiac pump [9, 10]. However, peripheral factors related to microvascular blood flow are no less important because the undisturbed microcirculation is an absolute prerequisite for the sufficient oxygen supply to the tissue as well as the disposal of metabolic remnants [12]. Central and peripheral alterations are closely linked, requiring an integrative approach to understanding the limitations and mechanisms responsible for circulation disorders in CHF [4 , 25].

Generalized restricted blood flow and endothelial dysfunction are hallmarks of CHF of any etiology [14, 19], but the extent of restriction of the microcirculation and the role of intrinsic blood properties in heart failure remain unknown. The hydrodynamic resistance of a microvascular network with a specific angioarchitectonics depends on the apparent viscosity of blood flowing in the microvessels. Coronary reserve capacity is severely impaired in heart failure due to hemodynamic changes, and microcirculatory and hemorheological abnormalities can further deteriorate tissue perfusion [24].

Therefore, the aim of our study was to estimate the cutaneous microvascular blood flow and hemorheological properties in CHF patients to test the hypothesis that CHF patients, compared with age-matched healthy controls, have altered peripheral blood flow which contributes to the tissue perfusion disturbances and blood supply to tissues.

2 Materials and methods

2.1 Study population

This study conformed to the principles of the Declaration of Helsinki. The ethical committee of Yaroslavl State Medical University approved the research protocol. Individuals of both sexes were enrolled, comprising 33 healthy volunteers (mean age 54.1 ± 7.9 years) and 46 patients with chronic heart failure (New York Heart Association Class III) with preserved ejection fraction (HF-PEF) (mean age 57.4 ± 9.5 years), who were receiving optimal medical therapy: ACEI/ARB, beta-blockers, statins, aspirin and diuretics (loop diuretics, spironolactone or both). The exclusion criteria for patients were any previous myocardial infarction, cerebral vascular accident, diabetes mellitus, malignant tumors, and severe liver and kidney dysfunction. All patients were compensated NYHA III outpatients without acute worsening at the time of the study. Written informed consent was obtained from all subjects.

2.2 Microcirculation measurements

Cutaneous blood flux was estimated using the multifunctional laser analyzer of blood microcirculation LAKK-2 modification 4 (SPE “LAZMA”, Moscow, Russia). Optical probe was placed on the upper forearm; all measurements were conducted after 15 minutes of adaptation period inside at 23±2°C. This device was created on the base of two diagnostic technologies: Laser Doppler Flowmetry (LDF) and Optical Tissue Oximetry (OTO) allowing simultaneously evaluate three parameters of blood microcirculation: alteration of blood perfusion in tissue (MI), oxygen saturation of hemoglobin (SO₂) and relative content of hemoglobin fractions in a tested area (Vr).

2.2.1 Laser Doppler technique

The microcirculation index (MI), standard deviation (σ), coefficient of variation (Kv) and amplitude frequency characteristics of reflected signal were registered. The MI depends on the average velocity of blood and erythrocyte concentration in a tested area; σ and Kv are the characteristics of time-dependent variability of microcirculation. Microvascular blood flow is unstable and variable: it is affected by complex nerve, humoral and local factors, including the response of the vascular wall. The effect of the majority of these factors consists of not only constant component, but also a variable dynamic oscillatory component, which is very important at the level of microvessels [16]. Separate oscillatory components, reflecting impact of various regulatory mechanisms of microcirculation, are identified with spectral wavelet analysis of the skin blood flow oscillations. In the frequency range of microcirculation oscillations from 0.005 up to 2 Hz five groups of rhythms were singled out [20, 21]. Each rhythmic component is characterized by frequency and amplitude. The genesis of very low frequency rhythms (0.095–0.02 Hz) is still unclear, but they are presumably related with endothelium secretion of nitric oxide [15]; neurogenic rhythms (0.023–0.046 Hz) are caused by sympathetic adrenergic influences on skin flow. Myogenic ones (0.07–0.15 Hz) are determined by the activity of myocytes of precapillary sphincters and precapillary arterioles [18]. Respiratory (0.15–0.4 Hz) and cardiac (0.4–2.0 Hz) oscillations are important components of the peripheral blood flow, which take place in both large vessels and tissue microcirculation [17]. In human skin microvessels, the cardiac oscillations take place predominantly in resistive vessels (small arteries and arterioles), especially in those with an increased tone. The respiration-synchronized oscillations of the blood propagate in microvessels from the blood outflow side and can be detected in venules [11].

The maximal (Amax) and normalized (Amax/3σ) amplitudes of all kinds of rhythms were evaluated by means of spectral wavelet analysis of LDF-grams.

2.2.2 Optical tissue oximetry technique

Using spectrophotometric channel the following parameters were estimated: Vr – relative content of hemoglobin fractions in a tested area and SO₂ – oxygen saturation of hemoglobin. Index Vr was calculated as a ratio of laser light portion, absorbed by blood in a tested area (D_r) to the sum of light portions, absorbed by blood (D_r) and other (extraneous) optical absorbents in tissue (D_ex) according to: $V_{r} = D_{r} / (D_{r} + D_{ex}),$

HbO₂ percentage in whole blood in a tested area (SO₂) was calculated as a ratio of laser light amount absorbed by oxygenated fraction of hemoglobin (D_HbO2) to total sum of light absorbed by oxygenated and deoxygenated hemoglobin (D_Hb) fractions according to: ${SO}_{2} = D_{HbO 2} / (D_{HbO 2} + D_{Hb}),$

Based on these data the index of specific (unit) oxygen consumption by tissue (U) was calculated as: U = (100 – SO₂)/Vr.

2.3 Blood sampling and preparation

Blood samples were collected into heparinized (10 U/ml) tubes by antecubital venipuncture. All tests were completed within 4 hours after blood collection [3]. A portion of each sample was used to measure plasma and whole blood viscosity at native Hct. After centrifugation, erythrocytes from another portion of blood were washed 3 times with isotonic phosphate buffer (PBS, 285mOsm/kg) and then resuspended in autologous plasma or in isotonic solution at fixed Hct to measure their aggregability and deformability.

2.4 Hemorheological measurements

Plasma and whole blood viscosity were measured by a capillary viscometer with optoelectronically detection of flow. Red blood cell aggregation (RBCA) in native plasma at Hct 0.5% was assessed by direct microscopic method with computer image analysis. The set for RBCA measurement consisted of light microscope that was equipped with a digital camera DCM-500 connected with PC. This method gives two indexes of red cell aggregation: (1) extent of aggregation (EA) calculated as a ratio of the number of aggregates to the number of nonaggregated (single) red blood cells; (2) mean size of aggregate (SA) presented as a number of red blood cells per one aggregate [23].

To estimate the deformability of RBCs they were placed into a flow microchamber. The cells were attached to the bottom part of the chamber with “one point” and then were deformed by shear flow, under constant shear stress (τ= 0.78 Pa) [13]. Using special software the length (L) and width (W) of each of about hundred cells were measured and elongation index (EI) as an index of red cell deformability was calculated according to: $EI = (L - W) / (L + W) .$

Hematocrit was evaluated by microcentrifugation and hematocrit/viscosity ratio was calculated as an index of oxygen supply to tissue [22, 27].

2.5 Statistics

Continuous variables were expressed as means±standard deviation. Comparisons between groups were performed using independent t-test. P < 0.05 was the threshold for statistical significance.

3 Results and discussion

The cutaneous microcirculation provides the skin with oxygen and is aimed to fulfil thermoregulation so that the skin anatomical and physiological specificities are designed to perform this function. Owing to its accessibility, the cutaneous microcirculation has been suggested as a model of generalized microvascular function and as a representative vascular bed to examine the mechanisms of generalized systemic microvascular dysfunction [7, 15]. This suggestion was supported by the findings of parallel aging mechanisms in the cutaneous and the systemic vasculature and cutaneous microvascular abnormalities in individuals with various cardiovascular risk factors and generalized systemic illnesses, such as diabetes and heart disease [7].

Laser Doppler technique provides an index of skin perfusion, which is quantified as a product of average red blood cell velocity and concentration. It is often referred to as flux because it does not provide an exact measure of flow (ml/min), but linear relationship between flux and actual flow has been demonstrated [1].

Compared with healthy controls, heart failure patients experienced markedly decreased (by 38%, P < 0.01) cutaneous flux. Variability of skin microcirculation (σ), was also reduced by 55% (P < 0.01), reflecting attenuation of regulatory mechanisms in CHF (Table 1).

Table 1
Microcirculation parameters in controls and in patients with CHF

Parameter Controls (n = 33) CHF (n = 46) P-value

MI, p.u. 11.5±6.1 7.16±3.71 <0.01

σ, p.u. 1.39±0.94 0.627±0.275 <0.01

Kv, % 12.4±5.2 12.7±9.7 >0.05

SO₂, % 54.3±9.0 71.5±5.6 <0.01

Vr, % 9.08±3.04 13.0±3.4 <0.01

U, r. u. 5.34±1.46 3.23±0.71 <0.01

Parameter	Controls (n = 33)	CHF (n = 46)	P-value
MI, p.u.	11.5±6.1	7.16±3.71	<0.01
σ, p.u.	1.39±0.94	0.627±0.275	<0.01
Kv, %	12.4±5.2	12.7±9.7	>0.05
SO₂, %	54.3±9.0	71.5±5.6	<0.01
Vr, %	9.08±3.04	13.0±3.4	<0.01
U, r. u.	5.34±1.46	3.23±0.71	<0.01

Values are means±SD, MI - microcirculation index; σ - standard deviation of MI; Kv - coefficient of variation of MI; SO₂ - HbO₂ percentage in whole blood in a tested area; Vr - relative content of hemoglobin fractions in a tested area; U – index of specific oxygen consumption by tissue; p.u. - perfusion units, r.u. - relative units.

Microcirculatory oscillations in CHF had significantly lower maximal amplitudes in the endothelial (by 45%, P < 0.01), neurogenic (by 74%, P < 0.01), myogenic (by 73%, P < 0.01), respiratory (by 60%, P < 0.01), and cardiac (by 48%, P < 0.01) frequency bands (Fig. 1). Normalized amplitudes of the endothelial, neurogenic, myogenic, and respiratory rhythms were reduced by 21% (P < 0.05), 41%, 40%, (P < 0.01), and 14%, (P < 0.05), respectively, and those of cardiac rhythms were by 35% higher than in controls (P < 0.01) (Fig. 2).

Fig.1

Maximal amplitudes of microcirculation oscillation (E – endothelial, N – neurogenic, M – myogenic, R – respiratory, C – cardiac rhythms).

Fig.2

Normalized amplitudes of microcirculation oscillation (E – endothelial, N – neurogenic, M – myogenic, R – respiratory, C – cardiac rhythms).

Bulk flow in microcirculatory bed is determined by the activity of cardiac rhythms providing influx and respiratory rhythms ensuring blood outflow. Depression of these regulatory mechanisms in CHF as well as decreased MI indicated the restricted blood flow in microcirculatory network. Markedly reduced amplitudes of microvascular oscillations of neurogenic and myogenic origin are evidence of elevated tonus of resistance microvessels additionally restricting blood flow. Endothelial rhythms, depending on the vasodilatory activity of microvessel endothelium, were depressed in CHF pointing the abnormalities in vasomotor function of microvessel endothelium in these patients. Thus, our data indicated that the abnormal vasomotor tone of microvessels in CHF was due to the increased vasoconstrictor influences as well as due to the decreased vasodilator capacity of endothelium. Maximal amplitudes of cardiac rhythms (0.168 r.u. vs 0.322 r.u. in control) were markedly reduced in CHF, but normalized amplitudes of these oscillations (9.2% vs 6.8% in healthy control) were enhanced due to the substantially decreased variability of microvascular blood flow (σ) in CHF. In the case of abrupt change of microcirculation index (MI) and its standard deviation (σ), normalized amplitudes are useful for the evaluation of the differentiated contribution of various regulatory rhythms in microvascular blood flow modulation. Increased normalized amplitude of cardiac oscillations in CHF pointed the elevated contribution of these rhythms in the modulation of the microcirculation, aiming to ensure the blood supply to tissues; but these efforts were insufficient because of the malfunction of cardiac pump. Such complex deterioration of microvascular blood flow in CHF caused the dramatically decrease of oxygen supply to tissue. Oxygen saturation of hemoglobin (SO₂) as well as the relative content of hemoglobin fractions in a tested area (Vr) in CHF were substantially higher than in control mainly due to the increase of Hct value (Tables 1, 2), but the index of specific oxygen consumption by tissue (U) was by 38% (P < 0.05) lower compared to the healthy control.

Table 2

Hemorheological parameters in controls and in patients with CHF

Parameter	Controls (n = 33)	CHF (n = 46)	P-value
Hct, %	43.5±4.2	45.2±3.9	<0.05
Plasma viscosity, mPa · s	2.14±0.24	2.30±0.20	<0.01
EA, r.u.	0.114±0.064	0.177±0.086	<0.01
SA, r.u.	4.98±1.13	5.24±2.16	>0.05
EI, r.u.	0.362±0.012	0.333±0.026	<0.01
HVR, r.u.	6.69±0.75	5.59±0.77	<0.01

Values are means±SD, EA - extent of RBC aggregation; SA - mean size of RBC aggregates; EI - index of elongation of erythrocytes; HVR - hematocrit-to-viscosity ratio, r.u. - relative units.

One of the factors causing hindered gas exchange between the blood and tissues are altered microrheological properties of red blood cells (their deformability and aggregability). Increased aggregability of RBC impedes oxygen diffusion to tissue causing formation of vascular wall plasma cell-free layer. RBC aggregation also has been shown to be an important determinant of endothelial function through its effects on RBC axial distribution and wall shear stress [2].

Hemorheological parameters in heart failure patients were unfavorably changed: whole blood viscosity in CHF was enhanced by 23% at high-shear flow (P < 0.01) and by 33% at low-shear flow (P < 0.01) versus controls (Fig. 3). We also noted increases in Hct (by 4%, P < 0.05), plasma viscosity (by 33%, p < 0.01), extent of red blood cell aggregation (by 56%, p < 0.01), and a decline in erythrocyte deformability (by 8%, p < 0.01) (Table 2). The main determinants of whole blood viscosity are: Hct, plasma viscosity, RBC aggregability and deformability [3]. All these rheological parameters were negatively altered in CHF – the rise of high shear blood viscosity was determined by the increase of Hct, plasma viscosity and to some extent by the decrease of RBC deformability. Slight increase of erythrocyte rigidity might extend their residence time within microvessels favoring oxygen extraction and tissue perfusion and may be considered as a compensatory mechanism aimed to improve oxygen supply to tissue in CHF [5]. The main reason of the low shear blood viscosity elevation was dramatically increased erythrocyte aggregation. Enhanced blood and plasma viscosity facilitates the rise of wall shear stress, causing compensatory vasodilation and enhancing bulk flow in norm, but in CHF this mechanism cannot be realized because endothelial vasodilatory capacity is exhausted.

Fig.3

Whole blood viscosity in control and in CHF under various shear stress: 1 – 1.06 Pa; 2 – 0.85 Pa; 3 – 0.64 Pa; 4 – 0.42 Pa; 5 – 0.21 Pa.

It was found that the rheological disorders are manifested in the early stages of the cardiovascular disease before its functional manifestation. A negative relationship between erythrocyte aggregability and the ejection fraction of the left ventricle and the positive correlation between erythrocyte aggregability and left ventricle hypertrophy (p < 0.01) were registered [26]. Urdulashvili et al. (2006) concluded that the blood rheological disorders represent themselves a factor that plays a significant role in pathogenesis of the coronary heart disease and they are not only risk factors as it is generally believed but they might serve as predictors of the disease.

Hypoxemia observed in heart failure causes increased erythrocyte production and hematocrit rise, aiming to enhance oxygen transport, but excessive hematocrit can lead to blood hyperviscosity with a concomitant increase of tissue hypoxia [24]. Despite the increase of Hct (the number of RBC - main carrier of oxygen) in CHF, hemorheological index of oxygen supply to tissue (HVR) was by 16% (P < 0.01) lower than in control due to the dramatically worsened blood viscosity. The hematocrit-to-viscosity ratio (HVR) has been widely used for estimation of red blood cell oxygen transport effectiveness into the microvasculature or as an oxygen delivery index. It was demonstrated that microvascular oxyhemoglobin saturation measured by spatial resolved near-infrared spectroscopy at cerebral and muscle levels was positively correlated with HVR, pointing that this index may to some extent reflect blood oxygen capacity not excluding the role of other determinants modulating microvascular blood flow and oxygenation, such as vascular geometry and vasomotor reserve [27]. So that HVR may be considered as a powerful indicator of blood oxygen transport efficacy at the microcirculation level in CHF because vasomotor reserve in these patients is exhausted.

Significant changes in hemorheological properties (increased blood and plasma viscosity, elevated red blood cell aggregation) likely accelerate disease progression in heart failure, because the concomitant tissue hypoxia affects a vicious circle, aggravating heart failure. In CHF, when the vascular autoregulatory reserve is exhausted, hemorheological disturbances that can be easily compensated in healthy individuals will have deleterious effects [8].

4 Conclusion

The hallmarks of functioning of system of microcirculation in CHF were restricted microvascular blood flow and attenuation of regulatory mechanisms. In these conditions the hemorheological factors could acquire special significance; while dramatically deteriorated in CHF blood rheological properties could not be compensate by depressed autoregulatory mechanisms. This complex impairment of peripheral blood flow caused the reduced oxygen utilization that probably contributes to worsening of symptoms and advance of heart failure.

Footnotes

Acknowledgments

Work was supported by the Russian Foundation for Basic Research grant 14-04-01703-a. The authors comply with the Ethical Guidelines for Publication in Clinical Hemorheology and Microcirculation as published on the IOS Press website and in Volume 63, 2016, pp. 1-2 of this journal.

References

Ahn

, Johansson

, Lundgren

and Nilsson

G.E.

, In vivo evaluation of signal processors for laser Doppler tissue flowmeters, Med Biol Eng Comput 25(2) (1987), 207–211.

Baskurt

O.K.

, In vivo correlates of altered blood rheology, Biorheology 45(6) (2008), 629–382.

Baskurt

O.K.

, Hardeman

M.R.

, Rampling

M.R.

and Meiselman

H.J.

, Handbook of hemorheology and hemodynamics. Amsterdam: IOSPress; 2007.

Edvinsson

M.-L.

, Uddman

and Andersson

S.E.

, Deteriorated function of cutaneous microcirculation in chronic congestive heart failure, J Geriatr Cardiol 8(2) (2011), 82–87. doi: 10.3724/SP.J.1263.2011.00082

Gori

, Forconi

, Endothelium and Hemorheology, in: Handbook of Hemorheology and Hemodynamics, Baskurt

O.K.

, Hardeman

M.R.

, Ramling

M.W.

, Meiselman

eds, Amsterdam: IOS Press, 2007, pp. 339–350.

Hirai

D.M.

, Copp

S.W.

, Holdsworth

C.T.

, Ferguson

S.K.

, McCullough

D.J.

, Behnke

B.J.

, Musch

T.I.

and Poole

D.C.

, Skeletal muscle microvascular oxygenation dynamics in heart failure: Exercise training and nitric oxide-mediated function, Am J Physiol Heart Circ Physiol 306(5) (2014), H690–H698. doi: 10.1152/ajpheart.00901.2013

Holowatz

L.A.

and Kenney

W.L.

, Peripheral mechanisms of thermoregulatory control of skin blood flow in aged humans, J Appl Physiol 109(5) (2010), 1538–1544. doi: 10.1152/japplphysiol.00338.2010

Intaglietta

, Increased blood viscosity: Disease, adaptation or treatment? Clin Hemorheol Microcirc 42 (2009), 305–306. doi: 10.3233/CH-2009-1236

Kitzman

D.W.

, Nicklas

, Kraus

W.E.

, Lyles

M.F.

, Eggebeen

, Morgan

T.M.

and Haykowsky

, Skeletal muscle abnormalities and exercise intolerance in older patients with heart failure and preserved ejection fraction, Am J Physiol Heart Circ Physiol 306(9) (2014), H1364–H1370. doi: 10.1152/ajpheart.00004.2014

10.

Knaut

, Matschke

, Plötze

, Steinmann

, Mrowietz

and Jung

, Cutaneous and muscular microcirculation in patients with terminal heart failure awaiting transplantation, Clin Hemorheol Microcirc 52(2-4) (2012), 217–227. doi: 10.3233/CH-2012-1599

11.

Kvandal

, Landsverk

S.A.

, Bernjak

, Stefanovska

, Kvernmo

H.D.

and Kirkebøen

K.A.

, Low-frequency oscillations of the laser Doppler perfusion signal in human skin, Microvasc Res 72(3) (2006), 120–127.

12.

Matschke

and Jung

, Regulation of the myocardial microcirculation, Clin Hemorheol Microcirc 39(1–4) (2008), 265–279.

13.

Muravyev

A.V.

, Tikhomirova

I.A.

, Muravyev

A.A.

, Bulayeva

S.V.

and Maimistova

A.A.

, Methods of the experimental and clinical studies of erythrocyte deformability, Klin Lab Diagn 1 (2010), 28–32.

14.

Negrao

C.E.

, Hamilton

M.A.

, Fonarow

G.C.

, Hage

, Moriguchi

J.D.

and Middlekauff

H.R.

, Impaired endothelium-mediated vasodilation is not the principal cause of vasoconstriction in heart failure, Am J Physiol Heart Circ Physiol 278(1) (2000), H168–H174.

15.

Rossi

, Matteucci

, Gaddeo

, Giampietro

and Santoro

, Preserved endothelial-dependent and endothelial-independent skin vasodilator responses in relatives of type 1 diabetes patients, Microvasc Res 78(2) (2009), 253–255. doi: 10.1016/j.mvr.2009.04.007

16.

Roustit

and Cracowski

J.L.

, Non-invasive assessment of skin microvascular functions in humans: An insight into methods, Microcirculation 19(1) (2012), 47–64. doi: 10.1111/j.1549-8719.2011.00129.x

17.

Roustit

and Cracowski

J.-L.

, Assessment of endothelial and neurovascular function in human skin microcirculation, Trends in Pharmacol Sci 34(7) (2013), 373–384. doi: 10.1016/j.tips.2013.05.007

18.

Schmid-Schönbein

, Ziege

, Grebe

, Blazek

, Spielmann

and Linzenich

, Synergetic interpretation of patterned vasomotor activity in microvascular perfusion: Discrete effects of myogenic and neurogenic vasoconstriction as well as arterial and venous pressure fluctuations, Int J Microcirc Clin Exp 17(6) (1997), 346–359.

19.

Shantsila

, Wrigley

, Andrew

, Blann

, Gill

and Lip

, A contemporary view on endothelial function in heart failure, Eur J Heart Fail 14(8) (2012), 873–881. doi: 10.1093/eurjhf/hfs066

20.

Stefanovska

, Bracic

and Kvernmo

H.D.

, Wavelet analysis of oscillations in the peripheral blood circulation measured by laser Doppler technique, IEEE Trans Biomed Eng 46(10) (1999), 1230–1239.

21.

Stefanovska

, Lotric

M.B.

, Strle

and Haken

, The cardiovascular system as coupled oscillators? Physiol Meas 22(3) (2001), 535–550.

22.

Stoltz

J.F.

, Donner

, Muller

and Larcan

, Hemorheology in clinical practice. Introduction to the notion of hemorheologic profile, J Mal Vasc 16(3) (1991), 261–270.

23.

Tikhomirova

, Oslyakova

and Mikhailova

, Microcirculation and blood rheology in1 patients with cerebrovascular disorders, Clin Hemorheol Microcirc 49(1–4) (2011), 295–305. doi: 10.3233/CH-2011-1480

24.

Toth

, Kesmarky

, Alexy

, Clinical significance of hemorheological alterations, in: Handbook of Hemorheology and Hemodynamics, Baskurt

O.K.

, Hardeman

M.R.

, Ramling

M.W.

, Meiselman

, eds, Amsterdam: IOS Press; 2007, pp. 392–432.

25.

Trinity

J.D.

and Richardson

R.S.

, Integrative research: The key to unlocking the mysteries of chronic heart failure and skeletal muscle dysfunction, Am J Physiol Heart Circ Physiol. 299(6) (2010), H1750–H1752. doi: 10.1152/ajpheart.00984.2010

26.

Urdulashvili

, Momtselidze

, Mantskava

, Narsia

and Mchedlishvili

, Hemorheological, microvascular and hemodynamic disorders during coronary heart disease, Georgian Med News 136 (2006), 55–57.

27.

Waltz

, Hardy-Dessources

M.D.

, Lemonne

, Mougenel

, Lalanne-Mistrih

M.L.

, Lamarre

, Tarer

, Tressières

, Etienne-Julan

, Hue

and Connes

, Is there a relationship between the hematocrit-to-viscosity ratio and microvascular oxygenation in brain and muscle? Clin Hemorheol Microcirc 59(1) (2015), 37–43. doi: 10.3233/CH-131742