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REFERENCES Mgr. Farag Hassan Anais - Masaryk University

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REFERENCES Mgr. Farag Hassan Anais - Masaryk University

    Masaryk University

    Faculty of Medicine

    Department of Preventive Medicine

    BAROREFLEX HEART RATE SENSITIVITY

    IN PATIENTS WITH ISCHEMIC

    HEART DISEASE

    Dissertation thesis

Supervisor of dissertation thesis: Author:

    Prof. MUDr. Jarmila Siegelová, DrSc. Mgr. Farag Hassan Anbais

    Brno, November 2010

Author„s name and surname: Mgr. Farag Hassan Anbais

    Name of disseration thesis: Baroreflex heart rate sensitivity in patients with ischemic

    heart disease

Working compartment: Masaryk University, Faculty of Medicine

    Dept. of Preventive Medicine

Dissertation thesis supervisor: Prof. MUDr. Jarmila Siegelová, DrSc.

Year of dissertation thesis defense: 2010

    Annotation: This disseration thesis deals with autonomic nervous system dysfunction studied using baroreflex heard rate sensitivity in patients with ischemic heart disease before and after cardiac rehabilitation. For determination baroreflex heart rate sensitivity the measurement of blood pressure beat by beat was used to analyze of baroreflex sensitivity. Cardiac exercise training increased baroreflex heart rate sensitivity.

    I agree with archivation of dissertation thesis in library of Masaryk University Brno and publication with quoting according to valid norms.

PROCLAMAITON

    I declare that this dissertation prepared under the direction of self under supervision of prof. MUDr. Jarmila Siegelová, DrSc. and that I stated in the list of bibliographic citations, which is part of this work, all the literary and technical resources

     .........................................

    Brno, CZ Mgr. Farag Hasan Anbais

    I would like to thank all my colleagues from the Department of Physiotherapy and Rehabilitation, Department of Functional Diagnostics and Rehabilitation and Department of Preventive Medicine, Medical Faculty, Masaryk University and professor MUDr. Jarmila Siegelová, DrSc. for the support.

    CONTENT

    1 INTRODUCTION ............................................................................................................. 7

    Baroreflex mechanisms ..................................................................................................... 7 Anatomical units ............................................................................................................... 7 Elementary Reflex Arc of the baroreceptor ....................................................................... 8

    Single-Fiber Recordings ................................................................................................... 9 Multifiber Recordings ..................................................................................................... 10 The results on multifibre experiments ............................................................................. 11 Anatomy of nervous structures ........................................................................................ 12 Connections to other nervous centers ............................................................................. 13 Output from the nucleus tractus solitarius....................................................................... 13

    Motor Systems of sympathetic motor fibres ..................................................................... 14

    Arterial Baroreceptor Function and Exercise ................................................................... 15 Cardiovascular Responses to Exercise ............................................................................ 15 Static Exercise ................................................................................................................ 16 Rhythmic Exercise .......................................................................................................... 16 Resetting of Arterial Baroreceptors During Exercise ....................................................... 18 Studies in Humans .......................................................................................................... 19 Baroreflex testing ........................................................................................................... 19

    Baroreflex sensitivity testing during challenge maneuvers .................................................... 20

    Pharmacological approach .............................................................................................. 21 Neck suction ................................................................................................................... 21

    Sinusoidal neck suction ................................................................................................... 23 Valsalva maneuver ......................................................................................................... 24 Baroreflex sensitivity testing at rest ................................................................................ 25 Cardiovascular rehabilitation ......................................................................................... 26 Cardiology and Cardiovascular Rehabilitation Unit ....................................................... 28

    Aerobic exercise testing .................................................................................................. 30 Aerobic exercise training ................................................................................................ 32 Resistant training ........................................................................................................... 32

    2 AIM ................................................................................................................................ 34

    3.1 EXERCISE TRAINING LASTING 12 WEEKS IN PATIENTS WITH .................. 35

    CORONARY ARTERY DISEASE ................................................................................ 35

3.1.1 Introduction ....................................................................................................... 35

3.1.2 Aim of the study.................................................................................................. 35

3.1.3 Methods ............................................................................................................. 35

3.1.4 Results ............................................................................................................... 40

3.1.5 Discussion.......................................................................................................... 45

3.1.6 Conclusion ......................................................................................................... 45

3.2 COMBINED AEROBIC AND RESISTANCE CARDIOVASCULAR TRAINING

    IN PATIENTS WITH CORONARY HEART DISEASE: CONTINUOUS AEROBIC

    TRAINING .................................................................................................................... 46

    3.2.1 Introduction ....................................................................................................... 46 3.2.2 Aim of the study.................................................................................................. 46 3.2.3 Methods ............................................................................................................. 47 3.2.4 Results ............................................................................................................... 50 3.2.5 Discussion.......................................................................................................... 57 3.2.6 Conclusion ......................................................................................................... 57 3.3 COMBINED AEROBIC AND RESISTANCE CARDIOVASCULAR TRAINING

    IN PATIENTS WITH CORONARY HEART DISEASE: INTERVAL AEROBIC

    TRAINING .................................................................................................................... 58

    3.3.1 Introdustion ....................................................................................................... 58 3.3.2 Aim of the study.................................................................................................. 58 3.3.3 Methods ............................................................................................................. 58 3.3.4 Results ............................................................................................................... 62 3.3.5 Discusision ........................................................................................................ 68 3.3.6 Conclusion ......................................................................................................... 69 4 DISCUSSION ................................................................................................................. 70

    5 CONCLUSION ............................................................................................................... 73

    6 SUMMARY .................................................................................................................... 74

    7 REFERENCES ................................................................................................................ 76

    REFERENCES Mgr. Farag Hassan Anbais ......................................................................... 90

1 INTRODUCTION

Baroreflex mechanisms

    Baroreflex plays the important role in control of blood pressure. It is a reflex feed-back mechanism that operates to stabilize the blood pressure and heart rate. Baroreflex is composed from receptors, afferent pathways, cardioexcitatory and cardioinhibitory centres and vasomotor centers in central nervous system, efferent pathways and effectors-heart and blood vessels.

    Anatomical units

    The elements of the baroreceptor reflex are the sensory receptors called baroreceptors. The nerves which run from them to the brain stem, the central integrating nuclei, the sympathetic and parasympathetic motor fibers, and the heart and the blood vessels.

    Arterial baroreceptors are: the carotid sinus receptors and the aortic arch receptors. Carotid receptors lie in the wall of the internal carotid artery on either side. Baroreceptor sends impulses in the nerve of Hering, which also carries information centrally from the carotid chemoreceptors. Aortic arch baroreceptors are found in the vicinity of the aortic arch. From the aortic receptors, excitation travels centrally in small vagal branches containing baroreceptor fibers and other sensory and motor nerve fibres. Peripheral aortic fibers originate at the right subclavian artery (Heymans C, Neil E 1958). Nervous fibres from the receptors in the aortic region form two aortic depressor nerves which carry nervous impulses centrally, as part of the vagal trunk.

    The cardiopulmonary receptors send their nervous impulses centrally through small vagal branches. Impulses from arterial baroreceptors are carried to the nucleus tractus solitarius in the medulla, the site of the first synapse in the baroreceptor reflex. The output from nucleus tractus solitarius is to sympathetic preganglionic neurons in the inter-medio-lateral cell column of the thoracic spinal cord and the nucleus ambiguus and the dorsal motor nucleus of the vagus (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

    The sympathetic outflow passes to the sympathetic white ramus fibres and form the postganglionic sympathetic fibres. These fibres innervate the heart and the arterioles in most vascular beds. The parasympathetic outflow is via cardiac vagal efferents which exit from the main vagal trunk. The sympathetic nervous fibres innervate the heart, where they alter heart rate atrioventricular conduction, myocardial contractility and coronary vascular resistance.

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    The vagal nervous fibres significantly alter heart rate and also have effects on atrioventricular conduction (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

Elementary Reflex Arc of the baroreceptor

    The baroreceptor reflexes are sensitive to pressure and rate of change of pressure and increase their firing rate as either of these increases. The receptors send impulses to the medullary integrating centres in nucleus tractus solitarius, which transform the firing of the sensory nerves to impulses in the motor sympathetic and vagal fibres from the medulla oblongata is via vagal efferents and sympathetic efferent fibres. The vagal efferents significantly control the heart rate, and the sympathetic efferents control the heart rate, myocardial contractility and peripheral resistance (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

    If arterial pressure decreases as in a hemorrhage, baroreceptor firing will decrease, sympathetic motor firing will due to reflex mechanism increase, and vagal firing will due to reflex mechanism decrease. With the decrease in vagal firing and increase in sympathetic firing, the heart rate will increase. The increased sympathetic motor activity will also increase myocardial contractility and the vascular resistance of most of the peripheral arterioles. Both contractility and resistance will increase. The result of a fall in arterial pressure will be an increased heart rate and contractility, which will tend to increase cardiac output or minimize its decrease, and an increase in peripheral vascular resistance. The product of cardiac output and peripheral resistance is arterial blood pressure. A fall in blood pressure therefore initiates compensatory changes in output and resistance which tend to restore the blood pressure and blood flow (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

    Our knowledge of the baroreceptor function is based on the earlier experiments. They are some components of the baroreflex which are studied in different animal preparations. The

    scientists studied the conversion of arterial pressure to nerve firing in single-fiber or multi-fiber preparations. They analyzed and examined the conversion of sensory information (nerve activity from the baroreceptors) into sympathetic and vagal motor nerve activity within the medulla. They also examined the conversion of the motor nerve activity into changes in heart rate and peripheral resistance. The systemic control of blood pressure was examined as the changes in heart rate and peripheral resistance and changes in arterial blood pressure (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

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Single-Fiber Recordings

    There are differences between receptors which have myelinated axons and those which have unmyelinated axons, and there are differences between the carotid and aortic receptors, but these will not be considered here (Koushanpour et al. 1991, Brown et al.1980). The effector side of the reflex, will be concerned with the reflex effects of individual carotid receptors or aortic receptors with the effects of variations in arterial pressure profile on the receptors. Receptor responses are best studied in single nerve fibres from baroreceptors. The receptors show a threshold to static pressure. Above this threshold the baroreceptors increase firing quite linearly with increase in pressure. At a high pressure, the response levels off or limits. The description is valide in condition of nonpulsatile pressure (Brown et al. 1976). In response to a positive-going ramp of pressure at a single receptor, the firing level at a given pressure will be higher than for a static pressure at that pressure. For a decreasing pressure ramp, the firing level will be lower (Landgren et al. 1952).

    When a pulsatile pressure change, like the arterial pressure pulse, is superimposed on a mean pressure which is just below the static firing threshold, the receptor will discharge when the instantaneous pressure is below the threshold. Positive rate of change of pressure will make the receptor fire slightly below the static threshold. As the pressure decreases, the receptor will turn off. The effect of the added pressure pulsations here is to make the receptor fire at a mean pressure below the static threshold. This is a dynamic nonlinear effect. A study by Katona et al. (1977) indicates that, when subjected to pressure changes like normal arterial pressure waveform, the receptor has a nearly invariant firing pattern, but with repeated slow ramp-like changes the firing pattern may vary slightly.

    In a study of the responses of single baroreceptor fibres to pulsatile pressure, Arndt et al. examined the correlation between several stimulus variables systolic pressure, diastolic

    pressure, mean pressure, pulse pressure, peak positive rate of change of pressure (dp/dt) and

    several response variables e.g. average discharge rate, peak instantaneous frequency, average burst frequency. They found that the only significant relationships were between the nonphasic pressure terms (systolic, diastolic, or mean pressure) and the average discharge rate. Examinations of their plots of the activity of single fibres shows a very linear relationship between average discharge rate and mean pressure over a range of 100 mmHg pressure change above the threshold (Arnt et al., 1977). They did not discuss the combined effects of mean and pulse pressure changes.

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    The studies cited above have been performed on single fibers dissected out of the whole baroreceptor nerve. This is a tedious dissection, but the results are clear and can easily be quantified. The changes in spike frequency can usually be determined visually. A possible disadvantage is that a single fibre so studied may not be representative of all other fibres, but recordings might be made from several fibres in this fashion and the results summed or averaged. The most important characteristics of the single baroreceptor fibres are studied in non-pulsative and pulsative conditions. They generally exhibit a threshold below which no firing occurs when the receptors are subjected to static - nonpulsatile pressures. At the threshold, the receptor begins to fire at a rate of many impulses per second. The threshold is abrupt and not gradual. We can conclude the results in single fibre record. Above this threshold, the firing increases linearly with pressure over a substantial pressure range and the receptor show limiting at high pressure (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

    With pulsatile pressure the receptors show a response to rate of change of pressure. This can cause the receptor to fire at a pressure below the static threshold. It can lead to a nonlinear behaviour of the receptor since near threshold firing can increase with positive rates of change of pressure, but cannot decrease symmetrically with decreasing rates of change of pressure.

Multifiber Recordings

    Nerve fibers from the individual carotid and aortic baroreceptors join the carotid sinus nerve and the aortic depressor nerve. In many studies of receptors, records are taken from these nerves directly or from several or many fibres separated from these nerves.

    Recording from several or many nerve fibres has its advantages it gives a sample of whole

    nerve activity and it avoids the arduous task of splitting a whole nerve down to a single strand. The nerve may be damaged during the dissection, and may dry out and cease to fire more easily after the dissection. It has several disadvantages which make quantification of the firing difficult (Persson, Kirchheim, 1991, Malik 1998, Hilz 2002).

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