Brief Overview of Autonomic Function Tests
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For most of us, stress maybe be a exam, a presentation or some personal goal you are working on. Stress is a word with broad meaning and is part and parcel of our day to day life. Now lets think or a patient with say, orthostatic hypotension, the mere act of standing up from a chair is a stress that he gives to the body. So regardless of whatever the stressor is, there is a system in our body which works tirelessly day after night in the background, that carefully orchestrates the body machinery to meet the challenges we throw at it. That strives for the golden state, that we physiologists love , homeostasis or the maintenance of milieu interior. That system to which we should be thankful to is the autonomic system. Now in this presentation, we will talk about it but mainly about a brief overview of the autonomic function tests that are used for its assessment.
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Brief Overview of Autonomic Function Tests
- 1. Brief overview of Autonomic Function Tests Presenter : Dr. Saran A K Preceptors : First Unit Faculty DM Seminar | 08 December 2023 DEPT. OF PHYSIOLOGY, AIIMS PATNA 1
- 2. 2
- 3. homeostasis DEPT. OF PHYSIOLOGY, AIIMS PATNA 3
- 4. Autonomic Nervous System DEPT. OF PHYSIOLOGY, AIIMS PATNA 4
- 5. DEPT. OF PHYSIOLOGY, AIIMS PATNA 5 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 6. DEPT. OF PHYSIOLOGY, AIIMS PATNA 6 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 7. Autonomic Nervous System • Controls visceral functions. • Maintains homeostasis. • Rapidity and Intensity Autonomic (adj) /ɔːtəˈnɒmɪk/ self governing, functionally independent DEPT. OF PHYSIOLOGY, AIIMS PATNA 7
- 8. Divisions of ANS 1. Sympathetic Nervous System 2. Parasympathetic Nervous System 3. Enteric Nervous System DEPT. OF PHYSIOLOGY, AIIMS PATNA 8
- 9. DEPT. OF PHYSIOLOGY, AIIMS PATNA 9 Introduction to Quantitative EEG and Neurofeedback, 3rd Edition
- 10. How does the ANS work? Operates via the visceral reflex, top-down control of higher centers Viscera Integration center in CNS Receptor Afferent Pathway Efferent Pathway DEPT. OF PHYSIOLOGY, AIIMS PATNA 10
- 11. ANS General Organization Pre-ganglionic Neuron Post- ganglionic Neuron Target Organ Located in CNS Located in peripheral ganglia DEPT. OF PHYSIOLOGY, AIIMS PATNA 11
- 13. Dysautonomia / Autonomic Dysfunction • The types of dysfunction can range from complete autonomic failure to autonomic hyperactivity. • Causes like drugs, neurodegenerative diseases, trauma, inflammatory processes, and neoplasia DEPT. OF PHYSIOLOGY, AIIMS PATNA 13
- 14. Clinical Manifestations • Autonomic failure : orthostatic hypotension, neurogenic syncope, erectile dysfunction, neurogenic bladder, gastrointestinal dysmotility, sudomotor failure, and Horner syndrome. • Autonomic hyperactivity : can be the basis for neurogenic hypertension, cardiac arrhythmias, neurogenic pulmonary oedema etc. DEPT. OF PHYSIOLOGY, AIIMS PATNA 14
- 15. DEPT. OF PHYSIOLOGY, AIIMS PATNA 15 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 16. DEPT. OF PHYSIOLOGY, AIIMS PATNA 16 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 17. Autonomic Function Testing 1. Quantitative evaluation of autonomic function domains 2. Assess severity and distribution of dysautonomia 3. In determining the site of the lesion 4. To ascertain whether the abnormality is of primary or secondary 5. Monitor disease course and responses to treatment 6. Research uses DEPT. OF PHYSIOLOGY, AIIMS PATNA 17 Low PA, Tomalia VA, Park KJ. Autonomic function tests: some clinical applications. J Clin Neurol. 2013;9(1):1-8.
- 18. Autonomic Function Tests Test Domain Systems Tested Tests Physiological Cardiovascular Deep Breathing Test, Tilt Table Test, Valsalva Maneuver, Isometric exercise, Cold Pressor Test, Orthostatic Test Sudomotor Sweat Glands Thermoregulatory Sweat test, Quantitative Sudomotor Axon Reflex Test, Sympathetic skin response Biochemical General Plasma noradrenaline, Renin activity, Urinary catecholamines, Urodynamics Renal Urodynamic studies, Sphincter Electromyography Sexual Reproductive Penile Plethysmography Ophthalmological Vision Schimmer’s Test, Pupillary Functions DEPT. OF PHYSIOLOGY, AIIMS PATNA 18 Sathyaprabha TN, Kaviraja Udupa, Autonomic Nervous System Evaluation : Bedside Conventional Methods, CNSW2023 NIMHANS
- 19. Autonomic Function Tests • Cardio autonomic Testing • Ewing's Battery of Tests • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor Testing DEPT. OF PHYSIOLOGY, AIIMS PATNA 19
- 20. DEPT. OF PHYSIOLOGY, AIIMS PATNA 20 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 21. DEPT. OF PHYSIOLOGY, AIIMS PATNA 21 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 22. A. Ewing's Battery Battery of 5 clinical tests to assess cardiac autonomic reflexes 1. Head-up Tilt (HUT) / Lying to Standing Test (LST) 2. Deep Breathing Test 3. Valsalva Manoeuvre 4. Isometric Handgrip Test 5. Cold Pressor Test DEPT. OF PHYSIOLOGY, AIIMS PATNA 22
- 23. DEPT. OF PHYSIOLOGY, AIIMS PATNA 23 Baroreceptor reflex Threshold 50 mmHg with maximal sustained firing at approximately 200 mm Hg. Ganong’s Review of Medical Physiology 22nd Edition
- 24. 1. Head-up Tilt (HUT) / Lying to Standing Test (LST) • A fall in systolic BP (SBP) up to 20 m Hg and diastolic BP (DBP) up to 10 mm Hg is considered normal. DEPT. OF PHYSIOLOGY, AIIMS PATNA 24
- 25. DEPT. OF PHYSIOLOGY, AIIMS PATNA 25 Cheshire, W.P., Goldstein, D.S. Autonomic uprising: the tilt table test in autonomic medicine. Clin Auton Res 29, 215–230 (2019).
- 26. DEPT. OF PHYSIOLOGY, AIIMS PATNA 26
- 27. 1. Head-up Tilt (HUT) / Lying to Standing Test (LST) • 30:15 Ratio – longest RR interval in ECG around 30th beat / longest RR interval in ECG around 15th beat after adoption of standing/head tilt posture should be greater than 1.04. • Test for parasympathetic function DEPT. OF PHYSIOLOGY, AIIMS PATNA 27
- 28. DEPT. OF PHYSIOLOGY, AIIMS PATNA 28 = 1.03 (↓) 30th RR 15th RR 30:15 Ratio
- 29. 2. Deep Breathing Test • Test of parasympathetic influence. • The subject is asked to breathe slowly and almost fully to their vital capacity - 5 seconds inspiration, 5 seconds expiration. • Deep breathing difference (DBD) is calculated from the mean of differences between maximum heart rate during inspiration and minimum heart rate during expiration for six such cycles. • DBD of more than 15 is considered normal. DEPT. OF PHYSIOLOGY, AIIMS PATNA 29
- 30. DEPT. OF PHYSIOLOGY, AIIMS PATNA 30 Deep Breathing Difference = 10 (↓) 2 3 4 5 6
- 31. • The increase of heart rate during inhalation and a decrease during exhalation, known as the respiratory sinus arrhythmia is pronounced in DBT. • Expiratory-inspiratory ratio (E:I ratio), which is the ratio of the longest RR interval during expiration and the shortest RR interval during inspiration from 5 cycles, can also be determined and should be higher than 1.2. DEPT. OF PHYSIOLOGY, AIIMS PATNA 31
- 32. 3. Valsalva Manoeuvre • Valsalva manoeuvre, a forced breathing exercise with open glottis and an expiratory pressure of 45mmHg for 15 seconds against resistance. • Used to assess the cardiovagal heart rate response as well as and the sympathetic adrenergic blood pressure response. DEPT. OF PHYSIOLOGY, AIIMS PATNA 32
- 33. Phase Maneuver Blood Pressure Heart Rate I Onset of expiration against partially closed glottis Rises due to aortic compression Decreases II early Continued expiration Falls due to decreased venous return Increases II late Continued expiration Increased sympathetic discharge causing increased total peripheral vascular resistance Increases at a slower rate III End of expiration Falls due to increased capacitance of pulmonary bed Increases further IV Recovery Increases (overshoot) due to vasoconstriction and increased cardiac output. Compensatory bradycardia DEPT. OF PHYSIOLOGY, AIIMS PATNA 33 Sathyaprabha TN, Kaviraja Udupa, Autonomic Nervous System Evaluation : Bedside Conventional Methods, CNSW2023 NIMHANS
- 34. DEPT. OF PHYSIOLOGY, AIIMS PATNA 34
- 35. • As a measure of parasympathetic function, the heart rate response in the Valsalva maneuver is analyzed by the Valsalva ratio. • Valsalva ration is calculated by maximum phase II tachycardia and minimum phase IV bradycardia . • A larger Valsalva ratio indicates more “normal” parasympathetic function (Normal >1.21) DEPT. OF PHYSIOLOGY, AIIMS PATNA 35
- 36. DEPT. OF PHYSIOLOGY, AIIMS PATNA 36 Phase 2 Tachycardia Phase 4 Bradicardia Valsalva Ratio = 1.06 (↓)
- 37. • Sympathetic adrenergic function is assessed by the beat-to-beat blood pressure response during late phase II and during phase IV. • A normal response would be a • Recovery of the blood pressure within 4–7s (late phase II) • An overshooting of blood pressure in phase IV. DEPT. OF PHYSIOLOGY, AIIMS PATNA 37
- 38. 4. Isometric Hand Grip • Diastolic pressure response for an isometric task is measured. • The subject is asked to maintain the handgrip at 30% of maximal voluntary contraction for 4 min and the blood pressure change at pre- release is compared with the baseline values • The generalized increase in sympathetic activity - sympathetically mediated vasoconstriction - increase in diastolic pressure. DEPT. OF PHYSIOLOGY, AIIMS PATNA 38
- 39. The test result is presented as • The difference between the highest diastolic pressure during the examination and the average diastolic pressure at rest • Normally higher than 15 mmHg. • Test for sympathetic response DEPT. OF PHYSIOLOGY, AIIMS PATNA 39
- 40. DEPT. OF PHYSIOLOGY, AIIMS PATNA 40 Highest Diastolic Pressure during examination Isometric Hand Grip Test (rise in DBP) = 35 (N)
- 41. 5. Cold Pressor Test • Immersion of hands or feet for about 60-90 seconds in cold water (4°C) • It causes activation of afferent pain and temperature fibers leading to sympathetic activation and an increase in blood pressure and heart rate. • The rise in diastolic blood pressure during the test is calculated and it should normally exceed 15 mmHg. DEPT. OF PHYSIOLOGY, AIIMS PATNA 41
- 42. DEPT. OF PHYSIOLOGY, AIIMS PATNA 42 Sympathovagal balance tilted towards Sympathetic dominance.
- 43. DEPT. OF PHYSIOLOGY, AIIMS PATNA 43 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 44. DEPT. OF PHYSIOLOGY, AIIMS PATNA 44 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 45. • Healthy biological systems exhibit complex patterns of variability. • A healthy heart is not a metronome. • Heart rate variability (HRV) consists of changes in the time intervals between consecutive heartbeats called interbeat intervals (IBIs). • Allow the cardiovascular system to rapidly adjust to sudden physical and psychological challenges. DEPT. OF PHYSIOLOGY, AIIMS PATNA 45 B. Heart Rate Variability
- 46. • Reflects the effects of the ANS and other physiological control mechanisms on cardiac function. • Depends on the balance between sympathetic and parasympathetic drives to myocardium. • Non-invasive method of detecting early autonomic impairment of heart. DEPT. OF PHYSIOLOGY, AIIMS PATNA 46
- 47. Generation of HRV • The intrinsic heart rate (HR) generated by SA Node in the absence influence is about 100 to 120 BPM • However, in healthy individual, the HR is ranging between 60 and 90 beats per minute (BPM). DEPT. OF PHYSIOLOGY, AIIMS PATNA 47
- 48. DEPT. OF PHYSIOLOGY, AIIMS PATNA 49 Lakshman, Rama & Spiroski, Ana-Mishel & McIver, Lauren & Murphy, Michael & Giussani, Dino. (2021). Noninvasive Biomarkers for Cardiovascular Dysfunction Programmed in Male Offspring of Adverse Pregnancy. Hypertension. 78.
- 49. Sources of Heart Rate Variability Extrinsic Intrinsic Activity Mental Stress Physical Stress Sleep Apnea Smoking Respiratory Sinus Arrhythmia Baroreceptor Regulation Thermoregulation Neuroendocrine Regulation Circadian rhythms Unknown Rhythms DEPT. OF PHYSIOLOGY, AIIMS PATNA 50
- 50. Clinical Utility of HRV • Reduced HRV is a powerful and independent predictor of an adverse prognosis in patients with heart disease and in general population. • In diagnosis of diabetic neuropathy, (Pagani et al 1988) • Risk of cardiac electrical instability after myocardial infarction (Bigger et al 1991) DEPT. OF PHYSIOLOGY, AIIMS PATNA 51
- 51. DEPT. OF PHYSIOLOGY, AIIMS PATNA 52 Taskforce established by the Board of the European Society of Cardiology The standards of measurement, physiological interpretation and clinical use was the major goal of the task force. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation. 1996 Mar 1;93(5):1043-65.
- 52. Cautions - measurement and analysis HRV Environmental Requirement Before the measurement During the measurement Measurement Time Appropriate environment No caffeine No heavy meal Adjustment Time Position and breathing DEPT. OF PHYSIOLOGY, AIIMS PATNA 53
- 53. DEPT. OF PHYSIOLOGY, AIIMS PATNA 54 Signal Processing Steps in HRV Analysis
- 54. RR Tachogram DEPT. OF PHYSIOLOGY, AIIMS PATNA 55
- 55. Methodology and Terminology of HRV Analysis All the standard methods used in HRV analysis is derived from the RR Tachogram. DEPT. OF PHYSIOLOGY, AIIMS PATNA 56
- 56. DEPT. OF PHYSIOLOGY, AIIMS PATNA 57 HRV Analysis Linear Methods Frequency Domain Analysis Time Domain Analysis Non-Linear Methods
- 57. Time Domain Parameters Time-domain indices quantify the amount of variability in measurements of the RR intervals, during monitoring periods that may range from <1 min to >24 h. • Simple Time Domain Measures • Mean RR Interval • Mean Heart rate • Difference between RRmin and RRmax DEPT. OF PHYSIOLOGY, AIIMS PATNA 58 • Minimum RR interval • Maximum RR Interval
- 58. • Complex Time Domain Measures DEPT. OF PHYSIOLOGY, AIIMS PATNA 59 Kleiger RE, Stein PK, Bigger JT Jr. Heart rate variability: measurement and clinical utility. Ann Noninvasive Electrocardiol. 2005;10(1):88-101.
- 59. SDNN • Reflects all the cyclical components responsible for variability in the period of the recording. • The actual value of SDNN depend on the length of recording. • Both SNS and PNS activity contribute to SDNN and it is highly correlated with ULF, VLF and LF band power, and total power, RMSSD • The RMSSD reflects the beat-to-beat variance in HR and is the primary time-domain measure used to estimate the vagally mediated changes reflected in HRV. DEPT. OF PHYSIOLOGY, AIIMS PATNA 60
- 60. DEPT. OF PHYSIOLOGY, AIIMS PATNA 61 1. Nunan D, Sandercock GR, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing Clin Electrophysiol. 2010 Nov;33(11):1407-17. 2. Ernst G. Hidden Signals-The History and Methods of Heart Rate Variability. Front Public Health. 2017 Oct 16;5:265. doi: 10.3389/fpubh.2017.00265.
- 61. DEPT. OF PHYSIOLOGY, AIIMS PATNA 62
- 62. Frequency Domain Parameters • Power Spectral Density Analysis - Fast Fourier Transformation (FFT) to separate HRV into its component rhythms. • Frequency-domain measurements estimate the distribution of absolute or relative power into four frequency bands. • Ultra-low-frequency (ULF), very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) bands (Task Force) DEPT. OF PHYSIOLOGY, AIIMS PATNA 63
- 63. • Absolute power is calculated as ms squared divided by cycles per second (ms2/Hz). The signal energy found within a frequency band. • Relative power is estimated as the percentage of total HRV power or in normal units (nu). DEPT. OF PHYSIOLOGY, AIIMS PATNA 64
- 64. DEPT. OF PHYSIOLOGY, AIIMS PATNA 65
- 65. DEPT. OF PHYSIOLOGY, AIIMS PATNA 66 Karayannis, Georgios & Giamouzis, Gregory & Cokkinos, Dennis & Skoularigis, John & Triposkiadis, Filippos. (2012). Diabetic cardiovascular autonomic neuropathy: Clinical implications. Expert review of cardiovascular therapy. 10. 747-65. 10.1586/erc.12.53. LF:HF : Sympatho-vagal balance
- 66. DEPT. OF PHYSIOLOGY, AIIMS PATNA 67
- 67. DEPT. OF PHYSIOLOGY, AIIMS PATNA 68 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 68. DEPT. OF PHYSIOLOGY, AIIMS PATNA 69 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 69. C. Baroreceptor Sensitivity • It combines information derived from both heart rate and blood pressure. • Changes in heart period to changes in SBP induced by intravenous sodium nitroprusside followed by a bolus injection of phenylephrine hydrochloride. • Baroreflex sensitivity (BRS) would be the measure in which baroreflex vigor is expressed. • BRS is defined as the change in interbeat interval (IBI) in milliseconds per unit change in BP. DEPT. OF PHYSIOLOGY, AIIMS PATNA 70
- 70. DEPT. OF PHYSIOLOGY, AIIMS PATNA 71 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 71. DEPT. OF PHYSIOLOGY, AIIMS PATNA 72 Overview • Autonomic System Organisation • Autonomic Function Testing - General Principles • Cardio autonomic Function Testing – Ewing’s Battery • Heart Rate Variability • Baroreflex Sensitivity • Sudomotor testing • Summary DEPT. OF PHYSIOLOGY, AIIMS PATNA
- 72. Thermoregulatory Sweat Test (TST) DEPT. OF PHYSIOLOGY, AIIMS PATNA 73 alizarin red mixed with cornstarch and sodium carbonate
- 73. Quantitative Sudomotor Axonal Reflex Testing (qSART) DEPT. OF PHYSIOLOGY, AIIMS PATNA 74
- 74. DEPT. OF PHYSIOLOGY, AIIMS PATNA 75 Clinical evaluation of Dysautonomia.Journal of Neuroeuropsychiatry, 57(4) (2023)
- 75. Summary • Autonomic Function Tests are the main stay to evaluate the structural and functional integrity of autonomic system. • The classical tests employed are the Ewings Battery of tests to evaluate cardiac autonomic function, heart rate variability and sudomotor tests. • Ewings Battery of tests – Head up Tilt/ lying to standing, Deep Breathing Test, Valsalva, Isometric Handgrip and Cold Pressor test • Heart rate variability – Time Domain and Frequency Domain Analysis • With the help of these test a wide variety of dysautonomia – from autonomic failure to hyperreactivity can be diagnosed. DEPT. OF PHYSIOLOGY, AIIMS PATNA 76
- 76. References 1. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Circulation. 1996 Mar 1;93(5):1043-65. 2. Autonomic Failure: A Textbook of Clinical Disorders of the Autonomic Nervous System Christopher J. Mathias, Sir Roger Bannister 3. Ganong’s Review of Medical Physiology 26th Edition 4. Textbook of Medical Physiology, G K Pal 5. Sathyaprabha TN, Kaviraja Udupa, Autonomic Nervous System Evaluation : Bedside Conventional Methods, CNSW2023 NIMHANS 6. Nunan D, Sandercock GR, Brodie DA. A quantitative systematic review of normal values for short-term heart rate variability in healthy adults. Pacing Clin Electrophysiol. 2010 Nov;33(11):1407-17. DEPT. OF PHYSIOLOGY, AIIMS PATNA 77
- 77. THANK YOU ! saran.adhoc@gmail.com DEPT. OF PHYSIOLOGY, AIIMS PATNA 78
Editor's Notes
- Food – resting, suddenly danger, mention the changes you need.
- The autonomic nervous system (ANS) is made up of the sympathetic nervous system (SNS) (noradrenergic, adrenergic and cholinergic), the parasympathetic nervous system (PNS) cholinergic and the enteric nervous system.
- The ANS rules functioning of the milieu intérieur, arterial pressure (AP), heart rate (HR), thermoregulation, breathing, gastriontestinal, urogenital and pupillary system. (1)
- The terms dysautonomia, and autonomic dysfunction only describe a ANS compromise; however, in the study of one patient with autonomic symptoms it is necessary to identify if the compromise mainly affects SNS, PNS, the enteric system or all three systems. ANS compromise is present in diseases: 1. Of the central nervous system, such as multiple-system atrophy, 2. of the peripheral nervous, such has diabetic polyneuropathy, 3. primary of the ANS, such as pure autonomic failure. The ANS compromise may also be functional, with no evidence of a structural lesion of the autonomic ways, such as the vasovagal syncope.
- ANS compromise is present in diseases: Central nervous system, such as multiple-system atrophy. Peripheral nervous, such has diabetic polyneuropathy, Primary of the ANS, such as pure autonomic failure. Functional, with no evidence of a structural lesion of the autonomic ways, such as the vasovagal syncope.
- In a patient with a suspected autonomic disorder the major aims of investigation are- to determine whether autonomic function is normal or abnormal- to assess the degree of dysfunction, in determining the site of the lesion- to ascertain whether the abnormality is of primary or secondary to recognized disorders, as the prognosis and management will depend on the diagnostic category.- to obtain information on the underlying pathophysiological processes, and effect of stimuli in daily life on autonomic responses as the former are of importance in development of novel treatment, and the latter for ensuring holistic management especially in generalized autonomic disorders.
- The baroreceptors (or pressoreceptors) are stretch receptors located in the carotid sinuses and in the aortic arch. Increases in arterial blood pressure induce vascular stretch and deformation of the walls of the carotid sinus and aortic arch enhances the frequency of firing of baroreceptor nerves (CN IX and X) These fibers release glutamate to excite neurons in the nucleus of the tractus solitarius (NTS) in the medulla which in turn excite neurons in the caudal ventrolateral medulla (CVLM). This causes them to release the inhibitory neurotransmitter aminobutyric acid (GABA) into the rostral ventrolateral medulla (RVLM) to reduce their firing rate to the thoracolumbar intermediolateral horn (IML). Excitatory projections also extend from the NTS to the vagal motor neurons in the nucleus ambiguus and dorsal motor nucleus. Increased baroreceptor discharge inhibits the tonic discharge of sympathetic nerves and excites the vagal innervation of the heart It producing vasodilation of the veins and arterioles throughout the peripheral circulatory system along with a decrease in heart rate and strength of contraction. This causes a reflex decrease in the arterial pressure because of the decrease in both peripheral resistance as well as cardiac output.
- Fig. 3a–f Representative continuous beat-to-beat BP and HR recordings in selected patients demonstrating common abnormal profles on passive head-up tilt table testing. a In initial OH (seen more typically during active standing), a transient drop in BP of >40 mmHg occurs within 5–15 s and recovers within 1 min. b In non-neurogenic OH, there is a sustained decrease in systolic BP of >20 mmHg. In most cases, unless the patient is taking a beta blocker or has a pacemaker, compensatory tachycardia occurs. c In neurogenic OH, there is a larger sustained decrease in systolic BP, typically >30 mmHg, and in most cases compensatory tachycardia is absent. Supine hypertension may be present. A diagnosis of neurogenic OH should be confrmed by detecting inadequate BP responses to the Valsalva maneuver. D In delayed OH, the BP does not reach the threshold for OH within the frst 3 min of head-up tilt, but a further gradual decrease in BP occurs, reaching the criterion for OH beyond 3 min of standing or head-up tilt. e In syncope caused by neurally mediated hypotension, a delayed decrease in BP occurs more suddenly than that of delayed OH. This profle is typical of a vasodepressor response and is accompanied by relative bradycardia. Note the preceding tachycardia (which in this patient qualifes for POTS) and oscillations in BP indicating the sympathoadrenal imbalance typical of the presyncopal prodrome. At the moment of loss of consciousness, the table was returned to the horizontal position and the patient regained consciousness and baseline BP. f In POTS, the HR sharply rises during the frst 30 s of headup tilt and remains elevated as long as the patient is in the upright position. OH does not occur. Oscillations in beat-to-beat BP and HR may be seen while in the head-up position
- DBD tends to decrease with age, the value being around 15-20 beats/min in persons of 20 years of age and 5-10 over the age of 60 years.
- It was Karl Ludwig, in 1847, who first noted that the heart rate increased with inspiration and decreased with expiration. This phenomenon called sinus arrhythmia occurs normally and is mediated by the parasympathetic output to the heart. During inspiration, the stretch receptors in the lungs are stimulated and send impulses through the vagus, causing inhibition of the cardio-inhibitory area in the medullary oblongata(24,91,92). In addition, the fall in intrathoracic pressure on inspiration causes an increase in the venous return to the right side of the heart, resulting in stretch of the low-pressure atrial receptors and elicits the Bainbridge reflex. Moreover, there is spillover of impulses from the respiratory center to the cardiac center in the medulla. All these factors lead to a decrease in the tonic vagal discharge responsible for keeping the heart rate slow, thereby leading to a rise in heart rate on inspiration(5,28,29). This variation in heart rate is more pronounced at a breathing rate of 5 to 6 breaths per 104 minute(93). The difference between the average of the largest accelerations during inspiration and the average of the largest decelerations during expiration is calculated in beats per minute(73).
- In patients with mild sympathetic dysfunction, there is a reduced and/or delayed recovery after 7s in phase II and reduced and/or delayed phase IV overshoot. Severe sympathetic dysfunction is characterised by a continued fall in blood pressure throughout the expiratory effort with no evidence of a late phase II blood pressure recovery and absent overshoot in phase IV.
- 50 percent 1 min debilated )
- from the skin as well as emotional arousal.
- This represents the net effect of the parasympathetic (vagus) nerves, which slow HR, and the sympathetic nerves, which accelerate it.
- Acute changes in BP are restored via the baroreflex. A change in BP is detected by arterial baroreceptors, which signal to the medulla. This triggers a compensatory change in HR, and thus cardiac output [CO], via reciprocal modulation of sympathetic and vagal activity to the cardiac sinoatrial node. There is also a change in sympathetic outflow to peripheral arterioles, resulting in a compensatory change in total peripheral vascular resistance (TPR). Very-low-frequency (VLF; red box) blood pressure variability (BPV) occurs due to myogenic responses creating a VLF oscillation in peripheral arteriolar tone and thus TPR. The VLF BPV activates the baroreflex leading to compensatory VLF HRV. Low-frequency (LF) BPV and HRV originate from baroreflex loop resonance (red box). At the resonant frequency, the time delay in this negative feedback loop means the input and output are in phase, generating self-sustained oscillations. High-frequency (HF) BPV and HRV correspond to respiration (red box). The mechanical changes during respiration lead to HF BP oscillations (inspiration lowers intrathoracic pressure, leading to increased venous return, stroke volume [SV], and, therefore, CO), which then activate the baroreflex to produce compensatory HR oscillations
- HRV has been used to study the Risk of cardiac electrical instability after myocardial infarction (Bigger et al 1991) To diagnose diabetic neuropathy To assess re-innervations after cardiac transplantation (Sands et al 1989)
- Both SNS and PNS activity contribute to SDNN and it is highly correlated with ULF, VLF and LF band power, and total power In short-term resting recordings, the primary source of the variation is parasympathetically-mediated RSA, especially with slow, paced breathing (PB) protocols (12). In 24 h recordings, LF band power makes a significant contribution to SDNN The SDNN is the "gold standard" for medical stratification of cardiac risk when recorded over a 24 h period SDANN is not a surrogate for SDNN since it is calculated using 5 min segments instead of an entire 24 h time series (9) and it does not provide additional useful information
- This is analogous to a prism that refracts light into its component wavelengths Power is the signal energy found within a frequency band.
- which divides the absolute power for a specific frequency band by the summed absolute power of the LF and HF bands.
- The VLF band (0.0033–0.04 Hz) requires a recording period of at least 5 min, but may be best monitored over 24 h. Within a 5-min sample, there are about 0–12 complete periods of oscillation The ULF band (≤0.003 Hz) indexes fluctuations in IBIs with a period from 5 min to 24 h and is measured using 24 h recordings (10). The VLF band (0.0033–0.04 Hz) is comprised of rhythms with periods between 25 and 300 s. The LF band (0.04–0.15 Hz) is comprised of rhythms with periods between 7 and 25 s and is affected by breathing from ~3 to 9 bpm. Within a 5 min sample, there are 12–45 complete periods of oscillation (9). The HF or respiratory band (0.15–0.40 Hz) is influenced by breathing from 9 to 24 bpm (11). The ratio of LF to HF power (LF/HF ratio) may estimate the ratio between sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) activity under controlled conditions. Total power is the sum of the energy in the ULF, VLF, LF, and HF bands for 24 h and the VLF, LF, and HF bands for short-term recordings