Heart Rate Variability
Heart rate variability or HRV refers to changes in the duration of consecutive cardiac cycles or heartbeats. Heart rate variability (HRV) involves measuring the specific changes in time (or variability) between successive heart beats and using that data to determine the current physical state of the body. The time between beats is measured in milliseconds (ms) and is called an 'R-R interval' or 'inter-beat interval' (IBI). HRV provides deep insight into the body's systemic condition. It is a non-invasive biomarker that tracks stress tolerance, adaptability and resiliency.
HRV is a directly associated with our Autonomic Nervous System (ANS). ANS is divided into two branches - Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). Autonomic nervous system as a whole controls the physiological rate variation of the heart. The Sympathetic Nervous System controls our body's 'fight or flight' reactions and increases heart rate during stress situations. The Parasympathetic Nervous System activates our body's rest phase and is associated with recovery. Thus measuring HRV helps us understand the synchronization between sympathetic and parasympathetic nervous system and how well our Autonomic nervous system, as a whole,is functioning.
If the heart beats with uniform intervals between each pulse, it indicates low heart rate variability and is not desirable. High heart rate variability is characterized by heart beats with intervals of varying length. A high HRV indicates efficient functioning of of the parasympathetic response, that promotes relaxation, digestion, sleep, and recovery. The parasympathetic system is known as the 'feed and breed' or 'rest and digest' system. A low HRV indicates malfunctioning of the sympathetic response, the fight or flight nervous system associated with stress, overtraining, and inflammation.
HRV and cardiac health
High HRV is an indication of healthy autonomic and cardiovascular response. Higher heart rate variability suggests a higher ability to adapt to stress and also effective recovery, and acts as a good shield from stress related disorders and diseases. Low HRV may indicate that the poor functioning of sympathetic and parasympathetic nervous systems and lack of coordination between two systems. It is is a marker for cardiovascular disorders such as coronary heart disease, hypertension, ventricular arrhythmia, and heart failure. Autonomic imbalance results in morbidity and mortality from various conditions and diseases, including cardiovascular disease. Thus monitoring the autonomic nervous system through HRV is extremely helpful in monitoring our health status, particularly cardiovascular health.
HRV in fitness and sports
HRV measurement is increasingly being used by athletes and fitness enthusiasts in guiding their training workouts. Measuring HRV helps in preventing overtraining and exertion. Most often excess training and workouts lead to illness and injury and hence athletes need to understand and be able to measure the breaking point at which they need to stop and allow the body to rest and regenerate before springing back into action. Thus HRV is a good indicator of whether your central nervous system is in a fight or flight mode or at rest and repair mode and helps in accurately deciding on optimal training loads.
Earlier HRV monitoring was taking place in a controlled environment, such as a lab. However, with advanced technology, measuring the HRV has become pretty simple now. All we need to have is a smart phone, a heart rate strap and a small ECG receiver to plug into the headphone jack. There are many HRV apps available, download any app of your choice, and you are set to measure your HRV in no time.There is no set range for HRV because it is unique to each individual. One needs to create a baseline by observing data over a period of time. After few weeks you can notice certain patterns and ranges emerge, and these become standard parameters. Normally measurement is taken at resting phase and the ideal time for measurement is just after waking. Once the score is arrived, colored indicators flash on the screen. Most often, apps come with green, orange and red colored indicators indicating the readiness, mild stress and severe stress respectively.
Neurotmesis etymology: Neurotmesis refers to most serious and severe nerve injury. Neurotmesis is brachial plexus injury. These brachial plexus injuries can occur in live births. The type of injury to the brachial plexus and the stretch damage will determine where the injury takes place. Various types of injuries can occur once the nerve rootlets form mixed nerve root. In some instances, the extent of the nerve damage may not be fully apparent but complete loss of motor, sensory and autonomic functions occurs. This type of complete rupture of the brachial plexus is called Neurotmesis. Neurotmesis is part of Seddon's classification scheme used to classify nerve damage. Seddon classified the nerve injury based on the extent of damage to the nerves on the basis of structural changes in cut nerves. The Seddon classification divides nerve injuries into three types namely:
Neurotmesis: Complete anatomic division of the nerve fibers with obvious discontinuity of the nerve sheath.
Axonotmesis: Microscopic division of nerve fibers without obvious discontinuity of nerve sheath.
Neuropraxia: There is injury without any anatomical discontinuity but resulting in functional disruption or nerve concussion. This is short term or sometimes lasts months with severe compression.
Neuropraxia Symptoms : Nerve Damage Symptoms: Common symptoms of Neurotmesis include loss of sensation and change in taste, expression and speech. There might be emotional and psychological disturbances. In the final stages, there could be a complete loss of motor, sensory and autonomic functions.
Diagnosis of Nerve Injury: There are many ways to diagnose the extent of the nerve injury. One of the common ways is Nerve conduction Velocity Test which tests the speed and strength of a signal being transmitted by nerve cells. Testing these factors can reveal the nature of nerve injury, such as damage to nerve cells or to the protective myelin sheath (protective coating on axons).
The test Electroneurography (EneG) which is also known as nerve conduction study or usually as a Nerve Conduction Velocity test(NCV) will help determine the nerve damage and further explore the choice of treatment.
Other than Peripheral nerve injuries, NCV is also helpful for the diagnosis of the following conditions:
Guillain Barré syndrome
Herniated disc disease
Charcot Marie Tooth disease
Special tests for assessment of Neurotmesis include electromyography, Strength duration curve, nerve conduction study and thermography. EMG test will be able to determine the presence, location and access the extent of diseases that caused the damage to the nerves and muscles. In some cases, a nerve biopsy may be needed where a small minute portion of the damaged nerve is surgically removed and analyzed.
Prognosis: Recovery from trauma is dependent on the age of the patient, type of injury and degree of injury. Without surgical intervention and repair this injury has very poor prognosis. Even with surgical repair, there could be significant loss of motor and sensory neurons which are responsible for normal conduction.
Multiple System Atrophy
Multiple system atrophy (MSA) is an alarming neurological disease that can cause adverse effects on the body. The primary targets for this condition are the involuntary muscles. MSA is a rare form of neurological disorder. It damages the control and co-ordination of muscle related physiology. This degenerative disease has no underlying etiology. The damage is predominantly in the striatonigral and olivopontocerebellar regions of the brain.
This disease was also known as Shy Drager syndrome. Due to its association with Parkinsons-like symptoms and also partly with amyotrophic lateral sclerosis (ALS), it has been categorized as Multiple System Atrophy to specify the symptoms. This has enabled medical centers to evaluate and diagnose the disorder in an effective manner. Studies indicate that the populations that are affected by the MSA are often elderly groups.
Classification and clinical manifestations
Multiple system atrophy is classified into two types for definitive diagnosis during the evaluation of the patient based on the symptoms.
The Parkinsonian category: In this form of MSA, the symptoms associated are very closely related to the Parkinson's pattern. It is also called MSA-P. Muscle rigidity is observed along with slow movements of the muscles, which are also referred to as Bradykinesia. Muscle cell degeneration predominantly occurs in the striatonigral region leading to tremors, lack of balance and postural impairment.
Cerebellar category: This form of MSA is called MSA-C, which is associated with the ataxia of cerebellar region. Loss of balance and prominent gait are the noticeable symptoms. The onset of dysarthria affects the vocal muscles and the patient's voice slows down and sometimes becomes inaudible. This is followed by difficulty in swallowing as the muscles lose their control sustenance from the cerebral region. In addition to this, blurred vision and dizziness have been reported in MSA-C.
Other associated symptoms of Multiple System Atrophy are urinary incontinence, orthostatic hypotension, erectile dysfunction, urinary retention, constipation and uncontrolled bowel movements. Patients experience light-headedness, dizziness and also low blood pressure because of the slow responses associated with the autonomic nervous system. The reflex arc and its respective functions are also impaired especially in Parkinsonian category.
Autonomic function tests are done to detect the onset of MSA-P and MSA-C at an earlier stage. Research affirms that although MSA is a rare form of neurological disorders, the occurrence in elderly people is slowly increasing. This is because of the lifestyle patterns and also underlying medical conditions such as diabetic neuropathy and Alzheimer's. Statistics indicate that the MSA occurs in 4 in every 100,000 people.
In most cases, diagnosis is done through a complete study of the muscle physiology and skeletal muscle responses after a certain age. In males, prostrate related carcinomas and myelomas can also aggregate this disorder in a larger way as it deteriorates the muscle tissue causing abnormal rise of non-functional proteins in the body.
Diagnosis and Treatment
MSA is diagnosed by evaluating the history of the patient and through physical examination. Tests such as muscle extension, flexion, and response to stimuli, vocal tone strength and posture are done to evaluate the muscle dexterity and functionality. Laboratory diagnosis of blood samples are done to evaluate liver and kidney function tests. In men prostrate examination is also done to study the urological coherence to the respective disease. Urology tests such as uroflowmetry and urinary control is investigated to study the extent of atomic nervous system and cerebellar functionality. Cardiac evaluations are performed to study hypotension and arrhythmia associated with it. Radiological examinations such as CT, PET and MRI are done to understand the involvement of central nervous control damage.
Therapeutic treatments are most often used with MSA. In many cases physical, occupational and speech therapies are done to increase the muscle movements and response of the patient. For Parkinsonian related MSA, L-Dopa, amantadines are administered for better results. Other drugs include Fludrocortisone, Midodrine, Oxybutinin, and Trospium chloride and botulinum toxin incase of dystonia.
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Diseases, Symptoms, Tests and Treatment arranged in alphabetical order:
Bibliography / Reference
Collection of Pages - Last revised Date: January 22, 2020