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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.

Measuring HRV

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.

Mad Cow Disease

Bovine Spongiform Encephalopathy, commonly known as mad cow disease, is a degenerative, slowly progressive and fatal disease affecting the central nervous system of adult cattle. An abnormal version of a protein normally found on cell surfaces called a prion is the infectious agent causing the disease. This alters the protein and destroys nervous system tissue, the brain and spinal cord.

Mad cow disease and humans

While humans cannot get mad cow disease, in rare cases they may get a human form of mad cow disease called variant Creutzfeldt Jakob Disease or CJD which is fatal. This is caused by eating beef products contaminated with central nervous system tissue such as brain and spinal cord from cattle infected with mad cow disease. The United States Department of Agriculture (USDA) believes that any cow products from high risk cattle, older cattle, animals that are unable to walk, and any animal that shows any signs of neurological problem should not enter the US food supply and therefore believes that this practice can effectively safeguard US public health from vCJD.


The disease can affect all age groups. It is hard to diagnose until it has nearly run its course. In the early stages, vCJD has symptoms related to nervous system such as depression, loss of coordination, dementia, illness and brain abnormalities. Tingling, burning, or prickling in the face, hands, feet and legs are other symptoms. Psychotic behavior, inability to walk and finally coma are other signs. If a person eats nerve tissue from an infected cow, he or she may not feel sick right away but usually within thirteen months of the onset of symptoms it can be fatal.


The leading theory is that vCJD is caused by infectious proteins called prions which are found in infected cows. There is no proof that prions are found in muscle meat such as steak. However, milk and milk products are not believed to pose any risk for causing mad cow disease in humans. When a cow is slaughtered and parts of it are used for human consumption, it affects the people if they eat the brain or spinal cord of infected cattle.

The first case of vCJD was reported in 1996 and since then there has been few cases of vCJD reported in the world. Most cases have been from parts of the United Kingdom. In 2003 mad cow disease was discovered in one cow in the US. In 2004 three more cows in the US have been found with mad cow disease. The most recent was found in April 2012 in a cow in California.


There is no single test to diagnose vCJD. Doctors base their assumptions upon where the person has lived and the person's symptoms and past health. Imaging tests such as MRI are done to check for brain changes caused by vCJD. As of now no blood test is available although researchers are trying to develop a blood test. A brain biopsy is the only way to confirm diagnosis of vCJD.


There is no cure for vCJD. Treatment includes managing the symptoms that occur as the disease gets worse. Researchers at New York University School of Medicine have taken a key step in developing an effective treatment. They found four compounds that significantly delayed the disease onset in mice. As prion diseases are extremely slow to develop, any treatment that can delay initial symptoms for a longer duration can be significantly life saving. Clinical trials of some anti-prion compounds are in progress. While presently little is known about prion diseases, they might probably prove simpler to treat than bacterial infections. Researchers are hopeful that tests of trimipramine and fluphenazine in people with CJD will begin soon.

Striking facts about mad cow disease

Humans cannot get the disease by simply eating regular cow meat. If someone is infected with CJD, they will probably will not know until years later.

Latest case of mad cow disease is attributed to random mutation. The cow did not contract the disease by consuming infected cattle feed since the deceased cow showed little symptoms of the disease when tests were performed randomly on dead cows.

Mad cow destroys the brain and spine in cattle as the disease attacks and destroys the brain and spinal cord in cattle. Thoroughly cooking meat will not help as prions are not affected by heat or other methods used to kill food-borne pathogens. Prions can survive in extremes up to 1800 degrees of heat to be neutralized so much so that even sterilization process used in hospitals is largely ineffective.

The mad cow disease is on the decline and is far less common than it was about a decade ago. There is at least a 99 percent decline worldwide since the disease peaked in 1992 with 37,311 cases.


Allergies are one of the most common types of acquired health conditions as the causes include various factors. Most of these factors are related to the environment such as dust, pollen, virus and chemicals. Allergic reaction signifies the defense mechanism of the immune system to a foreign particle. Allergic reactions if untreated can lead to bigger complications such as bronchitis and sinusitis. Antihistamines were first synthesized by Daniel Bovet. They play a major role in controlling the release of histamines in the body which are produced as response to an allergen. Histamines are chemicals which are released from the mast cell damage. These chemicals initiate the process of allergic reaction in the blood and tissues which causes discomfort. Histamines have three types of receptors H1, H2 and H3 which are specific for different organ systems. The H1 receptor is associated with vasodilation and smooth muscle stimulation, H2 receptor is associated with the cardiac stimulation and H3 is associated with the feedback inhibition process regulated by the central nervous system.

Types of antihistamines

Antihistamines mainly act upon the receptors of the type of histamine released. Each antihistamine has a tendency to compete in binding to the receptors to inhibit the process of allergic stimulation caused in the organ system. There are two major classes of antihistamines. The first generation and the second generation are classified based on their sedative effect on the patient during the course of their action. The first generation of antihistamines are sedatives as they act upon the parasympathetic nervous system in preventing the release of acetylcholine. Their anticholinergic properties enable them to act fast in providing relief within a few minutes. People who experience motion sickness are often suggested to take antihistamines because it suppresses the ear balance discomfort.

The most common ingredients present in these medications are chlorpheneramine, doxylamine, brompheneramine and dimenhydrinate. Most of these first generation antihistamines are recommended in allergic reactions such as hay fever, viral infection, pollen and dander as they suppress the central nervous system. Patients experience drowsiness for a period of time during the first generation antihistamine treatment.

Second generation antihistamines are not sedative in nature and they have large molecular size and electrostatic nature which makes them noncompeting to cross the blood and brain barrier. The response pertaining to their action is comparatively slow as they do not act upon the central nervous system. Studies have shown the increased administration of non-sedative antihistamines in the recent times. Some of these second generation antihistamines have been banned from the market due to their adverse side effects such as arrhythmia. Most of these antihistamines are prescribed during seasonal allergies.

Side effects of antihistamines

The common side effect of most first generation antihistamines is drowsiness or dizziness. The other side effects include nausea, feeling of dryness in mouth and nostrils and sometimes blurred vision. These happen because of the inhibition of secretions from salivary, nasal and lachrymal glands during the onset of an allergic response. The suppression of central nervous system activity may initiate confusion, disorientation and sometimes hallucination in patients.

Rashes, chest congestion and difficulty in breathing have also been reported as adverse effects of antihistamine administration. In case of H2 receptor antihistamines, diarrhea is significant side effect along with headache. Most of the side effects caused by antihistamine intake subside within a few hours. However increased sensitivity to a certain type of antihistamine has to be immediately reported to the physician.

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Collection of Pages - Last revised Date: November 11, 2019