A Heartless Crime

Alice is talking to Bob using their cell phones. It is very very tough to 'listen' to what they are saying by simply tuning to the same frequency. It is because, the conversation is 'encrypted'. You have to 'decode' this if you want to eavesdrop on them.

In humans with cardiac implants, particularly automated implantable cardioverter defibrillators (ICD) are vulnerable in this regard that these machines can be intercepted. ICDs are devices that diagnose and treat arrhythmia by giving a 'shock'. Some ICDs send signals to doctors on once-a-day (or so) basis, via a bedside device. The doctor then may/may not 're-program' the ICD remotely, depending on the report the ICD sends. However, the data protocol is unencrypted, and could be easily read and manipulated by 'hackers'.

They may steal the patient's name, medical ID number, date of birth, even the social security number. The hackers may 'reset/change' the above or worst, they could even disable the device.

When a mobile phone sends signals to a tower (cell), it encrypts the data, the receiving tower acknowledges it and they both share a common dialect. Thus snooping on them is quite tough. Compare this with the data flow in land phones. You can very easily listen ('tapping') the data/conversation that flows. Just use a simple electronic circuit, consisting of an inductor, resistor and a transistor (NOT even a power supply); you can hear the sounds of both the parties in an FM radio. You may even record it if you want. Spying on unencrypted wireless handsets is also very easy. Just tune to the same frequency, the rest is easy cake!

Hence it may be time that these devices be made a little bit tougher by using 128 bit or better still, 256 bit encryption. Taking off this 'headache' off the shoulder from the heart patients may better their lifestyle (by cutting down sympathetic discharges).

I found this article that researchers at University of Massachusetts at Amherst has developed a countermeasure to this menace. There will be an alert when someone attempts to interact with their device.

Last modified: Aug 21, 2008
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Pumping Iron To Stay Healthy

Who doesn't know the importance of exercise? Your skeletal muscle bulk increases, performance of the lung is increased, the metabolic profile gets better and most importantly the cardiovascular health is improved.

Exercise may be aerobic or anaerobic, depending on oxygen requirements. A sprinter running at top speed spends energy very fast. The amount of energy produced by oxidative burning alone is insufficient to meet the demand. The muscles have to make energies without the use of oxygen, in addition. Thus activities such as these would require anaerobic glycolysis as well: anaerobic exercise.

On the other hand, a marathoner who is jogging at a much leisurely pace, does not burn energy at such a humongous pace and the amount of energy that comes via aerobic glycolysis is the major source to meet his energy requirement: aerobic exercise.

They can also be classified as isotonic and isometric. When someone is trying to lift a heavy load but can not really accomplish it, is said to be doing isometric exercise; Iso meaning 'same' and metric refers to length 'meter'. Conversely, when a guy is lifting weights or doing push-ups, is contracting his muscles, and this is known as isotonic exercise; signifying that the tone remains the same but the length of the muscle changes. Physics hardly gives any credit to the one doing isometric exercise; dismissing it since they are doing no work (work= force x distance; the displacement here is zero).

Whether isometric or isotonic, the heart rate rises in both occasions. It is effected by increased sympathetic discharge in response to stimulation of mechanoreceptors and chemoreceptors in the muscle. The mere thought of exercise stimulates the motor cortex as well as the sympathetic centers in the brain.Blood flow in the skeletal muscular circulation increases 15-30 fold. Increased sympathetic cholinergic vasodilator discharge, raised temperature, pCO2,K+,H+, and decreased pO2 are responsible for the vasodilation. This vasodilation opens up dormant capillaries by dilating them, increasing the total surface area available for gas exchange. Vasodilation also raises the hydrostatic pressure leading to possible development of edema due increased exudation in the interstitium. Raised osmotic overload from accumulation of osmotically active particles like lactic acid also contribute to build up of fluid in the intercellular spaces. Increased levels of lactic acid, H+, 2,3 DPG and raised temperature all shift oxyhemoglobin dissociation curve to the right, implying that more O2 is delivered to the tissues. In fact, oxygen consumption is increased about 100 fold!

The picture is a bit different in the systemic circulation. Both systolic and diastolic blood pressure raises (due to rise in the peripheral resistance) in isometric exercise while the stroke volume remains almost unchanged. In isotonic exercises, stroke volume increases. Rise in blood pressure stretches the vessel walls, by shear stress. This causes elaboration of nitric oxide (NO), a chemical that relaxes the smooth muscles. Previously called EDRF (endothelium derived relaxing factor), this chemical acts as a vasodilator and cellular messenger. The diastolic BP remains normal, may even fall due to widespread vasodilation leading to diminished peripheral resistance. Increase in venous return is aided by increased activity of the thoracic pump (increased depth of respiration or hyperpnea and increased rate or tachypnea), increased activity of the muscle pump, increased venoconstriction from sympathetic stimulation, pressure on the veins by the distended arteries and enhanced blood flow from the viscera from splanchnic vasoconstriction.

This increase in venous return is essential to maintain the end diastolic volume (EDV), when we realize that the diastole has shortened considerably due to increased heart rate. However, the size of the heart decreases rather than increases (as would be predicted by Frank-Starling's law). Regular exercise enables one to burn fatty acids more efficiently, as an energy source. This has its own advantage of not driving the pH too low, delimiting enzymatic reactions and curbing the production of lactate, the chemical that causes muscle cramps. Above all, scientists from University of Bonn, at Germany have conclusively proven that exercising gives us the runners' high, an euphoric effect due to increase in the level of endorphins, in the central nervous system (CNS). Endorphins are analogous to endogenous morphines (opioids) that are responsible for the elevation of mood.

Decide now: Are you going to give yourself a go today?
Last modified: never
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Impulse Propagation In The Heart

In the previous article, we discussed how the pacemaker of our heart, the SA node, was generating the rhythmic impulses. For the impulse to have any effect, it has to be travel to various parts of the heart, which will then contract as a result.

After its generation, the impulse goes to the AtrioVentricular Node. It supplies both the atria, while on their way to the AV Node. The sojourn of impulse, between the SA and the AV node, is via the internodal pathway.

There is a delay of about 0.09 second in the AV node itself. The anatomy and physiology of the AV node is responsible for it. It is said that the nodal cells have fewer gap junctions among themselves, making ionic flow highly resistive. Nevertheless, this delay serves a useful purpose. As seen in the animation, the atria contract when they are stimulated and fill the ventricles with blood. Were it not for the delay, the ventricles would fire near simultaneously, without their quota of blood from the atria, and thus producing hemodynamically ineffective cardiac output. It gives the ventricle vital time to fill. Since the junction between the atria and ventricles is electrically non-conducting (due to the presence of a fibrous partition between the two chambers of the heart. The conduction pathway is like electrical cabling between 2 floors of a building), the impulse must find a route to pass through. It has only one way, in normal physiology, through which it can travel: through the penetrating portion of the AV bundle.

So, from here onwards, the impulse is carried via the AV bundle, down the interventricular septum. The AV bundle then bifurcates into right and left bundle branches, which traverse along right and left ventricle respectively. From there, Purkinje fibres arise which ultimately supplies the ventricular muscles.

As the impulse travels down the septum, it reaches the apex of the heart, and supplies the ventricular muscles. Next, the impulse travels along the ventricular musculature upwards towards the atrioventricular septum, the top portion of the inter ventricular septum and the posterobasal portion of the heart. These are the areas to be depolarized last. While doing this part of the journey, the impulse also spreads from the endocardium to the epicardium; that is they travel from the inside of the heart to the outside. All these can be seen in the adjoining picture/animation. This animation also portrays how the ECG would be like, with the spread of the wavefront. The state of the heart valves can also be seen during systole and diastole, i.e. during the contraction/relaxation of the cardiac chambers.

The conduction system comprising of internodal tracts, AV bundle, His-Purkinje fibers are all specialized muscle cells, that carry electricity at high speeds. Also, all these depolarizations are followed by repolarizations, making the cells ready for the next impulse. The action potential characteristic of cardiac muscles are different from that of the pacemaker cells.

In some idiopathic degenerative diseases, the fibrous skeleton of the heart may be calcified and sclerosed, as in Lev's disease, or there may be sclerodegenerative changes within the conducting system sparing the myocardium or the fibrous skeleton, as in Lenegre's disease. Here the 'electric cable connecting the first and the second floor of the heart' (i.e. the piercing AV bundle); is naturally snapped (due to the interposition of non conductive sclerosed material), leading to AV block and bradycardia of varying degree.

PS: Click on the animation if it doesn't animate on its own.

Last modified: Mar 20, 2009
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