POISON IN AIR!

  • The Effects of Air Pollution on the Cardiovascular System

    Dr. O.P. Yadava, Chief Consultant Cardiac Surgeon & CEO,National Heart Institute.

  • We all know that the urban environments that we live in have turned into a cesspool of poisonous gases that are detrimental to our health. Of major concern in the past decade is the potential deleterious effects of these pollutants on our cardiovascular system i.e., the heart and blood vessels. In focus are environmental air pollutants that include carbon monoxide, oxides of nitrogen, sulphur dioxide, ozone, lead, and particulate matter. These pollutants are associated with increased hospitalisation and death due to cardiovascular disease, especially in persons with heart failure, frequent rhythm disturbances, or both. The well-established causal associations between active and passive smoking with heart disease and stroke support the possibility of an adverse effect of these pollutants on the cardiovascular system. Before going into greater detail, a brief outline of major air pollutants is in order:

  • Particulate matter (PM)-PM consists of a mixture of solid and liquid particles suspended in air, continually varying in size and chemical composition. Primary particles are emitted directly into the atmosphere, such as diesel soot, whereas secondary particles are created through physicochemical transformation of gases, such as nitrate and sulphate formation from gaseous nitric acid and sulphur dioxide (SO2), respectively. The numerous sources of PM include motor vehicle emissions, tyre fragmentation and road dust, power generation and other industrial combustion, smelting and other metal processing, agriculture, construction and demolition activities, residential wood burning, windblown soil, pollens and moulds, forest fires and combustion of agricultural debris, volcanic emissions, and sea spray. Some of the more common constituents of PM include nitrates, sulphates, elemental and organic carbon, organic compounds (e.g., polycyclic aromatic hydrocarbons), biological compounds (e.g., endotoxin, cell fragments), and a variety of metals (e.g., iron, copper, nickel, zinc, and vanadium). The importance of these substances is that they can easily lodge themselves in our respiratory passages.

  • Particulate matter (PM) Nitrogen oxides- Most research has focused on Nitrogen dioxide (NO2), because (1) NO2 is one of the regulated air pollutants for which standards are available worldwide; (2) Nitric oxide (NO) from vehicular exhaust and power plants is largely converted to NO2; and (3) NO2 plays a primary role in the formation of atmospheric ozone. The major source of these group of pollutants is automobile emission and power generation processes.

  • Carbon monoxide- Probably the most well-known of air pollutants, it is produced by incomplete combustion of fossil fuels. Its danger lies in the fact that it is colourless, odourless and binds with far greater affinity to haemoglobin in the blood than oxygen, thereby interfering with oxygen delivery to tissues.

  • Sulphur dioxide- Sulphur dioxide (SO2) is a highly irritating, colourless, soluble gas with a pungent odour and taste. In contact with water, it forms sulphurous acid, which accounts for its strong irritant effects on eyes, mucous membranes, and skin. Major sources are diesel engines and power plants.

  • Ozone (O3)- is a highly reactive, colourless-to-bluish gas with a characteristic odour associated with electrical discharges. We are constantly exposed to it at low levels, because O3 is formed by natural processes as well as by human activities. Ozone is formed in the stratosphere by the action of solar radiation on molecular oxygen (O2). Because stratospheric O3 prevents high-energy UV radiation from penetrating the atmosphere, we are dependent on it for protection from harmful UV rays. Hence it is a double-edged sword, being a major component of smog formed by interaction with other pollutants, notably nitrogen oxides.

  • Second Hand smoke (SHS) -Another well-known pollutant, its association with lung diseases including cancer and atherosclerotic heart disease is well established. The impact of SHS on heart disease and stroke is also supported by the remarkable “natural experiment” observed when Helena, Mont, a US town banned public smoking beginning June 5, 2002. During the 6-month period of the ban, admissions to the local hospital for acute myocardial infarction dropped by a staggering 40%, a decline that was not observed in any of the other hospitals from surrounding communities who had not enforced the ban!

    The impetus to assess the effect of air pollution on cardiovascular health was spurred by the observation of increased deaths during major pollution events like the London fog incident of 1952. One of the first major studies on long-term effects of pollution on deaths due to cardiovascular disease was by Dockery in 1993, covering 6 US cities. The investigators found an increased mortality from heart and lung disease in populations exposed to a greater concentration of mainly PMs and sulphur dioxides. An ominous finding with regard to short term exposure to ambient pollutants was a steep rise in exposure to PMs just a day prior to death from cardiovascular disease! Another study found a significant rise in hospital admissions for heart failure and heart attack with each unit rise in ambient PMs. It is now reasonably well established that both short-term and chronic air pollution exposures are related to cardiovascular diseases. Whether there are specific individuals or subsets of patients at increased risk is less clear. A few observations have suggested that the elderly and those with low socioeconomic status may be particularly susceptible populations. Whether increased age itself or the high prevalence of underlying cardiovascular disease and other risk factors explains the enhanced risk observed in elderly populations is unclear. The presence of preexisting chronic lung disease, coronary heart disease, and heart failure may also elevate short-term risk of death from cardiovascular disease. Most recently, research provides evidence that the acute risk for cardiovascular events in patients with diabetes mellitus may be twice that for nondiabetics.

  • All this begs the question: just how does air pollution wreak such havoc? The potential biological mechanisms linking air pollution to heart disease involve.

    Direct effects of pollutants on the cardiovascular system, blood, and lung receptors

    Indirect effects mediated through inflammatory responses to the pollutants.

  • Direct Effects may occur via agents that readily cross the airway lining in our respiratory passages into the circulation, such as gases, or ultrafine PMs. These responses excite further instability in pre-existing cholesterol deposits in the blood vessels and also initiate de novo deposits and narrowing of blood vessels, leading to devastating cardiovascular events like heart attacks.

    As ordinary citizens, what can we do to stave off at least this aspect of risk of cardiovascular disease? As has often been said, the simplest of measures makes the greatest of impact; and some simple steps we all can implement are:

    1. Stop burning of garden waste in the open, as it is a major source of PM and sulphur oxides. Burying them achieves the twin-fold ends of reducing pollution, as well as composting...besides the spin-off of greater physical exercise involved in digging ditches to bury the waste!

    2. Avoid going for jogs or brisk walks in areas with heavy traffic, as it would expose us to a greater concentration of PM, Carbon monoxide and Sulphur oxides

    3. Avoid early morning exercise in the open, especially in winter months due to greater smog density at those hours. It would be prudent for the smog to clear before venturing out for our daily fix of physical exercise.

    4. Reduce dependence on fossil fuels as much as possible, something that has been drummed into our heads since our school days!

    This leads to the foregone conclusion that stricter control on air pollution is the need of the hour to stave off the potential burden of healthcare costs on the national economy, apart from the avowed benefits on our fragile ecosystem. This can only be effectively implemented by nations working together towards a common goal as these are issues affecting health and humankind as a whole.

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