 Hyperventilation Aircraft Oxygen Systems Carbon Monoxide Poisoning 16-3 Figure 16-3.  An example of a carbon monoxide detector sold in  the aviation market. CO GUARDIAN ST SC SP 552 RST CO ALERT 105 PPM There are many types of carbon monoxide detectors available  to alert aviators of the presence of this gas. Some are made  to be permanently installed in the instrument panel, while  others are portable. The simplest carbon monoxide detectors  are chemical tabs mounted on cardboard that hang on or  adhere to something in the cockpit. When carbon monoxide  is present, the tab changes color due to a chemical reaction.  More sophisticated detectors provide a digital output in  parts per million of carbon monoxide present or illuminate  a light and/or an audible alarm sounds.  [Figure 16-3]  If  contaminated, a carbon monoxide portable test unit can be  returned to service by installing a new indicating element. Another physiological phenomenon of interest to aviators  is hyperventilation. Its symptoms greatly resemble hypoxia.  When various cells in the body use oxygen and food delivered  to them by the blood, carbon dioxide is a by-product. Blood  carries this carbon dioxide to the lungs where it is exhaled.  Carbon dioxide functions in the body to regulate the depth  and frequency of breathing. A high level of carbon dioxide  in the blood triggers rapid, deep breathing to expel it. This  also promotes the intake of a greater amount of oxygen for  active cells to use. A low carbon dioxide level causes more  relaxed breathing resulting in less oxygen intake. Therefore,  an oxygen/carbon dioxide balance exists in the blood.  Occasionally, fear, panic, or pain triggers excessive rapid  breathing in a person. With it comes a reduction of carbon  dioxide in the blood, even though the body does not need this.  The lower carbon dioxide level signals the body that there is  enough oxygen available and blood vessels constrict, causing  hypoxia-like symptoms because insufficient oxygen is being  delivered to the cells. Note that the onset of hypoxia described  in the previous section occurs without the rapid breathing that  accompanies hyperventilation. Hyperventilation can often  be alleviated by having the person calm down and breathe  normally, which restores the oxygen/carbon dioxide balance  in the bloodstream.  Aircraft that utilize exhaust shroud-type heating systems or  combustion heaters are more likely to have carbon monoxide  introduced into the cabin from these devices. It is very  important to discover the source of carbon monoxide if it  is detected. Various leak checks and testing for cracks are  performed regularly whenever a combustion source is also  the source for cabin heat. The negative effects of reduced atmospheric pressure at  flight altitudes, forcing less oxygen into the blood, can be  overcome. There are two ways this is commonly done:  increase the pressure of the oxygen or increase the quantity  of oxygen in the air mixture.  Carbon monoxide is a colorless, odorless gas produced by  incomplete combustion of hydrocarbon fuels, such as those  used in aviation. The human body does not require this gas to  function. Its presence, however, can prevent a sufficient level  of oxygen to be maintained in the body, resulting in hypoxia.  This is also known as carbon monoxide poisoning. As with  all forms of oxygen deprivation, extended exposure to carbon  monoxide can result in unconsciousness and even death. Hemoglobin is the substance in the blood that attaches to  oxygen in the lungs and circulates it to cells in the body  for use. Carbon monoxide more readily attaches itself to  hemoglobin than oxygen. If carbon monoxide is present in the  lungs, hemoglobin attaches to it and not oxygen. This results  in cells not receiving the amount of oxygen they need. The  insufficient oxygen level results in hypoxia-like symptoms. A real danger of carbon monoxide poisoning is that long  exposure to slight traces of carbon monoxide can result in  oxygen deprivation just as easily as short-term exposure to  a concentrated amount. The onset of its effects can be very  subtle.