The Circulation System — Page 26, Lesson 45

I want to walk you through the final part of the Circulation System chapter, focusing on what happens when the heart is in trouble and how we manage oxygen delivery to the tissues. Let's start with cardiac arrest. If a patient's essential circulation can be supported by cardiac massage and assisted ventilation, they may survive while waiting for a defibrillator to become available. Without treatment, cardiac arrest is fatal within 4 minutes. That's a hard limit — four minutes without circulation, and the brain and other vital organs begin to die. Now, for those who survive the first 24 hours after a myocardial infarction — that's a heart attack — they have a good chance of recovery. However, retrieval of a flying licence will not be possible without extensive investigation. And in any case, a restriction to multi-crew operations will always be imposed. So even if a pilot recovers well, they will never fly single-pilot again under a professional licence. Let's look at the factors that predispose a person to a heart attack. The book lists them in order of importance. First is family history — heredity. Second is age. Third is a previous history of cardiovascular problems. Fourth is raised blood pressure, which we call hypertension. Fifth is smoking. Sixth is raised blood cholesterol. Seventh is lack of exercise. Eighth is diabetes. Other factors such as stress, obesity, alcohol, and certain dietary considerations are less clearly understood. But here's a striking statistic: coronary disease is responsible for 70% of pilot deaths during their careers. That's seven out of every ten pilots who die while still flying. So this is not an academic topic — it's the single biggest killer in our profession. Now, what about incapacitation in flight? The dramatic and sudden incapacitation of a pilot during flight is uncommon and very rarely the cause of an accident. The book mentions the aircraft accident at Staines as one of the very few major accidents in civil aviation due to the pilot suffering a heart attack. Rigorous medical selection and periodic health checks minimize the risk of total incapacitation due to heart disease, epilepsy, and similar conditions. As the pilot grows older, the frequency of medical checks increases. ECG — electrocardiogram — and EEG — electroencephalogram — recordings are used more and more to spot those at risk. Let's move to the next topic: insufficient oxygen carried to the cells. The cells of the various tissues may be deprived of the oxygen they need because of three main causes. First, insufficient haemoglobin or red blood cells — this condition is called anaemia. Anaemia can be primarily caused by the breakdown of the production process of haemoglobin in the bone marrow, or by excessive bleeding. Haemoglobin is the protein in red blood cells that actually carries oxygen, so if you don't have enough of it, your blood can't transport enough oxygen even if you're breathing perfectly. Second, insufficient pressure of oxygen in the air. The pressure of oxygen in the air — its partial pressure — reduces with altitude. People who live at high altitude for a prolonged period produce more red blood cells than those who live at sea level, as a natural adaptation. In other cases, it will be necessary to add oxygen to the air breathed. This topic is treated fully in the next chapter, so we'll come back to it. Third, a lack of iron. Iron is essential for the production of haemoglobin, so without enough iron in your diet, your body cannot make enough haemoglobin, and oxygen transport suffers. That covers the key points from this part of the chapter: the four-minute window for cardiac arrest, the recovery and licensing restrictions after a heart attack, the risk factors in order of importance, the rarity of in-flight incapacitation, and the three causes of insufficient oxygen delivery to the tissues.