Stress, Health & Disease - Why Zebras Don't Get Ulcers (ch3)

Chapter 3: Stroke, Heart Attacks, and Voodoo Death

In moments of crisis, for example when you have to run very fast, you have to increase your cardiovascular output. This is done by:

1. Getting your heart to beat faster, done by:

• Turning down parasympathetic tone, and activating the sympathetic nervous system
• Your glucocorticoids activating neurons in the brain stem that stimulate sympathetic arousal and enhancing the effects of epinephrirne and norepinephrine on heart muscle

2. Increase the force of which your heart beats:

• Your sympathetic nervous system causes your veins to constrict, to get more rigid. And that causes the returning  blood   to blast through those  veins with more force.

3. Distributing the blood prudently throughout  that sprinting body of yours:

• Arteries that lead to your muscles dilate, increasing blood flow and energy delivery there.
• There is a dramatic decrease in blood flow to nonessential parts of your body (e.g.: your digestive tract and skin)

4. Conserving water in your body:

• The most likely place to be losing water is urine formation. Therefore, your kidneys stop this process and reabsorb water instead.

Once the threat is over:

• The hormones of the stress-response turn off
• Your parasympathetic nervous system begins to slow down your heart via something called the vagus nerve

How does stress-induced elevation of blood  pressure during chronic psychological stress   wind up causing cardiovascular disease?

• Chronic stress causes  your blood pressure to go up  chronically --> hypertension
• With chronically increasing your blood pressure, the vessels have to work harder to regulate blood flow -->thicker muscle layer is built around the vessels --> vessels are more resistant to the force of blood flow -->further increase of blood pressure
• Blood returning to the heart is with increasing force --> wall thickens (also called: left ventricular hypertrophy) àirregular heartbeat --> heart muscle requires more blood than the coronary arteries can supply --> cardiac risk
• Stress can promote plaque formation by increasing the odds of blood vessels being damaged and inflamed

How can you measure the amount of inflammatory damage?

• C-reactive protein (CRP) is made in the liver liver and is secreted in response to a signal indicating an injury. Among other things, it helps traop bad cholesterol in the inflamed aggregate. CRP is turning out to be a better predictor of cardiovascular risk than cholesterol.       

Kaplan: monkeys under social stress are most at risk for plaque formation

Damage caused by plaques:

• From enough atherosclerotic plaques to seriously obstruct flow to the lower half of the body you get claudication, which means your legs and chest don’t receive enough oxygen and glucose whenever you walk. This makes you a candidate for bypass surgery.
• If you increase stress blood pressure, you increase the chances of tearing the plaque loose, rupturing it. The teared-up plaque is called a thrombus. This can make you clog up blood vessels.
• Clog up a coronary artery and you’ve got a myocardial infarct, a heart attack
• Clog up a blood vessel in the brain and  you have a brain infarct (a stroke).

Once the cardiovascular system is damaged, it appears to be immensely sensitive to acute stressors, whether physical or psychological

How can you diagnose a vagus nerve that’s not doing its part to calm down the cardiovascular system at the end of a stressor?

• The length of time between heartbeats tends to be shorter when you’re inhaling than exhaling. But if chronic stress has blunted the ability of your parasympathetic nervous system to kick the vagus nerve into action, your heart won’t slow down when you exhale and won’t increase the time intervals between beats. Cardiologists can monitor this time interval.

Sudden cardiac death:

• Sudden cardiac death  is simply an extreme version of acute stress causing ventricular arrhythmia or, even worse, ventricular fibrillation plus ischemia in the heart
• A strong emotion like anger doubles  the risk of a heart attack during the subsequent two hours
• It can also be caused by extreme joy. With regard to the cardiovascular system, extreme joy and extreme anger are similar
• Women are less subject to heart attacks than men, however women are more at risk for heart disease

Voodoo death

• People who are “cursed” by someone often truly die as a consequence
• “In some instances, the shaman ma spot people who are already very sick and, by claiming to have hexed them, gain brownie points when the person kicks off”. Or, the shaman could also poison the hexed person.
• It is also possible that once someone is cursed, others don’t treat him/her equally anymore. E.g.: they don’t give food to someone who is said to die soon anyway
• Perhaps the hexed person becomes so nervous that the sympathetic system kicks into gear and vasoconstricts blood vessels to the point of rupturing them, causing a fatal drop in blood pressure

Resources: Sapolsky, R. Why zebras don’t get ulcers: The acclaimed guide to stress, stress-related diseases, and coping. New York (NY): Henry Holt and Company. 2004 3rd edition