Dear Doctor: Every morning upon waking, I feel an even/steady pulsing of about 200 beats per minute, although my pulse is normally about 60 beats per minute. I'm 84, with no symptoms of atrial fibrillation and a body mass index of 24. I take no medications and have no aches and pains. Again, this high pulse rate occurs only when I wake up, and I feel normal at the time. What could be causing this, and should I be concerned?

Dear Reader: Yes, you should be concerned. At the age of 84, even with extreme exertion, your pulse should not be so high.

Before we explore potential causes, let's discuss what creates the pulse, or heart rate. The pulse rate that you feel in your wrist or neck occurs with contraction of the ventricles, the large muscular portions of the heart. Normally, the atria, which sit atop the ventricles, initiate the pulse, which then travels down the ventricles.

The pulse rate can be affected by, among other things, disorders of the atria, including -- as you mentioned -- atrial fibrillation. This haphazard rhythm of the atria can indeed produce pulse rates of 200, but not the even, steady pulse that you describe. Atrial flutter -- a regular rapid beating of the heart that, like fibrillation, can originate from multiple parts of the atria -- is possible but perhaps unlikely because the fast beating of the atria would only be able to cause contraction of the ventricles at certain intervals. Thus, pulse rates of 300, 150, 100, 75 or 60 are possible, but a 200 rate would occur only under certain conditions. Atrial tachycardia -- a regular rapid beating originating from one section of the atrium -- can cause rates of 200, so this is a possibility.

Disorders of the ventricles also can cause a very rapid heart rate. Here, instead of the atria initiating the pulse rate, a portion of the ventricles creates its own rate. This can occur when the muscular part of the heart is damaged, leading to an electrical impulse that causes the whole ventricle to contract. Ventricular fibrillation, like atrial fibrillation, is a disorganized rhythm of the heart and the leading cause of sudden cardiac death. Due to your lack of symptoms and the regularity to your pulse rate, this seems unlikely.

Perhaps most likely is ventricular tachycardia, which has a regular rhythm with rates greater than 100 and can have rates as high as 250. Besides having a fast heart rate, those with short bursts of ventricular tachycardia may not feel any other symptoms.

We also have to consider the fact that this happens only in the morning. That takes us to our bodies' circadian rhythm, which means the core processes of the body fluctuate depending upon the time of day. For that reason, increased blood pressure, heart rate, blood vessel constriction and clotting are greatest in the morning. Similarly, heart attacks are more frequent in the morning, as are ventricular fibrillation and tachycardia.

Note that alcohol withdrawal and intoxication can increase this risk of abnormal heart rhythms.

Conditions like atrial fibrillation and atrial flutter increase your risk for strokes, while ventricular fibrillation and tachycardia may increase the risk of sudden death. Undoubtedly, I recommend seeing your doctor. He or she can order a heart monitor to measure your heart rate and, more important, determine what type of rhythm is causing this.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: It seems like doctors always want to schedule surgeries as early as possible. But I recently read that heart surgery survival chances are better in the afternoon. Why would this be? Should people push their doctors for afternoon surgeries?

Dear Reader: You're referring to the results of a study published in the journal Lancet last month. Over the course of six years, scientists from the University of Lille in France examined the medical data of close to 600 patients who underwent a heart surgery known as aortic valve replacement. In this surgery, the aortic valve, which regulates blood flow to the heart, is replaced with either animal or synthetic tissue. What the researchers wanted to know was whether the time of day that these surgeries took place played a role in which patients went on to experience serious complications.

The results were surprising. Researchers found that patients whose surgeries were performed after noon had half the risk of heart attack, acute heart failure or death in the 500 days after surgery than did those whose procedures took place in the morning. A separate analysis of 44 patients who had morning surgery, and 44 who had afternoon surgery, examined the rate of a certain type of tissue injury that can occur when the patients are taken off bypass during the operation and blood flow returns to the repaired structures of the heart. Once again, the patients with afternoon surgeries fared measurably better than those with morning surgeries.

These findings seem to add to a growing body of evidence that circadian rhythms -- that is, our biological clocks -- have an effect on health care interventions. Previous studies in mice have suggested that the body responds best to chemotherapy during certain times of day. A large-scale study into flu shots found that, among older people, those who received the vaccine in the morning produced more antibodies than those who got an afternoon injection.

Ongoing research continues to show that circadian rhythms play a role in all aspects of physical and mental health. Here at UCLA, scientists are looking into the connection between chronic disruption of circadian rhythms, as in workers on swing or night shifts, and the increased risk of developing diabetes and metabolic syndrome. Previous research has shown that circadian disruption affects learning, mental and emotional health, and can even lead to death. This line of inquiry is considered to be so important that last year the Nobel Prize in Medicine went to three researchers who identified the molecular mechanisms that control our body clocks.

That said, there are certain caveats regarding this new heart surgery study. As an analysis by the National Institutes of Health notes, 600 patients make a small sample size. Each of these patients was treated at the same hospital, which begs the question whether it was the time of day of the surgeries, or the specific surgical teams that performed them, that had the greatest effect on the outcomes.

We need additional studies in multiple medical sites, and with a diversity of heart procedures, before we can conclusively link time of day to better surgical outcomes.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: How is one screened for/diagnosed with Alzheimer's or other forms of dementia? What type of doctors does one see? What sorts of tests do they run? It runs in my family, and lately I've been forgetting conversations soon after they happen. But I don't know where to look for answers.

Dear Reader: Your concern is understandable. The degeneration of the brain's ability to incorporate new information -- and the loss of the hardwiring that controls our everyday tasks -- affect not only an individual but everyone who cares for that person as well. Further, the genetic linkage is greatest for people with a parent or sibling who developed dementia prior to the age of 65. (The linkage grows progressively weaker with the family member's age of diagnosis, so much so that if the person was diagnosed after 85, one's own risk is no different than if there were no family history.)

Further, the rates of dementia are increasing in this country, with Alzheimer's dementia affecting 5.4 million people in the United States in 2016. Some of this may be due to our ability to diagnose the disease, but our increasing rates of risk factors -- diabetes, obesity and lack of physical activity -- play a role as well. The majority of people are diagnosed after the age of 65, with the overall incidence of dementia doubling every 10 years after the age of 60.

Diagnosis typically starts with your primary care doctor. While blood tests can pick up some non-Alzheimer's causes for memory loss, such as B12 deficiency, the standard screening exam is the Mini-Mental Status Examination (MMSE), a memory and writing test. That said, another test, the Montreal Cognitive Assessment (MoCA), has greater sensitivity in identifying losses in the abilities to use language and perform tasks -- both common markers for encroaching dementia -- so your doctor may use this as well.

These tests can effectively identify people who already have dementia, but they are less effective at identifying people in the early stages of memory loss or those who have memory loss but also have a higher level of brain function. In these cases, much longer and more formal neuropsychological tests may be necessary. This testing is often done by a psychologist associated with a neurologist.

A neurologist may also order imaging tests of the brain. These tests can include an MRI, positron emission tomography (a PET scan) and possibly functional brain imaging that assesses areas of the brain with low activity. Although some findings might suggest Alzheimer's, these tests are used primarily to rule out other causes; they can't yield a definitive Alzheimer's diagnosis.

The potential to use cerebrospinal fluid biomarkers to help diagnose Alzheimer's disease is still in the investigational phase and unlikely to be used by a neurologist currently.

So start by talking to your primary care doctor about the change in your memory, how long it's been happening and whether it's rapidly getting worse. Your doctor will likely conduct a standardized test for memory, along with blood work to rule out other causes of memory loss. If that suggests a problem, but no other physical cause, you should see a neurologist for more formal testing.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)