COVID-19 affects sense of smell differently than colds, flu

Q: Why are people making a big deal out of the fact that you can lose your sense of smell and taste when you get sick with COVID-19? The same thing happens to me when I've got a plain old cold.

A: Many of us who have slogged through the unpleasant symptoms of a cold or the flu know that losing your sense of smell, and often a large portion of your sense of taste, is a common part of the experience. The same has proved to be true with COVID-19. However, it turns out that this loss of the sense of smell, known as anosmia, occurs for two very different reasons.

Let's start with a cold and the flu. Our immune systems fight these infections on multiple fronts, including the one-two punch of mucus production and inflammation. This combination does an excellent job of blocking our sinuses. Since the sense of taste is closely linked to the sense of smell, both take a steep dive during the plugged-up phase of an illness. With specialized nerve endings in the nasal passages unable to send a full range of information to the brain, the subtleties of taste are gone. What we're left with are the broad strokes of bold flavors. That's why, when we're fighting a cold or the flu, the sweetness of hot tea with honey or the saltiness of chicken soup tastes particularly good.

When it comes to COVID-19, researchers have recently uncovered the surprising reason for anosmia as one of the earliest symptoms of infection. Rather than congestion, as with a cold or the flu, the loss of smell in people with COVID-19 occurs due to how the virus affects the nervous system.

According to a study published by researchers at Harvard University earlier this summer, SARS-CoV-2, the virus that causes COVID-19, attacks certain cells whose job is to support the olfactory sensory neurons. These are the specialized nerve cells that detect the chemical compounds that make up a scent, known as odorants, and transmit that information to the brain. The brain then decodes the electrical impulses, which allows us to experience them as scent. By damaging the support cells, the virus prevents the olfactory sensory neurons from responding to the molecules that make up different types of scents. The good news is that for most patients, recovery from COVID-19 includes a return of their sense of smell.

As we've mentioned here before, researchers are still in the earliest stages of learning about the novel coronavirus and COVID-19. That makes each new bit of information important.

As cases began to mount, it became clear that only about half of contagious people presented with a fever as an early symptom. At the same time, it emerged that a loss of the sense of smell was one of the first symptoms of infection. Since early intervention gives people who become ill with COVID-19 a better chance of recovery, this has been a significant finding. Thus, the widespread news stories and discussions you have noticed.

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Breathing into a paper bag can calm anxiety attack

Q: I was having a panic attack and thought I might faint. My dad had me breathe into a paper bag, and it helped me calm down. I've only ever seen that on TV. Why did it work? Was it because I ended up doing deep breathing?

A: It's interesting how, when a TV character hyperventilates, someone just happens to have a brown paper lunch bag for them to breathe into. And while the rhythmic nature of that breathing may contribute to calming down the person, the actual theory behind the maneuver is rooted in biochemistry.

To understand why, let's start with the anxiety attack. Often referred to a panic attack, it's the sudden onset of symptoms associated with fear, despite the absence of genuine peril. Among the many unpleasant and unsettling symptoms of a panic attack is the rapid and uncontrolled breathing known as hyperventilating. When this happens, it quickly causes the concentrations of oxygen and carbon dioxide in the blood to get out of balance.

Unlike in controlled breathing, which allows the respiratory system to take in oxygen and expel carbon dioxide in optimal amounts, hyperventilation causes a surplus of oxygen and a deficit of carbon dioxide, also known as C02. Since C02 is a metabolic byproduct - sometimes it's referred to as a waste product - that may not seem like a bad thing. Too much C02 dissolved in the blood can cause symptoms that range from dizziness, drowsiness, headache, confusion and shortness of breath to heart arrhythmias, seizures and loss of consciousness. However, too little C02 is also a problem.

Our blood has an optimal pH, which is maintained by a specific ratio of dissolved oxygen and carbon dioxide. When you hyperventilate, that ratio is disturbed. Too much oxygen causes the pH of the blood to rise and become too alkaline. This is known as respiratory alkalosis. Symptoms can include anxiety, dizziness, dry mouth, tingling in the fingers and arms, chest pain or tremors. In fact, some research has suggested a link between panic disorders and poor regulation of blood pH.

All of which brings us back to the person now breathing into a paper bag. With every exhale, they are filling the bag with C02. With every inhale, they make that C02 available to their over-oxygenated blood. When you inhale your own exhaled air, it's known as rebreathing. The theory is that, after a moment or two, rebreathing will begin to stabilize blood pH and perhaps ease your symptoms.

However, it's important to note that rebreathing is unsafe for certain people, particularly those with heart or lung problems. Having too little oxygen in the blood, which is known as hypoxemia, can share symptoms with an anxiety attack. These include shortness of breath, dizziness and rapid breathing. If someone experiencing hypoxemia practices rebreathing with a paper bag, they're not only making their immediate condition worse, they're putting themselves in danger.

The bottom line is, unless you know beyond a shadow of a doubt that you're hyperventilating due to an anxiety attack, leave the paper bag maneuver to the TV writers.

<h3 class="leadin">Gutoscopy uses smart pill to collect samples

Q: What on earth is a "gutoscopy?" We saw it on the news - something about a pill that goes in one end and comes out the other, but it sounded more like science fiction than anything real.

A: Your question brings us to the brave new world of what are sometimes referred to as "smart pills." These are tiny devices, small enough to be swallowed, that perform a range of functions as they move along the gastrointestinal tract. This can include the precision delivery of medication, the collection of different types of data, and keeping track of whether or not someone is taking a prescription as needed.

Certain types of smart pills are equipped with biosensors, pH and chemical sensors, or imaging capabilities. Classified as ingestible sensors, they can be used to collect information such as pressure readings, pH and temperature data. The data they gather can shed light on the workings of the stomach, small bowel and colon. Rather than an invasive procedure that requires surgery or an instrument threaded through a catheter, the patient swallows a capsule that contains the miniature sensor. The device then transmits its findings to a computer.

Some types of smart pills are engineered to collect samples from inside the body for study and analysis. That's the case with the "gutoscopy" device you're referring to in your question. Developed several years ago by researchers at Purdue University, the team published a paper about its findings earlier this year. Their goal was to devise a noninvasive method to learn more about the billions of microscopic organisms that live within the human gut.

Research continues to link the workings of the gut microbiome to an ever-expanding array of biological functions and health conditions. This includes obesity, diabetes, mood, digestive disorders, cardiovascular health and certain cancers. The composition of the gut microbiome has also been linked to various neurological diseases, including Parkinson's disease, multiple sclerosis, autism spectrum disorder and Alzheimer's disease.

The "gutoscopy" capsule, which is still in the research phase, is made of nontoxic 3D-printed resin. It's formulated to dissolve at a specific pH within the gut. This allows the release of a "thirsty" gel, similar to that used in moisture-absorbing pads and diapers. The hydrogel collects gut bacteria from the fluid of the intestine. The capsule is designed to travel the length of the bowel, carried along by the natural wavelike contractions of the digestive process. It collects samples as it goes, until a change in pressure forces the capsule to close. The device passes from the body in a bowel movement. Researchers can then open the capsule, collect the gel and analyze the array of gut flora that it contains.

Unlike existing diagnostic tests, such as a colonoscopy or an endoscopy, this new capsule can travel the entire length of the gut, and it wouldn't have to be administered in a clinical setting. The goal is to learn more about the diversity of microorganisms living within the gut. That information can help researchers better understand disease processes, and craft medications and therapies.

• Dr. Eve Glazier is an internist and associate professor of medicine at UCLA Health. Dr. Elizabeth Ko is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu.