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Can you ever breathe so much air that it’s bad for you? If so what about it makes it bad? by brioDesigns in askscience

[–]baloo_the_bear 1 point2 points  (0 children)

There are several ways to divide lung volumes, and what you described is correct. But in the context of mechanical ventilation, tidal volume is the volume delivered per breath by the machine. When not on mechanical ventilation, a person has a certain inspiratory capacity determined by lung compliance, abdominal compliance and chest wall recoil. At rest, tidal volume is the volume of each breath. When on mechanical ventilation, however, we manually set the tidal volume. It is determined by ideal body weight as a function of height. In some pathological states, the compliance of the lung is reduced causing elevated pressures for a given lung volume. So if the lung volume is too high, you can cause volutrauma to the lung.

Can you ever breathe so much air that it’s bad for you? If so what about it makes it bad? by brioDesigns in askscience

[–]baloo_the_bear 0 points1 point  (0 children)

Well not exactly. The V/Q mismatch from hypoeroxia definitely increases CO2 retention, as well as the Haldane and Bohr effects with elevated partial pressures of O2 in the blood. Respiratory drive does play a role as well.

Can you ever breathe so much air that it’s bad for you? If so what about it makes it bad? by brioDesigns in askscience

[–]baloo_the_bear 3 points4 points  (0 children)

There’s a few things to consider when thinking about supplemental oxygen.

Respiratory physiology looks at oxygenation and ventilation. Oxygenation refers to how well the lungs can extract O2 from the alveoli. The alveolar gas equation is used to see if there’s what’s called an A-a gradient. A normal A-a gradient is under 20, and varies with age. Large gradients can indicate lung parenchyma pathology. Supplemental oxygen can be given in these cases to increase the fraction of inspired oxygen (FiO2). High FiO2 for a prolonged time can cause oxygen toxicity, reactive oxygen species, or fibrosis.

Ventilation deals more with CO2 levels, and it refers to how well gas is cleared from the lungs. Many things can cause elevated CO2 levels, and arterial pH is intimately tied to CO2 levels and CO2 dissolves in serum to crest carbonic acid. The kidneys also play a role in pH management but cannot react to changes as quickly as the lungs.

Respiratory drive is primarily controlled by pH, not hypoxia. In those patients with chronic hypercapnia, the pH receptors become desensitized to high CO2 levels, and hypoxia becomes the driver of respiration. This is why putting these patients on high FiO2 can be dangerous, as the respiratory drive drops, CO2 levels rise, and the patient can end up in CO2 narcosis.

Can you ever breathe so much air that it’s bad for you? If so what about it makes it bad? by brioDesigns in askscience

[–]baloo_the_bear 16 points17 points  (0 children)

Yes you can. There are a couples things to think about when it comes to breathing.

If you hyperventilate you will blow off too much CO2, causing a respiratory alkalosis. Changes in pH outside normal homeostasis have many effects, none of which are good. This is linked mainly to respiratory rate.

There is also the total volume of each breath, tidal volume. If the volume inhaled is too high, the pressures in the lung go up. High pressures in the lung can cause trauma to the lung parenchyma leading to many lung pathologies. This is usually only an issue on patients on a mechanical ventilator.

Together, tidal volume and respiratory rate make up the minute ventilation, a volume of breaths over a minute. High minute ventilation can be caused by a number of things, and is an important clue in clinical medicine.

Why is poo almost always brown, regardless of what we eat? by Jimcube27 in askscience

[–]baloo_the_bear 63 points64 points  (0 children)

Just going to say now I kinda wish my name was barloo. You're right that anything you eat can affect the color of feces; though, the major factor in overall color is stercobilin.

Why is poo almost always brown, regardless of what we eat? by Jimcube27 in askscience

[–]baloo_the_bear 1164 points1165 points  (0 children)

The brown color of feces comes from the pigment stercobilin, one of the final products of heme (red blood cell) breakdown. Urobilin is similar; it also comes from heme catabolism. However it is yellow and excreted in the urine due to high water solubility. Changes in fecal color can indicate a wide range of issues, in the appropriate clinical context.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 3 points4 points  (0 children)

Heart rate is partly controlled by the vagus nerve via parasympathetic drive. The heart itself has its own pacemaker, the sino-atrial node. The cells in this area slowly build up a cell membrane potential due to concentration gradients set up by the biochemistry of the cell. Specific transmembrane protein channels will react to the change in voltage once it reaches a critical level. At the critical level the channels change shape to open wide, allowing specific ions to cross the membrane freely, resulting in electrical activity that propagates through the organ. This is why a heart will beat even once removed from the body. The heart also responds to sympathetic drive, local factors, and metabolites.

The diaphragm is innervated by the phrenic nerve, which forms from parts of third through fifth cervical spine nerve roots. The respiratory drive center is a loop between the medulla and pons. Respiratory drive is stimulated by two things: pH and oxygen saturation. The primary driver is pH. Carbon dioxide dissolves into the blood as carbonic acid. As CO2 rises pH drops, and the change stimulates cells in the carotid sinus to send signals up to the central nervous system to stimulate the respiratory center. However, if a patient has bad lung disease and has elevated CO2 levels chronically, the carotid sinus loses sensitivity to pH, and hypoxia becomes the major drive. This is why putting oxygen on a COPD patient who is chronically hypercapnic on oxygen can actually cause a drop in respiratory drive leading to CO2 narcosis. Respiratory drive can be temporarily overridden, but eventually you'd fatigue if hyperventilating or pass out if holding your breath.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 2 points3 points  (0 children)

I agree it's pretty vague. I'm not a neuroanatomist by any stretch of the imagination. I consider mesencephalon separate from and above brainstem; I'm not sure of the actual cutoff.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 0 points1 point  (0 children)

I'd say everything above CN VIII or so is above the brainstem/medulla. All of them are above the spinal cord.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 0 points1 point  (0 children)

Loss of cranial nerve function indicates severe brain damage. Cranial nerve reflexes are tested to determine the level of brain damage a person may have. Typically damage occurs from the top down, ie cerebral/executive function is lost first, progressing to loss of pupil reaction, etc on the way down. Check out my comment above on the functions of each nerve.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 12 points13 points  (0 children)

Facial sensation has its own nerve, the trigeminal nerve. I don’t know if anything regarding the nerve itself that makes it more sensitive. There is a strip in the brain responsible for sensory input from all over the body. The area that takes input from the face is oversized, indicating a higher level of sophistication and sensitivity. The hands/fingers are also represented by a relatively oversized area. The strip is called the homunculus and is located in the parietal lobe iirc.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 32 points33 points  (0 children)

Dolls eye is where you take the patients head and turn it side to side, looking for an intact vestibulo-ocular reflex. Caloric testing is when you put cold or warm water into the ear to cause fluid movement in the semicircular canals of the ear (simulating head movement) and you look for eye movement again as part of the V-O reflex.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 190 points191 points  (0 children)

The cranial nerves:

  • CN I: olfactory - smell
  • CN II: optic - vision, pupil control
  • CN III: oculomotor - most muscles of eye movement, pupil control, some eyelid control
  • CN IV: trochlear - eye movement
  • CN V: trigeminal - facial sensory
  • CN VI: abducens - eye movement
  • CN VII: facial - facial motor, some taste
  • CN VIII: vestibulocochlear - balance and hearing
  • CN IX: glossopharyngeal - oral sensation, taste, salivation
  • CN X: vagus - parasympathetic innervation to the body, many many functions
  • CN XI: accessory - shoulder shrug
  • CN XII: hypoglossal - tongue movement

Testable reflexes:

  • Pupil reflex - nerves 2,3 - diencephalon
  • Corneal reflex - nerves 5,7 - mesencephalon
  • Dolls eye/caloric testing - nerve 8 - mesencephalon
  • Gag reflex - nerves 9, 10, 11 - medulla
  • Spontaneous breathing - brainstem/ medulla

What is the difference between sleeping and just laying down to rest? How do the 2 differ when it comes to your health? by P1ka_chu in askscience

[–]baloo_the_bear 0 points1 point  (0 children)

SSRIs typically suppress REM sleep and increase sleep latency. Some SSRIs can also worsen or unmask primary sleep disorders like restless leg syndrome, bruxism, nightmares, etc.

Why can completely paralyzed people often blink voluntarily? by hash8172 in askscience

[–]baloo_the_bear 9037 points9038 points  (0 children)

Blinking is a motor function controlled by the facial nerve, the seventh cranial nerve. Cranial nerves come directly from the brainstem, bypassing the spinal cord. Cranial nerve reflexes are often used to assess levels of brain function (diencephalon, mesencephalon, and medulla).