The Causative Agent, vol 3
7/4/2022
Pulse oximeters are less accurate on dark skin.
A pulse oximeter is a non-invasive way to determine how much oxygen is being carried around by circulating red blood cells. It fits over the end of your finger, shining a red and an infrared light through your skin. Oxygenated and de-oxygenated red blood cells absorb light differently, allowing more or less of the light to pass through your finger to the other side of the device where a detector measures it. This is a nearly ubiquitous way to determine your level of blood oxygenation, and ideal levels are 95-99%. If the pulse oximeter reads 94% saturation or less, then oxygen supplementation is begun (and during COVID-19, this threshold was also used to determine if anti-virals like Remdesivir should be admnistered).
A new study in JAMA shows that pulse oximeters often overestimate how much oxygen is in the bloodstream of Black, Asian, and Hispanic individuals (due to differences in skin tone and pigmentation)… leading the clinician to believe that the person is getting more oxygen to their tissues than they really are. This can cause delays in treatment or inequities of care.
In a study of 1216 COVID-19 patients who had their blood oxygen levels assayed by both a pulse oximeter and by directly measuring oxygen in a blood sample, they found that the pulse oximeter overestimated the oxygen levels in the blood of Asian, Black and Hispanic patients far more often than in Whites. Patients having less than 88% actual oxygen saturation (but whose pulse oximeter read as normal) was discovered in 30.2% of Asian patients, 28.5% of Black patients, 29.8% of Hispanic patients, and 17.2% of White patients.
This “occult hypoxemia” (undiscovered low oxygen saturation) resulted in patients not getting the treatment that they needed (like oxygen supplementation or Remdesivir). Compared to Whites, Blacks had a 29% lower chance of being recognized as needing treatment, and Hispanics had a 23% lower chance. Its interesting that there was no reduction in recognition of Asian patients, especially since they had some of the most unreliable pulse oximeter readings, but there were far fewer Asians included in this study than any of the other ethnic groups.
The Rundown: Pulse Oximeters can be unreliable in all groups, but seem to be more inaccurate in Asians, Blacks and Hispanics. These inaccurate readings may lead patients to not receive the critical emergency care that they need.
Breast cancer spreads at night
Image from: The metastatic spread of breast cancer accelerates during sleep.
In this study from Nature, the researchers probed into the phenomenon that breast cancer outcomes seem to be connected with circadian rhythm and sleep cycle (previous studies have shown that people with disrupted circadian rhthyms like those that do shift work, have an increased risk in incidence of breast tumors). This study found that breast cancer tumor metastasis (the movement of tumors cells from one site of the body to another, leading to spreading of the cancer) was far more likely to happen during rest periods (nighttime for humans, daytime for nocturnal mice).
In the figure above, 21 patients (pat) with early stage breast cancer, and 22 patients with late stage breast cancer, gave blood samples during the day and the night. Circulating Tumor Cells (CTC) representing breast cancer cells that are moving around the body, were found in abundance at night (red color in the pie chart) and far less likely during the day (blue color). Similar results were found in mice.
In the experimental mice model, the researchers also found that this effect seemed to be modulated by three hormones that have a circadian pattern: dexamethasone (a steroid similar to hormones produced by the adrenal glands), testosterone, and insulin. All three of these hormones are present in higher concentrations during the active phase, and lower concentrations during the rest phase. Mice with breast cancer were given these hormone injections during the rest phase (when concentrations should be low) and they found that the level of Circulating Tumor Cells dropped significantly…. this would reduce the chance of the cancer spreading. Interestingly, rest-phase injection of insulin reduced CTC levels during rest, but increased CTC levels during the active-phase. This is not the first time that insulin has been shown to affect breast cancer. People with insulin resistance (leading to a high level of insulin in the blood stream) have an increased level of many types of cancer, including breast cancer.
The Rundown: Breast cancer cells are more likely to metastasize during rest, in both humans and mice. This effect could be explained by the different levels of hormones (like dexamethasone, testosterone and insulin) that are tied to the circadian cycle. Timing cancer treatments to the circadian rhthym may ultimately make them more effective in preventing metastasis. This is also another indication that managing insulin levels has a preventative effect on breast cancer incidence and progression.
The metastatic spread of breast cancer accelerates during sleep.
Circadian clocks and breast cancer
Magic Musroom microdosing is associated with better mental health
A surge in research using banned substances like MDMA, LSD, ketamine and psilocybin (the hallucinogenic component of “magic mushrooms”) has shown many positive effects on mental health. Sessions of drug administration, in the presence of a therapist, have had enormous beneficial effects on the treatment of post-traumatic stress disorder, anxiety, depression, addiction and end-of-life issues. Some of these studies have taken place at very well respected institutions like Johns Hopkins, lending credence to this emerging field. Now, a new study in Nature looks at the effect of “microdosing”, or taking these substances in quantities so small that it does not impair functioning.
This study compared 953 people taking microdoses of psilocybin (alone or alongside Lions Mane mushrooms or niacin) with 180 non-microdosers over the course of one month. They found that the microdosers had a significant reduction in depression, anxiety and stress compared to their non-microdosing counterparts. Interestingly, the reduction in depression seemed to be even greater in females. Microdosing also seemed to improve mood across the month, with no differences in gender. Microdosing was also associated with an improvement of cognitive funtioning. The addition of lion’s mane mushroom and niacin boosted that effect even more in older participants (over age 55).
While this study is better than previous microdosing studies in that they included a well-matched control group, they did not include a placebo. This opens the door to the possibility that placebo effects could be responsible for the improvements.
The Rundown: Psilocybin given in doses large enough to induce a psychadelic experience (alongside talk therapy) has been shown in the past to be very beneficial to an array of psychological disorders. Now, we see that microdosing may also have beneficial psychological and cognitive effects. Psilocybin is still illegal in the United States, so much more work needs to be done at the clinical level to possibly take this compound off the Controlled Substances list. Several cities have decriminalized psilocybin though, including: Denver, CO; Oakland and Santa Cruz, CA; and Washington D.C.
Stay happy, healthy and informed,
Jessica at 42Therapies