Monday, November 17, 2014
Posted by Rob at 3:40 PM
Monday, November 10, 2014
Posted by Rob at 7:24 PM
Friday, November 07, 2014
High altitude environments present many challenges for human physiology. These challenges are due to the thin air at higher elevations. The partial pressure of oxygen decreases with air pressure and air pressure decreases exponentially with altitude. Air pressure is half of sea-level air pressure at 5000m. This decreased availability of oxygen at higher altitudes, or hypoxia, causes altitude sickness and potentially fatal high altitude pulmonary edema and high altitude cerebral edema. The frequency of these conditions and others increase with increasing altitude.
Mere mortal lowlanders are able to partially adapt to these physiological challenges. Initially, low oxygen partial pressure is detected by the carotid body triggering increased breathing rate. Additionally at high altitudes the heart beats faster with a lower stroke volume. Longer term exposure, over days or weeks, results in further acclimatization to altitude. The most well known acclimatization feature is an increase in hemoglobin and red blood cell (RBC) mass in order to increase the amount of oxygen that can be carried by the blood. Increased RBC mass leads to increased demand on the heart, and other complications such as hypertension, chronic mountain sickness, and high fetal mortality.
The Tibetan highlanders often live at elevations of over 3500m above sea level. One of the hallmark evolutionary adaptation of these populations is a lack of increased hemoglobin at high elevations correlating with a variant of the HIF2A gene encoding HIF2alpha. The HIF2alpha transcription factor protein is active under low oxygen conditions and helps control RBC production. The HIF2A gene variant found in Tibetan highlanders traces its ancestry to a recently discovered extinct human relative - the Densisovans. So this particular adaptation is due to interbreeding between the Denisovans and the ancestors of modern Tibetans. EGLN1 and PPARA are also positively correlated with Tibetans low hemoglobin adaptation to hypoxia. Other unique traits of Tibetans contribute to their altitude aptitude including an increased basal breathing rate that does not go away when exposed to lower elevation, a larger lung capacity, and a higher blood nitric oxide (NO) concentration which can help blood vessel dilation and circulation. Tibetans also have experienced selection for genes involved in metabolism, DNA damage response, DNA repair, and genes for high infant birth weight.
Genetic adaptation to high altitude among Andean populations are distinct from the Tibetan adaptations. While HIF2A and EGLN1 both exhibit evidence of selection pressure in these populations the particular variants are not associated with decreased hemoglobin. In fact these populations demonstrate the same temporary increase in hemoglobin with increasing altitude that lowlanders experience. They do have an increased oxygen level in their hemoglobin and thus a more efficient oxygen blood carrying capacity. The Andeans do not have an increased breathing rate, however one Andean subpopulation also has increased NO blood concentrations. The Andeas are the least well adapted to high altitude as evidenced by the frequency of chronic mountain sickness. An examination of Andeans with chronic mountain sickness found that many individuals have maladapted gene variants of SENP1 and ANP32D.
The Amhara of Ethiopia are also unique in their adaptations to a low oxygen, high altitude environment. This population are immune to the dangers of high elevations over 2500m, and have been inhabiting these environments for much longer, yet they do not have either the decreased hemoglobin or high oxygen saturation of the Tibetans or Andeans respectively. However one study had identified several candidate genes for involvement in high-altitude adaptation in Ethiopia. Two of these play a role in the HIF1alpha pathway, suggesting some degree of convergent evolution.
|An O2 mask is a pretty good altitude adaptation|
Posted by Rob at 7:12 PM
Tuesday, October 14, 2014
Posted by Rob at 2:46 PM
Tuesday, August 26, 2014
Posted by Kamel at 9:12 AM
Wednesday, July 16, 2014
|Slip on a shirt, slop on sunscreen, slap on a hat and wrap on shades.|
Getting lots of UV radiation causes skin damage and ages skin. A higher mean UV index has also been associated with increased incidence of melanoma in non-Hispanic whites. A prospective study of UV exposure and cancer incidence also confirms a higher incidence of melanoma in those receiving higher UV exposure. This same study however found a decreased risk of non-Hodgkin's Lymphoma and colon cancer with increasing UV exposure. The study also found significant protection from thyroid, pancreatic and squamous cell lung cancer at intermediate UV exposure levels. Over nine years this study found that UV exposure was inversely correlated to total cancer incidence. The authors hypothesize that the protective effect is due to vitamin D production that occurs in human skin under exposure to sunlight. Is it surprising that the benefits of sun exposure aren't nearly as well known as the risks? I clearly have not done a thorough literature search however there doesn't seem to be much information on UV exposure and total cancer risk. The benefits of UV exposure are possibly less established and have an unconfirmed mechanism which may contribute to the lack of publicity. Also various authorities on skin cancer encourage acquisition of vitamin D through dietary sources.
Posted by Rob at 4:20 PM
Friday, July 04, 2014
Posted by Rob at 2:27 PM
Wednesday, May 21, 2014
A past bayblab post on the topic of human pheromones suggested that there isn't much good data on the topic. A recent TED talk on the subject is an example of a good TED talk. The speaker Tristram Wyatt talks about the background and history of pheromones and the recent discovery of a potentially genuine human pheromone that acts on babies.
Posted by Rob at 11:39 AM
Friday, January 31, 2014
Posted by Rob at 3:02 PM
Wednesday, January 22, 2014
Posted by Rob at 6:17 PM
Sunday, January 19, 2014
Sweeping is done by one or more players on the team whose rock is being shot. The players sweep the ice, using specific curling brooms, directly in the path of the travelling rock. Sweeping reduces the deceleration and the degree to which the path of the rock curls.
A common belief is that sweeping melts a thin layer of ice ahead of the rock and that the resulting thin layer of water decreases friction between the rock and the ice. An investigation into ice temperatures resulting from sweeping demonstrated that sweeping raised the ice temperature by 1.5C and achieved a maximum ice temperature of -1C. It was also found that raising the temperature of the ice was crucial for the effectiveness of sweeping but the temperature measurements, as determined by infrared camera, suggested that sweeping doesn't melt the ice. I do not understand the exact methodology or much about infrared cameras but I remain skeptical that a sufficiently thin layer of ice temperature can be measured in this way. It is known that the melting point of ice is decreased under pressure, such as the pressure experienced by ice under the weight of the rock. Therefore I don't know how conclusive it is that the effectiveness of sweeping is not due to contributing to the creation of a thin layer of lubricating water. Nonetheless, it is the momentarily increased ice temperature created by sweeping immediately ahead of the moving rock that makes it effective.
Not surprisingly, the mechanism by which sweeping increases the temperature of the ice is friction. The evolution of materials used for curling brooms reflects this fact, with the latest fabric broom heads enabling a dense contact surface area with the ice. The latest innovation in sweeping brooms is the incorporation of a heat reflective material behind the fabric broom head [link to patent (pdf)]. This reflects some of friction heat back towards the ice to increase the efficiency of sweeping.
None of the above information is going to help one's curling performance, however I did find a review that does have some practical applications for curlers. The first thing that I learned from this review is that it is actually against the rules to not sweep across the entire width of the contact point of the rock with the ice. 'Corner sweeping', as it is known, is when the rock is swept only on one side. By reducing the friction asymmetrically as the rock travels, the amount of curling can be influenced. While 'corner sweeping' is illegal, it is perfectly legal to sweep from either side of the rock. The review points out that more sweeping force is produced on the side closer to the sweeper. Therefore changing the side on which the rock is swept, or having the stronger sweeper on a particular side, might be advantageous for some shots.
Another big question is 'hurry or hard' when sweeping. The review finds that sweeping fast for fast moving rocks and hard for slow moving rocks produces the most friction heat beneath the moving rock. Sweeping fast for fast moving rocks makes sense as the speed of the rock may prevent multiple sweeping passes over the surface area under the rock. When the rock is moving slower it is easy to do multiple passes so it is best to push down hard when sweeping to maximize the heat produced by friction.
In reality none of this information is going to make me a better curler. However, at least the old boys I play with can't say that my poor performance is due to ignorance.
Posted by Rob at 5:38 PM
Wednesday, December 18, 2013
Posted by Rob at 4:10 PM
Tuesday, December 10, 2013
In a recent example of an interesting article at NERS, Ed Yong writes about the effects of the gut microbiome on cancer drug efficacy. Ed puts together the work of two groups and simplifies the case for a major role for gut bacteria in modulating anti-cancer treatments in mice. NERS is definitely worth a bookmark if you want to keep up to date on interesting and surprising findings like these.
Posted by Rob at 4:44 PM
Wednesday, November 27, 2013
Posted by Rob at 2:18 PM
Wednesday, October 16, 2013
As a fan of the ideals of open access publishing I do believe this was an important finding. Clearly there are problems with the peer review process in these journals. This needs to be addressed.
What I find strange is that the conclusions of this experiment fail basic logic. This experiment had no controls. There were no submissions of the spoof article to closed access journals, therefore it is impossible to conclude that the acceptance of poor scientific manuscripts is specific to open access journals. This stunt was also not a test of the open access ideology or business model, it was only a test of the peer review process of these journals. No doubt, those open access journals that accepted the article clearly failed the most basic requirement of scientific publishing, however Science magazine has also mistakenly accepted flawed papers. I found a more balanced assessment of the meaning of this experiment at National Geographic.
Posted by Rob at 2:23 PM
Wednesday, October 02, 2013
One source that we have to mention, despite the fact that it is not strictly science, is Numberphile. Numberphile is a Youtube channel that consists of "videos about numbers and stuff." Again, the host is excellent and there are some very interesting videos.
For example, in these days of revelations of the NSA's activities, the history of encryption seems a relevant topic. The Code Book by Simon Singh is a great read covering exactly this topic. Among other encryption stories, The Code Book explains the detailed workings of the Nazi encryption machine known as Enigma. This impressive encryption machine and the cracking of Enigma encryption played a significant role in the course of WWII. While I highly recommend reading The Code Book if you are interested in this topic, two Numberphile videos covering the amazingly complex encryption arising from a seemingly primitive machine do a very good job. The first video explains how the Enigma machine works and reels you in for the second video explaining the flaw that made the Enigma machine possible to crack. In its historical context it is a very compelling story.
I also found it nerdily satisfying that Simon Singh, author of The Code Book, made an appearance on Numberphile to briefly discuss Fermat's last theorem.
Posted by Rob at 1:21 PM
Monday, September 23, 2013
|A personal brewery could fit in there.|
A recent 'news' story caught my attention as it was about a man with a bizarre affliction. The subject was apparently drunk to varying degrees for five years straight. Of course this isn't that unusual, except that he was not drinking alcohol, the flora in his gut was fermenting dietary carbohydrates into ethanol. After years of being a suspected 'closet drinker' he was treated with antifungal medication and is now free of his involuntary inebriation.
According to the linked news article the condition is very rare, however upon searching for this syndrome on pubmed I am given a different impression. The only article I found that examined frequency of endogenous ethanol production examined patients blood for a glucose tolerance test. Baseline measurements in 2.7% of patients demonstrated the presence of some ethanol after receiving capsules of glucose. Most surprisingly, over 60% of the patients had an increase in ethanol one hour after receiving oral glucose. Those who had a baseline ethanol measurement also had the greatest increase in blood ethanol levels. Sixty percent is not a rare occurrence and it makes one wonder if endogenous ethanol production is clinically relevant in the context of some health conditions. This has been proposed before but I haven't seen anything convincing.
For context, an 80kg male drinking three drinks in two hours will have a blood ethanol concentration of 33mg/dL, while the measured increases in this study averaged under 3mg/dL and the highest measured increase was 7mg/dL. Clearly, none of the patients would notice the effects of ethanol from dietary carbohydrate ingestion. Additionally, it has already been argued that the possibility of having this syndrome is not a credible defence against a drunk driving charge.
Unfortunately the most 'beneficial' effects of ethanol are achieved, most often, at levels requiring an exogenous source. Fortunately beer is tasty.
Wednesday, September 11, 2013
A recent SciShow describes some basic facts about Sarin gas, the nerve agent that recently killed hundreds of Syrian civilians. The video describes Sarin as an inhibitor of acetylcholinesterase. Sarin's inhibition of this enzyme prevents removal of actylecholine from neuromuscular junctions resulting in continuously contracting muscles and death from asphyxia due to the inability to control the muscles involved in breathing function.
Interestingly there are antidotes for sarin gas exposure and the resulting irreversible inhibition of acetylcholinesterase. Some antidotes simply inhibit acetylcholine receptors preventing the action of the accumulated acetylcholine and are themselves a poison. However pralidoxime (2-pyridine aldoxime methyl chloride,) or 2-PAM actually restores function to the irreversibly inhibited enzyme. It reacts with organophosphorus nerve agents such as sarin and reverses the covalent bond to the serine in the active site of acetylcholinesterase resulting in a reactivated enzyme. I have never heard of such an antidote or reaction. While I guess it is comforting to think there are antidotes to these weapons they are largely impractical due to the time frame in which they must be administered.
Are there any other examples of molecules that can reverse the irreversible inhibition of an enzyme?
Posted by Rob at 4:08 PM
Tuesday, April 23, 2013
Where I'm living black bears are quite commonly seen around town. While I have yet to hear of a really bad bear encounter many bears are destroyed every year for getting too familiar with town. Most people here merely avoid them when they see them. Alternatively, aggressive responses to threatening bear encounters include firearms and pepper spray. While obtaining a firearm requires getting a firearms license and many restrictions, getting bear spray is as simple as purchasing some from Canadian Tire.
Wednesday, October 31, 2012
We have previously posted and pondered on the condition, amusia, also known as tune deafness here at the Bayblab. Essentially amusia sufferers have difficulty following pitch changes in music. You have probably heard sufferers of this condition at Karaoke night, and you can take this very interesting test to see if you too are tune deaf and have made others suffer on Karaoke night.
A recent study has found that indeed amusia has consequences for language processing. While the importance of tune in music is obvious, tune is also important to communicate an emotional quality to spoken words. Pitch changes in language can indicate sarcasm, irony, irritation and other emotions that are independent of the words that are spoken. As you might guess, according to this study, it is the interpretation of these emotional tonal cues of language that are deficient in sufferers of congenital amusia. Of course, this doesn't mean that sufferers can not interpret body language or other cues, however the deficit is significant enough that some sufferers are aware of their difficulty in this respect. I have been looking for any information on amusia in people who speak tonal languages as I imagine it would be very debilitating. In any case, next time someone you tell someone how fantastically frequent Bayblab updates have been recently, and they agree, don't let them sing at Karaoke night.