Folks have lengthy been fascinated with hearts—how they work, how they alter and the way they break. The Grinch’s coronary heart grew three sizes. Sgt. Pepper had a band for lonely hearts. And the Physician on the British science-fiction tv collection Physician Who has two hearts, beating in double time.
Hearts function a robust metaphor in Physician Who, which follows a time-traveler referred to as the Physician, who belongs to an alien species referred to as the Time Lords. It’s attention-grabbing that somebody largely unconstrained by time has not one however two organs dependent upon it. Our “tickers” operate as metronomes of life, marking out time inside our chests. This could be why the Physician wants two of them: their timeline doesn’t march to a single beat.
As an aspiring medical physician and avid Physician Who fan, I discovered myself questioning in regards to the anatomy and physiology of the Time Lord cardiovascular system. How are the 2 hearts related, and the way are the heartbeats regulated? How does the Physician survive centuries with out growing age-related coronary heart illness? How may a twin cardiac system have advanced? I needed to discover out. Sadly, Time Lords are tough to review due to their small inhabitants and tendency to indicate up for appointments within the improper century. So to reply these questions, I analyzed information on cardiac incidents from 13 seasons of Physician Who (2005 to 2023), pored over the cardiovascular literature on people and different species, and consulted varied consultants in these and associated fields. By means of my in depth research, I’ve developed what I believe are believable solutions to my questions in regards to the Time Lord’s two hearts.
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Particulars of the Physician’s twin cardiac system emerge piecemeal all through the collection. We first be taught that Time Lords have two hearts within the season one episode entitled “Dalek,” when the Physician is physique scanned by a collector of alien artifacts. Later, a medical examination of the Physician by Dr. Martha Jones in season three reveals a twin heartbeat. These offset heartbeats mark 4 beats per cardiac cycle: “lub-dub-lub-dub (pause) lub-dub-lub-dub,” contrasting with the human “lub-dub (pause) lub-dub.” This rhythm means that the 2 hearts’ contractions are regulated collectively. The final format of Time Lord hearts, proven within the episodes “Dalek” and season seven’s “The Power of Three,” signifies one coronary heart on all sides of the chest.
The Physician’s signs when certainly one of their hearts fails present additional perception into the format of their cardiovascular system. Evidently, one coronary heart is sufficient to quickly maintain a Time Lord however not with out vital ache and problem shifting—most definitely from lack of oxygen reaching their tissues.
By watching the Physician’s hearts fail, we are able to perceive how they operate. In “The Power of Three,” one of many Physician’s hearts wanted an electrical shock to the chest. However in “The Shakespeare Code” (season three), it was restarted by placing the sternum with the facet of the fist. In consulting my mentor Janak Chandrasoma, an anesthesiologist on the College of Southern California, I realized that these methods are well-established medical therapies for human ventricular fibrillation and ventricular tachycardia—each harmful coronary heart rhythms. In “The Stolen Earth” (season 4) an much more extreme coronary heart drawback necessitated using extrahuman talents to restore the harm, in all probability due to asystole, or a “flatline”—a nonshockable rhythm.
In people, electrical shocks can even cease hearts, relying on a person’s well being and the shock’s location and timing. The Physician has frequent run-ins with their archenemies the Daleks, who wield a type of gun that fires demise rays slightly than bullets. Although we don’t but know the precise mechanism of the Dalek demise ray, it presumably delivers a type of shock. Like people, the Physician seems to have diverse physiological responses to cardiac stressors, as demonstrated by their inconsistent responses to Dalek assaults. In “The Stolen Earth,” a demise ray stops one of many Physician’s hearts, however in “The Big Bang” (season 5) the weapon seems to cease each of their hearts. As in people, completely different cardiac accidents in several circumstances result in completely different outcomes.
In all three of those cardiovascular crises, the center with the issue has been on the left. These findings recommend that their cardiovascular system could also be asymmetrical—that’s to say, particular person nonessential organs such because the abdomen and intestines don’t essentially get an equal share of blood from every coronary heart. However though all of our information are based mostly on incidents with the Physician’s left coronary heart—we all know nothing of proper coronary heart issues—this sample could also be a coincidence. Different proof suggests Time Lord circulatory programs aren’t essentially asymmetrical. When the Physician experiences left-sided coronary heart collapse, their signs apart from chest ache aren’t localized to 1 facet. Their mobility loss and ischemic ache—that’s, ache that comes from a scarcity of oxygen reaching the tissues—is systemic, suggesting that every coronary heart is concerned in sending blood to each side of the physique.
The present doesn’t specify whether or not the Physician’s blood runs in collection, flowing by one coronary heart after the opposite, or in parallel, with two streams flowing facet by facet. We additionally don’t know whether or not the hearts fail when open or closed. However we are able to make some educated guesses based mostly on the anatomy and functioning of human hearts.
The job of the center in any animal is to pump blood all through the physique to provide tissues with oxygen and vitamins. To do this, it should create sufficient strain to push the blood by the physique’s community of arteries, veins and capillaries. The guts generates this strain by forcefully contracting to squeeze out blood and overcome the resistance of the blood vessels. When two hearts are in parallel, rising one coronary heart’s resistance can solely enhance the overall resistance by a lot. The other is true for hearts in collection: if both coronary heart has infinite resistance, the resistance of the entire system goes to infinity. Thus, if a coronary heart in collection fails whereas closed, then all blood circulation stops. As a result of we all know the Physician can partially operate with one operational coronary heart, we are able to rule out the chance that their hearts are organized in collection and fail whereas closed.
Time Lords have two hearts within the tv collection Physician Who. The present doesn’t specify whether or not the hearts are organized in parallel or in collection, however the obtainable proof signifies they’re in parallel. On this picture of the 2 doable configurations, the resistors characterize the interior resistance of the hearts and the overall peripheral vascular resistance.
When the Physician had a one-sided coronary heart disaster in “The Power of Three,” they skilled signs of very excessive blood strain, together with chest ache and shortness of breath. Albert Herrera, a professor of organic sciences on the College of Southern California, helped me perceive these signs mathematically. Ohm’s regulation states that the voltage (analogous to blood strain) is the same as the present (circulation price) occasions the resistance: V = IR. When a coronary heart in parallel fails closed, the systemic resistance will increase. All of the blood is shunted by the wholesome coronary heart because it makes an attempt to keep up its typical heartbeat. Extreme filling of the center with blood in people with a single coronary heart causes issues in the long run, however within the brief time period, it helps preserve the circulation price roughly steady. If the circulation price is roughly fixed and resistance will increase, then blood strain will increase—explaining the Physician’s signs. So we are able to conclude from this statement that the Physician’s two hearts are organized in parallel.
To find out whether or not the Physician’s hearts fail whereas open or closed, we’ve to take a more in-depth take a look at blood circulation. If the hearts have been to fail whereas open, then in accordance with Ohm’s regulation, there can be a drop in blood strain proportional to the (low however nonzero) resistance of the hearts. The failed coronary heart would nonetheless enable for blood circulation, however and not using a heartbeat, it could be unable to contribute to systemic blood strain. The resistance of each the failed coronary heart and the system as an entire would stay unchanged, however the systemic circulation price would lower (just one coronary heart beating as a substitute of two), so the overall blood strain would lower.
Very low blood strain, or hypotension, just isn’t instantly deadly—however it might probably trigger dizziness and fainting, not signs the Physician experiences throughout acute single-heart collapse in “The Power of Three.” As a result of the Physician doesn’t exhibit signs of hypotension after single-heart collapse, it’s cheap to presume that Time Lord hearts don’t fail when open. The one remaining possibility is that the Physician’s hearts are organized in parallel and fail whereas closed.
At this level you could be questioning, as I’ve, in regards to the development of the hearts themselves. Human hearts have 4 muscular chambers; two pump blood to the lungs to select up oxygen, and two pump that blood by the remainder of the physique to ship oxygen and vitamins. Some animals have completely different coronary heart configurations: fish hearts have two chambers, as an illustration; amphibian hearts have three. However assuming the Physician has two hearts as a result of Time Lord our bodies have vital circulatory calls for, it follows that every coronary heart has advanced to maximise effectivity. So it’s unlikely that the hearts have two or three chambers as a result of these configurations enable for the blending of oxygenated and deoxygenated blood, lowering effectivity.
As a substitute I theorize that Time Lord hearts have 4 chambers. Every coronary heart, working in parallel, dedicates two chambers to a pulmonary circuit, sending blood by the lungs, and two chambers to a systemic circuit, sending blood by the remainder of the physique. Each hearts ship blood into the lungs through a merged pulmonary artery, the place deoxygenated blood from the 2 programs combine. We all know that each hearts provide the important organs with blood as a result of the Physician survived a number of hours between single coronary heart collapse and defibrillation in “The Power of Three.” The Physician’s symmetrical dysfunction suggests that every coronary heart pumps blood to each side of the physique.
The creator proposes that within the Time Lord cardiovascular system, every coronary heart sends blood to the important organs in addition to a subset of the much less crucial organs.
The rhythm of the 4 consecutive Time Lord heartbeats has been woven into prophecies, desires and even songs all through the TV collection. How do these two hearts preserve time? Human coronary heart charges are regulated by a small mass of specialised tissue inside the center referred to as the sinoatrial, or “pacemaker,” node. The sinoatrial node usually generates an everyday electrical stimulus 60 to 100 occasions a minute. In people this node can function with out enter from the mind, though indicators from the mind can inform the center to hurry up or decelerate. If this pacemaker fails, a distinct mass of tissue within the coronary heart, the atrioventricular node, takes over.
I hypothesize that Time Lords, like people, have a pacemaker node that’s primarily liable for figuring out coronary heart price. However the Time Lord pacemaker regulates each hearts: if one coronary heart fails, the opposite has to maintain working. The Time Lord pacemaker should due to this fact be positioned outdoors of the hearts. I surmise that it’s positioned within the mind. This sino-cerebral node, as I name it, coordinates each hearts to make sure that they keep an acceptable offset heartbeat. With out such coordination, the hearts may simply fall out of step and begin pumping concurrently, a much less environment friendly and probably harmful situation.
A lot because the human coronary heart has the atrioventricular node to again up the pacemaker if it fails, Time Lord hearts certainly even have backups: the sinoatrial and atrioventricular nodes can each stand in for the sino-cerebral node if it falters. If an issue happens inside one coronary heart, the dysfunction stays remoted. If an issue happens throughout the mind, then every coronary heart regulates its price independently, creating an uncoordinatedrhythm. Now we have but to see the latter sort of cardiac disaster on-screen; thus far, each case of documented Time Lord coronary heart issues has originated inside one of many hearts.
By the way, there are a small variety of people with two hearts. Some individuals who endure coronary heart transplants have their diseased coronary heart instantly related to a donor coronary heart, in order that the 2 hearts are hooked up in parallel. In contrast to Time Lord hearts, although, the hearts in recipients of those so-called piggyback transplants are regulated individually; every beats to its personal rhythm.
In people who obtain heterotopic or “piggyback” coronary heart transplants, the diseased coronary heart is instantly related to the donor coronary heart, such that the 2 hearts are hooked up in parallel.
Two hearts could be higher than one. However methods to preserve heart problems at bay? The Physician isn’t identified for making heart-healthy dietary decisions; they’ve a documented love of meals excessive in saturated fats—together with fish fingers and custard (season 5)—which may result in excessive ldl cholesterol. The danger of heart problems will increase over time as ldl cholesterol (particularly, atherosclerotic plaque) builds up within the arteries. Though age is difficult with time vacationers, the Physician is estimated to be 1000’s of years previous. So how does the Physician regulate ldl cholesterol to guard their hearts?
People with excessive blood levels of cholesterol are generally handled with bile acid sequestrants. These drugs stop the reabsorption of bile acids within the massive gut for reuse. Bile acids, which assist within the absorption of dietary fats, are made out of ldl cholesterol. By minimizing bile reabsorption, the physique has to make most of its bile from scratch—utilizing a lot of the obtainable ldl cholesterol within the course of. If the Physician has an inefficient bile reabsorption system, maybe nearly all of their ldl cholesterol will get excreted as bile earlier than it might probably construct up of their arteries and probably trigger a coronary heart assault or stroke.
Not all ldl cholesterol is created equal. HDL ldl cholesterol is taken into account to be good ldl cholesterol as a result of it clears the dangerous LDL ldl cholesterol from peripheral tissues and brings it to the liver for degradation. Although there are at present no drugs (on Earth, no less than) to extend HDL ldl cholesterol, low HDL ranges might be improved with food regimen and train modifications. The Physician actually has an terrible lot of operating to do as they journey by time and house to save lots of worlds, rescue civilizations and defeat horrible creatures. Nonetheless, common train isn’t going to be sufficient to counteract 1000’s of years of plaque buildup. Possibly there’s some intrinsic biochemical adaptation within the ldl cholesterol of Time Lords that permits them to outlive centuries with out growing coronary artery illness.
The Physician’s exceptional cardiac well being would possibly consequence from excessive ranges of very efficient HDL ldl cholesterol, very low ranges of LDL ldl cholesterol, or each. Coronary artery illness threat in people has been proven to be proportional to the ratio of LDL ldl cholesterol to apolipoprotein A1 (ApoA1), a protein discovered on the floor of HDL ldl cholesterol particles. Theoretically, the Physician can cut back their threat of coronary heart illness by both lowering LDL, rising ApoA1, or each.
ApoA1 is liable for accepting fat into HDL particles, lowering the chance of hardened arteries (atherosclerosis). HDL particles that include excessive ranges of ApoA1 are extraordinarily efficient at selecting up LDL ldl cholesterol from arteries and organs, so individuals with excessive ApoA1 density have decreased threat of coronary heart illness. Conversely, individuals with low ApoA1 of their HDL particles are at elevated threat of untimely coronary artery illness. If Time Lord HDL particles have a excessive density of ApoA1, they might be at decrease threat of coronary heart illness from fatty plaque buildup. One other risk is that Time Lord HDL particles are greater on the within and thus in a position to take away extra ldl cholesterol from tissues than their human equivalents.
LDL particles ship ldl cholesterol across the physique, together with the partitions of arteries, inflicting coronary artery illness. Excessive LDL is related to an elevated threat of coronary artery illness, whereas decrease LDL decreases threat. People with excessive LDL might be handled with statins, a sort of treatment that inhibits the crucial enzyme concerned in producing LDL ldl cholesterol, HMG-CoA reductase. If Time Lords by some means have low HMG-CoA reductase exercise, they might successfully have a built-in statin to maintain their levels of cholesterol in examine.
Coronary heart illness threat is basically influenced by the degrees and efficacy of HDL and LDL ldl cholesterol. I suggest that top ApoA1 density and low HMG-CoA reductase exercise optimize each of those metrics to permit Time Lords to dwell lengthy lives with a low threat of coronary heart illness.
Having a single coronary heart is the norm in vertebrate creatures, so it’s exhausting to think about how Time Lords advanced their twin cardiac system. However in speaking with marine biologist Edie Widder of the Ocean Analysis and Conservation Affiliation, I realized that there are some real-world examples of animals with a number of hearts. For instance, most cephalopods, a bunch that features squids and octopuses, have three of them: one principal “systemic” coronary heart and two supplementary “branchial” hearts. The three-chambered systemic coronary heart does many of the work, whereas the one-chambered branchial hearts help increased blood circulation by the gills.
Why do cephalopods have three hearts? Their mollusk ancestors, which advanced greater than 500 million years in the past, have been in all probability slow-moving creatures that ate up sedentary prey, together with sea sponges and algae. As cephalopods advanced to feed on cell prey, comparable to fish and crustaceans, they developed increased metabolic charges and higher-capacity circulatory and respiratory programs that allowed them to maneuver quicker. Evolving a number of hearts helped help this extra energetic lifestyle.
Maybe the twin cardiac system of Time Lords advanced to satisfy related energetic calls for. However in that case, why not evolve one massive coronary heart as a substitute? Redundancy. Coronary heart illness is the worldwide main reason behind demise in people. Cardiac operate is a serious limiting issue on lifespan. With two hearts, Time Lords can survive cardiac accidents that may in any other case show deadly.
Nature asks, “What if?” incrementally by evolution. As people, we are able to ask, “What if?” at scale by utilizing our imaginations to, amongst different issues, have interaction with science fiction. That’s the fantastic thing about sci-fi: the power to discover deeply human questions and experiences in novel contexts. Pondering alien species frees our minds to see ourselves anew. Because the Physician stated in season 5, “We’re all stories in the end. Just make it a good one.” Maybe “a good one” is one which helps us perceive one thing about ourselves and one another—one thing that strikes our hearts.
