Does Blood Flow Without the Heart? The Fourth Phase of Water

Blood can keep flowing for a while without a beating heart. In the laboratory of Gerald H. Pollack at the University of Washington, blood in a 3-day-old chick embryo kept moving for about 50 minutes after the heart had been arrested. The vessel network measured roughly 3 centimeters across. The flow was slower, settling near 25 micrometers per second in the veins, and it ran in its normal direction, from artery to vein, in every experiment. Switching on an infrared source raised the speed of this post-mortem flow from about 41 to about 153 micrometers per second. Deprived of infrared energy, blood in the capillaries stopped moving altogether. Zheng Li and Gerald H. Pollack reported these measurements in PLOS ONE in 2023, based on 6 experiments after cardiac arrest and 5 in the living embryo.

Their explanation leads to a subject that long sat at the margins of biology: how water behaves at surfaces. From there, it leads on to what Pollack calls a fourth phase of water.

Why blood flow without a pump sounds implausible

A pump is a device that moves fluid by creating a difference in pressure. That is exactly how we have described circulation since William Harvey published his treatise on the motion of the heart in 1628, almost 400 years ago. The heart builds pressure, pressure drives the blood, and without pressure the blood stands still. Anyone hearing for the first time that something else also moves blood will naturally be skeptical at first.

Measurements alone do not get you far here. As long as nobody can say what sets a fluid in motion without a pressure gradient, every figure sounds like a measurement error. So it pays to look at the mechanism first and at the measurements second.

That blood keeps flowing after cardiac arrest is not a new observation at all, and that is exactly where the study starts. Li and Pollack (2023) cite findings in 4 animal groups: mice, rats, dogs, and chick embryos. Depending on the model, the blood kept flowing for anywhere from 15 minutes to several hours. Some amphibian larvae even survived up to 15 days after surgical removal of the heart and continued to develop. Because obvious explanations were at hand, such as gravity or the contraction of the vessels, the phenomenon long went unexamined. In the authors' words, “as a result of these potentially trivial explanations, the phenomenon has received little attention.”

How a tube moves water without anyone pushing

A hydrophilic surface is a surface that water clings to instead of beading off. Glass belongs in this group, as do many plastics, gels, and the inner lining of blood vessels. In 2020, three years before the blood flow study, the Pollack lab reported that water flows on its own through narrow, horizontal hydrophilic tubes once they are immersed in water. There was no slope, no pump, and no suction. The flow kept going anyway.

The explanation starts at the boundary. Where liquid water meets a hydrophilic surface, a zone forms directly against that surface that pushes dissolved particles out. It is called the exclusion zone. It was first described in 2003 next to polymer gels. Tiny beads added to the water stayed out of a band on the order of 100 micrometers wide, many times what conventional theory predicted (Zheng & Pollack, Physical Review E 68, 031408, 2003). Six years later the same group showed that incident light enlarges this zone reversibly and in a wavelength-dependent way (Chai, Yoo & Pollack, Journal of Physical Chemistry B 113, 13953–13958, 2009). The zone carries a negative charge, and the protons released while it forms move into the open core of the tube.

The result inside the tube is a charge distribution: a negatively charged ring along the wall and a cluster of positively charged protons in the middle. Like charges repel each other. As that repulsion grows, protons are forced out at one end of the tube while water flows in at the other end. The process repeats as long as the conditions hold. A chemical concentration gradient turns into motion.

Blood vessels are an obvious place to look for the same effect. Blood consists mostly of water, and the inner wall of a vessel is hydrophilic. Li and Pollack therefore tested whether this mechanism operates in the circulation.

Where the energy for surface-driven flow comes from

Infrared radiation is electromagnetic radiation with wavelengths longer than visible light, and every warm body gives it off. Li and Pollack trace the flow back to this energy source. Building the exclusion zone takes incoming energy, and the effect is strongest in the infrared range. The two researchers had shown this in 2020 with laboratory tubes, in Science Advances, under the title Surface-induced flow: A natural microscopic engine using infrared energy as fuel (DOI 10.1126/sciadv.aba0941).

This energy is actually all around us. The metabolism of every living organism produces heat, which leaves the body as infrared radiation according to Planck's law of radiation. From outside, the sun adds to it: roughly half of the solar energy reaching Earth arrives in the infrared range.

That reasoning yields a prediction you can test. If infrared is the fuel, then extra infrared must speed up the flow and missing infrared must slow it down, even when nothing else changes. That is exactly what Li and Pollack tested in their experiment.

What was measured in the chick embryo

The test model is the yolk-sac vessel network of a chick embryo after 72 to 75 hours of incubation. The network is about 3 centimeters in diameter and lies almost flat on the yolk. That layout rules out two standard explanations for blood flow without a heartbeat. Gravity drops out because the blood would have to move within a plane, partly uphill. Vessel contraction drops out because the smooth muscle is not yet fully functional at this stage. The heart was stopped by injecting 10 to 30 microliters of potassium chloride solution and came to rest within one to two seconds. The speed of the red blood cells was filmed at up to 80 frames per second and analyzed.

Condition	Measured result
After cardiac arrest	flow continues for about 50 minutes; venous flow in the natural direction in every experiment
Venous speed without a heartbeat	settles at about 25 micrometers per second
Infrared after cardiac arrest (n = 6)	rises from about 41 to about 153 micrometers per second, falls again after switch-off
Infrared in the living embryo (n = 5)	venous speed about 30 percent higher
Infrared deficit at 19 to 23 °C	capillary flow stops, red blood cells stall; reversible

In their abstract, the authors sum up their result like this:

“Hence, this IR-dependent, vessel-based flow-driving mechanism may indeed operate in the circulatory system, complementing the action of the heart.”

Li & Pollack, On the driver of blood circulation beyond the heart, PLOS ONE 18(10): e0289652 (2023)

How carefully Li and Pollack frame their results

A limitation is the place in a scientific paper where the authors themselves say how far their data reach. Li and Pollack handle this with great care.

• Heart and vessels in the living embryo. Under infrared, the heart rate in the living embryo rose markedly along with venous flow, from about 100 to about 140 beats per minute. Li and Pollack (2023) write: “the reciprocal causation between the cardiac output and venous return makes it difficult to distinguish whether the added IR impacted venous blood flow via the heart or via the blood vessels.”
• The layer along the vessel wall. The researchers saw a cell-free layer directly along the vessel wall. They write that “the nature of this clear zone has not yet been explored” and that it “may correspond” to the exclusion zone.
• The series of experiments. The study covered 6 embryos after cardiac arrest and 5 in the living state.
• The model. The two researchers worked with the chick embryo precisely because its musculature is still immature. How the mechanism behaves in an adult circulation is the exciting next question.
• The language of the conclusions. The paper says “may indeed operate,” “may well be the dominating driver,” and for the living state “may merely augment the heart-driven flow”: the mechanism complements the heart. (Source: Li & Pollack, PLOS ONE 18(10): e0289652, 2023, for every point in this list.)

How the university press release words the findings

The University of Washington presented the paper to a wide audience in a press release on October 25, 2023, and in a few places the release sounds more pointed than the paper itself:

UW news release (October 25, 2023)	Paper: Li & Pollack (2023)
“the circulation has two independent drivers”	“may indeed operate … complementing the action of the heart”; in the living state “may merely augment”
“could confirm the mechanism's signature feature – infrared energy – was the driver”	“IR energy appears to fuel this postmortem blood flow”
“observed in half a dozen laboratories over the past century, but their conclusions had been ignored”	“confirmed in mice, rats, dogs, and chick embryos”; the phenomenon “has received little attention”
Title: “On the Driver of the Circulation Beyond the Heart”	Title: “On the driver of blood circulation beyond the heart”

Anyone who wants to quote the results does best to use the wording of the paper itself. It is freely available online under a Creative Commons Attribution 4.0 license, so anyone can read it in full.

What Pollack's fourth phase of water has to do with blood flow

The fourth phase of water is Pollack's name for the ordered state he describes in the exclusion zone next to hydrophilic surfaces, a state alongside solid, liquid, and vapor. On his faculty page at the University of Washington, he writes: “My laboratory has discovered that water has a fourth phase, which has a central role in human health.” (Source: faculty page of Gerald Pollack, University of Washington.)

How to interpret the zone is still being discussed in the scientific literature. Several groups have observed the exclusion zone independently of one another. A 2020 review weighs the competing explanations. It finds diffusiophoresis, the migration of particles along concentration gradients, more convincing than a distinct phase of water (Elton et al., International Journal of Molecular Sciences 21, 5041, 2020). We have covered both views in more depth in Does Water Have Memory? What Physics Has Actually Measured and in Is Structured Water Real? What Measurements Show.

The measurements in the embryo stand on their own, however the water physics behind them is eventually interpreted.

Why this research interests Qi Blanco

Qi Blanco works on water and on cells, which is why we follow publications like this one closely. Li and Pollack describe how water behaves at interfaces inside the body and generates forces there, and that is exactly the field we work in. We find the role of infrared especially intriguing. It is the warmth every body gives off, and roughly half of what reaches us from the sun: something that surrounds us every day. The study comes from Pollack's lab at the University of Washington. Readers who want the broader biophysical picture of water inside cells will find it in Cellular Hydration: What Water Really Does Inside Your Cells. The research we cite on our own subjects is collected on our studies page.

Frequently asked questions about the study

Does blood really keep flowing when the heart stops?

Yes. Researchers have observed blood flow after cardiac arrest repeatedly, in mice, rats, dogs, and chick embryos, over minutes to hours depending on the model. In the experiments by Li and Pollack, the chick embryo's blood kept moving for close to an hour. The venous flow ran in its natural direction in every experiment, without exception.

Does that mean the heart is not needed?

The authors describe the mechanism as a complement to the heart. In the living state, they write, it “may merely augment” the flow the heart drives. Without a heartbeat, the blood moved much more slowly than normal. Venous flow settled at about 25 micrometers per second, compared with about 1,500 micrometers per second with the heart beating.

Has the finding been independently confirmed?

Several groups have observed blood flow after cardiac arrest over more than a century. The explanation through a surface-driven flow fueled by infrared energy comes from Gerald Pollack's lab, and the field is still discussing how to interpret the exclusion zone behind it.

Can I draw conclusions about my own health from this study?

Li and Pollack studied chick embryos after 72 to 75 hours of incubation, in 6 experiments after cardiac arrest and 5 in the living state. It is basic research into how blood flows through fine vessels and what role water and infrared play in that.

Key takeaways from the study

• Blood in the chick embryo kept flowing for about 50 minutes after cardiac arrest, more slowly and in its natural direction, in every experiment (Li & Pollack, PLOS ONE 2023).
• Infrared radiation more than tripled this flow; without infrared energy, flow in the capillaries stopped, reversibly.
• The proposed mechanism is surface-driven flow: a charged exclusion zone forms at hydrophilic surfaces, repelled protons push fluid through the tube, and infrared supplies the energy.
• The authors describe the mechanism as a complement to the heart, in their words “complementing the action of the heart.”
• The exclusion zone has been observed independently several times; its interpretation as a fourth phase of water is discussed in the scientific literature (Elton et al., IJMS 2020).

Sources and further reading

Every source is linked where it is used in the text. Full references:

• Li, Z., Pollack, G. H.: On the driver of blood circulation beyond the heart. PLOS ONE 18(10): e0289652 (2023). DOI 10.1371/journal.pone.0289652. License CC BY 4.0. Full text at PLOS
• Li, Z., Pollack, G. H.: Surface-induced flow: A natural microscopic engine using infrared energy as fuel. Science Advances 6(19): eaba0941 (2020). DOI 10.1126/sciadv.aba0941.
• University of Washington, Department of Bioengineering: Pollack lab shows that it's not just the heart that pumps blood, news release of October 25, 2023.
• Faculty page of Gerald Pollack, University of Washington, Department of Bioengineering.
• Zheng, J. M., Pollack, G. H.: Long-range forces extending from polymer-gel surfaces. Physical Review E 68, 031408 (2003). DOI 10.1103/PhysRevE.68.031408.
• Chai, B., Yoo, H., Pollack, G. H.: Effect of radiant energy on near-surface water. Journal of Physical Chemistry B 113, 13953–13958 (2009). DOI 10.1021/jp908163w.
• Pollack, G. H.: The Fourth Phase of Water: Beyond Solid, Liquid, and Vapor. Ebner and Sons, Seattle (2013).
• Elton, D. C., Spencer, P. D., Riches, J. D., Williams, E. D.: Exclusion Zone Phenomena in Water—A Critical Review of Experimental Findings and Theories. International Journal of Molecular Sciences 21, 5041 (2020). DOI 10.3390/ijms21145041.