The Physics of Negative Pressure

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FA 2016

Editor’s Note:

We all deal with the concepts of positive and negatives pressures, and certainly pay attention to those values during the course of a bypass run, or ECMO, or a myriad of other perfusion modalities.

This is a rather insightful and esoteric view of the basic perfusion principle that we both respect and fear- NEGATIVE PRESSURE.

Have an excellent Wednesday 🙂

Frank

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The Romantic poet John Keats once defined a state of mind wherein a person “is capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason.” He called it negative capability. It stands in direct contrast to the quality known as negative pressure, a scientific conundrum that recently caused much irritable grasping after fact and reason among Discover readers.

The trouble started last September, when Discover published my Works in Progress column about how water gets to the tops of trees. As water evaporates from a tree’s leaves, I reported, it tugs on water remaining in the xylem, a network of inert pipes that reaches from roots to shoots. Water molecules in the xylem, I innocently explained, are linked by bonds that form among their positively and negatively charged poles. As water evaporates up top, it stretches the bonds between interlinked molecules in the column below, generating considerable tension. “The pressure inside the xylem tubes of the tallest trees could be as low as -20 atmospheres,” I wrote.

And the irritable grasping began. “Negative pressures of 20 atmospheres? Impossible,” one reader wrote. “You can’t make empty space more empty!” another protested. “Please tell me that the Works in Progress is a misplaced April Fools’ Day article,” yet another implored.

For what it’s worth, the negative-pressure theory of water transport is enshrined in plant physiology textbooks. But plant physiologists do not have the last word in physics. So I called Princeton University physicist Paul Steinhardt, whom I’d interviewed a year before for an article about the accelerating universe. Steinhardt had gone to great lengths to explain the cosmological version of negative pressure to me. Einstein’s equations allow for a ubiquitous, inward-pulling force in the universe that behaves like a rubber band, Steinhardt said. The more you stretch it, the more it pulls back. No one knows exactly what’s doing the pulling, but the contracting force could exist in empty space because the vacuum is full of energy and other intangibles.

I asked Steinhardt if the same negative pressure that is tugging on the firmament could also be pulling water to the tops of trees. Not a chance, he said. Liquids can’t have negative pressure.

I called plant physiologist Michele Holbrook at Harvard University, a source for the tree story, to give her the bad news. She wasn’t buying it. Negative pressure is a legitimate component of fluid dynamics, she told me emphatically, if not irritably. Then she gave me a list of physicists who would vouch for it.

There ensued a messy interlude in which I consulted a sampling of knowledgeable experts, including my brother, Harold. Hal, a high school physics teacher, is wont to say that “the universe doesn’t suck; it blows.” He means that fluids flow along pressure gradients, from higher to lower pressures. Sucking on a straw, for example, creates a low-pressure area at the top of the straw, and the higher atmospheric pressure pushes the fluid up from the bottom.

Unfortunately, Hal’s law falls short of explaining how water climbs trees. Experiments have shown that atmospheric pressure alone can only push water 33 feet up a vertical tube, and trees can grow much taller than that. Also, I had been told repeatedly that the water in xylem tubes is under tension—which sounded like pulling, not pushing, to me.

Finally, through a contact on Holbrook’s list, I found Pablo Debenedetti, an expert in fluid thermodynamics at Princeton whose book, Metastable Liquids, includes a section on water transport in trees. In the parlance of fluid dynamics, Debenedetti told me, negative pressure is tension—the stress resulting from the elongation of an elastic body. Liquids really can stretch. Under certain conditions, if you pull on them, they pull back. “You can actually have the liquid ‘suck’ a vessel,” Debenedetti said. “In laboratory experiments, you can make vessels implode.”

All liquids can have tensile strength, he added, generated by the momentary accumulations of charge from quantum fluctuations in atoms. Tension in liquids has been studied since the mid-1800s. In the 1950s, the National Institute of Standards and Technology determined the tensile strength of a variety of liquids by suspending them in Z-shaped glass tubes with open ends. Each tube was put in a centrifuge and spun around until a bubble formed in the liquid; the liquid’s tensile strength was calculated from the centrifugal force required to form the bubble.

Debenedetti confirmed that water’s tensile strength is partly a result of attractions between opposite charges on the poles of water molecules. Still, he said, the concept of negative pressures in liquids isn’t obvious. At equilibrium, water and other liquids don’t support tension. It’s only a property of metastable liquids—liquids prevented from entering a new phase by an energy barrier. Water can be kept liquid, for example, at temperatures more than 300 degrees Fahrenheit above its boiling point, because it needs a onetime injection of energy to start vaporizing. A liquid under tension wants to be vapor, but it needs a boost, or a lowering of its energy barrier, to change phases. Until that happens—when the liquid is shaken, for instance, or its tension is increased—the liquid stretches. Such is the case in the xylem tubes of trees.

Debenedetti and Steinhardt don’t work in the same building at Princeton, but they know of each other because their daughters share the same piano teacher. At my request, the two exchanged a few e-mails and concluded that each man’s negative pressure was a stranger to the other. I also approached cosmologist Michael Turner at the University of Chicago, who conferred with his friend Humphrey Maris, a physicist and fluid-dynamics expert at Brown University. After talking to Maris, Turner helped put the two realms together.

“We’re not talking about the same phenomena,” he said. The two kinds of negative pressure are related, though, “in the sense that they are examples of things that behave elastically. And both are a bit counterintuitive.”

If there is a unifying theme here, Turner said, it’s direction—an inward, imploding, or contracting force, rather than the outward-pushing force typically defined as pressure. The minus sign next to those atmospheres doesn’t mean “less than nothing”; it’s an arbitrary signifier denoting “in the direction opposite of positive.” Solids have negative pressure when they pull in, like stretched rubber bands or springs. Liquids can have negative pressure in metastable states, when they resist turning to vapor. And, according to the astrophysicists, even empty space can have negative pressure.

Gases are still the dark horse in the meta-stable. Steinhardt has heard that metastable gases can have negative pressure, but he isn’t sure how. Debenedetti is skeptical. “The whole point of being a gas is that the forces between molecules don’t matter much,” he says. Turner is noncommittal.

Since the many facets of negative pressure are obscure enough to escape career physicists, I figure readers can be forgiven their confusion. Negative pressure, it seems, is the perfect remedy for overstretched intellects.

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Surgical (operative) Air: A Historical Perspective

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FA 2016

Editor’s Note:

I was reviewing some data related to the accidental de-priming of the MPS Microplegia delivery system, when in the process, I came up upon this very good article relating to the evolution of the body of knowledge concerning accidental introduction of air to the patient during surgery.  It is a fascinating read, and well worth your time 🙂

Frank

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Surgical (operative) Air

 

In 1914, the danger of air embolism during cardiac surgery was reported by Carrel (151), who wrote, “The opening of the ventricles or of the pulmonary artery and the aorta is always followed by entrance of air into the heart.” Support for his statement was the observation of ventricular fibrillation and death in animals after coronary artery air embolism.

Air embolism on the left side of the heart was well known to thoracic surgeons before the advent of open heart surgery. Reyer and Kohl (152) reported 10 cases of venous or arterial air embolism, 5 of which resulted in the patients’ deaths, during a variety of surgical or diagnostic procedures. Kent and Blades (153) further warned that the two major hazards of thoracic surgery were infection and embolic phenomena. In their animal experiments, air embolism was found to be well tolerated on the venous side, in the absence of a patent foramen ovale, but fatal with small injections of air into the pulmonary veins.

Geoghegan and Lam (154) reported that the mechanism of death due to air embolism in dogs (0.25 to 2.0 mL/kg) was either coronary (immediate death) or cerebral (severe brain damage). Benjamin et al. (155) further sought to define the mechanisms of air embolism by injecting varying amounts of air (0.5 to 8.0 mL/kg) into the left atrium, left ventricle, aortic root, common carotid, or descending aorta of dogs. Left atrial air embolism was fatal 100% of the time, whereas the same volumes of air injected into the left ventricle caused death in 83% of the animals. Aortic root and carotid air embolism were better tolerated, and large volumes of air (up to 10 mL/kg) were required to cause death when given into the descending aorta. They, like other investigators (156–164), noted the dangers of left heart air but concluded that small amounts of air in the systemic circulation were generally well tolerated during surgical procedures if appropriate resuscitative maneuvers were undertaken when required.

Many retrospective reviews of early clinical experience with CPB have been published. Callaghan et al. (165) analyzed 60 deaths in 250 CPB patients operated on between 1956 and 1961. A variety of causes described included seven cases of cerebral damage, four of which were from air embolism. Ehrenhaft et al. (166) reported 19 of 244 (7.7%) patients undergoing open heart surgery suffered cerebral damage. Systemic air embolism was the suspected etiology because many operations involved closure of septal defects. Like Carrel nearly 50 years earlier, they warned of air entrance to the left side of the heart or aorta with subsequent embolization when the normal circulation was restored. Allen (167) reported cerebral damage in 18 of 500 (3.6%) patients undergoing repair of valvular or congenital cardiac defects and warned of the propensity of air to collect in the left atrium near the right superior pulmonary vein. Sloan et al. (168) reported 78 of 600 (13%) patients died after CPB; air trapped in the left ventricle was identified as the source of the air and was believed responsible for 49 deaths. Nicks (169) reported systemic air embolism in 40 of 340 (11.7%) patients undergoing congenital or valvular procedures; 10 patients died. Fishman et al. (170) later confirmed the left atrium and pulmonary veins as locations of trapped air whenever the left heart was opened. Anderson et al. (171) and Lin (172) also warned of the risks of pulmonary hypertension due to right-sided air embolism.

The preference of cannulation of the ascending aorta for CPB, although much safer than the femoral artery site, increased the risk of cerebral air embolism. Gomes et al. (173) found that air embolism via the femoral artery was five times less likely to involve the cerebral vessels if the air originated from the CPB arterial line. Beckman et al. (174) determined the optimum method of placement of the ascending aortic cannula to lessen the risk of air entry. Direct insertion of the cannula without use of a side-biting clamp, which tended to trap a small amount of air, was found to be safest.

In the article by Mills and Ochsner (114) on mechanisms of air embolism, two additional surgical sources were described: unexpected resumption of the heart beat and inadequate steps to remove air after cardiotomy. Coronary air embolism with cardioplegia techniques was reported in 1981 (175) and 1986 (110). Although air embolism was generally thought not to occur during coronary bypass operations, Hughes (176) reported the possibility of intraventricular air with right superior pulmonary vein venting that could draw air in via coronary arteriotomy, especially when the left anterior descending coronary artery was opened. Robicsek and Duncan (177) and Lee (178) subsequently confirmed this mechanism. Air also can be drawn retrograde through an opened coronary artery if an aortic root vent is used and placed under significant negative pressure.

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AngioVac 101: A Perfusion Primer

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FA 2016

Editor’s Note:

Thought I would drop a quick primer on the use of the AngioVac system for percutaneous clot extraction.  The YouTube video right below is very comprehensive and should explain 90%of our involvement as well as the process.

Have an excellent Monday!  🙂

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Product Description

 

All contents are sterile/single-use only. This circuit pack is designed for use during procedures that require extracorporeal circulatory support. It is not designed for long term use (greater than six hours). The pack includes tubing, connectors, stop-cocks, filters, clamps and a centrifugal blood pump head (read completely the instructions for use for the pump head and bubble trap filter prior to use). The centrifugal pump head utilizes a rotating, vaned impeller design to move blood by centrifugal force and intended for use only with the appropriate centrifugal pump consoles (refer to the console operator’s manual for console operating instructions and procedures.)

 

Indications

This perfusion pack is indicated for use in procedures requiring extracorporeal circulatory support for periods of up to six hours. Contraindications Alone, this circuit is not a medical treatment device. Selection of the patient as a candidate for use with this product and for such procedures as it is intended is the physicians’ sole responsibility. There are no known contraindications for this product.

 

Warnings & Precautions

  • It is recommended that one pack be set up and evaluated in a laboratory or bench test prior to first clinical use. Instructions for use
  • The patient should be prepared and draped in the usual and typical sterile manner for percutaneous/ surgical vascular procedures. • Sterile vascular cannulation should be performed utilizing typical percutaneous or open surgical techniques after anticoagulation has been initiated.
  • Remove all protective caps.
  • Tighten all luer locks and fittings to finger-tight to the desired components. Make sure all connections are secure and do not over tighten.
  • Connect the pump head to the circuit in the appropriate position and place the pump head into the pump motor drive receptacle.
  • Connect the circuit to other components as appropriate.
  • Prime the extracorporeal circuit completely with the desired priming fluid ensuring removal of all air from the circuit and being careful not to introduce any air into the circuit during the priming procedure.
  • Visually inspect the entire circuit to ensure it is free of air bubbles and leaks. • Ensure all clamps are in the appropriate open or closed position.
  • When infusing solutions from bags, remove all air from the bag during setup to prevent air from entering the circuit.
  • Carefully monitor for both inflow and outflow obstruction/ occlusion of the circuit during use.
  • Initiate adequate systemic anticoagulation therapy prior to patient cannulation and utilization of this product for the conduct of extracorporeal circulation. A strict anticoagulation protocol should be followed and anticoagulation should be carefully monitored during all procedures. (Target ACT’s -160-180)
  • Do not exceed appropriate pressure ratings of the circuit (520mmHg/10psi).
  • Initiate flow in the circuit once it is completely primed to ensure appropriate function of the circuit, components and the pump console as well as appropriate flow rates.
  • Discontinue flow and divide the inflow and outflow lines of the circuit at the appropriate connection.
  • Connect the inflow and outflow lines to the appropriate cannulae/catheter, ensuring no air is introduced into the circuit. • Ensure all appropriate clamps are again in the appropriate open or closed position and that there is no inflow or outflow obstruction. • Once adequate anticoagulation has been achieved, initiate extracorporeal circulation as desired.

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There are A LOT of JOBS! Perfusion.Com

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Click Image above to got to Perfusion.com Job Site 🙂

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Cardiac Surgery Employment

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Job Title Employer Location Date
Autotransfusionist Cardiovascular Insights St. Petersburg, Florida, US Aug 11 2016
Cardiovascular Perfusionist UI Heart & Vascular Center Iowa City, Iowa, US Aug 8 2016
Staff Perfusionist Lehigh Valley Health Network Allentown, Pennsylvania, US Aug 8 2016
Clinical Manager – Perfusion (New Opportunity!) SpecialtyCare Abilene, Texas, US Aug 8 2016
Sales Rep, Cardiovascular Perfusion – Sacramento, CA Shamrock Surgical Sacramento, California, US Aug 5 2016
Perfusionist (Lexington, KY, New Grads Welcome!) SpecialtyCare Lexington, Kentucky, US Aug 4 2016
BOSTON STRONG – STAFF PERFUSIONIST INVOCIRC INC. BOSTON, Massachusetts, US Aug 3 2016
Cardiovascular Perfusionist University of Rochester Rochester, New York, US Aug 3 2016
Clinical Perfusionist (Cape Girardeau, MO) Perfusion.com, Inc. Cape Girardeau, Missouri, US Aug 3 2016
Clinical Perfusionist (Yuma, AZ) Perfusion.com, Inc. Yuma, Arizona, US Aug 3 2016
Chief Perfusionist (East Stroudsburg, PA) Perfusion.com, Inc. East Stroudsburg, Pennsylvania, US Aug 3 2016
Staff Perfusionist-West Virginia Comprehensive Care Services Morgantown, West Virginia, US Aug 2 2016
Perfusionist (Minneapolis, MN – Experienced or New Grad) SpecialtyCare Minneapolis/St. Paul, Minnesota, US Jul 29 2016
Perfusionist (5k Sign-on Bonus!) SpecialtyCare Abilene, Texas, US Jul 29 2016
Perfusionist (Las Vegas) SpecialtyCare Las Vegas, Nevada, US Jul 29 2016
Perfusionist (Wichita, KS) SpecialtyCare Wichita, Kansas, US Jul 29 2016
Perfusionist (Generous Sign-On Bonus) SpecialtyCare Honolulu, Hawaii, US Jul 29 2016
Staff Perfusionist Southland Perfusion Services Wichita Falls, Texas, US Jul 25 2016
Staff Perfusionist Phoenix Perfusion Services, LLC Phoenix, Arizona, US Jul 22 2016
Staff Perfusionist Phoenix Perfusion Services, LLC Prescott, Arizona, US Jul 22 2016
Lead Pediatric Perfusionist NorCal Perfusion Services, Inc. San Francisco, California, US Jul 21 2016
Perfusionist – FT – Wexford, PA Perfusion Professionals, Inc. Wexford, Pennsylvania, US Jul 18 2016
Associate Director, School of Perfusion – Pittsburgh UPMC Pittsburgh, Pennsylvania, US Jul 15 2016
ECMO Perfusionists – York, Pa. UPMC York, Pennsylvania, US Jul 15 2016
Staff Perfusionist Stormont Vail Health Topeka, Kansas, US Jul 13 2016
Perfusionist – FT – DuBois, PA Perfusion Professionals, Inc. DuBois, Pennsylvania, US Jul 13 2016
Perfusionist NorthShore University HealthSystem Evanston, Illinois, US Jul 12 2016
Perfusionist, Full Time SUPPORT SERVICES OF WNY Buffalo, New York, US Jul 9 2016
Perfusionist (Washington, D.C) SpecialtyCare Washington, District of Columbia, US Jul 5 2016
Staff Perfusionist I Perfusion Alliance Oklahoma City, Oklahoma, US Jul 2 2016
Staff Perfusionist II Perfusion Alliance Oklahoma City, Oklahoma, US Jul 2 2016
Perfusionist (Atlantic City, NJ) SpecialtyCare Atlantic City, New Jersey, US Jul 1 2016
Staff Perfusionist-Birmingham, AL Comprehensive Care Services Birmingham, Alabama, US Jul 1 2016
Perfusionist Needed in Stunning Traverse City MI Munson Healthcare Traverse City, Michigan, US Jun 30 2016
FULL TIME PERFUSIONIST-SIGN ON BONUS Cardiopulmonary Perfusion Associates,INC Little Rock, Arkansas, US Jun 29 2016
Perfusionist (Phoenixville, PA – Sign-on Bonus) SpecialtyCare Phoenixville, Pennsylvania, US Jun 29 2016
Perfusionist (Reading, PA – Sign-on Bonus!) SpecialtyCare Reading, Pennsylvania, US Jun 29 2016
Staff Perfusionist-William Beaumont-Royal Oak Michigan Comprehensive Care Services Royal Oak, Michigan, US Jun 29 2016
Staff Perfusionist CardioPulmonary Services, LLC Boston, Massachusetts, US Jun 28 2016
Cardiac Perfusionist Valley Children’s Hospital Fresno, California, US Jun 28 2016
Perfusionist- Heart & Vascular Center UVA Health System Charlottesville, Virginia, US Jun 28 2016
Perfusionist – Tufts Medical Center Tufts Medical Center Boston, Massachusetts, US Jun 28 2016
Staff Perfusionist University Medical Center Lubbock, Texas, US Jun 27 2016
Perfusionist Distinctive Home & Healthcare Bethesda, Maryland, US Jun 23 2016
Staff Perfusionist-Jackson Memorial-Florida Comprehensive Care Services Miami, Florida, US Jun 22 2016
STAFF PERFUSIONIST Geisinger Health System Danville, Pennsylvania, US Jun 21 2016
Perfusionist (10k Sign-On Bonus) SpecialtyCare Tulsa, Oklahoma, US Jun 20 2016
Traveling Perfusionist (Full Time Primary East Coast US) Perfusion.com, Inc. East Coast Traveler, Florida, US Jun 16 2016
Perfusionist UnityPoint Clinics – Peoria Peoria, Illinois, US Jun 16 2016
CARDIAC PERFUSIONIST St. Francis Hospital Roslyn, New York, US Jun 15 2016