negative pressure – All Sensors | Put the Pressure on Us

Using Pressure to Find Undersea Treasures

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

Using Pressure to Find Undersea Treasures

For treasure hunters and salvagers trying to find historical and valuable items from ships that sank centuries ago, there are two options: sucking up or blowing away the sand — both involve pressure. Vacuuming sand from the bottom of port channels is common for dredging operations that relocate the sand to provide accessibility to ships. One recent project used a vacuum (negative pressure) approach with a two-mile-long, 30-inch-wide pipeline to transport the sand.

In contrast, treasure hunters just need to move the sand out of the way so they can see objects that have settled below layers of silt. They are not concerned with where the sand goes, so positive pressure has proven to be the technique of choice. Using a method invented in the 1960s by legendary salvager Mel Fisher, steel tubes called mailbox blowers, redirect engine wash from a boat’s propellors downward to clear the ocean bottom some 30 feet underwater. For a given size opening, the size of the props and their speed determine the depth and intensity of the jet from the prop wash.

Two 33-inch diameter mailbox blowers clear away sand 30 feet underwater. Source: History Channel.

The amount of pressure developed is not measured, but it must be sufficient to reveal the desired objects.

Salvaged Spanish gold coin from the wreck of the 1715 Treasure Fleet was located by pressure.
Source: History Channel Beyond Oak Island.

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Body Pressures

Body Pressures

Common body pressure measurements include blood pressure (80/120-mm (300 mm Hg, max)), respiratory pressure (4 kPa) and intraocular pressure for glaucoma testing (15 mm Hg). However, there are several other pressure measurements made at different body locations, most are made for diagnostic purposes. These include:

intra-bladder pressure (IBP) 12.3 ± 4.5 mmHg depending on body position to about 22 mmHg.
intragastric pressure, (IGP) 15.5 ± 3.5 mmHg vs 18.0 ± 8.7 mmHg
intra-abdominal pressure (IAP) typically less than 12 mmHg
anorectal manometry (ARM) 49 ± 3 mmHg resting to 238 ± 38 mmHg maximum squeeze range
vacuum (negative pressure) for an electric breast pump 0-270 mmHg

Similar to blood pressure and intraocular pressure, higher than normal readings identify potentially dangerous health situations. For example, an IAP equal to or above 12 mmHg is called Intra-abdominal Hypertension (IAH). Also, an IAP above 20 mmHg with evidence of organ dysfunction/failure defines abdominal compartment syndrome (ACS). Both of these higher than normal readings are known to cause significant morbidity and mortality among critically ill patients.

For healthy subjects, anal pressure is highly reproducible on separate days. ARM measurements in resting mode vary from 49 ± 3 to 58 ± 3 mmHg in women and from 49 ± 3 to 66 ± 6 mmHg in men. In contrast, maximum pressures range from 90 ± 9 to 159 ± 45 mm Hg in women and from 218 ± 18 to 238 ± 38 in men.

Oral to anal pressures vary depending on the location of the muscle cross sectional area (MCSA).
Source: Physiology of the Gastrointestinal Tract .

Depending on the location, a significantly lower pressure can be a problem, too. For most people, blood pressure in the foot is similar to the blood pressure in the arm. A pressure drop of as little as 10% can indicate peripheral artery disease (PAD).

Not all pressures are positive measurements or made for diagnostic purposes. For example, an electric breast pump uses a vacuum (negative pressure) as high as 270 mmHg to collect milk for newborns.

For all of these body pressure measurements, highly accurate microelectromechanical systems (MEMS) pressure sensors can provide an essential tool for optimum healthcare.

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Getting the Right Medical Room Pressure

Getting the Right Medical Room Pressure

With airborne infectious diseases that can easily spread from one person to another, such as the COVID-19 virus, isolation is critical. In a hospital or clinic, an isolation room needs negative pressure to have airflow into the room and avoid pathogens, or germs, from escaping. In addition to viruses, other undesirable contaminants to keep away from the rest of the population and sterile equipment in a hospital include bacteria, fungi, yeasts, molds, pollens, gases, volatile organic compounds (VOCs), small particles and chemicals.

The airflow to create and maintain the negative pressure (vacuum) in the room requires a consistent pressure differential of about 0.01 inch water gauge (in. w.g.) or 2.5 Pascals (Pa).

According to the Facility Guidelines Institute’s (FGI’s) most recent 2018 FGI Guidelines ANSI/ASHRAE/ASHE Standard 170-2017, other rooms that should be negatively pressurized include:

Emergency Department Public Waiting Areas
Emergency Department Decontamination
Radiology Waiting Rooms
Triage
Bathrooms
Airborne Infection Isolation (AII) Rooms
Most Laboratory Work Areas
Autopsy Rooms
Soiled Workrooms or Soiled Holding Rooms
Soiled or Decontamination Rooms in Sterile Processing Department
Soiled Linen Sorting and Storage
Janitors’ Closets

In contrast, protecting the patient and sterile medical and surgical supplies in an operating room requires positive pressure to keep undesirable contaminants outside. The positive pressure room is achieved by pumping in filtered, clean air.

Isolation (Low) vs. operating room (High) pressure.
Source: Minnesota Department of Health

In fact, some portable, headgear-mounted air purifying respirator systems use positive pressure to protect the wearer.

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Negative Pressure Wound Therapy

Negative Pressure Wound Therapy

Unlike Hyperbaric Oxygen Therapy (HBOT) that employs a chamber with a pressure higher than 1 atmosphere absolute, negative pressure wound therapy (NPWT) uses a vacuum to enhance and promote wound healing in acute, chronic and burn wounds. In this medical procedure, a sealed wound dressing is attached to a pump that creates a negative pressure environment for the wound.

The vacuum helps to increase blood flow to the area and draw out excess fluid from the wound and depending on the type of wound type or location, it can either be applied continuously or intermittently. This type of therapy can be implemented for a few days to several months at a time.

The types of wounds that can benefit from negative pressure wound therapy, include:

diabetic ulcers
venous ulcers
arterial ulcers
pressure ulcers
first and second-degree burns
chronic wounds
wounds with large amounts of drainage
surgical and acute wounds at high risk for infection

Used in its V.A.C.ULTA™ Therapy System and other wound care products, Acelity’s SENSAT.R.A.C.™ Technology is a real-time pressure feedback system that adjusts its pump’s output, compensating for wound distance, wound position, exudate characteristics and patient movement. Source: Acelity.

The applied negative pressure in NPWT can range from -125 to -75 mmHg (-2.4 to -1.5 psi) depending on the type of wound and the patient’s tolerance. For this application, All Sensor’s DLV-005D with its digital output would be an easy way to measure the vacuum level for both the machine’s use and the health care provider’s and patient’s observation.

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