Question | Answer |
How is pressure measured under the Systeme Internationale? | Newton/meter sq., or Pascale |
How is the Pascale usually referred to as? | kPa |
What does Pascale's principle state? | Pressure applied to a completely enclosed fluid is transmitted undiminished to all parts of the fluid and its enclosing walls |
What do we now know about pressure in a fluid that is enclosed in a container? | There are differences in wall tension in different parts of the fluid |
What is an aneurysm? | Localized enlargement of an artery caused by weakening of the artery wall |
The pressures exerted on the walls of an aneurysm are (lesser/greater) than the pressures exerted on the surrounding arterial walls. | greater |
Why are the dilated walls of a vessel more prone to rupturing or dissection? | The forces exerted at the weak point are greater than elsewhere in the vessel that do not have a weak point |
What does LaPlace’s Law state? | Wall tension increases with vessel radius |
What are four physiologic scenarios where LaPlace's Law is seen? | COPD, difficulty of a baby's first breath, alveolar role in exhalation, aneurysms |
LaPlace's Law explains the relationship between what three factors? | Pressure, surface tension, radius |
What is the LaPlace equation? | P=2T/R |
Pressure and surface tension are expressed as _________. | dynes/cm sq |
The Law of LaPlace describes the magnitude of (inward/outward) pressure. | Inward |
What is the implication of LaPlace’s Law in regards to alveoli? | Larger surface tension involves a larger force pushing inward into the alveoli and with 2 alveoli connected in the airway, it is implied that the smaller alveoli would collapse and push its gases into larger alveoli (smaller radius=more pressure) |
What prevents the collapse of contents of smaller alveoli into larger alveoli? | surfactant |
What does pulmonary surfactant decrease and where does it have a greater effect? | decreases surface tension; greater effect in smaller alveoli |
Increased wall tension is described by ________ Law, but offset by the effects of ________. | LaPlace's; surfactant |
What is the function of the aortic cross clamp in open heart surgery? | Divert blood to the cardio-bypass machine |
What determines LV response to the aortic cross clamp? | Length-tension-velocity relation of the myocardium |
Tension is obtained by multiplying what two factors? | pressure & radius |
What are the principle determinants of afterload? | ventricular dimensions (radius) and systolic intraventricular pressure |
What are two other surgical scenarios that utilize cross-clamping? | Abdominal aneurysmectomy and infrarenal aortic cross-clamping |
Tubes are pathways in which the ________ is greater than the _______. | Length; diameter |
An orifice is a pathway whose ______ is greater than its ______. | Diameter; length |
What are the 5 factors that determine the rate of flow through a tube? | 1)Cross section (radius) 2)proximal to distal pressure gradient (P1-P2) 3)tube length 4)fluid viscosity 5)solution density |
What is the definition of the “flow” of fluid? | Quantity of fluid (gas or liquid) passing through in a unit of time |
What is the equation for flow? | F=Q/T |
What must be present in order for flow to occur through a tube? | Proximal to distal pressure gradient |
Flow rate is (directly/indirectly) proportional to pressure. | directly |
How much is flow reduced if the diameter of a tube is reduced to ½ the original size? | Reduced to 1/16th the original value |
How does flow change if a tube is cut in half? | Flow is doubled |
What has more influence on flow through a tube: altering the diameter or the length? | Diameter |
What is the definition of the meniscus? | A curve in the surface tension of a liquid caused by the contact of liquid against the sides of a container |
What are two possible shapes of a meniscus? | Concave or convex |
When does a convex meniscus occur? | When the molecules of the liquid repel the molecules of the container or object |
Where can a convex meniscus be seen? | mercury barometers |
When does a concave meniscus occur? | When the molecules of a liquid attract those of the container |
When can an example of a concave meniscus be seen? | water in a glass |
What property creates the concave meniscus of water up the sides of a glass and downward in the center? | surface tension |
The force exerted by atoms and molecules is defined as __________. | Pressure |
How is pressure generated? | kinetic energy |
Kinetic energy is produced by atoms and molecules that are in __________. | motion |
What is the equation for pressure? | force/area |
The English unit of pressure, the pound, is a unit of (mass/force). | force |
What are two ways that the English unit of pressure is measured? | lbs/ft sq; lbs/sq in |
What is the international unit of pressure? | newton/meter sq or "Pascal" |
1 atmosphere of pressure is equivalent to _______ kPa or _______ lbs/sq in. | 101.3 kPa; 14.69 lbs/sq in |
When is pressure exerted at the molecular level? | When molecules of gases collide |
What is cylinder pressure? | The sum of molecular forces in a closed container |
How is cylinder pressure measured? | lbs per square in. gauge (PSIG) |
What two values are equal when a gas cylinder is empty? | cylinder and atmospheric pressures |
A full E cylinder of oxygen measures _________ PSIG. | 1900-2200 |
A full tank of N2O measures __________ PSIG. | 745 |
What does the Bourdon Gauge measure? | Pipeline or cylinder pressures |
What type of measurement is the Bourdon Gauge based on? | Aneroid |
An aneroid gauge operates (with/without fluid). | without |
What governing body sets standards for the readings on Bourdon-type gauges? | ASTM |
What do the terms mmHg and cmH20 measure? | Pressure of a gas other than compressed gas |
mmHg is also referred to as ______. | torr |
The tourniquet applied during knee surgery utilizes _______ as a form of measurement since it is not a compressed gas. | mmHg or torr |
High pressure and continuing pressure in an anesthesia machine is measured in units of _______. | cmH20 |
What are the three physics principles that apply to pressure in a liquid source? | 1)pressure in a liquid at a certain level is proportional to the height of the liquid 2)pressure in a liquid increases with the depth below the surface 3)pressure in a liquid is the same in all directions at the same depth |
Patients undergoing TURP are at risk of developing ____________. | Dilutional hyponatremia |
Why are TURP patients at risk of developing dilutional hyponatremia? | High-hanging bags of irrigation lead to absorption of irrigating solution by open venous channels |
What is the function of the pressure relief valve near the CGO? | Prevents transmission of high-pressures in the anesthesia machine to the patient |
What safety feature on the anesthesia machine may limit the ability to provide adequate jet ventilation? | Pressure relief valve |
What are the features in the anesthesia machine that ensure unidirectional flow of gases toward the patient from machine and away from the patient on exhalation? | Inspiratory and expiratory valves |
How is incompetence of unidirectional valves prevented? | Opening, cleaning, and if necessary, replacing discs |
What is the function of the pressure regulator (pressure reducing valve)? | Reduce pressure and control gas supply from the pipeline or cylinder |
How do pressure regulators function? | Balances force of a spring against the force of the compressed gas |
What is surface tension? | Attractive forces that occur between molecules at the surface of a liquid |
Where does surface tension occur? | At the air-liquid interface |
Surface tension creates a strong barrier between ______ and _____ molecules. | Air; liquid |
What property prevents fast evaporation of water as well as certain insects to walk on water? | Surface tension |
The dyne is a unit of (force/mass). | Force |
How is surface tension measured and at what temperature is it measured at? | Dynes/cm at 20 degrees celsius |
What lines the walls of alveoli in the lungs? | Thin film of liquid |
How does the surface tension of fluid in the lungs influence the alveoli? | The surface tension of the liquid influences the alveoli to want to collapse |
What endogenous chemical prevents the collapse of alveoli? | Surfactant |
Lung surfactant is secreted by _____________. | Type 2 alveolar epithelial cells |
What does the lung surfactant decrease? | Cohesive force of the liquid film, or surface tension |
What are the three physiological benefits of lung surfactant? | 1)increases lung compliance 2)reduces the tendency of small alveoli to empty into larger ones (collapse) 3)reduce fluid leak from pulmonary capillaries into alveoli |