Description: Of the four pressures that determine whether fluid moves from capillary blood into the interstitial space or vice versa, capillary hydrostatic pressure is the one that can change rapidly because it is controlled by vascular smooth muscle. "Capillary Pressure" allows the user to set arterial and venous pressures as well as the pre- and post-capillary resistances. It then calculates capillary hydrostatic pressure and blood flow as well as the pressure drops across the pre- and post-capillary resistances. Possible simulations include arteriolar vasoconstriction and dilation, venous obstruction, hypotension, reflex vasoconstriction, etc.
History: This is a program from the 1990s. The LabView® version of "Capillary Pressure" was used primarily in classroom demonstrations for dental and graduate students.
Status & Availability: For both Macs and Windows, free LabView® versions of "Capillary Pressure" can be downloaded from the American Physiological Society's archive of teaching materials:
An iPad/iPhone app of "Capillary Pressure" is available in Apple's App Store (SM).
Cardiovascular Physiology Models
Description: "Capillary Filtration" enables the user to perform a complete exploration of the Starling-Landis Equation. Manipulatable variables include arterial and venous pressures, the pre- and post-capillary resistances, protein concentration in blood, the osmotic reflection coefficient, capillary filtration coefficient, and others. The calculated variables include the transcapillary and lymphatic fluxes of water and protein and the hydrostatic and osmotic pressures in the blood and interstitial fluid. One of the most important concepts to demonstrate is the restoration of a new steady-state following a sudden change in one of the Starling forces.
History: This model was published as a chapter in A.P. Shepherd and D.N. Granger's book "Physiology of the Intestinal Circulation", Raven Press, NY, 1984, by J.N.Benoit, C.A. Navia, A.E. Taylor, and D.N. Granger, Mathematical Model of Intestinal Transcapillary Fluid and Protein. Shortly thereafter J.W. Kiel and A.P. Shepherd programmed the first LabView® version which was used for 25 years to stimulate small-group discussions among medical and graduate students.
Status & Availability: Free LabView® versions of "Capillary Filtration" will be donated to the American Physiological Society's archive of teaching materials: http://www.apsarchive.org/search.cfm
An iPad/iPhone app of "Capillary Filtration" is in the works.
Description: Using this program a student or instructor can explore the variables that affect the amplitude of the arterial pressure wave, the so-called "Pulse Pressure". The adjustable variables include venous return, heart rate, arterial compliance, and total peripheral resistance. Some of the possible simulations include doubling the heart rate of a "patient" at rest, decreasing arterial compliance to simulate the effects of aging, and exercise.
History: This program is based on a model created in the 1960s at the University of Mississippi Medical Center. T.G. Coleman and Fred R. Sias, Simulation of Biological Systems, Digital Equipment Users' Society, Maynard, MA, 1969. In the 1980s Kiel and Shepherd developed a LabView® version (A graphic computer language for physiology simulations. Computers in Life Science Education 5:49-56, 1988.). The LabView® version of "Pulse Pressure" was used primarily in classroom demonstrations for medical, dental, and graduate students.
Status & Availability: For both Macs and Windows, free LabView® versions of "Pulse Pressure" can be downloaded from the American Physiological Society's archive of teaching materials:
An iPad/iPhone app of "Pulse Pressure" is in the works.