Ambient Temperature & Osmolality
Rates and durations listed for ALZET pumps are based on use in vivo in mammals unless otherwise specified. In alternate settings, such as in vitro or in other species, the pumping rate and duration may differ since they are affected by temperature and osmolality. Both temperature and osmolality affect the rate at which water crosses the semi-permeable membrane and enters the osmotic sleeve.
The pumping rate of ALZET osmotic pumps varies in direct proportion to temperature. The graph on the left shows the representative pumping rates for two pump models from 4 degrees to over 40 degrees in 0.9% saline.
Use the following equations, or the interactive calculator, to predict the pumping rate in heterothermic animals or in those whose body fluids are hypertonic relative to mammals.
Models 2001, 2002, 2004, 2006, 2001D, 1004, 1003D, 1007D, 1002, and 1004
QT = Q0 [0.135 e(0.054T) – 0.004π + 0.03]
Models 2ML1, 2ML2, and 2ML4
QT = Q0 [0.141 e(0.051T) – 0.007π + 0.12]
• QT = the pumping rate at temperature T
• Q0 = the specified pumping rate at 37°C in µl/hr
• T = temperature in degrees Celsius
• π = osmolality of the solution outside the pump (atm)
These formulae are useful in the range of π = 0 to 25 atm and T = 4°C to 42°C. The equation is predictive within +/- 10%. At normal mammalian osmolality of 310 milliosmoles/l, the osmotic pressure is 7.5 atm. Environmental temperatures above 42°C have been found to cause fluctuating delivery rates and are not recommended.