A REVIEW OF THE EFFECTS OF BODY TEMPERATURE VARIATIONS ON RESPIRATORY MECHANICS: MEASUREMENTS BY THE END-INFLATION OCCLUSION METHOD IN THE RAT

Abstract

The temperature of body fluids is expected to affect tissues mechanical properties, including respiratory system tissues. This is because of the changes in airway smooth muscle tone and contractile properties, influencing airway frictional resistance to airflow, and because of the temperature effects on the stress–strain relationships of elastin and collagen, which determinates the elastic behavior of the lungs as reflected by their pressure–volume relationship. Alveolar surfactant biological and physical properties have also been shown to be affected by temperature changes, suggesting influences on the respiratory system hysteretic properties. Experimental works describing the effects of body temperature variations on respiratory mechanics are reviewed, including recent findings dealing with investigations on respiratory mechanics carried out by the end-inflation occlusion method in the rat. This method allows to determine, together with the elastance of the respiratory system, its resistive properties too. In particular, both the ohmic airway resistance due to frictional forces in the airway and the additional visco-elastic resistance exerted because of tissues stress-relaxation may be quantified. The effects of body temperature variations were assessed, and experimentally induced temperature increments and/or decrements allowed to conclude that respiratory system tissues stiffness, both the ohmic and the stress-relaxation linked resistances, and the hysteretic behavior of the respiratory system, decrease with temperature increments. The mechanisms responsible for these effects are analyzed.