Respiratory Physiology & Neurobiology 189 (2013) 52–58 Contents lists available at ScienceDirect Respiratory Physiology & Neurobiology j our na l ho me pa g e: www.elsevier.com/locate/resphysiol The effect of body cooling on respiratory system mechanics and hysteresis in rats Alessandro Rubini ∗ , Dania El-Mazloum, Francesco Morra, Gerardo Bosco Department of Biomedical Sciences, Physiology Section, University of Padova, Via Marzolo, 3, 35100 Padova, Italy a r t i c l e i n f o Article history: Accepted 25 June 2013 Keywords: Body temperature End-inflation occlusion method Rat Respiratory mechanics Work of breathing a b s t r a c t Literature reports and theoretical considerations suggest that body cooling may affect respiratory mechanics in vivo. To examine this hypothesis, healthy rats were studied using the end-inflation occlu- sion method under control conditions and after total body cooling. Respiratory mechanics parameters, hysteresis areas, the inspiratory work of breathing, and its elastic and resistive components, were cal- culated. After body cooling (mean rectal temperature from 36.6 ± 0.25 to 32.1 ± 0.26 ◦ C), the ohmic and the additional visco-elastic respiratory system resistances, the hysteresis, the total inspiratory work of breathing, and its resistive components, were all increased. No significant changes were detected for the static and dynamic respiratory system elastance mean values, and the related elastic component of the work of breathing. These data indicate that body cooling increases the mechanical inspiratory work of breathing by increasing the resistive pressures dissipation. This effect is evident even for limited temperature variations, and it is suggested that it may occur in the event of accidental or therapeutic hypothermia. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Literature reports strongly suggest that respiratory system mechanics may be dependent on body temperature variations (Rubini, 2011a). For example, rabbit airway smooth muscle cells exhibited increased isometric tension during methacholine chal- lenge when exposed to cooling (Bratton et al., 1987), suggesting that airway mean diameter may be decreased, hence resistance increased, by temperature lowering. Furthermore, elastin fibres, which are known to be well represented in the alveolar walls, where exert a decisive role in influencing the pressure–volume characteristics of lungs, have been shown to exhibit a temperature- dependent stress–strain relationship, with increased stiffness as a consequence of cooling (Weinberg et al., 1995). The alveolar surfactant content of the lungs tissues and lavage fluid has been described to decrease with temperature reduction (Kumar et al., 1980), suggesting that body temperature may affect lung hysteresis also. These possible temperature-dependent effects have not been extensively studied in vivo in the literature. A sole available paper described that total body warming induced a decrement in respiratory system hysteresis mean values in rats, although not significant (Rubini, 2011a). A hysteresis reduction ∗ Corresponding author. Tel.: +39 0498275310; fax: +39 0498275301; mobile: +39 3389344761. E-mail address: alessandro.rubini@unipd.it (A. Rubini). with temperature increment was also observed in excised rabbit lungs (Lempert and Macklem, 1971). However, although indirectly, other data suggest that respiratory system hysteresis may exhibit temperature dependence, because of body warming or cooling influences on the biological activity of alveolar surfactant (Kumar et al., 1980; Bruni et al., 1996). The possible consequences of temperature changes on respi- ratory system mechanics have been most of all investigated by means of cooling induction experiments in animals. For exam- ple, a reduction in lung static compliance has been reported in sheep subjected to total body cooling (Deal et al., 1970) and in positive-pressure ventilated excised rabbit lungs as an effect of temperature lowering (Nagao et al., 1977). Similar changes were also described in saline-filled excised dog lungs (Debes and Fung, 1992). Animal experiment in dogs showed a cooling-induced airway resistance increment, either as an effect of low temperature- elicited reflex (Pisarri and Giesbrecht, 1997), or because of a directly induced activation of airway smooth muscle cells contraction (Salonen et al., 1991). Furthermore, local airway cooling, induced by cold air breathing, was shown to cause bronchoconstriction, either as a directly induced effect (Guleria et al., 1969) in humans, or as a consequence of vagally mediated reflex effect (Jammes et al., 1983; McFadden and Ingram, 1986). Asthmatic subjects seem to be particularly sensible to the effects of airway cooling (Horton and Chen, 1979; Sheppard et al., 1982; McFadden and Ingram, 1986; Eschenbacher et al., 1992; Kaminsky et al., 1995, 2000). 1569-9048/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.resp.2013.06.024