Third metacarpal bone mineral density assessment in the standing horse by dual X-ray absorptiometry

Bone mineral density (BMD) is correlated to mechanical properties of bone. In the horse, dual energy X-ray absorptiometry (DXA) has yet only been performed ex-vivo, but a new portable DXA device would be ideal for in-vivo BMD measurement. We explored field suitability, precision and accuracy of this device for in-vivo third metacarpal density assessment. Precision was analysed by calculating measurement variation under repeated measurement tests with (reproducibility) and without (repeatability) limb repositioning. Repeatability and reproducibility were tested ex-vivo, at the same time that intra- and inter-operator reproducibility were assessed in-vivo. In order to test accuracy, bone mineral content (BMC) of several bone samples determined by DXA and ashing were compared. Repeatability was 1.47% and reproducibility 1.69% ex-vivo. In-vivo reproducibility varied between 2.91 and 4.06% for intraoperator test and between 3.13 and 5.53% for interoperator test. BMC measured by DXA and ash weight were highly correlated (R2>0.99). In conclusion, under described conditions this DXA device is usable, accurate and precise. Its sensitiveness reaches 8.23% in an individual longitudinal monitoring. Using the third metacarpal bone as an example, we have shown that this device is suitable for experimental or clinical monitoring.

Third metacarpal bone mineral density assessment in the standing horse by dual X-ray absorptiometry: suitability, precision and accuracy

Bone mineral density (BMD) is correlated to mechanical properties of bone. In the horse, dual energy X-ray absorptiometry (DXA) has yet only been performed ex-vivo, but a new portable DXA device would be ideal for in-vivo BMD measurement. We explored field suitability, precision and accuracy of this device for in-vivo third metacarpal density assessment. Precision was analysed by calculating measurement variation under repeated measurement tests with (reproducibility) and without (repeatability) limb repositioning. Repeatability and reproducibility were tested ex-vivo, at the same time that intra- and inter-operator reproducibility were assessed in-vivo. In order to test accuracy, bone mineral content (BMC) of several bone samples determined by DXA and ashing were compared. Repeatability was 1.47% and reproducibility 1.69% ex-vivo. In-vivo reproducibility varied between 2.91 and 4.06% for intra-operator test and between 3.13 and 5.53% for inter-operator test. BMC measured by DXA and ash weight were highly correlated (R2>0.99). In conclusion, under described conditions this DXA device is usable, accurate and precise. Its sensitiveness reaches 8.23% in an individual longitudinal monitoring. Using the third metacarpal bone as an example, we have shown that this device is suitable for experimental or clinical monitoring.

Augmented age-associated innate immune responses contribute to negative inotropic and lusitropic effects of lipopolysaccharide and interferon gamma

Innate immunity not only mediates early host defenses to infection, but also contributes to septic hemodynamic compromise through nitric oxide synthase (NOS2) induction and inhibition of cardiovascular adrenergic responses. Because of increased age-related susceptibility to sepsis, we hypothesized that hearts from old (28-29 months) adult rats would exhibit greater beta-adrenergic hyporesponsiveness than young (6-8 months) following lipopolysaccharide (LPS, 6 mg/kg) with and without interferon gamma (INF-gamma, 5000 units). LPS/INF-gamma depressed baseline +dP/dt and isoproterenol-stimulated inotropy in both old and young hearts. beta-adrenergic inotropic (+dP/dt) and lusitropic responses were more depressed in old v young LPS/INF-gamma hearts. Additionally isoproterenol-stimulated cAMP elaboration was less in old (1950+/-160 fmol/min/g) v young (2440+/-170 fmol/min/g, P=0.05) LPS/INF-gamma hearts. LPS alone also depressed basal +dP/dt and prolonged myocardial relaxation in old and young hearts, but suppressed isoproterenol +dP/dt responses only in old hearts. Depressed beta-adrenergic inotropic responses were augmented with the selective NOS2 inhibitor N-iminoethyl-L-lysine. To establish biochemical mechanisms for this, we tested whether induction of NOS2 and innate immune system receptors (CD14 and Toll-like receptor 4, TLR4) were enhanced in old v young hearts. Induction of myocardial NOS2 and CD14 (not present in control) by LPS/INF-gamma was approximately 2-3-fold greater in old compared to young animals. TLR4 was constitutively expressed in old and young hearts and was unaffected by LPS/INF-gamma. These findings indicate that advanced age is associated with augmented cardiac beta-adrenergic depression and enhanced CD14-NOS2 signaling in response to cytokines. Upregulation of cardiovascular innate immunity may have clinical implications for increased mortality in older individuals with systemic inflammatory response syndromes.