Impedance plethysmography in the diagnosis of asymptomatic deep vein thrombosis in hip surgery: a venography controlled study - Agnelli, G; Cosmi, B; Ranucci, V; Renga, C; Mosca, S; Lupattelli, L; Di Filippo, P; Rinonapoli, E; Nenci, G G (Arch Intern Med, 1991)