Platelet mitochondrial biochemistry during sepsis or cardiogenic shock. Activity of platelet respiratory chain enzymes was measured in healthy volunteers (white bars) and patients with sepsis (grey bars) or cardiogenic shock (black bars) (within 48 hours from admission to intensive care). Nicotinamide adenine dinucleotide dehydrogenase (NADH) (A), complex I (CI) (B), complex I + III (CI + III) (C), succinate dehydrogenase (SDH) (D), complex II + III (CII + III) (E), and complex IV (CIV) (F) activity is expressed relative to citrate synthase (CS) activity, a marker of mitochondrial density. P values refer to one-way analysis of variance (ANOVA) or one-way ANOVA on ranks (*P <0.05 vs. healthy volunteers on post hoc all-pairwise multiple comparisons (Tukey or Dunn’s test)). CS activity was 68 ± 8 nmol/minute/mg proteins in healthy volunteers, 67 ± 12 nmol/minute/mg proteins in patients with sepsis and 59 ± 9 nmol/minute/mg proteins in those with cardiogenic shock (*) (P = 0.026). Complex I, NADH–ubiquinone 1 reductase; complex I + III, NADH–cytochrome c reductase; complex II + III, succinate dehydrogenase–cytochrome c reductase; complex IV, cytochrome c oxidase.