Figure 1.

Decreased cerebral vascular oxygenation with age. (a) Examples of vascular pO₂ imaging in diving arterioles (1–2) and ascending venules (3–5) at the depth of ~20 µm in a young mouse. The scale bar is 100 µm. (b,c) Changes in mean arteriolar (A) and venular (V) pO₂ and SO₂ with age. Mean pO₂ and SO₂ for each vessel were obtained by averaging the values over the first 150 µm of depth. pO₂ values were converted to SO₂ using the Hill’s equation (for arterioles: Y, n = 21; M, n = 21; O, n = 26 vessels; for venules: Y, n = 23, M, n = 25, O, n = 31 vessels; data from 8 young, 8 middle-aged, and 8 old mice). (d) Oxygen extraction fraction (OEF) versus age, obtained from SO₂ values in (c). Error bars were obtained from SO₂ standard deviations using the theory of error propagation. (e) Arterial oxygen saturation (SpO₂) measured by pulse oximetry on the tail (Y, n = 15, M, n = 14, O, n = 14 mice). (f) Systemic hematocrit measured on a separate batch of mice (age-matched) by centrifugation of blood samples (Y, n = 10, M, n = 9, O, n = 8 mice). Y: young, M: middle-aged, O: old. Bar plots represent mean ± s.e.m. Statistical significance was calculated using ANOVA followed by Tukey HSD post hoc test. **p < 0.01 *p < 0.05, ^#p-value approaches significance (p < 0.1).