Aortic impedance in Little mice

The Little dwarf mouse lives 30% longer than its age-matched wild-type (WT) mouse. We determined aortic input impedance in 21 (8 Little, 13 WT) 4 month-old mice. Modulus of impedance was calculated from the Fourier transformed aortic pressure (P) and average luminal flow velocity (V(avg)) as |Z(i)| = |P|/|V(avg)|. Characteristic impedance was estimated by averaging the 2(nd)-10(th) harmonic of the impedance moduli. We found the impedance modulus |Z(i)| to be similar in the 2 groups (WT vs. Little; mean+/-SE) - peripheral resistance (10597+/-654 vs. 12932+/-1433 dyne-s/cm(3)), modulus at first harmonic (Z(1): 740+/-56 vs. 902+/-105 dyne-s/cm(3)), and characteristic impedance (Z(c): 441+/-34 vs. 470+/-60 dyne-s/cm(3)). Also, mean aortic velocity (20.1+/-1.1 vs. 16.5+/-1.8 cm/s) and mean aortic blood pressure (81.1+/-3.9 vs. 75.9+/-5.9 mmHg) were similar between the two groups. Impedance at low frequencies was slightly higher in the dwarf mice which may be due to the diminished systolic function as indicated by significant reduction in peak aortic velocity (84.0+/-3.2 vs. 70.1+/-1.2 cm/s, p<<0.01). Although modestly higher, the overall impedance in Little mice was similar to that in WT mice. This indicates that left ventricular (LV) afterload may not significantly be altered in Little mice.