= Ascending aorta
The \b[ascending aorta] is the upward-running proximal part of the <aorta> between its origin at the <left ventricle> and the <aortic arch>. The <coronary arteries> arise near its base in the <aortic sinuses>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§20.5, Aorta and Ascending Aorta; Figure 20.25 and Table 20.5]{ref} When describing measurements, the tubular <ascending aorta> is distinguished from the <aortic root> at the <sinotubular junction>.<Surgical anatomy of the aortic valve and root—implications for valve repair by Ruggero De Paulis and Andrea Salica>[General considerations; Figure 1, sinus-to-tubular transition]{ref}
This anatomical route and the propagation of a pulse answer different questions. In an original example, a <pressure> disturbance travels through a stipulated 6 cm segment with <pulse wave velocity> 6 m/s. Its propagation time is
$$
\Delta t_{\rm wave}=\frac{0.06}{6}=0.010\ \mathrm{s}.
$$
A represented parcel moving through the same segment at mean <blood flow> speed 0.6 m/s instead takes $\Delta t_{\rm parcel}=0.06/0.6=0.10$ s. The <pressure> signal can therefore arrive before that parcel. These are constructed speeds, not measurements or normal limits.
The wall can also store volume as it distends. In a local linear approximation with <vascular compliance> $C$, a <pressure> change $\Delta p$ gives $\Delta V\simeq C\Delta p$. Stipulated $C=0.05$ mL/mmHg and $\Delta p=20$ mmHg give 1 mL. This is a small-change model for a selected segment; it does not assign the compliance of the entire circulation to the <ascending aorta>.
An imaging measurement should consequently identify the sampled segment and phase of the <cardiac cycle>. A diameter in the <aortic root>, a diameter beyond the <sinotubular junction>, a local <blood flow> speed and a <pulse wave velocity> describe related but different observations.
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