The indicial response function for pulmonary artery tissue remodeling during recovery from hypoxic hypertension differs from that during hypertension development, indicating a major nonlinearity.
Does returning to normal oxygen levels reverse pulmonary arterial tissue remodeling symmetrically in rats with hypoxic hypertension?
The process of pulmonary arterial tissue recovery from hypoxic hypertension is not simply the reverse of the injury process, demonstrating a significant nonlinearity in tissue remodeling.
The reversibility of tissue remodeling is of general interest to medicine. Pulmonary arterial tissue remodeling during hypertension induced by hypoxic breathing is well known, but little has been said about the recovery of the arterial wall when the blood pressure is lowered again. We hypothesize that tissue recovery is a function of the oxygen concentration, blood pressure, location on the vascular tree, and time. We measured the changes of blood pressure, vessel lumen, vessel wall thicknesses, and opening angle of each segment of the blood vessel at its zero-stress state after step changes of the oxygen concentration in the breathing gas. The zero-stress state of each vessel is emphasized because it is important to the analysis of stress and strain and in morphometry. Experimental results are presented as histories of tissue parameters after step changes of the oxygen level. Tissue characteristics are examined under the hypothesis that they are linearly related to changes in the local blood pressure. Under this linearity hypothesis, each aspect of the tissue change can be expressed as a convolution integral of the blood pressure history with a kernel called the indicial response function. It is shown the indicial response function for rising blood pressure is different from that for falling blood pressure. This difference represents a major nonlinearity of the tissue remodeling process of the blood vessels.
Li et al. (2004) studied Hypoxic pulmonary hypertension (n=92). Hypoxia followed by normoxic recovery vs. Normoxia (20.9% O2) was evaluated on Indicial response functions of pulmonary artery tissue remodeling (opening angle, lumen area, wall thickness). The indicial response function for pulmonary artery tissue remodeling during recovery from hypoxic hypertension differs from that during hypertension development, indicating a major nonlinearity.