V/Q mismatch

Note that there is no difference between the ideal alveolar value and the normal arterial Pao2 of 13.3 kPa. In practice a difference of up to 2 kPa is allowable owing to ventilation-perfusion (V/Q) mismatch and shunt. 

Another cause of dialysis-induced hypoxemia is the use of bioincompatible dialyzer membranes, which activate complement (C3 and C5). This causes the formation of C3a and C5a, which are chemotactic for neutrophils and are ana-phylatoxic, thereby causing pulmonary sequestration of neutrophils and platelets (hence neutropenia and thrombocytopenia), with resultant ventilation-perfusion (V/Q) mismatch and hypoxemia. This is evidenced by the simultaneous development 15 minutes after the start of dialysis of hypoxemia, neutropenia, and high circulating levels of C3a and C5a (C2). 

Acetate is also said to contribute to hypoxemia by directly depressing the respiratory muscles and myocardium, the latter effect causing decreased cardiac output with subsequent pulmonary V/Q mismatch and hypoxemia (C2). Although not all workers agree that acetate is a significant myocardial depressant (A10), it may nevertheless cause hypotension by its peripheral vasodilatory effect. 

Classically, there are five causes of hypoxemia low inspired oxygen fraction (Fio ), increased diffusion barrier, hypoventilation, ventilation-perfusion (V/Q) mismatch, and shunt or venous admixture. 

Lung disease produces severe ventilation-perfusion (V/Q) mismatching (11,12). In many diseases, collapsed alveoli can be recruited during a positive-pressure breath (12-16). Three specific techniques to optimize this recruitment are the application of PEEP, the use of recruitment maneuvers, and prolongation of the inspiratory time. 

V/Q scan and CT scans are the most commonly used tests to diagnose PE. A V/Q scan measures the distribution of blood and air flow in the lungs. When there is a large mismatch between blood and air flow in one area of the lung, there is a high probability that the patient has a PE. Spiral CT scans can detect emboli in the pulmonary arteries. 

A(q) = e q) + q2/(2m ) — q.V being the energy mismatch between the the states in) and q). The second term in the square brackets in Eq. (7b) arises from the coupling-constant renormalization in Eq. (4) and compensates for the ultraviolet divergence of the first term. This compensation is completely analogous to that of the electron mass renormalization in calculations of the radiative shift of an atomic optical transition [Bethe 1947 Cohen-Tannoudji 1992],... 

Another example is related to the motion of defects (dislocations in the roll pattern) which constitutes the basic mechanism of wavevector selection. In the normal-roll regime, the stationary structure is characterized by the condition q II H. However, when changing the field direction one can easily induce a temporary wavevector mismatch Aq = q ew — qoid which relaxes via a ghde (v II q) motion of defects. Experiments have confirmed the validity of detailed theoretical predictions, both with respect to the direction (v J. Aq) and the magnitude (consistent with logarithmic divergence at Aq —> 0) of the defect velocity v [42]. 

Phung, Q., Winter, D., Cranston, A., Tarone, R., Bohr, V., Fishel, R., and Gearhart, P. (1998). Increased hypermutation ot G and C nucleotides in immunoglobulin varia ble genes from mice deficient in the MSH2 mismatch repair protein. I. Exp. Med. 187, 1745-1751. 

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