Structural Features of Microvascular Networks Trigger Blood Flow Oscillations.

We analyse mathematical models in order to understand how microstructural features of vascular networks may affect blood flow dynamics, and to identify particular characteristics that promote the onset of self-sustained oscillations. By focusing on a simple three-node motif, we predict that network "redundancy", in the form of a redundant vessel connecting two main flow-branches, together with differences in haemodynamic resistance in the branches, can promote the emergence of oscillatory dynamics. We use existing mathematical descriptions for blood rheology and haematocrit splitting at vessel branch-points to construct our flow model; we combine numerical simulations and stability analysis to study the dynamics of the three-node network and its relation to the system's multiple steady-state solutions. While, for the case of equal inlet-pressure conditions, a "trivial" equilibrium solution with no flow in the redundant vessel always exists, we find that it is not stable when other, stable, steady-state attractors exist. In turn, these "nontrivial" steady-state solutions may undergo a Hopf bifurcation into an oscillatory state. We use the branch diameter ratio, together with the inlet haematocrit rate, to construct a two-parameter stability diagram that delineates regimes in which such oscillatory dynamics exist. We show that flow oscillations in this network geometry are only possible when the branch diameters are sufficiently different to allow for a sufficiently large flow in the redundant vessel, which acts as the driving force of the oscillations. These microstructural properties, which were found to promote oscillatory dynamics, could be used to explore sources of flow instability in biological microvascular networks.

Biofeedback and hypnosis in weaning from mechanical ventilators.

Weaning patients from mechanical ventilation can be hindered by both physical and psychologic factors. Biofeedback has been used successfully as an adjunct in difficult weaning problems. We have used a combination of hypnosis and biofeedback to wean a patient with neurologic disease who previously failed weaning by standard procedures. A 30-year-old woman with respiratory failure secondary to multiple sclerosis with transverse myelitis was given eight sessions of biofeedback over 12 days in which the movements of her chest wall, as monitored by magnetometers, were displayed on an oscilloscope. The patient was praised for targeted respiratory rate, amplitude, and rhythm. These sessions included hypnosis in which the patient was given suggestions of well-being and that she could breathe as she had five years earlier. In this manner the patient was successfully weaned. Respiratory biofeedback and hypnosis appear to be useful adjuncts in weaning patients from ventilators.

Sarcoidosis and aspergilloma. The role of surgery.

Fibrocystic pulmonary disease is a common sequel of chronic pulmonary sarcoidosis, and the subsequent development of intracavitary aspergillomas is frequent, especially in black patients. Pulmonary hemorrhage from aspergilloma is second only to cardiorespiratory failure as the cause of death in sarcoidosis. Opinions regarding the role of resectional surgery are conflicting. We report observations on 38 patients with biopsy evidence of antecedent sarcoidosis and cultural or serologic identification of Aspergillus species as cause of the fungus balls. Pulmonary fibrosis was bilateral and extensive in most cases, making surgical treatment perilous. Ten patients had moderate impairment of pulmonary function. Seven had surgical resection with six satisfactory results and one death. Three patients in this category have not required surgery. Twenty-eight patients had severely compromised pulmonary function. Surgery was performed in seven because of intractable bleeding; four survived, but three later died of respiratory failure. Of the 21 in this category not treated by surgery, six survived, four died of hemorrhage and 11 of respiratory failure. Of the 37 patients with aspergilloma whose status is known, 19 are dead, 14 survived with positive precipitins and four, all treated surgically, recovered. It is concluded that surgical treatment of aspergilloma in patients with sarcoidosis should be avoided if possible, but is inescapable in a third of cases.

Pulmonary cystic disease in ankylosing spondylitis: two cases with unusual superinfection.

Two ankylosing spondylitis patients with upper lobe fibrocystic disease are reported. The occurrence of pulmonary parenchymal disease as part of the primary pathologic process in ankylosing spondylitis is now accepted as an integral part of the disease. The frequency of superinfection of cavitary lung disease with Aspergillus is noted. Another unusual superinfection, Mycobacterium scrofulaceum, is reported.

Pulmonary angiitis and granulomatosis. The relationship between histological features, organ involvement, and response to treatment.

The histologic findings, natural history, and response to treatment were investigated in 62 patients with pulmonary angiitis andgranulomatosis seen over a 23 year period. Three histologic types were recognized: lymphocyte depleted angiitis and granulomatosis, 24 cases (39 per cent); benign lymphocytic angiitis and granulomatosis, 14 cases (22 per cent); and malignant lymphoproiferative angiitis and granulomatosis, 24 cases (39 per cent). Lymphocyte depleted angiitis and granulomatosis corresponds to Wegener's granulomatosis of either the "limited" or "classic" variant. The lesions frequently show extensive liquefactive necrosis. Eosinophils may be abundant, but lymphocytes and plasma cells are relatively scarce. Histiocytic proliferation with the occasional presence of sarcoid-like granulomas was observed only in cases with no evidence of glomerular involvement. Cyclophosphamide is highly effective regardless of whether extrapulmonary manifestations are present. Benign lymphocytic angiitis and granulomatosis is characterized by dense benign infiltrates of lymphocytes, plasma cells, and histiocytes. Necrosis may be absent or minimal; the angiitis is usually mild to moderate. Only one of 14 patients (7 per cent) had extrapulmonary involvement (skin). Chlorambucil is highly effective, sometimes resulting in dramatic cures. Malignant lymphoproliferative angiitis and granulomatosis corresponds to lymphomatoid granulomatosis. Its lesions show extensive coagulative necrosis, a highly atypical lymphoreticular infiltrate with frequent mitoses, and angioinvasion. Extrapulmonary involvement is frequent (83 per cent), particularly in the skin (46 per cent) and central nervous system (33 per cent). The mortality is high: 65 per cent of the patients were dead within the first year of disease. Although cytotoxic drugs were of no value, corticosteroids were associated with prolonged remissions in three young patients.