Pathophysiological and clinical aspects of breathing after stroke.

Pathophysiology of respiratory control in stroke Neural control of respiration in man depends on a central drive to the respiratory muscles which is modulated by chemical and mechanical inputs. While many of the factors controlling established respiratory rhythm in mammals are understood, the neural mechanisms of rhythm generation remain obscure. It has proved diYcult, in man, to attribute precise respiratory function to localised anatomical substrates because lesions are rarely localised and coexisting pulmonary, cardiovascular, or autonomic influences may complicate the clinical picture. Furthermore accurate diagnosis of respiratory insuYciency has led to earlier therapeutic intervention with controlled ventilation. Also there is probably considerable redundancy and plasticity of the neural substrate of respiratory control, thus congenital, longstanding, or slowly progressive and destructive mass lesions can have little or no functional consequence while acute discrete lesions in a similar distribution may lead to profound respiratory impairment. Finally much of the literature is flawed because the extensive experimental animal work has been applied to man without any evidence for anatomicophysiological correlates. However in individual case studies abnormalities of respiration may be associated with small, discrete lesions of the central nervous system, defined by imaging or postmortem, particularly due to stroke. Such reports have complemented experimental animal work and have greatly increased our understanding of the mechanisms that control breathing in man. Central respiratory drive is mediated by three pathways, which are largely anatomically and functionally independent above the segmental level, although it is increasingly clear that these systems must interact with one another to some extent. 6