Journal of applied physiology
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Editorial Comment Review
Invited editorial on "Effect of enhanced supramaximal flows on cough clearance".
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The volume-pressure relationship of the vasculature of the body as a whole, its vascular capacitance, requires a measurement of the mean circulatory filling pressure (Pmcf). A change in vascular capacitance induced by reflexes, hormones, or drugs has physiological consequences similar to a rapid change in blood volume and thus strongly influences cardiac output. The Pmcf is defined as the mean vascular pressure that exists after a stop in cardiac output and redistribution of blood, so that all pressures are the same throughout the system. ⋯ A change in Pmcf provides a uniquely useful index of a change in overall venous smooth muscle tone if the blood volume is not concomitantly changed. The Pmcf also provides an estimate of the distending pressure in the small veins and venules, which contain most of the blood in the body and comprise most of the vascular compliance. Thus the Pmcf, which is normally independent of the magnitude of the cardiac output, provides an estimate of the upstream pressure that determines the rate of flow returning to the heart.
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Cough and bronchoconstriction are airway reflexes that protect the lung from inspired noxious agents. These two reflexes can be evoked both from the larynx and tracheobronchial tree and also from some extrarespiratory sites. Within the airways, certain sites are particularly sensitive to stimulation of cough (larynx and points of proximal airway branching), whereas bronchoconstriction can be triggered from the whole of the tracheobronchial tree. ⋯ C-fiber endings (bronchial and pulmonary) mediate bronchoconstriction. Inhalation of so-called "selective" C-fiber stimulants induces cough, but excitation of RARs has not been eliminated, and the possibility also exists that the cough is secondary to other lung actions mediated by these nerve endings. Although cough and bronchoconstriction may be mediated by the same type of receptor, they seem to have separate afferent neural pathways.