Capillary Blood Flow Distribution Research Articles

Distribution of capillary blood flow in the microcirculation of the hamster: An in vivo study using epifluorescent microscopy

In vivo epifluorescent microscopy (EPI) was used to study capillary perfusion in superfused hamster cheek pouch, and cremaster and sartorius muscle preparations. In cheek pouches and cremaster muscles, in vivo epifluorescence microscopy (EPI) was compared to in vivo transillumination microscopy (TRANS) and the former was found to allow detection of a larger number of capillaries—34% more capillaries in cheek pouch and 21% more in cremasters were observed with EPI. The fraction of capillaries containing erythrocytes alone, plasma alone or plasma plus red cells was determined in all three tissues. Also, the fraction of capillaries unperfused was noted. Less than 2% of the capillaries contained plasma alone. The number of capillaries which contained stationary erythrocytes varied with vasomotor tone. In control cremaster and sartorius muscles 17 and 13% of observed capillaries were unperfused but contained erythrocytes. Ninety-eight percent of capillaries contained stationary erythrocytes in cremaster muscles vasoconstricted with 21% oxygen. From these observations we conclude (1) functional capillary counts obtained with TRANS may represent underestimates of the true number; (2) plasma shunts do not appear to be a significant factor in normal microcirculatory function in the hamster cheek pouch, or in cremaster and sartorius muscles; (3) since unperfused capillaries contain red cells, red cells, red cell counts in histological sections will overestimate functional capillarity. The magnitude of the overestimation will be a function of vascular tone and capillary hematocrit.

Blood flow distribution during artificially induced respiratory hypocapnic alkalosis in the fowl

In birds, hyperthermia is normally associated with panting and progressive respiratory alkalosis. The effect of respiratory alkalosis on capillary blood flow distribution was examined by artificially hyperventilating normothermic fowls, thereby dissociating it of the normally occuring concomitant hyperthermia. In contrast with mammals, in which hyperventilation associated with hypocapnia reduced blood flow to the brain, uterus and other organs, in the hen blood flow distribution in most organs remained unaltered. This indicates that the potential change in acid-base balance which develops in the hyperthermic birds during panting is not likely to affect the regulation of blood flow. The comb and wattles were the only affected organs, in which capillary blood flow diminished to about 45% of normal values. This reduction did not prevent a vasodilation in those organs in hyperthermic fowls, though it probably limited its full expression.

The effects of hypercapnia and hypoxia on the distribution of capillary blood flow in the denervated intestinal vascular bed.

AbstractExperiments are described which demonstrate that both hypercapnia and hypoxia exert a potent relaxing influence on the resistance vessels of the denervated intestine. The effects on the capillary fluid exchange capacity, as indicated by the capillary filtration coefficient (CFC), are, however, more complex. During local hypoxia CFC increases considerably, probably reflecting a direct relaxing influence on the precapillary sphincter section. In contrast, during hypercapnia CFC decreases in spite of an augmented blood flow. This is assumed mainly to be due to an increased myogenic activity in the same sphincter section, elicited locally by a raised transmural pressure and blood flow. Functional implications of the results are briefly discussed. They suggest that neither high Pco2 accompanied by a low pH, nor low Po2 are of major importance for a functional intestinal hyperemia during digestion.

Respiratory insufficiency and chronic cor pulmonale.

Because of newer technics of treatment, a small but ever increasing number of patients with chronic pulmonary disease are surviving long enough to develop chronic cor pulmonale. An attempt has been made to correlate the newer knowledge of aberrations of cardiocirculatory and respiratory physiology in chronic pulmonary disease. Respiratory insufficiency may be due to varying proportions to the following: (1) ventilatory dysfunction or impairment of the ability to move air into or out of the lungs; this may be of two types: (a) obstructive, due primarily to airway narrowing and (b) restrictive, due to disordered function of the thoracic bellows or diminished pulmonary distensibility; (2) unequal distribution of inspired air to the alveoli (intrapulmonary mixing); (3) uneven perfusion or distribution of capillary blood flow; (4) impaired diffusion or transfer of oxygen across the alveolar capillary barrier and (5) impaired cleansing of the lung. The same abnormal physiologic change may result from pathologic conditions which differ widely in etiology; furthermore, a particular disease may give rise to widely differing functional patterns. The types of pulmonary disease causing chronic cor pulmonale may be divided into two main categories: (1) Type I, pulmonary diseases associated with chronic diffuse obstructive emphysema. (2) Type II, pulmonary diseases in which the pathologic process tends to be localized in or about the pulmonary vessels. In some instances, a case belongs mainly in one category but may demonstrate some features of the other. The strain on the right ventricle is a result of: (1) increased resistance to pulmonary blood flow and (2) increased cardiac output (when present). Increased resistance to pulmonary flow may be due to: (a) reduction in caliber and distensibility of the pulmonary vascular bed which may be structural or related to hypoxia, (b) polycythemia and (c) intrapulmonary vascular shunts. Respiratory insufficiency may be suspected from the history. Physical and roentgenologic examinations may be confirmatory, but pulmonary function tests are necessary for a precise evaluation of the functional abnormalities. The recording of a physiologic, as well as a pathologic diagnosis, is a useful practice in the individual case. The presence of right ventricular enlargement can only be detected clinically when the chronic cor pulmonale is moderately advanced. However, clinical and roentgenologie evidence of pulmonary hypertension in chronic pulmonary disease indicates that right ventricular hypertrophy is probably present. The electrocardiogram may be helpful even in the absence of a definite right heart strain pattern since the electric position of the heart is often suggestive. Cardiac catheterization provides the best method for the early detection of pulmonary hypertension. The treatment of chronic cor pulmonale is much more hopeful today than in the past. It is most satisfactory when cor pulmonale is due to pulmonary disease of type I. Intensive therapy of the bronchopulmonary disease is as important as specific cardiac measures. The objectives of therapy are to combat infection, produce an adequate airway and improve effective alveolar ventilation. This may partially reverse many of the pathologic changes in the lung which are responsible for hypoxia and the anatomic reduction in the pulmonary vascular bed.