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Biomedical subjects

W B Wead

Publications and source records attributed to W B Wead.

24 records · Page 2Linked to original sources
PubMed1987

Changes in left ventricular geometry during spontaneous breathing.

The purpose of these experiments was to determine the effects of a spontaneously generated inspiration on the size and shape of the left ventricle (LV) in anesthetized supine dogs. We implanted markers in the LV to establish three perpendicular axes and recorded the motion of these markers using biplane cinefluoroscopy at 60 Hz. The primary changes in LV size that accompanied inspiration occurred at end diastole (ED). The largest change in LVED dimension was a 2.46-mm narrowing of the septal-lateral wall dimension, but the apex-base dimension decreased also, by 0.74 mm. The anteroposterior dimension actually widened by 1.07 mm. The septal-lateral narrowing was caused by both a 1.0-mm narrowing of the distance between the septal marker and the apex-base axis, as well as by a 1.4-mm narrowing between the apex-base axis and the lateral wall marker. Narrowing of the septal portion seemed expected because of presumed enhanced right ventricular filling during inspiration. Narrowing of the lateral portion of the LV, while the anteroposterior dimension widened, was surprising because a change in LVEDV shape is implied. Assuming ventricular homogeneity, this change in LVED shape implies that the forces applied to the epicardial surface were not uniform. There must have been a retraction on the anterior and posterior surface that was not experienced by the lateral LV wall. The net effect of these dimensional changes of the LV at end diastole (estimated from the product of the three ED axes) was a 3.5-cm3 reduction in LVED volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Reflex cardiovascular responses caused by stimulation of pulmonary C-fibers with capsaicin in dogs.

The purpose of these studies was to determine quantitatively the reflex cardiovascular responses to stimulation of the pulmonary C-fibers in dogs. We used a preparation in which the airway, pulmonary artery, and the pulmonary veins to the left lung were cannulated in situ. Ventilation and perfusion of the right lung maintained the animal in relatively normal homeostasis. Capsaicin, a decylenic acid amide of vanillylamine that selectively stimulates nerve endings of unmyelinated fibers (C-fibers), was injected into the left pulmonary artery in 5-ml boluses. Maximal reflex responses were obtained with concentrations as low as 0.8-1.6 X micrograms-1 X kg-1. Heart rate, hindlimb resistance, and left ventricular contractility were lowered transiently (the maximal responses showing declines of 40, 13, and 15.2%, respectively). As a result of these changes, combined with vasodilation in other resistance vessels, cardiac output fell 28% and blood pressure fell 35%. Interrupting the afferent neural pathway by severing the ipsilateral cervical vagus nerve eliminated these responses, confirming the distribution of their reflex origin. Although the role of these reflexes in homeostasis has not been decided, the results of this study suggest that the lungs of dogs, if appropriately stimulated, potentially can exert a major inhibitory influence on the neural regulation of cardiovascular function.

Afferent Pathways↗
PubMed1981

Effects of intrapleural pressure changes on canine left ventricular function.

Left ventricular diameter, pressure, and dP/dt, as well as aortic and intrapleural pressures, were recorded simultaneously from 10 acute anethetized mongrel dogs. Normal inspiration produced a significant decrease in end-diastolic diameter (46.9 +/- 1.2 to 43.1 +/- 1.0 mm) and end-systolic diameter (35.5 +/- 1.4 to 34.2 +/- 1.7 mm), reducing stroke diameter 2.5 mm. Airway occlusion (greater than or equal to 60%) produced a reduction in the decrease of end-diastolic diameter seen with normal inspiration and, to a lesser degree, in end-systolic diameter. Because only acute airway occlusion greater than or equal to 80% produced a significant increase in left ventricular afterload, the authors conclude that normal spontaneous inspiration results in a decrease in left ventricular preload due to pooling of blood in the pulmonary vasculature. The data suggest that this decrease in left ventricular preload is the predominant mechanism responsible for the inspiratory decrease in left ventricular stroke volume.

Airway Obstruction↗