Journal of applied physiology
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Comparative Study
Interrelationships between regional blood flow, blood volume, and ventilation in supine humans.
Positron emission tomography was used to measure alveolar gas volume, pulmonary blood volume (VB), regional alveolar ventilation (VA), and the regional ventilation-to-perfusion ratio (VA/Q) in a transaxial slice at midheart level in eight supine subjects and one prone normal subject during quiet breathing. These relationships allow regional blood flow (Q) to be calculated as VA/(VA/Q). No significant differences between right and left lung were found. ⋯ VA and Q were well matched except at the dorsal lung thoracic border where low values of VA/Q due to a reduction in ventilation were occasionally found even in these normal subjects. VB and Q were reasonably well matched, implying that variations in vascular transit time due to gravity are kept to a minimum. The coefficient of local variation of peripheral vascular transit times (VB/Q) (33%) was, therefore, less than would have been expected if VB and Q were uncorrelated (57%).
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We applied near-infrared spectroscopy (NIRS) for the simultaneous measurement of forearm blood flow (FBF) and oxygen consumption (VO2) in the human by inducing a 50-mmHg venous occlusion. Eleven healthy subjects were studied both at rest and after hand exercise during vascular occlusion. FBF was also measured by strain-gauge plethysmography. ⋯ VO2 values were 4.6 +/- 1.3 microM O2 x 100 ml-1.min-1 at rest and 24.9 +/- 11.2 microM O2 x 100 ml-1.min-1 after hand exercise. The scatter of the FBF and VO2 values showed a good correlation between the two variables (r = 0.93). The results demonstrate that NIRS provides the particular advantage of obtaining the contemporary evaluation of blood flow and VO2, allowing correlation of these two variables by a single maneuver without discomfort for the subject.
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Glibenclamide, iberiotoxin, and apamin (blockers of ATP-sensitive, large-conductance, and small-conductance Ca(2+)-activated K+ channels, respectively) were infused into the diaphragmatic vasculature of anesthetized indomethacin-treated dogs to assess the contribution of K+ channels to active hyperemia. Diaphragmatic blood flow (Qphr) and O2 uptake (VO2di) were measured at rest and during 2 min of continuous left phrenic nerve stimulation at 0.5, 1, 2, and 4 Hz. These measurements were repeated before (control) and after the infusion of a selective K+ channel blocker in three groups of animals. ⋯ Neither iberiotoxin nor apamin influenced resting or stimulated VO2di. In all groups diaphragmatic tension measured after the infusion of K+ channel blockers remained similar to control values. These results indicate that K+ channels, especially those sensitive to glibenclamide, modulate the increase in Qphr and VO2di in response to moderate augmentation of metabolic demands.