Acta physiologica Scandinavica. Supplementum
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Acta Physiol Scand Suppl · Jan 1990
ReviewRenal function curves and control of body fluids and arterial pressure.
The purpose of this paper has been to emphasize the extreme importance of the renal function curve in determining the long-term level of arterial pressure. The reason for this importance is that the renal-body fluid-pressure control system exhibits the phenomenon of "infinite feedback gain". ⋯ This renal mechanism for controlling the body fluids and simultaneously controlling the arterial pressure, because of its infinite feedback gain capability for controlling arterial pressure, requires that other pressure control mechanisms must interact with this mechanism either to alter the renal function curve or to make the animal change its intake of salt and water if the other pressure mechanisms are to have any effect on the long-term arterial pressure level. Therefore, in virtually any analysis of long-term arterial pressure regulation, the renal function curve or its mathematical equivalent plays a central role.
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Changes in respiratory drive, as assessed by mouth occlusion pressure (P0.1), and in breathing pattern were studied in 19 healthy subjects who exercised on a cycle ergometer with work loads ranging from loadless pedalling up to the highest load that could be sustained for 4 min. In the P0.1 studies, experiments were carried out both at normal atmospheric pressure and during hyperbaric conditions in which the density (D) of the respired gas was increased. Analyses of observed changes in P0.1 and in the interrelations of minute ventilation (V), tidal volume (VT), inspiratory (TI), expiratory (TE) and total breath (Ttot) durations, and lung volumes yielded the following results and conclusions: Analyses of inspiratory and expiratory volume threshold curves in terms of the relations between end-inspiratory volume and TI on one hand, and end-expiratory volume and TE on the other, suggest that the termination of inspiration during cycle exercise is dependent on volume-related afferent feedback from the lungs and/or chest wall, not only in the high but also in the low volume range, and expiratory muscle activity occurs already at low exercise intensities, combined with active control of expiratory flow, end-expiratory volume and TE as exercise hyperpnea intensifies. ⋯ Respiratory impedance, P0.1/(VT/TI), increased with both D and VT/TI. The relationship of P0.1, D and VT/TI approximated the equation P0.1 = K X D0.5(VT/TI)b, where K varies among subjects due to differences in i.a. vital capacity, and b has a value close to 1.5. The observed changes in P0.1 suggest that the respiratory drive was reflexly enhanced in response to loading as airway resistance increased with D and/or VT/TI, whereby any depression of V or VT/TI attributable to the increased respiratory impedance was counteracted.
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Acta Physiol Scand Suppl · Jan 1983
Microvascular blood flow distribution in skeletal muscle. An intravital microscopic study in the rabbit.
Distribution patterns of the microvascular blood flow and interactions of various microvascular elements were studied in the tenuissimus muscle of the rabbit with the aid of intravital microscopy. The modified technique employed permitted observation, with high resolution, of the microcirculation in the tenuissimus muscle in situ, with only minor surgical preparation and incision. Preparation and exposure of the muscle for vital microscopy did not alter the resting blood flow and did not limit the normal range of vascular control. ⋯ A majority of the transverse arterioles also supplied, in addition to the muscle capillaries, the connective tissue. The distribution of the arteriolar flow between these two vascular areas was determined by the interaction between the larger transverse and smaller terminal arterioles and their relative contributions to the vascular resistance. The terminal arterioles were clearly more responsive than the transverse arterioles to changes in ambient oxygen availability.(ABSTRACT TRUNCATED AT 400 WORDS)