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  • Title: Renal effects of continuous negative pressure breathing.
    Author: Kinney MJ.
    Journal: Aviat Space Environ Med; 1975 Nov; 46(11):1358-62. PubMed ID: 1212140.
    Abstract:
    Continuous negative pressure breathing (CNPB) was utilized to simulate the thoracic vascular distension of zero G or Space, in 11 anesthetized rats. The animals underwent renal clearance and micropuncture renal nephron studies before, during, and after CNPB. Four rats were pretreated with a high salt diet and I-M desoxycorticosterone (DOCA) in excess. None of these rats diuresed with CNPB. In contrast, five of the seven remaining rats increased the fraction of the filtered sodium excreted (CNa/GFR, p less than 0.05) and their urinary flow rate (V, p less than 0.05). Potassium excretion increased (UK V, p less than 0.05). End proximal tubular fluid specimen's TF/P inulin ratios were unchanged. Whole kidney and single nephron glomerular filtration rates fell 10%. CNPB, a mechanism for atrial distension, appears to cause in the rat a decrease in distal tubular sodium and water reabsorption. Exogenous mineral-corticoid prevents the diuresis, saluresis, and kaluresis. In a separate group of five rats, the CNPB was prolonged or excessive (CNPB greater than 3.5 cm H2O negative pressure); in these, the diuresis ceased and/or antidiuresis occurred. This confirmed the adequacy of other nonatrial volume control mechanisms in regulating renal salt and water conservation in opposition to the studied atrial-renal (Henry-Gauer) reflex of thoracic vascular distension. It encourages us to suggest that the atrial distension reflex diuresis that occurs with shifts of blood to the thorax in assuming a weightless condition, if comparable to the thoracic vascular distension of this model, will not progressively impair the circulation or the mammal but will be minor and short-lived.
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