Ten experiments were conducted on anesthetized dogs ventilated with a Starling pump and breathing oxygen. While tidal volume, respiratory rate, and arterial pH and pCO
2
were kept constant, lung volume was varied by using either a negative, zero, or positive end-expiratory pressure, leading to average changes in lung volume of -32, 0, and +75 per cent. Pulmonary vascular resistance (PVR) increased with either decreased or increased lung volume, indicating that the relationship between resistance and lung volume is a U-shaped curve. Since the transmural distending pressures of large pulmonary vessels either increased or remained unchanged during these procedures, changes in PVR cannot be ascribed to changes in systemic circulatory dynamics, such as cardiac output.
It was noted that cardiac output increased with negative end-expiratory pressure (effectively, negative-pressure breathing) and decreased with positive end-expiratory pressures (effective, positive-pressure breathing), as previously reported. A hypothesis is presented for explaining the U-shaped curve relating resistance and lung volume.
Arterial pH of anesthetized dogs was held constant during infusion of HCl or NaHCO3 by appropriate alterations in alveolar ventilation. While plasma potassium concentration dropped somewhat (presumably due to gradual potassium depletion), there was no significant difference in plasma potassium during the two types of infusions. The implication is that metabolic and respiratory acid-base disturbances having comparable effects on pH also have similar effects on the plasma potassium concentration. Other data support this conclusion and also indicate that effects of acidosis and alkalosis are quantitatively similar. On the basis of data of this study and of other data in the literature, it appears that the ratio of change in potassium concentration to change in blood pH ordinarily averages –3.0 to –5.0 in a steady state and that achieving a steady state requires 1–2 hours of equilibration. Data are presented which support the concept that extracellular K concentration, rather than total extracellular K, is physiologically regulated and that this involves rapid exchanges with intracellular K.
Concurrent sexual partnerships, or sexual partnerships that overlap in time, have been associated with HIV and sexually transmitted infections (STI) infection. How best to measure concurrency and the personal characteristics and predictors of concurrency are not yet well understood. We compared two frequently used concurrency definitions, including a self-reported measure based on participant response regarding overlapping sex with partners, and the UNAIDS measure based on overlapping dates of last sex and intention to have sex again. We performed multivariable logistic regression analyses to identify socio-demographic, behavioral, and structural predictors of concurrency among 1,542 patients at an urban STI clinic in Jackson, Mississippi. Nearly half (44%) reported concurrency based on self-reported sex with other partners, and 26% reported concurrency according to the UNAIDS concurrency measure. Using the self-reported concurrency measure, the strongest predictors of concurrency were perceived partner concurrency, drug use at last sex, having more than 10 lifetime partners, and being recently incarcerated. Strongest predictors of concurrency using the UNAIDS measure were lifetime number of partners and perceived partner concurrency. Concurrency is highly prevalent in this population in the Deep South and social, structural and behavioral factors were important predictors of concurrency for both measures. Future research should use time anchored data collection methods and biomarkers to assess whether both definitions of concurrency are associated with HIV outcomes.
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