Journal of applied physiology
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Mechanisms underlying failure of autoresuscitation from hypoxic apnea were investigated. Failure was induced by repeated exposure to hypoxia. The influence of maturation was studied in adults, weanlings, and 10- and 5-day-old mice. ⋯ In addition, heart block occurred with increasing frequency on later successful trials, but conversion to sinus rhythm always preceded successful autoresuscitation. Heart block was also frequent in SWR mice and had similar consequences. BALB/c mice exposed to continuous anoxia survived longer than SWR mice, indicating increased endurance of components of the autoresuscitation mechanism not directly related to the ventilatory function of gasping (e.g., cardiovascular components).(ABSTRACT TRUNCATED AT 250 WORDS)
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The effect of severe generalized edema on respiratory system mechanics is not well described. We measured airway pressure, gastric pressure, and four vertical pleural pressures in 13 anesthetized paralyzed pigs ventilated in the upright position. Pressure-volume relationships of the respiratory system, chest wall, and lung were measured on deflation from total lung capacity to residual volume and during tidal breathing both before (control) and 50 min after one of two interventions. ⋯ Tidal compliances of the respiratory system, chest wall, and lung decreased 36, 31, and 49%, respectively (all P less than 0.05). The effect of abdominal balloon inflation on respiratory system mechanics was similar to that of volume infusion. We conclude that infusing large volumes of fluid markedly alters chest wall mechanics, mainly by causing abdominal distension that prohibits descent of the diaphragm.
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Comparative Study
Validity of pulse oximetry during exercise in elite endurance athletes.
Eleven highly trained male cyclists [maximal aerobic power (VO2max) = 70.6 +/- 4.2 ml.kg-1.min-1] performed both high intensity constant load (90-95% VO2max) and incremental cycle exercise tests with arterial blood sampling to evaluate the accuracy of pulse oximeter estimates (%SpO2) of arterial oxyhemoglobin fraction of total hemoglobin (%HbO2). Three subjects also performed an incremental exercise test in hypoxic conditions (inspired partial pressure of O2 = 89, 93, or 100 Torr). Arterial %HbO2 was determined via CO-oximetry and ranged from 72 to 99%. ⋯ When aerobic power was greater than 81% of VO2max (n = 75), the finger probe's mean error was -0.01 +/- 1.40%. Finger probe %SpO2 and %HbO2 were highly correlated (r = 0.97, SEE = 1.32%, P less than 0.0001). These results indicate that this pulse oximeter is a valid predictor of %HbO2 in elite athletes during cycle exercise.
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To explain the contradictory results in the literature regarding the effects of inspiratory diaphragmatic descent on inferior vena caval (IVC) venous return, we evaluated changes in total IVC flow as well as regional splanchnic and nonsplanchnic IVC flows by use of ultrasound flow probes placed around the thoracic and subhepatic abdominal IVC during phrenic nerve stimulation (PNS) in anesthetized open-chest dogs. With the abdomen closed (n = 6), PNS under hypervolemic conditions increased the total IVC flow by enhancing the splanchnic IVC flow, with a transient decrease in the nonsplanchnic IVC flow (P less than 0.05). Under hypovolemic conditions, PNS initially increased the total IVC flow but later decreased the total IVC flow by reducing the nonsplanchnic IVC flow, associated with a venous pressure gradient in the IVC across the diaphragm (P less than 0.05), consistent with development of a vascular waterfall. ⋯ Appl. Physiol. 69: 1961-1972, 1990) is useful as a global approximation to understand the effects of respiratory-induced changes in Pab's on the total and regional IVC venous return. Nonhomogeneous distribution of Pab's during diaphragmatic descent may need to be considered to explain all aspects of the behavior of the intact IVC system.