Journal of applied physiology
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Numerous pathophysiological conditions induce hypoxemia-related cardiopulmonary perturbations, decrements in exercise capacity, and debilitating symptoms. Accordingly, this study investigated the efficacy of an allosteric hemoglobin modulator (voxelotor) to enhance arterial oxygen saturation during low-intensity exercise in hypoxia. Eight normal healthy subjects (36 ± 7 yr; 73.8 ± 9.5 kg; 3 women) completed a submaximal cycling test (60 W) under normoxic ([Formula: see text]: 0.21; O2 partial pressure: 144 mmHg) and hypoxic ([Formula: see text]: 0.125; O2 partial pressure: 82 mmHg) conditions before (day 1) and after (day 15) 14 days of oral drug administration. ⋯ NEW & NOTEWORTHY In humans, a novel allosteric hemoglobin-oxygen affinity modulator was administered to comprehensively examine the cardiopulmonary consequences of stabilizing a portion of the available hemoglobin in a high-oxygen affinity state during submaximal exercise in normoxia and hypoxia. Oral administration of voxelotor enhanced arterial oxygen saturation during submaximal exercise without altering oxygen consumption and central hemodynamics; however, the partial pressure of arterial carbon dioxide was reduced and the partial pressure of arterial oxygen was increased implying that hyperventilation also contributed to the increase in oxygen saturation. The preservation of arterial oxygen saturation and content was particularly evident during hypoxic submaximal exercise, when arterial desaturation typically occurs, but this did not influence arterial-venous oxygen difference.
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Patients with moderate to severe acute respiratory distress syndrome (ARDS) benefit from prone positioning. Although the accuracy of esophageal pressure (Pes) to estimate regional pleural pressure (Ppl) has previously been assessed in the supine position, such data are not available in the prone position in ARDS. In six anesthetized, paralyzed, and mechanically ventilated female pigs, we measured Pes and Ppl into dorsal and ventral parts of the right pleural cavity. ⋯ Prone position narrowed end-expiratory dorsal-to-ventral Ppl vertical gradient, likely because of a more even distribution of mechanical forces over the chest wall. NEW & NOTEWORTHY In a porcine model of acute respiratory distress syndrome, we found that static end-expiratory esophageal pressure did not change significantly in prone position compared with supine position at any positive end-expiratory pressure (PEEP) tested between 5 and 20 cmH2O. Prone position was associated with an increased ventral pleural pressure and reduced end-expiratory dorsal-to-ventral pleural pressure (Ppl) vertical gradient, likely due to a more even distribution of mechanical forces over the chest wall.
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Tidal expiratory flow limitation (EFL), which may herald airway closure (AC), is a mechanism of loss of aeration in ARDS. In this prospective, short-term, two-center study, we measured static and dynamic chest wall (Est,cw and Edyn,cw) and lung (Est,L and Edyn,L) elastance with esophageal pressure, EFL, and AC at 5 cmH2O positive end-expiratory pressure (PEEP) in intubated, sedated, and paralyzed ARDS patients. For EFL determination, we used the atmospheric method and a new device allowing comparison of tidal flow during expiration to PEEP and to atmosphere. ⋯ NEW & NOTEWORTHY Expiratory flow limitation (EFL) and airway closure (AC) were observed in 32% and 52%, respectively, of 25 patients with ARDS investigated during mechanical ventilation in supine position with a positive end-expiratory pressure of 5 cmH2O. The performance of dynamic lung elastance to detect expiratory flow limitation was good and better than that to detect airway closure. The vast majority of patients with EFL also had AC; however, AC can occur in the absence of EFL.
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The second gas effect occurs when high inspired concentrations of a first gas, usually nitrous oxide, enhance the uptake of other gases administered simultaneously. The second gas effect is greater in blood than in the gas phase, persists well into the period of nitrous oxide maintenance anesthesia, increases as the degree of ventilation-perfusion mismatch increases, and is most pronounced with the low soluble agents in current use. Yet, how low gas solubility and increased ventilation-perfusion mismatch can combine to improve gas transfer remains unclear, which is the focus of the present study. ⋯ NEW & NOTEWORTHY Gas exchange in the lung can always be represented as the sum of two components: gas exchange at constant volume followed by gas exchange on volume correction. Using this sequence to study the second gas effect, low gas solubility and increased ventilation-perfusion mismatch are shown to act together to enhance second gas uptake. While appearing to contravene classical concepts of gas exchange, a detailed theoretical analysis shows it is fully consistent with these concepts.
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Cardiac output (CO) monitoring is useful for sports performance training, but most methods are unsuitable as they are invasive or hinder performance. The performance of PhysioFlow (PF), a portable noninvasive transthoracic bioimpedance CO monitor, was evaluated and compared with a reference Doppler CO monitor, USCOM, using a head-up tilt (HUT) test. With ethics committee approval, 20 healthy well-trained athletes were subjected to HUT in a fixed order of 0°, 70°, 30°, and 0° for 3 min each. ⋯ Accuracy in tracking hemodynamic changes deteriorated with higher tilt, implying a gravitational influence on its performance. Stroke volume measurements were overestimated, but the changes were underestimated. Despite its convenient physical features, the suitability of PhysioFlow for sports use is questionable.