Journal of applied physiology
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The purpose of this study was to compare the magnitude and mechanisms of ankle dorsiflexor muscle fatigue in 20 young (33 +/- 6 yr, mean +/- SD) and 21 older (75 +/- 6 yr) healthy men and women of similar physical activity status. Noninvasive measures of central and peripheral (neuromuscular junction, sarcolemma) muscle activation, muscle contractile function, and intramuscular energy metabolism were made before, during, and after incremental isometric exercise. Older subjects fatigued less than young (P < 0.01); there was no effect of gender on fatigue (P = 0.24). ⋯ During exercise, intracellular concentrations of P(i) and H(2)PO increased more and pH fell more in young compared with older subjects (P < 0.01) and in men compared with women (P < 0.01). These varied metabolic responses to exercise suggest a greater reliance on nonoxidative sources of ATP in young compared with older subjects and in men compared with women. These results suggest that the mechanisms of fatigue vary with age and gender, regardless of whether differences in the magnitude of fatigue are observed.
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We hypothesized that upper airway collapsibility is modulated dynamically throughout the respiratory cycle in sleeping humans by alterations in respiratory phase and/or airflow regimen. To test this hypothesis, critical pressures were derived from upper airway pressure-flow relationships in six tracheostomized patients with obstructive sleep apnea. Pressure-flow relationships were generated by varying the pressure at the trachea and nose during tracheostomy (inspiration and expiration) (comparison A) and nasal (inspiration only) breathing (comparison B), respectively. ⋯ In contrast, we found that the inspiratory critical pressure fell markedly during nasal vs. tracheostomy breathing [1.1 +/- 1.5 (SE) vs. 6.1 +/- 1.9 cmH(2)O; P < 0.01], indicating that upper airway collapsibility is markedly influenced by differences in airflow regimen. Tracheostomy breathing was also associated with a reduction in both phasic and tonic genioglossal muscle activity during sleep. Our findings indicate that both phasic factors and airflow regimen modulate upper airway collapsibility dynamically and suggest that neuromuscular responses to alterations in airflow regimen can markedly lower upper airway collapsibility during inspiration.
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Many hemoglobin-based oxygen carriers (HBOCs) produce systemic and pulmonary hypertension and may increase microvascular permeability as a consequence of nitric oxide (NO) scavenging. In this study, we examined the effects of two recombinant human hemoglobin solutions, rHb1.1 and rHb2.0 for injection (rHb2.0), with different rates of NO scavenging on vasoconstrictor reactivity and vascular permeability in isolated, saline-perfused rat lungs. We hypothesized that rHb1.1, a first-generation HBOC with an NO scavenging rate similar to that of native human hemoglobin, would exacerbate pulmonary vasoconstriction and permeability and that rHb2.0, a second-generation HBOC with an NO scavenging rate approximately 20- to 30-fold lower than that of rHb1.1, would minimally influence these responses. ⋯ Finally, the capillary filtration coefficient was unaltered by either rHb1.1 or rHb2.0. We conclude that pulmonary hemodynamic responses to rHb2.0 are greatly reduced compared with those observed with rHb1.1, consistent with rHb2.0 having a diminished capacity to scavenge NO. In addition, neither hemoglobin solution measurably altered microvascular permeability in this preparation.
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Regional changes in ventilation and perfusion occurring in the early hours after smoke inhalation injury were evaluated through the use of positron emission tomography. Five lambs were imaged before and 1, 2, and 4 h after receiving 100 breaths of cotton smoke. ⋯ These findings, together with decreasing regional ventilation and fractional gas content in the dependent regions, correlated with decreasing arterial Pa(O(2)) values over the course of the study. A negative correlation between regional shunt fraction and regional gas content in dependent and middle regions suggests that shunt was caused by progressive alveolar derecruitment or flooding.
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Comparative Study
Detection of local lung air content by electrical impedance tomography compared with electron beam CT.
The aim of the study was to validate the ability of electrical impedance tomography (EIT) to detect local changes in air content, resulting from modified ventilator settings, by comparing EIT findings with electron beam computed tomography (EBCT) scans obtained under identical steady-state conditions. The experiments were carried out on six anesthetized supine pigs ventilated with five tidal volumes (VT) at three positive end-expiratory pressure (PEEP) levels. The lung air content changes were determined both by EIT (Goe-MF1 system) and EBCT (Imatron C-150XP scanner) in six regions of interest, located in the ventral, middle, and dorsal areas of each lung, with respect to the reference air content at the lowest VT and PEEP, as a change in either local electrical impedance or lung tissue density. ⋯ A good correlation between the changes in lung air content determined by EIT and EBCT was revealed. Mean correlation coefficients in the ventral, middle, and dorsal regions were 0.81, 0.87, and 0.93, respectively. The study confirms that EIT is a suitable, noninvasive method for detecting regional changes in air content and monitoring local effects of artificial ventilation.