Journal of applied physiology
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The peripheral vascular response to sepsis is characterized by a vasodilatation of the systemic arterial vessels. Pulmonary hypertension with an increase in resistance and back pressure to flow defined by pressure-flow (P-Q) relationships has been reported in experimental sepsis. We hypothesized that endotoxin can induce differential alterations in resistance and back pressure to flow in the liver venous and arterial beds. ⋯ Raising Pout from 0 to 15 mmHg decreased PV slope in the endotoxin group to a greater degree than in controls (P < 0.05). In the HA, endotoxin caused a decrease in slope but did not alter Pback. The simultaneous increase in the PV Pback and slope that occurs with endotoxemia decreases splanchnic venous return, pooling blood in the splanchnic compartment for a given total blood volume.(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
Cerebral hemodynamics during sensorimotor activation in humans.
We studied the time course and magnitude of cerebral blood flow velocity (CBFV) changes in the middle cerebral artery (MCA) and the regional cerebral blood flow (rCBF) in the MCA territory during stimulation of the left sensorimotor cortex. Healthy right-handed male subjects were examined during performance of right-hand finger movement sequences, vibratory stimulation, and somatosensory discrimination. In somatosensory discrimination there were significant increases of the mean CBFV (4.8 +/- 9.9 cm/s; P < 0.01) and the mean rCBF (10.2 +/- 4.2 ml.100 g-1.min-1; P < 0.01), whereas no significant changes of the mean CBFV and rCBF occurred in finger movement sequences or vibratory stimulation. ⋯ In the two tasks involving finger movements there was an increase of the respiratory rates (4.3 +/- 3.8 breaths/min; P < 0.05) and the pulse rates (11.6 +/- 5.5 beats/min; P < 0.05), respectively. Our data demonstrate a correspondence of mean CBFV and rCBF changes evoked by sensorimotor activation in the human brain. Furthermore, cerebral hemodynamic changes related to motor activity are accompanied by cardiorespiratory effects.
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We evaluated the effect of airflow and gas composition on the linearity of measurement of airflow by a new disposable flowmeter. The flowmeter is based on the principle of differential pressure measurement across two symmetrically disposed Pitot tubes. Nonlinearities arising from the pressure-to-airflow relationship and sensitivity to changes in gas density were linearized with appropriate software and monitoring of the gas composition. ⋯ However, because the errors were predictable, they were corrected by software to within 0.6% of the target volume. Measurement of minute ventilation during exercise was within 1-2% of that determined from bag collections. We conclude that this type of flowmeter can accurately measure exercise minute ventilation and has advantages over some other flowmeters because of its ruggedness, reproducibility, and ease of sterilization or replacement compared with other flowmeters.
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Comparative Study
Respiratory muscle pressure analysis in pressure-support ventilation.
The extent to which respiratory muscles are exerted during partially supported ventilation is difficult to differentiate, because these muscles and the ventilator work simultaneously to produce ventilation. We have developed a new method for determining the pressure developed by the respiratory muscles in partially supported ventilation. In seven patients on pressure-support ventilation (PSV), pressure, flow, and lung volume change were measured at the airway opening. ⋯ The respiratory muscle pressure, although less negative, had a shape that corresponded to the shape of airway occlusion pressure at each PSV level, and both pressures decreased concomitantly with increasing PSV. The respiratory muscle work progressively decreased with increasing PSV. This analysis enabled clear and continuous quantifications of the respiratory muscle force generation and inspiratory work during partially supported ventilation.
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Comparative Study
Effect of enhanced supramaximal flows on cough clearance.
Efficiency of cough for clearing mucus from the lungs is believed to be a function of peak airflow velocities in the airways. Initial transient supramaximal flows are characteristic of cough, and these peak flow rates can be enhanced by placing a triggered shutter at the mouth, serving the role of the epiglottis. Using radiolabeled monodispersed aerosols (99mTc-iron oxide) and gamma camera analysis, we measured over a 2-h period the efficacy of 60 voluntary vs. shutter coughs for clearing mucus from the airways of patients (n = 15) with chronic airway obstruction (mean ratio of forced expired volume in 1 s to forced vital capacity = 0.55). ⋯ Retention at 60 min (as a fraction of initial deposition) was significantly different for the 3 study days (control, 0.83 +/- 0.17; voluntary cough, 0.69 +/- 0.18; shutter cough, 0.75 +/- 0.19; P = 0.01), but only control vs. voluntary cough values were significantly different from each other (P = 0.01). In contrast, retention at 120 min was significantly different for the 3 days, but both voluntary and shutter coughs were significantly different from control (P = 0.01 and P = 0.02, respectively) (control, 0.73 +/- 0.16; voluntary cough, 0.61 +/- 0.20; shutter cough, 0.65 +/- 0.20). Patients studied with buffs showed a clearance rate faster than control and similar to that associated with voluntary cough.(ABSTRACT TRUNCATED AT 250 WORDS)