bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of different heavy-resistance exercise protocols on plasma beta-endorphin concentrations
Authors: Kraemer W. J. , Dziados J. E. , Marchitelli L. J. , Gordon S. E. , Harman E. A. , Mello R. , Fleck S. J. , Frykman P. N. , Triplett N. T.
Published: December 2017

To examine the changes of plasma beta-endorphin (beta-EP) concentrations in response to various heavy-resistance exercise protocols, eight healthy male subjects randomly performed each of six heavy-resistance exercise protocols, which consisted of identically ordered exercises carefully designed to control for the repetition maximum (RM) resistance (5 vs. 10 RM), rest period length (1 vs. 3 min), and total work (joules). Plasma beta-EP, ammonia, whole blood lactate and serum cortisol, creatine kinase, urea, and creatinine were determined preexercise, midexercise, immediately postexercise, and at various time points after the exercise session (5 min-48 h), depending on the specific blood variable examined. Only the high total work-exercise protocol [1 min rest, 10 RM load (H10/1)] demonstrated significant increases in plasma beta-EP and serum cortisol at midexercise and 0, 5, and 15 min postexercise. Increases in lactate were observed after all protocols, but the largest increases were observed after the H10/1 protocol. Within the H10/1 protocol, lactate concentrations were correlated (r = 0.82, P < 0.05) with plasma beta-EP concentrations. Cortisol increases were significantly correlated (r = 0.84) with 24-h peak creatine kinase values. The primary finding of this investigation was that beta-EP responds differently to various heavy-resistance exercise protocols. In heavy-resistance exercise, it appears that the duration of the force production and the length of the rest periods between sets are key exercise variables that influence increases in plasma beta-EP and serum cortisol concentrations. Furthermore the H10/1 protocol's significant challenge to the acid-base status of the blood, due to marked increases in whole blood lactate, may be associated with mechanisms modulating peripheral blood concentrations of beta-EP and cortisol.
Flexible intravenous microdialysis probe for blood sampling in freely moving rats
Authors: Rada P. , Parada M. , Hernandez L.
Published: December 2017

A flexible intravenous microdialysis probe was constructed from Silastic tubing (0.5 mm ID and 1.0 mm OD), with a cellulose hollow fiber tip 0.2 mm in diameter and 25 mm long with a 6,000 mol wt cut off. In vitro tests showed relative recovery rates of 39.1 +/- 1.9% for epinephrine. In vivo tests in freely moving rats, 36 h and 7 days after surgery, showed stable amounts of epinephrine and glucose. After intraperitoneal injections of 2-deoxy-D-glucose, circulating levels of epinephrine and glucose increased significantly. Similar results were obtained several days after implantation of the probe. We conclude that in situations where prolonged blood sampling is necessary, the flexible microdialysis probe provides a reliable means of accessing circulating levels of neuroactive compounds, nutrients, metabolites, and drugs.
Pulmonary vascular alpha 1-adrenoreceptor activity in conscious dogs after left lung autotransplantation
Authors: Nishiwaki K. , Nyhan D. P. , Stuart R. S. , Desai P. M. , Peterson W. P. , Rock P. , Pribble C. G. , Murray P. A.
Published: December 2017

We investigated the extent to which sympathetic alpha 1-adrenoreceptor activation is involved in chronic pulmonary vascular regulation in conscious dogs after left lung autotransplantation (LLA). Continuous left pulmonary vascular pressure-flow plots were generated in conscious dogs 3–4 wk post-LLA and in identically instrumented conscious dogs not subjected to LLA (sham-operated controls). LLA resulted in a marked upward shift in the baseline left pulmonary vascular pressure-flow relationship compared with the control group (P < 0.01), i.e., LLA caused a chronic increase in pulmonary vascular resistance. The sympathetic alpha 1-adrenoreceptor antagonist prazosin partially reversed (P < 0.01) the LLA-induced increase in pulmonary vascular resistance. Circulating concentrations of norepinephrine and epinephrine at 2 and 4 wk post-LLA were not significantly different from values measured in control dogs. However, the dose-response relationship to the exogenous administration of the sympathetic alpha 1-adrenoreceptor agonist phenylephrine was shifted (P < 0.05) to the left post-LLA compared with control, which indicates an increase in pulmonary vascular reactivity to alpha 1-adrenoreceptor activation. This effect was not due to a generalized increase in pulmonary vascular reactivity to vasoconstrictor stimuli because the dose-response relationship to the thromboxane analogue U-46619 was not significantly altered post-LLA compared with control. Thus LLA results in a chronic increase in pulmonary vascular resistance in conscious dogs. A component of the increase in pulmonary vascular resistance resulting from LLA is mediated by an enhanced reactivity to sympathetic alpha 1-adrenoreceptor activation.
Intrapulmonary shunt in excised dog lobes: comparison of oxygen and inert gas methods
Authors: Sato S. , Hlastala M. P. , Hildebrandt J.
Published: December 2017

We evaluated the contribution of measurement errors in PO2 to the discrepancy between the intrapulmonary shunt values simultaneously obtained by the conventional O2 method (O2-shunt) and the multiple inert gas elimination technique (IG-shunt). Excised left lower lobes of dogs were perfused at a constant flow and ventilated at constant volume. Variable degrees of intrapulmonary shunt were created by O2 absorption while the lobes were collapsed. IG-shunt ranged from 0 to 66%. Although the O2-shunt and IG-shunt values correlated well (r = 0.97), the slope was only 0.74 and the regression line crossed the line of identity at 12% IG-shunt. The gas-to-blood ratio of the oxygen electrode was constant over the range 80–687 Torr and therefore did not seem to be an important factor in the shunt discrepancy. Errors due to nonlinearity of the O2 electrode also had only a minor effect. However, PO2 history of the electrode just before injection of blood samples into the cuvette had a profound and complex effect on the measured PO2. We conclude that PO2 electrode hysteresis can be a major factor in the wide variability of PO2 measurements and could account for most of the differences between our O2-shunt and IG-shunt data.
Lack of heart rate variation between morning and afternoon exercise testing in coronary artery disease patients
Authors: Marriott J. D. , Hartley L. H. , Sherwood J.
Published: December 2017

The purpose of this study was to investigate cardiovascular [heart rate (HR), blood pressures, rate-pressure product (RPP)], physiological (oxygen uptake), and metabolic (blood plasma lactic acid concentration) responses during symptom-limited graded exercise testing (SL-GXT) during early morning and late afternoon hours in an unmedicated, regularly exercising, coronary artery disease population. Subjects, males ages 41–71 yr (n = 11), underwent SL-GXT via cycle ergometry at 8:30 A.M. and 4:30 P.M. HR, systolic blood pressure, diastolic blood pressure, and RPP were evaluated at rest and at submaximal and peak work. Oxygen uptake and rate of perceived exertion were also determined at submaximal and peak power output, with blood plasma lactic acid concentration measured at peak work. Data, analyzed by the paired t test, failed to demonstrate any significant variation in HR, systolic blood pressure, diastolic blood pressure, RPP, or blood plasma lactic acid responses during exercise at the two points used. Oxygen uptake did not significantly change at any submaximal intensity. Thus SL-GXT results obtained at early morning (8:30 A.M.) and late afternoon (4:30 P.M.) are a reproducible, reliable means of prescribing exercise HR and work intensities.
Total respiratory input impedance with the upper airway wall shunt minimized
Authors: Habib R. H. , Jackson A. C.
Published: December 2017

Respiratory impedances (Zrs) measured with the cheeks manually supported (Zsc) demonstrate an antiresonance (AR) at approximately 170 Hz, whereas those measured with the head generator (Zhg) have an AR at significantly lower frequencies (150 Hz). The differences in the AR between methods were previously attributed to upper airway wall (UAW) shunting in Zsc, and Zhg was believed to represent shunt-free impedance. To test this hypothesis, we measured four independent estimates of Zrs (4–256 Hz) in five healthy adults. Applying the oscillations at the mouth, we measured Zrs with the cheeks unsupported (Zuc) and when the subject's head and neck were enclosed in a rigid chamber completely filled with water (Zwa). We also measured Zhg with the oscillations applied around the head. Because water is incompressible, Zwa should minimize UAW shunt if not completely eliminate it. There were no significant differences in any of the AR features (e.g., location and bandwidth) of Zuc, Zsc, and Zwa. Conversely, all AR features of Zwa and Zhg were significantly different. To assess wall motion during both forms of oscillations (i.e., applied at the mouth and around the head), we measured two UAW local impedances by use of accelerometers placed on the cheeks (Zch) and submental (Zsm) region. Above 40 Hz, Zch and Zsm estimates were significantly dependent on the forcing method. Furthermore, Zch and Zsm made with the standard oscillations were consistent with the lumped UAW impedances measured with a head plethysmograph, whereas those made with the oscillations around the head were not. Therefore we conclude that, at > 32 Hz, Zsc more closely represents shunt-free impedance than does Zhg and hence should be preferred when Zrs are measured.
Effect of inhaled lyso-platelet-activating factor on airway microvascular leakage in the guinea pig
Authors: Sakamoto T. , Elwood W. , Barnes P. J. , Chung K. F.
Published: December 2017

Lyso-platelet-activating factor (PAF), the precursor and metabolite of PAF, is considered inactive, although it may be converted to PAF by airway cells. We have investigated the effects of inhaled lyso-PAF on bronchoconstriction and airway microvascular leakage in anesthetized guinea pigs. Lung resistance (RL) was measured for 6 min after inhalation of lyso-PAF (0.3, 1, and 3 mM; 30 breaths) followed by measurement of extravasation of intravenous Evans blue dye into airway tissues, which was used as an index of airway microvascular leakage. Inhaled lyso-PAF caused an increase in RL and leakage of dye at all airway levels in a dose-dependent fashion, but intravenous lyso-PAF (0.25 mg/kg) had no airway effect. The maximum dose of inhaled lyso-PAF increased RL significantly by approximately 200%. The amount of extravasation of dye induced was 96 +/- 4 (SE) ng/mg of tissue in trachea, 77 +/- 8 ng/mg in main bronchi, and 65 +/- 7 and 25 +/- 1 ng/mg in proximal and distal intrapulmonary airways respectively; these values were all significantly higher (P < 0.01) than control values. These responses were completely abolished by a specific PAF-receptor antagonist WEB-2086 (2 mg/kg iv). Our results show that inhaled lyso-PAF is potent in increasing airway microvascular leakage. The effects of lyso-PAF may result from its metabolic transformation to PAF by lyso-PAF:acetyl-CoA acetyltransferase in the airway.
Failure of vasodilator administration to increase blood flow to the fatiguing diaphragm
Authors: Supinski G. S. , Stofan D. , Nashawati E. , DiMarco A. F.
Published: December 2017

Recent studies have suggested that coronary and limb muscle vessels do not maximally vasodilate under conditions in which cardiac and limb muscle contractile function is dependent on the level of blood flow but, rather, maintain a "vasodilator reserve." If a vasodilator reserve is also present in the fatiguing diaphragm, it may be possible to augment flow to this muscle with vasodilator administration, improving muscle function. The purpose of the present study was therefore to examine the effect of administration of a potent vasodilator, nitroprusside, on the blood flow and contractile function of the fatiguing diaphragm. Studies were performed using an in situ canine diaphragmatic strip preparation that permitted direct measurement of force and blood flow; cardiac output was monitored with a thermodilution catheter. The effects of nitroprusside were examined with the diaphragm rhythmically contracting in response to both subfatiguing and fatiguing stimulation paradigms. For both contraction paradigms, nitroprusside infusions elicited appreciable increases in cardiac output. Nitroprusside infusions also produced significant increases in diaphragmatic blood flow during subfatiguing diaphragmatic contractions but had no effect on flow during fatiguing contractions. Nitroprusside also had no effect on the rate of diaphragmatic fatigue. These data suggest that, under the conditions examined, the diaphragm exhausts its vasodilator reserve during the development of fatigue and vasodilator administration has no appreciable effect on diaphragm blood flow and function. Moreover, although vasodilator drugs with actions similar to nitroprusside are used clinically to augment flow to vital organs, our data would indicate that these drugs have no functionally significant effect on blood flow to the fatiguing diaphragm.
Effects of intraphrenic injection of potassium on diaphragm activation
Authors: Supinski G. S. , Dick T. , Stofan D. , DiMarco A. F.
Published: December 2017

The purpose of the present study was to determine whether potassium, injected into the arterial supply of the diaphragm, would reflexly alter efferent diaphragmatic motor outflow and systemic arterial pressure. Studies were performed using in situ canine diaphragm muscle strips in which the inferior phrenic artery and vein were cannulated and all other sources of strip blood flow were ligated. Injection of potassium (0.1 meq) into the inferior phrenic artery elicited a small transient (1–2 breaths) decrease in the peak strip tension developed during spontaneous muscle contractions, in peak integrated strip electromyographic (EMG) activity, and in the peak integrated EMG activity of the contralateral hemidiaphragm. This was followed by a more pronounced and more sustained increase in each of these parameters as well as an increase in systemic arterial pressure. This latter excitatory response was qualitatively similar to that induced by the injection of capsaicin (5 and 25 micrograms) into the phrenic artery. Section of the left phrenic nerve abolished the effects of intra-arterial potassium and capsaicin on systemic arterial pressure and right hemidiaphragm EMG activity. These data support the existence of a potent excitatory phrenic-to-phrenic reflex that can be activated by potassium injection into the diaphragm. Activation of this pathway increases diaphragm motor activation and augments systemic arterial pressure.
Model-free numerical deconvolution of recirculating indicator concentration curves
Authors: Clough A. V. , Cui D. , Linehan J. H. , Krenz G. S. , Dawson C. A. , Maron M. B.
Published: December 2017

This paper investigates two model-free methods for numerical deconvolution of recirculating indicator concentration curves. The two methods, damped least squares and discrete orthogonal polynomial deconvolution, are applied to simulated data to verify the reliability of the algorithms. Both deconvolution methods provide damping that results in estimated transport functions that are smooth and reasonable estimates of the actual simulated transport function. On convolution with the simulated input curve, the estimated transport functions provide good fits to the simulated output curve. In addition, methods for identifying an optimal solution and for truncating the artifactually long oscillatory tails of the estimated transport functions are proposed, which appear to allow for reasonably accurate estimation of the mean transit times and variances of the transport functions as well. When either method was applied to indicator dilution data obtained from the pulmonary artery and left atrium, it was computationally stable while producing transport functions that when convolved with the input concentration curves provided good fits to the output concentration curves. The combined simulation and experimental results suggest that the proposed methods should be useful for estimating circulation transport functions from indicator dilution data.
Role of postural status in the nocturnal hemodynamic patterns of nonhuman primates
Authors: Engel B. T. , Talan M. I. , Chew P. H.
Published: December 2017

We compared the nocturnal hemodynamic patterns of seven tethered monkeys (Macaca mulatta) with those of seven chaired animals to determine whether the overnight changes are comparable in the two conditions. In both groups, we found a consistent hemodynamic pattern characterized by an overnight fall in cardiac output and central venous pressure and a rise in total peripheral resistance that maintained blood pressure homeostasis. The pattern of overnight change occurred despite major differences in response levels: cardiac output and central venous pressure were significantly elevated, and total peripheral resistance was significantly reduced at all times (from 1800 to 1200 h the following day) in the chaired animals relative to the tethered animals. This difference was probably due to an expanded plasma volume in the chaired animals, because stroke volume was also significantly elevated. Because the nocturnal hemodynamic pattern occurred under both conditions, it is likely that it is a stable biologic effect, which is probably related to an overnight loss in fluid volume that is not replaced in animals that sleep throughout the night.
Effects of training and immobilization on VO2 and DO2 in dog gastrocnemius muscle in situ
Authors: Bebout D. E. , Hogan M. C. , Hempleman S. C. , Wagner P. D.
Published: December 2017

To investigate the effects of exercise training and immobilization on peak O2 uptake (VO2) and effective O2 diffusive conductance (DO2) in skeletal muscle, three groups of purpose-bred hounds [control (C), exercise trained (E), and immobilized (I)] were studied. Group E exercised on a treadmill 1 h/day, 5 days/wk for 8 wk, while groups C and I were cage confined for 8 wk, with group I undergoing left hindlimb immobilization for the last 3 wk. Thereafter, each dog's left gastrocnemius was surgically isolated, pump perfused, and electrically stimulated to elicit peak VO2 in situ at three levels of arterial oxygenation. O2 delivery [(arterial O2 concentration x muscle blood flow)/100 g muscle] was kept constant among the three groups at each level of arterial oxygenation. Compared with group C, peak VO2/100 g muscle was 38, 33, and 19% greater and DO2/100 g muscle was 71, 75, and 68% greater during normoxia, moderate hypoxia, and severe hypoxia, respectively, in group E (P < 0.02), whereas no differences from control were found in group I. We conclude that O2 delivery is not the unique determinant of peak VO2 and that exercise training improves the functional blood-tissue gas exchange properties of the muscle itself. Immobilization sufficient to reduce muscle weight by 31% and citrate synthase activity by 68% has no effect on peak VO2/100 g muscle or DO2/100 g muscle.
Muscle sympathetic nerve responses to prolonged one-legged exercise
Authors: Ray C. A.
Published: December 2017

We previously demonstrated that brief dynamic one-legged knee extensions (DKE) performed in the upright position decreased muscle sympathetic nerve activity (MSNA). The present study was undertaken to investigate MSNA responses to prolonged DKE. DKE was performed for 40 min in the upright (sitting) position, and MSNA was recorded in the peroneal nerve of the contralateral leg by microneurography. DKE elicited a significant increase in mean arterial pressure (MAP) from 83 +/- 3 to 101 +/- 6 (SE) mmHg during the 5th min of exercise. The increase in MAP persisted for the remainder of exercise. In contrast, heart rate (HR) showed a gradual increase throughout the 40 min of exercise (80 +/- 3 to 110 +/- 5 beats/min at 40 min of exercise; P < 0.05). MSNA decreased from 34 +/- 3 to 28 +/- 3 bursts/min (P < 0.05) from control to the 5th min of DKE and then returned to control levels by 20 min (35 +/- 3 bursts/min) and remained unchanged for the remainder of exercise. During recovery, MSNA was significantly increased above control for 10 min postexercise (40 bursts/min) when HR and MAP had returned to control levels. These results confirm our previous finding that MSNA is decreased during the early stage of upright DKE. The two new findings are as follows: 1) prolonged DKE failed to increase MSNA above control levels, and 2) during recovery when HR and MAP are at control levels, MSNA is significantly elevated.
Effect of fasting and feeding on measurement of carbon dioxide production using doubly labeled water
Authors: Calazel C. M. , Young V. R. , Evans W. J. , Roberts S. B.
Published: December 2017

The doubly labeled water method is a noninvasive technique for measurement of rates of CO2 production and total energy expenditure in free-living human subjects. The experimental protocol used in validation studies usually involves prolonged fasting before and after the isotope dose is given to start the study, although it is not clear whether this intrusive aspect of the method is necessary. We investigated this issue in four healthy adults [3 women and 1 man: age 29 +/- 2 (SD) yr, body mass index 22 +/- 2.7 kg.m2] with monitored constant physical activity who underwent two doubly labeled water studies that differed only in the duration of fasting before and after isotope dosing (either 6 h of fasting before and 5 h after dosing or 0.5 h before and 3 h afterward). No significant difference between the two measurements was found in the rate constants for isotope disappearance, the ratio of the dilution spaces of the isotopes, or CO2 production rate. These results indicate that prolonged fasting before and after isotope administration should not be necessary in doubly labeled water studies.
A programmable inspiratory flow generator for aerosol bolus delivery
Authors: McNamee J. E. , Boykin A. B.
Published: December 2017

A microcomputer-controlled system that generates a discrete digital approximation of a desired inspiratory flow profile is described. Discrete flows between 0 and 387.5 ml/s can be achieved in increments of 12.5 ml/s with five solenoid valves. This pneumatic digital-to-analog converter is coupled to a mixing apparatus so that boluses of aerosol can be delivered at precise moments during an inspired breath. Between bolus deliveries, the system provides maintenance ventilation and allows flow pattern, tidal volume, inspiratory-to-expiratory time ratio, and respiratory rate to be programmed as desired.
Heat flux transducer measurement error: a simplified view
Authors: Frim J. , Ducharme M. B.
Published: December 2017

Heat flux transducers (HFTs) provide a simple and direct measurement of body heat exchange. Regrettably, HFTs perturb the heat flux at the measurement site, resulting in underestimations of the true heat flux. Equations to correct the discrepancy are available, but most require high-precision temperature measurements above and/or below the transducer and/or deep within the body tissues. Because this is not always feasible, the equations are of limited practical benefit. A theoretical basis for the magnitude of the correction factor in relation to the thermal resistances of the materials both above and below the HFT has been developed and has been verified experimentally. The theory is presented in a graph that can be used to drive the HFT correction factor directly or as a guide to know that heat flux was measured within a certain accuracy. This may obviate the use of complicated procedures and equations to perhaps needlessly apply a small correction factor to HFT data.
Effect of undernutrition on contractile and fatigue properties of rat diaphragm during development
Authors: Brozanski B. S. , Watchko J. F. , O'Day T. L. , Guthrie R. D.
Published: December 2017

The present study was designed to assess the effects of combined pre- and postnatal undernutrition on the in vitro contractile and fatigue properties of the rat diaphragm during development. In vitro direct stimulation of costal diaphragm from control (CTL) and undernourished (UN) rats was done on postnatal days 1, 4, 14, 21, 30, 40, 50, and 60. Combined pre- and postnatal undernutrition resulted in stunted animal growth but did not alter the diaphragm-to-total body weight ratio. Twitch contraction time, half-relaxation time, and force-frequency relationships were not consistently affected by undernutrition. Specific twitch force and specific tetanic force were also unchanged in the UN group. Fatigue resistance was high and comparable in UN and CTL groups at days 1 and 4. At day 14 and thereafter, fatigue resistance declined but was consistently higher in the UN than in the CTL group. We conclude that combined pre- and postnatal undernutrition results in a significant increase in fatigue resistance of the diaphragm compared with CTL, whereas diaphragm muscle contractile properties are not appreciably affected by prolonged undernutrition.
Fructose utilization during exercise in men: rapid conversion of ingested fructose to circulating glucose
Authors: Jandrain B. J. , Pallikarakis N. , Normand S. , Pirnay F. , Lacroix M. , Mosora F. , Pachiaudi C. , Gautier J. F. , Scheen A. J. , Riou J. P. , et al.
Published: December 2017

The aim of the present study was to compare the metabolic fate of repeated doses of fructose or glucose ingested every 30 min during long-duration moderate-intensity exercise in men. Healthy volunteers exercised for 3 h on a treadmill at 45% of their maximal oxygen consumption rate. "Naturally labeled" [13C]glucose or [13C]fructose was given orally at 25-g doses every 30 min (total feeding: 150 g; n = 6 in each group). Substrate utilization was evaluated by indirect calorimetry, and exogenous sugar oxidation was measured by isotope ratio mass spectrometry on expired CO2. Results were corrected for baseline drift in 13C/12C ratio in expired air due to exercise alone. Fructose conversion to plasma glucose was measured combining gas chromatography and isotope ratio mass spectrometry. Most of the ingested glucose was oxidized: 81 +/- 4 vs. 57 +/- 2 g/3 h for fructose (2P < 0.005). Exogenous glucose covered 20.8 +/- 1.4% of the total energy need (+/- 6.7 MJ) compared with 14.0 +/- 0.6% for fructose (2P < 0.005). The contribution of total carbohydrates was significantly higher and that of lipids significantly lower with glucose than with fructose. The blood glucose response was similar in both protocols. From 90 to 180 min, 55–60% of circulating glucose was derived from ingested fructose. In conclusion, when ingested repeatedly during moderate-intensity prolonged exercise, fructose is metabolically less available than glucose, despite a high rate of conversion to circulating glucose.
Monitoring of segmental intra- and extracellular volume changes using electrical impedance spectroscopy
Authors: Sasser D. C. , Gerth W. A. , Wu Y. C.
Published: December 2017

Osmotically induced cellular volume changes in the perfused rat hindlimb were used to validate the use of bioelectrical impedance spectroscopy as a method for observing fluid shifts between the intracellular and extracellular spaces. Electrical impedance spectra were measured as cell volumes were manipulated by perfusion with Krebs-Henseleit solutions having different concentrations of NaCl. A simple equivalent circuit model of current conduction through the monitored tissue was fit to each measured spectrum to obtain segmental values of the equivalent intracellular resistance, membrane capacitance, and extracellular resistance. These parameters are theoretically governed by variations in the average cell volume fraction and ionic concentrations in the intra- and extracellular fluid spaces. In accord with this theoretical dependence, the parameters changed systematically and reversibly in conformance with both the magnitudes and directions of the perfusate concentration changes and the resultant cell volume changes. Results indicate that bioelectrical impedance spectroscopy, coupled with computer-aided equivalent circuit analysis, can be used to monitor segmental intercompartmental fluid shifts at minute-by-minute resolution.
Myoglobin content of hamster skeletal muscles
Authors: Meng H. , Bentley T. B. , Pittman R. N.
Published: December 2017

Myoglobin (Mb) may facilitate O2 diffusion in muscle tissue, yet models of O2 transport are often simplified by ignoring the role of Mb. A recent analysis of O2 transport in hamster retractor muscle revealed a large discrepancy between the observed O2 diffusion from arterioles and that predicted by a mathematical model that did not include Mb. To establish whether this simplification was justified, we measured Mb content ([Mb]) in three hamster muscles that vary markedly in histochemical fiber type composition. [Mb] was determined spectrophotometrically using freshly excised tissues from hamsters of different ages (5–34 wk). [Mb] increased rapidly up to 15 wk of age and then rose more slowly. [Mb] in hamster muscles paralleled oxidative capacity. Our measurements of rat and dog muscles also show that [Mb] varies greatly among species and among muscles of a given species. The results indicate that in the hamster the variability in [Mb] with age and muscle should be taken into account when the potential role of Mb in studies on O2 transport is interpreted.
31P-magnetic resonance spectroscopy of leg muscle metabolism during exercise in children and adults
Authors: Zanconato S. , Buchthal S. , Barstow T. J. , Cooper D. M.
Published: December 2017

Gas exchange response to high-intensity exercise differs in children and adults. We hypothesized that these findings are related to a lower anaerobic ATP supply in children. We predicted therefore a maturation of muscle high-energy phosphate metabolism during exercise. To test this hypothesis, we measured calf muscle Pi, phosphocreatine (PCr), and pH with 31P-nuclear magnetic resonance spectroscopy during rest and progressive exercise in 10 children and 8 adults. No differences were found at rest in pH and Pi/PCr between children and adults. Exercise resulted in a greater increase in Pi/PCr (P < 0.001) and decrease in pH (P < 0.0001) in adults than in children. Six adults and five children exhibited a transition from a slow to a faster rate of Pi/PCr increase and pH decrease during exercise. No significant differences were found between the two groups in the initial slow-phase slopes of Pi/PCr and pH as a function of work rate. In contrast, during the fast phase, Pi/PCr increased (slope: adults 23.6 +/- 9.8, children 10.7 +/- 2.5; P < 0.05) and pH decreased (slope: adults -6.0 +/- 1.9, children -3.7 +/- 1.2; P < 0.05) more rapidly in adults than in children. In conclusion, high-intensity exercise results in different kinetics of Pi/PCr and pH between children and adults. These results suggest that children are less able than adults to affect ATP rephosphorylation by anaerobic metabolic pathways during high-intensity exercise.
Effects of acute sleep deprivation on control of the diaphragm during REM sleep in cats
Authors: Veasey S. C. , Hendricks J. C. , Kline L. R. , Pack A. I.
Published: December 2017

Recently, investigators demonstrated that acute sleep deprivation in healthy subjects results in significant periodic decrements in ventilation during recovery rapid-eye-movement (REM) sleep. The neural bases of such phenomena are unknown. The decrements in ventilation coincide with REM sleep-associated phasic activities, such as bursts of eye movements. The purpose of this study was to determine the effects of acute sleep deprivation on control of diaphragm activity during recovery REM sleep. In chronically implanted, naturally sleeping, unrestrained cats, we recorded the electroencephalogram, electrooculogram, pontogeniculooccipital waves, neck and diaphragmatic electromyograms, and the computed moving average of the diaphragm. Acute sleep deprivation resulted in an increase in REM sleep-associated phasic alterations in diaphragmatic control during recovery REM sleep. There was an increase in the percentage of bursts during recovery REM sleep with reduced inspiratory drive. Acute sleep deprivation resulted in a substantial increase in the number of brief pauses (fractionations) in diaphragmatic activity during recovery REM sleep. Respiratory timing was also affected by sleep deprivation, with a reduced expiratory time resulting in an increased duty cycle ratio. There was a significant increase in the percentage of bursts with decremented peak amplitude of the moving average of the diaphragm, a measure that correlates with tidal volume. Despite significant increases in respiratory-related phasic alterations, there were no parallel increases in excitatory phenomena, i.e., eye movements or pontogeniculooccipital waves. These results imply that respiratory control mechanisms in REM sleep are sensitive to the effects of prior sleep deprivation.
Effect of hypercapnia on the arousal response to airway occlusion during sleep in normal subjects
Authors: Berry R. B. , Mahutte C. K. , Light R. W.
Published: December 2017

The effect of an acute increase in PCO2 on the arousal response to occlusion of a mask covering the nose with the mouth sealed during non-rapid-eye-movement sleep was studied in six normal males aged 28.3 +/- 8.3 (SD) yr. Baseline occlusions, while subjects breathed a room air-O2 mixture adjusted to produce an arterial O2 saturation of 98%, were alternated with hypercapnic occlusions in which a small amount of 100% CO2 was added to increase the preocclusion end-tidal PCO2 by 3.5 +/- 0.59 Torr above the baseline value. The maximum deflections in supraglottic airway pressure (Pmax) were measured on the initial occluded breath (PmaxI) and the final breath preceding arousal (PmaxF). In the hypercapnic occlusions, the time to arousal was shorter (23.7 +/- 13.9 vs. 35.2 +/- 15.9 s, P < 0.03) and PmaxI and rate of change in Pmax were higher. However, the PmaxF in the baseline (20.2 +/- 4.1 cmH2O) and hypercapnic occlusions (20.4 +/- 4.4 cmH2O) did not differ. We conclude that an increase in PCO2 before airway occlusion shortens the time to arousal by increasing the initial occluded inspiratory effort (suction pressure) and the rate of increase in effort but does not change the arousal threshold.
Respiratory response to abdominal and rib cage muscle paralysis in dogs
Authors: Brichant J. F. , Gorini M. , De Troyer A.
Published: December 2017

To assess the respiratory response to abdominal and rib cage muscle paralysis, we measured tidal volume, esophageal and gastric pressures, arterial blood gases, and the electromyogram (EMG) of the diaphragm during progressive epidural anesthesia (lidocaine 2%) in 35 supine anesthetized dogs. The EMG activity of the diaphragm was measured with fine-wire electrodes; the abdominal cavity was thus left intact. Paralysis of the abdominal muscles alone did not produce any alterations. In contrast, when all rib cage muscles were also paralyzed, there were substantial increases in the peak height and the rate of rise of diaphragmatic EMG activity that were associated with a decrease in tidal volume and an increase in arterial PCO2 (PaCO2); swings in transdiaphragmatic pressure, however, were unchanged. The increased diaphragmatic activation due to rib cage muscle paralysis persisted after bilateral cervical vagotomy and was well explained by the increased PaCO2. These observations indicate that in the dog 1) the rib cage muscles contribute significantly to tidal volume, and their paralysis causes, through the increased hypercapnic drive, a compensatory increase in diaphragmatic activation; and 2) the rib cage inspiratory muscles enhance the diaphragm's ability to generate pressure during breathing.
Response of upper airway and chest wall muscles to selective brain stem hypoxia in the newborn
Authors: Cattarossi L. , Haxhiu-Poskurica B. , Haxhiu M. A. , Carlo W. A.
Published: December 2017

In animals with intact peripheral chemosensory afferents, hypoxia differentially affects upper airway (UA) and chest wall muscles. To determine the contribution of brain stem (BS) hypoxia to the response of UA and chest wall muscles during early life, we perfused the BS through a vertebral artery intermittently with blood from an extracorporeal circuit in nine newborn piglets (age 1–5 days). BS perfusions were performed with hypoxemic blood (arterial PO2 32 +/- 6 to 38 +/- 8 Torr) with different levels of BS PCO2 (28 +/- 2, 37 +/- 4, and 56 +/- 5 Torr) while systemic normocapnic hyperoxia was maintained (arterial PCO2 36 +/- 3 to 40 +/- 6 Torr, arterial PO2 345 +/- 73 to 392 +/- 37 Torr). Electromyograms (EMGs) of alae nasi (AN), external intercostal (EI), and diaphragm (DIA) were recorded. Normocapnic hypoxia of the BS induced a sustained increase in AN EMG (P < 0.01, analysis of variance) and depression of EI and DIA EMGs without a transient increase. These contrasting responses were also observed during hypocapnic and hypercapnic hypoxia of the BS and were not affected by inputs from the peripheral chemoreceptors or rostral cerebral structures that were not exposed to hypoxia. We conclude that, despite eliciting the known central respiratory depression, BS hypoxia causes an increase in the respiratory drive to an UA airway muscle. Thus, BS hypoxia elicits a selective rather than a generalized respiratory muscle depression. The respiratory muscles with high energy expenditure (DIA and EI) are depressed while UA muscles are stimulated or disinhibited. This response is independent of the level of BS arterial PCO2.
Baroreflex function and cardiac structure with moderate endurance training in normotensive men
Authors: McDonald M. P. , Sanfilippo A. J. , Savard G. K.
Published: December 2017

Changes in arterial and cardiopulmonary baroreflex function and cardiac structure were followed throughout 10 wk of moderate endurance training [60 min of cycling, 3 days/wk, 60% maximal O2 uptake (VO2max)] in sedentary normotensive men (22–34 yr old). Subjects were randomly assigned to an exercise training group (ET; n = 9) or to a control group (UT; n = 4). Decreases in resting heart rate (8.9 +/- 2.6%, P < 0.01) and mean arterial pressure (7.0 +/- 2.3%, P < 0.05) and an increase in VO2max occurred after 10 wk in ET. An increase in the gain or slope of the spontaneous baroreflex response at rest was found after 10 wk in ET (50.1 +/- 6.3%, P < 0.01) but not in UT. An upward shift in the resting carotid-cardiac baroreflex response curve also occurred after 10 wk in ET, although the maximum range and gain of the response and the vagally mediated peak reflex sinus node responses were unchanged. Cardiopulmonary baroreflex function (reflex changes in forearm vascular conductance) and measured indexes of left ventricular structure were not altered in either ET or UT, although peak transmitral inflow velocity increased in ET (P < 0.05). These findings demonstrate that moderate exercise training results in an enhancement in the ability to reflexly adjust heart rate with spontaneous changes in arterial pressure within the operating range. This occurs independently of any changes in carotid-cardiac baroreflex function over the full response range in cardiopulmonary baroreflex function or in cardiac structure.
Perilla ketone increases endothelial cell monolayer permeability in vitro
Authors: Waters C. M. , Alexander J. S. , Harris T. R. , Haselton F. R.
Published: December 2017

Perilla ketone (PK) is a potent lung toxin that causes increased microvascular permeability pulmonary edema in grazing animals. Because the mechanism of action of PK is not know, we investigated whether PK directly affects endothelial cells. Bovine aortic endothelial cells were grown to confluence on Cytodex-3 microcarrier beads and placed in a chromatographic cell column. Monolayer permeability was evaluated from the elution profiles of three optical tracers: blue dextran (2 x 10(6) mol wt), sodium fluorescein (NaF, 342 mol wt), and cyanocobalamin (B12, 1,355 mol wt). Perfusion with 1.2 mM PK increased permeability within 15 min to NaF and B12 by 51 +/- 6 and 54 +/- 11%, respectively. Permeability returned to baseline after PK removal. These in vitro results suggest that PK produces a rapid and reversible increase in endothelial permeability directly. Staining of fixed cells with rhodamine-phalloidin revealed a major disruption of actin microfilaments after PK treatment. Because previous reports suggested that PK may be activated via cytochrome P-450, we attempted to block this using the cytochrome P-450 inhibitor ketoconazole. Ketoconazole alone did not significantly affect permeability, and the combination of PK and ketoconazole resulted in permeability increases similar to those measured for PK alone. This suggests that PK may not require cytochrome P-450 to increase vascular permeability.
Personal computer system for tracking cardiac vulnerability by complex demodulation of the T wave
Authors: Nearing B. D. , Verrier R. L.
Published: December 2017

Complex demodulation of the T wave permits tracking of susceptibility to ventricular fibrillation under the clinically relevant conditions of acute myocardial ischemia and reperfusion. To facilitate the processing and to increase the applicability of the methods, we have developed algorithms and applied mathematical transformations that can be carried out with a personal computer. The program is self-contained and menu driven and transforms the data into a three-dimensional graphic display of magnitude of alternans (mV x ms), time in the cardiac cycle, and duration of the assessment. It is suitable for investigations with diverse experimental procedures such as coronary artery occlusion and release, autonomic interventions, behavioral stress testing, and drug administration. Our methodology may be employed in clinical conditions such as postmyocardial infarction. Prinzmetal's angina, and the long QT syndrome, wherein T wave alternans has been reported in body surface leads. Ultimately, T wave alternans analysis with use of the personal computer system may help guide therapeutic interventions.
Comparison of three techniques for body composition analysis in cystic fibrosis
Authors: Lands L. C. , Gordon C. , Bar-Or O. , Blimkie C. J. , Hanning R. M. , Jones N. L. , Moss L. A. , Webber C. E. , Wilson W. M. , Heigenhauser G. J.
Published: December 2017

Body composition analysis is an important component of nutritional assessment in cystic fibrosis (CF). No gold standard of measurement exists, and techniques applicable to healthy populations may be unsuitable for CF patients. We assessed lean body mass (LBM) in 12 children with CF by skinfold (SK) measurements, bioelectrical impedance analysis (BIA), and dual-photon absorptiometry (DPA) and repeated these measures in 10 subjects 6 mo later. SK and DPA measures in eight older CF patients and eight healthy controls were compared to evaluate any effect of disease on estimates of LBM by use of DPA. Good agreement between the measures was seen at baseline and 6 mo by use of concordance plots. However, the limits of agreement between measures ranged up to 19% of SK-derived LBM measures (baseline: SK and DPA, 2.63 to -3.93 kg; SK and BIA, 2.36 to -1.24 kg; BIA and DPA, 1.88 to -4.28 kg; 6 mo: SK and DPA, 2.10 to -3.58 kg; SK and BIA, 6.28 to -5.49 kg; BIA and DPA, 5.53 to -7.79 kg). The change in LBM over 6 mo did not correlate among the three measures. Only BIA change in LBM correlated with weight change (r = 0.716, P < 0.02), probably due to the inclusion of weight in the regression equations for determining LBM from impedance. The relationship between SK and DPA measures did not differ between the CF and control groups, suggesting that there was no effect of disease on the DPA measure. The results suggest that none of these methods is precise enough to follow short-term changes in the nutritional status of CF patients longitudinally.
Neutral endopeptidase inhibitor potentiates allergic bronchoconstriction in guinea pigs in vivo
Authors: Kawano O. , Kohrogi H. , Yamaguchi T. , Araki S. , Ando M.
Published: December 2017

To determine whether endogenous tachykinins are released in allergic airway response to contribute to bronchoconstriction and whether neutral endopeptidase (NEP), which effectively cleaves tachykinins, modulates that bronchoconstriction, we studied the effects of the NEP inhibitor phosphoramidon on bronchoconstriction induced by allergic response in anesthetized guinea pigs. We mechanically ventilated the guinea pigs sensitized with ovalbumin (OVA) in a bodyplethysmograph and measured the pulmonary resistance (RL). We exposed the sensitized guinea pigs to doubling concentrations of OVA aerosols from 2(-5)% (wt/vol) until the transpulmonary pressure increased more than twofold from the baseline. After the final exposure, we exposed them to phosphoramidon (10(-4) M) or its vehicle. Phosphoramidon significantly potentiated the increased RL induced by OVA challenge. Phosphoramidon also significantly potentiated the increased RL in the guinea pigs treated with atropine, but the potentiation was significantly reduced. In contrast, phosphoramidon failed to potentiate the increased RL induced by OVA in guinea pigs pretreated with capsaicin. These results suggest that 1) endogenous tachykinin-like substances are released in allergic airway response and that 2) when endogenous NEP is inhibited in the guinea pig airways in vivo, the substances contribute to bronchoconstriction by partly activating the parasympathetic nerve.
Effect of indomethacin on the pressor responses to sustained isometric contraction in humans
Authors: Davy K. P. , Herbert W. G. , Williams J. H.
Published: December 2017

The purpose of this study was to test the hypothesis that prostaglandins participate in metaboreceptor stimulation of the pressor response to sustained isometric handgrip contraction in humans. To accomplish this, mean arterial pressure, heart rate (n = 10), and plasma norepinephrine levels (n = 8) were measured in healthy male subjects during sustained isometric handgrip at 40% of maximal voluntary contraction force to exhaustion and during a period of postcontraction muscle ischemia. The subjects were given a double-blind and counterbalanced administration of placebo or a single 100-mg dose of indomethacin. A period of 1 wk was allowed for systemic clearance of the drug. Mean arterial pressure increased 25 +/- 5 vs. 22 +/- 4 mmHg during the final minute of isometric handgrip contraction and 26 +/- 2 vs. 21 +/- 5 during the last minute of postcontraction muscle ischemia in the placebo vs. the indomethacin trial (P > 0.05), respectively. Heart rate was increased 21 +/- 4 vs. 17 +/- 3 beats/min during the final minute of isometric handgrip contraction in the placebo vs. the indomethacin trial (P > 0.05), respectively, and returned to control values during postcontraction muscle ischemia. Plasma norepinephrine levels increased 343 +/- 89 vs. 289 +/- 89 pg/ml after isometric handgrip contraction and 675 +/- 132 vs. 632 +/- 132 pg/ml after postcontraction muscle ischemia (P > 0.05) in the placebo vs. the indomethacin trial, respectively. These results suggest that prostaglandin inhibition does not significantly modulate muscle contraction-induced stimulation of mean arterial pressure, heart rate, or plasma norepinephrine levels.