bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasi-static pressure-volume hysteresis in the canine respiratory system in vivo
Authors: Shardonofsky F. R. , Sato J. , Bates J. H.
Published: December 2017

We investigated the quasi-static pressure-volume (P-V) hysteresis of the normal canine lung in vivo by performing 15-s flow interruptions at various points throughout the breathing cycle in mechanically ventilated anesthetized paralyzed dogs. By measuring the transpulmonary pressure (Ptp) at 5 s after each interruption, we built up a quasi-static P-V loop of the lungs. We found, however, that the area of the loop was significantly smaller (by a factor of 4-6) than has been reported by others for the isolated canine lung. We also found the hysteresis loop area of the chest wall to be of similar magnitude. If we measured Ptp 10-15 s after interruption, we found it always decreased at a rate expected to result from continuing gas exchange in the lungs. We conclude that 1) the areas of the quasi-static P-V loop in vivo for the total respiratory system, as well as the lungs and chest wall separately, are significantly smaller than has been reported previously for isolated lungs and 2) continuing gas exchange in the lungs places a lower limit on the frequencies (equivalent to flow interruptions of greater than 5- to 7-s duration) at which the P-flow-V behavior of the lungs in vivo can be considered in purely mechanical terms.
Fiber subtype distribution of pharyngeal dilator muscles and diaphragm in the cat
Authors: Dick T. E. , van Lunteren E.
Published: December 2017

In previous studies differences were frequently found between the pharyngeal dilator muscles and the thoracic respiratory muscles in their patterns of electrical and mechanical activity during the respiratory cycle, with both resting and stimulated breathing. However, little is known about the intrinsic properties of the pharyngeal muscles and how they relate to the intrinsic properties of the diaphragm. In the present study, the fiber subtype distributions of two pharyngeal dilator muscles, the geniohyoid and the sternohyoid, were ascertained histochemically in the cat. The geniohyoid and the sternohyoid muscles had a preponderance of fast glycolytic (FG) fibers (mean 48 and 55%, respectively), a smaller number of fast oxidative-glycolytic (FOG) fibers (mean 36 and 31%, respectively), and few slow oxidative (SO) fibers (mean 16 and 14%, respectively). The percentages of SO fibers of both hyoid muscles were significantly (P less than 0.01) lower than that of the costal diaphragm, and the percentages of FOG and FG fibers were significantly higher than that of the diaphragm. In conclusion, the geniohyoid and sternohyoid muscles have histochemical characteristics usually associated with fast contraction and intermediate endurance properties.
Morphological evidence for alveolar recruitment during inflation at high transpulmonary pressure
Authors: Lum H. , Huang I. , Mitzner W.
Published: December 2017

The effect of continuous inflation of lungs at 30 cmH2O transpulmonary pressure (Ptp) on air-space size was assessed by chord length-frequency distribution analysis. Lungs from gerbils were excised, allowed to collapse freely, and inflated to 30 cmH2O Ptp in a humidified chamber kept at 37 degrees C. When the lungs appeared fully inflated with no observable pleural surface atelectasis, the left lung was occluded while the right was maintained at 30 cmH2O for 10 min longer and then occluded. During this time, the right lung increased its volume from 70 to 100%. Then both lungs were quick frozen, freeze dried, and embedded in glycol methacrylate, and 1- to 2-microns-thick histological sections cut. Lungs from a control group of gerbils were similarly inflated to 30 cmH2O, both left and right were occluded, the left was quick frozen immediately, and the right was frozen 10 min later. Chord lengths of air spaces from cranial and caudal lobes of lungs were acquired using a Dapple Systems image analyzer, and a two-population frequency distribution was generated for analysis with an IBM PC. The results indicate that the volume increase during continuous inflation at 30 cmH2O Ptp was associated with a shift in the chord length distribution toward the smaller chord lengths. A two-population statistical analysis indicated that the inflation resulted in an increase in the relative proportion of smaller chord lengths, with no increase in the mean of this smaller population. We conclude that continuous inflation at 30 cmH2O Ptp results in alveolar recruitment.
Relationships between permeable vessels, nerves, and mast cells in rat cutaneous neurogenic inflammation
Authors: Baraniuk J. N. , Kowalski M. L. , Kaliner M. A.
Published: December 2017

Electrical stimulation of rat sensory nerves produces cutaneous vasodilation and plasma protein extravasation, a phenomenon termed “neurogenic inflammation”. Rat skin on the dorsum of the paw developed neurogenic inflammation after electrical stimulation of the saphenous nerve. In tissue sections, the extravasation of the supravital dye monastral blue B identified permeable vessels. Mast cells were identified by toluidine blue stain. Permeable vessels were significantly more dense in the superficial 120 microns of the dermis than in the deeper dermis, whereas mast cells were significantly more frequent in the deeper dermis. The relationships between nociceptive sensory nerve fibers, permeable vessels, and mast cells were examined by indirect immunohistochemistry for calcitonin gene-related peptide (CGRP), neurokinin A (NKA), and substance P (SP). CGRP-, NKA-, and SP-containing nerves densely innervated the superficial dermis and appeared to innervate the vessels that became permeable during neurogenic inflammation. In contrast, mast cells were not associated with either permeable vessels or nerve fibers. These data suggest that electrical stimulation of rat sensory nerves produces vascular permeability by inducing the release of neuropeptides that may directly stimulate the superficial vascular bed. Mast cells may not be involved in this stage of cutaneous neurogenic inflammation in rat skin.
Skeletal muscle oxidative capacity, antioxidant enzymes, and exercise training
Authors: Laughlin M. H. , Simpson T. , Sexton W. L. , Brown O. R. , Smith J. K. , Korthuis R. J.
Published: December 2017

The purposes of this study were to determine whether exercise training induces increases in skeletal muscle antioxidant enzymes and to further characterize the relationship between oxidative capacity and antioxidant enzyme levels in skeletal muscle. Male Sprague-Dawley rats were exercise trained (ET) on a treadmill 2 h/day at 32 m/min (8% incline) 5 days/wk or were cage confined (sedentary control, S) for 12 wk. In both S and ET rats, catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX) activities were directly correlated with the percentages of oxidative fibers in the six skeletal muscle samples studied. Muscles of ET rats had increased oxidative capacity and increased GPX activity compared with the same muscles of S rats. However, SOD activities were not different between ET and S rats, but CAT activities were lower in skeletal muscles of ET rats than in S rats. Exposure to 60 min of ischemia and 60 min of reperfusion (I/R) resulted in decreased GPX and increased CAT activities but had little or no effect on SOD activities in muscles from both S and ET rats. The I/R-induced increase in CAT activity was greater in muscles of ET than in muscles of S rats. Xanthine oxidase (XO), xanthine dehydrogenase (XD), and XO + XD activities after I/R were not related to muscle oxidative capacity and were similar in muscles of ET and S rats. It is concluded that although antioxidant enzyme activities are related to skeletal muscle oxidative capacity, the effects of exercise training on antioxidant enzymes in skeletal muscle cannot be predicted by measured changes in oxidative capacity.
Hypoxia and ion activities within the brain stem of newborn rabbits
Authors: Trippenbach T. , Richter D. W. , Acker H.
Published: December 2017

Eleven rabbits between the 1st and 28th days of life were anesthetized (ketamine 40 mg/kg and acepromazine 3 mg/kg im) thoracotomized, paralyzed, and artificially ventilated with 50% O2 and 10% O2 in N2 or 100% N2. Three-barreled ion-sensitive microelectrodes were used to measure direct-current potentials, potassium (aK+o) and calcium (aCa2+o) activities, and tissue PO2. During control, mean levels of aK+o and aCa2+o were 4.4 +/- 1.1 and 1.3 +/- 0.3 mM, respectively. During hypoxia, changes in aCa2+o were inconsistent, and aK+o revealed three phases: slow (phase I) and fast (phase II) rate of rise and a saturation level (phase III) at the group mean of 6.8 +/- 2.3 mM. Durations of phases I and II decreased, and their slopes increased with maturation. Hypoxia-related excitation of phrenic nerve activity (PHR) occurred during phase I, and gasplike PHR and/or apnea occurred during phases II and III. During recovery after hypoxia, PHR was independent of aK+o levels. Vagal nerve stimulation caused a rapid increase in aK+o followed by a continuous decay even though stimulation continued. Hypoxia had no significant effect on maximal aK+o increase. We concluded that ion homeostasis is less sensitive to the reduced availability of O2 shortly after birth than it is later in life. This age dependence may have an important role in the high resistance to lack of O2 during the early postnatal period in mammals.
Evidence that the metabolic acidosis threshold is the anaerobic threshold
Authors: Koike A. , Weiler-Ravell D. , McKenzie D. K. , Zanconato S. , Wasserman K.
Published: December 2017

We evaluated maximal O2 uptake (VO2max), the metabolic acidosis threshold determined by the V-slope analysis [plot of CO2 output (VCO2) as a function of oxygen uptake (VO2)], the ratio of increase in VO2 to work rate increment (delta VO2/delta WR), the upper slope (S2) of the V-slope analysis, and the VO2 for work below and above the metabolic acidosis threshold to determine whether the changes in O2 transport caused by increased carboxyhemoglobin (HbCO) affected these parameters and variables. Ten normal subjects (aged 32.8 +/- 7.1 yr) performed symptom-limited incremental exercise tests in a ramp pattern on a cycle ergometer while breathing air and air with added carbon monoxide to cause HbCO to be approximately 11% and 20%. VO2max decreased by 11.6 and 19.3%, the metabolic acidosis threshold decreased by 11.9 and 19.6%, delta VO2/delta WR decreased by 8.9 and 14.0%, and S2 increased by 13.6 and 21.8% when HbCO was increased to 11 and 20%, respectively. Most importantly, VO2 was unchanged related to work rate below the metabolic acidosis threshold during the tests with increased HbCO but was reduced at the work rates above the metabolic acidosis threshold. These findings are consistent with the concept that the metabolic acidosis threshold is synonymous with an anaerobic threshold, i.e., the latter demarcating the VO2 above which the contracting muscles are not adequately supplied with O2 but below which they are.
Simulation of the effects of mechanical nonhomogeneities on expiratory flow from human lungs
Authors: Lambert R. K.
Published: December 2017

A computational model for expiration from lungs with mechanical nonhomogeneities was used to investigate the effect of such nonhomogeneities on the distribution of expiratory flow and the development of alveolar pressure differences between regions. The nonhomogeneities used were a modest constriction of the peripheral airways and a 50% difference in compliance between regions. The model contains only two mechanically different regions but allows these to be as grossly distributed as left lung-right lung or to be distributed as a set of identical pairs of parallel nonhomogeneous regions with flows from each merging in a specified bronchial generation. The site of flow merging had no effect on the flow-volume curve but had a significant effect on the development of alveolar pressure differences (delta PA). With the peripheral constriction, greater values of delta PA developed when flows were merged peripherally rather than centrally. The opposite was true in the case of a compliance nonhomogeneity. The delta PA values were smaller at submaximal flows. Plots of delta PA vs. lung volume were similar to those obtained experimentally. These results were interpreted in terms of the expression used for the fluid mechanics of the merging flows. delta PA was greater when the viscosity of the expired gas was increased or when its density was reduced. Partial forced expirations were shown to indicate the presence of mechanical nonhomogeneity.
Clearance of lung edema into the pleural space of volume-loaded anesthetized sheep
Authors: Broaddus V. C. , Wiener-Kronish J. P. , Staub N. C.
Published: December 2017

To determine whether lung edema leaks into the pleural space, we measured flow rates of visceral pleural liquid from exposed sheep lungs during volume loading and then compared the protein concentration of visceral pleural liquid and lung interstitial liquids (lymph and peribronchovascular cuff liquid). For 4 h, we volume loaded 24 anesthetized ventilated sheep with one side, both sides, or neither side of the chest open. During the experiment, we collected visceral pleural liquid from a bag surrounding the exposed lung and lung lymph; after the experiment, we collected peribronchovascular cuff liquid. We found that during volume loading visceral pleural liquid flow increased significantly by 2 h, and its protein concentration over the final hour was the same as that of lung interstitial liquids. The volume of visceral pleural liquid correlated with excess lung water and wedge pressure elevation. By our estimates, clearance of edema from the lung into the pleural space constituted 23-29% of all edema liquid collected, similar to measured lymph edema clearance. We conclude that edema liquid leaks directly from edematous sheep lungs into the pleural space and that this leakage provides an important additional route of edema clearance.
Brain glutamate metabolism during hypoxia and peripheral chemodenervation
Authors: Hoop B. , Masjedi M. R. , Shih V. E. , Kazemi H.
Published: December 2017

Glutamate stimulates resting ventilation by altering neural excitability centrally. Hypoxia increases central ventilatory drive through peripheral chemoreceptor stimulation and may also alter cerebral perfusion and glutamate metabolism locally. Therefore the effect of hypoxia and peripheral chemodenervation on cerebrospinal fluid (CSF) transfer rate of in vivo tracer amidated central nervous system glutamate was studied in intact and chemodenervated pentobarbital-anesthetized dogs during normoxia and after 1 h of hypoxia induced with 10 or 12% O2 in N2 breathing at constant expired ventilation and arterial CO2 tension. Chemodenervation was performed by bilateral sectioning of the carotid body nerves and cervical vagi. CSF transfer rates of radiotracer 13NH4+ and [13N]glutamine synthesized via the reaction, glutamate + NH4(+)----glutamine, in brain glia were measured during normoxia and after 1 h of hypoxia. At normoxia, maximal glial glutamine efflux rate jm = 103.3 +/- 11.2 (SE) mumol.l-1.min-1 in all animals. After 1 h of hypoxia in intact animals, jm = 78.4 +/- 10.0 mumol.l-1.min-1. In denervated animals, jm was decreased to 46.3 +/- 4.3 mumol.l-1.min-1. During hypoxia, mean cerebral cortical glutamate concentration was higher in denervated animals (9.98 +/- 1.43 mumol/g brain tissue) than in intact animals (7.63 +/- 1.82 mumol/g brain tissue) and corresponding medullary glutamate concentration tended to be higher in denervated animals. There were no differences between mean glutamine and gamma-aminobutyric acid concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
Release of luteinizing hormone and growth hormone after recovery from maximal exercise
Authors: Weltman J. Y. , Seip R. L. , Weltman A. , Snead D. , Evans W. S. , Veldhuis J. D. , Rogol A. D.
Published: December 2017

Pulsatile properties of luteinizing hormone (LH) and growth hormone (GH) release were evaluated in 19 eumenorrheic untrained females [mean age 31.1 +/- 1.1 yr, height 165.2 +/- 1.4 cm, weight 64.8 +/- 2.1 kg, peak oxygen uptake (Vo2) 41.6 +/- 1.4 (SE) ml.kg-1.min-1] during the early follicular phase of the menstrual cycle (days 3-4 after the onset of menses). Each subject was studied during two consecutive menstrual cycles under each of two conditions in random order: 1) no formal exercise for 72 h (C) and 2) 12-24 h after two maximal exercise bouts (peak Vo2/lactate threshold treadmill evaluation and a 3,200-m time-trial run or a maximal Vo2 inclined treadmill test) performed on consecutive days (EX). Blood sampling was performed every 10 min for 12 h. LH and GH pulsatile parameters were identified and characterized by the Cluster pulse detection algorithm. No significant differences were noted in the number of peaks, peak amplitude, interpeak interval, peak increment, or 12-h integrated concentrations between C and EX for LH or GH. We conclude that maximal exercise protocols typically used for exercise evaluation do not have an effect on the pulsatile characteristics of LH or GH release in untrained women during the early follicular phase of the menstrual cycle if 12-24 h of recovery are allowed before evaluation of the pulsatile secretion of gonadotropins or GH.
Thyroarytenoid muscle activity during hypoxia, hypercapnia, and voluntary hyperventilation in humans
Authors: Insalaco G. , Kuna S. T. , Cibella F. , Villeponteaux R. D.
Published: December 2017

Intramuscular electromyographic activity of the thyroarytenoid (TA) muscle, a vocal cord adductor, was recorded in nine normal adult humans during progressive isocapnic hypoxia and hyperoxic hypercapnia. Four of the nine subjects also performed voluntary isocapnic hyperventilation. During quiet breathing of room air, the TA exhibited phasic activity in expiration and often tonic activity throughout the respiratory cycle. Both phasic and tonic TA activity progressively decreased with either increasing hypoxia or hypercapnia. Tonic activity appeared to decrease more rapidly than phasic activity with increasing chemical stimulation. At comparable tidal volume increments, the relative decrease in phasic TA activity appeared to be greater under hypoxic than under hypercapnic conditions. During voluntary isocapnic hyperventilation, phasic TA activity decreased without significant change in tonic activity. At tidal volumes approximately double those of base line, the relative decrease in TA activity was similar during both hypercapnia and voluntary hyperventilation, although differences appeared at higher tidal volumes. The results, in combination with recent findings in humans regarding the posterior cricoarytenoid muscle, a vocal cord abductor, suggest that vocal cord position is dependent on the net balance of counteracting forces not only during quiet breathing but also during involuntary and voluntary hyperpnea.
Response of antioxidant enzymes to intermittent and continuous hyperbaric oxygen
Authors: Harabin A. L. , Braisted J. C. , Flynn E. T.
Published: December 2017

Rats and guinea pigs were exposed to O2 at 2.8 ATA (HBO) delivered either continuously or intermittently (repeated cycles of 10 min of 100% O2 followed by 2.5 min of air). The O2 time required to produce convulsions and death was increased significantly in both species by intermittency. To determine whether changes in brain and lung superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSHPx) correlated with the observed tolerance, enzyme activities were measured after short or long HBO exposures. For each exposure duration, one group received continuous and one intermittent HBO; O2 times were matched. HBO had marked effects on these enzymes: lung SOD increased (guinea pigs 47%, rats 88%) and CAT and GSHPx activities decreased (33%) in brain and lung. No differences were seen in lung GSHPx or brain CAT in rats or brain SOD in either species. In guinea pigs, but less so in rats, the observed changes in activity were usually modulated by intermittency. Increases in hematocrit, organ protein, and lung DNA, which may also reflect ongoing oxidative damage, were also slowed with intermittency in guinea pigs. Intermittency benefited both species by postponing gross symptoms of toxicity, but its modulation of changes in enzyme activities and other biochemical variables was more pronounced in guinea pigs than in rats, suggesting that there are additional mechanisms for tolerance.
Fluctuation in timing of upper airway and chest wall inspiratory muscle activity in obstructive sleep apnea
Authors: Hudgel D. W. , Harasick T.
Published: December 2017

An imbalance in the amplitude of electrical activity of the upper airway and chest wall inspiratory muscles is associated with both collapse and reopening of the upper airway in obstructive sleep apnea (OSA). The purpose of this study was to examine whether timing of the phasic activity of these inspiratory muscles also was associated with changes in upper airway caliber in OSA. We hypothesized that activation of upper airway muscle phasic electrical activity before activation of the chest wall pump muscles would help preserve upper airway patency. In contrast, we anticipated that the reversal of this pattern with delayed activation of upper airway inspiratory muscles would be associated with upper airway narrowing or collapse. Therefore the timing and amplitude of midline transmandibular and costal margin moving time average (MTA) electromyogram (EMG) signals were analyzed from 58 apnea cycles in stage 2 sleep in six OSA patients. In 86% of the postapnea breaths analyzed the upper airway MTA peak activity preceded the chest wall peak activity. In 86% of the obstructed respiratory efforts the upper airway MTA peak activity followed the chest wall peak activity. The onset of phasic electrical activity followed this same pattern. During inspiratory efforts when phasic inspiratory EMG amplitude did not change from preapnea to apnea, the timing changes noted above occurred. Even within breaths the relative timing of the upper airway and chest wall electrical activities was closely associated with changes in the pressure-flow relationship. We conclude that the relative timing of inspiratory activity of the upper airway and chest wall inspiratory muscles fluctuates during sleep in OSA.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of sleep and sleep deprivation on ventilatory response to bronchoconstriction
Authors: Ballard R. D. , Tan W. C. , Kelly P. L. , Pak J. , Pandey R. , Martin R. J.
Published: December 2017

To characterize ventilatory responses to bronchoconstriction during sleep and to assess the effect of prior sleep deprivation on ventilatory and arousal responses to bronchoconstriction, bronchoconstriction was induced in eight asthmatic subjects while they were awake, during normal sleep, and during sleep after a 36-h period of sleep deprivation. Each subject was bronchoconstricted with increasing concentrations of aerosolized methacholine while ventilatory patterns and lower airway resistance (Rla) were continually monitored. The asthmatic patients maintained their minute ventilation as Rla increased under all conditions, demonstrating a stable tidal volume with a mild increase in respiratory frequency. Inspiratory drive, as measured by occlusion pressure (P0.1), increased progressively and significantly as Rla increased under all conditions (slopes of P0.1 vs. Rla = 0.249, 0.112, and 0.154 for awake, normal sleep, and sleep after sleep deprivation, respectively, P less than 0.0006). Chemostimuli did not appear to contribute significantly to the observed increases in P0.1. Prior sleep deprivation had no effect on ventilatory and P0.1 responses to bronchoconstriction but did significantly raise the arousal threshold to induced bronchoconstriction. We conclude that ventilatory responses to bronchoconstriction, unlike extrinsic loading, are not imparied by the presence of sleep, nor are they chemically mediated. However, prior sleep deprivation does increase the subsequent arousal threshold.
Fractal properties of pulmonary blood flow: characterization of spatial heterogeneity
Authors: Glenny R. W. , Robertson H. T.
Published: December 2017

The heterogeneity of pulmonary blood flow was examined using a fractal analytic procedure, and the results were compared with the traditional gravitational model of flow distribution. 99mTc-labeled macroaggregate was injected intravenously at functional residual capacity in six supine anesthetized dogs. The lungs were fixed in situ and sliced in transverse sections. The slices were imaged on a planar gamma camera, and a three-dimensional array of blood flow measurements was reconstructed for each lung. Fractal analysis was used to examine the spatial heterogeneity or RDs (relative dispersion = SD/mean) as a function of the number of pieces into which the flow array was subdivided. RDs was fractal and could be characterized by a fractal dimension (Ds) of 1.09 +/- 0.02, where a Ds of 1.0 reflects homogeneous flow and 1.5 indicates a random flow distribution. The data fit the fractal model exceptionally well with an average r = 0.98. RDs was examined in gravitational and isogravitational planes and as expected was greatest in the gravitational direction. However, the difference was small, suggesting that gravitation plays a secondary role to an underlying process producing heterogeneity. Within the limits of resolution attained by this study (piece volumes greater than 0.25 cm3), the heterogeneity of pulmonary blood flow is well characterized by a fractal model.
Effect of saline infusion during exercise on thermal and circulatory regulations
Authors: Nose H. , Mack G. W. , Shi X. R. , Morimoto K. , Nadel E. R.
Published: December 2017

To quantify the effect of an acute increase in plasma volume (PV) on forearm blood flow (FBF), heart rate (HR), and esophageal temperature (Tes) during exercise, we studied six male volunteers who exercised on a cycle ergometer at 60% of maximal aerobic power for 50 min in a warm [(W), 30 degrees C, less than 30% relative humidity (rh)] or cool environment [(C), 22 degrees C, less than 30% rh] with isotonic saline infusion [Inf(+)] or without infusion [Inf(-)]. The infusion was performed at a constant rate of 0.29 ml.kg body wt-1.min-1 for 20-50 min of exercise to mimic fluid intake during exercise. PV decreased by approximately 5 ml/kg body wt within the first 10 min of exercise in all protocols. Therefore, PV in Inf(-) was maintained at the same reduced level by 50 min of exercise in both ambient temperatures, whereas PV in Inf(+) increased toward the preexercise level and recovered approximately 4.5 ml/kg body wt by 50 min in both temperatures. The restoration of PV during exercise suppressed the HR increase by 6 beats/min at 50 min of exercise in W; however, infusion had no effect on HR in C. In W, FBF in Inf(+) continued to increase linearly as Tes rose to 38.1 degrees C by the end of exercise, whereas FBF in Inf(-) plateaued when Tes reached approximately 37.7 degrees C. The infusion in C had only a minor effect on FBF.(ABSTRACT TRUNCATED AT 250 WORDS)
Cardiovascular responses to arm cranking and FNS-induced leg exercise in paraplegics
Authors: Davis G. M. , Servedio F. J. , Glaser R. M. , Gupta S. C. , Suryaprasad A. G.
Published: December 2017

Twelve spinal cord-injured males performed arm-crank exercise (ACE) with and without concurrent functional neuromuscular stimulation (FNS) of paralyzed leg muscles to investigate the hypothesis that FNS would augment cardiovascular performance during submaximal ACE. Six men who exhibited vigorous isometric contractions of thigh and calf muscles were classed as "responders" to FNS (R), and the remaining subjects with poor or nonexistent contractions served as "nonresponder controls" (C). Steady-state heart rate and oxygen uptake during ACE at 30, 60, and 90 W were not appreciably different from the ACE + FNS condition. However, cardiac outputs in R were augmented by 30% during FNS at rest (from 4.9 to 6.4 l/min), by 18% during 30-W ACE + FNS (from 8.6 to 10.1 l/min), and by 28% during 90-W ACE + FNS (from 12.1 to 15.6 l/min). Similarly, resting stroke volumes were increased by 18% (9 ml) and by 23% (19 ml) at 60 W during FNS in the R group. Calculated total peripheral resistance was reduced at rest and during 90-W ACE + FNS by approximately 24%. In contrast, no alterations of circulatory hemodynamics were observed for C subjects. These data indicate that FNS-induced contractions of paralyzed leg muscles augment venous return to aid central cardiovascular control during upper-body submaximal exercise in paraplegics.
Ventilatory control during exercise with increased respiratory dead space in goats
Authors: Mitchell G. S.
Published: December 2017

Our objectives were to determine 1) the effects of increased respiratory dead space (VD) on the ventilatory response to exercise and 2) whether changes in the ventilatory response are due to changes in chemoreceptor feedback (rest to exercise) vs. changes in the feedforward exercise stimulus. Steady-state ventilation (VI) and arterial blood gas responses to mild or moderate hyperoxic exercise in goats were compared with and without increased VD. Responses were compared using a simple mathematical model with the following assumptions: 1) steady state, 2) linear CO2 chemoreceptor feedback, 3) linear feedforward exercise stimulus proportional to CO2 production (VCO2) and characterized by an exercise gain (Gex), and 4) additive exercise stimulus and CO2 feedback producing the system gain (Gsys = delta VI/delta VCO2). Model predictions at constant Gex [assuming VD-to-tidal volume (VT) ratio independent of VCO2] are that increased VD/VT will 1) increase arterial PCO2 (PaCO2) and VI at rest and 2) increase Gsys via changes in chemoreceptor feedback due to a small increase in the PaCO2 vs. VCO2 slope. Experimental results indicate that increased VD increased VD/VT, PaCO2, and VI at rest and increased Gsys during exercise. However, measurable changes in the PaCO2 vs. VCO2 slope occurred only at high VD/VT or running speeds. Gex was estimated at each VD for each goat by using the model in conjunction with experimental measurements. With 0.2 liter VD, Gex increased 40% (P less than 0.01); with 0.6 liter VD, Gex increased 110% between 0 and 2.4 km/h and 5% grade (P less than 0.01) but not between 2.4 and 4.8 km/h. Thus, Gex is increased by VD through a limited range. In goats, increases in Gsys with increased VD result from increases in both Gex and CO2 chemoreceptor feedback. These results are consistent with other experimental treatments that increase the exercise ventilatory response, maintaining constant relative PaCO2 regulation, and suggest that a common mechanism linked to resting ventilatory drive modulates Gex.
Spatial distribution of collagen and elastin fibers in the lungs
Authors: Mercer R. R. , Crapo J. D.
Published: December 2017

Surface tension forces acting on the thin-wall alveolar septa and the collagen-elastin fiber network are major factors in lung parenchymal micromechanics. Quantitative serial section analysis and morphometric evaluations of planar sections were used to determine the spatial location of collagen and elastin fibers in Sprague-Dawley rat and normal human lung samples. A large concentration of connective tissue fibers was located in the alveolar duct wall in both species. For rats, the tissue densities of collagen and elastin fibers located within 10 microns of an alveolar duct were 13 and 9%, respectively. In human lung samples, the tissue densities of collagen and elastin fibers within 20 microns of an alveolar duct were 18 and 16%, respectively. In both species, bands of elastin fibers formed a continuous ring around each alveolar mouth. In human lungs, elastin fibers were found to penetrate significantly deeper into alveolar septal walls than they did in rat lungs. The concentration of connective tissue elements in the alveolar duct walls of both species is consistent with their proposed roles as the principal load-bearing elements of the lung parenchyma.
Stress adaptation and low-frequency impedance of rat lungs
Authors: Peslin R. , Duvivier C. , Bekkari H. , Reichart E. , Gallina C.
Published: December 2017

At transpulmonary pressures (Ptp) of 7-12 cmH2O, pressure-volume hysteresis of isolated cat lungs has been found to be 20-50% larger than predicted from their amount of stress adaptation (J. Hildebrandt, J. Appl. Physiol. 28: 365-372, 1970). This behavior is inconsistent with linear viscoelasticity and has been interpreted in terms of plastoelasticity. We have reinvestigated this phenomenon in isolated lungs from 12 Wistar rats by measuring 1) the changes in Ptp after 0.5-ml step volume changes (initial Ptp of 5 cmH2O) and 2) their response to sinusoidal pressure forcing from 0.01 to 0.67 Hz (2 cmH2O peak to peak, mean Ptp of 6 cmH2O). Stress adaptation curves were found to fit approximately Hildebrandt's logarithmic model [delta Ptp/delta V = A - B.log(t)] from 0.2 to 100 s, where delta V is the step volume change, A and B are coefficients, and t is time. A and B averaged 1.06 +/- 0.11 and 0.173 +/- 0.019 cmH2O/ml, respectively, with minor differences between stress relaxation and stress recovery curves. The response to sinusoidal forcing was characterized by the effective resistance (Re) and elastance (EL). Re decreased from 2.48 +/- 0.41 cmH2O.ml-1.s at 0.01 Hz to 0.18 +/- 0.03 cmH2O.ml-1.s at 0.5 Hz, and EL increased from 0.99 +/- 0.10 to 1.26 +/- 0.20 cmH2O/ml on the same frequency range. These data were analyzed with the frequency-domain version of the same model, complemented by a Newtonian resistance (R) to account for airway resistance: Re = R + B/ (9.2f) and EL = A + 0.25B + B . log 2 pi f, where f is the frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
Measurement of the body composition of living gray seals by hydrogen isotope dilution
Authors: Reilly J. J. , Fedak M. A.
Published: December 2017

The body composition of living gray seals (Halichoerus grypus) can be accurately predicted from a two-step model that involves measurement of total body water (TBW) by 2H or 3H dilution and application of predictive relationships between body components and TBW that were derived empirically by slaughter chemical analysis. TBW was overestimated by both 2HHO and 3HHO dilution; mean overestimates were 2.8 +/- 0.9% (SE) with 2H and 4.0 +/- 0.6% with 3H. The relationships for prediction of total body fat (TBF), protein (TBP), gross energy (TBGE), and ash (TBA) were as follows: %TBF = 105.1 - 1.47 (%TBW); %TBP = 0.42 (%TBW) - 4.75; TBGE (MJ) = 40.8 (mass in kg) - 48.5 (TBW in kg) - 0.4; and TBA (kg) = 0.1 - 0.008 (mass in kg) + 0.05 (TBW in kg). These relationships are applicable to gray seals of both sexes over a wide range of age and body conditions, and they predict the body composition of gray seals more accurately than the predictive equations derived from ringed seals (Pusa hispida) (Stirling et al., Can. J. Zool. 53: 1021-1027, 1975) and from the equation of Pace and Rathbun (J. Biol. Chem. 158: 685-691, 1945), which has been reported to be generally applicable to mammals.
Acute lung injury from mechanical ventilation at moderately high airway pressures
Authors: Tsuno K. , Prato P. , Kolobow T.
Published: December 2017

We have explored adverse pulmonary effects of mechanical ventilation at a peak inspiratory pressure of 30 cmH2O in paralyzed and anesthetized healthy sheep. A control group of eight sheep (group A) was mechanically ventilated with 40% oxygen at a tidal volume of 10 ml/kg, a frequency of 15 breaths/min, a peak inspiratory pressure less than 18 cmH2O, and a positive end-expiratory pressure of 3-5 cmH2O. During the ensuing 48 h, there were no measurable deleterious changes in lung function or arterial blood gases. Another 19 sheep were ventilated with 40% oxygen at a peak inspiratory pressure of 30 cmH2O under a different set of conditions and were randomly assigned to two groups. In group B, the respiratory rate was kept near 4 breaths/min to keep arterial PCO2 in the normal range; in group C, the frequency was kept near 15 breaths/min by including a variable dead space in the ventilator circuit to keep arterial PCO2 near baseline values. There was a progressive deterioration in total static lung compliance, functional residual capacity, and arterial blood gases. After some hours, there were abnormal chest roentgenographic changes. At time of death we found severe pulmonary atelectasis, increased wet lung weight, and an increase in the minimum surface tension of saline lung lavage fluid.
Bronchial circulatory reversal of methacholine-induced airway constriction
Authors: Wagner E. M. , Mitzner W. A.
Published: December 2017

Although a role for the bronchial circulation in clearance of bronchoactive agents has been frequently proposed, experimental evidence is limited. In this study, we determined the importance of bronchial blood flow (QBA) in the recovery from methacholine-(MCh) induced bronchoconstriction. In 10 pentobarbital-anesthetized ventilated sheep, the bronchial branch of the bronchoesophageal artery was cannulated and perfused (0.7 ml.min-1.kg-1) with blood pumped from the femoral artery. MCh was infused directly into the bronchial artery at increasing concentrations (10(-7) to 10(-5) M). MCh infusion caused a concentration-dependent increase in airway resistance at constant QBA. However, the time constant of recovery (TC) from airway constriction after cessation of the MCh infusion was not dependent on the MCh concentration or the magnitude of the increases in airway resistance. When QBA was at 50, 100, and 200% of control level, with constant MCh concentration, TC was 44 +/- 6, 25 +/- 2, and 24 +/- 2 (SE) s at each flow level, respectively. TC at 50% of control QBA was significantly greater than at control QBA (P less than 0.01). Thus the magnitude of QBA can alter the time course of recovery from MCh-induced increases in airway resistance. These results document the importance of QBA in reversing agonist-induced constriction and suggest that an impaired bronchial circulation may contribute to the mechanism of airway hyperreactivity.
Centrifugal intensity and duration as countermeasures to soleus muscle atrophy
Authors: D'Aunno D. S. , Thomason D. B. , Booth F. W.
Published: December 2017

Mechanical acceleration is a countermeasure that may be employed to prevent atrophy of slow-twitch muscle during non-weight bearing. In the present study, daily centrifugation of rats for different durations (1 or 2 h) and at different gravitational intensities (1.5 or 2.6 G) was used to test whether mechanical acceleration could ameliorate the atrophy of the soleus muscle induced by non-weight bearing (tail-traction model). The soleus muscle atrophied 32% during 7 days of non-weight bearing without countermeasures. Centrifugation treatment did not completely prevent atrophy relative to precontrol wet weight of the soleus muscle. Non-weight-bearing groups receiving 2-h daily treatments of 1, 1.5, or 2.6 G had 48, 56, and 65%, respectively, of the atrophy observed in the non-weight-bearing-only group compared with the precontrol group. No evidence was obtained that centrifugation at 2.6 G was more effective than exposure to 1 or 1.5 G as a countermeasure to non-weight-bearing-induced atrophy of the soleus muscle.
In vivo study on medullary H(+)-sensitive neurons
Authors: Kogo N. , Arita H.
Published: December 2017

Using the micro pressure ejection technique, we examined responses of medullary neurons with nonphasic discharges (164 units) to direct application of acidified mock cerebrospinal fluid (CSF, pH 6.85-7.05) in decerebrated spontaneously breathing cats. We found 16 H(+)-sensitive cells; they were excited promptly on application of approximately 500 pl of acidified mock CSF in the vicinity of the neuron under investigation, whereas they were unaffected by microejection of the control mock CSF (pH 7.25-7.60). Of the 16 H(+)-sensitive cells, 10 units were further found to be excited by transcapillary stimulation of the central chemoreceptors by using a method of intravertebral arterial injection of CO2-saturated saline. The discharges increased in a similar time course to that of ventilatory augmentation. Distributions of these 10 specific H(+)-sensitive cells were found in the vicinity of nucleus tractus solitarii as well as deep in the ventrolateral medulla. The present results suggest a possibility that pH-dependent central chemoreceptors, if any, would be located in two distinct medullary regions described in this study.
Hormonal and growth factor responses to heavy resistance exercise protocols
Authors: Kraemer W. J. , Marchitelli L. , Gordon S. E. , Harman E. , Dziados J. E. , Mello R. , Frykman P. , McCurry D. , Fleck S. J.
Published: December 2017

To examine endogenous anabolic hormone and growth factor responses to various heavy resistance exercise protocols (HREPs), nine male subjects performed each of six randomly assigned HREPs, which consisted of identically ordered exercises carefully designed to control for load [5 vs. 10 repetitions maximum (RM)], rest period length (1 vs. 3 min), and total work effects. Serum human growth hormone (hGH), testosterone (T), somatomedin-C (SM-C), glucose, and whole blood lactate (HLa) concentrations were determined preexercise, midexercise (i.e., after 4 of 8 exercises), and at 0, 5, 15, 30, 60, 90, and 120 min postexercise. All HREPs produced significant (P less than 0.05) temporal increases in serum T concentrations, although the magnitude and time point of occurrence above resting values varied across HREPs. No differences were observed for T when integrated areas under the curve (AUCs) were compared. Although not all HREPs produced increases in serum hGH, the highest responses were observed consequent to the H10/1 exercise protocol (high total work, 1 min rest, 10-RM load) for both temporal and time integrated (AUC) responses. The pattern of SM-C increases varied among HREPs and did not consistently follow hGH changes. Whereas temporal changes were observed, no integrated time (AUC) differences between exercise protocols occurred. These data indicate that the release patterns (temporal or time integrated) observed are complex functions of the type of HREPs utilized and the physiological mechanisms involved with determining peripheral circulatory concentrations (e.g., clearance rates, transport, receptor binding). All HREPs may not affect muscle and connective tissue growth in the same manner because of possible differences in hormonal and growth factor release.
The acoustocardiogram: a noninvasive method for measuring heart rate of avian embryos in ovo
Authors: Rahn H. , Poturalski S. A. , Paganelli C. V.
Published: December 2017

A method is presented for measuring the heart rate of avian eggs noninvasively during the last half of incubation. The technique involves briefly placing an egg in tightly sealed vessel containing an inexpensive condenser microphone. The amplified output of the microphone, termed the acoustocardiogram (ACG), is nearly sinusoidal in shape and synchronous with the electrocardiogram. The ACG can also be obtained by mounting the microphone directly on the shell with Plasticine. The method offers advantages over previously described techniques in simplicity, low cost, and noninvasiveness.
Myoelectric manifestations of fatigue in voluntary and electrically elicited contractions
Authors: Merletti R. , Knaflitz M. , De Luca C. J.
Published: December 2017

The time course of muscle fiber conduction velocity and surface myoelectric signal spectral (mean and median frequency of the power spectrum) and amplitude (average rectified and root-mean-square value) parameters was studied in 20 experiments on the tibialis anterior muscle of 10 healthy human subjects during sustained isometric voluntary or electrically elicited contractions. Voluntary contractions at 20% maximal voluntary contraction (MVC) and at 80% MVC with duration of 20 s were performed at the beginning of each experiment. Tetanic electrical stimulation was then applied to the main muscle motor point for 20 s with surface electrodes at five stimulation frequencies (20, 25, 30, 35, and 40 Hz). All subjects showed myoelectric manifestations of muscle fatigue consisting of negative trends of spectral variables and conduction velocity and positive trends of amplitude variables. The main findings of this work are 1) myoelectric signal variables obtained from electrically elicited contractions show fluctuations smaller than those observed in voluntary contractions, 2) spectral variables are more sensitive to fatigue than conduction velocity and the average rectified value is more sensitive to fatigue than the root-mean-square value, 3) conduction velocity is not the only physiological factor affecting spectral variables, and 4) contractions elicited at supramaximal stimulation and frequencies greater than 30 Hz demonstrate myoelectric manifestations of muscle fatigue greater than those observed at 80% MVC sustained for the same time.
Effect of partial spinal cord ablation on exercise hyperpnea in ponies
Authors: Pan L. G. , Forster H. V. , Wurster R. D. , Murphy C. L. , Brice A. G. , Lowry T. F.
Published: December 2017

We addressed the role of spinal afferent information in the exercise hyperpnea. Arterial PCO2 (PaCO2) was assessed in 10 normal ponies during low (1.8 mph 7% or 17% grade) or moderate (6 mph 7% grade) treadmill exercise. After control studies, bilateral spinal ablation (SA) of the dorsolateral sulcus and dorsolateral funiculus at L2 was performed in seven ponies. In normal ponies within the first 90 s of exercise, PaCO2 initially decreased 2.7, 4.1, and 5.2 Torr below rest at the three work loads, respectively (P less than 0.05). PaCO2 thereafter increased toward resting levels but remained 1.1, 2.9, and 4.9 Torr below rest during the steady state of exercise (P less than 0.05). One month post-SA, PaCO2 at the exercise onset decreased 1.5, 2.3, and 5.2 Torr and in the steady state was 0.7, 1.9 and 4.9 Torr below rest at the three work loads, respectively. The changes in PaCO2 from rest to exercise (delta PaCO2) were calculated for each pony in the rest to work transition and between rest and steady-state exercise and then averaged for each group of ponies. After SA, delta PaCO2's were significantly less than pre-SA only in the rest to work transition at the low work loads (P less than 0.05). No differences were found in steady-state delta PaCO2's. The modest attenuation of the exercise hypocapnia at the lower workloads in SA ponies suggests that spinal afferent information does play some role in the exercise hyperpnea in awake ponies. Our data probably underestimate this role because our SA surgery is only a partial deafferentation.
Effects of a 36-hour fast on human endurance and substrate utilization
Authors: Zinker B. A. , Britz K. , Brooks G. A.
Published: December 2017

To determine if prolonged fasting affects substrate utilization and endurance time, seven trained men exercised to exhaustion on a cycle ergometer at 50% maximum oxygen consumption (VO2max) in an overnight-fasted [postabsorptive (PA)] state and after a 36-h fast (F). Fasting produced significant elevations in the resting concentrations of blood free fatty acids (FFA; 1.16 +/- 0.05 vs. 0.56 +/- 0.06 mM, F vs. PA, respectively, a 107% increase), beta-hydroxybutyrate (beta-OH, 2.06 +/- 0.66 vs. 0.15 +/- 0.06 mM, a 1,270% increase), and glycerol (0.12 +/- 0.03 vs. 0.04 +/- 0.01 mM, a 200% increase), with a significant decline in glucose (79.79 +/- 2.12 vs. 98.88 +/- 3.11 mg/dl, a 19% decrease). Exercise in the F trial increased FFA, decreased glucose, and significantly elevated beta-OH and glycerol over the PA trial. There was no difference in blood glucose concentration between trials at exhaustion. However, F produced a significant decrement in exercise endurance time compared with the PA trial (88.9 +/- 18.3 vs. 144.4 +/- 22.6 min, F vs. PA, a 38% decrease). Based on the respiratory exchange ratio, fasting led to a greater utilization of lipids during rest and exercise. It was concluded that 1) a 36-h fast significantly altered substrate utilization at rest and throughout exercise to exhaustion, 2) glucose levels do not appear to be the single determinant of time to exhaustion in submaximal exercise, and 3) despite the apparent sparing of carbohydrate utilization with the 36-h fast, endurance performance was significantly decreased.