bluuebunny/crossref_metadata_2025 huggingface dataset:
Urethan anesthesia protects rats against lethal endotoxemia and reduces TNF-α release
Authors: Kotanidou Anastasia , Choi Augustine M. K. , Winchurch Richard A. , Otterbein Leo , Fessler Henry E.
Published: December 2017

Kotanidou, Anastasia, Augustine M. K. Choi, Richard A. Winchurch, Leo Otterbein, and Henry E. Fessler. Urethan anesthesia protects rats against lethal endotoxemia and reduces TNF-α release. J. Appl. Physiol. 81(5): 2304–2311, 1996.—Urethan is a commonly used animal anesthetic for nonrecovery laboratory surgery. However, urethan has diverse biological effects that may complicate the interpretation of experimental findings. This study examined the effect of urethan on the response to an intravenous bolus of lipopolysaccharide (LPS; 30 mg/kg) in rats. In instrumented rats, urethan (1.2 gm/kg ip) completely prevented the fall in arterial pressure immediately after LPS administration but did not prevent late cardiovascular collapse. In uninstrumented rats, urethan also attenuated indexes of organ injury measured 4 h after LPS administration, including mural bowel hemorrhage, hemoconcentration, hypoglycemia, metabolic acidosis, and lung myeloperoxidase activity, a measure of neutrophil sequestration. The peak increase in tumor necrosis factor-α (TNF-α) 90 min after LPS administration was reduced 88% by urethan (2,060 ± 316 vs. 16,934 ± 847 pg/ml; P < 0.001). In uninstrumented animals, urethan at 1.2 gm/kg reduced the 90% mortality rate of a lethal dose of LPS to 0–10% when given up to 24 h before LPS administration but did not reduce mortality when given 2 h after LPS. Urethan neither directly bound LPS by Limulus assay nor inhibited LPS-stimulated TNF-α mRNA expression in cultured mouse peritoneal macrophages, but TNF-α mRNA expression was suppressed by serum from a urethan-treated rat. Moreover, rauwolscine, which shares α2-adrenoceptor-blocking activity with urethan, also prevented death from a subsequent 90% lethal dose LPS bolus. We conclude that urethan or its metabolites protect against LPS, in part, by reducing TNF-α release and speculate that this may be mediated by α2-adrenoceptors. These actions of urethan make it an undesirable anesthetic agent for in vivo studies of sepsis or LPS.
Fluid and electrolyte hormonal responses to exercise and acute plasma volume expansion
Authors: Grant S. M. , Green H. J. , Phillips S. M. , Enns D. L. , Sutton J. R.
Published: December 2017

Grant, S. M., H. J. Green, S. M. Phillips, D. L. Enns, and J. R. Sutton. Fluid and electrolyte hormonal responses to exercise and acute plasma volume expansion. J. Appl. Physiol. 81(6): 2386–2392, 1996.—To investigate the effect of acute graded increases in plasma volume (PV) on fluid and regulatory hormone levels, eight untrained men (peak aerobic power 45.2 ± 2.2 ml ⋅ kg−1 ⋅ min−1) performed prolonged cycle exercise (46 ± 4% maximal aerobic power on three occasions, namely, with no PV expansion (Con) and after 14% (Low) and 21% (High) expansions, respectively. The exercise plasma levels of aldosterone (Aldo), arginine vasopressin (AVP), and atrial natriuretic peptide (ANP) were all altered by acute PV increases. A pronounced blunting ( P < 0.05) of the Aldo response during exercise was observed, the magnitude of which was directly related to the amount of hypervolemia (Con < Low < High). At 120 min of exercise, Aldo concentrations were 660 ± 71, 490 ± 85, and 365 ± 78 pg/ml for Con, Low, and High conditions, respectively. In contrast, the lower AVP and the higher ANP observed during exercise appeared to be due to the effect of PV expansion on resting concentrations. Because osmolality did not vary among conditions, the results indicate that PV represents an important primary stimulus in the response of Aldo to exercise. The lower exercise blood concentrations of both epinephrine and norepinephrine observed with PV expansion would suggest that a lower sympathetic drive may be implicated at least in the lower Aldo responses.
Effect of hypoxia on abdominal motor unit activities in spontaneously breathing cats
Authors: Mateika J. H. , Essif E. , Fregosi R. F.
Published: December 2017

Mateika, J. H., E. Essif, and R. F. Fregosi. Effect of hypoxia on abdominal motor unit activities in spontaneously breathing cats. J. Appl. Physiol. 81(6): 2428–2435, 1996.—These experiments were designed to examine the behavior of external oblique motor units in spontaneously breathing cats during hypoxia and to estimate the contribution of recruitment and rate coding to changes in the integrated external oblique electromyogram (iEMG). Motor unit activities in the external oblique muscle were identified while the cats expired against a positive end-expiratory pressure (PEEP) of 1–2.5 cmH2O. After localization of unit activity, PEEP was removed, and recordings were made continuously for 3–4 min during hyperoxia, normoxia, and hypoxia. A total of 35 single motor unit activities were recorded from 10 cats. At each level of fractional concentration of end-tidal O2, the motor unit activity was characterized by an abrupt increase in mean discharge frequency, at ∼30% of expiratory time, which then continued to increase gradually or remained constant before declining abruptly at the end of expiration. The transition from hyperoxia to normoxia and hypoxia was accompanied by an increase in the number of active motor units (16 of 35, 20 of 35, and 29 of 35, respectively) and by an increase in the mean discharge frequency of those units active during hyperoxia. The changes in motor unit activity recorded during hypoxia were accompanied by a significant increase in the average peak amplitude of the abdominal iEMG. Linear regression analysis revealed that motor unit rate coding was responsible for close to 60% of the increase in peak iEMG amplitude. The changes in abdominal motor unit activity and the external oblique iEMG that occurred during hypoxia were abolished if the arterial [Formula: see text] was allowed to fall. We conclude that external oblique motor units are activated during the latter two-thirds of expiration and that rate coding and recruitment contribute almost equally to the increase in expiratory muscle activity that occurs with hypoxia. In addition, the excitation of abdominal motor units during hypoxia is critically dependent on changes in CO2 and/or tidal volume.
Interaction of leg stiffness and surface stiffness during human hopping
Authors: Ferris Daniel P. , Farley Claire T.
Published: December 2017

Ferris, Daniel P., and Claire T. Farley. Interaction of leg stiffness and surface stiffness during human hopping. J. Appl. Physiol. 82(1): 15–22, 1997.—When mammals run, the overall musculoskeletal system behaves as a single linear “leg spring.” We used force platform and kinematic measurements to determine whether leg spring stiffness ( kleg) is adjusted to accommodate changes in surface stiffness ( ksurf) when humans hop in place, a good experimental model for examining adjustments to klegin bouncing gaits. We found that klegwas greatly increased to accommodate surfaces of lower stiffnesses. The series combination of klegand ksurf[total stiffness ( ktot)] was independent of ksurfat a given hopping frequency. For example, when humans hopped at a frequency of 2 Hz, they tripled their klegon the least stiff surface ( ksurf= 26.1 kN/m; kleg= 53.3 kN/m) compared with the most stiff surface ( ksurf= 35,000 kN/m; kleg= 17.8 kN/m). Values for ktotwere not significantly different on the least stiff surface (16.7 kN/m) and the most stiff surface (17.8 kN/m). Because of the klegadjustment, many aspects of the hopping mechanics (e.g., ground-contact time and center of mass vertical displacement) remained remarkably similar despite a >1,000-fold change in ksurf. This study provides insight into how klegadjustments can allow similar locomotion mechanics on the variety of terrains encountered by runners in the natural world.
Relationship between maximum aerobic power and resting metabolic rate in young adult women
Authors: Smith D. A. , Dollman J. , Withers R. T. , Brinkman M. , Keeves J. P. , Clark D. G.
Published: December 2017

Smith, D. A., J. Dollman, R. T. Withers, M. Brinkman, J. P. Keeves, and D. G. Clark. Relationship between maximum aerobic power and resting metabolic rate in young adult women. J. Appl. Physiol. 82(1): 156–163, 1997.—The literature is inconclusive as to the chronic effect of aerobic exercise on resting metabolic rate (RMR), and furthermore there is a scarcity of data on young women. Thirty-four young women exhibiting a wide range of aerobic fitness [maximum aerobic power (V˙o2 max) = 32.3–64.8 ml ⋅ kg−1⋅ min−1] were accordingly measured for RMR by the Douglas bag method, treadmillV˙o2 max, and fat-free mass (FFM) by using Siri’s three-compartment model. The interclass correlation ( n = 34) between RMR (kJ/h) and V˙o2 max(ml ⋅ kg−1⋅ min−1) was significant ( r = 0.39, P < 0.05). However, this relationship lost statistical significance when RMR was indexed to FFM and when partial correlation analysis was used to control for FFM differences. Furthermore, multiple linear-regression analysis indicated that only FFM emerged as a significant predictor of RMR (kJ/h). When high- ( n = 12) and low-fitness ( n = 12) groups were extracted from the cohort on the basis ofV˙o2 maxscores, independent t-tests revealed significant between-group differences ( P < 0.05) for RMR (kJ ⋅ kg−1⋅ h−1) andV˙o2 max(ml ⋅ kg−1⋅ min−1) but not for RMR (kJ/h), RMR (kJ ⋅ kg FFM−1⋅ h−1), and FFM. Analysis of covariance of RMR (kJ/h) with FFM as the covariate also showed no significant difference ( P = 0.56) between high- and low-fitness groups. Thus the results suggest that 1) FFM accounts for most of the differences in RMR between subjects of varyingV˙o2 maxvalues and 2) the RMR per unit of FFM in young healthy women is unrelated toV˙o2 max.
Sources of error ina- aD O 2 calculated from blood stored in plastic and glass syringes
Authors: Wu Eugene Y. , Barazanji Khalid W. , Johnson Robert L.
Published: December 2017

Wu, Eugene Y., Khalid W. Barazanji, and Robert L. Johnson, Jr. Sources of error in a-aDO2 calculated from blood stored in plastic and glass syringes. J. Appl. Physiol. 82(1): 196–202, 1997.—We studied the effects of time delay on blood gases, pH, and base excess in blood stored in glass and plastic syringes on ice and the effects of resulting errors on calculated alveolar-to-arterial [Formula: see text] difference (a-[Formula: see text]). Matched samples of dog whole blood were tonometered with gas mixtures of 5% CO2-12% O2-83% N2 ( mixture A), 10% CO2-5% O2-85% N2 ( mixture B), and 2.88% CO2-4% O2-93.12% N2 ( mixture C). Tonometered blood samples were transferred to 5-ml glass (5G), 5-ml plastic (5P), and 3-ml plastic (3P) syringes and stored on ice. Blood gases were measured every 1 h up to 6 h. In 5G,[Formula: see text] progressively decreased in blood tonometered with mixture A but rose in blood tonometered with mixtures B and C. O2 saturation progressively fell in all cases. In 5G, blood [Formula: see text]progressively rose regardless of which gas mixture was used, and pH as well as base excess progressively fell. The rise in[Formula: see text] was faster in plastic than in glass syringes, and O2 saturation always rose in plastic syringes. Differences between storage in plastic and glass syringes on [Formula: see text] change were greatest when initial blood [Formula: see text] was highest ( mixture A). At the highest[Formula: see text], O2 exchange was faster in 3P than in 5P. The rise of [Formula: see text] was just as fast in plastic as in glass syringes, but in both the rise in[Formula: see text] was faster at a higher initial[Formula: see text] ( mixture B) than at lower initial[Formula: see text] ( mixtures B and C). Rates of[Formula: see text] and[Formula: see text] change in matched samples were significantly faster in 3P than in 5P. Errors due to rises in[Formula: see text] and[Formula: see text] cause additive errors in calculateda-[Formula: see text], and when blood is stored in plastic syringes for >1 h significant errors result. Errors are greater in normoxic blood, in which estimateda-[Formula: see text]decreased by >10 Torr after 6 h on ice in plastic syringes, than in hypoxic blood.
Modulation of myosin isoform expression by mechanical loading: role of stimulation frequency
Authors: Caiozzo Vincent J. , Baker Michael J. , Baldwin Kenneth M.
Published: December 2017

Caiozzo, Vincent J., Michael J. Baker, and Kenneth M. Baldwin. Modulation of myosin isoform expression by mechanical loading: role of stimulation frequency. J. Appl. Physiol. 82(1): 211–218, 1997.—This study tested the hypothesis that mechanical loading, not stimulation frequency per se, plays a key role in determining the plasticity of myosin heavy chain (MHC) protein isoform expression in muscle undergoing resistance training. Female Sprague-Dawley rats were randomly assigned to resistance-training programs that employed active 1) shortening ( n = 7) or 2) lengthening contractions ( n = 8). The medial gastrocnemius (MG) muscles in each group trained under loading conditions that approximated 90–95% of maximum isometric tetanic tension but were stimulated at frequencies of 100 and ∼25 Hz, respectively. Lengthening and shortening contractions were produced by using a Cambridge ergometer system. The MG muscles trained every other day, performing a total of 16 training sessions. Both training programs produced significant ( P < 0.01) and similar reductions in the fast type IIB MHC protein isoform in the white MG muscle, reducing its relative content to ∼50% of the total MHC protein isoform pool. These changes were accompanied by increases in the relative content of the fast type IIX MHC protein isoform that were of similar magnitude for both groups. The results of this study clearly demonstrate that stimulation frequency does not play a key role in modulating MHC isoform alterations that result from high-resistance training.
Effect of N ω-nitro-l-arginine on ventilatory response to hypercapnia in anesthetized cats
Authors: Teppema Luc , Berkenbosch Aad , Olievier Cees
Published: December 2017

Teppema, Luc, Aad Berkenbosch, and Cees Olievier Effect of N ω-nitro-l-arginine on ventilatory response to hypercapnia in anesthetized cats. J. Appl. Physiol. 82(1): 292–297, 1997.—The effect of intravenous administration of 40 mg/kg N ω-nitro-l-arginine (l-NNA), an inhibitor of the synthesis of nitric oxide (NO), on the ventilatory response to CO2 was studied in anesthetized cats. The ventilatory response to CO2 was assessed during normoxia by applying square-wave changes in end-tidal[Formula: see text] of ∼1 kPa. Each CO2 response was separated into a fast peripheral and slow central component characterized by a CO2 sensitivity (Spand Sc, respectively), time constant, time delay, and an offset (apneic threshold). l-NNA reduced Sp, Sc, and the apneic threshold significantly by ∼30%. However, the ratio Sp/Scwas not changed. It is argued that the reduction in Sp and Sc, Sp/Scremaining constant, may be due to a potent inhibitory action ofl-NNA on the brain stem respiratory-integrating centers and on the neuromechanical link between these centers and respiratory movements. It is concluded that NO plays an important role in the control of breathing.
Ventilation and metabolism among rat strains
Authors: Strohl Kingman P. , Thomas Agnes J. , St. Jean Pamela , Schlenker Evelyn H. , Koletsky Richard J. , Schork Nicholas J.
Published: December 2017

Strohl, Kingman P., Agnes J. Thomas, Pamela St. Jean, Evelyn H. Schlenker, Richard J. Koletsky, and Nicholas J. Schork.Ventilation and metabolism among rat strains. J. Appl. Physiol. 82(1): 317–323, 1997.—We examined ventilation and metabolism in four rat strains with variation in traits for body weight and/or blood pressure regulation. Sprague-Dawley [SD; 8 males (M), 8 females (F)], Brown Norway (BN; 10 M, 11 F), and Zucker (Z; 11 M, 12 F) rats were compared with Koletsky (K; 11 M, 11 F) rats. With the use of noninvasive plethysmography, frequency, tidal volume, minute ventilation (V˙e), O2 consumption, and CO2 production were derived at rest during normoxia (room air) and during the 5th minute of exposure to each of the following: hyperoxia (100% O2), hypoxia (10% O2-balance N2), and hypercapnia (7% CO2-balance O2). Statistical methods probed for strain and sex effects, with covariant analysis by body weight, length, and body mass. During resting breathing, strain effects were found with respect to both frequency (BN, Z > K, SD) and tidal volume (SD > BN, Z) but not to V˙e. Sex influenced frequency (F > M) alone. Z rats had higher values for O2 consumption, CO2 production, and respiratory quotient than the other three strains, with no independent effect by sex. During hyperoxia, frequency was greater in BN and Z than in SD or K rats; SD rats had a larger tidal volume than BN or Z rats; Z rats had a greater V˙e than K rats; and M had a larger tidal volume than F. Strain differences persisted during hypercapnia, with Z rats exhibiting the highest frequency andV˙e values. During hypoxic exposure, strain effects were found to influenceV˙e (SD > K, Z), frequency (BN > K), and tidal volume (SD > BN, K, Z). Body mass was only a modest predictor of V˙e during normoxia, of both V˙e and tidal volume with hypoxia, hypercapnia, or hyperoxia, and of frequency during hypercapnia. We conclude that strain of rats, more than their body mass or sex, has major and different influences on metabolism, the pattern and level of ventilation during air breathing, and ventilation during acute exposure to hypercapnia or hypoxia.
Airway smooth muscle orientation in intraparenchymal airways
Authors: Lei M. , Ghezzo H. , Chen M. F. , Eidelman D. H.
Published: December 2017

Lei, M., H. Ghezzo, M. F. Chen, and D. H. Eidelman.Airway smooth muscle orientation in intraparenchymal airways. J. Appl. Physiol. 82(1): 70–77, 1997.—Airway smooth muscle (ASM) shortening is the central event leading to bronchoconstriction. The degree to which airway narrowing occurs as a consequence of shortening is a function of both the mechanical properties of the airway wall as well as the orientation of the muscle fibers. Although the latter is theoretically important, it has not been systematically measured to date. The purpose of this study was to determine the angle of orientation of ASM (θ) in normal lungs by using a morphometric approach. We analyzed the airway tree of the left lower lobes of four cats and one human. All material was fixed with 10% buffered Formalin at a pressure of 25 cmH2O for 48 h. The fixed material was dissected along the airway tree to permit isolation of generations 4–18 in the cats and generations 5–22 in the human specimen. Each airway generation was individually embedded in paraffin. Five-micrometer-thick serial sections were cut parallel to the airway long axis and stained with hematoxylin-phloxine-saffron. Each block yielded three to five sections containing ASM. To determine θ, we measured the orientation of ASM nuclei relative to the transverse axis of the airway by using a digitizing tablet and a light microscope (×250) equipped with a drawing tube attachment. Inspection of the sections revealed extensive ASM crisscrossing without a homogeneous orientation. The θ was clustered between −20° and 20° in all airway generations and did not vary much between generations in any of the cats or in the human specimen. When θ was expressed without regard to sign, the mean values were 13.2° in the cats and 13.1° in the human. This magnitude of obliquity is not likely to result in physiologically important changes in airway length during bronchoconstriction.
Effects of unilateral lesions of retrotrapezoid nucleus on breathing in awake rats
Authors: Akilesh Manjapra R. , Kamper Matthew , Li Aihua , Nattie Eugene E.
Published: December 2017

Akilesh, Manjapra R., Matthew Kamper, Aihua Li, and Eugene E. Nattie. Effects of unilateral lesions of retrotrapezoid nucleus on breathing in awake rats. J. Appl. Physiol. 82(2): 469–479, 1997.—In anesthetized rats, unilateral retrotrapezoid nucleus (RTN) lesions markedly decreased baseline phrenic activity and the response to CO2 (E. E. Nattie and A. Li. Respir. Physiol. 97: 63–77, 1994). Here we evaluate the effects of such lesions on resting breathing and on the response to hypercapnia and hypoxia in unanesthetized awake rats. We made unilateral injections [24 ± 7 (SE) nl] of ibotenic acid (IA; 50 mM), an excitatory amino acid neurotoxin, in the RTN region ( n = 7) located by stereotaxic coordinates and by field potentials induced by facial nerve stimulation. Controls ( n = 6) received RTN injections (80 ± 30 nl) of mock cerebrospinal fluid. A second control consisted of four animals with IA injections (24 ± 12 nl) outside the RTN region. Injected fluorescent beads allowed anatomic identification of lesion location. Using whole body plethysmography, we measured ventilation in the awake state during room air, 7% CO2 in air, and 10% O2 breathing before and for 3 wk after the RTN injections. There was no statistically significant effect of the IA injections on resting room air breathing in the lesion group compared with the control groups. We observed no apnea. The response to 7% CO2 in the lesion group compared with the control groups was significantly decreased, by 39% on average, for the final portion of the 3-wk study period. There was no lesion effect on the ventilatory response to 10% O2. In this unanesthetized model, other areas suppressed by anesthesia, e.g., the reticular activating system, hypothalamus, and perhaps the contralateral RTN, may provide tonic input to the respiratory centers that counters the loss of RTN activity.
Enlargement of glycogen store in rat liver and muscle by fructose-diet intake and exercise training
Authors: Murakami Taro , Shimomura Yoshiharu , Fujitsuka Noriaki , Sokabe Masahiro , Okamura Koji , Sakamoto Shuichi
Published: December 2017

Murakami, Taro, Yoshiharu Shimomura, Noriaki Fujitsuka, Masahiro Sokabe, Koji Okamura, and Shuichi Sakamoto. Enlargement of glycogen store in rat liver and muscle by fructose-diet intake and exercise training. J. Appl. Physiol.82(3): 772–775, 1997.—This study investigated the effect of long-term intake of a fructose diet and exercise training on glycogen content in liver and skeletal muscle in female rats. Thirty-six rats (8 wk old) were divided into two dietary groups and were fed with a control (chow) diet or fructose diet (containing 20% fructose) for 12 wk. During this period, one-half of the rats in each dietary group were trained by using a motor-driven treadmill (running speed of 25 m/min and duration of 90 min/day, 5 days/wk). The liver glycogen was increased by intake of a fructose diet and exercise training, and the content was in the following order: control-diet and sedentary rats < fructose-diet and sedentary rats ≤ control-diet and trained rats < fructose-diet and trained rats in the ratio of 1:3.4:3.6:5.0. The glycogen content in gastrocnemius muscle showed the same trend as that in liver; the ratio was 1:1.3:1.3:1.6. These results indicate that both long-term intake of the fructose diet and exercise training synergistically increased glycogen in both tissues.
Ventilation inhomogeneity in oleic acid-induced pulmonary edema
Authors: Tsang John Y. C. , Emery Michael J. , Hlastala Michael P.
Published: December 2017

Tsang, John Y. C., Michael J. Emery, and Michael P. Hlastala. Ventilation inhomogeneity in oleic acid-induced pulmonary edema. J. Appl. Physiol.82(4): 1040–1045, 1997.—Oleic acid causes permeability pulmonary edema in the lung, resulting in impairment of gas-exchange and ventilation-perfusion heterogeneity and mismatch. Previous studies have shown that by using the multiple-breath helium washout (MBHW) technique, ventilation inhomogeneity (VI) can be quantitatively partitioned into two components, i.e., convective-dependent inhomogeneity (cdi) and diffusive-convective-dependent inhomogeneity (dcdi). Changes in VI, as represented by the normalized slope of the phase III alveolar plateau, were studied for 120 min in five anesthetized mongrel dogs that were ventilated under paralysis by a constant-flow linear motor ventilator. These animals received oleic acid (0.1 mg/kg) infusion into the right atrium at t = 0. MBHWs were done in duplicate for 18 breaths every 40 min afterward. Three other dogs that received only normal saline served as controls. The data show that, after oleic acid infusion, dcdi, which represents VI in peripheral airways, is responsible for the increasing total VI as lung water accumulates progressively over time. The cdi, which represents VI between larger conductive airways, remains relatively constant throughout. This observation can be explained by increases in the heterogeneity of tissue compliance in the periphery, distal airway closure, or by decreases in ventilation through collateral channels.
Contributions of pulmonary perfusion and ventilation to heterogeneity in V˙a/Q˙measured by PET
Authors: Treppo Steven , Mijailovich Srboljub M. , Venegas José G.
Published: December 2017

Treppo, Steven, Srboljub M. Mijailovich, and José G. Venegas. Contributions of pulmonary perfusion and ventilation to heterogeneity in V˙a/Q˙measured by PET. J. Appl. Physiol. 82(4): 1163–1176, 1997. To estimate the contributions of the heterogeneity in regional perfusion (Q˙) and alveolar ventilation (V˙a) to that of ventilation-perfusion ratio (V˙a/Q˙), we have refined positron emission tomography (PET) techniques to image local distributions of Q˙ andV˙a per unit of gas volume content (sQ˙ and sV˙a, respectively) and Va/Q˙ in dogs. sV˙a was assessed in two ways: 1) the washout of 13NN tracer after equilibration by rebreathing (sV˙a i), and 2) the ratio of an apneic image after a bolus intravenous infusion of 13NN-saline solution to an image collected during a steady-state intravenous infusion of the same solution (sV˙a p). sV˙a p was systematically higher than sV˙a i in all animals, and there was a high spatial correlation between sQ˙ and sV˙a p in both body positions (mean correlation was 0.69 prone and 0.81 supine) suggesting that ventilation to well-perfused units was higher than to those poorly perfused. In the prone position, the spatial distributions of sQ˙, sV˙a p, and V˙a/Q˙ were fairly uniform with no significant gravitational gradients; however, in the supine position, these variables were significantly more heterogeneous, mostly because of significant gravitational gradients (15, 5.5, and −10%/cm, respectively) accounting for 73, 33, and 66% of the corresponding coefficient of variation (CV)2 values. We conclude that, in the prone position, gravitational forces in blood and lung tissues are largely balanced out by dorsoventral differences in lung structure. In the supine position, effects of gravity and structure become additive, resulting in substantial gravitational gradients in sQ˙ and sV˙a p, with the higher heterogeneity inV˙a/Q˙ caused by a gravitational gradient in sQ˙, only partially compensated by that in sV˙a.
Doublet potentiation during eccentric and concentric contractions of cat soleus muscle
Authors: Sandercock Thomas G. , Heckman C. J.
Published: December 2017

Sandercock, Thomas G., and C. J. Heckman. Doublet potentiation during eccentric and concentric contractions of cat soleus muscle. J. Appl. Physiol. 82(4): 1219–1228, 1997.—The addition of an extra stimulus pulse, or doublet, at the beginning of a low-frequency train has been shown to substantially increase isometric force. This study examined the effects of muscle movement on this doublet potentiation. The soleus muscles of anesthetized cats were stimulated at 10 Hz for 1 s, with and without an added doublet (0.01-s interval). Isovelocity releases reduced but did not eliminate peak and early doublet potentiation (average 0.0–0.5 s after the doublet). Large releases, >0.4 s after the doublet, completely abolished sustained doublet potentiation (average 0.5–1.0 s after the doublet). In contrast, early isovelocity stretches boosted peak doublet potentiation. Yet, large stretches later in the stimulus almost completely eliminated sustained doublet potentiation. This suggests that a different mechanism is responsible for early and sustained doublet potentiations. Because peak and average initial doublet potentiation were not strongly affected by movement, doublets still offer a viable control strategy to increase force during movement while minimizing the number of stimulus pulses.
Mechanical advantage of sternomastoid and scalene muscles in dogs
Authors: Legrand Alexandre , Ninane Vincent , De Troyer André
Published: December 2017

Legrand, Alexandre, Vincent Ninane, and André De Troyer. Mechanical advantage of sternomastoid and scalene muscles in dogs. J. Appl. Physiol. 82(5): 1517–1522, 1997.—Theoretical studies have led to the prediction that the maximal effect of a given respiratory muscle on airway opening pressure (Pao) is the product of muscle mass, the maximal active muscle tension per unit cross-sectional area, and the fractional change in muscle length per unit volume increase of the relaxed chest wall. It has previously been shown that the parasternal intercostals behave in agreement with this prediction (A. De Troyer, A. Legrand, and T. A. Wilson. J. Physiol. (Lond.) 495: 239–246, 1996; A. Legrand, T. A. Wilson, and A. De Troyer. J. Appl. Physiol. 80: 2097–2101, 1996). In the present study, we have tested the prediction further by measuring the response to passive inflation and the pressure-generating ability of the sternomastoid and scalene muscles in eight anesthetized dogs. With 1-liter passive inflation, the sternomastoids and scalenes shortened by 2.03 ± 0.17 and 5.98 ± 0.43%, respectively, of their relaxation length ( P < 0.001). During maximal stimulation, the two muscles caused similar falls in Pao. However, the sternomastoids had greater mass such that the change in Pao (ΔPao) per unit muscle mass was −0.19 ± 0.02 cmH2O/g for the scalenes and only −0.07 ± 0.01 cmH2O/g for the sternomastoids ( P < 0.001). After extension of the neck, there was a reduction in both the muscle shortening during passive inflation and the fall in Pao during stimulation. The ΔPao per unit muscle mass was thus closely related to the change in length; the slope of the relationship was 3.1. These observations further support the concept that the fractional changes in length of the respiratory muscles during passive inflation can be used to predict their pressure-generating ability.
Partitioning airway and lung tissue resistances in humans: effects of bronchoconstriction
Authors: Kaczka David W. , Ingenito Edward P. , Suki Bela , Lutchen Kenneth R.
Published: December 2017

Kaczka, David W., Edward P. Ingenito, Bela Suki, and Kenneth R. Lutchen. Partitioning airway and lung tissue resistances in humans: effects of bronchoconstriction. J. Appl. Physiol. 82(5): 1531–1541, 1997.—The contribution of airway resistance (Raw) and tissue resistance (Rti) to total lung resistance (R l ) during breathing in humans is poorly understood. We have recently developed a method for separating Raw and Rti from measurements of Rland lung elastance (El) alone. In nine healthy, awake subjects, we applied a broad-band optimal ventilator waveform (OVW) with energy between 0.156 and 8.1 Hz that simultaneously provides tidal ventilation. In four of the subjects, data were acquired before and during a methacholine (MCh)-bronchoconstricted challenge. The Rland Eldata were first analyzed by using a model with a homogeneous airway compartment leading to a viscoelastic tissue compartment consisting of tissue damping and elastance parameters. Our OVW-based estimates of Raw correlated well with estimates obtained by using standard plethysmography and were responsive to MCh-induced bronchoconstriction. Our data suggest that Rti comprises ∼40% of total Rlat typical breathing frequencies, which corresponds to ∼60% of intrathoracic Rl. During mild MCh-induced bronchoconstriction, Raw accounts for most of the increase in Rl. At high doses of MCh, there was a substantial increase in Rlat all frequencies and in El at higher frequencies. Our analysis showed that both Raw and Rti increase, but most of the increase is due to Raw. The data also suggest that widespread peripheral constriction causes airway wall shunting to produce additional frequency dependence in El.
Fractional changes in lung capillary blood volume and oxygen saturation during the cardiac cycle in rabbits
Authors: Topulos George P. , Lipsky Nina R. , Lehr John L. , Rogers Rick A. , Butler James P.
Published: December 2017

Topulos, George P., Nina R. Lipsky, John L. Lehr, Rick A. Rogers, and James P. Butler. Fractional changes in lung capillary blood volume and oxygen saturation during the cardiac cycle in rabbits. J. Appl. Physiol. 82(5): 1668–1676, 1997.—Changes in local pulmonary capillary blood volume (Vc) and oxygen saturation (S) have been difficult to measure in live animals. By utilizing the differences in absorption of light at two wavelengths (650 and 800 nm), we estimated the fractional change in Vc and S during the course of the cardiac cycle in eight anesthetized, ventilated rabbits at low and high lung volumes. Observations were made of the pattern of diffusely backscattered light, from an ∼1-cm3 volume of lung illuminated with a point source placed on the pleural surface through a thoracotomy. At low lung volume, the fractional change in Vc was ∼13%, the change in S was ∼4.6%, and the mean S was close to 77%. The fluctuations in Vc and S lagged behind peak systemic blood pressure by about one-fifth and three-fifths of a cycle, respectively. At high lung volume, there were no important fluctuations in Vc or S, and the mean S was ∼82%. These results are consistent with fluctuations in pulmonary capillary pressure and gas exchange over the cardiac cycle, and with decreasing capillary compliance with increasing lung volume.
Increase in percutaneous muscle biopsy yield with a suction-enhancement technique
Authors: Hennessey James V. , Chromiak Joseph A. , Dellaventura Shirley , Guertin Jennifer , Maclean David B.
Published: December 2017

Hennessey, James V., Joseph A. Chromiak, Shirley DellaVentura, Jennifer Guertin, and David B. MacLean. Increase in percutaneous muscle biopsy yield with a suction-enhancement technique. J. Appl. Physiol. 82(6): 1739–1742, 1997.—The percutaneous muscle biopsy technique is used in clinical practice and biomedical research. We developed a new enhanced-suction technique [suction-enhancing nipples (SEN)] and compared it with techniques currently in practice by assessing biopsy yields on anesthetized pigs. We applied the enhanced-suction technique to human subjects participating in a clinical trial. In the pig, there was a mean 91% (1.9-fold) increase in the size of the samples obtained with the 4-mm needle when SEN was used and a mean 507% (fivefold) increase in sample size when the SEN was applied to the 6-mm needles. Nine passes of the 6-mm needle with SEN obtained from five consecutive human subjects yielded a mean individual sample size of 109.4 mg or 219.4 mg per needle pass when using the double-sample technique. Adequate tissue samples for histomorphometric and other analyses were obtained in all samples obtained. The percutaneous muscle biopsy performed with enhanced suction using inexpensive, readily available nipples enhances tissue yield two- to fivefold.
Responses of group III and IV muscle afferents to dynamic exercise
Authors: Adreani Christine M. , Hill Janeen M. , Kaufman Marc P.
Published: December 2017

Adreani, Christine M., Janeen M. Hill, and Marc P. Kaufman.Responses of group III and IV muscle afferents to dynamic exercise. J. Appl. Physiol. 82(6): 1811–1817, 1997.—Tetanic contraction of hindlimb skeletal muscle, induced by electrical stimulation of either ventral roots or peripheral nerves, is well known to activate group III and IV afferents. Nevertheless, the effect of dynamic exercise on the discharge of these thin fiber afferents is unknown. To shed some light on this question, we recorded in decerebrate cats the discharge of 24 group III and 10 group IV afferents while the mesencephalic locomotor region (MLR) was stimulated electrically. Each of the 34 afferents had their receptive fields in the triceps surae muscles. Stimulation of the MLR for 1 min caused the triceps surae muscles to contract rhythmically, an effect induced by an α-motoneuron discharge pattern and recruitment order almost identical to that occurring during dynamic exercise. Eighteen of the 24 group III and 8 of the 10 group IV muscle afferents were stimulated by MLR stimulation. The oxygen consumption of the dynamically exercising triceps surae muscles was increased by 2.5-fold over their resting levels. We conclude that low levels of dynamic exercise stimulate group III and IV muscle afferents.
Involvement of the fastigial nuclei in vagally mediated respiratory responses
Authors: Xu Fadi , Frazier Donald T.
Published: December 2017

Xu, Fadi, and Donald T. Frazier. Involvement of the fastigial nuclei in vagally mediated respiratory responses. J. Appl. Physiol. 82(6): 1853–1861, 1997.—Previous studies have demonstrated that the cerebellum, especially the fastigial nucleus (FN), is capable of modulating respiratory responses to chemical and mechanical stimuli. Because there is evidence to show projections from vagal afferents to the FN, the goal of this study was to determine the role of the FN in the respiratory reflexes elicited by activation of vagal afferents. Experiments were performed in anesthetized (chloralose), paralyzed, and artificially ventilated cats with an occipital exposure of the cerebellum. Administration of capsaicin (Cap; 5–10 μg/kg) via the right external jugular vein at the end of inspiration and application of lung inflation (LI; 10 cmH2O) during inspiration were carried out to stimulate nonmyelinated and myelinated vagal afferents, respectively. The phrenic neurogram was recorded as an index of the respiratory motor output. Control cardiorespiratory variables [expiratory duration (Te), arterial blood pressure] and their immediate responses to stimuli were compared before and after bilateral lesions of the FN. The results showed the following. 1) Cap injection and LI resulted in a dramatic increase in Te (apnea). 2) FN lesions did not significantly alter the control Te; however, the apneic duration induced by Cap injection was prolonged. 3) Neither FN lesions nor cerebellectomy affected the apneic duration that resulted from application of LI. 4) Cold blockade of the vagi (6–8°C) eliminated the respiratory responses elicited by LI but not Cap injection; vagotomy abolished the responses to both stimuli. 5) FN lesions did not change the control ABP or its responses to either LI or Cap injection. It is concluded that the FN is involved in vagally mediated respiratory reflexes elicited by activation of nonmyelinated (C-fiber) vagal afferents.
Skeletal muscle biochemical adaptations to exercise training in miniature swine
Authors: McAllister Richard M. , Reiter Brian L. , Amann John F. , Laughlin M. Harold
Published: December 2017

McAllister, Richard M., Brian L. Reiter, John F. Amann, and M. Harold Laughlin. Skeletal muscle biochemical adaptations to exercise training in miniature swine. J. Appl. Physiol. 82(6): 1862–1868, 1997.—The primary purpose of this study was to test the hypothesis that endurance exercise training induces increased oxidative capacity in porcine skeletal muscle. To test this hypothesis, female miniature swine were either trained by treadmill running 5 days/wk over 16–20 wk (Trn; n = 35) or pen confined (Sed; n = 33). Myocardial hypertrophy, lower heart rates during submaximal stages of a maximal treadmill running test, and increased running time to exhaustion during that test were indicative of training efficacy. A variety of skeletal muscles were sampled and subsequently assayed for the enzymes citrate synthase (CS), 3-hydroxyacyl-CoA dehydrogenase, and lactate dehydrogenase and for antioxidant enzymes. Fiber type composition of a representative muscle was also determined histochemically. The largest increase in CS activity (62%) was found in the gluteus maximus muscle (Sed, 14.7 ± 1.1 μmol ⋅ min−1 ⋅ g−1; Trn, 23.9 ± 1.0; P < 0.0005). Muscles exhibiting increased CS activity, however, were located primarily in the forelimb; ankle and knee extensor and respiratory muscles were unchanged with training. Only two muscles exhibited higher 3-hydroxyacyl-CoA dehydrogenase activity in Trn compared with Sed. Lactate dehydrogenase activity was unchanged with training, as were activities of antioxidant enzymes. Histochemical analysis of the triceps brachii muscle (long head) revealed lower type IIB fiber numbers in Trn (Sed, 42 ± 6%; Trn, 10 ± 4; P < 0.01) and greater type IID/X fiber numbers (Sed, 11 ± 2; Trn, 22 ± 3; P < 0.025). These findings indicate that porcine skeletal muscle adapts to endurance exercise training in a manner similar to muscle of humans and other animal models, with increased oxidative capacity. Specific muscles exhibiting these adaptations, however, differ between the miniature swine and other species.
Effect of intermittent weight bearing on soleus fiber force-velocity-power and force-pCa relationships
Authors: Bangart J. J. , Widrick J. J. , Fitts R. H.
Published: December 2017

Bangart, J. J., J. J. Widrick, and R. H. Fitts. Effect of intermittent weight bearing on soleus fiber force-velocity-power and force-pCa relationships. J. Appl. Physiol. 82(6): 1905–1910, 1997.—Rat permeabilized type I soleus fibers displayed a 33% reduction in peak power output and a 36% increase in the free Ca2+concentration required for one-half maximal activation after 14 days of hindlimb non-weight bearing (NWB). We examined the effectiveness of intermittent weight bearing (IWB; consisting of four 10-min periods of weight bearing/day) as a countermeasure to these functional changes. At peak power output, type I fibers from NWB animals produced 54% less force and shortened at a 56% greater velocity than did type I fibers from control weight-bearing animals while type I fibers from the IWB rats produced 26% more absolute force than did fibers from the NWB group and shortened at a velocity that was only 80% of the NWB group mean. As a result, no difference was observed in the average peak power of fibers from the IWB and NWB animals. Hill plot analysis of force-pCa relationships indicated that fibers from the IWB group required similar levels of free Ca2+to reach half-maximal activation in comparison to fibers from the weight-bearing group. However, at forces <50% of peak force, the force-pCa curve for fibers from the IWB animals clearly fell between the relationships observed for the other two groups. In summary, IWB treatments 1) attenuated the NWB-induced reduction in fiber Ca2+sensitivity but 2) failed to prevent the decline in peak power that occurs during NWB because of opposing effects on fiber force (an increase vs. NWB) and shortening velocity (a decrease vs. NWB).
Anabolic influences of insulin-like growth factor I and/or growth hormone on the diaphragm of young rats
Authors: Lewis Michael I. , Lorusso Thomas J. , Fournier Mario
Published: December 2017

Lewis, Michael I., Thomas J. LoRusso, and Mario Fournier.Anabolic influences of insulin-like growth factor I and/or growth hormone on the diaphragm of young rats. J. Appl. Physiol. 82(6): 1972–1978, 1997.—It is controversial whether insulin-like growth factor I (IGF-I), growth hormone (GH), or their combination might enhance body growth and/or tissue anabolism in the well-fed animal with an intact somatotrophic axis. To assess this further, we studied four groups of adolescent rats: 1) control (Ctr), 2) GH, 3) IGF-I, and 4) GH/IGF-I. IGF-I was given via an osmotic minipump, whereas GH was injected subcutaneously for a period of 72 h. Diaphragm (Dia) contractile and fatigue properties were determined in vitro. Quantitative histochemical and morphometric analyses were performed on Dia fibers. Total serum IGF-I levels were significantly increased in the groups receiving growth factors. Although body weight increased to a greater extent in the animals receiving growth factors, a further synergistic effect was noted in the GH/IGF-I animals compared with either GH or IGF-I groups. Costal Dia mass was greater in the groups receiving growth factors. The Dia of GH/IGF-I animals was more fatigue resistant than the Dia in Ctr. The cross-sectional area of types IIa and IIx fibers were increased to a similar extent in all groups receiving growth factors compared with Ctr. Succinate dehydrogenase activity of type IIa fibers was significantly greater in the GH/IGF-I animals compared with the other groups. We conclude that the short-term provision of growth factors to well-nourished, normally growing adolescent rats can accelerate body growth and promote selective hypertrophy of predominantly type II Dia fibers.
A finite-element model of oxygen diffusion in the pulmonary capillaries
Authors: Frank Andreas O. , Chuong C. J. Charles , Johnson Robert L.
Published: December 2017

Frank, Andreas O., C. J. Charles Chuong, and Robert L. Johnson. A finite-element model of oxygen diffusion in the pulmonary capillaries. J. Appl. Physiol. 82(6): 2036–2044, 1997.—We determined the overall pulmonary diffusing capacity (Dl) and the diffusing capacities of the alveolar membrane (Dm) and the red blood cell (RBC) segments (De) of the diffusional pathway for O2 by using a two-dimensional finite-element model developed to represent the sheet-flow characteristics of pulmonary capillaries. An axisymmetric model was also considered to assess the effect of geometric configuration. Results showed the membrane segment contributing the major resistance, with the RBC segment resistance increasing as O2 saturation ([Formula: see text]) rises during the RBC transit: RBC contributed 7% of the total resistance at the capillary inlet ([Formula: see text] = 75%) and 30% toward the capillary end ([Formula: see text] = 95%) for a 45% hematocrit (Hct). Both Dm and Dlincreased as the Hct increased but began approaching a plateau near an Hct of 35%, due to competition between RBCs for O2 influx. Both Dm and Dl were found to be relatively insensitive (2∼4%) to changes in plasma protein concentration (28∼45%). Axisymmetric results showed similar trends for all Hct and protein concentrations but consistently overestimated the diffusing capacities (∼2.2 times), primarily because of an exaggerated air-tissue barrier surface area. The two-dimensional model correlated reasonably well with experimental data and can better represent the O2 uptake of the pulmonary capillary bed.