bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence of O2 supply-dependentV˙o 2 max in the exercise-trained human quadriceps
Authors: Richardson R. S. , Grassi B. , Gavin T. P. , Haseler L. J. , Tagore K. , Roca J. , Wagner P. D.
Published: December 2017

Maximal O2 delivery and O2 uptake (V˙o 2) per 100 g of active muscle mass are far greater during knee extensor (KE) than during cycle exercise: 73 and 60 ml ⋅ min−1 ⋅ 100 g−1 (2.4 kg of muscle) (R. S. Richardson, D. R. Knight, D. C. Poole, S. S. Kurdak, M. C. Hogan, B. Grassi, and P. D. Wagner. Am. J. Physiol. 268 ( Heart Circ. Physiol. 37): H1453–H1461, 1995) and 28 and 25 ml ⋅ min−1 ⋅ 100 g−1 (7.5 kg of muscle) (D. R. Knight, W. Schaffartzik, H. J. Guy, R. Predilleto, M. C. Hogan, and P. D. Wagner. J. Appl. Physiol. 75: 2586–2593, 1993), respectively. Although this is evidence of muscle O2 supply dependence in itself, it raises the following question: With such high O2 delivery in KE, are the quadriceps still O2 supply dependent at maximal exercise? To answer this question, seven trained subjects performed maximum KE exercise in hypoxia [0.12 inspired O2 fraction ([Formula: see text])], normoxia (0.21 [Formula: see text]), and hyperoxia (1.0 [Formula: see text]) in a balanced order. The protocol (after warm-up) was a square wave to a previously determined maximum work rate followed by incremental stages to ensure that a true maximum was achieved under each condition. Direct measures of arterial and venous blood O2 concentration in combination with a thermodilution blood flow technique allowed the determination of O2 delivery and muscleV˙o 2. Maximal O2 delivery increased with inspired O2: 1.3 ± 0.1, 1.6 ± 0.2, and 1.9 ± 0.2 l/min at 0.12, 0.21, and 1.0 [Formula: see text], respectively ( P < 0.05). Maximal work rate was affected by variations in inspired O2 (−25 and +14% at 0.12 and 1.0 [Formula: see text], respectively, compared with normoxia, P < 0.05) as was maximal V˙o 2(V˙o 2 max): 1.04 ± 0.13, 1.24 ± 0.16, and 1.45 ± 0.19 l/min at 0.12, 0.21, and 1.0[Formula: see text], respectively ( P < 0.05). Calculated mean capillary [Formula: see text] also varied with[Formula: see text] (28.3 ± 1.0, 34.8 ± 2.0, and 40.7 ± 1.9 Torr at 0.12, 0.21, and 1.0 [Formula: see text], respectively, P < 0.05) and was proportionally related to changes inV˙o 2 max, supporting our previous finding that a decrease in O2 supply will proportionately decrease muscleV˙o 2 max. As even in the isolated quadriceps (where normoxic O2 delivery is the highest recorded in humans) an increase in O2 supply by hyperoxia allows the achievement of a greater V˙o 2 max, we conclude that, in normoxic conditions of isolated KE exercise, KEV˙o 2 max in trained subjects is not limited by mitochondrial metabolic rate but, rather, by O2 supply.
LMR spectroscopy: a new sensitive method for on-line recording of nitric oxide in breath
Authors: Mürtz Petra , Menzel Lars , Bloch Wilhelm , Hess Alexander , Michel Olaf , Urban Wolfgang
Published: December 2017

Laser magnetic resonance spectroscopy (LMRS) is a sensitive and isotope-selective technique for determining low concentrations of gaseous free radicals with high time resolution. We used this technique to analyze the nitric oxide (NO) concentration profile while simultaneously measuring the flow and expired volume during several single breathing cycles. Eight healthy, nonallergic volunteers were investigated. An initial NO peak was found in all breathing cycles before the NO concentration dropped to a relatively stable plateau in the late phase of expiration. The nasal NO peak was significantly higher than the oral NO peak. The nasal NO plateau was always higher than the oral NO plateau. The height of the initial nasal and oral NO peak rose with increasing duration of breath hold, whereas the late expiratory NO plateau changed only little for either the nasal or the oral breathing cycles. Our findings demonstrate, in line with other reports using other techniques, that the nose is the primary source for NO within the airways.
Compliance and stability of the bronchial wall in a model of allergen-induced lung inflammation
Authors: Mitchell H. W. , Turner D. J. , Gray P. R. , McFawn P. K.
Published: December 2017

Airway wall remodeling in response to inflammation might alter load on airway smooth muscle and/or change airway wall stability. We therefore determined airway wall compliance and closing pressures in an animal model. Weanling pigs were sensitized to ovalbumin (OVA; ip and sc, n = 6) and were subsequently challenged three times with OVA aerosol. Control pigs received 0.9% NaCl ( n = 4) in place of OVA aerosol. Bronchoconstriction in vivo was assessed from lung resistance and dynamic compliance. Semistatic airway compliance was recorded ex vivo in isolated segments of bronchus, after the final OVA aerosol or 0.9% NaCl challenge. Internally or externally applied pressure needed to close bronchial segments was determined in the absence or presence of carbachol (1 μM). Sensitized pig lungs exhibited immediate bronchoconstriction to OVA aerosol and also peribronchial accumulations of monocytes and granulocytes. Compliance was reduced in sensitized bronchi in vitro ( P < 0.01), and closing pressures were increased ( P< 0.05). In the presence of carbachol, closing pressures of control and sensitized bronchi were not different. We conclude that sensitization and/or inflammation increases airway load and airway stability.
Capsaicin-sensitive C-fiber-mediated protective responses in ozone inhalation in rats
Authors: Vesely Keith R. , Hyde Dallas M. , Stovall Mary Y. , Harkema Jack R. , Green Jerry F. , Schelegle Edward S.
Published: December 2017

To assess the role of lung sensory C fibers during and after inhalation of 1 part/million ozone for 8 h, we compared breathing pattern responses and epithelial injury-inflammation-repair in rats depleted of C fibers by systemic administration of capsaicin as neonates and in vehicle-treated control animals. Capsaicin-treated rats did not develop ozone-induced rapid, shallow breathing. Capsaicin-treated rats showed more severe necrosis in the nasal cavity and greater inflammation throughout the respiratory tract than did control rats exposed to ozone. Incorporation of 5-bromo-2′-deoxyuridine (a marker of DNA synthesis associated with proliferation) into terminal bronchiolar epithelial cells was not significantly affected by capsaicin treatment in rats exposed to ozone. However, when normalized to the degree of epithelial necrosis present in each rat studied, there was less 5-bromo-2′-deoxyuridine labeling in the terminal bronchioles of capsaicin-treated rats. These observations suggest that the ozone-induced release of neuropeptides does not measurably contribute to airway inflammation but may play a role in modulating basal and reparative airway epithelial cell proliferation.
Chronic exposure to nicotine alters endothelium-dependent arteriolar dilatation: effect of superoxide dismutase
Authors: Mayhan William G. , Sharpe Glenda M.
Published: December 2017

The first goal of this study was to determine whether chronic injection of nicotine alters endothelium-dependent arteriolar dilatation. We measured the diameter of cheek pouch resistance arterioles (∼50 μm in diameter) in response to endothelium-dependent (acetylcholine and ADP) and -independent (nitroglycerin) agonists in control hamsters and hamsters treated with nicotine (2 μg ⋅ kg−1 ⋅ day−1for 2–3 wk). In control hamsters, acetylcholine (0.1 and 1.0 μM) dilated arterioles by 13 ± 2 and 31 ± 3%, respectively, and ADP (1.0 and 10 μM) dilated arterioles by 18 ± 1 and 30 ± 1%, respectively. In contrast, acetylcholine (0.1 and 1.0 μM) dilated arterioles by only 5 ± 2 and 12 ± 3%, respectively, and ADP (1.0 and 10 μM) dilated arterioles by only 7 ± 2 and 13 ± 3%, respectively, in animals treated with nicotine ( P < 0.05 vs. response in control hamsters). Nitroglycerin produced similar dose-related dilatation of cheek pouch arterioles in control and nicotine-treated hamsters. Our second goal was to examine a possible mechanism for impaired endothelium-dependent arteriolar dilatation during chronic treatment with nicotine. We found that superfusion of the cheek pouch microcirculation with superoxide dismutase (150 U/ml) restored impaired endothelium-dependent, but did not alter endothelium-independent, arteriolar dilatation in hamsters treated with nicotine. Superfusion with superoxide dismutase did not alter endothelium-dependent or -independent arteriolar dilatation in control hamsters. We suggest that chronic exposure to nicotine produces selective impairment of endothelium-dependent arteriolar dilatation via a mechanism related to the synthesis/release of oxygen-derived free radicals.
Stimulation of myofibrillar synthesis by exercise is mediated by more efficient translation of mRNA
Authors: Welle Stephen , Bhatt Kirti , Thornton Charles A.
Published: December 2017

Resistance exercises stimulate protein synthesis in human muscle, but the roles of changes in mRNA concentrations and changes in the efficiency of mRNA translation have not been defined. The present study was done to determine whether resistance exercise affects concentrations of total RNA, total mRNA, actin mRNA, or myosin heavy-chain mRNA (total and isoform specific). Eight subjects, 62–75 yr old, performed unilateral knee extensions at 80% of their one-repetition-maximum capacity on days 1, 3, and 6 of the study. On day 7, biopsies of exercised and nonexercised vastus lateralis muscles were obtained. Myofibrillar synthesis was determined by stable- isotope incorporation, and mRNA concentrations were determined by membrane hybridization and PCR-based methods. The exercise stimulated myofibrillar synthesis [30 ± 6 (SE)%] without affecting RNA or mRNA concentrations. The effect of exercise on protein synthesis in individual subjects did not correlate with the effect on total RNA and mRNA concentrations. These data suggest that the stimulation of myofibrillar synthesis by resistance exercise is mediated by more efficient translation of mRNA.
Effect of chronic sodium cyanate administration on O2 transport and uptake in hypoxic and normoxic exercise
Authors: McCanse Web , Henderson Kyle , Urano Tetsuya , Kuwahira Ichiro , Clancy Richard L. , Gonzalez Norberto C.
Published: December 2017

Systemic O2 transport during maximal exercise at different inspired [Formula: see text]([Formula: see text]) values was studied in sodium cyanate-treated (CY) and nontreated (NT) rats. CY rats exhibited increased O2affinity of Hb (exercise O2half-saturation pressure of Hb = 27.5 vs. 42.5 Torr), elevated blood Hb concentration, pulmonary hypertension, blunted hypoxic pulmonary vasoconstriction, and normal ventilatory response to exercise. Maximal rate of convective O2 transport was higher and tissue O2extraction was lower in CY than in NT rats. The relative magnitude of these opposing changes, which determined the net effect of cyanate on maximal O2 uptake (V˙o 2 max), varied at different [Formula: see text]:V˙o 2 max(ml ⋅ min−1 ⋅ kg−1) was lower in normoxia (72.8 ± 1.9 vs. 81.1 ± 1.2), the same at 70 Torr [Formula: see text] (55.4 ± 1.4 vs. 54.1 ± 1.4), and higher at 55 Torr[Formula: see text] (48 ± 0.7 vs. 40.4 ± 1.9) in CY than in NT rats. The beneficial effect of cyanate on V˙o 2 max at 55 Torr [Formula: see text] disappeared when Hb concentration was lowered to normal. It is concluded that the effect of cyanate on V˙o 2 maxdepends on the relative changes in blood O2 convection and tissue O2 extraction, which vary at different [Formula: see text]. Although uptake of O2 by the blood in the lungs is enhanced by cyanate, its release at the tissues is limited, probably because of a reduction in the capillary-to-tissue[Formula: see text] diffusion gradient secondary to the increased O2 affinity of Hb.
Enhanced peripheral chemoreflex function in conscious rabbits with pacing-induced heart failure
Authors: Sun Shu-Yu , Wang W. , Zucker I. H. , Schultz H. D.
Published: December 2017

The present study aimed to determine whether peripheral and/or central chemoreflex function is altered in chronic heart failure (CHF) and whether altered chemoreflex function contributes to sympathetic activation in CHF. A rabbit model of pacing-induced CHF was employed. The development of CHF (3–4 wk of pacing) was characterized by an enlarged heart, an attenuated contractility, and an elevated central venous pressure. Renal sympathetic nerve activity (RSNA) and minute volume (MV) of ventilation in response to stimulation of peripheral chemoreceptors by isocapnic/hypoxic gases were measured in the conscious state. It was found that the baseline RSNA at normoxia was higher in CHF rabbits than in sham rabbits (35.00 ± 4.03 vs. 20.75 ± 2.87% of maximum, P < 0.05). Moreover, the magnitudes of changes in RSNA and MV in response to stimulation of the peripheral chemoreceptors and the slopes of RSNA-arterial[Formula: see text] and MV-arterial[Formula: see text] curves were greater in CHF than in sham rabbits. Inhibition of the peripheral chemoreceptors by inhalation of 100% O2decreased RSNA in CHF but not in sham rabbits. The central chemoreflex function, as evaluated by the responses of RSNA and MV to hyperoxic/hypercapnic gases, was not different between sham and CHF rabbits. These data suggest that an enhancement of the peripheral chemoreflex occurs in the rabbit model of pacing-induced CHF and that the enhanced peripheral chemoreflex function contributes to the sympathetic activation in the CHF state.
Effects of activation frequency and force on low-frequency fatigue in human skeletal muscle
Authors: Binder-Macleod Stuart A. , Russ David W.
Published: December 2017

No comparison of the amount of low-frequency fatigue (LFF) produced by different activation frequencies exists, although frequencies ranging from 10 to 100 Hz have been used to induce LFF. The quadriceps femoris of 11 healthy subjects were tested in 5 separate sessions. In each session, the force-generating ability of the muscle was tested before and after fatigue and at 2, ∼13, and ∼38 min of recovery. Brief (6-pulse), constant-frequency trains of 9.1, 14.3, 33.3, and 100 Hz and a 6-pulse, variable-frequency train with a mean frequency of 14.3 Hz were delivered at 1 train/s to induce fatigue. Immediately postfatigue, there was a significant effect of fatiguing protocol frequency. Muscles exhibited greater LFF after stimulation with the 9.1-, 14.3-, and variable-frequency trains. These three trains also produced the greatest mean force-time integrals during the fatigue test. At 2, ∼13, and ∼38 min of recovery, however, the LFF produced was independent of the fatiguing protocol frequency. The findings are consistent with theories suggesting two independent mechanisms behind LFF and may help identify the optimal activation pattern when functional electrical stimulation is used.
Cortical and subcortical control of tongue movement in humans: a functional neuroimaging study using fMRI
Authors: Corfield D. R. , Murphy K. , Josephs O. , Fink G. R. , Frackowiak R. S. J. , Guz A. , Adams L. , Turner R.
Published: December 2017

We have used voluntary tongue contraction to test whether we can image activation of the hypoglossal nuclei within the human brain stem by using functional magnetic resonance imaging (fMRI). Functional images of the whole brain were acquired in eight subjects by using T2-weighted echo planar imaging (blood oxygen level development) every 6.2 s. Sequences of images were acquired during 12 periods of 31-s “isometric” rhythmic tongue contraction alternated with 12 periods of 31-s tongue relaxation. Noise arising from cardiac- and respiratory-related movement was removed either by filtration (high pass; cutoff 120 s) or by inclusion in the statistical analysis as confounding effects of no interest. For the group, tongue contraction was associated with significant signal increases ( P < 0.05 corrected for multiple comparisons) in the sensorimotor cortex, supplementary motor area, operculum, insula, thalamus, and cerebellum. For the group and for six of eight individuals, significant signal increases were also seen within the medulla ( P < 0.001, predefined region of interest with no correction for multiple comparisons); this signal is most likely to reflect neuronal activation associated with the hypoglossal motor nuclei. The data demonstrate that fMRI can be used to detect, simultaneously, the cerebral and brain stem control of tongue movement.
Age effect on expression of myosin heavy and light chain isoforms in suspended rat soleus muscle
Authors: Saitoh Ayako , Okumoto Tadashi , Nakano Hiroshi , Wada Masanobu , Katsuta Shigeru
Published: December 2017

This study was designed to test the hypothesis that myosin heavy (MHC) and light chain (MLC) plasticity resulting from hindlimb suspension (HS) is an age-dependent process. By using an electrophoretic technique, the distribution of MHC and MLC isoforms was quantitatively evaluated in the soleus muscles from 3- or 12-wk-old rats after 1–3 wk of HS treatment was maintained. In normal 12- and 15-wk-old rats, the soleus muscles contained a predominance of MHCI(∼94%) with small amounts of MHCIIa, but not MHCIIdor MHCIIb. The suspended muscles of adult rats were characterized by the appearance of MHCIIband MHCIId, the latter reaching ∼6% after 3 wk of HS treatment. In contrast to changes in MHC, HS did not induce a transition in the MLC pattern in the soleus muscles from adult rats. Compared with adult rats, in juveniles HS had a much more pronounced effect on the shift toward faster MHC and MLC isoform expression. The soleus muscles of 6-wk-old rats after 3 wk of HS were composed of 37.0% MHCI, 19.1% MHCIIa, 23.7% MHCIId, and 20.2% MHCIIb. Changes in MLC isoforms consisted of an increase in MLC1fand MLC2fconcomitant with a decrease in MLC2s. These results indicate the existence of a differential effect of HS on MHC and MLC transitions that appears to be age dependent. They also suggest that the suspended soleus muscles from young rats may acquire the intrinsic contractile properties that are intermediate between those in the normal soleus and typical fast-twitch skeletal muscles.
Acute mountain sickness is not related to cerebral blood flow: a decompression chamber study
Authors: Baumgartner Ralf W. , Spyridopoulos Ioakim , Bärtsch Peter , Maggiorini Marco , Oelz Oswald
Published: December 2017

To evaluate the pathogenetic role of cerebral blood flow (CBF) changes occurring before and during the development of acute mountain sickness (AMS), peak mean middle cerebral artery flow velocities ([Formula: see text]) were assessed by transcranial Doppler sonography in 10 subjects at 490-m altitude, and during three 12-min periods immediately (SA1), 3 (SA2), and 6 (SA3) h after decompression to a simulated altitude of 4,559 m. AMS cerebral scores increased from 0.16 ± 0.14 at baseline to 0.44 ± 0.31 at SA1, 1.11 ± 0.88 at SA2( P < 0.05), and 1.43 ± 1.03 at SA3( P < 0.01); correspondingly, three, seven, and eight subjects had AMS. Absolute and relative[Formula: see text] at simulated altitude, expressed as percentages of low-altitude values (%[Formula: see text]), did not correlate with AMS cerebral scores. Average %[Formula: see text] remained unchanged, because %[Formula: see text]increased in three and remained unchanged or decreased in seven subjects at SA2 and SA3. These results suggest that CBF is not important in the pathogenesis of AMS and shows substantial interindividual differences during the first hours at simulated altitude.
Metabolic cost of generating horizontal forces during human running
Authors: Chang Young-Hui , Kram Rodger
Published: December 2017

Previous studies have suggested that generating vertical force on the ground to support body weight (BWt) is the major determinant of the metabolic cost of running. Because horizontal forces exerted on the ground are often an order of magnitude smaller than vertical forces, some have reasoned that they have negligible cost. Using applied horizontal forces (AHF; negative is impeding, positive is aiding) equal to −6, −3, 0, +3, +6, +9, +12, and +15% of BWt, we estimated the cost of generating horizontal forces while subjects were running at 3.3 m/s. We measured rates of oxygen consumption (V˙o2) for eight subjects. We then used a force-measuring treadmill to measure ground reaction forces from another eight subjects. With an AHF of −6% BWt,V˙o2increased 30% compared with normal running, presumably because of the extra work involved. With an AHF of +15% BWt, the subjects exerted ∼70% less propulsive impulse and exhibited a 33% reduction inV˙o2. Our data suggest that generating horizontal propulsive forces constitutes more than one-third of the total metabolic cost of normal running.
Effect of oral glutamine on whole body carbohydrate storage during recovery from exhaustive exercise
Authors: Bowtell J. L. , Gelly K. , Jackman M. L. , Patel A. , Simeoni M. , Rennie M. J.
Published: December 2017

The purpose of this study was to determine the efficacy of glutamine in promoting whole body carbohydrate storage and muscle glycogen resynthesis during recovery from exhaustive exercise. Postabsorptive subjects completed a glycogen-depleting exercise protocol, then consumed 330 ml of one of three drinks, 18.5% (wt/vol) glucose polymer solution, 8 g glutamine in 330 ml glucose polymer solution, or 8 g glutamine in 330 ml placebo, and also received a primed constant infusion of [1-13C]glucose for 2 h. Plasma glutamine concentration was increased after consumption of the glutamine drinks (0.7–1.1 mM, P < 0.05). In the second hour of recovery, whole body nonoxidative glucose disposal was increased by 25% after consumption of glutamine in addition to the glucose polymer (4.48 ± 0.61 vs. 3.59 ± 0.18 mmol/kg, P < 0.05). Oral glutamine alone promoted storage of muscle glycogen to an extent similar to oral glucose polymer. Ingestion of glutamine and glucose polymer together promoted the storage of carbohydrate outside of skeletal muscle, the most feasible site being the liver.
Ultrastructural muscle damage in young vs. older men after high-volume, heavy-resistance strength training
Authors: Roth Stephen M. , Martel Gregory F. , Ivey Frederick M. , Lemmer Jeffrey T. , Tracy Brian L. , Hurlbut Diane E. , Metter E. Jeffrey , Hurley Ben F. , Rogers Marc A.
Published: December 2017

This study assessed ultrastructural muscle damage in young (20–30 yr old) vs. older (65–75 yr old) men after heavy-resistance strength training (HRST). Seven young and eight older subjects completed 9 wk of unilateral leg extension HRST. Five sets of 5–20 repetitions were performed 3 days/wk with variable resistance designed to subject the muscle to near-maximal loads during every repetition. Biopsies were taken from the vastus lateralis of both legs, and muscle damage was quantified via electron microscopy. Training resulted in a 27% strength increase in both groups ( P < 0.05). In biopsies before training in the trained leg and in all biopsies from untrained leg, 0–3% of muscle fibers exhibited muscle damage in both groups ( P = not significant). After HRST, 7 and 6% of fibers in the trained leg exhibited damage in the young and older men, respectively ( P < 0.05, no significant group differences). Myofibrillar damage was primarily focal, confined to one to two sarcomeres. Young and older men appear to exhibit similar levels of muscle damage at baseline and after chronic HRST.
Reversal of weightlessness-induced musculoskeletal losses with androgens: quantification by MRI
Authors: Wimalawansa Sunishka M. , Chapa Maria T. , Wei Jingna N. , Westlund Karin N. , Quast Michael J. , Wimalawansa Sunil J.
Published: December 2017

Microgravity causes rapid decrement in musculoskeletal mass is associated with a marked decrease in circulatory testosterone levels, as we reported in hindlimb-suspended (HLS) rats. In this model which simulates microgravity, we hypothesized that testosterone supplementation should prevent these losses, and we tested this in two studies. Muscle volumes and bone masses were quantitated by using magnetic resonance imaging (MRI) on day 12. In the first study, 12-wk-old Sprague-Dawley rats that were HLS for 12 days lost 28.5% of muscle volume (53.3 ± 4.8 vs. 74.5 ± 3.6 cm3in the ground control rats; P < 0.001) and had a 5% decrease in bone mineral density (BMD) ( P < 0.05). In the second study, 30 male 12-wk-old Wistar rats were HLS and were administered either a vehicle (control), testosterone, or nandrolone decanoate (ND). An additional 20 rats were used as ground controls, one-half of which received testosterone. HLS rats had a significant reduction in muscle volume (42.9 ± 3.0 vs. 56 ± 1.8 cm3in ground control rats; P < 0.01). Both testosterone and ND treatments prevented this muscle loss (51.5 ± 2 and 51.6 ± 1.2 cm3, respectively; a 63% improvement; P < 0.05). There were no statistical differences between the two active treatment groups nor with the ground controls. Similarly, there was an 85% improvement in BMD in the testosterone group (1.15 ± 0.04 vs. 1.04 ± 0.04 density units in vehicle controls; P< 0.05) and a 76% improvement in the ND group (1.13 ± 0.07 density units), whereas ground control rats had a BMD of 1.17 ± 0.03 density units. Because serum testosterone levels are markedly reduced in this model of simulated microgravity, androgen replacement seems to be a rational countermeasure to prevent microgravity-induced musculoskeletal losses.
Acute manipulations of plasma volume alter arterial pressure responses during Valsalva maneuvers
Authors: Fritsch-Yelle Janice M. , Convertino Victor A. , Schlegel Todd T.
Published: December 2017

The effects of changes in blood volume on arterial pressure patterns during the Valsalva maneuver are incompletely understood. In the present study we measured beat-to-beat arterial pressure and heart rate responses to supine Valsalva maneuvers during normovolemia, hypovolemia induced with intravenous furosemide, and hypervolemia induced with ingestion of isotonic saline. Valsalva responses were analyzed according to the four phases as previously described (W. F. Hamilton, R. A. Woodbury, and H. T. Harper, Jr. JAMA 107: 853–856, 1936; W. F. Hamilton, R. A. Woodbury, and H. T. Harper, Jr. Am. J. Physiol. 141: 42–50, 1944). Phase I is the initial onset of straining, which elicits a rise in arterial pressure; phase II is the period of straining, during which venous return is impeded and pressure falls (early) and then partially recovers (late); phase III is the initial release of straining; and phase IV consists of a rapid “overshoot” of arterial pressure after the release. During hypervolemia, early phase II arterial pressure decreases were significantly less than those during hypovolemia, thus making the response more “square.” Systolic pressure hypervolemic vs. hypovolemic falls were −7.4 ± 2.1 vs. −30.7 ± 7 mmHg ( P = 0.005). Diastolic pressure hypervolemic vs. hypovolemic falls were −2.4 ± 1.6 vs. −15.2 ± 2.6 mmHg ( P = 0.05). A significant direct correlation was found between plasma volume and phase II systolic pressure falls, and a significant inverse correlation was found between plasma volume and phase III-IV systolic pressure overshoots. Heart rate responses to systolic pressure falls during phase II were significantly less during hypovolemia than during hypervolemia (0.7 ± 0.2 vs. 2.82 ± 0.2 beats ⋅ min−1 ⋅ mmHg−1; P = 0.05) but were not different during phase III-IV overshoots. We conclude that acute changes in intravascular volume from hypovolemia to hypervolemia affect cardiovascular responses, particularly arterial pressure changes, to the Valsalva maneuver and should be considered in both clinical and research applications of this maneuver.
Human skeletal sarcoplasmic reticulum Ca2+uptake and muscle function with aging and strength training
Authors: Hunter Sandra K. , Thompson Martin W. , Ruell Patricia A. , Harmer Alison R. , Thom Jeanette M. , Gwinn Tom H. , Adams Roger D.
Published: December 2017

This study investigated the adaptations of skeletal muscle sarcoplasmic reticulum (SR) Ca2+uptake, relaxation, and fiber types in young (YW) and elderly women (EW) to high-resistance training. Seventeen YW (18–32 yr) and 11 EW (64–79 yr) were assessed for 1) electrically evoked relaxation time and rate of the quadriceps femoris; and 2) maximal rates of SR Ca2+uptake and Ca2+-ATPase activity and relative fiber-type areas, analyzed from muscle biopsies of the vastus lateralis. EW had significantly slower relaxation rates and times, decreased SR Ca2+uptake and Ca2+-ATPase activity, and a larger relative type I fiber area than did YW. A subgroup of 9 young (YWT) and 10 elderly women (EWT) performed 12 wk of high-resistance training (8 repetition maximum) of the quadriceps and underwent identical testing procedures pre- and posttraining. EWT significantly increased their SR Ca2+uptake and Ca2+-ATPase activity in response to training but showed no alterations in speed of relaxation or relative fiber-type areas. In YWT none of the variables was altered after resistance training. These findings suggest that 1) a reduced SR Ca2+uptake in skeletal muscle of elderly women was partially reversed with resistance training and 2) SR Ca2+uptake in the vastus lateralis was not the rate-limiting mechanism for the slowing of relaxation measured from electrically evoked quadriceps muscle of elderly women.
Effects of resistance training on selected indexes of immune function in elderly women
Authors: Flynn M. G. , Fahlman M. , Braun W. A. , Lambert C. P. , Bouillon L. E. , Brolinson P. G. , Armstrong C. W.
Published: December 2017

Women aged 67–84 yr were randomly assigned to either resistance exercise (RE, n = 15) or control group (C, n = 14). RE group completed 10 wk of resistance training, whereas C group maintained normal activity. Blood samples were obtained from the RE group (at the same time points as for resting C) at rest, immediately after resistance exercise, and 2 h after exercise before ( week 0) and after ( week 10) training. Mononuclear cell (CD3+, CD3+CD4+, CD3+CD8+, CD19+, and CD3−CD16+CD56+) number, lymphocyte proliferative (LP) response to mitogen, natural cell-mediated cytotoxicity (NCMC), and serum cortisol levels were determined. Strength increased significantly in RE subjects (%change 8-repetition maximum = 148%). No significant group, exercise time, or training effects were found for CD3+, CD3+CD4+, or CD3+CD8+cells, but there was a significant exercise time effect for CD3−CD16+CD56+cells. LP response was not different between groups, across exercise time, or after training. NCMC was increased immediately after exercise for RE subjects at week 0 and for RE and C groups at week 10. The week 0 and week 10 NCMC values were above baseline for both RE and C groups 2 h after exercise. In conclusion, acute resistance exercise did not result in postexercise suppression of NCMC or LP, and 10 wk of resistance training did not influence resting immune measures in women aged 67–84 yr.
Predicting risk of decompression sickness in humans from outcomes in sheep
Authors: Ball Robert , Lehner Charles E. , Parker Erich C.
Published: December 2017

In animals, the response to decompression scales as a power of species body mass. Consequently, decompression sickness (DCS) risk in humans should be well predicted from an animal model with a body mass comparable to humans. No-stop decompression outcomes in compressed air and nitrogen-oxygen dives with sheep ( n = 394 dives, 14.5% DCS) and humans ( n = 463 dives, 4.5% DCS) were used with linear-exponential, probabilistic modeling to test this hypothesis. Scaling the response parameters of this model between species (without accounting for body mass), while estimating tissue-compartment kinetic parameters from combined human and sheep data, predicts combined risk better, based on log likelihood, than do separate sheep and human models, a combined model without scaling, and a kinetic-scaled model. These findings provide a practical tool for estimating DCS risk in humans from outcomes in sheep, especially in decompression profiles too risky to test with humans. This model supports the hypothesis that species of similar body mass have similar DCS risk.
Comparison of short-term diet and exercise on insulin action in individuals with abnormal glucose tolerance
Authors: Arciero Paul J. , Vukovich Matthew D. , Holloszy John O. , Racette Susan B. , Kohrt Wendy M.
Published: December 2017

The effects of a 10-day low-calorie diet (LCD; n = 8) or exercise training (ET; n = 8) on insulin secretion and action were compared in obese men ( n = 9) and women ( n = 7), aged 53 ± 1 yr, with abnormal glucose tolerance by using a hyperglycemic clamp with superimposed arginine infusion and a high-fat drink. Body mass (LCD, 115 ± 5 vs. 110 ± 5 kg; ET, 111 ± 7 vs. 109 ± 7 kg; P < 0.01) and fasting plasma glucose (LCD, 115 ± 10 vs. 99 ± 4 mg/dl; ET, 112 ± 4 vs. 101 ± 5 mg/dl, P < 0.01) and insulin (LCD, 23.9 ± 5.6 vs. 15.2 ± 3.9 μU/ml; ET, 17.6 ± 1.9 vs. 13.9 ± 2.4 μU/ml; P < 0.05) decreased in both groups. There was a 40% reduction in plasma insulin during hyperglycemia (0–45 min) after LCD (peak: 118 ± 18 vs. 71 ± 14 μU/ml; P < 0.05) and ET (69 ± 14 vs. 41 ± 7 μU/ml; P < 0.05) and trends for reductions during arginine infusion and a high-fat drink. The 56% increase in glucose uptake after ET (4.95 ± 0.90 vs. 7.74 ± 0.82 mg ⋅ min−1⋅ kg fat-free mass−1; P < 0.01) was significantly ( P < 0.01) greater than the 19% increase (5.72 ± 1.12 vs. 6.80 ± 0.94 mg ⋅ min−1⋅ kg fat-free mass−1; P = not significant) that occurred after LCD. The marked increase in glucose disposal after ET, despite lower insulin levels, suggests that short-term exercise is more effective than diet in enhancing insulin action in individuals with abnormal glucose tolerance.
Estrogen has rapid tissue-specific effects on rat bone
Authors: Turner R. T. , Kidder L. S. , Zhang M. , Harris S. A. , Westerlind K. C. , Maran A. , Wronski T. J.
Published: December 2017

The decrease in cancellous bone formation after estrogen treatment is generally thought to be coupled with a prior decrease in bone resorption. To test the possibility that estrogen has rapid tissue-specific actions on bone metabolism, we determined the time course (1–32 h) effects of diethylstilbestrol on steady-state mRNA levels for immediate-response genes, extracellular matrix proteins, and signaling peptides in the proximal tibial metaphysis and uterus by using Northern blot and RNase protection assays. The regulation of signaling peptides by estrogen, although tissue specific, followed a similar time course in bone and uterus. The observed rapid decreases in expression of insulin-like growth factor I, a growth factor associated with bone formation; decreases in mRNA levels for bone matrix proteins; evidence for reduced bone matrix synthesis; failure to detect rapid increases in mRNA levels for signaling peptides implicated in mediating the inhibitory effects of estrogen on bone resorption (interleukin-1 and -6) as well as other cytokines that can increase bone resorption; and the comparatively long duration of the bone remodeling cycle in rats indicate that estrogen can decrease bone formation by a mechanism that does not require a prior reduction in bone resorption.
Alterations in pulmonary surfactant after rapid arousal from torpor in the marsupialSminthopsis crassicaudata
Authors: Lopatko Olga V. , Orgeig Sandra , Palmer David , Schürch Samuel , Daniels Christopher B.
Published: December 2017

Torpor in the dunnart, Sminthopsis crassicaudata, alters surfactant lipid composition and surface activity. Here we investigated changes in surfactant composition and surface activity over 1 h after rapid arousal from torpor (15–30°C at 1°C/min). We measured total phospholipid (PL), disaturated PL (DSP), and cholesterol (Chol) content of surfactant lavage and surface activity (measured at both 15 and 37°C in the captive bubble surfactometer). Immediately after arousal, Chol decreased (from 4.1 ± 0.05 to 2.8 ± 0.3 mg/g dry lung) and reached warm-active levels by 60 min after arousal. The Chol/DSP and Chol/PL ratios both decreased to warm-active levels 5 min after arousal because PL, DSP, and the DSP/PL ratio remained elevated over the 60 min after arousal. Minimal surface tension and film compressibility at 17 mN/m at 37°C both decreased 5 min after arousal, correlating with rapid changes in surfactant Chol. Therefore, changes in lipids matched changes in surface activity during the postarousal period.
Incorporation and utilization of [3-13C]lactate and [1,2-13C]acetate by rat skeletal muscle
Authors: Bertocci Loren A. , Lujan Barbara F.
Published: December 2017

Skeletal muscle can utilize many different substrates, and traditional methodologies allow only indirect discrimination between oxidative and nonoxidative uptake of substrate, possibly with contamination by metabolism of other internal organs. Our goal was to apply1H- and13C-nuclear magnetic resonance spectroscopy to monitor the patterns of [3-13C]lactate and [1,2-13C]acetate (model of simple carbohydrates and fats, respectively) utilization in resting vs. contracting muscle extracts of the isolated perfused rat hindquarter. Total metabolite concentrations were measured by using NADH-linked fluorometric assays. Fractional oxidation of [3-13C]lactate was unchanged by contraction despite vascular endogenous lactate accumulation. Although label accumulated in several citric acid cycle (CAC) intermediates, contraction did not increase the concentration of CAC intermediates in any muscle extracts. We conclude that 1) the isolated rat hindquarter is a viable, well-controlled model for measuring skeletal muscle13C-labeled substrate utilization; 2) lactate is readily oxidized even during contractile activity; 3) entry and exit from the CAC, via oxidative and nonoxidative pathways, is a component of normal muscle metabolism and function; and 4) there are possible differences between gastrocnemius and soleus muscles in utilization of nonoxidative pathways.
Lung mechanics and end-expiratory lung volume during hypoxia in rats
Authors: Bonora M. , Vizek M.
Published: December 2017

We investigated whether an hypoxia-induced increase in airway resistance mediated by vagal efferents participates in the increase in end-expiratory lung volume (EELV) observed in hypoxia. We also assessed the contribution of the end-expiratory activity of the diaphragm (De) to this phenomenon. Therefore, we measured EELV, total lung resistance (Rl), dynamic lung compliance (Cdyn), De, and minute ventilation (V˙e) in anesthetized rats during normoxia and hypoxia (10% O2) before (control) and after administration of atropine or saline. In the control group, hypoxia increased EELV, Cdyn, De, andV˙e but slightly decreased Rl. These changes were unaffected by saline or atropine, except that, in the atropine-treated rats, hypoxia did not change Rl. These results suggest that 1) the increase in EELV observed in hypoxia cannot result from an increase in airway resistance; 2) the increased and persistent activity of inspiratory muscles during expiration is the most likely cause of the increase in EELV during hypoxia; and 3) the decrease in Rl induced by hypoxia could result from the increase in lung volume including EELV.
Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes
Authors: Jarreau Pierre-Henri , Louis Bruno , Dassieu Gilles , Desfrere Luc , Blanchard Perre W. , Moriette Guy , Isabey Daniel , Harf Alain
Published: December 2017

Endotracheal tubes (ETTs) constitute a resistive extra load for intubated patients. The ETT pressure drop (ΔPETT) is usually described by empirical equations that are specific to one ETT only. Our laboratory previously showed that, in adult ETTs, ΔPETT is given by the Blasius formula (F. Lofaso, B. Louis, L. Brochard, A. Harf, and D. Isabey. Am. Rev. Respir. Dis. 146: 974–979, 1992). Here, we also propose a general formulation for neonatal and pediatric ETTs on the basis of adimensional analysis of the pressure-flow relationship. Pressure and flow were directly measured in seven ETTs (internal diameter: 2.5–7.0 mm). The measured pressure drop was compared with the predicted drop given by general laws for a curved tube. In neonatal ETTs (2.5–3.5 mm) the flow regime is laminar. The ΔPETT can be estimated by the Ito formula, which replaces Poiseuille’s law for curved tubes. For pediatric ETTs (4.0–7.0 mm), ΔPETT depends on the following flow regime: for laminar flow, it must be calculated by the Ito formula, and for turbulent flow, by the Blasius formula. Both formulas allow for ETT geometry and gas properties.
Postnatal hemodynamic changes in very-low-birthweight infants
Authors: Yanowitz Toby Debra , Yao Alice C. , Pettigrew Karen D. , Werner John C. , Oh William , Stonestreet Barbara S.
Published: December 2017

The purpose of this study was to characterize postnatal changes in regional Doppler blood flow velocity (BFV) and cardiac function of very-low-birthweight infants and to examine factors that might influence these hemodynamic changes. Mean and end-diastolic BFV of the middle cerebral and superior mesenteric arteries, cardiac output, stroke volume, and fractional shortening were measured in 20 infants birthweight 1,002 ± 173 g, gestational age 28 ± 2 wk) at 6, 30, and 54 h after birth and before and after feedings on days 7 and 14. Postnatal increases in cerebral BFV, mesenteric BFV, and cardiac output were observed that were not associated with changes in blood pressure, hematocrit, pH, arterial[Formula: see text], or oxygen saturation. The postnatal pattern of relative vascular resistance (RVR) differed between the cerebral and mesenteric vasculatures. RVR decreased in the middle cerebral but not the superior mesenteric artery. Physiological patency of the ductus arteriosus did not alter postnatal hemodynamic changes. In response to feeding, mesenteric BFV and stroke volume increased, and mesenteric RVR and heart rate decreased. Postprandial responses were not affected by postnatal age or the age at which feeding was initiated. However, the initiation of enteral nutrition before 3 days of life was associated with higher preprandial mesenteric BFV and lower mesenteric RVR than was later initiation of feeding. We conclude that in very-low-birthweight infants over the first week of life 1) systemic, cerebral, and mesenteric hemodynamics exhibit region-specific changes; 2) asymptomatic ductus arteriosus patency and early feedings do not significantly influence these postnatal hemodynamic changes; and 3) cardiac function adapts to increase local mesenteric BFV in response to feedings.
Reflex control of cutaneous vasoconstrictor system is reset by exogenous female reproductive hormones
Authors: Charkoudian Nisha , Johnson John M.
Published: December 2017

To determine whether cardiovascular influences of exogenous female steroid hormones include effects on reflex thermoregulatory control of the adrenergic cutaneous vasoconstrictor system, we conducted ramp decreases in skin temperature (Tsk) in eight women in both high- and low (placebo)-progesterone/estrogen phases of oral contraceptive use. With the use of water-perfused suits, Tsk was held at 36°C for 10 min (to minimize initial vasoconstrictor activity) and was then decreased in a ramp, ∼0.2°C/min for 12–15 min. Subjects rested supine for 30–40 min before each experiment, and the protocol was terminated before the onset of shivering. Skin blood flow was monitored by laser-Doppler flowmetry and arterial pressure by finger photoplethysmography. In all experiments, cutaneous vasoconstriction began immediately with the onset of cooling, and cutaneous vascular conductance (CVC) decreased progressively with decreasing Tsk. Regression analysis of the relationship of CVC to Tsk showed no difference in slope between phases (low-hormone phase: 17.67 ± 5.57; high-hormone phase: 17.40 ± 8.00 %baseline/°C; P > 0.05). Additional studies involving local blockade confirmed this response as being solely due to the adrenergic vasoconstrictor system. Waking oral temperature (Tor) was significantly higher on high-hormone vs. low-hormone days (36.60 ± 0.11 vs. 36.37 ± 0.09 °C, respectively; P < 0.02). Integrative analysis of CVC in terms of simultaneous values for Tsk and Tor showed that the cutaneous vasoconstrictor response was shifted in the high-hormone phase such that a higher Tor was maintained throughout cooling ( P < 0.05). Thus reflex thermoregulatory control of the cutaneous vasoconstrictor system is shifted to higher internal temperatures by exogenous female reproductive hormones.
Aging and acute exercise enhance free radical generation in rat skeletal muscle
Authors: Bejma J. , Ji L. L.
Published: December 2017

Reactive oxygen species (ROS) are implicated in the mechanism of biological aging and exercise-induced oxidative damage. The present study examined the effect of an acute bout of exercise on intracellular ROS production, lipid and protein peroxidation, and GSH status in the skeletal muscle of young adult (8 mo, n = 24) and old (24 mo, n = 24) female Fischer 344 rats. Young rats ran on a treadmill at 25 m/min and 5% grade until exhaustion (55.4 ± 2.7 min), whereas old rats ran at 15 m/min and 5% grade until exhaustion (58.0 ± 2.7 min). Rate of dichlorofluorescin (DCFH) oxidation, an indication of ROS and other intracellular oxidants production in the homogenate of deep vastus lateralis, was 77% ( P < 0.01) higher in rested old vs. young rats. Exercise increased DCFH oxidation by 38% ( P < 0.09) and 50% ( P < 0.01) in the young and old rats, respectively. DCFH oxidation in isolated deep vastus lateralis mitochondria with site 1 substrates was elevated by 57% ( P < 0.01) in old vs. young rats but was unaltered with exercise. Significantly higher DCFH oxidation rate was also found in aged-muscle mitochondria ( P < 0.01), but not in homogenates, when ADP, NADPH, and Fe3+ were included in the assay medium without substrates. Lipid peroxidation in muscle measured by malondialdehyde content showed no age effect, but was increased by 20% ( P < 0.05) with exercise in both young and old rats. Muscle protein carbonyl formation was unaffected by either age or exercise. Mitochondrial GSH/ GSSG ratio was significantly higher in aged vs. young rats ( P < 0.05), whereas exercise increased GSSG content and decreased GSH/GSSG in both age groups ( P < 0.05). These data provided direct evidence that oxidant production in skeletal muscle is increased in old age and during prolonged exercise, with both mitochondrial respiratory chain and NADPH oxidase as potential sources. The alterations of muscle lipid peroxidation and mitochondrial GSH status were consistent with these conclusions.
Free radical activity, antioxidant enzyme, and glutathione changes with muscle stretch injury in rabbits
Authors: Best Thomas M. , Fiebig Russel , Corr David T. , Brickson Stacey , Ji Lili
Published: December 2017

The present study investigated changes in rate of free radical production, antioxidant enzyme activity, and glutathione status immediately after and 24 h after acute muscle stretch injury in 18 male New Zealand White rabbits. There was no change in free radical production in injured muscles, compared with noninjured controls, immediately after injury ( time 0; P = 0.782). However, at 24 h postinjury, there was a 25% increase in free radical production in the injured muscles. Overall, there was an interaction (time and treatment) effect ( P = 0.005) for free radical production. Antioxidant enzyme activity demonstrated a treatment (injured vs. control) and interaction effect for both glutathione peroxidase ( P = 0.015) and glutathione reductase ( P = 0.041). There was no evidence of lipid peroxidation damage, as measured by muscle malondialdehyde content. An interaction effect occurred for both reduced glutathione ( P = 0.008) and total glutathione ( P = 0.015). Morphological analysis (hematoxylin and eosin staining) showed significant polymorphonuclear cell infiltration of the damaged region at 24 h postinjury. We conclude that acute mechanical muscle stretch injury results in increased free radical production within 24 h after injury. Antioxidant enzyme and glutathione systems also appear to be affected during this early postinjury period.