bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibitory effect of inhaled wood smoke on the discharge of pulmonary stretch receptors in rats
Authors: Lai C. J. , Kou Y. R.
Published: December 2017

We investigated the inhibition of slowly adapting pulmonary stretch receptors (PSRs) by inhaled wood smoke. Impulses were recorded from PSRs in 68 anesthetized, open-chest, and artificially ventilated rats. Eighty-one of one hundred five PSRs were inhibited within one or two breaths when 6 ml of wood smoke were delivered into the lungs. As a group ( n = 105), PSR activity significantly decreased from a baseline of 19.0 ± 1.3 (SE) to a lowest level of 12.9 ± 1.2 impulses/breath at the fourth or fifth breath after smoke delivery. This afferent inhibition usually persisted for 5–18 breaths. In contrast, smoke delivery did not affect transpulmonary pressure. Delivery of gas-phase smoke or a hypercapnic gas mixture containing CO2 at a concentration (15%) matching that in the smoke produced a nearly identical inhibition in the same PSRs ( n = 10). This afferent inhibition was largely prevented by pretreatment with acetazolamide (an inhibitor of carbonic anhydrase; n = 10) but was not affected by pretreatment with the vehicle for acetazolamide ( n = 8) or isoproterenol (a bronchodilator; n = 10). These results suggest that 1) an increase in H+ concentration resulting from hydration of CO2 in the smoke may be responsible for the inhibitory effect of wood smoke on the discharge of PSRs and 2) changes in lung mechanics are not the cause of this afferent inhibition.
Functional magnetic stimulation of expiratory muscles: a noninvasive and new method for restoring cough
Authors: Lin Vernon W. H. , Hsieh Caleb , Hsiao Ian N. , Canfield James
Published: December 2017

The purpose of this study was to assess the effectiveness of functional magnetic stimulation (FMS) for producing expiratory function in normal human subjects. Twelve able-bodied normal subjects were recruited for this study. FMS of the expiratory muscles was performed by using a magnetic stimulator and placing the magnetic coil along the lower thoracic spine. Results showed that peak expired pressure, volume, and flow rate generated by FMS at the end of normal inspiration (102.5 ± 13.62 cmH2O, 1.6 ± 0.16 liters, and 4.8 ± 0.35 l/s, respectively) were comparable to their voluntary maximal levels ( P > 0.1). The optimal coil placement was between T7 and T11, and the optimal stimulation parameters were a frequency of 25 Hz and 70–80% of maximal intensity. We conclude that 1) FMS of the lower thoracic nerves in normal subjects resulted in a significant expiratory function comparable to their voluntary maximum; 2) FMS was noninvasive and was well tolerated by all subjects; and 3) FMS may be useful to produce cough in patients in critical care or perioperative settings, or in patients with neurological disorders.
Catecholamine response during 12 days of high-altitude exposure (4,300 m) in women
Authors: Mazzeo Robert S. , Child Avon , Butterfield Gail E. , Mawson Jacinda T. , Zamudio Stacy , Moore Lorna G.
Published: December 2017

We have previously demonstrated that acclimatization to high altitude elicits increased sympathetic nerve activity in men. The purpose of this investigation was to determine 1) whether women respond in a similar manner as found previously in men and 2) the extent to which menstrual cycle phase influences this response. Sixteen eumenorrheic women (age, 23.6 ± 1.2 yr; weight, 56.2 ± 4.3 kg) were studied at sea level and during 12 days of high-altitude exposure (4,300 m) in either their follicular (F; n = 11) or luteal (L; n = 5) phase. Twenty-four-hour urine samples were collected at sea level and during each day at altitude. Catecholamines were determined by high-performance liquid chromatography with electrochemical detection. Compared with sea-level values, urinary norepinephrine excretion increased significantly during altitude exposure, peaking on days 4–6. Thereafter, levels remained constant throughout the duration of altitude exposure. The magnitude of this increase was similar between the F (138%) and L (93%) phase. Urinary epinephrine levels were elevated on day 2 of altitude exposure compared with sea-level values for both F and L subjects (93%). Thereafter, urinary epinephrine excretion returned to sea-level values, and no differences were found between F and L subjects. Plasma catecholamine content was consistent with urinary values and supports the concept of an elevation in sympathetic activity over time at altitude. Mean and diastolic blood pressure as well as heart rate adjustments to high altitude correlated significantly with urinary norepinephrine excretion rates. It was concluded that 1) urinary and plasma catecholamine responses to 12 days of high-altitude exposure in women are similar to those previously documented to occur for men; 2) whereas no differences in catecholamine levels were observed between F- and L-phase assignments, for a given urinary norepinephrine excretion rate, blood pressure and heart rates were lower for F vs. L subjects; and 3) several cardiovascular adaptations associated with high-altitude exposure correlated with 24-h urinary norepinephrine excretion rates and thus sympathetic nerve activity.
Surfactant replacement increases compliance in premature lamb lungs during partial liquid ventilation in situ
Authors: Tarczy-Hornoch Peter , Hildebrandt Jack , Standaert Thomas A. , Jackson J. Craig
Published: December 2017

Treatments available to improve compliance in surfactant-deficient states include exogenous surfactant (ES) and either partial (PLV) or total liquid ventilation (TLV) with perfluorochemical (PFC). Because of the additional air-lung and air-PFC interfaces introduced during PLV compared with TLV, we hypothesized that compliance would be worse during PLV than during TLV. Because surfactant is able to reduce interfacial tension between air and lung as well as between PFC and lung, we further hypothesized that compliance would improve with surfactant treatment before PLV. In excised preterm lamb lungs, we used Survanta for surfactant replacement and perflubron as the PFC. Compliance during PLV was intermediate between TLV and gas inflation, both with and without surfactant. Surfactant improved compliance during PLV, compared with PLV alone. Because of the force-balance equation governing the behavior of immiscible droplets on liquid surfaces, we predict that PFC droplets spread during PLV to cover the alveolar surface in surfactant-deficient lungs during most of lung inflation and deflation but that the PFC would retract into droplets in surfactant-sufficient lungs, except at end inspiration.
Effects of short-term inactivity on glucose tolerance, energy expenditure, and blood flow in trained subjects
Authors: Arciero Paul J. , Smith Denise L. , Calles-Escandon Jorge
Published: December 2017

The purpose of this investigation was to examine the effects of 7–10 days of inactivity (IA) on glucose tolerance (GT), resting metabolic rate (RMR), thermic effect of a meal (TEM), and limb blood flow in endurance-trained men. Eight highly trained (peak O2consumption 64 ± 2 ml ⋅ kg−1⋅ min−1) endurance athletes participated in this study involving two identical test days, one ∼24 h after a normal training bout (Tr) and the second after 7–10 days of IA. The following tests were conducted at each visit: 75-g oral glucose tolerance test (OGTT), RMR, and TEM and measurements of calf and forearm blood flow (BF) by using venous occlusive plethysmography. Body weight remained unchanged during this short period of IA (Tr, 78.5 ± 1 kg; IA, 78.7 ± 1 kg). The area under the glucose and insulin curves increased 65% (Tr, 3,375 ± 877 vs. IA, 5,559.4 ± 621 mg ⋅ dl−1⋅ 180 min−1) and 73% (Tr, 2,182.5 ± 270 vs. IA, 3,793.1 ± 739 μU ⋅ ml−1⋅ 180 min−1) after IA, respectively ( P < 0.01). RMR decreased significantly (4%; 1.5 ± 0.02 vs. 1.44 ± 0.02 kcal/min; P < 0.05) and respiratory exchange ratio during the OGTT increased (4%, 0.812 ± 0.011 vs. 0.842 ± 0.009; P < 0.05) after IA, whereas TEM increased similarly in the Tr and IA states. In the Tr state, mean calf BF increased by 22% (3.17 ± 0.22 vs. 3.87 ± 0.38 ml ⋅ 100 ml−1⋅ min−1; P < 0.05) during the OGTT but remained unchanged after IA, whereas no differences at rest or during OGTTs existed between the two conditions for forearm BF. Incremental insulin area above fasting during the OGTT was correlated with mean calf BF in the Tr ( r = 0.76, P < 0.05) and IA ( r = 0.72, P < 0.05) states. In conclusion, 7–10 days of IA results in a deterioration in GT and a reduction in RMR. After glucose ingestion, calf BF was elevated compared with resting levels in the Tr state but was unchanged in the IA state; however, limb BF was not related to GT or RMR. Thus our findings raise questions regarding the relative contribution of BF in modulating glucose tolerance and energy expenditure in endurance athletes in their habitual Tr or IA state.
Body composition by air-displacement plethysmography by using predicted and measured thoracic gas volumes
Authors: McCrory Megan A. , Molé Paul A. , Gomez Terri D. , Dewey Kathryn G. , Bernauer Edmund M.
Published: December 2017

The BOD POD, a new air-displacement plethysmograph for measuring human body composition, utilizes the inverse relationship between pressure and volume (Boyle’s law) to measure body volume directly. The quantity of air in the lungs during tidal breathing, the average thoracic gas volume (Vtg), is also measured by the BOD POD by using a standard plethysmographic technique. Alternatively, the BOD POD provides the use of a predicted Vtg (Vtgpred). The validity of using Vtgpred in place of measured Vtg (Vtgmeas) to determine the percentage of body fat (%BF) was evaluated in 50 subjects (36 women, 14 men; ages 18–56 yr). There was no significant difference between Vtgmeas and Vtgpred (mean difference ± SE, 53.5 ± 63.3 ml) nor in %BF by using Vtgmeas vs. Vtgpred (0.2 ± 0.2 %BF). On an individual basis, %BF measured by using Vtgmeas vs. Vtgpred differed within ±2.0% BF for 82% of the subjects; maximum differences were −2.9 to +3.0% BF. For comparison, data from 24 subjects who had undergone hydrostatic weighing were evaluated for the validity of using predicted vs. measured residual lung volume (Vr pred vs. Vr meas, respectively). Differences between Vr meas and Vr pred and in %BF calculated by using Vr meas vs. Vr pred were significant (187 ± 46 ml and 1.4 ± 0.3% BF, respectively; P < 0.001). On an individual basis, %BF determined by using Vr meas vs. Vr preddiffered within ±2.0% BF for 46% of the subjects; maximum differences were −2.9 to +3.8% BF. With respect to %BF measured by air displacement, our findings support the use of Vtgpred for group mean comparisons and for purposes such as screening in young to middle-aged individuals. This contrasts with the use of Vr pred in hydrostatic weighing, which leads to significant errors in the estimation of %BF. Furthermore, although the use of Vtgpred has some application, determining Vtgmeas is relatively simple in most cases. Therefore, we recommend that the use of Vtgmeas remain as standard experimental and clinical practice.
Head-up suspension in humans: effects on sympathetic vasomotor activity and cardiovascular responses
Authors: Shamsuzzaman A. S. M. , Sugiyama Y. , Kamiya A. , Fu Q. , Mano T.
Published: December 2017

We hypothesized that muscle sympathetic nerve activity (MSNA) and cardiovascular responses to the conventional head-up tilt (HUT) are different from those to head-up suspension (HUS) because of antigravity muscle activity. The MSNA from the tibial nerve, heart rate, blood pressure, stroke volume, cardiac output, and calf blood flow were measured in 13 healthy young subjects. Left atrial diameter was measured by two-dimensional echocardiography in another nine subjects. The resting MSNA and cardiovascular responses at a low level (20°) of orthostasis were similar during both modes. At higher levels (40 and 60°), the responses of MSNA, heart rate, stroke volume, and cardiac output were significantly stronger and there was a smaller reduction in calf blood flow during HUT than during HUS ( P < 0.05). Left atrial diameter was decreased significantly from the resting values during HUT and HUS without any significant difference between the modes of orthostasis. The results provide evidence that the engagement of antigravity muscles during HUT may have additive effects on sympathetic vasoconstrictor and cardiovascular responses to orthostatic stress.
l-Arginine-NO pathway and CNS oxygen toxicity
Authors: Bitterman Noemi , Bitterman Haim
Published: December 2017

The involvement of thel-arginine-nitric oxide (NO) pathway in the pathogenesis of hyperoxia-induced seizures was studied by using agents controlling NO levels. We selected two inhibitors of nitric oxide synthase, the systemic inhibitor N ω-nitro-l-arginine methyl ester (l-NAME) and the novel cerebral-specific inhibitor 7-nitroindazole, and two generators of NO, the NO donor S-nitroso- N-acetylpenicillamine and the physiological precursorl-arginine. Rats with chronic cortical electrodes were injected intraperitoneally with different doses of one of the agents or their vehicles before exposure to 0.5 MPa O2 and O2 with 5% CO2 at an absolute pressure of 0.5 MPa. The duration of the latent period until the onset of electrical discharges in the electroencephalogram was used as an index of central nervous system O2 toxicity. The two nitric oxide synthase inhibitorsl-NAME and 7-nitroindazole significantly prolonged the latent period to the onset of seizures on exposure to both hyperbaric O2 and to the hypercapnic-hyperoxic mixture. Pretreatment with the NO donor S-nitroso- N-acetylpenicillamine significantly shortened the latent period, whereasl-arginine, the physiological precursor of NO, significantly prolonged the latent period to onset of seizures. Our results suggest that thel-arginine-NO pathway is involved in the pathophysiology of hyperoxia-induced seizures via various regulating mechanisms.
Heat acclimation, aerobic fitness, and hydration effects on tolerance during uncompensable heat stress
Authors: Cheung Stephen S. , McLellan Tom M.
Published: December 2017

—The purpose of the present study was to determine the separate and combined effects of aerobic fitness, short-term heat acclimation, and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40°C, 30% relative humidity). Men who were moderately fit [(MF); <50 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 7] and highly fit [(HF); >55 ml ⋅ kg−1 ⋅ min−1maximal O2 consumption; n = 8] were tested while they were euhydrated or hypohydrated by ∼2.5% of body mass through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after 2 wk of daily heat acclimation (1-h treadmill exercise at 40°C, 30% relative humidity, while wearing the nuclear, biological, and chemical protective clothing). Heat acclimation increased sweat rate and decreased skin temperature and rectal temperature (Tre) in HF subjects but had no effect on tolerance time (TT). MF subjects increased sweat rate but did not alter heart rate, Tre, or TT. In both MF and HF groups, hypohydration significantly increased Tre and heart rate and decreased the respiratory exchange ratio and the TT regardless of acclimation state. Overall, the rate of rise of skin temperature was less, while ΔTre, the rate of rise of Tre, and the TT were greater in HF than in MF subjects. It was concluded that exercise-heat tolerance in this uncompensable heat-stress environment is not influenced by short-term heat acclimation but is significantly improved by long-term aerobic fitness.
Altered metabolic response of iron-depleted nonanemic women during a 15-km time trial
Authors: Zhu Y. Isabel , Haas Jere D.
Published: December 2017

In this double-blinded study, 37 women with iron depletion without anemia (age 19–36 yr) were randomly assigned to receive either an iron supplement (135 mg/day) or a placebo. Endurance capacity was assessed during a 15-km simulated time trial (TT) on a cycle ergometer before and after the 8-wk treatment. After the treatment, although the iron-supplemented group did not have shorter time to finish the TT (time), it had 2.0 kJ/min lower energy expenditure and 5.1% lower fractional utilization of peak oxygen consumption during the TT compared with the placebo group, after controlling for work rate ( P < 0.05). Time, fractional utilization of peak oxygen consumption, and plasma lactate concentration at the 5th km of the TT were all negatively associated with hemoglobin levels, after controlling for work rate ( P < 0.05). In conclusion, repletion of iron stores to women with iron depletion without anemia increased their energetic efficiency, and oxygen transport capacity of the blood was found to be an important determinant of endurance capacity and energy metabolism in nonanemic women.
Velocity, force, power, and Ca2+sensitivity of fast and slow monkey skeletal muscle fibers
Authors: Fitts Robert H. , Bodine Sue C. , Romatowski Janell G. , Widrick Jeffrey J.
Published: December 2017

In this study, we determined the contractile properties of single chemically skinned fibers prepared from the medial gastrocnemius (MG) and soleus (Sol) muscles of adult male rhesus monkeys and assessed the effects of the spaceflight living facility known as the experiment support primate facility (ESOP). Muscle biopsies were obtained 4 wk before and immediately after an 18-day ESOP sit, and fiber type was determined by immunohistochemical techniques. The MG slow type I fiber was significantly smaller than the MG type II, Sol type I, and Sol type II fibers. The ESOP sit caused a significant reduction in the diameter of type I and type I/II (hybrid) fibers of Sol and MG type II and hybrid fibers but no shift in fiber type distribution. Single-fiber peak force (mN and kN/m2) was similar between fiber types and was not significantly different from values previously reported for other species. The ESOP sit significantly reduced the force (mN) of Sol type I and MG type II fibers. This decline was entirely explained by the atrophy of these fiber types because the force per cross-sectional area (kN/m2) was not altered. Peak power of Sol and MG fast type II fiber was 5 and 8.5 times that of slow type I fiber, respectively. The ESOP sit reduced peak power by 25 and 18% in Sol type I and MG type II fibers, respectively, and, for the former fiber type, shifted the force-pCa relationship to the right, increasing the Ca2+activation threshold and the free Ca2+concentration, eliciting half-maximal activation. The ESOP sit had no effect on the maximal shortening velocity ( Vo) of any fiber type. Voof the hybrid fibers was only slightly higher than that of slow type I fibers. This result supports the hypothesis that in hybrid fibers the slow myosin heavy chain would be expected to have a disproportionately greater influence on Vo.
Bioenergetics of contracting skeletal muscle after partial reduction of blood flow
Authors: Hogan Michael C. , Gladden L. Bruce , Grassi Bruno , Stary Creed M. , Samaja Michele
Published: December 2017

The purpose of this study was to examine the bioenergetics and regulation of O2uptake (V˙o2) and force production in contracting muscle when blood flow was moderately reduced during a steady-state contractile period. Canine gastrocnemius muscle ( n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s (Hz) immediately followed by a reduction of blood flow [ischemic (I) condition] to 46 ± 3% of the value obtained at 0.5 Hz with normal blood flow. TheV˙o2of the contracting muscle was significantly ( P < 0.05) reduced during the I condition [6.5 ± 0.8 (SE) ml ⋅ 100 g−1⋅ min−1] compared with the same stimulation frequency with normal flow (11.2 ± 1.5 ml ⋅ 100 g−1⋅ min−1), as was the tension-time index (79 ± 12 vs. 123 ± 22 N ⋅ g−1⋅ min−1, respectively). The ratio ofV˙o2to tension-time index remained constant throughout all contraction periods. Muscle phosphocreatine concentration, ATP concentration, and lactate efflux were not significantly different during the I condition compared with the 0.5-Hz condition with normal blood flow. However, at comparable rates of V˙o2and tension-time index, muscle phosphocreatine concentration and ATP concentration were significantly less during the I condition compared with normal-flow conditions. These results demonstrate that, in this highly oxidative muscle, the normal balance of O2supply to force output was maintained during moderate ischemia by downregulation of force production. In addition, 1) the minimal disruption in intracellular homeostasis after the initiation of ischemia was likely a result of steady-state metabolic conditions having already been activated, and 2) the difference in intracellular conditions at comparable rates ofV˙o2and tension-time index between the normal flow and I condition may have been due to altered intracellular O2tension.
Ventrolateral medullary respiratory network and a model of cough motor pattern generation
Authors: Shannon Roger , Baekey David M. , Morris Kendall F. , Lindsey Bruce G.
Published: December 2017

The primary hypothesis of this study was that the cough motor pattern is produced, at least in part, by the medullary respiratory neuronal network in response to inputs from “cough” and pulmonary stretch receptor relay neurons in the nucleus tractus solitarii. Computer simulations of a distributed network model with proposed connections from the nucleus tractus solitarii to ventrolateral medullary respiratory neurons produced coughlike inspiratory and expiratory motor patterns. Predicted responses of various “types” of neurons (I-DRIVER, I-AUG, I-DEC, E-AUG, and E-DEC) derived from the simulations were tested in vivo. Parallel and sequential responses of functionally characterized respiratory-modulated neurons were monitored during fictive cough in decerebrate, paralyzed, ventilated cats. Coughlike patterns in phrenic and lumbar nerves were elicited by mechanical stimulation of the intrathoracic trachea. Altered discharge patterns were measured in most types of respiratory neurons during fictive cough. The results supported many of the specific predictions of our cough generation model and suggested several revisions. The two main conclusions were as follows: 1) The Bötzinger/rostral ventral respiratory group neurons implicated in the generation of the eupneic pattern of breathing also participate in the configuration of the cough motor pattern. 2) This altered activity of Bötzinger/rostral ventral respiratory group neurons is transmitted to phrenic, intercostal, and abdominal motoneurons via the same bulbospinal neurons that provide descending drive during eupnea.
Elicited pontogeniculooccipital waves and phasic suppression of diaphragm activity in sleep and wakefulness
Authors: Hunt Wendy K. , Sanford Larry D. , Ross Richard J. , Morrison Adrian R. , Pack Allan I.
Published: December 2017

Fractionations are 20- to 100-ms pauses in diaphragm activity that occur spontaneously during rapid-eye-movement (REM) sleep, sometimes in association with pontogeniculooccipital (PGO) waves. Auditory stimuli can elicit fractionations or PGO waves during REM sleep, non-REM (NREM) sleep, and waking; however, their interrelationship has not been investigated. To determine whether the two phenomena are produced by a common phasic-event generator in REM sleep, we examined PGO waves and fractionations that were elicited by auditory stimuli (tones) presented to freely behaving cats across states. Tones elicited PGO waves and two types of fractionations: short-latency fractionation responses (SFRs; 10- to 60-ms latencies) and long-latency fractionation responses (LFRs; 60- to 120-ms latencies). Both a PGO wave and a SFR were elicited in 60–70% of trials across states, but each could be elicited alone. The latencies and durations of elicited SFRs were similar across states, but the latencies of elicited PGO waves in REM sleep (mean 62.5 ms) were significantly longer than in waking or NREM sleep. Elicited SFRs consistently occur with shorter latencies than do PGO waves, in contrast to spontaneous fractionations, which have a variable relationship to PGO waves and usually occur 10–40 ms after the onset of the PGO wave. The LFR then, elicited most frequently during REM sleep, resembles a spontaneous fractionation in its temporal relationship to the PGO wave and may reflect the bias toward motoneuronal inhibition characterizing REM sleep but not NREM sleep or waking. We conclude that, although PGO waves and SFRs share some features, like LFRs they probably are generated by different neuronal populations. In three cats there was no correlation between PGO waves and fractionations, whereas in one cat they were associated in REM sleep (LFRs and SFRs) and waking (SFRs only). Thus the majority of evidence argues against the existence of a common phasic-event generator in REM sleep.
Muscle performance and enzymatic adaptations to sprint interval training
Authors: MacDougall J. Duncan , Hicks Audrey L. , MacDonald Jay R. , McKelvie Robert S. , Green Howard J. , Smith Kelly M.
Published: December 2017

Our purpose was to examine the effects of sprint interval training on muscle glycolytic and oxidative enzyme activity and exercise performance. Twelve healthy men (22 ± 2 yr of age) underwent intense interval training on a cycle ergometer for 7 wk. Training consisted of 30-s maximum sprint efforts (Wingate protocol) interspersed by 2–4 min of recovery, performed three times per week. The program began with four intervals with 4 min of recovery per session in week 1 and progressed to 10 intervals with 2.5 min of recovery per session by week 7. Peak power output and total work over repeated maximal 30-s efforts and maximal oxygen consumption (V˙o 2 max) were measured before and after the training program. Needle biopsies were taken from vastus lateralis of nine subjects before and after the program and assayed for the maximal activity of hexokinase, total glycogen phosphorylase, phosphofructokinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, malate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase. The training program resulted in significant increases in peak power output, total work over 30 s, andV˙o 2 max. Maximal enzyme activity of hexokinase, phosphofructokinase, citrate synthase, succinate dehydrogenase, and malate dehydrogenase was also significantly ( P < 0.05) higher after training. It was concluded that relatively brief but intense sprint training can result in an increase in both glycolytic and oxidative enzyme activity, maximum short-term power output, andV˙o 2 max.
Hypertrophy of rat plantaris muscle fibers after voluntary running with increasing loads
Authors: Ishihara Akihiko , Roy Roland R. , Ohira Yoshinobu , Ibata Yasuhiko , Edgerton V. Reggie
Published: December 2017

There have been no systematic comparisons of skeletal muscle adaptations in response to voluntary wheel running under controlled loading conditions. To accomplish this, a voluntary running wheel for rats and mice was developed in which a known load can be controlled and monitored electronically. Five-week-old male Sprague-Dawley rats (10 rats/group) were assigned randomly to either a 1) sedentary control group (Control); 2) voluntary exercised with no load (Run-No-Load) group; or 3) voluntary exercised with additional load (Run-Load) group for 8 wk. The load for the Run-Load group was progressively increased to reach ∼60% of body weight during the last week of training. The proportions of fast glycolytic (FG), fast oxidative glycolytic (FOG), or slow oxidative (SO) fibers in the plantaris were similar in all groups. The absolute and relative plantaris weights were greater in the Run-Load group compared with the Control and Run-No-Load groups. The mean fiber cross-sectional areas of FG, FOG, and SO fibers were 20, 25, and 15% greater in the Run-Load than in Control rats. In addition, these fiber types were 16, 21, and 12% larger in Run-Load than in Run-No-Load rats. The muscle weights and mean cross-sectional areas of each fiber type were highly correlated with the average running distances and total work performed in the Run-Load, but not the Run-No-Load, group. The slope of the relationship between fiber size and running distance and total work performed was significant for each fiber type but was higher for FG and FOG fibers compared with SO fibers. These data show that the load on a rat running voluntarily can determine the magnitude of a hypertrophic response and the population of motor units that are recruited to perform at a given loading condition.
Direct measurement of the energy expenditure of physical activity in preterm infants
Authors: Thureen Patti J. , Phillips Robert E. , Baron Karen A. , DeMarie Mark P. , Hay William W.
Published: December 2017

The energy cost of physical activity (EEA) has been estimated to account for 5–17% of total energy expenditure (TEE) in neonates. To directly measure EEA, a force plate was developed and validated to measure work outputs ranging from 0.3 to 40 kcal ⋅ kg−1⋅ day−1. By use of this force plate plus indirect calorimetry, TEE and EEA were measured and correlated with five activity states in 24 infants with gestational age of 31.6 ± 0.5 (SE) wk and postnatal age of 24.8 ± 3.7 days. TEE and EEA were 69.2 ± 1.5 and 2.4 ± 0.2 kcal ⋅ kg−1⋅ day−1, respectively. EEA per state was 0.5 ± 0.0 (quiet sleep), 2.4 ± 0.2 (active sleep), 2.8 ± 0.4 (quiet awake), 7.5 ± 0.8 (active awake), and 15.1 ± 2.3 (crying) kcal ⋅ kg−1⋅ day−1. This provides the first direct measurement of the contribution of physical activity to TEE in preterm infants and will enable measurement of caloric expenditure from muscle activity in various disease conditions and development of nursing strategies to minimize unnecessary energy losses.
Comparisons of two-, three-, and four-compartment models of body composition analysis in men and women
Authors: Withers R. T. , LaForgia J. , Pillans R. K. , Shipp N. J. , Chatterton B. E. , Schultz C. G. , Leaney F.
Published: December 2017

This study compared the traditional two-compartment (fat mass or FM; fat free mass or FFM) hydrodensitometric method of body composition measurement, which is based on body density, with three (FM, total body water or TBW, fat free dry mass)- and four (FM, TBW, bone mineral mass or BMM, residual)-compartment models in highly trained men ( n = 12), sedentary men ( n = 12), highly trained women ( n = 12), and sedentary women ( n = 12). The means and variances for the relative body fat (%BF) differences between the two- and three-compartment models [2.2 ± 1.6 (SD) % BF; n = 48] were significantly greater ( P ≤ 0.02) than those between the three- and four-compartment models (0.2 ± 0.3% BF; n = 48) for all four groups. The three-compartment model is more valid than the two-compartment hydrodensitometric model because it controls for biological variability in TBW, but additional control for interindividual variability in BMM via the four-compartment model achieves little extra accuracy. The combined group ( n = 48) exhibited greater ( P < 0.001) FFM densities (1.1075 ± 0.0049 g/cm3) than the hydrodensitometric assumption of 1.1000 g/cm3, which is based on analyses of three male cadavers aged 25, 35, and 46 yr. This was primarily because their FFM hydration (72.4 ± 1.1%; n = 48) was lower ( P ≤ 0.001) than the hydrodensitometric assumption of 73.72%.
Pennes’ 1948 paper revisited
Authors: Wissler Eugene H.
Published: December 2017

A paper published by Harry H. Pennes in Volume 1 of the Journal of Applied Physiology defined the theoretical basis for a considerable body of analysis performed by many investigators during the ensuing half century. However, during the past decade, the Pennes’ model of heat transfer in perfused tissue has been criticized for various reasons, one of which is that his own experimental data seemed to be at variance with the model. More specifically, the shape of the mean temperature-depth relationship measured by Pennes was distinctly different from the shape of the theoretical curve. In this paper, I show that Pennes used an inappropriate procedure to analyze his data and that, when the data are analyzed in a more rigorous manner, they support his theory. Additional support for Pennes’ theory is provided by the experimental data of H. Barcroft and O. G. Edholm [ J. Physiol. (Lond.) 102: 5–20, 1942 and 104: 366–376, 1946], who had previously studied cooling of the forearm during immersion in water at various temperatures.
Rat brain VEGF expression in alveolar hypoxia: possible role in high-altitude cerebral edema
Authors: Xu Fengping , Severinghaus John W.
Published: December 2017

The mechanism by which hypoxia causes high-altitude cerebral edema (HACE) is unknown. Tissue hypoxia triggers angiogenesis, initially by expressing vascular endothelial growth factor (VEGF), which has been shown to increase extracerebral capillary permeability. This study investigated brain VEGF expression in 32 rats exposed to progressively severe normobaric hypoxia (9–6% O2) for 0 (control), 3, 6, or 12 h or 1, 2, 3, or 6 days. O2concentration was adjusted intermittently to the limit of tolerance by activity and intake, but no attempt was made to detect HACE. Northern blot analysis demonstrated that two molecular bands of transcribed VEGF mRNA (∼3.9 and 4.7 kb) were upregulated in cortex and cerebellum after as little as 3 h of hypoxia, with a threefold increase peaking at 12–24 h. Western blot revealed that VEGF protein was increased after 12 h of hypoxia, reaching a maximum in ∼2 days. The expression of flt-1 mRNA was enhanced after 3 days of hypoxia. We conclude that VEGF production in hypoxia is consistent with the hypothesis that angiogenesis may be involved in HACE.
Cardiac output and mixed venous O2 content measurements by a tracer bolus method: animal validation study
Authors: Clark Justin S. , Lin Yuxiang J. , Criddle Michael J. , Jones Roger , Koppert Erik , Swier Patrick
Published: December 2017

A bolus method for noninvasive measurement of cardiac output (CO) and mixed venous oxygen content ([Formula: see text] [Formula: see text]) has been tested against absolute CO and[Formula: see text] [Formula: see text]standards in dogs. No statistical differences in CO were found between bolus method and electromagnetic flowmeter measurement comparisons in an 18-dog study in which CO varied from 0.5 to 3.0 l/min. The SD for all paired differences was 0.14 l/min; however, data averaging over 10-min intervals were found to reduce the CO measurement uncertainty to <0.08 l/min. The ability of the bolus method to follow rapid CO changes, experimentally produced by control of a pump (surgically placed between the superior and inferior vena cava and the right atrium), was documented and found to satisfy CO monitoring requirements of unstable subjects.[Formula: see text] [Formula: see text]bolus values were found to be statistically equivalent to reference measurements.
Effects of respiratory muscle work on cardiac output and its distribution during maximal exercise
Authors: Harms Craig A. , Wetter Thomas J. , McClaran Steven R. , Pegelow David F. , Nickele Glenn A. , Nelson William B. , Hanson Peter , Dempsey Jerome A.
Published: December 2017

We have recently demonstrated that changes in the work of breathing during maximal exercise affect leg blood flow and leg vascular conductance (C. A. Harms, M. A. Babcock, S. R. McClaran, D. F. Pegelow, G. A. Nickele, W. B. Nelson, and J. A. Dempsey. J. Appl. Physiol. 82: 1573–1583, 1997). Our present study examined the effects of changes in the work of breathing on cardiac output (CO) during maximal exercise. Eight male cyclists [maximal O2 consumption (V˙o 2 max): 62 ± 5 ml ⋅ kg−1 ⋅ min−1] performed repeated 2.5-min bouts of cycle exercise atV˙o 2 max. Inspiratory muscle work was either 1) at control levels [inspiratory esophageal pressure (Pes): −27.8 ± 0.6 cmH2O], 2) reduced via a proportional-assist ventilator (Pes: −16.3 ± 0.5 cmH2O), or 3) increased via resistive loads (Pes: −35.6 ± 0.8 cmH2O). O2 contents measured in arterial and mixed venous blood were used to calculate CO via the direct Fick method. Stroke volume, CO, and pulmonary O2 consumption (V˙o 2) were not different ( P > 0.05) between control and loaded trials atV˙o 2 max but were lower (−8, −9, and −7%, respectively) than control with inspiratory muscle unloading atV˙o 2 max. The arterial-mixed venous O2difference was unchanged with unloading or loading. We combined these findings with our recent study to show that the respiratory muscle work normally expended during maximal exercise has two significant effects on the cardiovascular system: 1) up to 14–16% of the CO is directed to the respiratory muscles; and 2) local reflex vasoconstriction significantly compromises blood flow to leg locomotor muscles.
Single-exhalation profiles of NO and CO2in humans: effect of dynamically changing flow rate
Authors: Tsoukias Nikolaos M. , Tannous Ziad , Wilson Archie F. , George Steven C.
Published: December 2017

Endogenous production of nitric oxide (NO) in the human lungs has many important pathophysiological roles and can be detected in the exhaled breath. An understanding of the factors that dictate the shape of the NO exhalation profile is fundamental to our understanding of normal and diseased lung function. We collected single-exhalation profiles of NO and CO2from normal human subjects after inhalation of ambient air (∼15 parts/billion) and examined the effect of a 15-s breath hold and exhalation flow rate (V˙E) on the following features of the NO profile: 1) series dead space, 2) average concentration in phase III with respect to time and volume, 3) normalized slope of phase III with respect to time and volume, and 4) elimination rate at end exhalation. The dead space is ∼50% smaller for NO than for CO2and is substantially reduced after a breath hold. The concentration of exhaled NO is inversely related to V˙E, but the average NO concentration with respect to time has a stronger inverse relationship than that with respect to volume. The normalized slope of phase III NO with respect to time and that with respect to volume are negative at a constantV˙Ebut can be made to change signs if the flow rate continuously decreases during the exhalation. In addition, NO elimination at end exhalation vs.V˙Eproduces a nonzero intercept and slope that are subject dependent and can be used to quantitate the relative contribution of the airways and the alveoli to exhaled NO. We conclude that exhaled NO has an airway and an alveolar source.
Effect of exercise training on passive stiffness in locomotor skeletal muscle: role of extracellular matrix
Authors: Gosselin Luc E. , Adams Christopher , Cotter Tiffani A. , McCormick Richard J. , Thomas D. Paul
Published: December 2017

The purpose of this study was to evaluate the effect of endurance exercise training on both locomotor skeletal muscle collagen characteristics and passive stiffness properties in the young adult and old rat. Young (3-mo-old) and senescent (23-mo-old) male Fischer 344 rats were randomly assigned to either a control or exercise training group [young control (YC), old control (OC), young trained (YT), old trained (OT)]. Exercise training consisted of treadmill running at ∼70% of maximal oxygen consumption (45 min/day, 5 days/wk, for 10 wk). Passive stiffness (stress/strain) of the soleus (Sol) muscle from all four groups was subsequently measured in vitro at 26°C. Stiffness was significantly greater for Sol muscles in OC rats compared with YC rats, but in OT rats exercise training resulted in muscles with stiffness characteristics not different from those in YC rats. Sol muscle collagen concentration and the level of the nonreducible collagen cross-link hydroxylysylpyridinoline (HP) significantly increased from young adulthood to senescence. Although training had no effect on Sol muscle collagen concentration in either age group, it resulted in a significant reduction in the level of Sol muscle HP in OT rats. In contrast, exercise had no effect on HP in the YT animals. These findings indicate that 10 wk of endurance exercise significantly alter the passive viscoelastic properties of Sol muscle in old but not in young adult rats. The coincidental reduction in the principal collagen cross-link HP also observed in response to training in OT muscle highlights the potential role of collagen in influencing passive muscle viscoelastic properties.
Naloxone does not alter the “regulated” decrease in core temperature during hypoxemia in guinea pigs
Authors: Crisanti Kim C. , Fewell James E.
Published: December 2017

In newborns and adults of a number of species, exposure to acute hypoxemia produces a “regulated” decrease in core temperature, the mechanism of which is unknown. The present experiments were carried out in chronically instrumented newborn (5–10 days of age; n = 59) and older (25–30 days of age; n = 61) guinea pigs to test the hypothesis that the endogenous opioids mediate this regulated decrease in core temperature. During an experiment, core temperature, oxygen consumption, and selected ambient temperature were measured in a thermocline (linear temperature gradient of 10–40°C) during a control period of normoxemia, an experimental period of normoxemia or hypoxemia (inspired oxygen fraction 0.10), and during a recovery period of normoxemia following an intraperitoneal injection of naloxone hydrochloride (a nonspecific opioid antagonist; 1, 2, or 4 mg/kg) or vehicle. Naloxone did not significantly alter basal core temperature or the core temperature response to acute hypoxemia in newborn or older guinea pigs. Naloxone did, however, decrease basal oxygen consumption in newborn and older guinea pigs and altered the thermoregulatory effector mechanism used to decrease core temperature during hypoxemia in the newborn guinea pigs. Our data do not support the hypothesis that the endogenous opioids mediate the regulated decrease in core temperature that occurs in newborn and older guinea pigs during exposure to acute hypoxemia.
Exercise training in swine promotes growth of arteriolar bed and capillary angiogenesis in heart
Authors: White Francis C. , Bloor Colin M. , McKirnan M. Dan , Carroll Susan M.
Published: December 2017

Exercise training induces coronary vascular adaptations. The goal of this study was to contrast the effects of training on capillary and arteriolar growth. Minipigs were trained for 1, 3, 8, and 16 wk and compared with controls. Maximal O2consumption increased continuously throughout the study. Capillary and arteriolar densities and diameters, and proliferation of vascular cells in these vessels, were determined in perfusion-fixed tissue. The arterioles were subdivided into five groups according to diameter: 10–19.9, 20–30, 31–40, 41–70, and 71–120 μm. The total vascular bed cross-sectional area increased by 37% at 16 wk, mainly because of an increase in the number of the small arterioles and an increase in the diameter of the larger vessels. Capillary density increased at 3 wk and then returned to control levels by 16 wk; concomitantly, the number of arterioles (20–30 μm) increased at 16 wk. We speculate that the “extra” capillaries observed at 3 wk were the source of the new arterioles.
Training-induced alterations of carbohydrate metabolism in women: women respond differently from men
Authors: Friedlander Anne L. , Casazza Gretchen A. , Horning Michael A. , Huie Melvin J. , Piacentini Maria Francesca , Trimmer Jeffrey K. , Brooks George A.
Published: December 2017

We examined the hypothesis that glucose flux was directly related to relative exercise intensity both before and after a 12-wk cycle ergometer training program [5 days/wk, 1-h duration, 75% peak O2 consumption (V˙o 2 peak)] in healthy female subjects ( n = 17; age 23.8 ± 2.0 yr). Two pretraining trials (45 and 65% of V˙o 2 peak) and two posttraining trials [same absolute workload (65% of oldV˙o 2 peak) and same relative workload (65% of newV˙o 2 peak)] were performed on nine subjects by using a primed-continuous infusion of [1-13C]- and [6,6-2H]glucose. Eight additional subjects were studied by using [6,6-2H]glucose. Subjects were studied postabsorption for 90 min of rest and 1 h of cycling exercise. After training, subjects increasedV˙o 2 peak by 25.2 ± 2.4%. Pretraining, the intensity effect on glucose kinetics was evident between 45 and 65% ofV˙o 2 peak with rates of appearance (Ra: 4.52 ± 0.25 vs. 5.53 ± 0.33 mg ⋅ kg−1 ⋅ min−1), disappearance (Rd: 4.46 ± 0.25 vs. 5.54 ± 0.33 mg ⋅ kg−1 ⋅ min−1), and oxidation (Rox: 2.45 ± 0.16 vs. 4.35 ± 0.26 mg ⋅ kg−1 ⋅ min−1) of glucose being significantly greater ( P ≤ 0.05) in the 65% than in the 45% trial. Training reduced Ra (4.7 ± 0.30 mg ⋅ kg−1 ⋅ min−1), Rd (4.69 ± 0.20 mg ⋅ kg−1 ⋅ min−1), and Rox (3.54 ± 0.50 mg ⋅ kg−1 ⋅ min−1) at the same absolute workload ( P ≤ 0.05). When subjects were tested at the same relative workload, Ra, Rd, and Rox were not significantly different after training. However, at both workloads after training, there was a significant decrease in total carbohydrate oxidation as determined by the respiratory exchange ratio. These results show the following in young women: 1) glucose use is directly related to exercise intensity; 2) training decreases glucose flux for a given power output; 3) when expressed as relative exercise intensity, training does not affect the magnitude of blood glucose flux during exercise; but 4) training does reduce total carbohydrate oxidation.
Fundamental concepts in statistics: elucidation and illustration
Authors: Curran-Everett Douglas , Taylor Sue , Kafadar Karen
Published: December 2017

Fundamental concepts in statistics form the cornerstone of scientific inquiry. If we fail to understand fully these fundamental concepts, then the scientific conclusions we reach are more likely to be wrong. This is more than supposition: for 60 years, statisticians have warned that the scientific literature harbors misunderstandings about basic statistical concepts. Original articles published in 1996 by the American Physiological Society’s journals fared no better in their handling of basic statistical concepts. In this review, we summarize the two main scientific uses of statistics: hypothesis testing and estimation. Most scientists use statistics solely for hypothesis testing; often, however, estimation is more useful. We also illustrate the concepts of variability and uncertainty, and we demonstrate the essential distinction between statistical significance and scientific importance. An understanding of concepts such as variability, uncertainty, and significance is necessary, but it is not sufficient; we show also that the numerical results of statistical analyses have limitations.
Effects of nitric oxide synthase inhibition on cutaneous vasodilation during body heating in humans
Authors: Shastry Shubha , Dietz Niki M. , Halliwill John R. , Reed Ann S. , Joyner Michael J.
Published: December 2017

We sought to examine further the potential role of nitric oxide (NO) in the neurally mediated cutaneous vasodilation in nonacral skin during body heating in humans. Six subjects were heated with a water-perfused suit while cutaneous blood flow was measured by using laser-Doppler flowmeters placed on both forearms. The NO synthase inhibitor N G-monomethyl-l-arginine (l-NMMA) was given selectively to one forearm via a brachial artery catheter after marked cutaneous vasodilation had been established. During body heating, oral temperature increased by 1.1 ± 0.1°C while heart rate increased by 30 ± 6 beats/min. Mean arterial pressure stayed constant at 84 ± 2 mmHg. In the experimental forearm, cutaneous vascular conductance (CVC; laser-Doppler) decreased to 86 ± 5% of the peak response to heating ( P < 0.05 vs. pre-l-NMMA values) afterl-NMMA infusion. In some subjects, l-NMMA caused CVC to fall by ∼30%; in others, it had little impact on the cutaneous circulation. CVC in the control arm showed a similar increase with heating, then stayed constant whilel-NMMA was given to the contralateral side. These results demonstrate that NO contributes modestly, but not consistently, to cutaneous vasodilation during body heating in humans. They also indicate that NO is not the only factor responsible for the dilation.