bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma [H+] regulation and whole blood [CO2] in exercising ponies
Authors: Forster H. V. , Murphy C. L. , Brice A. G. , Pan L. G. , Lowry T. F.
Published: December 2017

The major objective was to determine in ponies whether factors in addition to changes in blood PCO2 contribute to changes in plasma [H+] during submaximal exercise. Measurements were made to establish in vivo plasma [H+] at rest and during submaximal exercise, and CO2 titration of blood was completed for both in vitro and acute in vivo conditions. In 19 ponies arterial plasma [H+] was decreased from rest 4.5 neq/l (P less than 0.05) during the 7th min of treadmill running at 6 mph, 5% grade (P less than 0.5). A 5.6-Torr exercise hypocapnia accounted for approximately 2.9 neq/l of this reduced [H+]. The non-PCO2 component of this alkalosis was approximately neq/l, and it was due presumably to a 1.7-meq/l increase from rest in the plasma strong ion difference (SID). Despite the arterial hypocapnia, mixed venous PCO2 was 2.7 Torr above rest during steady-state exercise. Nevertheless, mixed venous plasma [H+] was 1.2 neq/l above rest during exercise, which was presumably due to the increase in SID. Also studied was the effect of submaximal exercise on whole blood CO2 content (CCO2). In vitro, at a given PCO2 there was minimal difference in CCO2 between rest and exercise blood, but plasma [HCO3-] was greater for exercise blood than for rest blood. In vivo, during steady-state exercise, arterial plasma blood. In vivo, during steady-state exercise, arterial plasma [HCO3-] was unchanged or slightly elevated from rest, but CaCO2 was 4 vol% below rest.(ABSTRACT TRUNCATED AT 250 WORDS)
Strength training and determinants of VO2max in older men
Authors: Frontera W. R. , Meredith C. N. , O'Reilly K. P. , Evans W. J.
Published: December 2017

The effects of strength training on maximal aerobic power (VO2max) and some of its determinants were studied in 12 healthy older men (60-72 yr). They underwent 12 wk of strength conditioning of extensors and flexors of each knee with eight repetitions per set, three sets per session, and three sessions per week at 80% of the one repetition maximum (1 RM). Left knee extensors showed a 107% increase in 1 RM, a 10% increase in isokinetic strength at 60 degrees/s, and a 23% increase in total work performed during 25 contractions on an isokinetic dynamometer. Strength measurements of the untrained left elbow extensors showed no change. Leg cycle ergometer VO2max per unit fat-free mass increased by an average 1.9 ml (P = 0.034) whereas arm cycle VO2max was unchanged. Pulmonary function, hemoglobin concentration, erythrocyte volume, plasma volume, and total blood volume did not change. Biopsies of the vastus lateralis showed a 28% increase in mean fiber area, no change in fiber type distribution, a 15% increase in capillaries per fiber, and a 38% increase in citrate synthase activity. The data suggest that the small increase in leg cycle VO2max in older men may be due to adaptations in oxidative capacity and increased mass of the strength-trained muscles.
Spontaneous running increases VO2max and running performance in rats
Authors: Lambert M. I. , Noakes T. D.
Published: December 2017

The effect of spontaneous running activity on maximal O2 consumption (VO2max), running performance, and submaximal O2 consumption (VO2submax, running economy) was studied in rats to determine whether this exercise mode can produce significant training adaptations. Twenty male Long-Evans rats (300 +/- 20 g) were housed in spontaneous activity running wheels, and after 8 wk they were divided into high-, average-, and low-performing groups according to the average spontaneous running distance and tested for maximal running performance, VO2max, and VO2submax. The average-performing rats ran 52% longer than the control rats (P less than 0.01) and 19% longer than the low-performing rats (P less than 0.05). There was no difference in maximum running time to exhaustion between the average- and high-performing rats. The low-performing rats ran 28% longer than the control rats (P less than 0.05). The VO2max of the average-performing rats was 12% greater than in the control rats (P less than 0.01). There were no differences in VO2max between either low-performing and control rats or between average- and high-performing rats. Although the VO2submax was not different between low-, average-, and high-performing rats, in all three groups it was lower than in the control rats (P less than 0.01). Accordingly, we recommend that only those Long-Evans rats that, on average, spontaneously run greater than 11.6 km/wk for a minimum of 8 wk be considered to have undergone a training effect. Rats that perform poorly can be identified as early as 2 wk after the start of training.
Stimulation of tracheal ciliary beat frequency by localized tissue incision
Authors: Wong L. B. , Yeates D. B.
Published: December 2017

Since measurements of basal ciliary beat frequency (CBF) were significantly lower in our intact canine experiments than reports of ciliary activity in rabbits involving surgical intervention, we hypothesized that local tissue trauma stimulates CBF. The effects of minor neck surgery on tracheal CBF in eight barbiturate-anesthetized eucapnically ventilated beagles were investigated. Each dog underwent two studies. Measurements of CBF were made at 1-min intervals on the right lateral midtracheal surface by means of heterodyne mode correlation analysis laser light scattering. In the control study, CBF was measured in each dog for at least 160 min. In the incision study, base-line CBF was measured for at least 40 min. The overlying sternohyoidus muscles were then separated, and a longitudinal 2- to 3-cm incision was made in the trachea caudally from the fourth to the fifth cartilage ring. CBF was measured at least 5 cm distally from the site of tracheal injury for an additional 120 min. Electrocardiogram, rectal temperature, tracheal pressure, exhaled CO2, and arterial blood pressure, PO2, PCO2, and pH remained stable throughout both studies. The mean base-line CBF was 4.7 +/- 0.4 Hz. It increased to 19.5 +/- 2.9 Hz (P less than 0.0001) 100 min after the incision and remained elevated until the end of the study period (P less than 0.0001). The mechanism(s) causing this stimulation may also be responsible for the high “basal” CBF observed in other studies.(ABSTRACT TRUNCATED AT 250 WORDS)
Diameters, generations, and orders of branches in the bronchial tree
Authors: Horsfield K.
Published: December 2017

Studies of bronchial tree data by West et al. (J. Appl. Physiol. 60: 1089-1097, 1986) have shown that plots of mean diameter against generation, using log-log scales, can be represented by a power function with harmonic modulations. Other studies have shown that the mean diameter of the airways is exponentially related to order of branching. This paper demonstrates that both observations are compatible with a fractal model of branching, and because airway branching is fractal, this may explain why both are also true of the bronchial tree. Furthermore, the exponential relationship of mean diameter with generation in the larger airways, demonstrated by Weibel, is shown to result from the exponential relation of diameter with order in the fractal model.
Spectral analysis of muscular sound during isometric contraction of biceps brachii
Authors: Orizio C. , Perini R. , Diemont B. , Maranzana Figini M. , Veicsteinas A.
Published: December 2017

The frequency content of muscular sound (MS), detected by placing a contact sensor transducer over the belly of the biceps brachii during 10 isometric contractions of 4 s each [10-100% of maximal voluntary contraction (MVC)] in seven sedentary men, was analyzed by the maximum entropy spectral estimation and the fast Fourier transform methods. With increasing %MVC, the power spectrum of the MS enlarges and tends to be multimodal beyond 30% MVC. Independent of the method, the mean frequency is approximately 11 Hz at the lower tasks, and then it increases up to 15 Hz at 80% MVC and to 22 Hz at 100% MVC. When the effort is increased the relative power in the 15- to 45-Hz bandwidth (range of firing rate of the motor units with fast-twitch fibers) from 20% reaches 55% of the power in the 6- to 45-Hz bandwidth (firing rate range of motor units with slow- and fast-twitch fibers). Our results obtained by the two different modeling approaches confirm the reliability of the sound signal. Moreover, it appears that from the MS the motor unit activation pattern can be retrieved.
Body composition and skin temperature variation
Authors: Frim J. , Livingstone S. D. , Reed L. D. , Nolan R. W. , Limmer R. E.
Published: December 2017

Temperature variations near four common torso skin temperature sites were measured on 17 lightly clad subjects exposed to ambient temperatures of 28, 23, and 18 degrees C. Although variations in skin temperature exceeding 7 degrees C over a distance of 5 cm were observed on individuals, the mean magnitude of these variations was 2-3 degrees C under the coolest condition and less at the warmer temperatures. There was no correlation between the temperature variation and skinfold thickness at a site or with estimations of whole body fat content. These findings imply that errors in mean skin temperature measurement could arise from probe mislocation and/or subcutaneous fat distribution and that the problem becomes more acute with increasing cold stress. However, the magnitudes of these errors cannot be easily predicted from common anthropometric measurements.
Effects of ischemic and hypoxic hypoxia on VO2 and lactic acid output during tetanic contractions
Authors: Stainsby W. N. , Brechue W. F. , O'Drobinak D. M. , Barclay J. K.
Published: December 2017

We measured O2 uptake (VO2), CO2 output (VCO2), and net lactic acid output (L) during a 30-min period of repetitive 1/s isotonic tetanic contractions of the dog gastrocnemius-plantaris muscle group. The conditions were modest ischemic hypoxia (ischemia), hypoxia hypoxia (hypoxia), and free-flow normoxia (control). The major goal was to assess the effects of these perturbations on L during contractions. Ischemia and hypoxia were initiated just before the start of the contractions and at minute 7 of contractions in separate groups of experiments. Whenever applied, both ischemia and hypoxia reduced VO2 compared with the control values. When ischemia was initiated at the start of contractions, L was reduced transiently compared with the controls. When ischemia began at minute 7, L was increased modestly but transiently compared with the controls. When hypoxia was initiated at the start of contractions, L was increased during the entire period of contractions. The L pattern was the same as in the controls, rising to a maximal value at 3 min and declining steadily to a lower value at 30 min. When hypoxia began at minute 7, L declined initially at a slower rate than it did in the controls and was thereby elevated above the controls from 9 to 30 min. Ischemia was associated with a more rapid reduction in mechanical performance than hypoxia. The data suggest that the mechanisms of the decreased mechanical performance and VO2 are different for ischemia and hypoxia.
EMG study of respiratory muscles in humans immersed at different water temperatures
Authors: Choukroun M. L. , Kays C. , Varene P.
Published: December 2017

The electromyograms of the rectus abdominis (EMGra) and of the diaphragm (EMGdi) have been recorded on human subjects immersed at two bath temperatures (TW), 25 and 40 degrees C. The recordings were obtained during a calibrated isometric contraction sustained for 20 s against a closed stopcock at functional residual capacity (FRC) level for EMGra (expiratory effort) and at pulmonary volume greater than 90% vital capacity for EMGdi and EMGra (inspiratory effort). After eliminating the electrocardiographic artifact, the EMG signal was processed to obtain its root-mean-square (rms) value and three parameters of its frequency spectrum, total energy (Etot), centroid frequency (fc), and high-to-low ratio (H/L). The results show that EMGdi is not modified by TW. On the other hand rms and Etot of EMGra are always increased at TW = 25 degrees C compared with TW = 40 degrees C, whereas fc and H/L decrease with temperature during the expiratory effort at FRC level but do not vary during inspiratory effort at high pulmonary volume. These results, compared with those previously published for cooled limb muscles, show that TW can elicit EMG alterations on the superficial respiratory muscles through two mechanisms, an intrinsic mechanism due to the local variation in muscle temperature and an extrinsic mechanism acting upon the control system of the muscle contraction. Linked alterations of the muscular mechanical activity probably account for the observed effects of TW on the statics and the dynamics of the pulmonary volumes.
Metabolic effects of exposure to hypoxia plus cold at rest and during exercise in humans
Authors: Robinson K. A. , Haymes E. M.
Published: December 2017

To determine effects on metabolic responses, subjects were exposed to four environmental conditions for 90 min at rest followed by 30 min of exercise: breathing room air with an ambient temperature of 25 degrees C (NN); breathing room air with an ambient temperature of 8 degrees C (NC); hypoxia (induced by breathing 12% O2 in N2) with a neutral temperature (HN); and hypoxia in the cold (HC). Hypoxia increased heart rate (HR), systolic blood pressure (SBP), pulmonary ventilation (VE), respiratory exchange ratio (R), blood lactate, and perceived exertion during exercise while depressing rectal temperature (Tre) and O2 uptake (VO2). Cold exposure elevated SBP, diastolic blood pressure (DBP), VE, VO2, blood glucose, and blood glycerol but decreased HR, Tre, and R. Shivering and DBP were higher and Tre was lower in HC compared with NC. HR, SBP, VE, R, and lactate tended to be higher in HC compared with NC, whereas VO2 and blood glycerol tended to be depressed. These results suggest that cold exposure during hypoxia results in an increased reliance on shivering for thermogenesis at rest whereas, during exercise, heat loss is accelerated.
Alveolar dead space does not affect indirect Fick cardiac output determinations
Authors: Badgwell J. M. , Heavner J. E.
Published: December 2017

We examined the influence of three variables (different breathing circuits, breath selected for analysis, and alveolar dead space ventilation) on the accuracy of noninvasive cardiac output determinations with the Fick CO2 (indirect) equation. We compared noninvasive determinations with invasive thermodilution measurements over a wide range of cardiac outputs in 17 2-mo-old pigs anesthetized with halothane and nitrous oxide and paralyzed with either pancuronium or d-tubocurare. We found that rebreathing and nonrebreathing circuits provide accurate cardiac output determinations and that the optimal breath for analysis with either the rebreathing or nonrebreathing technique appears to depend on the cardiac output. When alveolar dead space was increased by using positional changes and the intracardiac administration of glass beads, there was still a good correlation between noninvasive and invasive cardiac output determinations. We conclude that both rebreathing and nonrebreathing techniques of indirect Fick cardiac output determinations correlate well with thermodilution measures over a wide range of cardiac outputs and alveolar dead space/tidal volume fractions.
Respiratory muscle electromyogram responses to acute hypoxia in awake ponies
Authors: Brice A. G. , Forster H. V. , Pan L. G. , Lowry T. F. , Murphy C. L.
Published: December 2017

We determined the effect of acute hypoxia on the ventilatory (VE) and electromyogram (EMG) responses of inspiratory (diaphragm) and expiratory (transversus abdominis) muscles in awake spontaneously breathing ponies. Eleven carotid body-intact (CBI) and six chronic carotid body-denervated (CBD) ponies were studied during normoxia (fractional inspired O2 concn [FIO2] = 0.21) and two levels of hypoxia (FIO2 approximately 0.15 and 0.12; 6-10 min/period). Four CBI and five CBD ponies were also hilar nerve (pulmonary vagal) denervated. Mean VE responses to hypoxia were greater in CBI ponies (delta arterial PCO2 = -4 and -7 Torr in CBI during hypoxic periods; -1 and -2 Torr in CBD). Hypoxia increased the rate of rise and mean activity of integrated diaphragm EMG in CBI (P less than 0.05) and CBD (P greater than 0.05) ponies relative to normoxia. Duration of diaphragm activity was reduced in CBI (P less than 0.05) but unchanged in CBD ponies. During hypoxia in both groups of ponies, total and mean activities per breath of transversus abdominis were reduced (P less than 0.05) without a decrease in rate of rise in activity. Time to peak and total duration of transversus abdominis activity were markedly reduced by hypoxia in CBI and CBD ponies (P less than 0.05). Hilar nerve denervation did not alter the EMG responses to hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)
Measurement of intracellular pH in hamster diaphragm by absorption spectrophotometry
Authors: Zhang R. G. , Kelsen S. G. , LaManna J. C.
Published: December 2017

The regulation of intracellular pH (pHi) is important in controlling muscle contraction. In these experiments, a spectrophotometric method of determining pHi was developed, and the method was then used to study muscle pHi regulation during CO2-induced changes in extracellular pH (pHb). Studies were performed in vitro on 27 diaphragm muscle strips obtained from adult hamsters. pHi was measured from the ratio of the absorbances of the acid (lambda = 530 nm) and alkaline (lambda = 460 nm) forms of a vital dye, neutral red, using the unstained diaphragm spectrum as a reference blank. A standard neutral red calibration curve constructed from eight diaphragm muscle homogenates indicated that the absorbance ratio was highly linear, with pH over the range 6.00-8.00. In intact muscle strips gassed with 95% O2-5% CO2, pHb was 7.45 +/- 0.03 (SE) and pHi was 7.00 +/- 0.01 (SE). When the muscle was aerated with CO2 concentrations from 3 to 30%, pHb and pHi changed rapidly and reached a steady state in 10-15 min. However, when pHb ranged from 6.80-7.80, pHi changed little from the value observed when pHb was 7.40. When pHb was less than 6.80 or greater than 7.80, changes in pHi and pHb were quantitatively similar. The results suggest that, in the isolated diaphragm, overall pHi is stable and effectively buffered over a wide range of CO2-induced changes in buffer solution pH.
Antenatal betamethasone dose effects in preterm rabbits studied at 27 days gestation
Authors: Rider E. D. , Jobe A. H. , Ikegami M. , Yamada T. , Seidner S.
Published: December 2017

Pregnant rabbits received bethamethasone (0.05, 0.2, 0.4, or 0.5 mg.kg-1.day-1) or vehicle control for 2 days before delivery of fetuses at 27 days gestation to evaluate dose-related effects on surfactant pool sizes with and without ventilation, pressure-volume measurements, lung protein leaks, and precursor incorporation into lung saturated phosphatidylcholine (PC). Alveolar wash-saturated PC pool sizes in betamethasone-exposed fetuses were less than in controls (P less than 0.01). At higher doses, total lung saturated PC also decreased (P less than 0.01). Maximal lung volumes on pressure-volume loops were larger than controls only at the 0.4 mg.kg-1.day-1 dose (P less than 0.05). The larger maximal volumes, despite decreased saturated PC pools, indicated increased responsiveness of the steroid-treated lungs to the smaller saturated PC pool sizes. Vascular-to-alveolar iodinated albumin leak decreased with steroid treatment independently of dose (P less than 0.01). No consistent pattern of increased precursor incorporation into saturated PC by lung slices was seen. Our results indicate that, in preterm rabbits exposed to a range of maternal corticosteroid doses, the beneficial lung maturational effect of structural alterations with increased responses to endogenous saturated PC pools was maximal even at the lowest dose.
Rat skeletal muscle mitochondrial [Ca2+] and injury from downhill walking
Authors: Duan C. , Delp M. D. , Hayes D. A. , Delp P. D. , Armstrong R. B.
Published: December 2017

The purpose of this study was to evaluate the relationship between mitochondrial Ca2+ concentration (MCC) and the extent of muscle injury in rats that have performed prolonged downhill walking (eccentric exercise). MCC was used as an indicator of elevated [Ca2+] in the muscles, and injury was estimated from histochemical analysis of muscle cross sections by determining the numbers of intact fibers per unit area in the muscles. Elevations in MCC in the soleus and vastus intermedius muscles over time postexercise were inversely related (P less than 0.05) to the number of intact fibers per square millimeter in the respective muscles after downhill walking. Verapamil administration attenuated the elevation in MCC and injury in histochemical sections resulting from the downhill walking in soleus muscle, but intraperitoneal injection of the chelators EDTA or ethylene glycol-bis(beta-aminoethylether)-N,N,N′,N′- tetraacetic acid significantly attenuated the increases in MCC and injury to both the vastus intermedius and soleus muscles in the downhill walkers. The chelators appear to exert their “protective” effects within the specific muscles that show the injury and do not significantly affect serum [Ca2+]. It is concluded that increases in MCC occur during exercise-induced fiber injury and that elevations in cellular Ca2+ may have a role in the etiology of the injury process.
Mechanical effects of PEEP in patients with adult respiratory distress syndrome
Authors: Dall'ava-Santucci J. , Armaganidis A. , Brunet F. , Dhainaut J. F. , Nouira S. , Morisseau D. , Lockhart A.
Published: December 2017

In 10 patients with adult respiratory distress syndrome, we studied the effects on respiratory system mechanics of two levels of positive end-expiratory pressure (PEEP), best PEEP (BP) and half of this value (HBP), using a respiratory inductive plethysmograph (RIP) combined with a super syringe. We found the following. 1) Inflation compliance of pressure-volume (PV) curves did not change significantly. 2) End-expiratory volume increased with HBP and further with BP (278 +/- 186 and 464 +/- 313 ml, respectively, P less than 0.01). This increase was positively correlated with inflation compliance for HBP and BP (r = 0.794, P less than 0.01 and r = 0.876, P less than 0.01, respectively). 3) No dynamic hyper-inflation was detected on mechanical ventilation at zero end-expiratory pressure (ZEEP), and the time constant of the respiratory system was in the normal range (0.79 +/- 0.21 s). 4) Hysteresis of PVrip curves, which were corrected for gas exchange, decreased significantly with PEEP (P less than 0.05). We conclude that PEEP does not change inflation PV curve but induces an increase in intrathoracic volume whose magnitude is related to compliance and PEEP level. The reduction of hysteresis with PEEP suggests less gas trapping and thus a functional improvement.
Sympathoadrenergic regulation and the adrenoceptor system
Authors: Jost J. , Weiss M. , Weicker H.
Published: December 2017

We investigated the effects of endurance and high-intensity training periods on the plasma catecholamine (CA) concentration at rest; on the basal alpha- and beta-adrenoceptor density, regulation, and function on circulating cells; and on the cardiovascular adaptation in long-distance runners and swimmers. The findings of each period were compared with those of untrained men. Endurance training of the long-distance runners and the swimmers led both to a reduced sympathetic activity at rest, indicated by lower CA values, and to a lower beta-receptor density and responsiveness on circulating lymphocytes and an increased alpha 2-receptor sensitivity on circulating platelets. During the high-intensity training period beta-receptor density and responsiveness increased, alpha 2-receptor sensitivity normalized, and heart rate as well as blood pressure values increased in both trained groups. The basal sympathetic activity remained reduced, but the norepinephrine-to-epinephrine (NE/EPI) ratio increased. The NE/EPI ratio might play an important part in the regulation of adrenoceptor density during these different training periods. Swimming-specific characteristics caused different physiological impacts compared with running training, but an attenuated baroreceptor sensitivity might be indicated in both intensively trained groups.
Increased in vitro responses of tracheal smooth muscle from hyperresponsive guinea pigs
Authors: Ishida K. , Pare P. D. , Thomson R. J. , Schellenberg R. R.
Published: December 2017

Repeated aerosol antigen challenge of previously sensitized guinea pigs induces airway hyperresponsiveness to inhaled acetylcholine. To determine the mechanism producing these airway changes and assuming that changes in the trachealis muscle reflect changes in muscle of the entire tracheobronchial tree, we examined the in vitro smooth muscle mechanics and morphometric parameters of tracheae from guinea pigs demonstrating hyperresponsiveness in vivo vs. tracheae from control guinea pigs. No differences between these groups were found in luminal volume at zero transmural pressure, passive pressure-volume characteristics, or area of airway wall. Smooth muscle areas were slightly less in tracheae from hyperresponsive guinea pigs. Tracheae from hyperresponsive guinea pigs had both significantly increased isovolumetric force generation and isobaric shortening compared with tracheae from controls when evaluated over the range of transmural pressures from -40 to 40 cmH2O. We conclude that the in vivo airway hyperresponsiveness induced with repeated antigen challenge is associated with both increased force generation and shortening of tracheal smooth muscle without increased muscle mass, suggesting enhanced contractile activity.
Orocecal transit during mild exercise in women
Authors: Keeling W. F. , Harris A. , Martin B. J.
Published: December 2017

Little is known of the influence of exercise on movement of ingested food through the alimentary tract or of the association of several gastrointestinal hormones with transit rate in exercise. In this study, orocecal transit during mild exercise was measured in 21 women by detecting a rise in expired H2 after ingestion of 20 g lactulose in a 350-ml (360 kcal) liquid meal. Motilin, gastrin, and cortisol were measured in peripheral venous blood when, as evidenced by a breath H2 rise, the first portion of the meal arrived at the cecum. Comparison was made between seated rest and a treadmill walk at 5.6 km/h up a 2% grade. The walk predictably elevated heart rate, O2 uptake, and rectal temperature and also reduced transit time from 98 min at rest to 75 min during exercise (P less than 0.001). Faster transit in exercise was associated with a significant rise in cortisol, while gastrin and motilin levels were both unchanged. In conclusion, in women mild concurrent exercise accelerates orocecal transit rate of at least the first portion of nonabsorbable carbohydrate in a liquid meal. Although the mechanism for the effect remains unknown, it may be secondary to some aspect of the stress response to physical activity.
Bubble-induced dysfunction in acute spinal cord decompression sickness
Authors: Francis T. J. , Griffin J. L. , Homer L. D. , Pezeshkpour G. H. , Dutka A. J. , Flynn E. T.
Published: December 2017

Five anesthetized dogs undertook a chamber dive, on air, to 300 feet of seawater for 15 min. After the dive, spinal cord decompression sickness was detected by recording a reduced amplitude of the somatosensory evoked potential compared with predive base-line values. After the diagnosis of decompression sickness and rapid perfusion fixation of the animal, the spinal cord was removed and examined histologically. Numerous space-occupying lesions (SOL) that disrupted the tissue architecture were found in each cord, mainly in the white matter. The size and distribution of the SOL were determined using computerized morphometry. Although SOL occupied less than 0.5% of the white matter volume, we tested a number of algorithms to assess whether the SOL may have been directly involved in the loss of spinal cord function that followed the dive. We determined that the loss of somatosensory evoked potential amplitude may be attributed to the SOL if 30-100% of the spinal cord fibers that they displaced were rendered nonconducting. A number of possible mechanisms by which SOL may interfere with spinal nerve conduction are discussed.
Increases in coronary vein CO2 during cardiac resuscitation
Authors: Gudipati C. V. , Weil M. H. , Gazmuri R. J. , Deshmukh H. G. , Bisera J. , Rackow E. C.
Published: December 2017

We investigated the aortic, mixed venous, and great cardiac vein acid-base changes in eight domestic pigs during cardiac arrest produced by ventricular fibrillation and during cardiopulmonary resuscitation (CPR). The great cardiac vein PCO2 increased from a control value of 52 +/- 2 to 132 +/- 28 (SD) Torr during CPR, whereas the arterial PCO2 was unchanged (39 +/- 4 vs. 38 +/- 4). The coronary venoarterial PCO2 gradient, therefore, increased remarkably from 13 +/- 2 to 94 +/- 29 Torr. The simultaneously measured great cardiac vein lactate concentrations increased from 0.24 +/- 0.06 to 7.3 +/- 2.34 mmol/l. Much more moderate increases in the lactate content of aortic blood from 0.64 +/- 0.25 to 2.56 +/- 0.27 mmol/l were observed. Increases in great cardiac vein PCO2 and lactate were highly correlated during CPR (r = 0.91). After successful CPR, the coronary venoarterial PCO2 gradient returned to normal levels within 2 min after restoration of spontaneous circulation. Lactate content was rapidly reduced and lactate extraction was reestablished within 30 min after CPR. These studies demonstrate marked but reversible acidosis predominantly as the result of myocardial CO2 production during CPR.
Mucociliary interaction in vitro: effects of physiological and inflammatory stimuli
Authors: Seybold Z. V. , Mariassy A. T. , Stroh D. , Kim C. S. , Gazeroglu H. , Wanner A.
Published: December 2017

Mucociliary transport in the airways is governed by the interaction between ciliary activity and the depth and rheological properties of the liquids (mucus) covering the epithelial surface. A change in one of these parameters may not predict the direction and magnitude of a concomitant change in mucociliary transport. We therefore determined the effects of physiological (neurotransmitters) and pathological (inflammatory mediators) stimuli on ciliary beat frequency (CBF), surface liquid velocity (SLV), surface liquid depth (SLD), and viscoelasticity of mucus in pieces of sheep trachea (n = 5 for each treatment) mounted in a chamber such that the submucosal side was bathed with Krebs-Henseleit perfusate (KH) and the luminal side was exposed to conditioned air. SLV, SLD, and CBF were measured with a microscope provided with an electronic micrometer and strobe light. Apparent viscosity and shear elastic modulus were measured with a microcapillary method using mucus collected at the downstream end of the preparation. Control CBF, SLV, and SLD were 11.6 +/- 0.4 (SE) Hz, 91 +/- 8 micron/s, and 33 +/- 5 microns, respectively, at base line and did not change during KH perfusion for 100 min. Perfusion with both acetylcholine and epinephrine (10(-5) to 10(-3) M) produced concentration-dependent increases in mean CBF (maximum increases at 10(-3) M of 16 and 9%, P less than 0.05), whereas only acetylcholine increased mean SLV (+56% at 10(-3) M, P less than 0.05). Perfusion with platelet-activating factor (10(-7) to 10(-5) M) decreased both mean CBF and SLV in a dose-dependent fashion (-6 and -63% at 10(-5) M, P less than 0.05), whereas antigen perfusion (1:60 dilution) increased mean CBF (+10%, P less than 0.05) but decreased SLV (-47%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Blood flow to contracting human muscles: influence of increased sympathetic activity
Authors: Joyner M. J. , Lennon R. L. , Wedel D. J. , Rose S. H. , Shepherd J. T.
Published: December 2017

The purpose of this study was to examine the effects of the increased sympathetic activity elicited by the upright posture on blood flow to exercising human forearm muscles. Six subjects performed light and heavy rhythmic forearm exercise. Trials were conducted with the subjects supine and standing. Forearm blood flow (FBF, plethysmography) and skin blood flow (laser Doppler) were measured during brief pauses in the contractions. Arterial blood pressure and heart rate were also measured. During the first 6 min of light exercise, blood flow was similar in the supine and standing positions (approximately 15 ml.min-1.100 ml-1); from minutes 7 to 20 FBF was approximately 3-7 ml.min-1.100 ml-1 less in the standing position (P less than 0.05). When 5 min of heavy exercise immediately followed the light exercise, FBF was approximately 30-35 ml.min-1.100 ml-1 in the supine position. These values were approximately 8-12 ml.min-1.100 ml-1 greater than those observed in the upright position (P less than 0.05). When light exercise did not precede 8 min of heavy exercise, the blood flow at the end of minute 1 was similar in the supine and standing positions but was approximately 6-9 ml.min-1.100 ml-1 lower in the standing position during minutes 2-8. Heart rate was always approximately 10-20 beats higher in the upright position (P less than 0.05). Forearm skin blood flow and mean arterial pressure were similar in the two positions, indicating that the changes in FBF resulted from differences in the caliber of the resistance vessels in the forearm muscles.(ABSTRACT TRUNCATED AT 250 WORDS)
Inference of motor unit recruitment order in voluntary and electrically elicited contractions
Authors: Knaflitz M. , Merletti R. , De Luca C. J.
Published: December 2017

The relationship between surface myoelectric signal parameters and the level of voluntary or electrically elicited contractions was studied in 32 experiments on the tibialis anterior muscle of 22 healthy human subjects. Contractions were performed at 20 and 80% of the maximum voluntary contraction torque. Two levels of stimulation current were used, yielding, respectively, a maximum M wave and an M wave approximately 30% of the maximum. A four-bar electrode probe was used to detect single- and double-differential signals from which mean and median frequency of the power spectrum and average muscle fiber conduction velocity were estimated. Measurements obtained from voluntary contractions showed a positive correlation between contraction levels and both conduction velocity and spectral parameters. Conduction velocity increased by 21.2 +/- 10.9% when voluntary contraction level increased from 20 to 80% of the maximal value. Spectral parameters increased by similar amounts. Tetanic electrical stimulation was applied to a muscle motor point for 20 s via surface electrodes. Rectangular current pulses with 0.1-ms width and frequencies of 20, 25, 30, 35, and 40 Hz were used. Four types of behavior were observed with increasing stimulation level: 1) the two spectral parameters and conduction velocity both increased with stimulation in 15 experiments, 2) the two spectral parameters decreased and conduction velocity increased in 8 experiments, 3) the two spectral parameters and conduction velocity both decreased in 6 experiments, and 4) the two spectral parameters increased and conduction velocity decreased in 3 experiments. Conduction velocity increased with increasing stimulation current in 72% of the experiments, indicating a recruitment order similar to that of voluntary contractions, although it decreased in the other 28% of the cases, indicating a reverse order of recruitment. Contrary to what is observed in direct stimulation of nerves, motor units are not in general recruited in reverse order of size during electrical stimulation of a muscle motor point. This discrepancy may be the result of geometric factors or a lack of correlation between axonal branch diameter and the diameter of the parent motoneuron axon. Changes of conduction velocity and spectral parameters in opposite directions may be the result of the combined effect of the motor unit recruitment order and of the different tissue filtering function associated with the geometric location of the recruited motor units within the muscle.
Right ventricular function and three-dimensional modeling using computer-aided design
Authors: Spinale F. G. , Carabello B. A. , Crawford F. A.
Published: December 2017

Right ventricular (RV) volumetric and morphological analysis is complicated by the trabeculations and geometric configuration of the RV chamber. To improve RV analysis, custom computer-aided design programs were employed to obtain RV volumes and three-dimensional models from biplane ventriculograms. Biplane RV ventriculograms were analyzed from 14 anesthetized dogs and 22 RV casts. Computed volumes were highly correlated with reference RV volumes (r = 0.98, n = 36, P less than 0.01) with a range of 5-73 ml. Three-dimensional wire-frame and solid models constructed from the ventriculographic images provided excellent detail and a new perspective in chamber shape. This modeling technique was then used to examine RV volumes, geometric conformation, and regional shortening in 10 pigs during inotropic stimulation and preload reduction. Changes in RV volumes, ejection fraction, and regional motion were detected as well as alterations in chamber conformation. In summary 1) computer-aided design offers an accurate and simplified means to compute RV volumes using basic microcomputer equipment, and 2) three-dimensional reconstruction provided a unique view of RV geometry and a means to examine regional RV function.
Effect of 10 days of physical inactivity on glucose tolerance in master athletes
Authors: Rogers M. A. , King D. S. , Hagberg J. M. , Ehsani A. A. , Holloszy J. O.
Published: December 2017

Master athletes who exercise regularly appear to avoid the development of insulin resistance and deterioration of glucose tolerance (GT) commonly seen with aging. To evaluate the possibility that exercise prevents rather than masks the aging-related changes responsible for development of insulin resistance, we investigated the effects of 10 days of physical inactivity in 14 master athletes aged 61 +/- 2 (SE) yr. The response of 10 of these men to inactivity was similar to that of young athletes, with an unchanged plasma glucose response and a significantly greater insulin response to an oral glucose tolerance test (OGTT) after 10 days of inactivity. These 10 athletes appeared to have been protected against the aging-related changes in GT because their plasma glucose and insulin levels during the OGTT after 10 days of inactivity were not significantly different from those of young lean sedentary men. In contrast, a deterioration in GT occurred in four of the master athletes during 10 days of inactivity; this was sufficiently marked in two of them to be classified as impaired GT. We conclude that regular exercise may 1) protect against the development of insulin resistance and decline in GT with aging in individuals with normal GT and 2) normalize GT by means of short-term effects of exercise in some individuals with abnormal GT.
Influence of caffeine on metabolic responses of men at rest in 28 and 5 degrees C
Authors: MacNaughton K. W. , Sathasivam P. , Vallerand A. L. , Graham T. E.
Published: December 2017

Cold stress and caffeine ingestion are each reported to increase plasma catecholamines, free fatty acid (FFA) concentrations, and energy metabolism. This study examined the possible interaction of these two metabolic challenges in four double-blind counterbalanced trials. Young adult men (n = 6) ingested caffeine (5 mg/kg) or placebo (dextrose, 5 mg/kg) and rested for 2 h in 28 or 5 degrees C air. Cold stress alone elevated (P less than 0.05) plasma norepinephrine, metabolism (O2 consumption, VO2), and respiratory exchange ratio (RER). Caffeine alone increased (P less than 0.05) plasma epinephrine and FFA but not RER. When the two challenges were combined (caffeine plus 5 degrees C for 2 h) norepinephrine and epinephrine were increased (P less than 0.05) as was FFA. However, VO2, RER, and skin and rectal temperatures were not different from the responses observed at 5 degrees C after placebo ingestion. The data suggest that caffeine selectively increases plasma epinephrine, whereas cold air increases norepinephrine. During the cold exposure, increasing epinephrine and FFA above normal levels did not appear to influence the metabolic or thermal responses to the cold stress. In fact the increase in RER suggested a greater carbohydrate oxidation.
Relationship between thyroarytenoid activity and laryngeal resistance
Authors: Tully A. , Brancatisano A. , Loring S. H. , Engel L. A.
Published: December 2017

We examined the relationship between subglottic pressure (P), flow (V), and thyroarytenoid (TA) muscle activity in six anesthetized tracheostomized dogs while a constant flow (0.05-1.2 l/s) of warmed humidified air was passed through the upper airway in an expiratory direction. The TA activity was recorded by fine bipolar wire electrodes and was reflexly altered by changes in lung volume and chest wall compression. The integrated muscle activity was expressed as a percentage of a maximal peak integrated TA activity (%max). In the absence of TA activity the pressure-flow relationship was alinear and could be described by a power function. Log-log P-V plots at varying levels of TA activity were linear, with a slope a of 1.84 +/- 0.07 (SD). When TA activity increased, laryngeal resistance increased exponentially. An effective hydraulic diameter was calculated for increments in %max TA and decreased linearly with %max TA. In three dogs the glottic diameter was computed from glottic area measured by fiber-optic laryngoscopy, and it also decreased linearly as TA increased. Sectioning of the external motor branch of the superior laryngeal nerve to the cricothyroid muscle demonstrated no consistent effect on laryngeal resistance over a range of TA activity. The results indicate that laryngeal dimensions decrease linearly with TA activity. However, the P-V relationship of the larynx may be described by a power function, with a single exponent consistent with an orifice flow regimen. Spontaneous activity of the cricothyroid muscle does not measurably influence this relationship.
Rapidly adapting receptors monitor lung compliance in spontaneously breathing dogs
Authors: Pisarri T. E. , Jonzon A. , Coleridge J. C. , Coleridge H. M.
Published: December 2017

We examined the ability of rapidly adapting receptors (RARs) to monitor changes in dynamic lung compliance (Cdyn) in anesthetized spontaneously breathing dogs by recording RAR impulses from the vagus nerves. We decreased Cdyn in steps through the physiological range by briefly restricting lung expansion with an inflatable cuff around the chest and recording the response after deflating the cuff; we restored Cdyn to control by hyperinflating the lungs. Of 45 RARs, 34 were stimulated by a 40 +/- 2% reduction in Cdyn, their inspiratory discharge increasing on average more than threefold. Two-thirds of responsive RARs were stimulated by less than or equal to 20% reductions in Cdyn; in most, firing increased proportionately with lung stiffness (1/Cdyn) as Cdyn was decreased further. Stimulation by reduced Cdyn was not simply a function of the concomitant increase in transpulmonary pressure, because similar increases in pressure produced by increasing tidal volume produced smaller increases in firing. RAR stimulation was unaffected by atropine and, hence, was not dependent on neurally mediated changes in bronchomotor tone. Our results indicate that during spontaneous breathing RARs provide a signal inversely proportional to Cdyn.
Contraction-dependent modulations in regional diaphragmatic blood flow
Authors: Hu F. , Comtois A. , Grassino A. E.
Published: December 2017

Blood flow (Q) of the diaphragm was measured simultaneously with Doppler probes placed on diaphragmatic veins and an artery and by direct volumetric measurements obtained from cannulation of diaphragmatic blood vessels. The Doppler converting coefficients obtained were 6.27, 7.25, 4.21, and 41.07 ml.min-1.kHz-1 for left phrenic artery flow (Qpha), phrenic vein flow (Qphv), internal mammary vein flow (Qimv), and azygos vein flow (Qazv), respectively. The time course of Qpha, Qphv, Qimv, and Qazv after imposed patterns of diaphragmatic contraction was measured in nine anesthetized dogs. Each pattern consisted of various combinations of transdiaphragmatic pressure (Pdi), frequency of pacing (f), and duty cycle obtained by bilateral phrenic nerve stimulation. The dogs were prepared with chests open and loosely casted abdomens. Qpha, Qphv, Qimv, and Qazv were measured at rest (control, passive diaphragm, mechanical ventilation) and at two submaximal levels of stimulation (30 and 60% of Pdimax). The f was 10 or 30 cycles/min and the duty cycle was 0.25, 0.50, and 0.75. The results show 1) Qpha, Qphv, Qimv, and Qazv reached stable values (equilibration) after 30-36 s of pacing; 2) the steady Qpha, Qphv, and Qimv were linearly related to Pdi, and they were related by a parabolic function to duty cycle, whereas Qazv was not significantly affected by Pdi and increased linearly as a function of the duty cycle; 3) the diaphragmatic blood drainage was approximately 60% through the intercostal veins leading into the azygos trunk, 25% through the phrenic vein, and 15% through the internal mammary vein during pacing of the diaphragm at a duty cycle of 0.50 and 60% Pdimax; and 4) for a given pacing pattern, Qpha and Qphv increased with f, but Qimv and Qazv did not.
Endurance-training-induced cellular adaptations in respiratory muscles
Authors: Powers S. K. , Lawler J. , Criswell D. , Dodd S. , Grinton S. , Bagby G. , Silverman H.
Published: December 2017

Controversy exists concerning the adaptability of mammalian respiratory muscles in response to endurance training. We examined the effects of 8 wk of progressive treadmill exercise (45 min/day 5 days/wk) on the biochemical adaptations of rat diaphragm and intercostal muscles. Female Sprague-Dawley rats were randomly assigned to a sedentary control (n = 10) or an exercise-training group (n = 10). Endurance training resulted in an enhanced oxidative capacity in the anterior costal diaphragm as evidenced by a 29% increase (P less than 0.05) in the activity of succinate dehydrogenase (SDH) in trained animals compared with controls (4.15 +/- 0.13 vs. 3.21 +/- 0.17 mumol.g-1.min-1). Similarly, SDH activity in the intercostal muscles was 32% greater (P less than 0.05) in the trained animals than in the untrained animals (1.72 +/- 0.11 vs. 1.30 +/- 0.06 mumol.g-1.min-1). In contrast, the crural region of the diaphragm showed no significant increase (P greater than 0.05) in oxidative capacity as a result of the training program (3.28 +/- 0.12 vs. 3.13 +/- 0.18). Furthermore, training did not alter (P less than 0.05) lactate dehydrogenase activity in the intercostals or in the crural or the costal diaphragm. These data demonstrate that the oxidative capacity of the costal diaphragm and the intercostal muscles can be enhanced by increasing respiratory loads via regular endurance exercise. We speculate that the lack of metabolic adaptation in the crural region of the diaphragm was not due to limited plasticity of the fibers in this area but to failure to the exercise-training program to provide the appropriate stimulus for cellular adaptation.