bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological profile of world-class high-altitude climbers
Authors: Oelz O. , Howald H. , Di Prampero P. E. , Hoppeler H. , Claassen H. , Jenni R. , Buhlmann A. , Ferretti G. , Bruckner J. C. , Veicsteinas A. , et al.
Published: December 2017

The functional characteristics of six world-class high-altitude mountaineers were assessed 2–12 mo after the last high-altitude climb. Each climber on one or several occasions had reached altitudes of 8,500 m or above without supplementary O2. Static and dynamic lung volumes and right and left echocardiographic measurements were found to be within normal limits of sedentary controls (SC). Muscle fiber distribution was 70% type I, 22% type IIa, and 7% type IIb. Mean muscle fiber cross-sectional area was significantly smaller than that of SC (-15%) and of long-distance runners (LDR, -51%). The number of capillaries per unit cross-sectional area was significantly greater than that of SC (+ 40%). Total mitochondrial volume was not significantly different from that of SC, but its subsarcolemmal component was equal to that of LDR. Average maximal O2 consumption was 60 +/- 6 ml X kg-1 X min-1, which is between the values of SC and LDR. Average maximal anaerobic power was 28 +/- 2.5 W X kg-1, which is equal to that of SC and 40% lower that that of competitive high jumpers. All subjects were characterized by resting hyperventilation both in normoxia and in moderate (inspired O2 partial pressure = 77 Torr) hypoxia resulting in higher oxyhemoglobin saturation levels in hypoxia. The ventilatory response to four tidal volumes of pure O2 was similar to that of SC. It is concluded that elite high-altitude climbers do not have physiological adaptations to high altitude that justify their unique performance.
Increases in factor VIII complex and fibrinolytic activity are dependent on exercise intensity
Authors: Andrew M. , Carter C. , O'Brodovich H. , Heigenhauser G.
Published: December 2017

Components of the factor VIII complex increase and activation of the fibrinolytic system occur during exercise. The relation between the duration and intensity of exercise and the relative changes in the VIII complex and fibrinolytic system have not been previously examined. Five healthy male subjects were exercised with three protocols: a graded progressive exercise test to exhaustion on a cycle ergometer with 50-W increments every 4 min, steady-state exercise, 15 min at 5 and 125 W each, and an acute 30-s maximal exercise test on a cycle ergometer. Venous blood samples were drawn at base line, during the last 30 s of each power output in the graded exercise, at 5-min intervals for the steady-state exercise, and for up to 1 h after completion of exercise in all three protocols. At the maximum exercise intensities, increases in plasma lactate concentration ([La]), O2 uptake, and [H+] were observed. Components of the VIII complex [VIII procoagulant, VIII procoagulant antigen, VIII-related antigen (VIIIR:Ag), VIII ristocetin cofactor activity] abruptly rose at only the highest work intensities, whereas the whole blood clot lysis time began to gradually shorten much earlier at low work intensities. There were no qualitative changes in the factor VIIIR:Ag on crossed immunoelectrophoresis nor was there evidence of thrombin generation as determined by fibrinopeptide A generation. We conclude that during exercise the changes observed in the coagulation and fibrinolytic systems are related to the intensity of the exercise, which is reflected by increases in plasma [La] and [H+], and that the fibrinolytic system is activated before the changes in the VIII complex are observed.
Effects of irradiation on endothelial cell-polymorphonuclear leukocyte interactions
Authors: Dunn M. M. , Drab E. A. , Rubin D. B.
Published: December 2017

Prominent early effects of irradiation include neutrophilic vasculitis and interstitial inflammation. To examine the role of the endothelium in these events, bovine aortic endothelial cells (EC) were irradiated (5 Gy) under ambient conditions followed by measurements of neutrophil chemotaxis toward conditioned media and adherence to EC. Neutrophil chemotactic activity increased at 4, 24, and 72 h in both the sham-treated (4.2 +/- 2.5, 15.2 +/- 4.8, and 20.0 +/- 2.7 microns, respectively) and irradiated EC-conditioned media (5.0 +/- 2.1, 18.7 +/- 4.5, and 24.1 +/- 3.4 microns, respectively), and the difference between them was significant at 72 h. The chemoattractant was trypsin sensitive, heat resistant, and chemotactic. It was not present in the EC sonicate. Adherence of neutrophils to EC that were irradiated 4 h earlier (19.3 +/- 4.2%) increased compared with controls (11.1 +/- 2.4%) and was similar to EC pretreated with zymosan-activated serum (22.0 +/- 4.0%), which is a potent inducer of adherence. Thus, following irradiation, bovine aortic EC have greater neutrophil chemotactic activity in their media and are more adherent to polymorphonuclear leukocytes.
Ciliary responsiveness in allergic and nonallergic airways
Authors: Wanner A. , Sielczak M. , Mella J. F. , Abraham W. M.
Published: December 2017

Allergic asthma is associated with airway (smooth muscle) hyperresponsiveness to several chemical mediators of anaphylaxis; however, it is not known whether this is accompanied by mucociliary hyperresponsiveness. The purpose of this study was therefore to determine if airway ciliary activity, a component function of mucociliary clearance, exhibits exaggerated responses to prostaglandin E1 (PGE1), prostaglandin E2 (PGE2), and leukotriene D4 (LTD4) in allergic sheep when compared with nonallergic sheep, and the effects of LTD4 are direct or involve the generation of cyclooxygenase products of arachidonate metabolism. Ciliary beat frequency (CBF) was measured in a perfusion chamber with a microscopic technique using tracheal epithelial cells obtained from brushing of “allergic” (positive cutaneous reaction and previous bronchospastic response to inhaled specific antigen) and “nonallergic” (negative cutaneous reaction, no previous inhalation challenge with antigen) sheep. Mean base-line CBF was not different among the groups; PGE1, PGE2, and LTD4 induced dose-dependent increases in CBF, and these increases were not different in allergic and nonallergic sheep. At the highest agonist concentration the mean increase in CBF from base line varied between 13 and 16% (P less than 0.05). The ciliostimulatory effect of LTD4 was significantly blunted by both the sulfidopeptide leukotriene antagonist FPL-55712 and the cyclooxygenase inhibitor indomethacin. These results suggest that allergic sheep fail to exhibit ciliary hyperresponsiveness to selected chemical mediators of anaphylaxis and the ciliostimulatory effect of LTD4 depends on the activation of cyclooxygenase and possibly the generation of prostaglandins.
An isolated upper airway preparation in conscious dogs
Authors: Lee L. Y. , Morton R. F. , McIntosh M. J. , Turbek J. A.
Published: December 2017

The purpose of this study was to develop an isolated upper airway preparation in conscious dogs. Each of the four dogs was trained to wear an individually fitted respiratory mask and surgically prepared with two side-hole tracheostomies. After full recovery, one endotracheal tube was inserted caudally into the lower tracheostomy hole and another tube cranially into the upper tracheostomy. When the two endotracheal tubes were connected to a breathing circuit including a box-balloon system, the magnitude and pattern of the inspiratory flow through the upper airway were identical to that inhaled spontaneously into the lungs by the dogs, but the gas medium inhaled into the upper airway could be independently controlled. Thus it allowed test gas mixtures to be inhaled spontaneously through an isolated upper airway. One limitation was that the inspired gas remained in the upper airway during expiration, but this can be corrected by a simple modification of the breathing circuit. This preparation was tested in studying the respiratory effects of upper airway exposure to CO2 gas mixtures. Our results showed small but significant reduction in both rate and volume of respiration when the concentration of CO2 gas mixture inhaled through the upper airway exceeded 5%. Irregular breathing patterns were frequently elicited in these dogs by higher concentrations (greater than 12%) of CO2.
Retention of ventilatory pattern learning in normal subjects
Authors: Gallego J. , Ankaoua J. , Lethielleux M. , Chambille B. , Vardon G. , Jacquemin C.
Published: December 2017

Two procedures for training normal subjects to increase inspiratory duration (TI) were compared. In the first procedure (feedback), a visual signal informed subjects of their TI value just after the end of each inspiration; subjects were instructed to maintain TI for a set interval previously established by the experimenter. The second procedure (pacing) consisted of delivering a periodic signal to subjects and instructing them to adjust their respiratory frequency to this signal. All subjects participated in two identical sessions, 24 h apart. Comparison of performances between the two sessions provides evidence for a retention effect in feedback subjects only, suggesting the superiority of this method. Voluntary increase of TI during training induced a spontaneous increase of tidal volume, independent of any instruction. This increase in breathing amplitude cannot be explained in terms of chemical control of breathing.
Dependence of central airway resistance on frequency and tidal volume: a model study
Authors: Isabey D. , Chang H. K. , Delpuech C. , Harf A. , Hatzfeld C.
Published: December 2017

The resistance of a hollow cast of human central airways was measured during true sinusoidal airflow oscillations over a wide range of frequencies (0.5–40 Hz) and for various flow amplitudes up to 8 l/s. Pressure and flow were measured in the trachea with high-performance transducers, digitized and averaged over 100 cycles. Data were studied at two points in the flow cycle: at peak inspiratory and expiratory flows and in the two neighborhoods around zero flow where airway resistance (Rv approximately equal to o) was taken as the average slope of the pressure-flow (P-V) curve in each zone. When data obtained near peak flow were plotted in terms of dimensionless pressure drop vs. peak Reynolds number (Rem) and compared with steady-state data, we found no difference up to 2 Hz as previously reported (Isabey and Chang, J. Appl. Physiol. 51: 1338–1348, 1981), a slight decay in pressure drop between 4 and 8 Hz, a frequency-dependent increase in peak flow resistance at high frequencies (10–40 Hz) governed by the Strouhal number alpha 2/Rem beyond alpha 2/Rem = 0.5. On the other hand RV approximately equal to o was found to increase relative to steady state as local acceleration increases, e.g., as peak flow increases at a fixed frequency; this differs from the classical linear theory of oscillatory flow in a long straight tube. To explain these results, we had to use, as in our previous study, an alternative expression for the Strouhal number, i.e., epsilon = L X A X (dV/dt)/V2 (where L and A are the length and cross-sectional area of the trachea and V is a constant flow range over which resistance around flow reversal was computed), which accurately reflects the ratio of local acceleration [d(V/A)/dt)] to convective acceleration [(V/A)2/L] in developing branching flow. Finally, to delineate the regions of dominance of each of the dimensionless parameters, we compiled frequency-tidal volume diagrams for peak flows as well as for reversal. Epsilon, which is negligible near peak flows, appeared to govern the oscillatory P-V relationship near flow reversal in a transitional region of the diagram located between regions of steadiness, or moderate unsteadiness, and a region of dominant unsteadiness governed by alpha.
Comparison of two noninvasive techniques for estimating cardiac output during exercise
Authors: Hatcher D. D. , Srb O. D.
Published: December 2017

This study presents the comparison of two different noninvasive techniques for the estimation of cardiac output (Q). The two techniques used were transthoracic impedance plethysmography (Z) and the indirect Fick CO2 rebreathing (RB) method. Paired estimates of Q were made on 60 different male subjects at rest and during graded increments of work on a cycle ergometer. The mean resting Q as measured by the Z technique (COZ) was 7.46 +/- 0.35 and 5.96 +/- 0.43 l/min using the RB (CORB) technique. At 200 W the mean COZ was 18.67 +/- 0.72 l/min and the CORB was 23.73 +/- 0.84 l/min. Both the techniques were linearly correlated (R) with O2 consumption; i.e., RZ = 0.752, RRB = 0.855. The difference between these two R values is statistically significant (P less than 0.001). A linear relationship was found between the Z and RB techniques at all work loads (R = 0.75). This study suggests that both techniques are equally as reliable over a large range of work loads, with the Z technique being the simplest and most efficient to implement. It was also found that lung volume had no effect on the calculated COZ.
Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate
Authors: Coyle E. F. , Coggan A. R. , Hemmert M. K. , Ivy J. L.
Published: December 2017

The purpose of this study was to determine whether the postponement of fatigue in subjects fed carbohydrate during prolonged strenuous exercise is associated with a slowing of muscle glycogen depletion. Seven endurance-trained cyclists exercised at 71 +/- 1% of maximal O2 consumption (VO2max), to fatigue, while ingesting a flavored water solution (i.e., placebo) during one trial and while ingesting a glucose polymer solution (i.e., 2.0 g/kg at 20 min and 0.4 g/kg every 20 min thereafter) during another trial. Fatigue during the placebo trial occurred after 3.02 +/- 0.19 h of exercise and was preceded by a decline (P less than 0.01) in plasma glucose to 2.5 +/- 0.5 mM and by a decline in the respiratory exchange ratio (i.e., R; from 0.85 to 0.80; P less than 0.05). Glycogen within the vastus lateralis muscle declined at an average rate of 51.5 +/- 5.4 mmol glucosyl units (GU) X kg-1 X h-1 during the first 2 h of exercise and at a slower rate (P less than 0.01) of 23.0 +/- 14.3 mmol GU X kg-1 X h-1 during the third and final hour. When fed carbohydrate, which maintained plasma glucose concentration (4.2–5.2 mM), the subjects exercised for an additional hour before fatiguing (4.02 +/- 0.33 h; P less than 0.01) and maintained their initial R (i.e., 0.86) and rate of carbohydrate oxidation throughout exercise. The pattern of muscle glycogen utilization, however, was not different during the first 3 h of exercise with the placebo or the carbohydrate feedings. The additional hour of exercise performed when fed carbohydrate was accomplished with little reliance on muscle glycogen (i.e., 5 mmol GU X kg-1 X h-1; NS) and without compromising carbohydrate oxidation. We conclude that when they are fed carbohydrate, highly trained endurance athletes are capable of oxidizing carbohydrate at relatively high rates from sources other than muscle glycogen during the latter stages of prolonged strenuous exercise and that this postpones fatigue.
Superior vena caval blood flow velocities in adults: a Doppler echocardiographic study
Authors: Cohen M. L. , Cohen B. S. , Kronzon I. , Lighty G. W. , Winer H. E.
Published: December 2017

Superior vena caval blood flow velocity was measured in 30 normal adults (age 20–65, mean 36 yr). The flow velocities were measured by pulsed Doppler echocardiography, using a Duplex system with the transducer at the right supraclavicular fossa, approximating a 0 degrees Doppler angle. Four distinct flow waveforms were found during each cardiac cycle: A, a small retrograde flow during right atrial contraction (peak flow velocity 12.4 +/- 2.2 cm/s); B, a small antegrade flow during right atrial relaxation (15.7 +/- 5.0 cm/s); S, a large antegrade flow during ventricular systole (35.2 +/- 7.3 cm/s); and D, a large antegrade flow during ventricular diastole (23.2 +/- 3.1 cm/s). The wave duration was inversely related to heart rate. The peak flow velocities of the S and D waves were inversely related to the patients' ages. This study provides recognition of the pattern and range of normality essential to extension of this noninvasive technique to the diagnosis of pathological conditions.
Ventilatory effect of an adenosine analogue in unanesthetized rabbits during development
Authors: Runold M. , Lagercrantz H. , Fredholm B. B.
Published: December 2017

The effect of an adenosine analogue N6-L-(R-phenylisopropyl)adenosine (R-PIA) on respiration was studied in rabbit pups (1–8 days old). Respiration was monitored by a noninvasive barometric method during natural sleep. The adenosine analogue was given by an indwelling intraperitoneal catheter. R-PIA given in a dose of 0.1 mumol/kg (380 micrograms/kg) body wt caused a decrease of the ventilation. The respiratory decrease could be reversed or prevented by pretreatment with theophylline (10 mg/kg). R-PIA caused a considerably more pronounced effect in 1- to 3-day-old animals than in 8-day-old animals. This effect was seen both when the ambient temperature was held at 28 (P less than 0.01) and 32 degrees C (P less than 0.05). Determination of R-PIA receptors in whole brains of rabbit pups of various ages showed that R-PIA bound with higher affinity to membranes from newborn animals (Kd 0.53 nM) than older animals (Kd 0.7–1.26). Since adenosine is released during hypoxia, it may be involved in “hypoxic depression” of respiration in neonates and apnea of prematurity. This might also explain the potent therapeutic effect of the adenosine antagonist theophylline on recurrent apnea in preterm infants.
Contractile changes in opposing muscles of the human ankle joint with aging
Authors: Vandervoort A. A. , McComas A. J.
Published: December 2017

The effects of aging on maximal voluntary strength and on the isometric twitch were determined in the ankle dorsiflexor and plantarflexor muscles of 111 healthy men and women aged 20–100 yr. Men were found to be stronger than women at all ages. In both sexes, the average values for maximum voluntary strength of the dorsiflexors and plantarflexors began to decline in the 6th decade. Although the absolute loss of strength was greater for the plantarflexor muscles, the relative losses were similar in the two muscle groups. During maximum voluntary effort, stimulation of motor nerves produced no additional torque in the majority of elderly men and women, indicating that these subjects remained able to utilize their descending motor pathways for optimal muscle activation. Comparisons of muscle compound action potentials, twitch torques, and muscle cross-sectional areas suggested that a decrease in excitable muscle mass was entirely responsible for the lower strength of the elderly. An additional effect of aging was the gradual prolongation of twitch contraction and half-relaxation times throughout the adult life-span.
Endogenous modulation of alpha-adrenergic contraction in canine tracheal muscle
Authors: Tallet J. , Munoz N. M. , Fried R. , Leff A. R.
Published: December 2017

We studied the effect of passive stretch on the contraction of canine tracheal smooth muscle (TSM) to alpha-adrenergic agonists and acetylcholine (ACh) in 211 epithelium-free TSM strips from 42 dogs in vitro. Passive stretch at a resting tension of 100 g/cm2 caused a time-dependent decrease in the contractile response to alpha-adrenergic agonists after beta-adrenergic blockade with propranolol. Initial contraction elicited by 10(-3) M phenylephrine (PE) and clonidine (CLO) decreased at 2 h by 31 and 100%, respectively. Decrease in alpha-adrenergic contractility did not result from tachyphylaxis; no contraction was elicited by PE or CLO given for the first time after 4-h passive stretch at 100 g/cm2. The TSM response to ACh was unchanged over the same time in the same strips. When TSM strips were incubated at zero resting tension for 6 h, some attenuation of the alpha-adrenergic contractile still occurred but was not substantial. Similarly, when strips were incubated with 10(-6) M indomethacin (INDO) or 10(-5) M mefenamic acid (MEF) at 100 g/cm2 resting tension, time-dependent attenuation of the response to PE and CLO was reduced for at least 6 h, and initial contraction elicited by PE was augmented. Response of TSM to ACh was not affected by prostaglandin synthetase inhibition with INDO. We conclude that passive stretch of canine TSM in vitro leads to decreased responsiveness to alpha-adrenergic stimulation that can be prevented with INDO or MEF. These data are consistent with the synthesis of an inhibitory eicosanoid in epithelium-free canine TSM that may be activated by mechanical deformation of the muscle.
Trachea and lung dimensions in nonsmoking twins: morphological and functional studies
Authors: Kawakami Y. , Kusaka H. , Nishimura M. , Abe S.
Published: December 2017

To compare genetic and environmental factors that determine lung function and dimensions, chest radiographs and pulmonary function were measured in 17 pairs of nonsmoking twin adolescent boys (12 monozygotic pairs and 5 dizygotic pairs). Genetic factors dominated in tracheal width and lung dimensions (height, width, and apicofissural and fissurodiaphragmatic distances) at residual volume. Genetic factors also affected forced vital capacity, functional residual capacity, forced expiratory volume in 1 s, maximum expiratory flow at 25% vital capacity, and maximum flow at 50% vital capacity-to-forced vital capacity ratio. Peak expiratory flow correlated with tracheal width at residual volume. Age correlated with lung dimensions (width and depth) but not with tracheal width. These results indicate that genetic factors determine the dimensions and function of central airways, peripheral airways, and lung parenchyma in adolescent males. The effects of genetic factors on some functional measurements (airway resistance, closing volume-to-vital capacity ratio, and phase III in single-breath N2 washout) may be masked because of poor reproducibility of the tests.
Control of ventilation in extreme-altitude climbers
Authors: Masuyama S. , Kimura H. , Sugita T. , Kuriyama T. , Tatsumi K. , Kunitomo F. , Okita S. , Tojima H. , Yuguchi Y. , Watanabe S. , et al.
Published: December 2017

Ten climbers who participated in the Nepal-Japan Kangchenjunga Expedition (altitude, 8,478–8,586 m) in 1984 were examined for their hypercapnic and isocapnic hypoxic ventilatory responses (HCVR and HVR) at sea level before and after the expedition. Five climbers who reached an altitude higher than 8,000 m, [designated high-performance climbers (HPC)] exhibited significantly higher HVR than five climbers who did not [low-performance climbers (LPC)]. On the other hand, no significant difference in HCVR was seen between HPC and LPC. Our results were in agreement with the findings reported by Schoene et al. (J. Appl. Physiol. 56: 1478–1483, 1984) obtained in the American Medical Research Expedition to Everest in 1981. Significant depression in HVR in five climbers was found even 35–40 days after the expedition, which was accompanied by decreased arterial partial pressure of CO2 and increased pH at rest. Hence, the effect of altitude acclimatization in the climbers exposed to extreme altitude may have still persisted at the time of the postexpedition study. Our results confirmed that HRV evaluated at sea level may be used as an indicator of a climber's capability at great high altitude.
Cation transport in lung epithelial cells derived from fetal, newborn, and adult rabbits
Authors: Bland R. D. , Boyd C. A.
Published: December 2017

Recent studies done with fetal and adult sheep and with monolayers of cultured rat alveolar type II cells suggest that active transport of Na+ across the lung epithelium may contribute to liquid absorption from air spaces, an essential component of the normal switch from placental to pulmonary gas exchange at birth. The goals of this work were 1) to study the ontogeny of cation transport in lung epithelial cells derived from fetal, newborn, and adult rabbits and 2) to determine the influence of premature birth, air breathing, labor, and postnatal lung maturation on K+ uptake in these cells. We harvested granular pneumonocytes by tracheal instillation of proteolytic enzymes followed by centrifugation of the dispersed cells over a discontinuous density gradient of metrizamide. This procedure yielded 65–90% granular pneumonocytes, of which more than 80% excluded vital dye. Using freshly isolated cells, we measured uptake of 86Rb+, which mimics transmembrane movement of K+, in the presence or absence of 10(-4) M ouabain and in the presence or absence of 5 X 10(-4) M furosemide or bumetanide. In adult rabbit studies, 86Rb+ uptake was twice as fast in lung epithelial cells (98 +/- 7 nmol X 10(6) cells-1 X h-1) as it was in alveolar macrophages (51 +/- 6 nmol X 10(6) cells-1 X h-1). Ouabain inhibited 55–60% of the uptake by pneumonocytes, and “loop” diuretics inhibited an additional 15–20%. The rate of 86Rb+ uptake in fetal cells was less than 10% (6 +/- 1 nmol X 10(6) cells-1 X h-1) of the rate in adult cells; ouabain inhibited 80-85% of 86Rb+ uptake in fetal cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Arginine vasopressin, circulation, and kidney during graded water immersion in humans
Authors: Norsk P. , Bonde-Petersen F. , Warberg J.
Published: December 2017

Ten normal males rested sitting upright at an air temperature of 28 degrees C for 5.5 h (control, C) and underwent 4 h of graded water immersion (WI) to the umbilicus (UI), to the chest (CI), and to the neck (NI), respectively (water temperature = 34.5 degrees C), on different experimental days. Plasma arginine vasopressin (PAVP) was suppressed during WI compared with C and maximally so during NI. However, there was no change in PAVP comparing CI with UI even though central venous pressure (CVP) increased. CVP increased during CI and NI compared with C but was unchanged during UI, whereas cardiac output (rebreathing method), stroke volume, and plasma volume increased to approximately the same level during all three steps of WI compared with C. Heart rate and total peripheral vascular resistance decreased during UI, CI, and NI. Systolic arterial pressure (SAP) and pulse pressure (PP) were increased gradually from prestudy related to the degree of WI. Also diuresis, natriuresis, kaliuresis, osmotic excretion, and clearance were increased gradually compared with C, whereas free water clearance (CH2O) gradually decreased. There were weak negative but statistically significant correlations between PAVP and CVP and between changes in PAVP from prestudy and corresponding changes in SAP and PP. Furthermore, a statistically significant and negative correlation between CH2O and natriuresis could be established. We conclude that graded immersion gradually increases central blood volume and decreases PAVP. However, not only cardiopulmonary mechanoreceptors but also arterial baroreceptors may play a role in AVP suppression during WI in humans. In hydropenic subjects the suppression of PAVP during WI is apparently not effective in counteracting the decrease in CH2O induced by increased solute excretion.
Effects of 24-hour fast on cycling endurance time at two different intensities
Authors: Loy S. F. , Conlee R. K. , Winder W. W. , Nelson A. G. , Arnall D. A. , Fisher A. G.
Published: December 2017

Ten competitive cyclists were exercised to exhaustion to test the potential of a 24-h fast for increasing endurance. One group (n = 4) was tested at an initial intensity of 86% maximum O2 uptake (VO2max) (HI) and a second group (n = 6) at 79% VO2max (MI). Both groups repeated test rides in fasted and normal-diet conditions. Time to fatigue was designated at two points: fatigue 1 occurred when pedal frequency could not be maintained at the initial percent VO2max; fatigue 2 occurred when pedal frequency could not be maintained at a workload of approximately 65% VO2max. In both HI and MI the 24-h fast had no effect on resting muscle glycogen stores but significantly increased plasma free fatty acid (FFA) levels. Despite the increased FFA availability, time to fatigue was reduced in the fasted groups. Fatigue 1 and 2 times (mean +/- SE) for HI-fasted were 42.0 +/- 6.2 and 170.0 +/- 20.4 min, respectively, compared with those of the HI-normal diet of 115.3 +/- 25.6 and 201.0 +/- 14.8 min. Fatigue 1 and 2 times for MI-fasted were 142.0 +/- 19.6 and 167.5 +/- 10.5 min compared with those of the MI-normal diet of 191.3 +/- 25.0 and 214.3 +/- 18.9 min. The cause of fatigue at fatigue 1 was not readily apparent. Fatigue 2 in all groups seemed to be related to hypoglycemia as well as muscle glycogen depletion.
Evaluation of laser-Doppler flowmetry as a measure of tissue blood flow
Authors: Smits G. J. , Roman R. J. , Lombard J. H.
Published: December 2017

In this study the technique of laser-Doppler flowmetry was evaluated for the measurement of tissue blood flow by comparing laser-Doppler flow (LDF) signal in the renal cortex, gracilis muscle, and cremaster muscle of anesthetized rats to whole-organ blood flow measured with an electromagnetic flowmeter or radioactive microspheres. In vitro, LDF signal was closely correlated (r = 0.99) to changes in erythrocyte velocity generated with a rotating wheel. Although individual LDF readings varied in situ, mean LDF signal calculated from multiple readings on the tissue surface were significantly correlated (r = 0.74–0.95) with tissue blood flows measured at various perfusion pressures. However, significant differences in the slope of the LDF signal vs. blood flow relationship were observed in different tissues and with different methods of measurement in the same tissue. This study indicates that mean laser-Doppler flow signal provides a good estimate of tissue blood flow, provided a sufficient number of points is scanned. However, there appears to be no universal calibration factor for the method.
Effects of aerosol histamine and carbachol on central and peripheral airflow resistance in sheep
Authors: Snapper J. R. , Lefferts P. L.
Published: December 2017

Sixteen anesthetized artificially ventilated open-chest sheep were prepared with retrograde catheters to allow for measurement of dynamic compliance of the lungs (Cdyn), total airflow resistance of the lungs (RL), and central (Rc) and peripheral (Rp) airflow resistance. Twelve sheep received aerosol histamine and 12 sheep received aerosol carbachol. Eight sheep received and responded to both aerosol histamine and aerosol carbachol. Three sheep received both aerosol histamine and aerosol carbachol but failed to respond to both agents. Under base-line conditions, for the 16 sheep, 69% of total RL was located in the peripheral component, Rp, and 31% in the central component, Rc. Aerosol histamine caused only peripheral small airway changes while aerosol carbachol predominantly effected the central large airways. When aerosol histamine responsiveness, defined using Cdyn or Rp, was compared to aerosol carbachol responsiveness using Rc, a correlation was demonstrable (r = 0.84, n = 8, P less than 0.05). It is possible in sheep to cause relatively pure peripheral small airway and relatively pure central large airway changes by using different bronchoconstrictor agents. Aerosol histamine and aerosol carbachol responsiveness correlated with each other in these artificially ventilated anesthetized sheep.
Effect of nicotine and acetylcholine on crustacean muscle membrane potential
Authors: Taylor R. F. , Frazier D. T.
Published: December 2017

We have investigated the effect of nicotine and acetylcholine on the resting membrane potential of the crayfish extensor muscle in order to determine whether crustacean muscle can be activated by cholinergic compounds. Intracellular recordings from individual deep extensor abdominal muscle cells were made using standard glass microelectrode techniques. The resting membrane potential was measured before and after treatment with glutamate, nicotine, and acetylcholine. Glutamate, which is a known activator of crayfish muscle, was used to determine whether the muscle cell preparation was viable and capable of responding to any of the test substances. Our results confirm that application of glutamate is associated with a depolarization of the muscle membrane. However, muscle cells showed no depolarization after treatment with nicotine (50 microM) or acetylcholine (66 microM). These results argue against the notion that increases in muscle tension may be responsible for the increased receptor organ discharge observed in the presence of nicotine. Rather, it supports the hypothesis that nicotine is acting directly on the mechanoreceptor membrane to change its sensitivity.
Simultaneous determination of fluid shifts during thermal stress in a small-animal model
Authors: Durkot M. J. , Martinez O. , Brooks-McQuade D. , Francesconi R.
Published: December 2017

We have developed methodology to simultaneously measure fluid redistribution among the major compartments during moderate and severe hypohydration. Total body water (TBW) was determined using tritiated water, extracellular fluid volume (ECF) was measured using a single-injection [14C]inulin technique, and plasma volume (PV) was determined by indocyanine green dye dilution. Moderate (10% decrease in body wt) and severe (15%) hypohydration resulted in significant losses in TBW, ECF, and PV. Plasma volume was decreased by approximately 25% in both groups, and other fluid compartments were differentially affected. For example, the moderately dehydrated group maintained PV by shifting fluid from the interstitial fluid volume (ISF) compartment while preserving the intracellular fluid volume (ICF); conversely, the severely dehydrated group maintained PV by redistributing fluid from both the ISF and ICF compartments. The data indicated that the initial response to fluid loss was the movement of fluid from the ISF pool to sustain both PV and ICF. In severely hypohydrated rats, PV was maintained at the expense of ICF. These experiments indicated that PV and ICF were maximally protected, probably to preserve the integrity of the cardiovascular system and to minimize organ injury.
Effects of cognitive and psychomotor tasks on breath-holding span
Authors: Alpher V. S. , Nelson R. B. , Blanton R. L.
Published: December 2017

Bartlett (J. Appl. Physiol. 42: 717–721, 1977) demonstrated that a psychomotor task (hand dynamometer) extended breath holds at functional residual capacity (FRC) in a manner comparable to Valsalva and Mueller maneuvers. This led us to the hypothesis that distraction of a subject's attention from dyspneic sensations accounted for Bartlett's findings. This hypothesis was tested by comparing a hand dynamometer task (rubber-bulb squeeze) with a mental performance task (mental arithmetic). Results for tasks performed separately and concurrently in a within-subjects design showed comparable effects, without reaching a FRC breath-hold performance ceiling. Implications of results for effects of nonmechanical and nonchemical factors on respiratory drive are discussed.
Dynamic torquemeter calibration of bicycle ergometers
Authors: Russell J. C. , Dale J. D.
Published: December 2017

Bicycle ergometers as widely used in both clinical testing and exercise physiology studies are mechanical, hydraulic, or electromechanical devices. They are thus subject to change and error, creating a need for repeated calibration. We have developed a compact inexpensive torquemeter that permits dynamic calibration of the entire range of an ergometer. The torquemeter continuously measures the input torque at the pedal shaft of the ergometer and thus includes all work done in the drivetrain. It also permits adjustment of electrically braked ergometers to a specified torque using internal adjustments to give correct scale readings. The torquemeter depends on a high carbon steel torsion spring whose ends are rotated in angular deflection by increasing applied torque. Relative rotation is sensed through a multiturn potentiometer, the resistance of which is measured externally through a slip ring contact.
Ventilatory response to sustained hypoxia in normal adults
Authors: Easton P. A. , Slykerman L. J. , Anthonisen N. R.
Published: December 2017

We examined the ventilatory response to moderate (arterial O2 saturation 80%), sustained, isocapnic hypoxia in 20 young adults. During 25 min of hypoxia, inspiratory minute ventilation (VI) showed an initial brisk increase but then declined to a level intermediate between the initial increase and resting room air VI. The intermediate level of VI was a plateau that did not change significantly when hypoxia was extended up to 1 h. The relation between the amount of initial increase and subsequent decrease in ventilation during constant hypoxia was not random; the magnitude of the eventual decline correlated confidently with the degree of initial hyperventilation. Evaluation of breathing pattern revealed that during constant hypoxia there was little alteration in respiratory timing and that the changes in VI were related to significant alterations in tidal volume and mean inspiratory flow (VT/TI). None of the changes was reproduced during a sham control protocol, in which room air was substituted for the period of low fractional concentration of inspired O2. We conclude that ventilatory response to hypoxia in adults is not sustained; it exhibits some biphasic features similar to the neonatal hypoxic response.
Effects of bacterial endotoxin on protecting copper-deficient rats from hyperoxia
Authors: Spence T. H. , Jenkinson S. G. , Johnson K. H. , Collins J. F. , Lawrence R. A.
Published: December 2017

The administration of very low doses of bacterial endotoxin protects rats during exposure to hyperoxia and is associated with the induction of lung antioxidant enzyme activities. Copper-deficient rats have increased susceptibility to O2 toxicity, which may be related to their decreased lung superoxide dismutase activity (SOD) or decreased plasma ceruloplasmin concentrations. To determine whether endotoxin can protect against hyperoxia in this susceptible model, we exposed copper-deficient and control rats to a fractional inspiratory concentration of O2 greater than 0.95 for 96 h after pretreatment with 500 micrograms/kg of bacterial endotoxin or phosphate-buffered saline (PBS). Mortality in the copper-deficient and control rats given PBS and exposed to O2 for 96 h was 100%. Copper-deficient rats died significantly earlier during the exposure than controls. No mortality occurred in either group treated with endotoxin and hyperoxia despite the decreased activity of copper-dependent enzymes in the copper-deficient rats. Copper-deficient rats treated with endotoxin and exposed to hyperoxia did increase lung Cu-Zn-SOD activity, but activity remained below levels found in air-exposed controls. Mn-SOD activity was found to be induced above air-exposed controls in the copper-deficient rats treated with endotoxin and exposed to hyperoxia. Hyperoxic exposure resulted in a marked increase in plasma ceruloplasmin concentrations in the control rats, but no increases in ceruloplasmin occurred in the copper-deficient animals. Endotoxin protects copper-deficient rats from hyperoxia despite their decreased lung Cu-Zn-SOD activity, and decreased plasma ceruloplasmin.
Role of ventrolateral medulla in regulation of respiratory and cardiovascular systems
Authors: Millhorn D. E. , Eldridge F. L.
Published: December 2017

It is now widely accepted that the ventrolateral aspect of the medulla oblongata (VLM) plays an important role in regulation of the respiratory and cardiovascular systems. The VLM has been implicated as being involved in a number of different physiological functions, including central chemoreception, integration of afferent inputs from certain sense organs to the respiratory and cardiovascular controllers, the source of excitatory input to preganglionic sympathetic neurons in the spinal cord, and location of synaptic relay between the higher brain defense areas and spinal cord sympathetic elements. In recent years there have been a number of important findings concerning both the anatomical substrate and neurophysiological characteristics of VLM neurons involved in regulation of the respiratory and cardiovascular systems. New anatomical findings show that neuronal networks located in the VLM send projections to and receive projections from brain stem nuclei that have traditionally been associated with respiratory and cardiovascular regulation. Nevertheless, there are still many important questions concerning the role of the VLM in control of these vital systems that have yet to be answered. For instance, are the same VLM neurons involved in control of both systems? Is the VLM the only site for central respiratory chemoreception? This review will endeavor to examine new findings and to reexamine some older findings concerning the VLM.
Control of activity of the diaphragm in rapid-eye-movement sleep
Authors: Kline L. R. , Hendricks J. C. , Davies R. O. , Pack A. I.
Published: December 2017

Respiration in rapid-eye-movement sleep (REMS) is known to be highly variable. The purpose of this study was to investigate the source of this variability and to determine which ordering principles remained operative in REM sleep. In unrestrained, naturally sleeping cats we recorded the electroencephalogram, electrooculogram, neck electromyogram, and diaphragmatic electromyogram (EMG) and computed its moving average (MAdi). As a reference, we first examined MAdi during “tonic” REMS, since breathing is fairly regular in this state. “Control” ranges for peak amplitude (PEMG), inspiratory time (TI), duration of postinspiratory inspiratory activity, expiratory time, and the calculated inspiratory slope (PEMG/TI) were determined by overlaying individual breath traces of the time course of MAdi during tonic REMS to form a composite tracing. Next, the time course of the EMG during individual breaths in slow-wave sleep (SWS) and a complete period of consecutive breaths in REMS (both tonic and phasic) were compared with this tonic REMS composite. The number of eye movements per breath was tabulated as an index of phasic activity. The inspiratory slopes during SWS and tonic REMS were similar. However, during phasic REMS, many breaths displayed either increases (excitation) or decreases (inhibition) in slope compared with the “typical” breaths seen in tonic REMS. The occurrence of these altered slopes increased with the frequency of phasic events. TI was inversely related to the slope of the EMG, which tended to minimize changes in PEMG.(ABSTRACT TRUNCATED AT 250 WORDS)
Cardiorespiratory responses to hypoxia in intact and bilaterally vagotomized pigeons
Authors: Barnas G. M. , Gleeson M. , Rautenberg W.
Published: December 2017

Bilateral, cervical vagotomy in birds denervates, among other receptors, the carotid bodies. To test whether such neural section removes sensitivity to hypoxia, we measured respiratory, cardiovascular, and blood gas responses to hypoxia at 84-, 70-, and 49-Torr inspiratory O2 partial pressure (PIO2) in five pigeons with intact vagi and in five bilaterally, cervically vagotomized pigeons. Normoxic respiratory frequency (fresp) and expiratory flow rate (VE) were decreased after vagotomy. Intact pigeons showed large increases in VE in response to hypoxia, effected mostly by increases in fresp. VE also increased greatly in response to hypoxia in vagotomized pigeons, but increases were largely the result of tidal volume. O2 consumption, CO2 production, and respiratory exchange ratio increased slightly in all pigeons during hypoxia. Normoxic heart rate was greater after vagotomy; cardiac output increased in all pigeons in response to hypoxia, but stroke volume increased only in intact pigeons. During normoxia, arterial and mixed venous O2 partial pressure, O2 concentration, and pH were lower and arterial and mixed venous CO2 partial pressure was higher, after vagotomy. In all pigeons during hypoxia, arterial and mixed venous O2 and CO2 partial pressure and O2 concentration decreased and arterial and mixed venous pH increased; changes were roughly parallel in intact and vagotomized pigeons. The arteriovenous O2 concentration differences during normoxia and hypoxia were similar in all pigeons. We conclude that bilateral, cervical vagotomy in the pigeon causes hypoventilation and tachycardia during normoxia, but strong respiratory and cardiovascular responses to hypoxia are still present.
Variable site of airway narrowing among obstructive sleep apnea patients
Authors: Hudgel D. W.
Published: December 2017

The purpose of this was to determine whether the site of physiological narrowing within the upper airway was uniform or differed among patients with obstructive sleep apnea. Inspiratory pressures were measured with an esophageal balloon catheter and three catheters located at different sites along the upper airway: supralaryngeal airway, oropharynx, and nasopharynx. Peak inspiratory pressure differences between catheters allowed assessment of pressure gradients across three airway segments: lungs-larynx-retroepiglottal airway (esophageal-supralaryngeal pressure), hypopharynx (supralaryngeal-oropharynx pressure), and transpalatal airway (oropharynx-nasopharynx pressure). In five patients, hypopharyngeal obstruction was present, and in four patients no hypopharyngeal obstruction existed. In these four patients the site of obstruction was located at the level of the palate. In a given subject, the site of obstruction was the same during repeated measurements. The presence or absence of hypopharyngeal narrowing during sleep was not predictable from gradients measured across different segments of the upper airway during wakefulness. We conclude that the site of physiological upper airway obstruction varies among patients with obstructive sleep apnea and is not predictable from pressure measured during wakefulness. We speculate that uvulopalatopharyngoplasty may not relieve obstructive apneas in patients with hypopharyngeal obstruction.
Estimation of response curves in closed-loop physiological control
Authors: Poon C. S.
Published: December 2017

Several recent reports have addressed the problem of estimating the response slope from repeated measurements of paired data when both stimulus and response variables are subject to biological variability. These earlier approaches suffer from several drawbacks: useful information about the relationships between the error components in a closed-loop system is not fully utilized; the response intercept cannot be directly estimated; and the normalization procedure required in some methods may fail under certain circumstances. This paper proposes a new, general method of simultaneously estimating the response slope and intercept from corrupted stimulus-response data when the errors in both variables are specifically related by the system structure. A direct extension of the least-squares approach, this method [directed least squares (DLS)] reduces to ordinary least-squares methods when either of the measured variables is error free and to the reduced-major-axis (RMA) method of Kermack and Haldane (Biometrics 37: 30-41, 1950) when the magnitudes of the normalized errors are equal. The DLS estimators are scale invariant, statistically unbiased and always assume the minimum variance. With simple modifications, the method is also applicable to paired data. If, however, the relation between error components is uncertain, then the RMA method is optimal, i.e., having the least possible asymptotic bias and variance. These results are illustrated by using various types of closed-loop respiratory response data.
Overestimation of sheep lung lymph contamination
Authors: Drake R. E. , Laine G. A. , Allen S. J. , Katz J. , Gabel J. C.
Published: December 2017

We have previously reported that lymph from the chronic sheep lung lymph preparation contains 25-60% lymph from nonpulmonary sources. In subsequent studies we found that the lymph flow rate from cannulated lymph vessels depends on the resistance and position of the lymph cannula. Because we did not account for these factors in our estimate of the amount of nonpulmonary lymph in the sheep lung lymph preparation, our data were not accurate. We probably overestimated the amount of nonpulmonary lymph. However, the presence of nonpulmonary lymph remains a potentially serious problem with the sheep lung lymph preparation.