bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction of VO2max during cycle exercise in pregnant women
Authors: Sady S. P. , Carpenter M. W. , Sady M. A. , Haydon B. , Hoegsberg B. , Cullinane E. M. , Thompson P. D. , Coustan D. R.
Published: December 2017

We measured maximal O2 uptake (VO2max) during stationary cycling in 40 pregnant women [aged 29.2 +/- 3.9 (SD) yr, gestational age 25.9 +/- 3.3 wk]. Data from 30 of these women were used to develop an equation to predict the percent VO2max from submaximal heart rates. This equation and the submaximal VO2 were used to predict VO2max in the remaining 10 women. The accuracy of VO2max values estimated by this procedure was compared with values predicted by two popular methods: the Astrand nomogram and the VO2 vs. heart rate (VO2-HR) curve. VO2max values estimated by the derived equation method in the 10 validation subjects were only 3.7 +/- 12.2% higher than actual values (P greater than 0.05). The Astrand method overestimated VO2max by 9.0 +/- 19.4% (P greater than 0.05), whereas the VO2-HR curve method underestimated VO2max by only 1.6 +/- 10.3% in the same 10 subjects (P greater than 0.05). Both the Astrand and the VO2-HR curve methods correlated well with the actual values when all 40 subjects were considered (r = 0.77 and 0.85, respectively), but the VO2-HR curve method had a lower SE of prediction than the Astrand method (8.7 vs. 10.4%). In a comparison group of 10 nonpregnant sedentary women (29.9 +/- 4.5 yr), an equation relating %VO2max to HR nearly identical to that obtained in the pregnant women was found, suggesting that pregnancy does not alter this relationship. We conclude that extrapolating the VO2-HR curve to an estimated maximal HR is the most accurate method of predicting VO2max in pregnant women.
Diaphragmatic relaxation rate after voluntary contractions and uni- and bilateral phrenic stimulation
Authors: Wilcox P. G. , Eisen A. , Wiggs B. J. , Pardy R. L.
Published: December 2017

We compared the rate of relaxation of the diaphragm (RRdi) after unilateral phrenic nerve stimulation, bilateral phrenic nerve stimulations, and short sharp voluntary contractions (sniffs). RRdi was measured as the maximum rate of decline in transdiaphragmatic pressure (Pdi) corrected for the change in Pdi [maximum relaxation rate (MRR)/delta Pdi], the time constant (tau) of the later exponential decline in Pdi, and the time to half relaxation (1/2 RT). In five subjects there was no difference in mean RRdi apart from a smaller MRR/delta Pdi (P less than 0.05) for left unilateral compared with either right unilateral or bilateral needle stimulation. However, RRdi varied unpredictably between unilateral and bilateral stimulation of the phrenic nerve in individual subjects. In the same five subjects, sniffs were found to have a slower RRdi than bilateral stimulations (MRR/delta Pdi 0.0064 +/- 0.0007 vs. 0.0074 +/- 0.0018/ms, tau 57.2 +/- 8.7 vs. 48.2 +/- 7.4 ms, 1/2 RT 108.9 +/- 10.9 vs. 73.9 +/- 6.0 ms; all P less than 0.05). The application and inflation of an abdominal binder to an external pressure of 60 mmHg resulted in a decrease in functional residual capacity (-710 +/- 70 ml), but there was no effect on relaxation parameters. Our findings suggest that in the evaluation of RRdi 1) unilateral hemidiaphragmatic stimulations may not accurately reflect the in vivo contractile properties of the diaphragm, 2) sniff maneuvers are not voluntary equivalents of phrenic nerve stimulations, and 3) RRdi is not affected by abdominal binder inflation up to 60 mmHg.
Inhibition of cholinergic neurotransmission in human airways by beta 2-adrenoceptors
Authors: Rhoden K. J. , Meldrum L. A. , Barnes P. J.
Published: December 2017

The purpose of the study was to determine whether catecholamines modulate cholinergic neurotransmission in isolated human airway smooth muscle. Bronchial rings were suspended in organ baths for isometric measurement of tension, and contractions were induced by either electrical field stimulation (EFS) or exogenous acetylcholine (ACh). Isoproterenol, epinephrine, and norepinephrine in that order of potency produced concentration-dependent inhibition of comparable responses to EFS and ACh. However a potency difference of 100-fold for isoproterenol (IC50 = 4.80 X 10(-8) M for EFS and 3.70 X 10(-6) M for ACh) and 10-fold for both epinephrine and norepinephrine was observed for inhibition of responses to EFS compared with responses to ACh. The inhibitory effects of isoproterenol on responses to EFS were prevented by propranolol and ICI 118551 (a beta 2-antagonist) but not by betaxolol (a beta 1-antagonist). Tyramine had no effect on contractions elicited by EFS. These experiments demonstrate that beta-agonists inhibit cholinergic nerve-induced contractions of human bronchi more potently than contractions induced by exogenous ACh, suggesting modulation of cholinergic neurotransmission by prejunctional beta 2-receptors.
Accelerated decay of inspiratory pressure during hypercapnic endurance trials in humans
Authors: Ameredes B. T. , Clanton T. L.
Published: December 2017

Seven normal human subjects inspired a CO2-O2 mixture from a constant-flow generator while performing maximal inspiratory maneuvers from functional residual capacity. End-tidal CO2 (ETCO2) was maintained at either 5.5 (normocapnia), 3.5 (hypocapnia), or 7% (hypercapnia) on separate testing days. Subjects attained maximal mouth pressure (Pm) while breathing at either 1.25 or 1 l/s, utilizing a fixed breathing pattern (duty cycle 0.43) with an inspiratory time of 1.5 s. Maximal Pm was measured at rest and then during a 10-min endurance trial in which subjects repeated maximal voluntary inspirations with constant flow and breathing pattern. The endurance Pm data were fit to nonlinear exponential regression. The results indicated that 1) maximal Pm at rest was unaffected by changing ETCO2; 2) the rate of Pm decay over time was accelerated by hypercapnia, whereas hypocapnia showed no consistent effects; and 3) "sustainable" Pm, attained toward the end of the endurance trial, was not decreased; therefore sustainable force output was preserved in response to changing ETCO2.
CO2 sensitivity of cat phrenic neurogram during hypoxic respiratory depression
Authors: Melton J. E. , Neubauer J. A. , Edelman N. H.
Published: December 2017

The CO2 response of the phrenic neurogram before and during CO-induced isocapnic brain hypoxia was studied in peripherally chemodenervated, vagotomized, paralyzed, ventilated cats with blood pressure held constant. During inhalation of 0.5% CO in 40% O2, arterial O2 content (CaO2) was reduced to 40% and minute phrenic activity to 38.4 +/- 9.4% (SE; n = 9) of prehypoxic levels, primarily due to depression of peak phrenic amplitude (PP). CO2 response, defined as the slope of the plot of PP vs. end-tidal PCO2 during CO2 rebreathing, was unaffected by phrenic depression even to the point of total suppression of phrenic activity in two cats. The effect of the tissue metabolic acidosis associated with hypoxia on phrenic CO2 sensitivity was assessed in a separate group of cats by blocking lactate formation during hypoxia with dichloroacetate (DCA). Preventing lactic acidosis during hypoxia did not affect the CO2 response of the phrenic activity during hypoxia. We conclude that 1) hypoxic depression does not limit the ability of central respiratory neurons to respond to CO2, and 2) the failure of DCA to affect the CO2 response of the phrenic neurogram suggests that brain intracellular lactic acidosis does not modify the phrenic response to hypercapnia.
Activity-induced adaptations in skeletal muscles of iron-deficient rabbits
Authors: Harlan W. R. , Williams R. S.
Published: December 2017

The purpose of this study was to determine whether severe iron deficiency alters the adaptive response of skeletal muscle fibers to a sustained increase in tonic contractile activity. Seven weanling rabbits consumed a low iron diet and underwent phlebotomy twice weekly for 6 mo, resulting in severe anemia (mean Hb 5.5 g/dl). Compared with control animals, tibialis anterior skeletal muscles of iron-deficient animals exhibited reduced concentrations of cytochrome c (4.4 +/- 0.7 vs. 8.6 +/- 0.7 nmol/g tissue; P less than 0.01), and reduced activities of citrate synthase (83 +/- 10 vs. 133 +/- 13 mU/mg protein; P less than 0.01) and cytochrome-c oxidase (2.2 +/- 0.2 vs. 3.6 +/- 0.5 U/mg protein; P less than 0.05). In these muscles mitochondria were swollen and displayed deformed cristae. Less severe biochemical abnormalities were observed in cardiac and soleus skeletal muscles. Ten days of continuous electrical stimulation of the motor nerve supplying anterior compartment muscles of iron-deficient rabbits increased expression of mitochondrial proteins: cytochrome c was increased to 154% of control levels (P less than 0.05), and cytochrome-c oxidase and citrate synthase activities were increased to 199 and 272% of control levels, respectively (P less than 0.005). In addition, electrical pacing increased the fractional volume of mitochondria observed by electron microscopy and reduced the activity of aldolase A by 28% (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of physical training on peripheral sweat production
Authors: Buono M. J. , Sjoholm N. T.
Published: December 2017

The purpose of this study was to determine the in vivo secretory activity of sweat glands from sedentary and trained subjects. Peripheral sweat production was determined using pilocarpine iontophoresis in 40 volunteers (10 sedentary men, 10 endurance-trained men, 10 sedentary women, 10 endurance-trained women). Peripheral sweat rate was significantly (P less than 0.05) greater in trained men [6.9 +/- 0.6 (SE) g.m2.min-1] and women (6.1 +/- 0.7) compared with sedentary men (3.1 +/- 0.5) and women (2.5 +/- 0.4). Furthermore, peripheral sweat rate was significantly correlated (r = 0.73) with maximal O2 uptake. The above two findings would suggest that physical training improves the secretory activity of the human sweat gland. Such a result supports previous findings that have suggested that the potentiation in sweating seen after training is achieved via a peripheral mechanism. In addition, several gender-related differences were found in the sudorific response of men and women. Specifically, women have a significantly greater sweat gland density, whereas men have a greater sweat production per gland.
Relationship between maximal expiratory flows and lung volumes in growing humans
Authors: Martin T. R. , Feldman H. A. , Fredberg J. J. , Castile R. G. , Mead J. , Wohl M. E.
Published: December 2017

We examined airway vs. lung parenchymal growth, as inferred from maximal expiratory flows (MEF) and lung volumes (V), respectively, to determine whether the interindividual variability of airway size (inferred from MEF) changes during lung growth and whether a young child with large (or small) airways for his parenchymal size (inferred from V) maintains relatively large (or small) airways for his lung size as he grows to adulthood. Serial measurements of MEF and V were obtained from a cohort of healthy 6- to 27-yr-old males (n = 26) and females (n = 21) over a period of 18 yr. Data were analyzed using logarithmic transformation of the power law equation, MEF = aVb, to fit a regression line to each subject's data points. These growth trajectories were satisfactorily modeled as parallel lines with 20-30% variability of their y-intercepts, indicating that substantial intersubject variability of MEF relative to V is present in early childhood and remains constant during growth. The results further indicate that MEF does track V during lung growth. We conclude that dysanapsis originates in early childhood.
Inspiratory pressure generation: comparison of subjects with COPD and age-matched normals
Authors: Levine S. , Gillen M. , Weiser P. , Feiss G. , Goldman M. , Henson D.
Published: December 2017

We continuously monitored esophageal (Pes) and gastric (Pga) pressures and used these measurements in a three-component model to estimate instantaneous diaphragmatic (DIA), inspiratory accessory muscle (IAM), and postexpiratory recoil (PER) pressures at various times during inspiration. We validated our model both by volume-pressure relationships of the respiratory system (Vrc-Pga and Vab-Pga, where Vrc and Vab are the rib cage and abdominal volumes, respectively) as well as electromyography of the respiratory muscles. Measurements were carried out at rest and during graded treadmill exercise in 11 subjects with chronic obstructive pulmonary disease (COPDs) and 8 age-matched normal subjects (AMNs). AMNs were 59 +/- 2 (SE) yr and had a forced expiratory volume at 1 s (FEV1.0) of 3.6 +/- 0.2 liters; COPDs were 66 +/- 2 yr and had a FEV1.0 of 1.0 +/- 0.1 liters. We noted the following. At rest, both AMNs and COPDs exhibited an increasing DIA pressure (PDIA) across inspiratory time (TI) at rest. As expired minute ventilation increased with exercise intensity, AMNs continued to maintain this PDIA ramp across inspiration; in contrast, COPDs exhibited higher values of PDIA during the first half of TI than during the second half. At all intensities of exercise, COPDs exhibited higher IAM and PER pressures than the AMNs.
Respiratory reflex responses to stimulation of tracheal mucosa in enflurane-anesthetized humans
Authors: Nishino T. , Hiraga K. , Mizuguchi T. , Honda Y.
Published: December 2017

We investigated respiratory reflex responses to tracheal mucosa stimulation induced by injection of distilled water in 13 female patients under three different depths of enflurane anesthesia (0.7, 1.0, and 1.3 minimum alveolar concentration). Detailed analysis of the types of reflex responses revealed that there are at least six different responses: 1) the apneic reflex, 2) the expiration reflex, 3) spasmodic, panting breathing, 4) the cough reflex, 5) slowing of breathing, and 6) rapid, shallow breathing. Among these reflex responses, the cough reflex was the most sensitive and the apneic reflex followed by slowing of breathing was the most resistant to deepening anesthesia, whereas the sensitivity of other types of reflex responses was in between. Our results indicate that the types of respiratory reflex responses to tracheal mucosa stimulation are associated with depths of anesthesia and that the differences in sensitivity to anesthesia may be a valuable sign in clinical assessment of depth of anesthesia.
Temperature profiles with respect to inhomogeneity and geometry of the human body
Authors: Werner J. , Buse M.
Published: December 2017

Temperature profiles within the human body are highly dependent on the geometry and inhomogeneity of the body. Physical parameters such as density and heat conductivity of the various tissues and variables such as blood flow and metabolic heat production of different organs are spatially distributed and thereby influence the temperature profiles within the human body. Actual physiological knowledge allows one to take into account up to 54 different spatially distributed values for each parameter. An adequate representation of the anatomy of the body requires a spatial three-dimensional grid of at least 0.5-1.0 cm. This is achieved by photogrammetric treatment of three-dimensional anatomic models of the human body. As a first essential result, the simulation system has produced a realistic picture of the topography of temperatures under neutral conditions. Compatibility of reality and simulation was achieved solely on the basis of physical considerations and physiological data base. Therefore the simulation is suited to the extrapolation of temperature profiles that cannot be obtained experimentally.
Changes in fiber composition of soleus muscle during rat hindlimb suspension
Authors: Templeton G. H. , Sweeney H. L. , Timson B. F. , Padalino M. , Dudenhoeffer G. A.
Published: December 2017

Chronic reduction of gravitational load in the rear limbs of rats to simulate the influence of near-zero gravity in skeletal muscles has been shown previously to elicit atrophy in the soleus muscle. Use of this model by the present investigation indicates that soleus atrophy was characterized by a decline in the number of fibers in groups that contained the slow isoenzyme of myosin and which were classified as type I from intensity of staining to myofibrillar actomyosin adenosinetriphosphatase (ATPase) and to NADH tetrazolium reductase. Furthermore total fiber number was not changed, whereas fibers containing the intermediate isoenzyme and those classified as type IIa increased. There results could be explained by either a change in the composition within existing fibers or a simultaneous loss of slow fibers and de novo synthesis of intermediate and fast fibers. Evidence for transformation included an absence of embryonic or neonatal myosin in muscles from suspended rats and the constant fiber number that was unchanged by 4 wk of suspension. Furthermore although fiber areas of both groups of type I and IIa fibers declined during suspension, variability of the fiber areas within each group did not increase.
Changes in compartmental ventilation in association with eye movements during REM sleep
Authors: Millman R. P. , Knight H. , Kline L. R. , Shore E. T. , Chung D. C. , Pack A. I.
Published: December 2017

The effect of phasic eye movement activity on ventilation during rapid-eye-movement (REM) sleep was studied in seven healthy young adults by use of the respiratory inductive plethysmograph. Mean ventilation (VE) and ventilatory components during REM sleep were not significantly different from that seen in either stages 1-2 or 3-4 sleep. The percent of rib cage contribution to ventilation in REM sleep, 29.3 +/- 5.1%, was reduced compared with 54.4 +/- 5.8% in stage 1-2 and 52.2 +/- 4.3% in stage 3-4 sleep (P less than 0.005). When one separated breaths by the degree of associated phasic eye movement activity, it became apparent that breathing during REM sleep is very heterogeneous. Increasing eye movement activity was associated with inhibition of ventilation with a reduction in VE from 5.1 +/- 0.3 to 3.8 +/- 0.3 l/min. Tidal volume and frequency both fell, whereas inspiratory duration was unchanged. Compartmental ventilation was also affected, with the fall in the rib cage contribution from 37.8 +/- 6.4 to 15.3 +/- 5.6%. Chest wall and abdominal movement became more asynchronous as phasic-eye-movement activity increased and frank paradoxical breathing was seen.
Periodic weight support effects on rat soleus fibers after hindlimb suspension
Authors: Hauschka E. O. , Roy R. R. , Edgerton V. R.
Published: December 2017

The morphological and histochemical properties of the rat soleus were studied after 1 wk of hindlimb suspension, one model that removes the weight-bearing function of the hindlimbs. To examine the effectiveness of weight support activity in maintaining soleus mass, fiber size, and succinate dehydrogenase (SDH) activity, the hindlimbs of adult male Sprague-Dawley rats were suspended (HS) and half of these rats were walked on a treadmill for 40 min/day (10 min every 6 h) at 5 m/min and a 19 degree grade (HS-WS). Significant reductions in soleus mass and fiber size were found after 1 wk of HS. Weight support activity decreased the atrophic response by approximately 50%. In the alkaline myofibrillar adenosine triphosphatase (ATPase) dark-staining fibers, SDH activity was higher in the HS than control rats, whereas it was similar to control in the HS-WS rats. Total SDH activity (SDH activity X cross-sectional area) in fibers staining lightly for ATPase in HS and HS-WS rats was lower than in control rats, whereas in the darkly stained ATPase fibers it was similar among the three groups. No changes were observed in fiber type percentages after 1 wk of HS or HS-WS. The results suggest that short-duration, daily weight support activity can ameliorate, but not prevent, soleus atrophy induced by HS. Furthermore, fiber cross-sectional area is more responsive to periodic weight support in dark than light ATPase fibers. These results also demonstrate that muscle fiber atrophy need not be associated with a loss in SDH activity.
Mechanism of reduced LV afterload by systolic and diastolic positive pleural pressure
Authors: Fessler H. E. , Brower R. G. , Wise R. A. , Permutt S.
Published: December 2017

To investigate the mechanism by which increased pleural pressure (Ppl) assists left ventricular (LV) ejection, we compared the effects of phasic systolic or diastolic increases in Ppl (40-60 mmHg) with use of an isolated canine heart-lung preparation with constant venous return. Positive Ppl during systole (S) caused left atrial transmural pressure (Platm = Pla - Ppl) to decrease by 1.25 +/- 0.46 (SE) mmHg (P less than 0.025). Central blood volume (CBV), the volume of blood in the heart, lungs, and thoracic great vessels, decreased by 29 +/- 4.0 (SE) ml (P less than 0.001). When Ppl was raised for an equal duration during diastole (D), the decrease in Platm was not significant, but there was a significant decrease in CBV (10.5 +/- 4.1 ml, P less than 0.05). With constant venous return, these changes suggested that phasic elevations in Ppl in either S or D assisted LV ejection by decreasing LV afterload. To test the hypothesis that positive Ppl during D reduced afterload by emptying the thoracic aorta, we compared the effects of diastolic positive Ppl with a rigid aorta vs. a compliant aorta. Although there was no statistical difference in the effects of diastolic positive Ppl on Platm, the decrease in CBV was significantly greater when the aorta was compliant than when it was rigid (23 +/- 2.2 vs. 17 +/- 2.7 ml, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of endotoxin on systemic and skeletal muscle O2 extraction
Authors: Samsel R. W. , Nelson D. P. , Sanders W. M. , Wood L. D. , Schumacker P. T.
Published: December 2017

Patients with the adult respiratory distress syndrome (ARDS) show a pathological dependence of O2 consumption (VO2) on O2 delivery (QO2, blood flow X arterial O2 content). In these patients, a defect in tissues' ability to extract O2 from blood can leave tissue O2 needs unmet, even at a normal QO2. Endotoxin administration produces a similar state in dogs, and we used this model to study mechanisms that may contribute to human pathology. We measured systemic and hindlimb VO2 and QO2 while reducing cardiac output by blood withdrawal. At the onset of supply dependence, the systemic QO2 was 11.4 +/- 2.7 ml.kg-1.min-1 in the endotoxin group vs. 8.0 +/- 0.7 in controls (P less than 0.05). At this point, the endotoxin-treated animals extracted only 61 +/- 11% of the arterial O2, whereas control animals extracted 70 +/- 7% (P less than 0.05). Systemic VO2 rose by 15% after endotoxin (P less than 0.05) but did not change in controls. Despite this poorer systemic ability to extract O2 by the endotoxin-treated dogs, isolated hindlimb O2 extraction at the onset of supply dependence was the same in endotoxin-treated and control dogs. At normal levels of QO2, hindlimb VO2 in endotoxin-treated dogs was 23% higher than in controls (P less than 0.05). Fractional blood flow to skeletal muscle did not differ between control and endotoxin-treated dogs. Thus skeletal muscle was not overperfused in endotoxemia and did not contribute to a systemic extraction defect by stealing blood flow from other tissues. Skeletal muscle in endotoxin-treated dogs demonstrated an increase in VO2 but no defect in O2 extraction, differing in both respects from the intestine.
A new experimental approach for the study of cardiopulmonary physiology during early development
Authors: Wolfson M. R. , Tran N. , Bhutani V. K. , Shaffer T. H.
Published: December 2017

In this report, an experimental approach and newly designed apparatus for liquid ventilation of preterm animals are described. Findings of age-related changes in cardiopulmonary function of this animal preparation are presented. Thirty-one lambs, 102-137 days gestation (term 147 +/- 3 days), were studied. The carotid artery, jugular vein, and trachea of the exteriorized fetus were cannulated under local anesthesia. Immediately after cesarean section delivery, ventilation commenced; warmed (39 degrees C) and oxygenated (PIO2 greater than 500 Torr) liquid fluorocarbon (RIMAR 101) was delivered to the lung by a mechanically assisted liquid ventilation system. Skeletal muscle paralysis, low-dose exogenous buffering, and thermal support were maintained during the 3-h experiment. Pulmonary gas exchange, acid-base status, and cardiopulmonary and metabolic function were assessed. By utilizing these techniques, effective arterial oxygenation, CO2 elimination, acid-base status, and cardiovascular stability were supported independent of gestational age. The results demonstrate a developmental increase in specific lung compliance and mean arterial pressure and decrease in heart rate and systemic O2 consumption per kilogram with advancing gestational age. These findings demonstrate that liquid ventilation negates the dependency of effective pulmonary gas exchange on surfactant development, thereby extending the limits of viability of the immature extrauterine lamb. As such this new experimental approach is useful for the study of physiological development over an age range previously limited to fetal animal preparations and, therefore, may provide insight regarding adaptation of the premature to the extrauterine environment.
Energy cost and fatigue during intermittent electrical stimulation of human skeletal muscle
Authors: Bergstrom M. , Hultman E.
Published: December 2017

Force generation and ATP utilization under anaerobic conditions were studied in the quadriceps femoris muscle of six volunteers. Electrical stimulation (20 Hz) was used to produce contractions with a duration of 0.8 s in one leg and contractions with a duration of 3.2 s in the other leg. The two procedures were designed to give the same total contraction time of 51 s and used the same number of stimulation pulses. Muscle biopsies were taken at rest and after 22 and 51 s of work and analyzed for ATP, phosphocreatine, and glucolytic intermediates. The results were compared with previous studies on continuous and intermittent stimulation. Fatigue developed significantly faster with contractions of short duration, and the energy cost was higher. Since force at the end of stimulation had a negative correlation to ATP utilization, there is no indication that the energy resources limit force generation. By comparison of stimulations producing the same amount of isometric work but with a different number of contractions, we estimate that the energy cost for activation and relaxation of a 1-s contraction is approximately 37% of the total ATP consumption.
Costal vs. crural diaphragmatic blood flow during submaximal and near-maximal exercise in ponies
Authors: Manohar M.
Published: December 2017

The present study was carried out 1) to compare blood flow in the costal and crural regions of the equine diaphragm during quiet breathing at rest and during graded exercise and 2) to determine the fraction of cardiac output needed to perfuse the diaphragm during near-maximal exercise. By the use of radionuclide-labeled 15-micron-diam microspheres injected into the left atrium, diaphragmatic and intercostal muscle blood flow was studied in 10 healthy ponies at rest and during three levels of exercise (moderate: 12 mph, heavy: 15 mph, and near-maximal: 19-20 mph) performed on a treadmill. At rest, in eucapnic ponies, costal (13 +/- 3 ml.min-1.100 g-1) and crural (13 +/- 2 ml.min-1.100 g-1) phrenic blood flows were similar, but the costal diaphragm received a much larger percentage of cardiac output (0.51 +/- 0.12% vs. 0.15 +/- 0.03% for crural diaphragm). Intercostal muscle perfusion at rest was significantly less than in either phrenic region. Graded exercise resulted in significant progressive increments in perfusion to these tissues. Although during exercise, crural diaphragmatic blood flow was not different from intercostal muscle blood flow, these values remained significantly less (P less than 0.01) than in the costal diaphragm. At moderate, heavy, and near-maximal exercise, costal diaphragmatic blood flow (123 +/- 12, 190 +/- 12, and 245 +/- 18 ml.min-1.100 g-1) was 143%, 162%, and 162%, respectively, of that for the crural diaphragm (86 +/- 10, 117 +/- 8, and 151 +/- 14 ml.min-1.100 g-1).(ABSTRACT TRUNCATED AT 250 WORDS)
Redistribution of blood flow after thermal injury and hemorrhagic shock
Authors: Carter E. A. , Tompkins R. G. , Yarmush M. L. , Walker W. A. , Burke J. F.
Published: December 2017

Diminished mucosal mass and a diminished rate of DNA synthesis by the intestinal mucosa have been identified in the rat after thermal injury. Because these changes may be associated with ischemia, the distribution of intestinal blood flow was studied after a thermal injury and compared with the blood flow distribution after hemorrhagic shock. For the thermal injury, anesthetized animals received a standardized 20% body surface area, full-thickness injury and were given intraperitoneal saline resuscitation. By the use of 46Sc- or 141Ce-labeled microspheres, no changes in intestinal and hepatic blood flow occurred after thermal injury. In contrast, a marked redistribution of blood flow was identified after hemorrhagic shock in which a decrease in arterial blood flow was identified to the stomach and to the small and large intestine. Although clinical shock was not present, the cardiac output decreased to a comparable degree in the hemorrhagic shock and the thermal injury. These studies indicate that although physiological changes in intestinal mucosa can be demonstrated after burn injury, these changes are not due to decreases in mesenteric arterial blood flow.
Blood pressure regulation during cardiac autonomic blockade: effect of fitness
Authors: Smith M. L. , Hudson D. L. , Graitzer H. M. , Raven P. B.
Published: December 2017

The purpose of this study was to determine the role of the autonomic nervous system's control of the heart in fitness-related differences in blood pressure regulation. The cardiovascular responses to progressive lower-body negative pressure (LBNP) were studied during unblocked (control) and full blockade (experimental) conditions in 10 endurance-trained (T) and 10 untrained (UT) men, aged 20-31 yr. The experimental conditions included beta 1-adrenergic blockade (metoprolol tartrate), parasympathetic blockade (atropine sulfate), or complete blockade (metoprolol and atropine). Heart rate, blood pressure, forearm blood flow, and cardiac output were measured at rest and -16 and -40 Torr LBNP. Forearm vascular resistance, peripheral vascular resistance, and stroke volume were calculated from these measurements at each stage of LBNP. Blood pressure was maintained, primarily by augmented vasoconstriction, equally in T and UT subjects during complete and atropine blockade. The fall in systolic and mean pressure from 0 to -40 Torr was greater (P less than 0.05) in the T subjects during the unblocked and metoprolol blockade conditions. This reduced blood pressure control during unblocked condition was attributable to attenuated vaso-constrictor and chronotropic responses in the T subjects. We hypothesize that an autonomic imbalance (elevated base-line parasympathetic activity) in highly trained subjects restricts reflex cardiac responses, which accompanied by an attenuated vasoconstrictor response, results in attenuated blood pressure control during a steady-state hypotensive stress.
Role of cardiopulmonary baroreflexes during dynamic exercise
Authors: Mack G. , Nose H. , Nadel E. R.
Published: December 2017

To examine the role of cardiopulmonary (CP) mechanoreceptors in the regulation of arterial blood pressure during dynamic exercise in humans, we measured mean arterial pressure (MAP), cardiac output (Q), and forearm blood flow (FBF) during mild cycle ergometer exercise (77 W) in 14 volunteers in the supine position with and without lower-body negative pressure (LBNP). During exercise, MAP averaged 103 +/- 2 mmHg and was not altered by LBNP (-10, -20, or -40 mmHg). Steady-state Q during exercise was reduced from 10.2 +/- 0.5 to 9.2 +/- 0.5 l/min (P less than 0.05) by application of -10 mmHg LBNP, whereas heart rate (97 +/- 3 beats/min) was unchanged. MAP was maintained during -10 mmHg LBNP by an increase in total systemic vascular resistance (TSVR) from 10.3 +/- 0.5 to 11.4 +/- 0.6 U and forearm vascular resistance (FVR) from 17.5 +/- 1.9 to 23.3 +/- 2.6 U. The absence of a reflex tachycardia or reduction in arterial pulse pressure during -10 mmHg LBNP supports the hypothesis that the increase in TSVR and FVR results primarily from the unloading of CP mechanoreceptors. Because CP mechanoreceptor unloading during exercise stimulates reflex circulatory adjustments that act to defend the elevated MAP, we conclude that the elevation in MAP during exercise is regulated and not merely the consequence of differential changes in Q and TSVR. In addition, a major portion of the reduction in FBF in our experimental conditions occurs in the cutaneous circulation. As such, these data support the hypothesis that CP baroreflex control of cutaneous vasomotor tone is preserved during mild dynamic exercise.
Airway blood flow distribution and lung edema after histamine infusion in awake sheep
Authors: Kramer G. C. , Lindsey D. C. , Wu C. H. , Mertens S. , Russell L. A. , Cross C. E.
Published: December 2017

The present study was designed to evaluate the distribution of bronchial blood flow to major airways and peripheral lung and to quantitate lung edema during a 2-h histamine infusion (2 micrograms.kg-1.min-1) in unanesthetized sheep. By the use of radioactive microspheres, the blood flow to trachea and to tracheal cartilage, smooth muscle, and mucosa/submucosa was determined along with measurements of blood flow to different sized airway segments and the systemic blood flow to lung parenchyma. Histamine greatly increased blood flow to medium-sized (5- to 10-mm-diam) central airways in which blood flow increased 5-10 times base line, whereas in small (1- to 5-mm-diam) central airways the increase was 10-15 times. Blood flow in tracheal mucosa/submucosa increased six times base line, but in tracheal smooth muscle the increase was only three times base line, and in cartilage it remained at base line. Most of the systemic blood flow to the lung perfuses less than 1-mm-diam peripheral airways, and these airways demonstrated less vasodilation during histamine infusion. Mean blood flow to whole-lung parenchyma (whole lung minus trachea) was only two times base line during histamine infusion. Water content of trachea and main stem bronchi was significantly increased after histamine. Histopathologic findings after histamine infusions included congestion and edema of airways with only minor effects noted in alveoli. We conclude that histamine is a potent and selective vasodilator of bronchial vessels and particularly affects blood flow to central airways and to airway mucosal/submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of ciliary beat frequency by autonomic mechanisms: in vitro
Authors: Wong L. B. , Miller I. F. , Yeates D. B.
Published: December 2017

The ciliated epithelium of the mammalian trachea separates the neurohumoral milieu of the tissue from that of the environment of the airway lumen. To determine whether specific autonomic receptors regulating ciliary beat frequency (CBF) were located on mucosal or serosal sides, we measured CBF by heterodyne mode correlation analysis laser light scattering in bovine tracheal tissues mounted in a two-sided chamber. A beta 2-adrenergic agonist, fenoterol, at 10(-7) M, stimulated serosal CBF from 7.9 +/- 1.3 to 20.2 +/- 5.8 Hz (P less than 0.01) and mucosal CBF from 6.6 +/- 0.9 to 14.7 +/- 4.6 Hz (P less than 0.01). A muscarinic cholinergic agonist, methacholine, at 10(-7) M, increased mucosal CBF from 8.4 +/- 1.0 to 19.5 +/- 5.5 Hz (P less than 0.01) and serosal CBF from 8.0 +/- 0.9 to 15.4 +/- 5.0 Hz (P less than 0.01). The differences in stimulation of CBF on the mucosal and serosal sides between fenoterol and methacholine were significant (P less than 0.01). Studies in which these autonomic agonist stimulating effects were inhibited by their respective antagonists, propranolol and atropine sulfate, demonstrated that CBF can be regulated independently by mediators both in the submucosa and within the mucus lining.
A micromethod for measuring carbonic anhydrase activity using 18O exchange between CO2 and H2O
Authors: Bitterman N. , Lin L. , Forster R. E.
Published: December 2017

We have developed a method of measuring the activity and characteristics of carbonic anhydrase (CA) using the disappearance of 18O from CO2 in 1 ml of gas contained in a glass chamber as it exchanges with H2O in 0.01 ml 0.25 M NaHCO3 solution in a thin (25 micron) porous membrane. Serial gas samples (approximately 0.02 ml) are analyzed in a mass spectrometer to obtain the rate of disappearance of the label. The enzyme activity can be measured inside intact cell or particle membranes. As little as 10(-15) mol of high-activity type CA can be detected at 25 degrees C, and the activity of 200 times this amount can be measured. The uncatalyzed hydration reaction velocity constant was 0.056 +/- 0.004 s-1, in agreement with published data.
Decreased cardiac response to isoproterenol infusion in acute and chronic hypoxia
Authors: Richalet J. P. , Larmignat P. , Rathat C. , Keromes A. , Baud P. , Lhoste F.
Published: December 2017

The hypothesis of a blunted chronotropic response of cardiac beta-adrenergic receptors in altitude hypoxia was tested in nine subjects at sea level (SL) by infusion of isoproterenol. Observations were made at SL, in acute hypoxia (2 days at 4,350 m, condition H1), in more prolonged hypoxia [13 days between 850 and 4,800 m, condition H2] and in chronic hypoxia [21 days at 4,800 m, condition H3]. Resting heart rate was higher in all hypoxic conditions. Resting norepinephrine concentrations were found to be significantly higher in conditions H2 (1.64 +/- 0.59) and H3 (1.74 +/- 0.76) than at SL (0.77 +/- 0.18 ng/ml). Isoproterenol, diluted in saline, was infused at increasing doses of 0.0, 0.02, 0.04, and 0.06 micrograms.kg-1.min-1. For the highest dose, there was a significantly smaller increase in heart rate in conditions H1 (35 +/- 9), H2 (33 +/- 11), and H3 (31 +/- 11) than at SL (45 +/- 8 min-1). The increase in pulse (systolic/diastolic) pressure, considered as the vascular response to isoproterenol infusion, was smaller in condition H3 (29 +/- 16) than at SL (51 +/- 24 mmHg). There was a significant increase in the dose of isoproterenol required to increase heart rate by 25 min-1 and decrease in slope of heart rate increase vs. log(dose) relationship in conditions H2 and H3. Thus an hypoxia-related attenuated response of beta-adrenergic receptors to exogenous stimulation was found in humans.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of oxidants, eicosanoids, and neutrophils in amphotericin B lung injury in rats
Authors: McDonnell T. J. , Chang S. W. , Westcott J. Y. , Voelkel N. F.
Published: December 2017

Administration of the antifungal antibiotic amphotericin B (AmB, 1 mg/kg) to intact rats produced acute lung injury as indicated by the extravascular leakage of protein and water and histological examination. The injury was neutrophil independent because it occurred in neutropenic rats. AmB produced vasoconstriction and injury in isolated lungs perfused with a cell- and plasma-free physiological solution, and this injury was independent of pulmonary perfusion pressure. In vivo administration of AmB produced an increase in lung tissue and plasma-oxidized glutathione disulfide (GSSG) indicative of oxidant stress. In the isolated lung, the radical scavengers p-hydroxybenzoate (methylparaben) and catalase attenuated AmB lung injury as did 1-phenyl-3-pyrazolidone (Phenidone), a combined radical scavenger and lipoxygenase/cyclooxygenase inhibitor, and the leukotriene antagonist CGP 35949B. Methylparaben and CGP 35949B prevented the elevation in lung tissue leukotriene C4 and B4 levels noted after AmB. We conclude that AmB in the rat produces neutrophil-independent lung injury, which is associated with oxidant stress and eicosanoid production.
Coupling between rib cage and abdominal compartments of the relaxed chest wall
Authors: Deschamps C. , Rodarte J. R. , Wilson T. A.
Published: December 2017

The volume displacements of the rib cage and abdomen of relaxed seated subjects were measured as functions of pleural pressure with the chest wall expanded by airway pressure and with the chest wall distorted by an external force applied to the rib cage. From the measured displacements for the two independent loads, the three compliances that describe the mechanical properties of the relaxed chest wall modeled as a linear elastic system with two degrees of freedom were obtained. The cross compliance that describes the coupling between the rib cage and abdomen was found to be small and positive, 0.01-0.02 1/cmH2O. The displacement of the rib cage by the external force was consistent with the displacement predicted by use of standard methods for calculating the mechanical advantage of the force.
Potential for strength and endurance training to amplify endurance performance
Authors: Hickson R. C. , Dvorak B. A. , Gorostiaga E. M. , Kurowski T. T. , Foster C.
Published: December 2017

The impact of adding heavy-resistance training to increase leg-muscle strength was studied in eight cycling- and running-trained subjects who were already at a steady-state level of performance. Strength training was performed 3 days/wk for 10 wk, whereas endurance training remained constant during this phase. After 10 wk, leg strength was increased by an average of 30%, but thigh girth and biopsied vastus lateralis muscle fiber areas (fast and slow twitch) and citrate synthase activities were unchanged. Maximal O2 uptake (VO2max) was also unchanged by heavy-resistance training during cycling (55 ml.kg-1.min-1) and treadmill running (60 ml.kg-1.min-1); however, short-term endurance (4-8 min) was increased by 11 and 13% (P less than 0.05) during cycling and running, respectively. Long-term cycling to exhaustion at 80% VO2max increased from 71 to 85 min (P less than 0.05) after the addition of strength training, whereas long-term running (10 km times) results were inconclusive. These data do not demonstrate any negative performance effects of adding heavy-resistance training to ongoing endurance-training regimens. They indicate that certain types of endurance performance, particularly those requiring fast-twitch fiber recruitment, can be improved by strength-training supplementation.
Model analyses of capillary growth and tissue oxygenation during hypoxia
Authors: Snyder G. K.
Published: December 2017

Theoretical analyses were used to determine whether capillary growth is an adaptive response to hypoxia. Parameter values were obtained from models of transverse sections of muscles in which individual fibers were distributed in square-ordered arrays and capillaries were added to the perimeters of individual fibers in the arrays. Increasing the number of capillaries up to 2.0 per fiber increased hypoxic tolerance by 157% above that expected for a Krogh cylinder. However, increasing the number of capillaries from 2.0 to 4.0 per fiber increased hypoxic tolerance by only 18% and, assuming the entire perimeter of each fiber was perfused with blood, increased hypoxic tolerance by only 11% over the value obtained when capillary-to-fiber ratio was 4.0. Capillary growth during normal maturation may result in capillary-to-fiber ratios around 2.0, near the upper limit for producing marked changes in hypoxic tolerance. Therefore, capillary growth may not be an adaptive response to ambient hypoxia because there is little or no gas transport benefit derived from the additional capillaries.
A multicouple probe for temperature gradient measurements in biological materials
Authors: Ducharme M. B. , Frim J.
Published: December 2017

An easy-to-make, sensitive, thin, flexible, multisensor probe for in vivo tissue temperature profile measurement is described. It is essentially a multijunction thermocouple (i.e., a multicouple) of type-T composition. Enamel-insulated copper wires (38 gauge) were soldered 5 mm apart to one common uninsulated constantan wire (36 gauge) and introduced into a polyethylene tube sealed at one end. The total outside diameter of the multicouple probe is less than 1 mm, and the maximum number of junctions using the specified wire sizes is approximately 16. This design permits the instantaneous measurement of a tissue temperature profile at 5-mm intervals over a distance of approximately 8 cm. An extensive calibration for the thermal conductivity effect (k effect) along the multicouple wires by means of a limb model is presented. The results show that the temperature readings of the individual junctions are significantly affected by the k effect when a thermal gradient exists along the multicouple, as is usually the case during tissue temperature measurements. However, calibration of the multicouple for the k effect yields a measurement accuracy of +/- 0.1 degree C under a wide range of gradients. This probe can be implanted in tissues to measure thermal gradients under different physiological conditions.
On the modeling and interpretation of oxygen uptake kinetics from ramp work rate tests
Authors: Swanson G. D. , Hughson R. L.
Published: December 2017

Ramp work rate tests have been used to estimate aerobic parameters in exercise stress testing. Previous studies have suggested an assumption of a linear dynamic system for O2 uptake kinetics. The implication is that model parameters estimated from ramp tests should be similar to those estimated from other dynamic tests. In nine healthy subjects, we found that model parameters used to characterize O2 consumption ramp data were not consistent with those used to characterize step data, when the comparison was made on a subject-to-subject basis. Furthermore the ramp data model parameter values were highly dependent (P less than 0.0001) on the ramp slope. A linear dynamic system interpretation of the ramp data model does not appear to be appropriate, suggesting that caution is needed in the interpretation of ramp data aerobic parameters. The data may be better described by nonlinear or higher order function. Ramp exercise testing is not suitable for assessing dynamic control properties of the cardiorespiratory response to exercise.
Operation Everest. II: Nutrition and body composition
Authors: Rose M. S. , Houston C. S. , Fulco C. S. , Coates G. , Sutton J. R. , Cymerman A.
Published: December 2017

Progressive body weight loss occurs during high mountain expeditions, but whether it is due to hypoxia, inadequate diet, malabsorption, or the multiple stresses of the harsh environment is unknown. To determine whether hypoxia due to decompression causes weight loss, six men, provided with a palatable ad libitum diet, were studied during progressive decompression to 240 Torr over 40 days in a hypobaric chamber where hypoxia was the major environmental variable. Caloric intake decreased 43.0% from 3,136 to 1,789 kcal/day (P less than 0.001). The percent carbohydrate in the diet decreased from 62.1 to 53.2% (P less than 0.001). Over the 40 days of the study the subjects lost 7.4 +/- 2.2 (SD) kg and 1.6% (2.5 kg) of the total body weight as fat. Computerized tomographic scans indicated that most of the weight loss was derived from fat-free weight. The data indicated that prolonged exposure to the increasing hypoxia was associated with a reduction in carbohydrate preference and body weight despite access to ample varieties and quantities of food. This study suggested that hypoxia can be sufficient cause for the weight loss and decreased food consumption reported by mountain expeditions at high altitude.