bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of central hypervolemia on cardiac performance during exercise
Authors: Sheldahl L. M. , Wann L. S. , Clifford P. S. , Tristani F. E. , Wolf L. G. , Kalbfleisch J. H.
Published: December 2017

To investigate the effect of different levels of central blood volume on cardiac performance during exercise, M-mode echocardiography was utilized to determine left ventricular size and performance during cycling exercise in the upright posture (UP), supine posture (SP), and head-out water immersion (WI). At submaximal work loads requiring a mean O2 consumption (Vo2) of 1.2 1/min and 1.5 1/min, mean left ventricular end-diastolic and end-systolic dimensions were significantly greater (P less than 0.05) with WI than UP. In the SP during exercise, left ventricular dimensions were intermediate between UP and WI. Heart rate did not differ significantly among the three conditions at rest and at submaximal exercise up to a mean Vo2 of 1.8 1/min. However, at a mean Vo2 of 2.4 1/min, heart rate in the UP was significantly greater than WI (P less than 0.01) and the SP (P less than 0.05). Maximal Vo2 did not differ statistically in the three conditions. These data indicate that a change in central blood volume results in alterations in left ventricular end-diastolic and end-systolic dimensions during moderate levels of exercise and a change in heart rate at heavy levels of exercise.
Predictability of skeletal muscle tension from architectural determinations in guinea pig hindlimbs
Authors: Powell P. L. , Roy R. R. , Kanim P. , Bello M. A. , Edgerton V. R.
Published: December 2017

The position of small metallic markers embedded within the lung parenchyma and glued to the pleural surface of four excised right caudal dog lobes were determined during stepwise deflation from an airway opening pressure of 25 cmH2O in air-filled suspended lobes and 8 cmH2O in saline-filled lobes submerged in saline. Changes in the volumes of tetrahedrons formed by four noncoplanar markers were taken as regional lung volume changes at the centroids of the tetrahedron. In both air- and saline-filled lobes at all volumes below total lobe capacity (TLC) there was considerable variability in regional volume. The variability occurred at the first step below TLC and increased with deflation. Regions behaved consistently; regions that were proportionally larger or smaller than the overall lobe at any step tended to be larger or smaller, respectively, at all steps. There was a significant correlation between the regional behavior of the air- and saline-filled lobes. The variability of regional volume did not follow any clear topographical orientation. These results indicate there is considerable variability of lung compliance within small regions. This heterogeneity of regional parenchymal properties may be the anatomical basis of the nonuniformity of regional ventilation known to occur in intact animals and excised lobes within small regions at the same vertical height.
Near-maximal voluntary hyperpnea and ventilatory muscle function
Authors: Bai T. R. , Rabinovitch B. J. , Pardy R. L.
Published: December 2017

Because of its potential relevance to heavy exercise we studied the ventilatory muscle function of five normal subjects before, during, and after shortterm near-maximal voluntary normocapnic hyperpnea. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made at four levels of ventilation: 76, 79, and 86% maximal voluntary ventilation (MVV) and at MVV. Measurements of pleural and abdominal pressures and diaphragm electromyogram (EMG) during hyperpnea and of maximum respiratory pressures before and after hyperpnea were made. The pressure-stimulation frequency relationship of the diaphragm obtained by unilateral transcutaneous phrenic nerve stimulation was studied in two subjects before and after hyperpnea. Decreases in maximal inspiratory (PImax) and transdiaphragmatic (Pdimax) strength were recorded posthyperpnea at 76 and 79% MVV. Decreases in the pressure-frequency curves of the diaphragm and the ratio of high-to-low frequency power of the diaphragm EMG occurred in association with decreases in Pdimax. Analysis of the pressure-time product (P X dt) for the inspiratory and expiratory muscles individually indicated the increasing contribution of expiratory muscle force to the attainment of higher levels of ventilation. Demonstrable ventilatory muscle fatigue may limit endurance at high levels of ventilation.
Effect of beta-adrenergic blockade on lactate turnover in exercising dogs
Authors: Issekutz B.
Published: December 2017

Dogs with indwelling catheters in the jugular vein and in the carotid artery ran on the treadmill (slope: 15%, speed: 133 m/min). Lactate turnover and glucose turnover were measured using [U-14C]lactate and [3-3H]glucose as tracers, according to the primed constant-rate infusion method. In addition, the participation of plasma glucose in lactate production (Ra-L) was measured with [U-14C]glucose. Propranolol was given either (A) before exercise (250 micrograms/kg, iv) or (B) in form of a primed infusion administered to the dog running at a steady rate. Measurements of plasma propranolol concentration showed that in type A experiments plasma propranolol fell in 45 min below the lower limit of the complete beta-blockade. In the first 15 min of work Ra-L rose rapidly; then it fell below that of the control (exercise) values. During steady exercise, the elevated Ra-L was decreased by propranolol infusion close to resting values. beta-Blockade doubled the response of glucose production, utilization, and metabolic clearance rate to exercise. In exercising dogs approximately 40-50% of Ra-L arises from plasma glucose. This value was increased by the blockade to 85-90%. It is concluded that glycogenolysis in the working muscle has a dual control: 1) an intracellular control operating at the beginning of exercise, and 2) a hormonal control involving epinephrine and the beta-adrenergic receptors.
Reduced training frequency effects on aerobic power and muscle adaptations in rats
Authors: Hickson R. C. , Overland S. M. , Dougherty K. A.
Published: December 2017

Female rats were exercised by swimming up to 4 h/day either 2, 4, or 6 days/wk. After 7 wk they continued to train at these frequencies or had their training reduced from 6 to 4, 2, or 0 days/wk for an additional 9 wk. Ventricular weights and maximum O2 uptake (VO2max) were increased by 5-10% after training 2 days/wk, 15-17% after 4 days/wk, and 25-30% after 6 days/wk. Following reduced training, VO2max was similar when the 4- or 2-day/wk reduced training groups are compared with their 4- or 2-day/wk continued training counterparts. In contrast, VO2max was greater in the 0-day reduced than in the sedentary control group. No differences in mitochondrial markers or myoglobin content in red or mixed skeletal muscles were found between training 2 or 4 days/wk vs. reduced training at comparable frequencies. O2 uptake capacity of plantaris muscles and myoglobin concentration in fast-twitch red vastus lateralis muscles were greater in the 0-day reduced group than in the sedentary controls. These data show that VO2max and certain markers of aerobic metabolism in skeletal muscles of rats are lost at a slower rate than their rate of increase from the untrained state. However, a reduction of swimming frequency from 6 to 4 or 2 days/wk is not a sufficient stimulus to maintain VO2max, cardiac enlargement, or the increased aerobic potential of skeletal muscle at the 6-day/wk levels.(ABSTRACT TRUNCATED AT 250 WORDS)
Relationship of transdiaphragmatic pressure and latencies for detecting added inspiratory loads
Authors: Zechman F. W. , Muza S. R. , Davenport P. W. , Wiley R. L. , Shelton R.
Published: December 2017

The purpose of this investigation was to measure changes in transdiaphragmatic pressure (Pdi) developed during graded elastic (E) and resistive (R) loaded breaths and to correlate the emergence of such changes with the load-dependent alterations in latency for detection (Tdet). Five healthy adults were studied using three protocols, i.e., graded E, graded R, and graded R in the presence of elevated background R. In each protocol, loads were added for single inspirations, 10 times in random order and separated by three to five unloaded breaths. Subjects pressed a signal marker as soon as loads were detected. Inspiratory flow (VI), inspired volume (VI), mouth pressure, and Pdi of loaded breaths and the preceding unloaded breaths were recorded and computer averaged. Patterns of VI and VI were not altered prior to detection of the smallest added E and R loads but decreased with the higher loads. Group mean patterns of Pdi showed graded increases during loaded breaths. Augmentation of Pdi preceded Tdet and occurred earlier as Tdet decreased with graded E and R loads. Elevating the background R delayed both Tdet of added R and the augmentation of Pdi. Results are consistent with the hypothesis that load-induced changes in diaphragmatic tension may play a sensory role in detection of inspiratory loads.
Acute effects of cigarette smoke inhalation on peripheral airways in dogs
Authors: Nakamura M. , Haga T. , Sasaki H. , Takishima T.
Published: December 2017

We studied the acute effects of the inhalation of cigarette smoke on the central and peripheral airways of 35 open-chested and tracheotomized dogs by the direct measurement of central (Rc) and peripheral (Rp) airway resistances. Rc was calculated by dividing the pressure difference between a tracheal catheter and a retrograde catheter by mouth flow, and Rp was obtained by dividing the pressure difference between the retrograde catheter and a pleural capsule by mouth flow. The pleural capsule was attached to the pleural surface for alveolar pressure measurement. Rc and Rp were measured by the 2-Hz forced oscillation method. With lung inhalation of the smoke of two-thirds of one cigarette in vagi intact dogs, Rp increased to 239% of the control value and Rc increased to 112%. After bilateral vagotomy, Rp increased to 143% and Rc increased to 104%. Propranolol did not influence the results. Hexamethonium and atropine both blocked these responses when vagi were intact. When the upper trachea, larynx, and nasopharynx, which were completely blocked by vagotomy, were exposed to the smoke of two-thirds of a cigarette, Rp increased to 155% and Rc increased to 144%. We thus conclude that cigarette smoke causes a major increase in Rp, mainly via the vagal reflex and partially via the stimulation of parasympathetic ganglia (probably nicotine), and a minor increase in Rc via vagal reflex.
Partitioning of respiratory mechanics in halothane-anesthetized humans
Authors: Behrakis P. K. , Higgs B. D. , Bevan D. R. , Milic-Emili J.
Published: December 2017

In five spontaneously breathing anesthetized subjects [halothane approximately 1 minimal alveolar concentration (MAC), 70% N2O, 30% O2], flow, changes in lung volume, and esophageal and airway opening pressure were measured in order to partition the elastance (Ers) and flow resistance (Rrs) of the total respiratory system into the lung and chest wall components. Ers averaged (+/- SD) 23.0 +/- 4.9 cmH2O X l-1, while the corresponding values of pulmonary (EL) and chest wall (EW) elastance were 14.3 +/- 3.2 and 8.7 +/- 3.0 cmH2O X l-1, respectively. Intrinsic Rrs (upper airways excluded) averaged 2.3 +/- 0.2 cmH2O X l-1 X s, the corresponding values for pulmonary (RL) and chest wall (RW) flow resistance amounting to 0.8 +/- 0.4 and 1.5 +/- 0.5 cmH2O X l-1 X s, respectively. Ers increased relative to normal values in awake state, mainly reflecting increased EL. Rw was higher than previous estimates on awake seated subjects (approximately 1.0 cmH2O X l-1 X s). RL was relatively low, reflecting the fact that the subjects had received atropine (0.3–0.6 mg) and were breathing N2O. This is the first study in which both respiratory elastic and flow-resistive properties have been partitioned into lung and chest wall components in anesthetized humans.
Muscle and femoral vein temperatures during short-term maximal exercise in heart failure
Authors: Shellock F. G. , Swan H. J. , Rubin S. A.
Published: December 2017

Core temperature decreases throughout short-term maximal exercise in heart-failure patients. To investigate possible causes for this unusual response to exercise, we studied core (pulmonary arterial blood), femoral vein, muscle, and skin temperatures in eight patients with severe heart failure who performed maximal upright incremental bicycle exercise to 50 W. A normal group (n = 4) was exercised for comparison. In the heart-failure patients, core temperature was 36.95 +/- 0.37 degrees C at rest, significantly (P less than 0.05) decreased at 25 W of exercise to 36.59 +/- 0.40 degrees C, and at 50 W remained decreased to 36.57 +/- 0.40 degrees C. In comparison, we found that the resting core temperature in the normal subjects was 37.28 +/- 0.34 degrees C, was the same at 25 W (37.29 +/- 0.41 degrees C), and increased significantly (P less than 0.05) to 37.50 +/- 0.32 degrees C at 50 W of exercise. Femoral vein temperature in heart-failure patients (n = 6) was below core temperature throughout exercise to 25 and 50 W (36.22 +/- 0.62 and 36.34 +/- 0.65 degrees C, respectively). Muscle temperature (n = 7) was significantly (P less than 0.05) lower in the heart-failure patients (34.8 +/- 1.1 degrees C) at rest compared with the normal subjects (36.2 +/- 1.0 degrees C). During exercise, muscle temperature increased above core temperature in only four of the heart-failure patients and was significantly (P less than 0.05) lower (36.5 +/- 1.3 degrees C) compared with the normal subjects (38.0 +/- 0.2 degrees C).
Effects of exercise training on coronary transport capacity
Authors: Laughlin M. H.
Published: December 2017

Coronary transport capacity was estimated in eight sedentary control and eight exercise-trained anesthetized dogs by determining the differences between base line and the highest coronary blood flow and permeability-surface area product (PS) obtained during maximal adenosine vasodilation with coronary perfusion pressure constant. The anterior descending branch of the left coronary artery was cannulated and pump-perfused under constant-pressure conditions (approximately equal to 100 Torr) while aortic, central venous, and coronary perfusion pressures, heart rate, electrocardiogram, and coronary flow were monitored. Myocardial extraction and PS of 51Cr-labeled ethylenediaminetetraacetic acid were determined with the single-injection indicator-diffusion method. The efficacy of the 16 +/- 1 wk exercise training program was shown by significant increases in the succinate dehydrogenase activities of the gastrocnemius, gluteus medialis, and long head of triceps brachii muscles. There were no differences between control and trained dogs for either resting coronary blood flow or PS. During maximal vasodilation with adenosine, the trained dogs had significantly lower perfusion pressures with constant flow and, with constant-pressure vasodilation, greater coronary blood flow and PS. It is concluded that exercise training in dogs induces an increased coronary transport capacity that includes increases in coronary blood flow capacity (26% of control) and capillary diffusion capacity (82% of control).
Histamine dose-response curves in guinea pigs
Authors: Hulbert W. C. , McLean T. , Wiggs B. , Pare P. D. , Hogg J. C.
Published: December 2017

Histamine dose-response curves were performed on anesthetized tracheostomized guinea pigs that were paralyzed and mechanically ventilated at a constant tidal volume and breathing frequency. The dose was calculated by generating an aerosol of known concentration and measuring the volume delivered to the lung. Increasing the dose was accomplished by increasing the number of breaths of aerosol delivered. The response to each dose was determined by measuring the change in airway resistance (RL) and dynamic compliance (Cdyn) using the method of Von Neergaard and Wirz (Z. Klin. Med. 105: 51–82, 1927). With increasing doses of histamine, RL increased and reached a plateau at approximately five times the base-line value and Cdyn fell to approximately 20% of its initial value. The variability in the base-line and maximum response as well as the calculated sensitivity and reactivity was less than that previously reported. Propranolol pretreatment increased resting RL and shifted the dose-response curve for RL to the left of the controls, increasing reactivity but not sensitivity. Atropine shifted the dose-response curve to the right of the control, decreasing sensitivity but without changing reactivity. The data for Cdyn showed that atropine pretreatment caused a higher resting value and propranolol pretreatment a lower value at the highest histamine dose but no differences in either sensitivity or reactivity.
Carbon monoxide-cytochrome interactions in the brain of the fluorocarbon-perfused rat
Authors: Piantadosi C. A. , Sylvia A. L. , Saltzman H. A. , Jobsis-Vandervliet F. F.
Published: December 2017

Reflectance spectrophotometry through the skull was used to investigate carbon monoxide (CO) binding by tissue hemoproteins in the brains of barbiturate-anesthetized Sprague-Dawley rats. After splenectomy and extensive perfluorotributylamine exchange transfusion, steady-state spectral scans were obtained in Soret and visible wave-length regions during O2 ventilation, during subsequent exposure to O2-enriched gases containing 1, 3, or 5% CO, and finally after N2 anoxia. These CO exposures were well-tolerated and electroencephalograph (EEG) activity continued to be present. Initial difference spectra were influenced by CO binding to residual hemoglobin, but spectral evidence of CO-mediated b-type cytochrome reduction was obtained in the visible region as CO concentration was increased to 3 or 5%. This was associated with Soret spectra compatible with formation of the reduced cytochrome a3-CO complex. Reduction of cytochrome a at 605 nm and cytochrome c + c1 at 550 nm was absent. These findings may indicate respiratory chain branching through b cytochromes, either to a separate a3-like oxidase independent of the classical cytochrome aa3 or to an unidentified alternative CO-sensitive oxidase.
Effects of nifedipine on responses to exercise in normal subjects
Authors: Raffestin B. , Denjean A. , Legrand A. , Derrieux C. , Boillot J. , Comoy E. , Martre H. , Lockhart A.
Published: December 2017

The responses to sublingual nifedipine (20 mg) and placebo were compared in normal subjects during two studies on cycle ergometer [progressive exercise and constant work-load exercise at approximately 60% of maximal O2 consumption (VO2max)]. The use of nifedipine did not modify maximal power, ventilation (VE), VO2, and heart rate (HR) at the end of the multistage progressive exercise (30-W increments every 3 min). Over the 45 min of the constant-load exercise and the ensuing 30-min recovery we observed with nifedipine compared with placebo 1) no differences in VO2, VE, respiratory exchange ratio, and systolic arterial blood pressure; 2) a higher HR (P less than 0.001) and lower diastolic arterial blood pressure (P less than 0.01); 3) a greater and more prolonged rise in norepinephrine (P less than 0.01) and growth hormone (P less than 0.001); 4) no significant differences in epinephrine and insulin and a lesser increase in glucagon during recovery (P less than 0.01); and 5) a lesser fall in blood glucose (P less than 0.01) and greater increase in acetoacetate (P less than 0.001), beta-hydroxybutyrate (P less than 0.05), and blood lactate (P less than 0.001). Our data do not support the hypothesis that nifedipine reduces hormonal secretions in vivo and are best explained by an enhanced secretion of catecholamines compensating for the primary vasodilator effect of nifedipine.
Hypoxia and angiotensin II infusion redistribute lung blood flow in lambs
Authors: Hansen T. N. , Le Blanc A. L. , Gest A. L.
Published: December 2017

To assess the effects of alveolar hypoxia and angiotensin II infusion on distribution of blood flow to the lung we performed perfusion lung scans on anesthetized mechanically ventilated lambs. Scans were obtained by injecting 1–2 mCi of technetium-labeled albumin macroaggregates as the lambs were ventilated with air, with 10–14% O2 in N2, or with air while receiving angiotensin II intravenously. We found that both alveolar hypoxia and infusion of angiotensin II increased pulmonary vascular resistance and redistributed blood flow from the mid and lower lung regions towards the upper posterior region of the lung. We assessed the effects of angiotensin II infusion on filtration pressure in six lambs by measuring the rate of lung lymph flow and the protein concentration of samples of lung lymph. We found that angiotensin II infusion increased pulmonary arterial pressure 50%, lung lymph flow 90%, and decreased the concentration of protein in lymph relative to plasma. These results are identical to those seen when filtration pressure increases during alveolar hypoxia. We conclude that alveolar hypoxia and angiotensin II infusion both increase fluid filtration in the lung by increasing filtration pressure. The increase in filtration pressure may be the result of a redistribution of blood flow in the lung with relative overperfusion of vessels in some areas and transmission of the elevated pulmonary arterial pressure to fluid-exchanging sites in those vessels.
Assessment of fluid balance in isolated sheep lungs
Authors: Patterson G. A. , Mitzner W. A. , Sylvester J. T.
Published: December 2017

In this study we demonstrate the validity and utility of an isolated lung preparation developed for the study of pulmonary fluid balance. Lungs of 2- to 3-mo-old sheep were perfused in situ with autologous blood treated with indomethacin (20 micrograms/ml). Lung lymph flow (QL), uncontaminated by systemic lymph, was measured from either the efferent duct of the caudomediastinal lymph node or the thoracic duct in the superior mediastinum. Lung weight change (delta W) was measured as the opposite of the change in weight of the extracorporeal blood reservoir. A unique feature of this experimental model is the ability to assess lung fluid balance from simultaneous measurements of delta W and QL. In addition, hemodynamic and blood gas variables can be tightly controlled. Our results show that changes in QL and the lymph-to-plasma oncotic pressure ratio caused by an increase in microvascular pressure were comparable with those seen previously in intact sheep. When microvascular pressure was returned to control levels, QL fell despite a sustained increase in the amount of extravascular lung water, suggesting compartmentalization of the filtrate and/or effects of intravascular volume on lymph-driving pressure or resistance. Lymph flow was directly proportional to respiratory frequency over the range of 0–30 min-1 when the change in frequency was maintained for periods as long as 30 min. This preparation should prove useful in the study of lung fluid balance, particularly when it is desired to use interventions which are precluded or difficult in intact animals.
Pulmonary C-fibers reflexly increase secretion by tracheal submucosal glands in dogs
Authors: Schultz H. D. , Roberts A. M. , Bratcher C. , Coleridge H. M. , Coleridge J. C. , Davis B.
Published: December 2017

Stimulation of bronchial C-fibers evokes a reflex increase in secretion by tracheal submucosal glands, but the influence of pulmonary C-fibers on tracheal gland secretion is uncertain. In anesthetized dogs with open chests, we sprayed powdered tantalum on the exposed mucosa of a segment of the upper trachea to measure the rate of secretion by submucosal glands. Secretions from the gland ducts caused elevations (hillocks) in the tantalum layer. We counted hillocks at 10-s intervals for 60 s before and 60 s after we injected capsaicin (10–20 micrograms/kg) into the right atrium to stimulate pulmonary C-fiber endings. Right atrial injection of capsaicin increased the rate of hillock formation fourfold, but left atrial injection had no significant effect. The response was abolished by cutting the vagus nerves or cooling them to 0 degree C. We conclude that the reflex increase in tracheal submucosal gland secretion evoked by right atrial injection of capsaicin was initiated as capsaicin passed through the pulmonary vascular bed, and hence that pulmonary C-fibers, like bronchial C-fibers, reflexly increase airway secretion.
Metabolic and vasomotor insulative responses occurring on immersion in cold water
Authors: Strong L. H. , Gee G. K. , Goldman R. F.
Published: December 2017

Twenty male volunteers (17–28 yr of age) exhibiting a range of body weights (60 kg less than or equal to Wt less than or equal to 95 kg) and body fat (7% less than or equal to BF less than or equal to 23%) underwent total immersion while at rest in water between 36 and 20 degrees C. The metabolic heat production measured as a function of time and water temperature was converted to explicit linear functions of core (Tre) and mean skin (Tsk) temperature for each individual immersion. The metabolic functions defined planes of thermogenic activity that showed a fourfold steeper slope with respect to changes in Tsk for small lean subjects than for large fatter subjects. Small lean males also exhibited steeper slopes with respect to changes in Tre than heavier phenotypes. The time course of Tsk and Tre was simulated for each individual immersion with the aid of a time-dependent system of differential heat balance equations coupling different body compartments to the water bath. This formulation permitted the evaluation of internal and external conductances as a function of water temperature. Maximal internal insulation, indicating full vasoconstriction, was achieved at higher bath temperatures in small lean subjects than large fatter subjects. A decline in insulation is seen above a critical metabolic level (approximately 150 W) in small to average size subjects.
Histamine-induced pulmonary edema distal to pulmonary arterial occlusion
Authors: Walkenstein M. D. , Peterson B. T. , Gerber J. E. , Hyde R. W.
Published: December 2017

Histological studies provide evidence that the bronchial veins are a site of leakage in histamine-induced pulmonary edema, but the physiological importance of this finding is not known. To determine if a lung perfused by only the bronchial arteries could develop pulmonary edema, we infused histamine for 2 h in anesthetized sheep with no pulmonary arterial blood flow to the right lung. In control sheep the postmortem extravascular lung water volume (EVLW) in both the right (occluded) and left (perfused) lung was 3.7 +/- 0.4 ml X g dry lung wt-1. Following histamine infusion, EVLW increased to 4.4 +/- 0.7 ml X g dry lung wt-1 in the right (occluded) lung (P less than 0.01) and to 5.3 +/- 1.0 ml X g dry wt-1 in the left (perfused) lung (P less than 0.01). Biopsies from the right (occluded) lungs scored for the presence of edema showed a significantly higher score in the lungs that received histamine (P less than 0.02). Some leakage from the pulmonary circulation of the right lung, perfused via anastomoses from the bronchial circulation, cannot be excluded but should be modest considering the low pressures in the pulmonary circulation following occlusion of the right pulmonary artery. These data show that perfusion via the pulmonary arteries is not a requirement for the production of histamine-induced pulmonary edema.
Respiratory muscle and organ blood flow with inspiratory elastic loading and shock
Authors: Magder S. , Lockhat D. , Luo B. J. , Roussos C.
Published: December 2017

Since respiratory muscles fail when blood flow is inadequate, we asked whether their blood flow would be maintained in severe hypotensive states at the expense of other vital organs (brain, heart, kidney, gut, spleen). We measured blood flow (radiolabeled microspheres) to respiratory muscles and vital organs in 11 dogs breathing against an inspiratory elastic load, first with normal blood pressure (BP) and then hypotension produced by cardiac tamponade. With the elastic load alone, there was no change in BP or cardiac output; diaphragmatic blood flow (Qdi) increased from 12.8 +/- 7.0 to 34.1 +/- 15.6 ml/100 g, and total respiratory muscle flow (QTR) increased from 56.5 +/- 19.1 to 97.4 +/- 36.5 ml/100 g, but except for the brain, there was no change in blood flow to other organs. With tamponade (mean BP = 79 +/- 16 mmHg), flow decreased to all organs, whereas Qdi (39.0 +/- 19.4) did not change. QTR decreased, but not significantly, to 88.6 +/- 49.5. With more tamponade (mean BP = 53 +/- 13 mmHg), flow to all vital organs decreased as well as QTR (57.9 +/- 47.18), but Qdi did not significantly decrease and had the same relationship to respiratory force as with normal BP. Thus, with severe inspiratory elastic loading and severe hypotension, the diaphragm and external intercostal muscles did most of the respiratory work, and their flow was maintained at the expense of other vital organs.
Autonomic response characteristics of porcine airway smooth muscle in vivo
Authors: Leff A. R. , Munoz N. M. , Tallet J. , David A. C. , Cavigelli M. A. , Garrity E. R.
Published: December 2017

We studied the autonomic response characteristics of airways in 65 swine in vivo. Tracheal smooth muscle response was measured isometrically in situ; bronchial response was measured simultaneously as change in airway resistance and dynamic compliance. To determine the optimal resting length at which maximal tracheal contraction was obtained, length-tension studies were generated in four animals using maximal electrical stimulation of the vagus nerves determined from stimulus-response characteristics in eight other swine. Pharmacological studies were performed in 25 animals to determine the relative potency and intrinsic activity of agonists (acetylcholine greater than histamine much greater than norepinephrine) causing contraction of trachea and bronchial airways. In 13 swine, the effects of autonomic stimulation were studied by intravenous administration of dimethylphenylpiperazinium (DMPP) after muscarinic blockade with 1.5 mg/kg iv atropine. Tracheal contraction caused by topical application of 3.4 X 10(-4) mol histamine (13.4 +/- 1.54 g/cm) was 96 +/- 7.2% blocked by 25 micrograms/kg iv DMPP in adrenal-intact animals; minimal relaxation was demonstrated in adrenalectomized animals, indicating absence of substantial sympathetic innervation to porcine trachea. Nonadrenergic innervation was not demonstrated. After beta-adrenergic blockade, sympathetic stimulation caused alpha-adrenergic contraction in bronchial airways but not in trachea. These data define the unique response characteristics of the airways of swine and demonstrate their utility for acute experimental study of airway responses in vivo.
Cardiac output distribution and regional blood flow during hypocarbia in monkeys
Authors: Gelman S. , Fowler K. C. , Bishop S. P. , Smith L. R.
Published: December 2017

Cardiac output distribution and regional blood flow were studied during hypocarbia independent of changes in ventilatory parameters. Fifteen cynomolgus monkeys were anesthetized with methohexital sodium (8 mg/kg im) and hyperventilated through an endotracheal tube. Hypocarbia at two levels, 28 +/- 1.8 and 17 +/- 0.6 Torr, was achieved by a stepwise decreasing CO2 flow into the semiclosed system. Regional blood flow was determined with labeled microspheres. At each stage of experiments two sets of microspheres (9 and 15 microns diam) were used simultaneously. The use of two microsphere sizes allowed evaluation of the relationship between total (nutritive and nonnutritive) tissue blood flow, determined with 15-microns spheres, and nutritive blood flow, determined with 9-microns spheres. There was no change in cardiac output or arterial pressure during both degrees of studied hypocarbia. Hypocarbia was accompanied by a decrease in myocardial blood flow determined with 15-microns spheres and preservation of the flow determined with 9-microns spheres. Splenic blood flow was decreased, whereas hepatic arterial blood flow was increased during both levels of hypocarbia. Blood flow through the brain, renal cortex, and gut showed a biphasic response to hypocarbia: during hypocarbia at 28 +/- 1.8 Torr, blood flow determined with 15-microns spheres was unchanged (in the gut) or decreased (in the brain and kidneys), whereas blood flow determined with 9-microns spheres was decreased. During hypocarbia at 17 +/- 0.6 Torr, blood flow determined with 9-microns spheres had a tendency to restore to base-line values.
Lung protein leaks in ventilated lambs: effects of gestational age
Authors: Jobe A. , Jacobs H. , Ikegami M. , Berry D.
Published: December 2017

To study the protein permeability properties of the ventilated premature lung, we delivered groups of eight lambs at 122 and 135 days gestational age and ventilated the lambs equivalently. The lambs at 122 days gestational age had been treated with natural sheep surfactant at birth, and both groups of lambs had similar pH and blood gas values to 3 h of age. Three groups of lambs at 146 days gestational age also were studied for comparison; four lambs were ventilated to normalized PCO2 values, four lambs were ventilated equivalently to the premature lambs with supplemental CO2 used to normalize PCO2 values, and four lambs were treated with natural surfactant and ventilated similarly to the preterm lambs. The percent recovery into an alveolar wash and lung tissue of 131I-albumin given by intravascular injection and of 125I-albumin given into the airways was measured in each animal after killing at 3 h of age. Full-term lambs had a small bidirectional leak of albumin to and from the alveoli and lung tissue. The recovery of intravascular 131I-albumin in the alveolar wash was 5.8- and 4.1-fold higher in lambs at 122 and 135 days gestational age, respectively, than in full-term lambs. The loss of 125I-albumin from the airways and alveoli also increased as gestational age decreased. The bidirectional flux of albumin to and from the alveoli increased as gestational age decreased in the prematurely delivered and ventilated lambs.
Pressure-time product, flow, and oxygen cost of resistive breathing in humans
Authors: Collett P. W. , Perry C. , Engel L. A.
Published: December 2017

We examined the relationship between the pressure-time product (Pdt) of the inspiratory muscles and the O2 cost of breathing (VO2 resp) in five normal subjects breathing through an external inspiratory resistance with a tidal volume of 800 ml at a constant end-expiratory lung volume [functional residual capacity, (FRC)]. Each subject performed 30–40 runs, each of approximately 30 breaths, with inspiratory flow rates ranging from 0.26 +/- 0.01 to 0.89 +/- 0.04 l/s (means +/- SE) and inspiratory mouth pressures ranging from 10 +/- 1 to 68 +/- 4% of the maximum inspiratory pressure at FRC. In all subjects VO2 resp was linearly related to Pdt when mean inspiratory flow (VI) was constant, but the slope of this relationship increased with increasing VI. Therefore, Pdt is an accurate index of VO2 resp only when VI is constant. There was a linear relationship between the VO2 resp and the work rate across the external resistance (W) for all runs in each subject over the range of W 10 +/- 1 to 137 +/- 21 J/min. Thus, at a constant tidal volume the VO2 resp was related to the mean inspiratory pressure, independent of flow or inspiratory duration. If the VO2 resp were determined mainly during inspiration, then for a given rate of external work or O2 consumption, VI would be inversely related to mean inspiratory pressure. Efficiency (E) was 2.1 +/- 0.2% and constant over a large range of VI, pressure, work rate, or resistance and was not altered by the presence of a potentially fatiguing load. The constant E over such a wide range of conditions implies a complex integration of the recruitment, mechanical function, and energy consumption of the muscles utilized in breathing.
Myoelectric signal conduction velocity and spectral parameters: influence of force and time
Authors: Broman H. , Bilotto G. , De Luca C. J.
Published: December 2017

Reports on measurement of muscle fiber conduction velocity in humans are scarce. Inferences on the behavior of conduction velocity have been drawn from the behavior of myoelectric spectral parameters. The present report contains information on conduction velocity and spectral parameters studied at various muscle contraction levels and during and after sustained contractions. The following results have been obtained from measurements on the tibialis anterior muscle. Conduction velocity demonstrated a positive correlation with limb circumference and with muscle force output. Thus we conclude that the diameters of the muscle fibers of high-threshold motor units are, on an average, larger than those of low-threshold motor units. The study of a sustained contraction and on the recovery after such a contraction revealed that conduction velocity consistently decreased during a strong contraction as did various myoelectric spectral parameters. However, the spectral parameters decreased approximately twice as much as did the conduction velocity, and we conclude that factors other than the conduction velocity along the muscle fibers affect the myoelectric signal during a high-level contraction. These other factors appertain to changes in the firing statistics of individual motor units as well as the correlation between the firings of different motor units.
Mild exercise impedes glycogen repletion in muscle
Authors: Bonen A. , Ness G. W. , Belcastro A. N. , Kirby R. L.
Published: December 2017

Bicycle ergometric exercise was used to deplete glycogen by either 80 or 35% in the vastus lateralis of both legs. Thereafter, subjects from each group rested or maintained single-leg exercise [20% of maximal O2 consumption (Vo2max) for 4 h. All subjects ingested glucose (1.5 g/kg wt; 20% solution) at min 10–12 and min 130–132 of the 4-h period. With bed rest, significant glycogen increases occurred after exhaustive (+36%; P less than 0.05) and nonexhaustive exercise (+13%; P less than 0.05). With single-leg exercise, 1) a diminished glycogen repletion occurred in exercising (+11%; P less than 0.05) and nonexercising (+15%; P less than 0.05) muscle after exhaustive exercise, or 2) further glycogen loss occurred in exercising (-26%; P less than 0.05) and nonexercising muscle (-19%; P less than 0.05) after nonexhaustive exercise. Within both groups, glycogen concentrations did not differ between exercising and nonexercising muscles (P greater than 0.05). Single-leg exercise, not preceded by exercise, provoked differences in glycogen loss in exercising (-47%) and nonexercising (-24%) muscle (P less than 0.05). These experiments demonstrate that mild exercise 1) impedes glycogen resynthesis or 2) provokes glycogen loss in both exercising and nonexercising muscle. These findings cannot be ascribed to circulating glucose and insulin concentrations in these studies.
Arterial-alveolar CO2 equilibration in exercising dogs during prolonged rebreathing
Authors: Loeppky J. A. , Scotto P. , Rieke H. , Meyer M. , Piiper J.
Published: December 2017

Arterial-alveolar equilibration of CO2 during exercise was studied by normoxic CO2 rebreathing in six dogs prepared with a chronic tracheostomy and exteriorized carotid loop and trained to run on a treadmill. In 153 simultaneous measurements of PCO2 in arterial blood (PaCO2) and end-tidal gas (PE'CO2) obtained in 46 rebreathing periods at three levels of mild-to-moderate steady-state exercise, the mean PCO2 difference (PaCO2-PE'CO2) was -1.0 +/- 1.0 (SD) Torr and was not related to O2 uptake or to the level of PaCO2 (30–68 Torr). The small negative PaCO2-PE'CO2 is attributed to the lung-to-carotid artery transit time delay which must be taken into account when both PaCO2 and PE'CO2 are continuously rising during rebreathing (average rate 0.22 Torr/s). Assuming that blood-gas equilibrium for CO2 was complete, a lung-to-carotid artery circulation time of 4.6 s accounts for the observed uncorrected PaCO2-PE'CO2 of -1.0 Torr. The results are interpreted to indicate that in rebreathing equilibrium PCO2 in arterial blood and alveolar gas are essentially identical. This conclusion is at variance with previous studies in exercising humans during rebreathing but is in full agreement with our recent findings in resting dogs.
Bone and muscle atrophy with suspension of the rat
Authors: LeBlanc A. , Marsh C. , Evans H. , Johnson P. , Schneider V. , Jhingran S.
Published: December 2017

A modification of the Morey tail suspension model was used to determine atrophic responses of rat bone and muscle with 14–90 days unloading of the hindlimbs. Bone uptake of methylene diphosphonate followed a phasic pattern similar to changes in bone formation rate in immobilized dogs and rats. Increased uptake at 60 days (P = 0.01, femur) indicated an increased bone metabolism. Regional densitometry demonstrated a preferential loss of bone mineral in the trabecular mass (P = 0.02) at 30 days and in the cortical shaft by 90 days (P = 0.03). Maximal muscle atrophy occurred within 14–30 days. The gastrocnemius was less severely affected by suspension than by immobilization techniques, whereas the soleus atrophied (by weight) similarly, suggesting that muscle atrophy in the suspension model is distinctly different from immobilization atrophy. One significant response of skeletal muscle to suspension was an altered blood distribution. Muscle blood distribution changes reflect the hypodynamic state of muscle that continues to contract but probably at an altered rate in response to altered functional demands.
Physiological effects of high-P50 erythrocyte transfusion on piglets
Authors: Teisseire B. P. , Ropars C. , Vallez M. O. , Herigault R. A. , Nicolau C.
Published: December 2017

Rightward shifts of the O2 dissociation curve (ODC) were experimentally obtained in lysed and resealed erythrocytes following encapsulation of inositol hexaphosphate (IHP). This continuous lysing and resealing procedure led to in vitro P50 (Po2 at 50% hemoglobin saturation) increases up to 80 Torr (pH, 7.40; Pco2, 40 Torr; temp, 37 degrees C) for both human and pig erythrocytes. The Hill number of the transformed blood decreased when IHP was fixed on the hemoglobin, but the sigmoid shape of the ODC was maintained. The O2 hemoglobin binding capacity and the mean corpuscular hemoglobin content were found unchanged by the experimental procedure in human and pig erythrocytes. Isovolumic exchange transfusion of high-P50 erythrocytes in anesthetized and ambient air-ventilated piglets (n = 6) led to substantial in vivo P50 increases (range, 8–19 Torr). The rightward shift of the ODC was concomitant with an increase of the arterial Po2 and of the arteriovenous O2 content difference, 19 and 59% respectively above their control values. The mixed-venous Po2 (PVO2) remained unchanged. The cardiac output was shown to be inversely related to the P50 value. In spite of the O2-transport reduction (37%), O2 consumption was maintained due to enhanced O2 extraction.
Ascending spinal pathways for somatoautonomic reflexes in the anesthetized dog
Authors: Kozelka J. W. , Wurster R. D.
Published: December 2017

The ascending spinal pathways mediating pressor and heart rate responses to somatic afferent stimulation and induced exercise were studied in pentobarbital- and alpha-chloralose-anesthetized dogs. Bilateral sciatic nerve stimulation and induced exercise, via lumbosacral ventral root stimulation, produced pressor and heart rate responses that were blocked by bilateral dorsolateral sulcus (DLS) lesions of the lumbar spinal cord (L1-L3). Baroreceptor-mediated bradycardia were attenuated by sciatic stimulation but not by induced exercise. This attenuation was blocked by combined dorsolateral funiculus (DLF) and DLS lesions. Induced exercise with vascular occlusion to the muscle augmented the pressor and heart rate responses to exercise. These responses were blocked by combined DLS and DLF lesions. Such lesions did not influence responses to bilateral carotid occlusion, indicating that descending autonomic pathways were intact. Therefore, ascending spinal pathways mediating somatocardiovascular reflexes in anesthetized dogs are located in the lateral funiculus, extending from the dorsal root entry zone to a position somewhat ventral to the dentate ligament.
Ventilatory changes during exercise and arterial PCO2 oscillations in chronic airway obstruction patients
Authors: Prior J. G. , Powlson M. , Cochrane G. M. , Wolff C. B.
Published: December 2017

Ventilatory kinetics during exercise (30 W for 6 min) were studied in 3 asthmatics, 14 patients with chronic airway obstruction (11 with bronchial or type B disease, 3 with emphysematous or type A disease), and in 5 normal age-matched controls. The measure of ventilatory increase during early exercise, alpha 1–3%, was calculated as (avg minute ventilation over 1st-3rd min of exercise--resting minute ventilation)/(avg minute ventilation over 4th-6th min of exercise--resting minute ventilation) X 100. Arterial pH, PO2, and PCO2 (PaCO2) were measured in vitro at rest and within 20 s of termination of exercise. Respiratory PaCO2 oscillations had previously been monitored at rest in the patients (indirectly as in vivo arterial pH, using a fast-response pH electrode) and quantified by upslope (delta PaCO2/delta t). alpha 1–3% was normal in asthmatics (whose respiratory oscillations as a group showed least attenuation) and in type A patients (whose respiratory oscillations as a group were most attenuated). In type B patients reduction in alpha 1–3% correlated with attenuation of delta PaCO2/delta t (r = 0.75; P less than 0.01). There was no significant correlation between delta PaCO2/delta t and change of in vitro PaCO2 from rest to the immediate postexercise period. These findings are consistent with the hypothesis that attenuation of delta PaCO2/delta t slows ventilatory kinetics during exercise in type B but not type A patients. Intact respiratory oscillations are not necessary for CO2 homeostasis after the first few minutes of exercise.
Respiratory mechanical effects of abdominal distension
Authors: Gilroy R. J. , Lavietes M. H. , Loring S. H. , Mangura B. T. , Mead J.
Published: December 2017

We develop a theory to predict the partitioning of a change in volume of the abdominal contents into the end-expiratory volume changes of the lung, rib cage, and anterior abdominal wall. First, we calculate the distribution of such a volume change using the relative compliances of the three compartments. We then consider the inspiratory influence of abdominal pressure on the rib cage and its effect on the distribution of this volume. We test our theory by inducing gastric distension in three experienced laboratory personnel. We instilled and subsequently withdrew 1 liter of water from a gastric balloon and examined the effects of this change in gastric volume on the relaxation characteristics of the respiratory system. The distribution of the volume change that would be expected from the observed relative compliances of the three compartments would be approximately 66% into change in lung volume, 25% into change in rib cage volume, and 9% into change in abdominal volume. Instead, in line with our predictions for acute gastric distension, approximately 33% went into decrease in lung volume, 40% into increase in rib cage volume, and 26% into increase in abdominal volume. These results suggest that the interactions among the rib cage, abdomen, and diaphragm are such as to defend against large changes in end-expiratory lung volume in the face of abdominal distension.