bluuebunny/crossref_metadata_2025 huggingface dataset:
Respiratory muscle length measured by sonomicrometry
Authors: Newman S. , Road J. , Bellemare F. , Clozel J. P. , Lavigne C. M. , Grassino A.
Published: December 2017

The use of sonomicrometry to study the mechanical properties of the diaphragm in vivo is presented. This method consists of the implantation of piezoelectric transducers between muscle fibers to measure the fibers' changes in length. Ultrasonic bursts are produced by one transducer upon electrical excitation and sensed by a second transducer placed 1–2 cm away. The time elapsed between the generation of the ultrasound burst and its detection is used to calculate the intertransducer distance. Excitation and sampling are done at 1.5 kHz and the output is a DC signal proportional to the length change between the transducers. Neither irreversible injury to the diaphragm nor regional differences within an anatomical part or segment were noted. Measurements were stable within the physiological range of temperature. We measured costal and crural length and velocity of contraction in anesthetized dogs during spontaneous breathing, occluded inspirations, passive lung inflation, and supramaximal phrenic nerve stimulation. We found that shortening during spontaneous breathing was 11 and 6% for crural and costal, respectively. The crural leads the costal in velocity of shortening. Supramaximal stimulation results in a velocity of shortening of 5 resting lengths X s-1. During an occluded inspiration crural shortens as much as in the nonoccluded breath, whereas costal shortens less. During passive lung inflation there is a nearly linear relationship between lung volume and diaphragm length; however, the relationships of chest wall dimensions with diaphragm length are nonlinear and cannot be described by any simple function. Some of the implications of these data on the present understanding of diaphragmatic mechanics are discussed.
Adequacy of tissue oxygenation in intact dog intestine
Authors: Grum C. M. , Fiddian-Green R. G. , Pittenger G. L. , Grant B. J. , Rothman E. D. , Dantzker D. R.
Published: December 2017

Changes in O2 consumption, O2 extraction, and intramural pH, resulting from a decreasing O2 delivery, were studied in the intact dog intestine. The O2 delivery was decreased by ischemia, hypoxia, and combined hypoxia-ischemia. A noninvasive approach for determining intramural pH based on the principle of tonometry was used. There was a strong correlation between the changes in intramural pH and intestinal O2 consumption as O2 delivery was decreased. Intramural pH and O2 consumption were initially maintained in the face of decreasing O2 delivery, but after a critical point they decreased. This critical point was 60.3 +/- 1.6% of base-line O2 delivery in the ischemic group and 51.3 +/- 2.7% of base line in the hypoxic-ischemic group. Despite a decrease to 36.0 +/- 5.6% of base-line O2 delivery, the intramural pH and O2 consumption did not decrease in the hypoxic group. O2 extraction increased with decreasing O2 delivery but did not plateau, indicating no diffusion limitation. The data suggest that blood flow is the major factor limiting intestinal O2 consumption. It is concluded that the noninvasive measure of intramural pH is a good marker of the adequacy of tissue oxygenation in canine intestine.
Calibration methods in respiratory calorimetry
Authors: Young B. A. , Fenton T. W. , McLean J. A.
Published: December 2017

Methods for calibration of respiratory gas exchange measurement systems are evaluated. A new method is described in which O2 is removed from the subject chamber or gas stream and measured gravimetrically in a small combustion chamber containing steel wool. The “Fe-burner” method was tested by comparison with the N2-injection method and found to be of similar accuracy. The new method is easy to perform, quick, and readily applicable to both open- and closed-circuit respiratory systems. It has a rate of O2 uptake that can be adjusted to be similar to the rate by an experimental subject (10–600 kg). Complete calibration of open- and closed-circuit indirect calorimetric systems can be achieved when the Fe-burner method, involving measurement of O2 uptake, is combined with the gravimetric injection of specific gases (CO2, methane) produced by the subject.
Control of breathing at elevated lung volumes in anesthetized cats
Authors: Finkler J. , Iscoe S.
Published: December 2017

We monitored the steady-state ventilatory responses of anesthetized cats to increases in lung volume produced by expiratory threshold loads (ETL) to study the roles of peripheral and central neural mechanisms in controlling respiration at elevated lung volumes. Application of an ETL of 5 cmH2O produced a significant decrease in respiratory frequency (-18%) but no change in minute ventilation (VE) due to a significant increase in tidal volume (VT) (19.3%). The drop in frequency was due solely to an increase in expiratory duration. ETL of 10 cmH2O significantly reduced VE (-17.5%) for the same reason. VT was maintained or increased at elevated lung volumes due to both an increase in the rate of rise of phrenic activity and a maintenance of inspiratory duration (TI) despite increases in both chemical drive and pulmonary stretch receptor (PSR) activity. No PSR adapted completely to the maintained change in lung volume. The sensitivity of the inspiratory off-switch mechanism to increases in lung volume, given by the reciprocal of the VT-TI relationship, decreased significantly during breathing on ETL. The results are consistent with the hypothesis that central habituation, not just peripheral adaptation of PSR, determines breathing pattern at elevated lung volumes.
Chemical activation of group I and II muscle afferents has no cardiorespiratory effects
Authors: Waldrop T. G. , Rybicki K. J. , Kaufman M. P.
Published: December 2017

Although stimulation of group III and IV muscle afferents is known to cause reflex changes in cardiorespiratory function, it has not been resolved whether group I and II afferents contribute to this reflex activation. Therefore, we measured the effects of intra-arterial nonparalyzing doses of succinylcholine (50–100 micrograms/kg) on the firing of muscle afferents from the gastrocnemius muscle in one group of cats, and heart rate, blood pressure, and integrated phrenic nerve activity in a second group of cats. In nonparalyzed cats, succinylcholine injections caused muscular fasciculations and firing of all four groups of muscle afferents. However, succinylcholine stimulated only group I and II afferents after paralysis with gallamine triethiodide. Succinylcholine caused increases in blood pressure, heart rate, and phrenic nerve activity before paralysis. After paralysis, succinylcholine had no effects on any of the cardiorespiratory measures. We conclude that activation of only group I and II afferent fibers from the gastrocnemius muscle has no reflex effects on blood pressure, heart rate, or phrenic nerve activity. These afferents, therefore, are unlikely to play a role in increasing cardiorespiratory function during exercise.
Reflex regulation of sweat rate by skin temperature in exercising humans
Authors: Johnson J. M. , O'Leary D. S. , Taylor W. F. , Park M. K.
Published: December 2017

To find whether sweat rate (SR) and forearm skin blood flow ( SkBF ) were reflexly affected by skin temperature (Tsk) we used water-perfused suits to rapidly elevate Tsk during exercise. With this elevation in Tsk, there was a period of little net change in esophageal temperature (Tes) but marked responses in SR and SkBF . During this period a rise in Tsk of 4.2 +/- 0.3 degrees C was associated with an increase in SR of 0.44 +/- 0.09 mg X cm-2 X min-1 and an increase in SkBF of 3.27 +/- 0.42 ml X 100 ml-1 X min-1. Multiple linear regression analysis as well as comparison with control studies in which Tsk was kept cool also reveal a consistent role for Tsk in the reflex regulation of SR and SkBF . Responses in SR and FBF were much more marked at levels of Tsk below 33 degrees C. Below a Tsk of 33 degrees C, SR rose 0.30 +/- 0.06 mg X cm-2 X min-1 per degrees C rise in Tsk, whereas above 33 degrees SR rose only 0.05 +/- 0.01 mg X cm2 X min per degrees C. FBF rose 2.81 +/- 0.60 and 0.77 +/- 0.18 ml X 100 ml-1 X min-1 per degrees C rise in Tsk at the lower and upper ranges of Tsk, respectively.
Leukotriene synthesis and receptor blockers block hypoxic pulmonary vasoconstriction
Authors: Morganroth M. L. , Reeves J. T. , Murphy R. C. , Voelkel N. F.
Published: December 2017

We hypothesized that leukotrienes are involved in hypoxic pulmonary vasoconstriction, since they are pulmonary vasoconstrictors and cells capable of producing leukotrienes are located in the lung near resistance vessels. We investigated in isolated perfused rat lungs whether three structurally unrelated blockers [diethylcarbamazine citrate (DEC), U-60257, and FPL 55712] of leukotriene synthesis or action block hypoxic pulmonary vasoconstriction. DEC blocked ongoing and subsequent hypoxic pressor responses while minimally affecting the angiotensin II pressor response. The inhibition of the hypoxic pressor response by DEC was not affected by cyclooxygenase or H1-receptor blockers. Potassium-induced vasoconstriction, which is dependent on calcium entry, was largely blocked by verapamil but not by DEC, suggesting that DEC was not acting primarily as a calcium-entry blocker. U-60257 blocked the hypoxic pressor response without inhibiting the pressor response to angiotensin II or potassium chloride. FPL 55712, a leukotriene end-organ blocker, in a dose which inhibited vasoconstriction caused by exogenous leukotriene C4, inhibited the pressor response to hypoxia but not to angiotensin II. We conclude that leukotriene inhibitors preferentially inhibit hypoxic pulmonary vasoconstriction in isolated perfused adult rat lungs.
Albumin-induced plasma volume expansion: diurnal and temperature effects
Authors: Hubbard R. W. , Matthew W. T. , Horstman D. , Francesconi R. , Mager M. , Sawka M. N.
Published: December 2017

To develop a reliable procedure for the acute expansion of plasma volume (PV), 26 male volunteers were randomly assigned to either a thermoneutral (25 degrees C and 40% relative humidity) or hot-dry (37 degrees C and 25% relative humidity) environment; subsequently each subject was seated for at least 1 h and then infused intravenously with either 100 or 200 ml of a 25% albumin solution or 0.9% saline. On the day before each infusion, PV was estimated by dye dilution using indocyanine green. Net percent change in PV (using hematocrit and hemoglobin values) was calculated at 1, 3, 6, 9, 12, and 24 h postinfusion. The PV of subjects residing in the heat after a 100-ml saline infusion increased significantly over 1-h values at 6, 9, and 12 h postinfusion but not at 24 h. The same trend, although not significant, was apparent at room temperature. The data suggest a slow isooncotic circadian pattern of PV expansion and contraction. The infusion of hyperoncotic albumin produced rapid expansion of plasma volume. With the low dose (25 g) at 1 h postinfusion, the expansion was 379 +/- 102 ml in the heat and 301 +/- 160 ml at room temperature. With the high dose (50 g) at 1 h postinfusion, the expansion was 479 +/- 84 ml in the heat and 427 +/- 147 ml at room temperature. The high dose produced an expansion that persisted for at least 9 h in subjects in either environment. The data suggest a mechanism for the retention of fluid during heat acclimatization and a useful procedure for plasma volume expansion in humans.
Modulation of cardiovascular response to dynamic exercise by fastigial nucleus
Authors: Dormer K. J.
Published: December 2017

Mongrel dogs (n = 34) were used to record the cardiovascular responses during submaximal exercise-tolerance tests (ETT) before and after the placement of lesions in rostral portions of the cerebellar fastigial nucleus (FN). Sterile surgical procedures were used to implant solid-state pressure transducers into the left ventricle or descending aorta (anesthesia 1% halothane in O2) and multipolar stainless steel electrodes into FN (anesthesia alpha-chloralose 115 mg/kg iv). Heart rate (HR), maximal left ventricular systolic pressure ( LVPmax ) and its first derivative ( dLVP /dt), and mean arterial blood pressure (MAP) were recorded during a motorized treadmill ETT. Electrolytic direct-current or radio-frequency lesions were made through the indwelling FN electrodes, and the ETT was repeated following 10–14 days recovery. Two-way analysis of variance (ANOVA), with repeated measures on one, and one-way ANOVA for simple effects indicated a significant reduction in HR and MAP (P less than 0.01) but not LVPmax and dLVP /dt occurred during exercise as a result of rostral FN lesions. Although the trend for reduced LVPmax and dLVP /dt was also evident, a relatively greater decrease in blood pressure occurred in the peripheral vasculature during exercise. It was concluded that FN acts as a modulator of HR and MAP during dynamic exercise because of the observed deficits, and because FN is known to both send efferent projections to medullary vasomotor areas and receive projections from motor cortex and muscle and joint afferents.
Cardiopulmonary effects of unilateral airway pressure changes in intact infant lambs
Authors: Fuhrman B. P. , Everitt J. , Lock J. E.
Published: December 2017

Direct effects of airway pressure changes on the pulmonary vascular bed of the intact infant lamb were studied under chloralose anesthesia using a preparation developed to permit independent ventilation of right and left lungs and independent measurement of right and left lung blood flow. A specially designed endobronchial tube eliminated the need for thoracotomy the day of study. Unilateral changes in positive end-expiratory pressure (PEEP) during volume-regulated ventilation increased ipsilateral but not contralateral airway pressure, confirming adequate separation of right and left lungs and suggesting rigidity of the mediastinum. Such interventions ( UPEEP ) at levels of 5, 10, and 15 cmH2O reduced ipsilateral but not contralateral pulmonary blood flow (by 10, 25, and 46%, respectively) but did not alter end-tidal PCO2 of either lung. UPEEP had less effect on cardiac output, stroke volume, right atrial, left atrial, esophageal, and pulmonary arterial pressures than did PEEP applied to both lungs. Because this preparation separates the predominantly direct effects of UPEEP on the ipsilateral lung from its indirect effects on the contralateral lung, it is well suited to studies of direct pulmonary vascular effects of airway pressure changes in an intact closed-chest preparation with reactive pulmonary vasculature.
Endurance training effects on plasma hormonal responsiveness and sex hormone excretion
Authors: Bullen B. A. , Skrinar G. S. , Beitins I. Z. , Carr D. B. , Reppert S. M. , Dotson C. O. , Fencl M. D. , Gervino E. V. , McArthur J. W.
Published: December 2017

A prospective study of the hormonal effects of a moderate exercise training program (4-wk control, 8-wk training) was conducted in seven young women. Sixty-minutes continuous bicycle ergometer tests of fixed relative intensity were performed at the beginning, middle, and end of the training period. The capacity of these acute bouts of exercise to affect circulating levels of stress markers, reproductive hormones, and hormones with possible antireproductive potential was measured. In addition, the urinary excretion of reproductive hormones was monitored continuously via serial overnight urine collections. Within testing sessions, plasma concentrations of all stress markers and antireproductive hormones rose significantly. Across testing sessions, only beta-endorphin + beta-lipotropin and cortisol exhibited an increment in peak responses as training progressed. Plasma reproductive hormone levels showed insignificant acute changes, and cyclic menstruation and preovulatory gonadotropin surges continued in all subjects. However, ovarian function was disturbed in four subjects as evidenced by a decreased excretion of estriol, free progesterone, or both. Transient infertility is a known clinical accompaniment of hormonal changes of comparable subtlety.
No effect of sex steroids on compensatory muscle hypertrophy
Authors: Max S. R. , Rance N. E.
Published: December 2017

We studied the effects of sex steroids on muscle weight and oxidative capacity of rat plantaris muscles subjected to functional overload by removal of synergistic muscles. Eight weeks after bilateral synergist removal, plantaris muscles were strikingly hypertrophic compared with unoperated controls. After this period, there were selective alterations in the ability of the muscles to oxidize three substrates of oxidative metabolism. Thus 14CO2 production from [6-14C]glucose and [2-14C]pyruvate was significantly reduced, whereas there was no alteration in 14CO2 production from beta-[3-14C]hydroxybutyrate. Succinate dehydrogenase specific activity was decreased in overloaded muscle. There was no effect of sex hormone status on any of these parameters. Finally, 30 days of functional overload did not influence cytosolic androgen receptor binding. These results are not consistent with the idea that sex steroids and functional overload act synergistically.
Augmentation of CO2 drives by chlormadinone acetate, a synthetic progesterone
Authors: Kimura H. , Hayashi F. , Yoshida A. , Watanabe S. , Hashizume I. , Honda Y.
Published: December 2017

We studied 10 male subjects who were administered chlormadinone acetate (CMA), a potent synthetic progesterone, to clarify the physiological basis of its respiratory effects. Arterial blood gas tension, resting ventilation, and respiratory drive assessed by ventilatory and occlusion pressure response to CO2 with and without inspiratory flow-resistive loading were measured before and 4 wk after CMA administration. In all subjects, arterial PCO2 decreased significantly by 5.7 +/- 0.6 (SE) Torr with an increase in minute ventilation by 1.8 +/- 0.6 l X min-1, whereas no significant changes were seen in O2 uptake. During unloaded conditions, both slopes of occlusion pressure and ventilatory response to CO2 increased, being statistically significant in the former but showing nonsignificant trends in the latter. Furthermore, inspiratory flow-resistive loading (16 cmH2O X l(-1) X s) increased both slopes more markedly after CMA. The magnitudes of load compensation, assessed by the ratio of loaded to unloaded slope of the occlusion pressure response curve, were increased significantly. We concluded CMA is a potent respiratory stimulant that increases the CO2 chemosensitivity and neuromechanical drives in the load-compensation mechanism.
Relationship of ventilatory capacity to hyperbaric exposure in divers
Authors: Davey I. S. , Cotes J. E. , Reed J. W.
Published: December 2017

The results of divers' annual medical examinations were used to assess the effects of diving exposure independent of age, stature, and smoking on forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1). Cross-sectional analysis of records for 858 men showed a significant positive association between the maximal depth that subjects had experienced and FVC but not FEV1. There was a significant negative association for FEV1/FVC%, and this index was also positively correlated with years of diving exposure. Among a subsample of 81 men the forced expiratory flow rate at low lung volume was reduced relative to that of control subjects similarly assessed; the extent of the reduction from the reference value was significantly correlated with the diving exposure. Longitudinal analysis of results for 255 men over a minimum of 5 yr showed that the change in FVC per annum (positive or negative) was correlated with the change in maximal depth; there were no similar associations for FEV1 or FEV1/FVC%. Thus diving exposure affects the vital capacity and the forced expiratory flow rate at small lung volumes. The latter is evidence for narrowing of airways that might be secondary to diving-induced loss of lung elastic tissue; this hypothesis merits further investigation.
Control of neurotransmission by prostaglandins in canine trachealis smooth muscle
Authors: Walters E. H. , O'Byrne P. M. , Fabbri L. M. , Graf P. D. , Holtzman M. J. , Nadel J. A.
Published: December 2017

Contractile responses of canine tracheal smooth muscle to electrical field stimulation diminished over a 2-h period of incubation. However, addition of indomethacin (10(-5) M) for a similar time not only prevented this inhibition of contractile response, but actually markedly increased the response to electrical field stimulation, suggesting that prostaglandins were responsible for the time-dependent inhibition. Measured prostaglandin E2 increased in the tissue bath over 2 h in control tissues. Addition of prostaglandin E2 to the tissue produced similar inhibition of contractile responses to electrical field stimulation in a concentration-dependent manner. In contrast, incubation alone, treatment with indomethacin, or addition of prostaglandin E2 had little, if any, effect on contractions induced by acetylcholine. We conclude that the release of prostaglandins from canine tracheal smooth muscle that occurs with time has a predominantly inhibitory effect on cholinergic neurotransmission at a prejunctional site.
Human whole-blood oxygen affinity: effect of carbon monoxide
Authors: Zwart A. , Kwant G. , Oeseburg B. , Zijlstra W. G.
Published: December 2017

Oxygen dissociation curves (ODC) were recorded in the presence of carboxyhemoglobin fractions (FHbCO) up to 60%. The gradual shift to the left of the ODC at increasing amounts of HbCO was reflected in a gradual fall in the half-saturation pressure of the remaining Hb and was accompanied by a gradual change in the shape of the ODC to a hyperbolic one. The H+ factor (delta log PO2/delta pH) was determined over the entire oxygen saturation (SO2) range at three different FHbCO levels (14, 30, and 52%). At FHbCO = 14 and 30% and for the SO2 range 20–90%, the H+ factor vs. SO2 curve was not significantly different from that in the absence of HbCO. At FHbCO = 52%, however, the value found for the H+ factor (-0.55) was appreciably more negative than in the case of blood containing less than 1% HbCO (-0.44), and there was no dependence on SO2. Comparison of measured and calculated ODCs at varying HbCO fractions showed, for FHbCO less than or equal to 50%, that measured and calculated ODCs coincide over the greater part of the SO2 range. For FHbCO greater than 50%, the measured ODC was situated to the left of the calculated one over the entire SO2 range. We conclude that the heme-heme interaction for CO is appreciably larger than for O2 only for FHbCO greater than 50%, whereas for FHbCO less than 50% there is virtually no difference.
Diaphragmatic fatigue in unanesthetized adult sheep
Authors: Bazzy A. R. , Haddad G. G.
Published: December 2017

We studied diaphragmatic muscle function during inspiratory flow resistive (IFR) loaded breathing in unanesthetized sheep. We measured the change in transdiaphragmatic pressure (dPdi) and arterial blood gas tensions and recorded diaphragmatic electromyogram (EMG) from electrodes implanted on the muscle. We found that, with IFR loads less than 150 cmH2O X l–1 X s, dPdi and the integrated EMG increased, reached a plateau, and were maintained at high levels. The centroid frequency (fc) of the EMG power spectrum did not consistently change. With IFR loads greater than 150 cmH2O X l–1 X s, O2 was administered to prevent hypoxia, cyanosis, and agitation. With these loads, dPdi increased severalfold above base line, reached a plateau, and then started to decrease. Arterial PCO2 increasedsharply at the time when dPdi decreased. The integrated EMG (iEMG) and fc started to decrease gradually 10–20 min before dPdi started to decrease. We conclude that 1) the diaphragm is capable of generating large pressures for prolonged periods with no evidence of fatigue; 2) with very high IFR loads, mechanical failure of the diaphragm can occur in the unanesthetized awake sheep; 3) diaphragmatic fatigue is associated with acute hypercapnia and therefore failure of the entire respiratory pump;and 4) a decrease in iEMG and a concommitant shift in the power spectrum density towards lower frequencies precede the mechanical failure of the diaphragm.
Respiratory function of hyoid muscles and hyoid arch
Authors: Van de Graaff W. B. , Gottfried S. B. , Mitra J. , van Lunteren E. , Cherniack N. S. , Strohl K. P.
Published: December 2017

The position of the hyoid arch suggests that it supports soft tissue surrounding the upper airway (UA) and can act to maintain UA patency. We also suspected that muscles inserting on the hyoid arch might show respiratory patterns of activity that could be affected by respiratory stimuli. To test these possibilities, we moved the hyoid arch ventrally in six anesthetized dogs either by traction on it or by stimulation of hyoid muscles. UA resistance was decreased 73 +/- (SE) 6% and 72 +/- 6% by traction and stimulation during expiration and 57 +/- 15% and 52 +/- 8% during inspiration. Moving averages of the geniohyoid (GH) and thyrohyoid (TH) obtained in six other dogs breathing 100% O2 showed phasic respiratory activity while the sternohyoid (SH) showed phasic respiratory activity in only two of these animals and no activity in four. With progressive hypercapnia, GH and TH increased as did SH when activity was already present. Airway occlusion at end expiration augmented and prolonged inspiratory activity in the hyoid muscles but did not elicit SH activity if not already present. Occlusion at end inspiration suppressed phasic activity in hyoid muscles for as long as in the diaphragm. After vagotomy activity increased and became almost exclusively inspiratory. Activity appeared in SH when not previously present. Duration and amplitude of hyoid muscle activity were increased with negative UA pressure and augmented breaths. We conclude that the hyoid arch and muscles can strongly affect UA flow resistance. Hyoid muscles show responses to chemical, vagal, and negative pressure stimuli similar to other UA muscles.
Hypoxic pulmonary vasoconstriction during steady and pulsatile flow in ferrets
Authors: Gregory T. J. , Ellsworth M. L. , Newell J. C.
Published: December 2017

We examined the effects of hypoxia and pulsatile flow on the pressure-flow relationships in the isolated perfused lungs of Fitch ferrets. When perfused by autologous blood from a pump providing a steady flow of 60 ml/min, the mean pulmonary arterial pressure rose from 14.6 to 31.3 Torr when alveolarPO2 was reduced from 122 to 46 Torr. This hypoxic pressor response was characterized by a 10.1-Torr increase in the pressure-axis intercept of the extrapolated pressure-flow curves and an increase in the slope of these curves from 130 to 240 Torr X l–1 X min. With pulsatile perfusion from a piston-typepump, mean pulmonary arterial pressure increased from 17.5 to 36.3 Torr at the same mean flow.Thishypoxic pressor response was also characterized by increases in the intercept pressure and slope of thepressure-flow curves. When airway pressure was raised during hypoxia, the intercept pressure increased further to 25 +/- 1 Torr with a further increase in vascular resistance to 360 Torr X l–1 X min. Thus, in contrast to the dog lung, in the ferret lung pulsatile perfusion does not result in lower perfusion pressures during hypoxia when compared with similar mean levels of steady flow. Since the effects of high airway pressure and hypoxia are additive, they appear to act at or near the same site in elevating perfusion pressure.
Synergistic stimulation of food intake by simultaneous insulin and cold
Authors: Morrison S. D.
Published: December 2017

Insulin administered to rats during simultaneous exposure to cold increases food intake by more than the sum of the separate feeding responses and prevents the normal cold-induced loss of body weight. On withdrawal of insulin with cold maintained, all the body weight maintained by insulin is immediately lost and body weight thereafter is identical to that of rats exposed to cold only. Accumulated food intake for the joint treatment and after withdrawal of insulin with cold maintained is greater than for cold exposure only. There is no increase in metabolic cost due to insulin. Energy density of weight gain during insulin treatment is high and of weight loss on withdrawal of insulin with cold maintained is very low. These responses do not conform with commonly proposed models of feeding control.
Compliance of chest wall in obese subjects
Authors: Suratt P. M. , Wilhoit S. C. , Hsiao H. S. , Atkinson R. L. , Rochester D. F.
Published: December 2017

Whereas studies in awake subjects have demonstrated that chest wall compliance (Ccw) is low in obese subjects, the one study performed on paralyzed obese subject found Ccw to be normal. The purpose of this study was to measure Ccw in awake obese subjects with the pulse-flow technique, a method which appears to detect respiratory muscle relaxation. Seven normal males, 14 obese males, and 8 obese females [body mass index (BMI) varied from 20 to 83 kg/m2] were studied in the seated position. Ccw was measured by blowing air at a constant flow into the mouth and lungs for approximately 2 s and calculated by dividing airflow in liters per second by the change in esophageal minus body surface pressure in centimeters of water per second. In normal and obese subjects we found no correlation between BMI and Ccw. We conclude that obesity does not decrease Ccw.
Muscle architecture and force-velocity relationships in humans
Authors: Wickiewicz T. L. , Roy R. R. , Powell P. L. , Perrine J. J. , Edgerton V. R.
Published: December 2017

The in vivo torque-velocity relationships of the knee extensors (KE), knee flexors (KF), ankle plantarflexors (PF), and ankle dorsiflexors (DF) were determined in 12 untrained subjects using an isokinetic testing device (Cybex II). These data were then matched to the predicted maximum forces and shortening velocities derived from muscle architectural determinations made on three hemipelvectomies (36). The torque-velocity curves of all muscle groups resembled that predicted by Hill's (19, 20) equation except at the higher forces and lower velocities. The peak torques occurred at mean velocities ranging from 41–62 rad X s-1 for the KE, KF, and PF. Although the peak torque of the DF occurred at the isometric loading condition, it was also lower than that predicted by Hill's equation. The muscle fiber length and physiological cross-sectional area measurements indicate that the architecture of the human leg musculature has a major influence on the torque-velocity characteristics. These data corroborate previous findings (24) that some neural inhibitory mechanism exists in the control of the leg musculature, which limits the maximum forces that could be produced under optimal stimulating conditions.
Marathon performance, anaerobic threshold, and onset of blood lactate accumulation
Authors: Tanaka K. , Matsuura Y.
Published: December 2017

The study tested the hypothesis that running velocity corresponding to the anaerobic threshold (VAT) would more accurately approximate the actually measured marathon race velocity (VM) than would running velocity corresponding to the so-called onset of blood lactate (4 mM) accumulation (VOBLA). The VAT (4.57 m X s-1) well approximated the VM (4.49 m X s-1), whereas the VOBLA (5.30 m X s-1) differed significantly from the VM. In addition, the VAT (r = 0.781) correlated with VM to a greater extent than did the VOBLA (r = 0.682). When the VAT (X1) was combined with delta % maximum O2 consumption (VO2max) (%VO2max at the OBLA minus %VO2max at the AT; X2) and VO2max (ml X min-1 x kg-1; X3), variation in the VM accounted for increased profoundly from 61 to 88%. Thus one of the useful equations formulated with high predictive accuracy was VM (m X s-1) = 1.312X1 + 0.0346X2 – 0.00993X3 – 1.272. Our study demonstrates that the anaerobic threshold (AT) is more closely associated with marathon running performance and that the degree of the association is raised when delta %VO2max and/or VO2max are combined as additional information.
CO2 and mechanical factors reduce blood flow in a collapsed lung lobe
Authors: McFarlane P. A. , Gardaz J. P. , Sykes M. K.
Published: December 2017

Left lower lobe-to-total blood flow ratio (Ql/QT) was measured with electromagnetic flow probes in anesthetized open-chest dogs. There was a 66% reduction in Ql/QT during lobar collapse, a 53% reduction during lobar ventilation hypoxia with pulmonary venous PO2 and PCO2 equal to mixed venous tensions, and a 45% reduction during a similar degree of ventilation hypoxia but with normal end-tidal PCO2. We concluded that the reduction in blood flow during lobar collapse is due predominantly to hypoxic vasoconstriction, but that this mechanism is augmented by the raised PCO2 and mechanical factors present during collapse.
On the likelihood of decompression sickness
Authors: Weathersby P. K. , Homer L. D. , Flynn E. T.
Published: December 2017

The occurrence of decompression sickness in animals and humans is characterized by the extreme variability of individual response. Nevertheless, models and analyses of decompression results have generally used a critical value approach to separate safe and unsafe decompression procedures. Application of the principle of maximum likelihood provides a formal and consistent way to quantify decompression risk and to apply models to data on decompression outcome. By use of the maximum likelihood principle, a number of models were fit to data from dose-response and maximum pressure-reduction experiments with both rats and men. Several different formulations of two- and three-parameter models described the data well. In addition to summarizing data sets, the analyses provide a way to maximize the value of experimental observations, test theoretical predictions, estimate uncertainty in conclusions, and recommend safe practices.
Time domain analysis of diaphragmatic electromyogram during fatigue in men
Authors: Bower J. S. , Sandercock T. G. , Rothman E. , Abbrecht P. H. , Dantzker D. R.
Published: December 2017

Diaphragmatic fatigue has been correlated with a change in the electromyogram recorded from the diaphragm (EMGdi), which suggests that the electromyogram is a potential clinical tool to detect respiratory muscle fatigue. Changes in the EMGdi have previously been quantified by using the power spectral parameters high-low ratio or mean frequency. In this study, we developed an autoregressive model of the EMG in an attempt to improve the analysis of the EMGdi. This model was tested on recordings of the EMGdi that were obtained from an esophageal electrode in five normal subjects breathing to fatigue through an inspiratory resistor. The data obtained from the autoregressive model were directly compared with data from the high-low ratio and mean frequency techniques. The autoregressive model showed an excellent correlation with mean frequency. Both techniques were superior to the high-low ratio measurement. Because the autoregressive model requires much less computation than mean frequency and can be easily implemented in real time on a minicomputer, we propose this as a preferable approach.
Differential effects of sauna-, diuretic-, and exercise-induced hypohydration
Authors: Caldwell J. E. , Ahonen E. , Nousiainen U.
Published: December 2017

The physiological effects on submaximal and maximal exercise of three methods commonly used by athletes for achieving rapid weight loss were determined by measuring cardiorespiratory variables in 62 nonendurance athletes. A mean weight loss of 4.1% was achieved by those who followed either a sauna (SAU), diuretic (DIU), or exercise (ACT) protocol, compared with the average weight loss of 1.2% in the control group. At maximal exercise O2 consumption, O2 pulse, blood lactate concentration, and work load decreased in SAU and DIU groups relative to the ACT group, whereas only a few differences were observed at the aerobic threshold. Weight loss achieved over a 48-h period was less detrimental to an athlete than was a more rapid (24-h) weight reduction achieved through sauna bathing or the use of diuretics. We conclude that not only the quantity of weight loss but also the method itself may limit physical performance.
Effects of cell size and exercise on glucose uptake and metabolism in adipocytes of female rats
Authors: Craig B. W. , Foley P. J.
Published: December 2017

The purpose of this study was to attain a better understanding of how the adipocyte transports and metabolizes glucose with and without the influence of exercise training. Rates of 2-deoxyglucose and glucose oxidation, using [1-14C]-and [6-14C]glucose, were measured in adipocytes from exercise-trained and sedentary control female rats of the same age. The trained animals were exercised by swimming, 6 h/day, 5 days/wk for 10 wk. The fat cells of the sedentary rats were significantly larger (P less than 0.005) than the trained animals and had very low rates of glucose uptake and [1-14C]- and [6-14C]glucose oxidation. The adipocytes of the trained rats were very responsive to insulin with 2-deoxyglucose rates seven times higher than those of the control animals and [1-14C]- and [6-14C]-glucose oxidation rates 14- and 13-fold (respectively) larger than control values. Comparisons of the data from exercised animals to younger sedentary rats indicates that glucose oxidation remains normal in the adipocytes of the trained animals whereas glucose transport is greatly improved. If the older sedentary controls are compared to younger animals, it can be seen that as the cell enlarges it loses its ability to take up or metabolize glucose. The combination of a loss in glucose transporting capacity with cellular enlargement and an increase in glucose uptake with exercise training suggests that movement of glucose across the cell membrane may be a limiting factor in glucose utilization in fat cells.
Effect of respiratory muscle weakness on P0.1 induced by partial curarization
Authors: Holle R. H. , Schoene R. B. , Pavlin E. J.
Published: December 2017

Mouth occlusion pressure 0.1 s after onset of inspiration (P0.1) reflects central respiratory drive (CRD), but its dependence on respiratory muscle strength is unknown. To clarify this relationship, we produced progressive levels of respiratory muscle weakness by infusion of d-tubocurarine in eight supine spontaneously breathing normal subjects. Hypercapnic ventilatory response (HCVR) was measured before curarization and at mild (mean inspiratory effort 62 +/- 3% of control), moderate (42 +/- 3%), and severe (23 +/- 1%) weakness. At the severe level of weakness 1) supine functional residual capacity was not significantly changed from base line, 2) the percent of base-line slope of delta P0.1/delta PCO2 (122 +/- 27%) was significantly greater (P less than 0.01) than that for change in expired minute ventilation (delta VE)/delta PCO2 (39 +/- 10%), 3) the percent of base-line delta P0.1/delta VE (381 +/- 46%) during HCVR was significantly increased (P less than 0.01), 4) the P0.1 response was significantly increased from base line at two out of three specific levels of PCO2 while the VE was unchanged or significantly decreased, and 5) peak inspiratory resistance did not significantly change. Thus P0.1, unlike VE, did not decrease with even severe respiratory muscle weakness. Indeed, P0.1 increased at two out of three levels of PCO2 under circumstances when higher CRD is expected. One potential explanation for the results is that P0.1 may at least qualitatively reflect CRD up to the level of severe respiratory muscle weakness attained in this study.
Muscle fiber number in biceps brachii in bodybuilders and control subjects
Authors: MacDougall J. D. , Sale D. G. , Alway S. E. , Sutton J. R.
Published: December 2017

Muscle fiber numbers were estimated in vivo in biceps brachii in 5 elite male bodybuilders, 7 intermediate caliber bodybuilders, and 13 age-matched controls. Mean fiber area and collagen volume density were calculated from needle biopsies and muscle cross-sectional area by computerized tomographic scanning. Contralateral measurements in a subsample of seven subjects indicated the method for estimation of fiber numbers to have adequate reliability. There was a wide interindividual range for fiber numbers in biceps (172,085–418,884), but despite large differences in muscle size both bodybuilder groups possessed the same number of muscle fibers as the group of untrained controls. Although there was a high correlation between average cross-sectional fiber area and total muscle cross-sectional area within each group, many of the subjects with the largest muscles also tended to have a large number of fibers. Since there were equally well-trained subjects with fewer than normal fiber numbers, we interpret this finding to be due to genetic endowment rather than to training-induced hyperplasia. The proportion of muscle comprised of connective and other noncontractile tissue was the same for all subjects (approximately 13%), thus indicating greater absolute amounts of connective tissue in the trained subjects. We conclude that in humans, heavy resistance training directed toward achieving maximum size in skeletal muscle does not result in an increase in fiber numbers.
Hypoxemia increases plasma catecholamine concentrations in exercising humans
Authors: Escourrou P. , Johnson D. G. , Rowell L. B.
Published: December 2017

To determine whether plasma catecholamine concentrations (a measure of sympathetic nervous activity [SNA]) rise above normoxic levels during exercise with hypoxemia, we exercised seven men for 15 min at three loads that required from 40 to 88% of maximal O2 uptake (VO2max). Subjects breathed room air on one day and 11–12% O2 on another with relative work loads corrected for the 24% fall in VO2max during hypoxemia. Hypoxemia caused large increments in norepinephrine (NE) concentration (radioenzyme technique) to 1.21 +/- 0.20 ng/ml (mean +/- SE), 2.79 +/- 0.38, and up to 5.90 +/- 0.75 (hypoxemia) compared with 0.89 +/- 0.06, 1.66 +/- 0.16, and 3.95 +/- 0.39 in normoxia at the three loads, respectively (P less than 0.001). Epinephrine (E) concentration approximately doubled (P less than 0.001) in hypoxemia at each load when compared with normoxic levels (i.e., 0.10 +/- 0.01 ng/ml, 0.23 +/- 0.03, and 0.46 +/- 0.06 in normoxia). However, hypoxemia did not significantly alter linear relationships between log plasma NE concentration and either heart rate (HR) or percent VO2max utilized, or between HR and percent VO2max. Thus NE concentration, like HR, appeared to reflect relative severity of exercise and overall SNA in both hypoxemia and normoxia. Above 40% VO2max during hypoxemia, circulating NE and E far exceeded levels known to have direct vasoconstrictor and metabolic effects in normoxic humans, but hypoxemia may blunt vasoconstriction in some regions.
Influence of endothelial volume on kinetics of reacting indicators in the lung
Authors: Harris T. R.
Published: December 2017

The purpose of this work is to show mathematically the relationship between the classical maximum velocity of reaction, Vmax, for enzyme kinetics and an analogous parameter, Vmax, derived by Linehan and Dawson (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47:404–411, 1979) for the analysis of tracers which disappear by saturation kinetics from the lung circulation during the passage of indicators after bolus injection. Rederivation of the original equation for the combination of flow and reaction in a capillary showed that Vmax is equal to the product of enzyme Vmax and the volume of endothelium, Ve, in which the enzyme resides. This implies that Vmax interpreted from multiple-indicator curves in the lung by the Linehan-Dawson method is a combination of an enzyme characteristic Vmax and a measure of functioning capillary surface during passage, Ve. Lung injury could change Vmax, functioning surface (Ve), or both.
Neural control of relaxation in cat airways smooth muscle
Authors: Altiere R. J. , Szarek J. L. , Diamond L.
Published: December 2017

Functional innervation of cat airways smooth muscle was examined in isolated segments of trachea and bronchi using electrical field stimulation (EFS) techniques. Field stimulation caused contraction in tissues at resting tone and biphasic responses (contraction followed by relaxation) in tissues precontracted with 5-hydroxytryptamine (5-HT). Contractions were abolished by 10(-6) M atropine. Inhibitory responses were dependent on impulse voltage, duration, and frequency. At low voltages (less than or equal to 10 V) and pulse durations (less than or equal to 0.3 ms), EFS induced relaxations were abolished by 3 X 10(-6) M tetrodotoxin (TTX). Greater stimulus parameters elicited TTX-resistant relaxations. Pretreatment of the tissues with 10(-6) M propranolol and 10(-5) M guanethidine caused rightward shifts in relaxation frequency-response curves. These findings indicate that cat airways are innervated by excitatory cholinergic, inhibitory adrenergic, and inhibitory nonadrenergic noncholinergic (NANC) nerves. Pretreatment of the tissues with hexamethonium, cimetidine, indomethacin, or nordihydroguaiaretic acid did not affect NANC relaxation responses. It is concluded that NANC inhibitory responses in cat airway smooth muscle are mediated through intrinsic postganglionic nerve fibers and occur independently of histamine H2-receptor activation and without involvement of cyclooxygenase or lipoxygenase products of arachidonic acid metabolism.
Liposome-mediated augmentation of brain SOD and catalase inhibits CNS O2 toxicity
Authors: Yusa T. , Crapo J. D. , Freeman B. A.
Published: December 2017

Enzymes specific for O-2 and H2O2 metabolism [superoxide dismutase (SOD) and catalase] can be delivered to the rat brain following entrapment in liposomes and intravenous injection and will protect against hyperbaric O2-induced convulsions in rats. Liposome-mediated superoxide dismutase and catalase augmentation of brain enzyme activity was 2.7-fold and 1.9-fold, respectively, 15 min after intravenous injection of superoxide dismutase plus catalase-entrapped liposomes. Rats treated with liposomes containing superoxide dismutase plus catalase 2 h before 6 ATA 100% O2 exposure had the time to convulsion extended three times that of controls. This protective effect was dose-dependent and was primarily due to augmentation of catalase activity. These findings show O-2 and H2O2 are important mediators of hyperbaric O2-induced central nervous system toxicity and that liposome-mediated augmentation of brain antioxidant enzymes has a biological effect.
Independence of exercise hypocapnia and limb movement frequency in ponies
Authors: Forster H. V. , Pan L. G. , Bisgard G. E. , Flynn C. , Dorsey S. M. , Britton M. S.
Published: December 2017

The objective of this study was to determine whether changes in limb motion per se influence arterial CO2 partial pressure (PaCO2) during muscular exercise in ponies. Fifteen ponies were studied at rest and during 8 min of treadmill exercise when the work load was constant or when the work load was increased after the 4th min. Five different treadmill settings were selected to provide for a range of metabolic rate achieved with primary changes in either speed or grade (1.8 mph at 3, 8, and 15% grade; or 3 and 6 mph at 3% grade). The ponies exercised either on all four legs or on only the hindlegs. Step frequencies were 49, 66, and 99 at 1.8, 3, and 6 mph, respectively. During all work tasks PaCO2 decreased maximally 30-60 s after the work task was initiated from rest or from a less intense level of exercise. This nadir in PaCO2 was followed by some recovery with a stable level of mild hypocapnia (delta PaCO2) maintained after 3-4 min. The delta PaCO2 was directly related to O2 consumption (VO2) (P less than 0.01). The delta PaCO2-VO2 regression slopes did not differ between speed and grade VO2 changes nor between four- and two-legged exercise (P greater than 0.10). These data suggest that neither frequency of limb movement nor the number of limbs moving are major factors in the PaCO2 (and alveolar ventilation) response to exercise in ponies. We conclude that the apparent difference in PaCO2 regulation during exercise between ponies (hypocapnia) and humans (isocapnia during walking and bicycling) is not related to a species difference in the number of limbs employed in the exercise task.