Showing papers in "Journal of Applied Physiology in 1981"
TL;DR: It is concluded that a profile of aerobic function in man can be obtained from a single short-duration ramp test and the parameters determined faithfully reproduced those obtained from several standard procedures.
Abstract: A short-duration cycle ergometer exercise test has been developed that allows four parameters of aerobic function to be discerned. These are the maximum O2 uptake, anaerobic threshold, work efficiency, and the time constant for O2 uptake kinetics. The test form is a ramp of 4-8 min duration to the limit of tolerance. The parameters determined from the ramp faithfully reproduced those obtained from several standard procedures. We conclude that a profile of aerobic function in man can be obtained from a single short-duration ramp test.
640 citations
604 citations
TL;DR: The relationship between the electromyographic (EMG) power spectrum and muscle conduction velocity was investigated during both fatiguing and nonfatiguing contractions of the adductor pollicis muscle, suggesting that during fatigue of maximal voluntary contractions, factors other than changes in the wave form of individual muscle fiber action potentials must contribute to the observed shift in the total surface EMG frequency components.
Abstract: The relationship between the electromyographic (EMG) power spectrum and muscle conduction velocity was investigated during both fatiguing and nonfatiguing contractions of the adductor pollicis musc...
470 citations
TL;DR: There are very apparent breath-to-breath differences between the gas exchange measured by the two methods and the effect of inaccuracies due to errors in measuring gas flow or gas concentrations are similar in magnitude to those in the open-circuit method that has traditionally been used.
Abstract: A method has been developed for on-line breath-by-breath calculation of alveolar gas exchange by correcting the gas exchange measured at the mouth for changes in lung gas stores. The corrections ar...
463 citations
TL;DR: The finding suggests that the major factor responsible for the lower VO2max of the masters athletes, compared with the young athletes, is their slower heart rate.
Abstract: Sixteen highly trained masters endurance athletes, 59 +/- 6 yr, were compared with 16 young athletes, with whom they were matched on the basis of their training regimens, and with 18 untrained middle-aged men. On echocardiographic evaluation, both groups of athletes had a significantly greater left ventricular volume and mass than the untrained men; their were no significant differences in percent fiber shortening or velocity of fiber shortening among the three groups. Maximum O2 uptake (VO2max) averaged 15% less in the masters than in the young athletes (58.7 vs. 69 ml.kg-1.min-1). When expressed in terms of lean body mass to correct for differences in body fat content, VO2max of the masters athletes was about 60% higher than that of the middle-aged untrained men. Maximum heart rate was 14% lower in the masters athletes than in the young athletes (169 vs. 197 beats/min). The O2 pulse during maximum exercise (i.e., VO2max/heart rate at VO2max) was identical in the masters and young athletes. This finding suggests that the major factor responsible for the lower VO2max of the masters athletes, compared with the young athletes, is their slower heart rate.
444 citations
TL;DR: A simple one-step procedure that eliminates the need to calibrate the O2 analyzer or measure the flow past the animal is described for calibrating an open-flow respirometry system.
Abstract: A simple one-step procedure that eliminates the need to calibrate the O2 analyzer or measure the flow past the animal is described for calibrating an open-flow respirometry system. The technique is particularly useful for situations of high ambient humidity and for large or active animals where a mask is employed to capture expired gases. A measured N2 flow is used to calibrate the system. The equations describing the technique are given, and the accuracy of the method is discussed in detail. The errors associated with the technique are compared with those of more conventional procedures and are usually smaller.
340 citations
TL;DR: Differences in exercise did not significantly affect the relation between the time constant of the mean power frequency decrease and the endurance time, and the development of muscle fatigue was well correlated to change of the myoelectric rootmean-square amplitude and themean power frequency.
Abstract: In nine male volunteers, the endurance time for sustained isometric exercise (right-angle elbow flexion) and dynamic exercise (continuous concentric and eccentric elbow flexions) was measured at di...
327 citations
TL;DR: The findings reveal the existence of an intrinsic means of regulating bronchomotor toe by active changes in lung volume and that such a mechanism is impaired in asthma, and suggest that airway hyperactivity in asthma is perhaps less a reflection of enhanced end-organ responsiveness than a reflect of this impaired capacity.
Abstract: We examined the effects of lung inflation on induced airway obstruction in 14 atopic asthmatic and 14 atopic nonasthmatic subjects. Subjects were challenged with aerosols of methacholine (MCh) and pollen antigen (Ag), and the effects of inflation were assessed with partial ad full flow-volume curves and by comparing airway conductance measurements before and after deep inspiration to total lung capacity (TLC). Whereas bronchoconstriction was transiently abolished or reduced with inspiration in nonasthmatics, these effects were absent or diminished in asthmatic subjects. Dissimilarities could not be explained by differences in base-line lung function or degree of obstruction produced. Deep inspiration had a greater effect in reducing airway obstruction produced with MCh than with Ag in nonasthmatics. In addition, atropine pretreatment had no effect on inspiration responses in asthmatics given Ag, suggesting that vagal reflexes were not the cause of an impaired ability to reduce bronchomotor tone by lung inflation. Our findings reveal the existence of an intrinsic means of regulating bronchomotor toe by active changes in lung volume and that such a mechanism is impaired in asthma. We suggest that airway hyperactivity in asthma is perhaps less a reflection of enhanced end-organ responsiveness than a reflection of this impaired capacity.
302 citations
TL;DR: It is concluded that the ventilatory failure of cardiogenic shock is due to an impairment of the contractile process of the respiratory muscles, which avoids respiratory failure and prolongs survival, which may bear important therapeutic implications.
Abstract: The effect of cardiogenic shock (tamponade) on respiratory muscles performance was studied in 13 dogs breathing spontaneously. These 13 dogs were compared with 7 dogs artificially ventilated and paralyzed. Cardiac output amounted in both groups to 25-35% of the control value and was maintained constant. None of the dogs were hypoxic. All the spontaneously breathing dogs died on the average 140 +/- 15 min after the onset of cardiogenic shock, whereas the seven dogs artificially ventilated were all alive after 3 h and then killed. Death in the spontaneously breathing dogs was secondary to respiratory failure. Transdiaphragmatic pressure increased during the 1st h by 152 +/- 25% of control and then decreased by 286 +/- 18% in relation to the peak value before the death of the animals. No major changes in the mechanical properties of the respiratory system occurred. The decrease in transdiaphragmatic pressure occurred despite a marked increase per breath in the amplitude of the integrated electrical activity of the diaphragm and of the phrenic nerve. It is concluded that the ventilatory failure of cardiogenic shock is due to an impairment of the contractile process of the respiratory muscles. Artificial ventilation avoids respiratory failure and prolongs survival, which may bear important therapeutic implications.
299 citations
TL;DR: The data suggest type II fiber hypertrophy to be a plausible mechanism for the nonspecific improvement of the fast group; however, a neurological adaptation that enhances power at and below the training velocity cannot be excluded.
Abstract: College age males performed maximal two-legged isokinetic knee extensions three times per week for 6 wk at either 60 degrees/s (slow) or 300 degrees/s (fast) or both 60 and 300 degrees/s (mixed). The velocity specific and action specific (two-leg vs. one leg) improvements in peak torque (PT) were compared to a placebo group receiving low-level muscle stimulation. The slow group improved PT significantly (P less than 0.05) more than the placebo group only at its training velocity (60 degrees/s) and more so when the specific two-legged training action was mimicked (+32% with two legs vs. +19% with one leg). The mixed group enhanced PT by 24 and 16% at their respective training velocities of 60 and 300 degrees/s. These improvements were significantly larger than placebo and also significantly larger than the 9% improvement observed at the midvelocity of 180 degrees/s. The training specificity demonstrated by the slow and mixed groups suggest that neural mechanisms contributed to their improvements in power. This is supported by their unchanging muscle morphology. Training solely at 300 degrees/s (fast) however improved PT significantly more than placebo not only at the training velocity (+18%), but also at a slower velocity of 180 degrees/s (+17%). The fast group demonstrated a significant enlargement (+11%) of type II muscle fibers. These data suggest type II fiber hypertrophy to be a plausible mechanism for the nonspecific improvement of the fast group; however, a neurological adaptation that enhances power at and below the training velocity cannot be excluded.
297 citations
TL;DR: The effect of sleep state on ventilation and the mechanics of breathing was studied in nine normal adolescents by use of a respiratory inductive plethysmograph and surface electromyogram electrodes.
Abstract: The effect of sleep state on ventilation and the mechanics of breathing was studied in nine normal adolescents by use of a respiratory inductive plethysmograph and surface electromyogram electrodes. Minute ventilation was state dependent (P less than 0.01), decreasing by a mean of 8% from wakefulness to nonrapid-eye-movement (NREM) sleep and increasing 4% from NREM to rapid-eye-movement (REM) sleep. These changes were caused by changes in respiratory rate. Tidal volume (VT) was not affected by sleep state (P greater than 0.10). The pattern of breathing during wakefulness was similar to that of REM sleep. During NREM sleep intercostal and diaphragmatic muscle activity increased by a mean of 34% and 11%, respectively, as compared with wakefulness, indicating an increase in the respiratory work load. This was accompanied by a substantial increase in rib cage contribution to VT. REM sleep was associated with a marked decrease in intercostal muscle activity (P less than 0.05) and a diminished rib cage contribution; VT was maintained due to a mean increase of 34% in diaphragmatic muscle activity (P less than 0.05).
TL;DR: The position assumed by the ankle joint at rest depended on whether the subject was sitting, standing, or lying, but was always greater, in the plantarflexed direction, than the "optimum" position for torque development.
Abstract: A method is described for investigating the contractile properties of the dorsiflexor muscles of the ankle. With the joint in the midposition the tibialis anterior was found to contribute less than half of the maximum voluntary torque, the remainder presumably being provided by the long extensors of the toes. The mean contraction and half-relaxation times of tibialis anterior muscles in healthy young men were 81.2 +/- 7.4 (SD) ms and 83.6 +/- 17.2 ms, respectively. When the tibialis anterior was stretched, the twitch became slower and more complete fusion of the contractions occurred during tetanic stimulation at low frequencies. Stimulation of tibialis anterior at 30 and 40 Hz disclosed that the optimum length of the muscle corresponded to about 10 degrees of plantarflexion. Maximum voluntary torque was also developed at 10 degrees of plantarflexion and decreased sharply as the ankle was dorsiflex beyond 5 degrees. The position assumed by the ankle joint at rest depended on whether the subject was sitting, standing, or lying, but was always greater, in the plantarflexed direction, than the "optimum" position for torque development. At low rates of stimulation the torque continued to increase throughout the full range of plantarflexion, probably because of the elasticity of the tendon. During maximum effort motoneuronal excitability did not appear to be influenced significantly by changes in joint angle.
TL;DR: Both the body fluid and sweating responses during hypovolemia act to conserve circulating blood volume during exercise, and blood volume reduction significantly altered the control of sweating rate independent of changes in plasma osmolality.
Abstract: Five relatively fit men performed cycle ergometer exercise (65–70% VO2max) for up to 30 min at 30 degrees C, 40% rh. The data from control (normo-volemic), hypovolemic [8.7% reduction in blood volu...
TL;DR: The changes seen in the leveling-off phenomenon suggest that training at 1.68 rad .
Abstract: Seventeen male and female subjects (ages 20–38 yr) were tested pre- and posttraining for maximal knee extension torque at seven specific velocities (0, 0.84, 1.68, 2.51, 3.35, 4.19, and 5.03 rad . ...
TL;DR: Force exerted and power generated were measured during short-term exercise performed on a bicycle ergometer that had been modified by the addition of an electric motor driving the cranks at a chosen constant velocity to establish a parabolic function of crank velocity.
Abstract: Force exerted and power generated were measured during short-term exercise performed on a bicycle ergometer that had been modified by the addition of an electric motor driving the cranks at a chosen constant velocity. Five subjects made a series of 20-s maximum efforts at different crank velocities (range 23--171 rev/min). The forces exerted were continuously monitored with strain gauges bonded to the cranks. Peak force was exerted at approximately 90 degrees past top dead center in each revolution. During the 20-s effort peak force declined from the maximum level (PFmax) attained near the start of exercise, the rate of decline being velocity dependent. PFmax was found to be inversely and linearly related to crank velocity and when standardized for upper leg muscle (plus bone) volume (ULV) was given by PFmax (kgf/l ULV) = 27.51--0.125 crank velocity (rev/min). Integration of the force records with pedal velocity enabled power output to be calculated. Maximum power output was a parabolic function of crank velocity, the apex of the relationship indicating that the velocity for greatest power output was 110 rev/min. At this velocity our subjects achieved a maximum mean power output, averaged over a complete revolution, of 840 +/- 153 W (85 +/- 5 W/l ULV). This was compared with the calculated value for maximum mechanical power output from aerobic sources, which was 272 +/- 49 W (30 +/- 1 W/l ULV).
TL;DR: The hypothesis that with exercise, AVP release is a primary factor for fluid and electrolyte regulation as it is highly correlated with the plasma hyperosmolality produced by a net hypotonic plasma efflux is supported.
Abstract: Plasma volume (PV), renin activity (PRA), and osmotic (Osm), sodium (Na+), and arginine vasopressin (AVP) concentrations were measured in venous blood samples taken before and after three levels of cycle ergometer exercise (100, 175, and 225 W) in 15 young male volunteers. Plasma volume and solute concentrations changed significantly (P less than 0.05, denoted by *) with work intensity. The % delta PV was -3.7%* at 100 W, -8.8%* at 175 W, and -12.4%* at 225 W. Plasma Na+ concentration, Osm, and AVP increase were curvilinear with graded exercise and were significant only when work intensity exceeded 40% VO2max. PRA increase was linear and significant at all work levels. The % delta PV was significantly correlated with delta Osm (r = 0.99*) and delta Na+ (r = 0.89*) but had low correlations with delta AVP (r = 0.22, NS) and delta PRA (r = 0.12, NS). However, delta AVP was significantly correlated with delta Na+ (r = 0.86*) and delta Osm (r = 0.83*), whereas delta PRA had low correlations with delta Na+ (r = 0.33, NS), delta Osm (r = 0.29, NS), and delta AVP (r = 0.43, NS). The data support the hypothesis that a) with exercise, AVP release is a primary factor for fluid and electrolyte regulation as it is highly correlated with the plasma hyperosmolality produced by a net hypotonic plasma efflux; b) an exercise intensity greater than 40% VO2max is required to change plasma osmolality and, thus, stimulate significant AVP release; and c) the stimulation of the renin-angiotensin system is a more general stress response, which responds to increasing sympathetic nervous activity.
TL;DR: Data demonstrate that hypertrophy rather than hyperplasia was responsible for increases from 10 to over 100% in the weight of skeletal muscles.
Abstract: The effect of muscular enlargement produced by surgical ablation of a synergist and the combination of synergist ablation and exercise on the number of fibers in the soleus (S), plantaris (P), and extensor digitorum longus (EDL) muscles of the rat was studied. The number of fibers per muscle was determined by direct counts of individual fibers dissected from HNO3-treated muscles. Ablation of a synergist produced average enlargements of about 25, 45, and 29% for the S, P, and EDL muscles, respectively. Exercise and synergist ablation produced increases in wet weight to about 44 and 88% for the S and P muscles, respectively, whereas no further increases were observed in the EDL muscles. Intra-animal comparisons revealed that no differences existed for total fiber number or the incidence of fibers with bifurcations between the enlarged and contralateral control muscles. The difference in dry weight of fibers from the enlarged as compared with control muscles was closely correlated to differences in total muscle wet weight. These data demonstrate that hypertrophy rather than hyperplasia was responsible for increases from 10 to over 100% in the weight of skeletal muscles.
TL;DR: The luteal phase of the menstrual cycle induced increases in ventilatory drives and exercise ventilation in both athletes and controls, but the athletes, in contrast to controls, demonstrated no significant decrease in exercise performance in the lutenal phase.
Abstract: To investigate the influence of the midluteal and midfollicular phases of the menstrual cycle on exercise performance and ventilatory drives, we studied six outstanding female athletes, six controls with normal menstrual cycles, and six outstanding athletes who were amenorrheic. In all menstruating subjects resting minute ventilation (Ve) and mouth occlusion pressures (P0.1) were higher in the luteal phase (p less than k0.0001 and p less than 0.02, respectively),. Hypoxic (expressed as the hyperbolic shape parameter A) and hypercapnic (expressed as S, deltaVE/delta PAco2) ventilatory responses were increase in the luteal phase (p less than 0.01). The athletes had lower A values during the luteal phase than the nonathletes (p less than 0.001). Maximal exercise response, expressed either as total exercise time or maximum O2 consumption or CO2 production (VO2 max or Vco2 max) was decreased during the luteal phase but was significantly different at a p less than 0.05 level only among the nonathletes. Ventilatory equivalent (VE/VO2) during progressive exercise on a bicycle ergometer was significantly increased during the luteal phase. The amenorrheic athletes showed no changes between the two test periods. The luteal phase of the menstrual cycle induced increases in ventilatory drives and exercise ventilation in both athletes and controls, but the athletes, in contrast to controls, demonstrated no significant decrease in exercise performance in the luteal phase.
TL;DR: The increased rib cage motion characteristic of the upright posture owes to a combination of increased activation of rib cage inspiratory muscles plus greater activation of the diaphragm that, together with a stiffened abdomen, acts to move the rib cage more effectively.
Abstract: It is established that during tidal breathing the rib cage expands more than the abdomen in the upright posture, whereas the reverse is usually true in the supine posture. To explore the reasons for this, we studied nine normal subjects in the supine, standing, and sitting postures, measuring thoracoabdominal movement with magnetometers and respiratory muscle activity via integrated electromyograms. In eight of the subjects, gastric and esophageal pressures and diaphragmatic electromyograms via esophageal electrodes were also measured. In the upright postures, there was generally more phasic and tonic activity in the scalene, sternocleidomastoid, and parasternal intercostal muscles. The diaphragm showed more phasic (but not more tonic) activity in the upright postures, and the abdominal oblique muscle showed more tonic (but not phasic) activity in the standing posture. Relative to the esophageal pressure change with inspiration, the inspiratory gastric pressure change was greater in the upright than in the supine posture. We conclude that the increased rib cage motion characteristic of the upright posture owes to a combination of increased activation of rib cage inspiratory muscles plus greater activation of the diaphragm that, together with a stiffened abdomen, acts to move the rib cage more effectively.
TL;DR: The quadratic relationships evident after corrections were made for the additional work needed to move the legs more frequently may be explained at the lower pedaling rates by a less uniform pattern of blood flow caused by increasing the force requirement per pedal stroke and, at the higher pedal frequencies, by the recruitment of additional musculature to stabilize the trunk.
Abstract: This investigation was undertaken to determine the effect of pedal frequency on submaximal exercise responses. Seven well-trained competitive cyclists were studied riding their road-racing bicycles on a motor-driven treadmill at 80% of maximum O2 consumption (VO2 max) using different gear ratios. Cyclists were also studied during a series of unloaded trials to assess the effects of varying rates of limb movements independent of external work load. Heart rate (HR) increased, whereas net HR (after subtracting the HR during unloaded cycling) decreased with increasing pedal frequency during loaded cycling. Expiratory flow (VE), O2 consumption (VO2), blood lactate, net VO2 (after subtracting the VO2 of unloaded cycling), and net VE (after subtracting the VE during unloaded cycling) were quadratically related to pedal frequency. The quadratic relationships evident after corrections were made for the additional work needed to move the legs more frequently may be explained at the lower pedaling rates by a less uniform pattern of blood flow caused by increasing the force requirement per pedal stroke and, at the higher pedal frequencies, by the recruitment of additional musculature to stabilize the trunk. The average of preferred frequency for the group, which was also the most economical pedaling rate judged by most of the variables was 91 rpm, although the preferred pedaling rate for each subject ranged from 72 to 102 rpm.
TL;DR: It is suggested that this long-lasting element of fatigue might occur in patients with chronic obstructive lung disease, predisposing them to respiratory failure and that diaphragmatic strength after fatigue recovers faster at high than at low frequencies of stimulation.
Abstract: Transdiaphragmatic pressure (Pdi) was measured at functional residual capacity (FRC) in four normal seated subjects during supramaximal, supraclavicular transcutaneous stimulation of one phrenic nerve (10, 20, 50, and 100 Hz--0.1 ms duration) before and after diaphragmatic fatigue, produced by breathing through a high alinear inspiratory resistance. Constancy of chest wall configuration was achieved by placing a cast around the abdomen and the lower one-fourth of the rib cage. Pdi increased with frequency of stimulation, so that at 10, 20, and 50 Hz, the Pdi generated was 32 +/- 4 (SE), 70 +/- 3, and 98 +/- 2% of Pdi at 100 Hz, respectively. After diaphragmatic fatigue, Pdi was less than control at all frequencies of stimulation. Recovery for high stimulation frequencies was complete at 10 min, but at low stimulation frequencies recovery was slow: after 30 min of recovery, Pdi at 20 Hz was 31 +/- 7% of the control value. It is concluded that diaphragmatic fatigue can be detected in man by transcutaneous stimulation of the phrenic nerve and that diaphragmatic strength after fatigue recovers faster at high than at low frequencies of stimulation. Furthermore, it is suggested that this long-lasting element of fatigue might occur in patients with chronic obstructive lung disease, predisposing them to respiratory failure.
TL;DR: Breath sounds picked up over the trachea were characterized by power spectra typical to a broad spectrum sound with a sharp decrease of power at a cut-off frequency that varied between 850 and 1,600 Hz among the 10 healthy subjects studied.
Abstract: An objective and accurate measurement and characterization of breath sounds was carried out by a fast-Fourier-transform frequency-domain analysis. Normal vesicular breath sounds, picked up over the chest wall of 10 healthy subjects showed a characteristic pattern: the power of the signal decreased exponentially as frequency increased. Since the log amplitude vs. log frequency relationships were linear, they could be characterized by the values of the slope and the maximal frequency. The average slope of the power spectrum curves was found to be (in dB/oct +/- SD) 13.0 +/- 1.4 over the base of the right lung, 12.6 +/- 2.4 over the base of the left lung, 9.8 +/- 1.4 over the interscapular region, and 14.4 +/- 4.3 over the right anterior chest. The maximal frequencies of inspiratory and expiratory breath sounds, picked up over the base of the right lung, were (in Hz +/- SD) 446 +/- 143 and 286 +/- 53 (P less than 0.01), over the base of the left lung 475 +/- 115 and 284 +/- 47 (P less than 0.01), over the interscapular region 434 +/- 130 and 338 +/- 77 (P less than 0.05), and over the right anterior chest 604 +/- 302 and 406 +/- 205 (P less than 0.05). Breath sounds picked up over the trachea were characterized by power spectra typical to a broad spectrum sound with a sharp decrease of power at a cut-off frequency that varied between 850 and 1,600 Hz among the 10 healthy subjects studied.
TL;DR: The data indicate that in humans both diaphragm and genioglossus muscle share similar control mechanisms and suggest that upper airway function is intimately related to the regulation of breathing.
Abstract: To assess the relationship between central control of upper airway and respiratory muscle, simultaneously recorded diaphragmatic electromyogram (EMGdi) and genioglossal EMG (EMG ge) responses to CO2 rebreathing were compared in five supine volunteers. Both EMGs were quantitated in terms of inspiratory peak moving time-average activity. In all subjects both EMGdi and EMGge increased linearly with increasing alveolar CO2 pressure (r = 0.93 +/- 0.04 and 0.87 +/- 0.07, respectively), resulting in a significantly linear EMGge vs. EMGdi relationship (r = 0.91 +/- 0.04). CO2 response slopes of both EMGs were similar and linearly related (r = 0.96, P less than 0.001) such that subjects with low EMGdi response also had a low EMGge response and vice versa. Although the onset of EMGge activity preceded that of EMGdi, and the pattern of both EMGs were different, inspiration duration of both EMGs were similar. These data indicate that in humans both diaphragm and genioglossus muscle share similar control mechanisms and suggest that upper airway function is intimately related to the regulation of breathing.
TL;DR: While aerobic performance and the cardiorespiratory adaptations to exercise are not influenced by the phase of the menstrual cycle, performance of high-intensity exercise is improved, and lactate production appears to be decreased in the luteal phase when estradiol and progesterone levels are elevated.
Abstract: The effects of the menstrual cycle on cardiorespiratory variables, blood lactate, and performance were studied in exercising females. Nine healthy subjects, 20--24 yr of age, were investigated in midfollicular and midluteal phases of the menstrual cycle at 33, 66, and 90% of maximum power output (light, heavy, and exhaustive exercise). Occurrence of ovulation was confirmed in all subjects by measurement of progesterone, which increased from 0.6 +/- 0.1 (mean +/- SE) in the follicular to 8.9 +/- 2.2 ng/ml in the luteal phase. There was no difference in heart rate (HR), ventilation, O2 uptake, or CO2 output between the two phases during light and heavy exercise, and there was no difference in HR at exhaustion. Cardiac output measured midway through light and heavy exercise periods was not affected by the phase of testing. Time for which exhaustive exercise could be maintained increased from 1.57 +/- 0.32 in the follicular to 2.97 +/- 0.63 min in the luteal phase (P less than 0.02). Blood lactate was higher in the follicular phase after heavy exercise (6.62 +/- 0.8 vs. 4.92 +/- 0.5 mmol/l) (P less than 0.05) and at exhaustion (8.12 +/- 0.9 vs. 6.76 +/- 0.6 mmol/L) (P less than 0.01). A further study showed no effect of cycle phase on lactate disappearance during exercise. We conclude that while aerobic performance and the cardiorespiratory adaptations to exercise are not influenced by the phase of the menstrual cycle, performance of high-intensity exercise is improved, and lactate production appears to be decreased in the luteal phase when estradiol and progesterone levels are elevated.
TL;DR: Spontaneous nonfeeding swallows taken during wakefulness and sleep were identified in nine preterm infants by characteristic patterns in pharyngeal pressure, submental electromyogram, and respiratory airflow.
Abstract: Spontaneous nonfeeding swallows taken during wakefulness and sleep were identified in nine preterm infants by characteristic patterns in pharyngeal pressure, submental electromyogram, and respiratory airflow. Two hundred and seventeen swallows during ongoing respiration interrupted either inspiratory or expiratory airflow with airway closure for approximately 1 s. The duration of airway closure was independent of respiratory rate. A brief "swallow-breath" was associated with swallow onset in most instances. The respiratory nature of this movement was confirmed by simultaneous recording of a fall in pharyngeal or esophageal pressure and outward movement of the abdomen. Prolongation of the respiratory cycle was generally observed when a swallow interrupted ventilation at higher lung volumes, i.e., in late inspiration or early expiration. When the swallow interrupted ventilation at lower lung volume, i.e, in late expiration or early inspiration, the subsequent inspiratory effort was usually obstructed as it preceded airway opening at the end of the swallow synergism.
TL;DR: Results from the present study show that the sympathetic nervous activity is closely linked to the exercise demands and confirm earlier suggestions that it remains constant in relation to the relative work load.
Abstract: Plasma norepinephrine (NE) concentration was measured by means of a sensitive radioenzymatic assay in blood collected from an antecubital vein in 10 healthy male subjects (37 +/- 2 yr, mean +/- SE). The subjects were evaluated at rest and during exercise before and after a 20-wk training program on bicycle ergometer (three 30-min sessions per week at 80% of maximal heart rate). Following the training program, maximal oxygen uptake increased significantly from 33 +/- 2 to 42 +/- 1 ml . kg-1 . min-1. Resting plasma NE remained unchanged after training (167 +/- 38 before and 185 +/- 29 pg . ml-1 after training). For a given absolute work load (735 +/- 51 kg . m. min-1) the sympathetic nervous response was lower after training as reflected by the decrease in NE concentration (1,371 +/- 286 vs. 687 +/- 64 pg . ml-1). At the same relative work load (heart rate: 158 +/- 5 before and 157 +/- 5 beats . min-1 after training) plasma NE concentration was unchanged after training (1,371 +/- 286 vs. 1,729 +/0 371 pg . ml-1). Results from the present study show that the sympathetic nervous activity is closely linked to the exercise demands and confirm earlier suggestions that it remains constant in relation to the relative work load.
TL;DR: The feasibility of using the thermodilution method to monitor cardiac output during artificial ventilation was studied in anesthetized pigs and a satisfactory moment of injection for estimation of mean cardiac output appeared to be at the end of the spontaneous expiration.
Abstract: The feasibility of using the thermodilution method to monitor cardiac output during artificial ventilation was studied in anesthetized pigs. Normal saline (0.5 ml) at room temperature was injected into the left ventricle or the right atrium. The dilution curves were detected in the aortic arch and the pulmonary artery, respectively. The ventilation rate was 10 cycles/min at end-expiratory pressures of 0, 5, 10, and 15 cmH2O. For each level, 50 measurements of cardiac output were performed at regular intervals over the ventilatory cycle. The order of measurements were randomly selected. The average of each series of 50 measurements showed excellent correlation with the estimates of cardiac output based on the direct Fick method for oxygen. The maximum difference between the values of cardiac output randomly measured by the thermodilution method was 40% for the left side of the heart and 70% for the right side. However, when the values of cardiac output were sorted according to the specific phases of the respiratory cycle, there was a systematic variation with a small random error. For the left side of the heart, a satisfactory moment of injection for estimation of mean cardiac output appeared to be at the end of the spontaneous expiration. On the other hand, the analysis of cardiac output values at the right side did not reveal any satisfactory moment for injectate administration under changing circumstances, e.g., positive end-expiratory pressure.
TL;DR: The ability to estimate muscle mass conveniently and accurately from total plasma creatinine should prove valuable for future studies in physiology and body composition.
Abstract: Creatinine is a metabolite unique to striated muscle. Measurement of 24-h urinary creatinine excretion is an established method for estimating striated muscle mass. However, accurate assessment of ...
TL;DR: The determination of oxygen consumption (VO2) results in a considerable amplification of random measurement error, which becomes larger as the inspired oxygen fraction (FIO2) is made larger.
Abstract: On-line gas exchange monitors have been based on the measurement of both inspired and expired flows (method A) or on the measurement of expired flow only (method B). In both methods, the cancellati...
TL;DR: The faster rise in aortic flow in U with exercise represented an additional volume of blood passing through the aorta compared with S in the first 20s, which must be related to the rapid mobilization of pooled venous blood from the leg veins during U.
Abstract: A 3.0 MHz pulsed Doppler echocardiography was used to estimate instantaneous stroke volume (SV) and cardiac output (Q) in eight men during steady-state supine (S) and upright (U) exercise at 300 kpm/min. The mean transients in heart rate (HR), SV, and Q for the first 20 s of exercise in each posture were then determined. Center-line blood velocities were obtained in the ascending aorta with the transducer positioned manually in the suprasternal notch. Mean supine values for SV and Q at rest and exercise were 111 ml and 6.4 1/min and 112 ml and 9.71/min, respectively. The corresponding results for U were 76 ml and 5.61/min and 92 ml and 8.41/min, respectively. These values compare favorably with previous studies utilizing invasive procedures. The transient response of Q following the onset of exercise in U was about twice as fast as in S because of the rapid and almost immediate upsurge in SV. In S, only HR served to augment Q, as SV initially fell. The faster rise in aortic flow in U with exercise represented an additional volume (184 ml) of blood passing through the aorta compared with S in the first 20s. This must be related to the rapid mobilization of pooled venous blood from the leg veins during U.