Changes of ventilation and ventilatory response to hypoxia during the menstrual cycle

The relationship between change in hypoxic sensitivity in respiration, defined as increment in ventilation per drop of arterial O₂ saturation , with the phase change from follicular to luteal and those in resting pulmonary ventilation , mean inspiratory flow (V _T/T _I), alveolar partial pressures of CO₂ and O₂ ( and , respectively) and body temperature was studied in 10 women. There was a significant relationship between % increase in hypoxic sensitivity and decrement of resting that occurred in the luteal phase. However, no significant relationships were observed between change in hypoxic sensitivity and those in the remaining parameters studied. The intersubject variation in % increase in resting during the luteal phase was not associated with that in % increase in hypoxic sensitivity. The results indicate that the contribution of increased hypoxic sensitivity to increasing during the luteal phase is variable among subjects. Reasons for the increase in hypoxic sensitivity with hypocapnia are discussed.     

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.     

Central hypoxic-hypercapnic interaction in mild hypoxia in man

Hypoxic-hypercapnic interaction in mild hypoxia was studied in 12 healthy males. Steady state ventilatory responses to hypercapnic-hypoxia were obtained as the difference in ventilation between hypoxia (mean values ± S.D. of =7.36±0.20 kPa or of 7.10 ±0.41 kPa) and hyperoxia ( >26.7 kPa) with the same degree of hypercapnia ( 6.12±0.22 kPa). On the other band, withdrawal responses were obtained as the magnitude of depression in ventilation caused by two bicaths of O₂ from the above mentioned hypoxic hypercapnia. Averaged and were 9.57±5.45 and 6.45 ±4.90l/min, respectively, the difference being statistically significant (P<0.01). Furthermore, if we assume the presence of ventilatory depression to be due to tissue fall resulting from an increase in cerebral blood flow caused by hypoxia, the magnitude of central hypoxic-hypercapnic interaction was estimated to be as great as the value of .     

Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold

Summary Anaerobic threshold has been defined as the oxygen uptake ( ) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (AT_La), (2) systematic increase in ventilatory equivalent for O₂ with no change in the ventilatory equivalent for CO₂ ( ), and (3) non-linear increase in expired ventilation graphed as a function of ( ). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same as the AT_La. The highest correlation between a gas exchange anaerobic threshold and AT_La was found for and was r=0.63 (P<0.05). These data provide evidence that the AT_La and do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the AT_la.     

Ventilatory response during incremental exercise tests in weight lifters and endurance cyclists

Summary The effect of a progressively increasing work rate (15 W·min^–1) up to exhaustion on the time course of O₂ uptake ( ), ventilation ( ) and heart rate (HR) has been studied in weight lifters (WL) in comparison to endurance cyclists (Cycl) and sedentary controls (Sed). and were measured as average value of 30-s intervals by a semiautomatic open circuit method. was 2.55±0.33; 4.29±0.53 and 2.86±0.19·min^–1 in WL, Cycl and Sed respectively. With time and work rate, while and HR increased linearly, changed its slope at two levels. The 1st change occured at a work load corresponding to a mean (± SD) of 1.50±0.26; 1.93±0.34; and 1.23±0.14 l·min^–1 in WL, Cycl, and Sed respectively. values corresponding to the second change of slope were 2.18±0.32 in WL; 3.48±0.53 in Cycl and 2.17±0.28 l·min^–1 in Sed. The first change of slope might be the consequence of the different readjustment of on-response and hence of early lactate in the different subjects. The second change seems to be comparable to the conventional anaerobic threshold and is achieved in all subjects when vs time slope is 7–10 l·min^–1/min of exercise.This work has been supported in part by a grant from the Italian National Research Council (CNR)     

Some simple multiple linear regression equations for estimation of maximal aerobic power in healthy indian males

Summary An attempt has been made to evolve some simple multiple linear regression equations for the prediction of max from body weight, time for 3.2 km run and exercise dyspnoeic index (DI_std Ex%). The predictor variables have been selected by examining the product moment correlations of body weight, relative body weight indices, time for 3.2 km run, chest expansion, height, and DI_std Ex% with max, based on data collected on 320 healthy Indian males (17–22 years). It has been observed that body weight, time for 3.2 km run and DI_std Ex% attained maximum correlations with max. Thus, two regression equations with two and three predictor variables have been established in this paper to predict max. The first regression equation yielded a multiple correlation of 0.608 (P<0.001) with a standard error of 0.214 l·min^–1. In this equation, body weight and time for 3.2 km run were considered as significant predictors. To increase the precision of this equation, another multiple linear regression equation based on body weight, time for 3.2 km run and DI_std Ex% as predictors has been developed. This equation yielded a multiple correlation of 0.658 (P<0.001) with a standard error of 0.204 l·min^–1. Applications of these regression equations will be of practical importance to biomedical scientists engaged in the development of a simple procedure for indirect assessment of max, and may serve well as preliminary screening procedures for personnel selection.     

Respiratory frequency and the oxygen cost of exercise

Summary Although many studies indicate that the spontaneous breathing frequency minimizes breathing work, the consequences of this for exercise energetics have never been investigated. To see if the spontaneous exercise breathing frequency minimizes oxygen uptake, we compared during treadmill walking (2/3 max) at several alternative frequencies. The alternative frequencies ranged from the lowest sustainable to a frequency twice the spontaneous value. All eight subjects adjusted tidal volume to comfort. Exercise oxygen uptake was constant, independent of breathing frequency. At the same time, minute ventilation rose to be 65% greater at the highest frequency than at the lowest (P<0.01). We then reproduced the various exercise frequencies, tidal volumes, and ventilations during seated isocapnic hyperpnea to measure with locomotory muscles at rest. Once again, oxygen uptake was constant, independent of breathing frequency. We conclude that the spontaneous exercise breathing frequency fails to minimize during either exercise or resting reproduction of exercise ventilation.Supported in part by NIH Grant HL 26351     

Maximum oxygen uptake in healthy nonathletic males

Summary Maximum oxygen uptake ( max), maximum heart rate (MHR), blood lactic acid (LA) and pH were measured during bicycle ergometer exercise in 52 men, 22 to 60 years old, engaged in clerical and light manual work (prison personnel and prisoners in the Netherlands). max decreases with, age, but less than expected from previous studies in which the data on young subjects were probably biased in favor of well-trained individuals. The data provide provisional standard values for max in healthy untrained males, derived from a population in which physical activity was similar irrespective of age. MHR and LA decrease significantly with age after elimination of as a variable. In 20 subjects, max was measured with the steady-state method and with a single increasing load test; the differences were small for practical purposes. The increasing load method is useful to estimate aerobic capacity in a single test, even in subjects unaccustomed to exercise tests.This study was supported, in part, by a grant from the Medical Research Committee of the American Thoracic Society, the Medical Division of the National Tuberculosis Association.     

Metabolic responses to light arm and leg exercise when sitting

Summary Seven male subjects performed progressive exercises with a light work load on an upper limb or bicycle ergometer in the sitting position. At any comparable work load above zero, arm exercise induced higher oxygen uptake, ventilation, heart rate, oxygen pulse, respiratory rate and tidal volume than leg exercise. At similar levels of above 0.45 1 · min^–1, heart rate and ventilation were higher during arm exercise. A close linear relationship between carbon dioxide output and oxygen uptake was observed during both arm and leg exercises, the slope for arm work being steeper. The ventilatory equivalent for gradually decreased during both types of exercise. The ventilatory equivalent for remained constant (arm) while it rose (leg) to a peak at 9.8 W and then gradually decreased. Ventilation in relation to tidal volume had a linear relationship with leg exercise, but became curvilinear with arm exercise after tidal volume exceeded 1100ml. The observed differences in response between arm and leg exercises at a given work load appear to be influenced by differences in sympathetic outflow due to the greater level of static contraction of the relatively small muscle groups required by arm exercise.     

Effect of glucose polymer diet supplement on responses to prolonged successive swimming,cycling and running

Summary Fifteen male endurance athletes were studied to determine the effect of a glucose polymer (GP) diet supplement on physiological and perceptual responses to successive swimming, cycling and running exercise. Thirty min of swimming, cycling and running at 70% , followed by a run to exhaustion at 90% was performed after one week of training under two dietary conditions: 1) GP (230 g of GP consumed daily) and 2) placebo (P, saccharin-sweetened supplement consumed daily). During GP, daily carbohydrate (CHO) intake was higher (p<0.05) by 173 g or 14% of energy intake than during P, but total energy intake was not significantly different. During 90 min of exercise, CHO utilization and blood glucose were significantly higher under GP than P by an average of 20.2% and 14.5%, respectively, but heart rate, ventilation, oxygen uptake, ratings of perceived exertion, and plasma lactate were not different. Run time to exhaustion at 90% was significantly longer by 1.2 min (23%) under GP. The results suggest that a GP diet supplement may be of value during endurance exercise by increasing the availability of CHO.     

Effects of previous exercise on the ventilatory determination of the aerobic threshold

Summary To study the effects of previous submaximal exercise on the ventilatory determination of the Aerobic Threshold (AeT), 16 men were subjected to three maximal exercise tests (standard test = ST, retest = RT, and test with previous exercise = TPE) on a cycle ergometer. The protocol for the three tests consisted of 3 min pedalling against 25 W, followed by increments of 25 W every minute until volitional fatigue. TPE was preceded by 10 min cycling at a power output corresponding to the AeT as determined in ST, followed by a recovery period pedalling against 25 W until returned to values consistent with the initial response to 25 W. AeT was determined from the gas exchange curves (ventilatory equivalent for O₂, fraction of expired O₂, excess of , ventilation, and respiratory gas exchange ratio) printed every 30 s. The results showed good ST×RT reliability (r=0.89). TPE showed significantly higher AeT values (2.548±0.44 l·min^–1) when compared with ST (2.049±0.33 l·min^–1) and RT (2.083±0.30 l·min^–1). There were no significant differences for the sub-threshold respiratory gas exchange ratios among the trials. The sub-threshold response showed significantly higher values for TPE at power outputs above 50 W. It was concluded that the performance of previous exercise can increase the value for the ventilatory determination of the AeT due to a faster sub-threshold response.Supported by fellowship number 3660/80-3, CAPES, Brazil     

Ventilation studied with circulatory occlusion during two intensities of exercise

Summary Our purpose was to study the possible role of a pulmonary chemoreceptor in the control of ventilation during exercise. Respiratory gas exchange was measured breath-by-breath at two intensities of exercise with circulatory occlusion of the legs. Eight male subjects exercised on a cycle ergometer at 49 and 98 W for 12 min; circulation to the legs was occluded by thigh cuffs (26.7 kPa) for two min after six min of unoccluded exercise. PETCO₂ and decreased and PETO₂ increased significantly during occlusion at both workloads. Occlusion elicited marked hyperventilation, as evidenced by sharp increases in , and . A sudden sharp increase in PETCO₂ was seen 12.3±0.5 and 6.5±1.2 s after cuff release in all subjects during exercise at 49 and 98 W, respectively. At 49 W a post-occlusion inflection in was seen in 7 subjects 21.1±5.8 s after the PETCO₂ inflection. Three subjects showed an inflection in at 98 W 23.3±7.5 s after the PETCO₂ inflection. There were significant increases in PETCO₂, and after cuff release. mirrored better than , post occlusion. On the basis of a significant lag time between inflections in PETCO₂ and following cuff release, it is concluded that the influences of a pulmonary CO₂ receptor were not seen.     

Diffusion-limited gas mixing in the lung and its consequences for transpulmonary gas transport

The ratio of alveolar ventilations of He and SF₆ ( ) was determined in 7 healthy male subjects at rest and at three different levels of exercise on a bicycle ergometer (75, 150 and 225 W). This ratio was calculated from the ratio of the specific ventilations for these gases which were obtained from the decay of the end-tidal partial pressures of He and SF₆ during a simultaneous, multiple-breath washout. In all experiments, for He was larger than for SF₆. On the average, was equal to 1.09, and the mean values of this ratio at rest and at the three levels of exercise were not significantly different. Therefore, the difference in for He and SF₆ increased with increasing work load. Further, we used the mean value obtained for , to calculate the ratio of excretion values (E₁/E₂) for pairs of hypothetical tracer gases with equal blood-gas partition coefficients and with different diffusivities in the gas phase. E₁/E₂ ranged from anity for =0 to about 1.08 for =10. At a given , E₁/E₂ decreased with increasing ventilation-perfusion ratio of the lung. Thus, the difference between the excretion values of light and heavy tracer gases will be most pronounced under rest conditions and for gases that are well soluble in blood.     

Factors which alter the relationship between ventilation and carbon dioxide production during exercise in normal subjects

The slope of the linear relationship between ventilation and carbon dioxide production has been thought to indicate that is one of the major stimuli to . A group of 15 normal subjects undertook different incremental treadmill exercise protocols to explore the relationship between and . An incremental protocol using 1 instead of 3-min stages of exercise resulted in an increase in the to ratio [26.84 (SEM 1.23) vs 31.08 (SEM 1.36) (P < 0.008) for the first stage, 25.24 (SEM 0.86) vs 27.83 (SEM 0.91) (P < 0.005) for the second stage and 23.90 (SEM 0.86) vs 26.34 (SEM 0.81) (P = 0.001) for the third stage]. Voluntary hyperventilation to double the control level of during exercise resulted in an increase in the to slope [from 21.3 (SEM 0.71) for the control run to 35.1 (SEM 1.2) for the hyperventilation run (P < 0.001)]. Prolonged hyperventilation (5 min) during exercise at stage 2 of the Bruce protocol resulted in a continuted elevation of and the slope. A steady state of and metabolic gas exchange can only be said to have been present after at least 3 min of exercise. Voluntary hyperventilation increased the slope of the relationship between and . End-tidal carbon dioxide fell, but remained within the normal range. These results would suggest that a non-carbon dioxide factor may have been responsible for the increase we found in during exercise, and that factors other than increased dead space ventilation can cause an increased ventilation to slope, such as that seen in some pathophysiological conditions, such as chronic heart failure.     

Active sulfate reabsorption in the proximal convolution of the rat kidney: Specificity,Na+ and HCO 3 − dependence

Using the standing droplet technique in the proximal convolution and simultaneous microperfusion of the peritubular capillaries, the decrease in luminal sulfate concentration with time and the zero net flux transtubular concentration difference of sulfate ( ) at 45 s was determined — the latter being taken as a measure of the rate of active sulfate reabsorption. Starting with 0.5 mmol/l sulfate in both perfusates the value of 0.35 mmol/l was approached exponentially with a half value time of 4.3 s. The values in the early proximal and late proximal convolution did not deviate from each other. If the Na⁺ concentration in the perfusates was reduced, the approached zero and extrapolated to a slightly negative value (c _i>c _o). When 1 mmol/l ouabain was added to the perfusates decreased by 66% (the latter experiments were performed in the golden hamster which is more sensitive to ouabain than the rat). 1 mmol/l thiosulfate diminished by 68% and 1 mmol/l molybdate by 24%. Omitting or replacing bicarbonate by HEPES or glycodiazine reduced the sulfate reabsorption significantly, while acetazolamide (0.1 mmol/l) and increasing the CO₂-pressure from 4.66 to 14.0 kPa (i.e. 5–15% CO₂) had no effect. SITS 1 mmol/l had no effect on sulfate reabsorption.The data indicate that the sulfate reabsorption is driven by a Na⁺ gradient and inhibited by thiosulfate and molybdate, i.e. molecules which have a similar tetrahedral molecule structure. The sulfate reabsorption depends in an undefined manner on the presence of bicarbonate ions.     

Effect of training on the rating of perceived exertion at the ventilatory threshold

Summary The purpose of this study was to determine the effect of training on the rating of perceived exertion (RPE) at the ventilatory threshold. College students were assigned to either training (n=17) or control (n=10) groups. Trainers completed 18 interval training sessions (five × 5 min cycling at 90–100% ) and 8 continuous training sessions (40 min running or cycling) in 6 weeks. Pre- and post-training, cardiorespiratory, metabolic, and perceptual variables were measured at the ventilatory threshold during graded exercise tests on a cycle ergometer. Ventilatory threshold was that point above which increased abruptly relative to work rate. Post-training means of trained and control subjects were compared using analysis of covariance, with pre-training values as covariates. Following training, the adjusted means for the trained subjects were significantly greater (p<0.05) than for controls for (6%), and for work rate (20%), (23%), and % (13%) at the ventilatory threshold. However, adjusted means for RPE at the ventilatory threshold were not significantly different (2%). Both before and after training, exercise at the ventilatory threshold was perceived as somewhat hard to hard (RPE=13–15) by both groups. The relationship between RPE and % was altered by training, with trained subjects having a lower RPE at a given % . It is concluded that RPE at the ventilatory threshold is not affected by training, despite that after training the ventilatory threshold occurs at a higher work rate and is associated with higher absolute and relative metabolic and cardiorespiratory demands.     

Relationship between plasma renin activity and physical fitness in normal subjects

Summary The relationship between plasma renin activity (PRA) at rest and physical fitness was studied in 40 normal young subjects on a liberal sodium intake.Plasma renin activity was measured in arterial blood withdrawn at the end of a 30-min period of rest in recumbency, while physical fitness was expressed by the highest oxygen uptake achieved during an uninterrupted graded exercise test performed in the sitting position on an electromagnetically braked ergometer bicycle (peak ).Log PRA correlated significantly and inversely with peak adjusted for body weight (r=–0.34; P<0.05) in single regression analysis. Using multiple regression analysis with log PRA as dependent variable and adjusted peak , age, urinary sodium excretion and mean intra-arterial pressure as independent variables, no combination of two or more independent variables yielded significant partial correlation coefficients with log PRA.This correlation suggests that PRA at rest is inversely related to the subject's physical fitness.     

Energy sources in alpine skiing (giant slalom)

Summary The energy cost of a giant slalom event was measured in eight skiers of national level. The lap lasted on average 82 s. was measured during the first, the second and the last third of the lap in different trials and also during recovery from a complete lap. Blood lactate was measured at the end of a lap. From the data obtained it was possible to calculate that: a) , as measured during the lap, would correspond at steady state to 80% of the of the subjects; b) the total metabolic power delivered during the lap should be equal to about 72ml O₂·kg^–1·min^–1, corresponding to 120% of of the subjects. Considering the short duration of the trial and the power output delivered during maximal efforts on a bicycle ergometer, it appears that the giant slalom is not a very high energy demanding event.Preliminary results of this work have been presented at the XXII. World Congress on Sport Medicine, Vienna 1982     

Effect of lung resection on blood lactate threshold in lung cancer patients

Summary We studied the effect of a decrease in vital capacity (VC) on the blood lactate threshold detected during exercise in 16 preoperative (PRE) and 10 postoperative (POST) lung cancer patients who had undergone lobectomy or pneumonectomy. The PRE patients were selected on the basis of having normal preoperative pulmonary function. The POST patients were selected on the basis of having normal preoperative pulmonary function and a postoperative VC of less than 80%. The oxygen consumption/body surface area at a 2.2 m.mol·l^–1 arterial lactate concentration ( / BSA at La-2.2) was adopted as the blood lactate threshold. VC/BSA in the POST group significantly correlated with /BSA at La-2.2 (r=0.85, P<0.01), but not in the PRE group. SaO₂ at La-2.2 was 95.4+-1.5% in the PRE group and 95.2+-1.3% in the POST group. SaO₂ at La-2.2 did not correlate with VC/BSA in either group. The hemoglobin concentration (Hb) in the arterial blood correlated significantly with VC/BSA in the POST group (r= 0.65, P< 0.05) but not in the PRE group. These results indicate that /BSA at La-2.2 was restricted by VC in patients with restrictive pulmonary function disorder. Of the three elements of oxygen delivery, Hb was a limiting factor for /BSA at La-2.2 but SaO₂ was not. Cardiac output, which was not measured in our study, was speculated to be another limiting factor for _388-05 at La-2.2     

Cardiorespiratory and metabolic adaptations to hyperoxic training

This study examined the effects of hyperoxic training on specific cardiorespiratory and metabolic responses. A group of 19 male subjects trained for 5 weeks on a cycle ergometer at 70% of hyperoxic or normoxic maximal heart rate, the hyperoxic group (HG) breathing 70% O₂, the normoxic group (NG) breathing 21% O₂. The subjects were tested pre- and post-training under both hyperoxia and normoxia. Measurements included cardiac output , stroke volume (SV), heart rate (HR), pulmonary ventilation , oxygen consumption , partial pressure of oxygen (PO₂), partial pressure of inspired carbon dioxide (PCO₂), blood lactate concentration [L], and fiber type composition. The was significantly lower at submaximal work rates (P < 0.05) and maximal increased after training in both groups for both test conditions; hyperoxic was lower than normoxic (P < 0.05). The maximal increased significantly (P < 0.05) in both groups for both tests and was 11%–12% higher during hyperoxia. Post-training maximal heart rate (HR_max) was significantly decreased (P < 0.05) at the same absolute work rate regardless of the training group or test type. The SV was increased at each work rate and was unchanged. The maximal increased significantly (P < 0.05) for both groups and types of test: for normoxia: NG 27.3–30.4 l · min^–1 and HG 30.3–32.31 · min^–1 and for hyperoxia: NG 24.7–25.6 and HG 27.9–31.2 l · min^–1. Although working at the same intensity relative to HR_max, HG showed significantly lower [L] following a single training session, yet maximal values were unchanged after training. Both groups showed a significant increase in the percentage of type IIA fibers post-training but HG retained a larger percentage of HB fibers. Mitochondrial enzymes; citrate kinase, 3-hydroxyacyl CoA dehydrogenase, and cytochrome c-oxidase were increased in the normoxic trained subjects (P < 0.05). In summary, training induced adaptive responses in maximal aerobic power, HR, SV, , [L], and muscle fiber type composition, independent of inspired PO₂. Intramuscular data suggested there may be some differences between hyperoxic and normoxic training and these were substantiated by mitochondrial enzyme and lactate findings. Our data would suggest that transport mechanisms may limit the ability to increase aerobic power.