Breathing pattern and occlusion pressure during exercise in pre- and peripubertal swimmers

In two groups of young swimmers (prepubertal stage: group A; peripubertal stage: group B), the ventilatory response to graded exercise work with a cycle ergometer was studied. Ventilatory variables (ventilation, VE, tidal volume, VT, respiratory frequency,f, ratio between inspiratory period and total breath duration, TI/TTOT, and mean inspiratory flow, VT/TI) as well as mouth occlusion pressure measured at 100 msec (P0.1), effective impedance of the respiratory system (P0.1/VT/TI), inspiratory power for breathing (W) and O2 uptake (VO2) were measured during the third minute of each work load. At the same level of exercise both groups showed identical values of VT/TI, but VE was higher in group A individuals. This resulted from higher values of respiratory frequency with higher TI/TTOT ratios. P0.1, P0.1(VT/TI) and W were also much higher during work load in group A than in peripubertal subjects. When the above results were related to the same percentage of VO2 max, P0.1, W, respiratory frequency and duty cycle did not differ within both groups. However, VE, VT and VT/TI were lower in group A subjects with a higher P0.1/(VT/TI) ratio. Further corrections of VT, VT/TI and P0.1/(VT/TI) ratios by body weight cancelled all these differences. In conclusion, our results strongly suggest that biometric factors only determined interindividual differences in ventilatory response to exercise in prepubertal and peripubertal swimmers.     

Breathing pattern of neonates during nonnutritive sucking

Alteration of the breathing pattern seen during oral feeding has been attributed to the behavioral activity of sucking, repeated swallowing, and laryngeal chemoreceptor stimulation. Because it preserves the behavioral activity of sucking but eliminates the laryngeal chemoreceptor stimulation and repeated swallowing that occurs during nutritive sucking, the effects of nonnutritive sucking was evaluated in 19 term infants. The suck-pause pattern seen during nonnutritive sucking is similar to that of nutritive sucking. None of the variables measured (inspiratory duration, expiratory duration, breathing frequency, and tidal volume) were significantly altered during the overall period of nonnutritive sucking when compared with previously obtained control values. These results suggest that the alteration of breathing pattern observed during oral feeding cannot be accounted for by the behavioral activity of sucking per se. However, when the sucking phases of the nonnutritive period were compared with the intervening pauses, a reduction in the expiratory duration (P less than 0.05) and a reduction in tidal volume (P less than 0.05) were observed. Thus, the breathing pattern of human neonates is indeed altered during the sucking phase of the nonnutritive period; pressure changes associated with sucking may account for this alteration.     

Fat metabolism during high-intensity exercise in endurance-trained and untrained men

To determine whether trained individuals rely more on fat than untrained persons during high-intensity exercise, six endurance-trained men and six untrained men were studied during 30 minutes of exercise at 75% to 80% maximal oxygen consumption (VO2max). The rates of appearance (Ra) and disappearance (Rd) of glycerol and free fatty acids (FFAs) were determined using [1,1,2,3,3-2H]glycerol and [1-13C]palmitate, respectively, whereas the overall rate of fatty acid oxidation was determined using indirect calorimetry. During exercise, the whole-body rate of lipolysis (ie, glycerol Ra) was higher in the trained group (7.1 +/- 1.2 v 4.5 +/- 0.7 micromol x min(-1) x kg(-1), P < .05), as was the Ra (approximately Rd) of FFA (9.0 +/- 0.9 v 5.0 +/- 1.0 micromol x min(-1) x kg(-1), P < .001). FFA utilization was higher in trained subjects even when expressed as a percentage of total energy expenditure (10% +/- 1% v 7% +/- 1%, P < .05). However, this difference in plasma FFA flux could not account for all of the difference in fatty acid oxidation between trained and untrained subjects (20.8 +/- 3.3 v 7.9 +/- 1.6 micromol x min(-1) x kg(-1), or 23% +/- 3% v 13% +/- 2% of total energy expenditure, both P < .05). Thus, the oxidation of fatty acids derived from some other source also must have been greater in the trained men. We conclude that trained athletes use more fat than untrained individuals even during intense exercise performed at the same percentage of VO2max. The additional fatty acids appear to be derived from both adipose tissue and, presumably, intramuscular triglyceride stores.     

Breathing pattern and eye movement density during REM sleep in humans

Changes in the density of eye movement during rapid eye movement (REM) sleep are associated with changes in ventilation and ventilatory response in animals. Recent data in patients with chronic obstructive pulmonary disease suggest that periods of frequent eye movements may be associated with hypoxemia during REM sleep. We have therefore investigated the association between eye movements and ventilation and ventilatory pattern in 10 normal men. Expired ventilation was measured using a pneumotachograph attached to a valved face mask with a dead space of 50 ml and incorporating a peripheral CO2 leak detector. Ventilation was reduced (p less than 0.02) in all stages of sleep compared with that during wakefulness, with no difference between the level of ventilation in each sleep stage (awake, 7.18 +/- 0.43 SEM; Stage 2, 6.47 +/- 0.43; Stage 3/4, 6.45 +/- 0.52; REM sleep, 6.55 +/- 0.47 L/min). During REM sleep, eye movements (EMs) were associated with rapid shallow breathing. Dividing REM into 20-s epochs with or without EMs, EMs were associated with a raised breathing frequency (no EMs, 14.4 +/- 0.4 breaths/min; EMs, 15.8 +/- 0.5 breaths/min; p = 0.01), reduced tidal volume (0.49 +/- 0.03 L; 0.41 +/- 0.03 L; p less than 0.01), and reduced minute ventilation (6.87 +/- 0.45 L; 6.27 +/- 0.51 L; p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic exercise echocardiography of the left ventricle in physically trained children compared to untrained healthy children

To evaluate the effect of physical training on left ventricular function, we investigated 52 children, aged 7 to 14 years, who had trained for endurance sports over a period of at least 1 year. The children (24 boys and 28 girls) were investigated echocardiographically during supine exercise on a bicycle at increasing work loads of 6, 9, 12 and 15 kpm/min/kg body weight. The parameters of left ventricular function (specifically fractional shortening and the velocity of circumferential fiber shortening; both these parameters corrected for heart rate) were evaluated before, during and after the test. The values obtained were compared to those in untrained children investigated in a previous study. Fractional shortening in trained children rose from 37 +/- 5% to 54 +/- 5%, and in untrained children from 37 +/- 4% to 46 +/- 4%. The velocity of fiber shortening in trained children rose from 1.27 to 3.15 circ/sec while in untrained children it increased from 1.25 to 2.53 circ/sec. Left ventricular contraction, therefore was significantly greater in trained than in untrained children during exercise. While untrained children increased their cardiac output in the first minutes of exercise mainly by elevating their heart rate, trained children increased simultaneously the stroke volume. There were no significant differences between boys and girls, or between stages of maturity. Thus, physical training causes quick adaptations of left ventricular function to exercise in children of all ages.     

Breathing pattern affects airway wall temperature during cold air hyperpnea in humans

We studied the influence of flow rate on respiratory heat exchange in 9 healthy adult subjects using a new noninvasive technique, the single-breath temperature washout (SBTW) curve. The SBTW curve is a plot of exhaled gas temperature versus exhaled volume during a standard exhalation and consists of an initial rise (within the first 200 ml) to a plateau temperature that persists through the remainder of exhalation. We found that exhaled gas temperatures within the initial expirate were colder at every airway locus than corresponding intra-airway gas temperatures at end-inspiration, suggesting that heat exchange occurs between lumenal gas and the relatively cooler airway walls during exhalation. The SBTW plateau temperatures were: (1) lower after preconditioning the airways with rapid (80 L/min) isocapnic hyperpnea of frigid air than after less rapid (40 L/min) cold-air hyperpnea or after quiet breathing; (2) lower when, after identical airway preconditioning regimens, the SBTW exhalation was performed with a slower (0.5 versus 2.5 L/s) expiratory flow; and (3) lower when SBTW curves were obtained after airway preconditioning using respiratory patterns with larger inspiration-expiration duration (I:E) ratios (5:1 versus 1:5) at fixed minute ventilation and respiratory rate. Our results indicate that the global respiratory gas-wall heat transfer coefficient increases with velocity to the 0.9 power, a finding similar to that in previous studies of turbulent flow in rigid pipes.     

Breathing pattern in patients with Parkinson's disease

The improvement in motor performance resulting from levodopa administration in patients with Parkinson's disease (PD) provides the opportunity to investigate ventilatory changes brought about by the disease. The aim of this study has been to investigate these changes in order to specify the mechanisms of the impairment in breathing in PD. Breathing patterns at rest were investigated in 11 patients with idiopathic PD both before (OFF) and after (ON) administration of levodopa at a dose improving their motor performance by at least 30%. Airflow (Fleisch head mounted on a mask), rib cage and abdomen movements (inductance plethysmography) were recorded in the OFF condition 1 h after subjects woke up. Subjects then received levodopa and a new set of recordings was obtained 1 h later, in the ON condition. Breath-by-breath processing of recordings was carried out, and tidal volume (VT), inspiratory (TI) and expiratory (TE) durations were measured. The main finding was a lengthening of TI resulting in a decrease in ventilation and in VT/TI, and an increase in TI/TTOT in the ON compared to the OFF condition. In the ON condition abnormal rib cage-abdomen plots patterns were found in four out of six subjects. A hypothesis on the effect of PD on breathing is proposed on grounds of normal diaphragmatic activity but impaired activity of the other respiratory muscles and more specifically the intercostal muscles.     

Dichloroacetate: Effects on exercise endurance in untrained rats

The effect of dichloroacetate (DCA), an activator of pyruvate dehydrogenase, on the performance of fed, untrained rats was evaluated while swimming for different durations. DCA-treated rats were able to swim almost 40% longer than controls (354 ± 18 versus 255 ± 18 sec, p < .001). This was associated with lower levels of blood and muscle lactate at rest and after 210 and 240 sec of swimming. At exhaustion, blood lactate was the same in the two groups even though the DCA rats had worked for an additional 99 sec (16.9 ± 1.2 versus 15.8 ± 1.2 mM/L NS). Pretreatment with DCA did not alter the usual exercise-induced decreases in muscle ATP and creatine phosphate or liver glycogen. After 210 sec of exercise, plasma FFA and blood glucose and acetoacetate were also the same in the two groups; however, β-hydroxybutyrate was somewhat higher, and there was a small but significant sparing of muscle glycogen in the DCA group. The data indicate that DCA enhances the ability of rats to exercise at near maximal work loads. They are consistent with the notion that improved endurance is a consequence of a decreased rate of lactate accumulation; however, the possibility that it is secondary to some other action of DCA cannot be excluded.     

Breathing pattern in humans: diversity and individuality

In adult awake human subjects at rest, there exists a diversity in the breathing pattern not only in terms of tidal volume and inspiratory and expiratory duration and derived variables (TTOT, VT/TI and TI/TTOT) but also in the airflow profile. Besides this diversity, in every recording of ventilation at rest in steady-state condition breath-to-breath fluctuations are observed in ventilatory variables. This variability is non random and may be explained either by a central neural mechanism or by instability in the chemical feedback loops. Beyond this variability, each individual appears to select one particular pattern among the infinite number of possible combination of ventilatory variables and airflow profile. This one particular pattern appears to be a relatively stable characteristic of an adult individual being reproducible in several conditions and above all, after a long period of time. Consequences of this individuality of breathing pattern are discussed with regard to the selection of control subjects for a study and also per se: are there physiological situations where differences may be observed solely because of the differences in the pattern of breathing?     

Gas exchange during exercise in diabetic children.

The purpose of this study was to evaluate the cardiorespiratory and metabolic response to exercise in 33 children, aged 9 to 15 years, affected by type I diabetes mellitus, in comparison with 47 age-, sex-, weight-, and height-matched healthy children. All diabetic children were on a mixed split-dose insulin regimen, consisting of both regular and long-acting insulin in the morning and evening. The last insulin injection was administered on average 6 hours before the test. The mean duration of diabetes mellitus was 5.0 +/- 3.1 years. The metabolic control was evaluated on the basis of HbA1 levels (mean, 8.9 +/- 1.8%). Pulmonary function tests and progressive exercise tests on the treadmill were performed. Gas exchange, ventilation, and heart rate (HR) were monitored during the tests. The O2 pulse (VO2/HR) was calculated. There was no difference in the baseline oxygen uptake (VO2) between the diabetic children and the control group. VO2 peak was significantly lower (P less than 0.01) in the diabetic adolescents (41.2 +/- 5.9 mL/min/kg) compared to control subjects (46.3 +/- 9.6 mL/min/kg) and it was achieved at an earlier (P less than 0.01) time of run (7.5 +/- 1.8 vs. 9.1 +/- 2.8 min). Anaerobic threshold and minute ventilation were similar in the two groups. The O2 pulse throughout the test was significantly lower (ANOVA, P less than 0.001) in the diabetic group compared to the controls. No differences were found in resting and post-exercise spirometric values. In conclusion, our study shows that well-controlled diabetic adolescents have a reduced working capacity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breathing abnormalities during sleep

The purpose of this communication is to review obstructive and central breathing abnormalities that may occur during sleep, such as obstructive sleep apnea, and Cheyne-Stokes respiration. Emphasis is placed on noninvasive monitoring of the breathing pattern and intrapleural pressure swings by respiratory and surface inductive plethysmography, respectively, which establish the diagnosis of these abnormal breathing patterns.     

Breathing pattern during and after maximal exercise in patients with chronic obstructive lung disease, interstitial lung disease, and cardiac disease, and in normal subjects

Inspiratory muscle fatigue and pulmonary edema are both known to cause rapid shallow breathing. It has been suggested that exercise tolerance in patients with pulmonary disease and cardiac disease may be limited by the development of inspiratory muscle fatigue and pulmonary edema, respectively, at maximal exercise. If these hypotheses are correct, breathing pattern during recovery from maximal exercise in these patients should be rapid and shallow compared with that during exercise. This study was performed to test these hypotheses. Seven patients with chronic obstructive pulmonary disease (COPD), 8 patients with interstitial lung disease (ILD), 7 patients with cardiac disease (CD) (mitral valve disease or left ventricular dysfunction) and 8 normal (NR) subjects each performed maximal incremental exercise on a cycle ergometer. Exercise breathing pattern was compared with that during recovery by calculating the mean difference in tidal volume (at the same levels of minute ventilation) between exercise and recovery for each subject. Recovery breathing pattern was similar to that during exercise for the COPD, ILD, and NR subjects. In contrast, breathing pattern during recovery was rapid and shallow compared with that during exercise for the CD patients; recovery tidal volume was less than that during exercise for the same level of minute ventilation. The fact that rapid shallow breathing does not develop during recovery from maximal exercise in patients with COPD or ILD suggests that inspiratory muscle fatigue does not limit their exercise tolerance. The relative rapid shallow breathing during recovery from maximal exercise in patients with CD is probably due to the development of pulmonary edema at maximal exercise, but further studies are needed to confirm this.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breathing route during sleep

Nasal obstruction has been associated with apneic episodes during sleep. However, the normal distribution of nasal and oral air flow while asleep has not been investigated. To determine the normal route of ventilation during sleep, we studied 7 healthy men and 7 healthy women using a sealed face mask that mechanically separated nasal and oral air flow. Standard sleep staging techniques were employed. The subjects slept 297 +/- 29 (SEM) min, with a mean of 197 +/- 15 min of ventilation recorded. Ventilation was decreased during sleep as has been previously demonstrated. However, during sleep, we found that men breathed a greater percentage of total ventilation through the mouth (29.0 +/- 8.2%) than did women (5.0 +/- 1.0%, p less than 0.02). The same trend applied during wakefulness but did not reach significance (p = 0.06). Although none was symptomatic, 4 subjects, all men, had more than 3 apneas per hour. These 4 men had a greater percentage of mouth ventilation (37.3 +/- 19.0%) than did the other 10 subjects with few or no apneas (8.1 +/- 2.7%, p less than 0.02). It was also noted that increasing age in men was associated with an increasing percentage of mouth ventilation (r = 0.83 p less than 0.03) but this relationship was not observed in women. We conclude that mouth breathing may be associated with apneas during sleep and that breathing through the mouth occurs commonly in men, particularly in those who are older. This suggests that nasal breathing may be important in the maintenance of ventilatory rhythmicity during sleep.     

Breathing pattern and gas exchange at peak exercise in COPD patients with and without tidal flow limitation at rest.

Expiratory flow limitation (FL) at rest is frequently present in chronic obstructive pulmonary disease (COPD) patients. It promotes dynamic hyperinflation with a consequent decrease in inspiratory capacity (IC). Since in COPD resting IC is strongly correlated with exercise tolerance, this study hypothesized that this is due to limitation of the maximal tidal volume (VT,max) during exercise by the reduced IC. The present study investigated the role of tidal FL at rest on: 1) the relationship of resting IC to VT,max; and 2) on gas exchange during peak exercise in COPD patients. Fifty-two stable COPD patients were studied at rest, using the negative expiratory pressure technique to assess the presence of FL, and during incremental symptom-limited cycling exercise to evaluate exercise performance. At rest, FL was present in 29 patients. In the 52 patients, a close relationship of VT,max to IC was found using non-normalized values (r=0.77; p < 0.0001), and stepwise regression analysis selected IC as the only significant predictor of VT,max. Subgroup analysis showed that this was also the case for patients both with and without FL (r=0.70 and 0.76, respectively). In addition, in FL patients there was an increase (p < 0.002) in arterial carbon dioxide partial pressure at peak exercise, mainly due to a relatively low VT,max and consequent increase in the physiological dead space (VD)/VT ratio. The arterial oxygen partial pressure also decreased at peak exercise in the FL patients (p < 0.05). In conclusion, in chronic obstructive pulmonary disease patients the maximal tidal volume, and hence maximal oxygen consumption, are closely related to the reduced inspiratory capacity. The flow limited patients also exhibit a significant increase in arterial carbon dioxide partial pressure and a decrease in arterial oxygen partial pressure during peak exercise.     

Breathing during sleep in normal subjects

Despite considerable data, little is certain about changes in breathing during sleep, let alone possible mechanisms for these changes. This article reviews methodologic problems, including the definition of the normal subject, the definition of the sleep state, and the effects of instrumentation, and discusses data on respiration during REM and NREM sleep in normal humans. Although the evidence is incomplete, respiration during sleep appears fragile, prone to instability, to upper airway obstruction, to hypoventilation, and to ventilation-perfusion mismatch, jeopardizing the homeostatic function of CO2 output and O2 uptake.     

Breathing pattern and neuromuscular drive during CO2 rebreathing in normal man and in patients with COPD

In 11 normal subjects and in 10 patients with chronic obstructive pulmonary disease we evaluated breathing pattern and mouth occlusion pressure (PO.1), while breathing room air and during reinhalation of a hypercapnic hyperoxic gas mixture. In the breathing pattern we analyzed the time and volume components of the respiratory cycle: tidal volume (VT), inspiratory time (Ti), expiratory time (Te), total time of respiratory cycle (Ttot); mean inspiratory flow (VT/Ti) and Ti/Ttot ratios, respiratory frequency (RF) and instantaneous ventilation (VE). In the normal subjects, increase in VE during rebreathing mainly depended on an increase in both VT and VT/Ti without significant changes in Ti. During CO2 rebreathing the patients exhibited a lesser increase in VE compared to normals, due to a lesser increase in VT. However, expressing VT in percent of resting inspiratory capacity showed that VT attained at the end of rebreathing (VTmax) was similar to that noted in the normal subjects at the same minute of rebreathing. Furthermore, percent increase in VE, VT, VT/Ti and PO.1 between resting value and that at 56 mm Hg (delta %), were significant in both groups with a major increase in the normal subjects for VE and VT/Ti. In comparison, delta % decreases in both Te and Ttot were found to be significant only in the normal subjects. VT/Ti was related to VE in a similar way in the two groups. In contrast, in the normal subjects, Ti/Ttot did not increase with increasing VE. During rebreathing increase in PO.1 was found to be similar in the normal subjects and in patients. However, for a given neuromuscular drive VE and VT/Ti were greater in the normal subjects than in the patients. These data show that in the patients as a whole no significant changes in breath intervals occur during CO2 rebreathing. Furthermore, in patients, in spite of a similar increase in neuromuscular drive, the efficiency by which inspiratory muscle output (PO.1) is converted into VT/Ti was found to be reduced.