Clincal, immunologic, and genetic features of an autoimmune lymphoproliferative syndrome associated with abnormal lymphocyte apoptosis

To examine the effect of elastic loading on variational activity of breathing, we studied 11 healthy subjects breathing at rest and with inspiratory elastic loads of 9 and 18 cm H2O/L, applied randomly for 1 h each. Compared with rest, a load of 18 cm H2O/L decreased gross variability, quantitated as standard deviation, of tidal volume (VT) and expiratory time (TE) (p < 0.01 in both instances) but increased that of inspiratory time (TI) (p < 0.03). The autocorrelation coefficients at a lag of 1 breath for each breath component were not altered by elastic loading, although the number of breath lags with significant serial correlations for TE tended to increase with a load of 18 cm H2O/L (p = 0.08). A load of 18 cm H2O/L decreased only the fraction of variational activity of VT and TE due to uncorrelated, random behavior (white noise), while it increased that fraction for TI (p < 0.05 in each instance); the correlated and oscillatory fractions did not change. Uncorrelated random behavior constituted > 87% of the variance of each breath component, correlated behavior represented 3 to 11%, and oscillatory behavior represented < 1.5% during both rest and loaded breathing. Elastic loading changed the gross variability of each primary breath component by altering the random fraction of variational activity; it had no significant effect on the structured, correlated fraction. We speculate that the observed changes in variational activity may reflect an attempt by the controller to compensate for the increased load while simultaneously minimizing load-induced dyspnea.     

The effect of vagal blockade on the variability of ventilation in the awake dog

The present study examined the variability of breathing in five (5) awake tracheostomized dogs with the vagi intact and during complete vagal blockade produced by cooling exteriorized cervical vagal loops (VC). Breath by breath variations in both respiratory timing (assessed from the airflow signal) and the drive to the respiratory muscles (as assessed from the rate of inspiratory airflow (VI/TI) and occlusive pressure (P100) were examined. The degree of variability in the parameters characterizing breathing was evaluated from frequency distribution histograms and by calculation of the standard deviation. VC increased the mean values of VT, TI, TE, TI/TTOT, and decreased VT/TI and occlusion pressure, but had no consistent effect on the mean value of VE. The variability of VE, PACO2, VT, TI, TE, TI/TTOT was greater during VC in 4 of the 5 dogs. The increased variability of VE and PACO2 during VC appeared to be due to a poorer correlation between TI and TE. The present study suggests that vagal mechanoreceptors, presumably pulmonary stretch receptors, minimize breath by breath fluctuations in both the level and pattern of ventilation by controlling respiratory timing. An explanation, based on the model of inspiratory off-switching proposed by Beadley et al. (1975) is invoked.     

Effect of step duration during incremental exercise on breathing pattern and mouth occlusion pressure

We compared the effects of two step durations on breathing pattern, mouth occlusion pressure and "effective" impedance of the respiratory system during incremental exercise. Nine normal subjects (mean age: 27.8+/-1.21 years) performed two incremental exercise tests in randomized order: one test with step increments every 1 min 30s and the other, every 4 min. After a warm-up at 25 W for the 1 min 30 s test, the power was increased by 50 W from 50 W to exhaustion. During the last minute at each power, we measured ventilation (VE), tidal volume (VT), breathing frequency (fR), inspiratory and expiratory time (TI and TE), total time of the respiratory cycle (TTOT), TI/TTOT, mean inspiratory flow (VT/TI), mouth occlusion pressure (P0.1), "effective" impedance of the respiratory system (P0.1/(VT/ TI)) and venous blood lactate concentration ([La]). Our result showed that at maximal exercise the power was significantly higher (p < 0.01) and [La] lower (p < 0.01) in the 1 min 30 s test. At 100, 150 and 200 W, the 4 min test showed significantly higher oxygen uptake (VO2), carbon dioxide output (VCO2), VE, P0.1, fR, VT/TI and HR (p <0.001) and significantly lower TI, TE and TTOT (p<0.01). [La] was significantly higher at 150 W (p<0.05) and 200 W (p<0.001). At the same VCO2, P0.1 was not significantly different between the two tests, whereas VE showed a tendency to be higher (p = 0.08) and P0.1/(VT/TI) was significantly lower during the 4 min test. In conclusion, this study allowed us to quantify the difference in inspiratory neuromuscular output and ventilatory response between 1 min 30s and 4 min tests and showed that different step durations alter the relationship between inspiratory neuromuscular output and mean inspiratory flow.     

Effect of sleep on changes in breathing pattern accompanying sigh breaths

We studied the effect of sleep on the characteristics of sigh breaths and the associated changes in breathing pattern in breaths following spontaneous sighs in 4 unrestrained dogs with an intact upper airway. The sigh breath was characterized by its large tidal volume (VT), long TI and TE in comparison with the control breath. The volume of the sigh breath was larger in awake sighs than in those recorded during non-REM (NREM) and REM sleep. The strength of Hering-Breuer reflex as determined by duration of the post-sigh apnea was similar in NREM and REM sleep. Sighs occurring during wakefulness, NREM and REM sleep were associated with augmented activity of the parasternal muscles during inspiration, and a persistent tonic abdominal muscle activity during the expiratory period. Breathing pattern in the post-sigh period was characterized by a smaller VT and longer TE in the first post-sigh breath in all sleep states (compared with the control breath), but the pattern returned to control level within the second or third post-sigh breath in both NREM and REM sleep. Sighs did not precipitate periodic breathing or other forms of abnormal breathing patterns in either wakefulness or sleep. We conclude that the respiratory control mechanisms stabilizing breathing after a sigh in the awake dog are intact in NREM and REM sleep.     

Immediate response to inspiratory resistive loading in anesthetized patients with kyphoscoliosis: spirometric and neural effects

In kyphoscoliosis (KS), lung volumes are reduced, respiratory elastance and resistance are increased, and breathing pattern is rapid and shallow, attributes that may contribute to defense of tidal volume (VT) in the face of inspiratory resistive loading. The control of ventilation of 12 anesthetized patients about to undergo corrective spinal surgery was compared to that of 11 anesthetized patients free of cardiothoracic disease during quiet breathing and the first breath through one of three linear resistors. Mean forced vital capacity (FVC) of the KS group was 48% that of the controls (C). Passive elastance (Ers) and active elastance and resistance (E'rs and R'rs, respectively) were computed according to previously described techniques (Behrakis PK, Higgs BD, Baydur A, Zin WA, Milic-Emili J (1983) Active inspiratory impedance in halothane-anesthetized humans. J Appl Physiol 54: 1477-1481). Baseline tidal volume VT, inspiratory duration Tl, expiratory duration TE, duration of total breathing cycle TT, and inspiratory duty cycle TI/TT were significantly reduced, while VE was slightly decreased in the KS. Ers, E'rs, and R'rs, were, respectively, 72, 69, and 89% greater in the KS. Driving pressure (Pmus) was derived from the equation of motion, using active values of respiratory elastance. With resistive loading, there was greater prolongation of TI in the C, while percent reduction in VT and minute ventilation VE was less in KS. Compensation in both groups was achieved through three changes in the Pmus waveform. (1) Peak amplitude increased. (2) The duration of the rising phase increased. (3) The rising Pmus curve became more concave to the time axis. These changes were most marked with application of the highest resistance in both groups. Peak driving pressure and mean rate of rise of Pmus were greater in the KS. Increased intrinsic impedance, Pmus, and differences in changes in neural timing in anesthetized kyphoscoliotics contribute to modestly greater VT defense, compared to that of anesthetized subjects free of cardiorespiratory disease.     

Effects of body temperature on ventilatory response to hypoxia and breathing pattern in man

The ventilatory response to hypoxia (PAO2 55 and 45 Torr) at each of four levels of PACO2 was studied in five healthy subjects before and after a rise in rectal temperature of 1.4 degrees C had been induced by means of a heated flying suit. At a given level of chemical drive both ventilation and mean inspiratory flow increased after heating, frequency relatively more than tidal volume. In isoventilation comparisons mean inspiratory flow was identical in normo- and hyperthermia, whereas the durations of inspiration (TI) and expiration (TE) were proportionately shortened. It is suggested that a rise in temperature shortens TI by affecting a central "clock" and that TE changes are secondary to changes in end-inspiratory volume. The euoxic CO2 response in hyperthermia was suggestive of multiplication between CO2 and temperature. Hypoxic sensitivity was significantly increased, indicating a temperature effect on the arterial chemoreceptors. The breathing pattern was in either temperature condition identical in euoxia and in hypoxia.     

Breathing patterns in infants and children under halothane anesthesia: effect of dose and CO2

We studied the amplitude, timing, and shape of the airflow waveform at the mouth of spontaneously breathing children under two sets of conditions: 1) in 30 children aged 9 wk-4.5 yr at 2, 1, and 0% inspired halothane concentration and 2) in 22 children aged 5 mo-7 yr during hyperoxic CO2 rebreathing while recovering from anesthesia. Compared with control values, the relative changes in breath parameters at 1 and 2% halothane were, respectively, as follows: total cycle time -19 and -31%, tidal volume (VT) -30 and -44%, minute ventilation -11 and -17%, and VT/inspiratory time (TI) -16 and -20%. Parameters of timing and breath shape did not change except for the significant but small increase in TI/total cycle time (by 6 and 8%, respectively). With CO2 rebreathing, parameters reflecting inspiratory drive increased significantly in all patients as shown by the slopes of the regressions of these parameters against end-tidal PCO2. Mean slopes expressed in %control value per millimeter of mercury CO2 were 12.1 for minute ventilation, 8.3 for VT, and 10.67 for VT/TI. Parameters reflecting the timing and breath shape remained essentially unchanged. Our results suggest that, in children under halothane anesthesia, the amplitude, timing, and shape of the breathing pattern are controlled independently. In particular, the amplitude and timing of the breath may vary widely without any significant change in the shape.     

The effect of lung reflexes on the pattern of breathing in cats

Tidal volume (VT), and inspiratory (tI) AND EXPIRATORY (TE) durations have been measured in anaesthetized cats on stimulation of alveolar type J (nociceptive) and lung irritant receptors by intravenous injections of phenyl diguanide and of histamine acid phosphate respectively. The reflexes were studied during eupnoea, hypercapnic and hypoxic hyperpnoea, during rebreathing from hyperventilation apnoea and at different body temperatures. In all conditions the drugs caused rapid shallow breathing with reduction in VT, tI and tE. The VT/tI relationship for injection of the drugs was different from that caused by hypercapnic stimulation of breathing, but the tI/tE relationship was proportionally similar for all conditions. Recording single unit activity from phrenic motor fibres showed that the lung reflexes had little action on the initial frequency of discharge of the fibres, but cut short the discharge earlier than for the controls. The results are interpreted in terms of the ways in which lung reflexes can modify the pattern of breathing.     

Changes in maximal exercise ventilation and breathing pattern in boys during growth: a mixed cross-sectional longitudinal study

The aim of this mixed cross-sectional longitudinal study covering a total age range of 11-17 years, i.e. the entire pubertal growth period, was (1) to specify the changes in maximal breathing pattern during incremental exercise; (2) to determine what parts of the changes are due to anthropometric characteristics, physical fitness and inspiratory or expiratory muscle strength; and (3) to determine if the role of these variables is identical before, during and after pubertal growth spurt. This study was conducted in 44 untrained schoolboys separated into three groups, with an initial age of 11.2 +/- 0.2 years for group A, 12.9 +/- 0.25 years for group B, and 14.9 +/- 0.26 years for group C. These children were subsequently followed for 3 years, during the same time period each year. The maximal inspiratory and expiratory pressures (PI max and PE max) were used as an index of the respiratory muscle strength. During an incremental exercise test, maximal ventilation (VE max), tidal volume (VT max), breathing frequency (fmax), inspiratory and expiratory times (tI max and tE max) and mean inspiratory flow (VT/tI max) were measured at maximal oxygen uptake (VO2max). Our study showed that there was a marked increase with age in VE max, VT max, and VT/tI max, and no significant changes in fmax, tI max and tE max. PI max and PE max showed a general trend towards an increase between 11 and 17 years. The study of the linear correlations between maximal breathing pattern and the anthropometric characteristics, physical fitness and inspiratory or expiratory muscle strength showed that, in the three groups of children, (1) lean body mass was the major determinant of VE max, VT max and VT/tI max and the relationships were significantly different before, during and after the pubertal growth spurt; (2) physical fitness was the main determinant of tI max, tE max and fmax before and after the pubertal growth spurt; and (3) maximal respiratory strength did not play a significant role. In conclusion, this mixed cross-sectional longitudinal study showed, at maximal exercise, a significant increase in VE max during growth due only to a significant increase in VT max and VT/tI max, and that the relationships of anthropometric characteristics and physical fitness with maximal breathing pattern change during growth.     

The effects of CO2 on the components of breathing pattern

Experiments were performed on 12 rabbits in 4 experimental groups: A. breathing spontaneously; B. nonparalysed and ventilated by means of a pump driven by the integrated phrenic nerve activity; C. paralysed and ventilated as mentioned above; D. like in the group C, but subjected to bilateral vagotomy. The relationships were investigated between the chosen basic parameters describing the rhythm and depth of respiration in steady states during exposure to hypercapnic mixtures. A high correlation was found between the amplitude of the integrated phrenic nerve activity and the time of inspiration which is modified by the afferent activities from the lungs and thorax TI and TE seem to be controlled by different mechanisms, and the contribution of TE to the control of the cycle duration is greater than that of TI.     

Perceived exertion associated with breathing hyperoxic mixtures during submaximal work

The effect of an enriched inspired oxygen concentration on perceived exertion (RPE) was investigated while running at two submaximal treadmill loads. Twelve males (VO2 max = 49.3 ml/kg-min) worked at 50% and 80% VO2 max, breathing either air or 80% O2-20% N2 in random order using a single blind technique. Subjects were evaluated while running for 10 min and during a 20 min recovery. Heart rate (HR), ventilation (VE), respiration rate (RR), tidal volume (VT) and RPE were measured before, during and after work. Blood lactate was measured 1 min after work. Oxygen concentration did not statistically affect HR, VE, RR or VT during exercise or recovery. At both loads, RPE at the end of exercise was significantly reduced breathing the hyperoxic mixture. At 50% VO2 max, mean RPE decreased from 11.2 breathing room air to 9.6 breathing 80% O2 and, 80% VO2 max, from 13.8 to 11.7 (P less than 0.01). Blood lactates were significantly reduced breathing 80% O2; from 23.4 mg to 13.3 at 50% VO2 max and from 55.5 to 36.5 at 80% VO2 max (P less than 0.01). The RPE correlated with lactate (r=0.64) at the end of work. Results indicate that during moderate and heavy work RPE is significantly affected by the inspired O2 concentration and there is a significant relationship between RPE and blood lactate.     

Postreading question–answer interactions and children's learning from text.

111 average and above-average 5th grade students read 1 of 7 short, nonnarrative passages and wrote answers to a set of either textually explicit (TE), textually implicit (TI), schema-based (SB), or text-irrelevant (control) questions. One week later Ss were given a written free-recall test. The results of the analysis of the S's responses to the treatment questions indicate that TE and TI questions promoted text-based question–answer interactions, whereas SB questions promoted both text-based and SB interactions. The recall data indicate that TI question–answer interactions resulted in the generation of larger proportions of text-based inferences than the other types of interactions, without any loss in the amount of explicit information, text-based inferences, and SB inferences. Finally, SB question–answer interactions and interactions with text-irrelevant questions both resulted in larger proportions of SB inferences than either TE or TI interactions. These results are consistent with a schema–theoretic view of reading comprehension. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oscillopsia: visual function during motion in the absence of vestibulo-ocular reflex

Inspiratory muscle function has been shown to be related to general muscle weakness, weight loss, blood gas tensions, airway obstruction and hyperinflation. The aim of this study was to define (1) the factor that is the main determinant of the tension-time index of the inspiratory muscles (TTmus), and which this increases the risk of inspiratory muscle fatigue; and (2) whether a breathing strategy is adopted to avoid inspiratory muscle fatigue. Twenty-seven normal volunteers and 35 stable COPD outpatients (FEV1% predicted, range: 21-89%; and FRC/TLC, range: 49-77%) were studied. The TTmus was determined as follows: TTmus = PI/PImax.TI/Ttot, where Pi is the mean inspiratory pressure calculated from the mouth occlusion pressure (P0.1), PImax is the maximal inspiratory pressure, TI is the inspiratory time, and Ttot is the total time of the breathing cycle. COPD patients showed significantly lower PImax and higher P0.1, PI, PI/PImax, and TTmus than normal subjects. No patient had a TTmus value higher than the inspiratory muscle fatigue threshold of 0.33. The FEV1 was significantly correlated with TTmus and all its components in the patients. The FRC/TLC was also correlated with all components except PI. Body weight was only correlated with PImax. In a forward and backward stepwise regression analysis, FEV1 appeared to be the only significant factor explaining the variance of log (PI/PImax) and log (TTmus), whereas FRC/TLC was the principal determinant of PImax. In COPD patients, a non-linear relationship was found between TI and P0.1. A negative linear relationship was found between TI/Ttot and PI/PImax. In conclusion, although hyperinflation predominantly affected inspiratory muscle strength in a group of stable COPD patients with a wide range of severity, airway obstruction was the principal factor determining the magnitude of TTmus. In addition, in order to remain below the inspiratory muscle fatigue threshold, as the severity of airway obstruction increased, patients adopted a breathing strategy characterized by decreased TI/Ttot as inspiratory pressure demand increased.     

Assessment of ventilatory neuromuscular drive in patients with obstructive sleep apnea

The presence of abnormalities of the respiratory center in obstructive sleep apnea (OSA) patients and their correlation with polysomnographic data are still a matter of controversy. Moderately obese, sleep-deprived OSA patients presenting daytime hypersomnolence, with normocapnia and no clinical or spirometric evidence of pulmonary disease, were selected. We assessed the ventilatory control and correlated it with polysomnographic data. Ventilatory neuromuscular drive was evaluated in these patients by measuring the ventilatory response (VE), the inspiratory occlusion pressure (P.1) and the ventilatory pattern (VT/TI, TI/TTOT) at rest and during submaximal exercise, breathing room air. These analyses were also performed after inhalation of a hypercapnic mixture of CO2 (delta P.1/delta PETCO2, delta VE/delta PETCO2). Average rest and exercise ventilatory response (VE: 12.2 and 32.6 l/min, respectively), inspiratory occlusion pressure (P.1: 1.5 and 4.7 cmH2O, respectively), and ventilatory pattern (VT/TI: 0.42 and 1.09 l/s; TI/TTOT: 0.47 and 0.46 l/s, respectively) were within the normal range. In response to hypercapnia, the values of ventilatory response (delta VE/delta PETCO2: 1.51 l min-1 mmHg-1) and inspiratory occlusion pressure (delta P.1/delta PETCO2: 0.22 cmH2O) were normal or slightly reduced in the normocapnic OSA patients. No association or correlation between ventilatory neuromuscular drive and ventilatory pattern, hypersomnolence score and polysomnographic data was found; however a significant positive correlation was observed between P.1 and weight. Our results indicate the existence of a group of normocapnic OSA patients who have a normal awake neuromuscular ventilatory drive at rest or during exercise that is partially influenced by obesity.     

NMDA receptors mediate peripheral chemoreceptor afferent input in the conscious rat

N-methyl-D-aspartate (NMDA) glutamate receptors mediate critical components of cardiorespiratory control in anesthetized animals. The role of NMDA receptors in the ventilatory responses to peripheral and central chemoreceptor stimulation was investigated in conscious, freely behaving rats. Minute ventilation (VE) responses to 10% O2, 5% CO2, and increasing intravenous doses of sodium cyanide were measured in intact rats before and after intravenous administration of the NMDA receptor antagonist MK-801 (3 mg/kg). After MK-801, eupcapnic tidal volume (VT) decreased while frequency increased, resulting in a modest reduction in VE. Inspiratory time (TI) decreased, whereas expiratory time remained unchanged. The VE responses to hypercapnia were qualitatively similar in control and MK-801 conditions, with slight reductions in respiratory drive (VT/TI) after MK-801. In contrast, responses to hypoxia were markedly attenuated after MK-801 and were primarily due to reduced frequency changes, whereas VT was unaffected. Sodium cyanide doses associated with significant VE increases were 5 and 50 microg/kg before and after MK-801, respectively. Thus 1-log shift to the right of individual dose-response curves occurred with MK-801. Selective carotid body denervation reduced VE during hypoxia by 70%, and residual hypoxic ventilatory responses were abolished after MK-801. These findings suggest that, in conscious rats, carotid and other peripheral chemoreceptor-mediated hypoxic ventilatory responses are critically dependent on NMDA receptor activation and that NMDA receptor mechanisms are only modestly involved during hypercapnia.     

顶旋型湍流抑制器对单流板坯中间包内湍流行为的影响

摘要：设计了一种顶旋型湍流抑制器,使钢液产生旋转流场,降低钢/渣界面速度,促进夹杂物的去除,达到净化钢液的目的,并利用数值模拟的方法,对单流板坯中间包在稳态和非稳态时的流场进行研究。结果表明：使用新型抑制器相较于不使用和使用普通抑制器,对中间包稳态浇注流场有明显的改善,死区体积明显减小。拉速和中间包容量改变时,新型抑制器比普通抑制器对中间包液面波动的抑制效果更好。当拉速为1.15、1.55和1.85m/min时,使用新型抑制器的中间包自由液面的平均速度分别为0.040、0.053和0.062m/s,相较于普通抑制器分别降低了21.6%、24.3%和26.2%。当中间包容量为40、30和25t时,使用新型抑制器相比于普通抑制器,自由液面的湍动能分别减少了20.9%、25.0%和26.3%。     

Pressure support ventilation in adult respiratory distress syndrome: short-term effects of a servocontrolled mode

PURPOSE: To assess the short-term effects of pressure support ventilation in adult respiratory distress syndrome (ARDS), we studied 17 patients with moderate to severe ARDS using mandatory rate ventilation (MRV), a servocontrolled mode of PSV having respiratory rate as the targeted parameter. MATERIALS AND METHODS: Based on the duration of ARDS, the patients were divided into two groups: Group 1, early ARDS (duration up to 1 week), 10 patients; Group 2, intermediate ARDS (duration between 1 and 2 weeks). The patients were initially ventilated with assisted mechanical ventilation then with MRV, and finally with controlled mechanical ventilation. After a 20-minute period allowed for stabilization in each mode, ventilatory variables, gas exchange, hemodynamics, and patient's inspiratory effort were evaluated. RESULTS: During MRV blood gases, airway pressures and hemodynamic variables remained within acceptable limits in all patients. Compared with assisted mechanical ventilation, during MRV, patients of group 1 decreased their VT and V (from 0.64 +/- 0.04 to 0.42 +/- 0.03 L/sec) and increased their TI/TT (from 0.39 +/- 0.03 to 0.52 +/- 0.03). f did not change. PAO2 - PaO2 and QS/QT decreased (from 306 +/- 16 to 269 +/- 15 mm Hg, and from 20.2 +/- 1.4 to 17.5 +/- 1.1, respectively), while PaCO2 increased (from 44 +/- 3 to 50 +/- 3 mm Hg). On the contrary, patients of group 2 increased their VT (from 0.69 +/- 0.02 to 0.92 +/- 0.09 L), decreased their f (from 22.3 +/- 0.5 to 19.3 +/- 0.3 b/min), although they did not change their V and TI/TT. PAO2 - PaO2 and QS/QT remained stable. PaCO2 diminished (from 39 +/- 3 to 34 +/- 3 mm Hg). Pressure support level was higher in group 2 than in group 1 (29.4 +/- 3.0 v 19.8 +/- 2.9 cm H2O). CONCLUSIONS: We conclude that (1) PSV delivered by MRV may adequately ventilate patients with moderate to severe ARDS, preserving gas exchange and hemodynamics, at least for the short period tested; (2) early and intermediate ARDS respond in a different manner to MRV in terms of breathing pattern, gas exchange, and level of pressure assistance; and (3) patients with early ARDS are those who have an improvement in intrapulmonary oxygenation probably due, at least in part, to alveolar recruitment augmented by active diaphragmatic contraction.     

Gas exchange during exercise in healthy people II. Venous admixture

1. Venous admixture/cardiac output ratio (Qva/Qt) has been measured in twenty-four healthy volunteer subjects of both sexes aged 20-71 years, at rest and during the steady state of treadmill exercise at two rates of work, and breathing air and breathing oxygen. 2. With oxygen breathing, Qva/Qt was considerably less during exercise than during the time subjects were taking either normal or deep breaths of oxygen at rest, and did not significantly increase with the intensity of exercise. It is postulated that the increase in ventilation during exercise opens most or all of those alveoli which, during oxygen breathing at rest, close because of critically low ventilation/perfusion (V/Q) ratios. 3. With air breathing, Qva/Qt fell from rest to exercise (especially in older subjects), presumably due to improved ventilation of alveoli at the lung bases. With an increase in work rate Qva/Qt increased in all age groups. This increase was not due to increase in the shunt fraction (Qs/Qt), nor to limitation of diffusing capacity; it arose from an increase in V/Q variance. 4. Equations have been derived for the prediction of normal Qva/Qt during exercise, with or without correction for the effects of increasing pulmonary capillary temperature. These effects do not materially influence the accuracy of prediction, but may be relevant to some of the interpretations. In particular, they provide a further indication that Qs/Qt probably cannot be measured by breathing oxygen at rest, even in deep breathing.     

Effects of nasal continuous positive airway pressure on breathing pattern and respiratory drive in patients with obstructive sleep apnea syndrome

To examine the influence of continuous positive airway pressure (CPAP) therapy on respiratory center drive in patients with obstructive sleep apnea syndrome (OSAS), 20 normocapnic OSAS patients (group 0) and 20 simple snoring patients were studied. In the first night, diagnostic polysomnography (PSG) was performed. Before and after PSG monitoring, mouth occlusion pressure (P0.1), tidal volume (VT), minute ventilation (VE), respiratory rate (RR), inspiratory time (Ti), expiratory time (Te), total cycle duration (Ttot), inspiratory duty cycle (Ti/Ttot), mean inspiratory flow (VT/Ti) and effective inspiratory impedance (P0.1/VT/Ti, Ieff) were measured while they were breathing room air. In the following night the OSAS patients were treated with nasal CPAP and PSG monitoring and the above mentioned measurements were repeated. The results showed that pre-PSG values of P0.1, RR and P0.1/VT/Ti in the OSAS patients were significantly higher than those in the snoring patients, while VT, Ti, Te and Ttot values were lower. In the first night, the post-PSG P0.1 value in the OSAS patients increased markedly as compared with the pre-PSG. After overnight nasal CPAP therapy, the respiratory disorder index in the OSAS patients decreased markedly, the nadir SaO2 increased markedly, but the post-PSG P0.1 value did not increase significantly. It is concluded that, before sleep, OSAS patients exhibit a higher respiratory drive and a shallow and frequent breathing pattern as compared with simple snoring patients. After nocturnal sleep, the respiratory drive of OSAS patients increases significantly, the breathing pattern becomes more shallow and frequent. Nasal CPAP may effectively relieve the sleep apnea and hypopnea as well as the resulting hypoxemia and therefore correct the changes in breathing pattern and respiratory drive through nocturnal sleep in patients with OSAS.     

The effects of learning on the ventilatory responses to inspiratory threshold loading

Progressive threshold loading (PTL) is frequently used to assess inspiratory muscle endurance in health and disease. We and others have noted a systematic increase in endurance with the first few exposures to the task in subjects previously na?ve to PTL, which may not be related to conditioning of the muscles themselves. The purpose of this study was to investigate the mechanisms responsible for this increased endurance by examining the ventilatory responses to 3 PTL tests, each > 24 h apart, in 18 healthy subjects. During PTL, threshold pressure (Pth) was increased by approximately 10% every 2 min until task failure. Subjects were allowed to adopt any breathing pattern. Respiratory muscle strength (maximal inspiratory pressure [PImax]) was unchanged over successive tests while maximal Pth (Pthmax) during PTL increased (69 +/- 17, 77 +/- 16, and 86 +/- 11% of PImax, respectively, p < 0.05) (mean +/- SD), indicating that the increased Pthmax could not be attributed to improved respiratory muscle strength. Breathing pattern changed with successive tests, so that for comparative loads inspiratory time (TI), respiratory frequency (f ), and duty cycle (TI/Ttot) decreased. This change in breathing pattern did not alter respiratory muscle efficiency (respiratory muscle V O2/work), which was similar in each test (2.4 +/- 2.2%), but perceived effort (Borg Score), which was maximal at task failure in each test, decreased at comparative loads with successive tests. Thus, Pthmax during initial tests appeared to be limited by discomfort rather than respiratory muscle function. These findings suggest that the increased Pthmax with successive tests is a consequence of differences in the breathing pattern adopted, reflecting neuropsychological rather than respiratory muscle conditioning. Measurements from PTL should only be used to assess respiratory muscle performance after allowing time for learning.