Evoked corticospinal output to the human scalene muscles is altered by lung volume

Increases in lung volume inhibit the inspiratory output from the medulla, but the effect of lung inflation on the voluntary control of breathing in humans is not known. We tested corticospinal excitability using transcranial magnetic stimulation (TMS) to evoke a response in the scalene muscles. TMS was delivered at rest at three different lung volumes between functional residual capacity (FRC) and total lung capacity (TLC) during incremental inspiratory and incremental expiratory manoeuvres. Motor evoked potentials (MEPs) in scalenes were ～50% larger at a high lung volume (FRC+～90% inspiratory capacity [IC]) compared to lower lung volumes (FRC and FRC+～40% IC) in both inspiratory and expiratory manoeuvres (p<0.001). The change in MEP size was not due to differences in pre-stimulus EMG amplitude (p=0.29). The results suggest a differential effect of lung inflation on the automatic and voluntary control of breathing in humans.     

Role of the mechanical impairment on the ventilatory response to CO2 in chronic airway obstruction

The purpose of this study was to assess the relationship between the breathing pattern response to CO2 and the severity of mechanical impairment in twenty patients with COLD. The CO2 response was compared to that of a control group of twelve normal subjects. All patients had airway obstruction (FEV1 = 40 +/- 14% of predicted; means +/- SD) and hyperinflation (FRC = 154 +/- 23% of predicted). Tidal volume (VT), inspiratory and total cycle duration (TI, TT), occlusion pressure (P0.1) and endtidal PCO2 were measured at rest and during hyperoxic CO2 rebreathing. On the same day, in all patients, arterial blood gas analysis, spirometric and plethysmographic measurements were made. The slope (S) of the P0.1 response (SP 0.1) to increasing endtidal PCO2 was negatively correlated with airway resistance (r = -0.59; p less than 0.01). Although the flow response, S(VT/TI), was positively and closely correlated with SP 0.1 (r = 0.88; p less than 0.001), it also appeared to be independently influenced by obstruction (p less than 0.01). The tidal volume response, SVT, was principally correlated with inspiratory capacity (r = 0.90; p less than 0.001) and also, independently, with Vmax50 (p less than 0.01). SVT was diminished in seventeen patients, ten of whom only had a decreased S(VT/TI). The shortening in TI during hypercapnia was most marked in patients with the greatest S(P0.1), who did not have arterial hypercapnia at rest. These results suggest: that the poor VT response to CO2 in COLD patients is principally caused by a limitation in inspiratory volume expansion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of endurance training on the breathing pattern of professional cyclists

The aim of this longitudinal study was to clarify the changes induced by endurance training on the breathing pattern of 13 professional cyclists (age+/-SD: 24+/-2 years; VO(2 max) approximately 75 ml x kg(-1) x min(-1)) during the three periods (rest, precompetition, and competition) of a sports season. Both the volume and the intensity of training were quantified during these periods. In each session (corresponding to each of the three periods) all subjects performed (1) a pulmonary function test (to measure forced vital capacity [FVC], peak expiratory flow [PEF], and maximal voluntary ventilation [MVV]), and (2) a ramp test until exhaustion on a cycle ergometer (workload increases of 25 W x min(-1)). The following variables were recorded every 100 W until the end of the tests: pulmonary ventilation (VE, in l x min(-1) BTPS), tidal volume (VT, inl BTPS), breathing frequency (f(b), in breaths x min(-1)), ventilatory equivalents for oxygen (VE x VO(2)(-1)) and carbon dioxide (VE x VCO(2)(-1)), inspiratory (TI) and expiratory (TE) times (s), ratio of TI to total respiratory duration or inspiratory "duty cycle" (TI/TTOT, and mean inspiratory flow rate (VT)/TI), in l x s(-1)). The results showed no changes in any of these variables (p>0.05) between the three periods of study, despite significant changes in training loads (i.e., increases in the volume and/or intensity of training throughout the season). These findings suggest that endurance conditioning does not alter the breathing pattern of professional cyclists during an incremental exercise test.     

Interrelationships of the volume and time components of individual breaths in resting man.

1. The volume and time components of individual breaths have been investigated under 'steady-state' conditions during air-breathing in fifteen subjects and, in a further six subjects, also during the addition of 1-5 and 3% CO2 to the inspired gas. 2. A computer-assisted method has been used to derive from the air flow record the individual breath values of tidal volume (VT), inspiratory duration (TI), expiratory duration (TE) and cycle duration (TC = TI + TE) for a sequence of breaths in the various steady-state conditions. 3. When the subjects were breathing room air, for breath sequences of over 200 breaths (n = 228-365), mean values of TI (TI) mostly lay between 1 and 2-5 sec, TE between 2-0 and 3-5 sec and VT between 0-4 and 0-91. The distributions of VT, TI and TE were in general unimodal. 4. Significant negative correlations between VT and F, and positive correlations between VT and TC, have been confirmed. 5. In all fifteen subjects, a highly significant positive correlation existed between VT and TI (mean r = +0-704), which was stronger than that between VT and TC (mean r = +0-533). Weaker positive correlations were demonstrated between VT and TE, and between TI and TE (mean r = +0-359 and +0-381 respectively). 6. The intercept of the regression of VT on TI passed close to the origin, typically slightly positive on the VT axis (mean = +0-0991.). This, coupled with the strong positive correlation between VT and TI, indicates that the mean inspiratory flow rate (VI = VT/TI) for each breath is held relatively constant from breath to breath. 7. In the six subjects studied during CO2 inhalation, the mean % contributions of VT and F to the increase in ventilation associated with breathing 3% CO2 were 75 and 25% respectively. 8. At the three different levels of ventilation, neither VT, TI nor TE showed a wholly consistent trend, although VT tended to increase, TE to decrease and TI to be unchanged. In contrast, the average values of VI (VI) consistently increased as the chemical stimulus was raised. 9. It is concluded that the previously observed tendency for ventilation to be held constant from breath to breath during steady-state breathing depends predominantly on the tendency for VI to be held constant. Close restraints are evidently not imposed on the individual values of VT and TI under these conditions. The neural mechanism generating breathing appears to control ventilation principally by regulating the rate of inspiratory air flow and secondarily TE.     

The reflex effects on the respiratory regulation of the CO2 at the different flow rate and concentration

PURPOSE: The purpose of this study was to investigate the activation of the respiratory centers during insufflation of the larynx with CO2 at different flow rates and concentrations. MATERIALS AND METHODS: The experiments were carried out in spontaneous air breathing rabbits, anesthetized with thiopental sodium (25 mg kg(-1) i.v.). The larynx was separated from the oropharyngeal cavity and the trachea. The tidal volume (VT) and respiratory frequency (f min(-1)) were recorded from the lower tracheal cannula. The respiratory minute volume (VE) was calculated, the action potentials from the right phrenic nerve were recorded and the inspiratory (TI) and expiratory (TE) periods and the mean inspiratory flow rate (VT/TI) were calculated. The larynx was insufflated at flow rates of 500 mL min(-1) and 750 mL min(-1), with 7 and 12% CO2-Air by means of a respiratory pump. RESULTS: Insufflation of the larynx, with both gas mixtures, decreased the f and VT significantly. The TI and TE were found to increase significantly due to the decreasing in f. There was a significant decrease in VT/TI ratio. Following bilateral midcervical vagotomy, on the passing of both gas mixtures, significant decreases were observed in the VT, and the responses of f, TI and TE were abolished. After cutting the superior laryngeal nerve, the responses of the VT to both gas mixtures were abolished. CONCLUSION: In conclusion, the results of this study purpose that the stimulation of the laryngeal mechanoreceptors by the effect of hypercapnia decreases the activation of the respiratory center.     

Breathing pattern and lung volumes during exercise

The interrelationships of ventilation (V), tidal volume (VT), inspiratory (T1), expiratory (TE) and total breath (Ttot) durations, mean inspiratory (VT/TI) and expiratory (VT/TE) flows, and lung volumes were studied in normal subjects at rest and during exercise on a cycle ergometer. The ergometric load was increased by 10 W every minute, from zero W to 200 W. The TI/Ttot ratio increased with V in the range 15 to 60 1 X min-1, indicating that with increasing V the rate of increase of VT/TI decreased whereas that of VT/TE increased. Possible mechanisms responsible for the difference in behaviour of VT/TI and VT/TE are discussed. The VT-TI and VT-TE relationships both displayed three ranges with breakpoints at tidal volumes of about 1.4 and 2.4 1. The relations of TI and TE to end-inspiratory volume were approximately linear over the entire VT range studied, whereas the relations of TI and TE to end-expiratory volume showed three ranges with different characteristics. We conclude that the termination of inspiration during cycle exercise is dependent on volume-related afferent feedback from the lungs and/or chest walls, not only in the high but also in the low volume range.     

Evidence for phase-locking response to hypoxia in peripheral chemoreceptor activity in man.

A number of animal studies have demonstrated that the ventilatory response to stimulation of the peripheral chemoreceptors is well reproduced only when it is stimulated during inspiratory period. In humans, such a response has not been confirmed when using a mild hypoxic stimulus. We, therefore, hypothesized that this response may be detected when a more intense hypoxia is applied. To confirm this hypothesis, six healthy subjects inhaled N2 gas mixture with 5% CO2 in an amount of vital capacity. This procedure started from steady state mild hypoxia (PET02; 60-70 mmHg). Inspiratory and expiratory minute ventilation (VI and VE), tidal volume (VT), and inspiratory and expiratory time (TI and TE) of the breath, at the start of falling oxygen saturation, were analyzed. 21% O2 + 5% CO2 balanced with N2 was inhaled and a breath cycle with a similar latency as during N2 gas mixture inhalation was also analyzed as a control. When oxygen saturation began to drop at the inspiratory phase, the increment of ventilation and tidal volume were larger than the control. When it occurred at the expiratory phase, no significant difference from the control was seen. These results signify the presence of rectification of chemoreceptor afferent signal in humans and may support the concept of oscillation hypothesis as an effective ventilatory stimulus.     

Comparison between ventilatory and mouth occlusion pressure responses to hypoxia and hypercapnia in healthy sleeping man

Ventilatory and mouth occlusion pressure (P0.1) responses to progressive isocapnic-hypoxia and hyperoxic-hypercapnia were compared in eleven healthy sleeping men during the same night. Hypoxic and hypercapnic responses were determined during wakefulness, non-rapid and rapid-eye-movement sleep. The following parameters were measured: minute ventilation (VE), tidal volume (VT), 'duty cycle' (TI/TT), mean inspiratory flow rate (VT/TI) and P0.1, an index of the neuromuscular inspiratory drive. To allow a direct comparison between the two types of chemostimuli, responses were characterized by the value of the different parameters at 'equivalent' levels of hypoxia and hypercapnia, i.e., at levels which produced the same P0.1 during wakefulness: an oxyhaemoglobin saturation (Sao2) of 94% during the isocapnic-hypoxic tests (PETCO2 = 42.5 +/- 1.2 mmHg) was found to be equivalent to a PETCO2 of 47.4 +/- 3.7 mmHg during hypoxic-hypercapnic tests. For both tests, the arousal levels of the stimulus and of P0.1 were similar in all sleep stages. Sleep did not significantly modify P0.1 or breathing pattern responses to hypoxia (Sao2 = 94%). In contrast, at the 'equivalent' level of hypercapnic stimulation, P0.1 (P less than 0.05) and VE (P less than 0.01) responses were significantly impaired, particularly in REM sleep, with a decrease in VT (P less than 0.01) and VT/TI (P less than 0.05) responses. The results suggest that CO2 intracranial receptor mechanisms are more affected by sleep than the O2 peripheral receptor activity.     

Lung reflexes in anaesthetized rabbits with elastase-induced emphysema

The effects of elastase-induced emphysema on vagal pulmonary reflexes were studied in seven rabbits, given 600 IU of porcine pancreatic elastase intratracheally (E group), and eight untreated rabbits (U group) under pentobarbital anaesthesia. The presence of emphysema was confirmed by histological and pathological criteria and by documented changes in lung mechanics seven months after treatment. The strength of the Hering-Breuer inflation reflex (HBIR), indicative of pulmonary stretch receptor excitability, was unchanged in the U group, but was significantly increased in the E group at inflation volumes greater than the tidal volume (VT) range, as she slope of the curve relating HBIR to inflation volume was significantly steeper (0.40 vs 0.22 ml-1; p less than 0.05). The early ventilatory response (first 3 breaths) to right atrial injections of phenyldiguanide (20 and 30 micrograms X kg-1 i.v.) was used as an indication of the excitability of lung receptors with non-myelinated vagal afferents. This response, characterized by a significant decrease in expiratory duration (TE) without effect on VT or inspiratory time (TI), was not significantly different between the E and U groups. The overall pattern of breathing in the E group showed a significant decrease in VT associated with an increase in TI.     

Breathing patterns during slow and fast ramp exercise in man

Breathing frequency (fb), tidal volume (VT), and respiratory timing during slow (SR, 8 W min-1) and fast (FR, 65 W min-1) ramp exercise to exhaustion on a cycle ergometer was examined in seven healthy male subjects. Expiratory ventilation (VE), pulmonary gas exchange (VO2 and VCO2) and end-tidal gas tensions (PET,O2 and PET,CO2) were determined using breath-by-breath techniques. Arterialized venous blood was sampled from a dorsal hand vein at 2 min intervals during SR and 30 s intervals during FR and analysed for arterial plasma PCO2 (PaCO2). PET,CO2 increased with increasing work rates (WRs) below the ventilatory threshold (VT); at WRs > or = 90% VO2,max, PET,CO2 was reduced (P < 0.05) below 0 W values in SR but not in FR.fb and VT were similar for SR and FR at all submaximal WRs, resulting in a similar VE. At exhaustion VE was similar but fb was higher (P < 0.05) and VT was lower (P < 0.05) in SR (fb, 51 +/- 10 breaths min-1; VT, 2590 +/- 590 ml) than in FR (fb, 42 +/- 8 breaths min-1; VT, 3050 +/- 470 ml). The time of expiration (TE) decreased with increasing WR, but there was no difference between SR and FR. The time of inspiration (TI) decreased at exercise intensities > or = VT; at exhaustion, TI was shorter (P < 0.05) during SR (0.512 +/- 0.097 s) than during FR (0.753 +/- 0.100 s). The TI to total breath duration (TI/TTot) and the inspiratory flow (VT/TI) were similar during SR and FR at all submaximal exercise intensities; at VO2,max, TI/TTot was lower (P < 0.05) and VT/TI was higher (P < 0.05) during SR (TI/TTot, 0.473 +/- 0.030; VT/TI, 5.092 +/- 0.377 l s-1) than during FR (TI/TTot, 0.567 +/- 0.050; VT/TI, 4.117 +/- 0.635 l s-1). These results suggest that during progressive exercise, breathing pattern and respiratory timing may be determined, at least at submaximal work rates, independently of alveolar and arterial PCO2.     

Breathing pattern and occlusion pressure during moderate and heavy exercise

We studied changes in breathing pattern and mouth occlusion pressure (P0.1) in 11 healthy subjects performing graded steady-state exercise on a cycle ergometer up to the maximal load sustainable for 4 min. With increasing work intensity both the tidal volume (VT) and end-inspiratory volume relations to inspiratory (TI) and expiratory (TE) durations were linear in the moderate work load range; in the high load range VT and end-inspiratory volume tended to plateau with further decreases in TI and TE. The ratio of TI to total breath duration (TI/Ttot) increased with work intensity. Intraindividual coefficients of variation for VT, breathing frequency (f), mean inspiratory flow (VT/TI), and other respiratory variables decreased with increasing work intensity, indicating that breath-to-breath variations in breathing pattern became smaller as the level of ventilation increased. P0.1 rose with VT/TI as a power function with an exponent averaging 1.5 (range 1.3-1.9), indicating that the ratio P0.1/(VT/TI), an index of respiratory system impedance, increased with VT/TI and work intensity. We conclude that in moderate and heavy exercise the work of inspiration at a given ventilation is reduced because of the increase in TI/Ttot, the impedance of the respiratory system increases with work intensity because of both an increase in f and a flow-dependent rise in airway resistance, and the neuromuscular inspiratory activity is reflexly augmented because of internal flow-resistive loading.     

Hypercapnia during maximal exercise in patients with chronic airflow obstruction

The pattern of breathing during maximal oxygen uptake (Vo2max) was studied in 26 patients with chronic airflow obstruction (CAO), in whom the vital capacity (VC), forced expiratory volume in 1 s (FEV1) and residual volume (RV) were measured. The patients performed, on a cycle ergometer, in a sitting position, a submaximal (A) and a maximal (B) exercise in a single session during which three arterial blood samples (pH, PaCO2, PaO2, lactate) were taken: the first at rest, the second at the 10th min of steady-state 40 W exercise, and the third at maximal VO2. VE, VCO2, VO2, respiratory rate (RR) and VT were measured with an open circuit. Physiological dead space (VD) and alveolar to arterial O2 pressure differences (A-aPO2) were computed. According to the measured value of PaCO2 at maximal exercise, the patients were divided in non-hypercapnic (NH; PaCO2 less than 44 mmHg; n = 17) and hypercapnic (H; PaCO2 greater than 44 mmHg; n = 9) groups, and were compared with a group of normal subjects (N; n = 11). At rest, VC, FEV1, FEV1/VC ratio, TLC and PaO2 were more decreased in H than in NH patients. However, RV, VE, RR and VT did not differ between H and NH patients. PaCO2 at rest was comparable in N and H subjects but was significantly lower in NH patients. During B exercise, VE, VO2 and PaO2 were lower in H patients. With both A and B exercises, the H patients showed a lower VT and VT/VC ratio with a higher VD/VT ratio, while A-aPO2 were the same in NH and H patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hyperventilation with He-O2 breathing is not decreased by superimposed external resistance

The purpose of this study was to determine the effect of imposed external resistance on the ventilatory response to He-O(2) breathing during peak exercise. To accomplish this purpose, separate inspiratory and expiratory external resistances were applied to offset for the decrease in intrapulmonary airway resistance with He-O(2) breathing. Seven men and three women (69+/-3 years, mean+/-S.D.) with normal pulmonary function performed graded cycle ergometry to exhaustion breathing room air, He-O(2) (79% He, 21% O(2)), He-O(2) with imposed expiratory resistance, and He-O(2) with imposed inspiratory resistance. Ventilation (VE), lung mechanics, and PET(CO(2)) were measured during each 1 min increment in work rate and were analyzed by one-way ANOVA for repeated measures at rest, ventilatory threshold (VTh), and peak exercise. In response, VE was increased and PET(CO(2)) was decreased at VTh (P<0.01) and peak exercise (P<0.01) whenever breathing He-O(2). Thus, VE was increased during exercise above VTh with He-O(2) breathing regardless of increases in inspiratory or expiratory external resistance. In conclusion, these data suggest that inspiratory resistive unloading is no more important than expiratory resistive unloading to the increase in VE with He-O(2) breathing during heavy and peak exercise.     

Pulmonary function profile in patients with benign goiters without symptoms of respiratory compromise and the early effect of thyroidectomy

Background: A large number of patients in our country develop goiters which seem to be apparently asymptomatic. Conventional radiography does not address the abnormal air flow dynamics. Flow volume loop studies have shown characteristic dampening of both inspiratory and expiratory curves. Pulmonary function tests (PFT) can provide a simple noninvasive method of assessing airway compromise. Aim: To address the effect of longstanding asymptomatic, benign goiter by performing PFT on the preoperative airway dynamics and the early postoperative changes at six weeks. Setting and Design: Tertiary care center, Prospective study. Materials and Methods: Sixty-four patients with benign goiters were included after they satisfied the necessary exclusion and inclusion criteria. Pulmonary function tests were performed in the pre and postoperative period. Statistical Analysis Used: SPSS ver. 10 software, Pearson's Bivariate correlation and students T test. Results: The preoperative PFT showed significant reduction in the Vital capacity (VC), Forced Vital Capacity (FVC), Forced expiratory volume in one second (FEV1), mid expiratory flow (MEF 25) and MEF 50 in the females and VC, FVC and FEV1 in males. Postoperatively significant improvement was observed in the tidal volume (VT) and FEV1 in the females and airway resistance in males. Conclusions: Pulmonary function tests can demonstrate the unmanifested abnormal airflow dynamics in benign asymptomatic goiters, which would have otherwise taken years to manifest. This abnormality improved after thyroidectomy, especially the forced expiratory maneuvers. The duration and weight of the goiter correlated well with reduction in FEV1 and its subsequent improvement after surgery in females.     

A comparison of single breath and re-breathe diffusing capacity in emphysema patients and controls

In emphysema patients, gas dilutional alveolar volume is underestimated by a 10s single breath maneuver at total lung capacity (TLC) compared with re-breathing at functional residual capacity (FRC); corresponding underestimation of single breath diffusing capacity (DLCO) in emphysema has not been demonstrated. The purpose of this study was to quantify the degree to which re-breathe DLCO at FRC (DLCO(RB)) differs from single breath DLCO at TLC (DLCO(SB)) in emphysema. In 37 consecutively recruited patients with moderate to severe emphysema (FEV1/FVC 40%±10% predicted), DLCO(RB) as % predicted of 91 controls without cardiopulmonary disease was 79%±24%, significantly greater than % predicted DLCO(SB) (44%±19%; p<0.0001). DLCO(RB)/DLCO(SB) was inversely proportional to FEV1% predicted (R = -0.47, p=0.004), and FEV1/FVC (R = -0.54, p<0.001). These data indicate that a 10s single breath DLCO maneuver progressively under-represents re-breathe lung diffusing capacity in emphysema as airflow obstruction increases.     

Breath-holding time: effects of non-chemical factors in divers and non-divers

Two main factors (chemical and non-chemical factors) are involved in the determination of breath-holding time (BHT). Earlier studies have shown that chemical factors can be modified by training. The aim of this study was to establish whether BHT can be lengthened or shortened by changes in non-chemical factors according to the degree of training of the divers. Hyperoxic hypercapnic rebreathing challenges interrupted by different periods of voluntary apnoea (20, 40 and 50 s) were performed by divers (n=8) and non-divers (n=6). The relationships between ventilation (VE) and end-tidal PCO2 and mean inspiratory flow (VT/TI) where VT is the tidal volume and TI the inspiration time) and end-tidal PCO2 were measured before (pre) and after (post) apnoea for each population. The slopes of these linear regressions (VEs and VT/TI,s, respectively) reflected respiratory centre activity. VFs-post and VT/TIs-post increased with BHT and were higher in the non-divers than in divers. There were no significant differences between VFs-pre and VFs-post or between VT/TIs,-pre and VT/TIs-post in divers for all BHT. However, in non-divers, significant differences between pre and post values appeared at 20, 40 and 50 s for VT/TI,s and at 40 and 50 s for VEs. Non-chemical factorswere obtained by calculating the differences between pre and post values and were different at 20 and 40 s for VEs (P<0.05) and for all BHT for VT/TI,s (P<0.05). The non-chemical factors increased significantly with BHT and were higher in the non-divers. These adaptations in divers may modify the breath-hold breaking point and consequently increase BHT.     

Mean and breath-by-breath pattern of breathing in man during steady-state exercise.

1. The breathing pattern, that is the relation between tidal volume (VT) and the inspiratory (TI) and expiratory (TE) durations, has been studied for individual breaths (forty in each steady state). 2. Five healthy subjects were studied in steady-state exercise on a bicycle ergometer breathing air; three of them were also studied in hypercapnia, at rest and during exercise, and two of them also during exercise on a treadmill. 3. Tidal volume and respiratory frequency both increased with work load. The increase in frequency was largely due to a progressive decrease in TE; TI also decreased. 4. At any constant level of respiratory drive (constant work load or chemical load) VT was positively correlated with both TI and TE in more than 95% of cases. 5. A simple model of the respiratory cycle which fits both the observed mean and breath-by-breath patterns and which involves no new assumptions is presented.     

Role of small airways in asthma: investigation using high-resolution computed tomography

BACKGROUND: Small airways may have an important role in asthma but are more difficult to assess pathologically than central airways. Computed tomographic indices of lung density are assumed to reflect air trapping and may be a useful noninvasive measure of small airways disease, but their pathophysiological relevance remains undetermined. OBJECTIVE: To evaluate lung density on high-resolution computed tomography and examine its correlations with clinical and physiologic variables in 29 patients with stable asthma. METHODS: Both lungs were scanned at full-inspiratory and full-expiratory phases to quantify percentage of lung field occupied by low attenuation area (LAA%; < -960 Hounsfield units) and mean lung density. Asthma severity, pulmonary function, methacholine airway sensitivity and reactivity, and sputum eosinophil counts were evaluated. RESULTS: The mean lung density increased and LAA% decreased in all patients at expiratory phase compared with inspiratory phase. The inspiratory density indices and expiratory mean lung density correlated only with FEV(1)/forced vital capacity (FVC). Expiratory LAA% correlated more strongly than other variables with FEV(1)/FVC and with indices of peripheral airflow obstruction. Expiratory/inspiratory ratios of LAA% and mean lung density correlated, the former more strongly, with disease severity, residual volume/total lung capacity, and airway sensitivity, as well as with indices of global (FEV(1) and FEV(1)/FVC) and peripheral airflow obstruction. CONCLUSION: Expiratory/inspiratory high-resolution computed tomography is useful for assessing small airways disease in asthma. Small airways involvement is associated with airflow obstruction, airway hypersensitivity, and more severe disease. CLINICAL IMPLICATIONS: Small airways are an important therapeutic target in asthma.     

Effects of naloxone on the control of breathing in children with chronic obstructive pulmonary disease

The effect of naloxone on occlusion pressure (P0.1), the pattern of breathing and the expiratory flows during spontaneous ventilation was studied in 16 children with chronic obstructive pulmonary disease under control conditions, after isotonic saline injection and 5 (N5) and 25 (N25) min after i.v. injection of naloxone (2 micrograms X kg-1). At N5, no change was observed in tidal volume normalized for body weight (VTBW), inspiratory time (TI), respiratory frequency (f), mean inspiratory flow (VTBW/TI) and the ratio of TI and total duration of the respiratory cycle (TI/TT). P0.1 decreased significantly (p less than 0.001) at N5 and returned to control values at N25. The decrease in P0.1 without any change in the breathing pattern suggests that naloxone has an effect on respiratory mechanics. Indeed, at N5, the expiratory flows generated at 25% of VT, measured on the flow-volume curves during spontaneous ventilation, increased significantly when compared to control values. Moreover, the decrease of P0.1 after naloxone was found to be correlated to the reduction of dynamic lung compliance (CLdyn) (p less than 0.02). It is speculated that peripheral airway obstruction, as reflected by the decrease in CLdyn, might be a triggering factor for the release of endorphins. The bronchodilation observed after naloxone could then be due to naloxone's antagonistic effect on endorphin-induced bronchoconstriction.     

Respiratory responses to shivering produced by external and central cooling in the pigeon

Respiratory responses of pigeons to spinal cord cooling (5-6 degrees C) in neutral environment (Ta = 28 degrees C), to ambient cooling (Ta = 5 degrees C), and to simultaneous spinal cord and ambient cooling were measured. Spinal cord cooling produced shivering and a 242% increased in heat production (M); expiratory flow rate (VE) increased 216%, a result of increases in both respiratory frequency (160%) and tidal volume (140%). Increases produced by ambient cooling compared to thermoneutral controls were slightly, but not significantly, less than those during spinal cord cooling: M = 203%, VE = 199%, respiratory frequency (fR) = 146%, tidal volume (VT) = 138%. Spinal cord cooling at low ambient temperature produced greater increases in shivering, heat production and respiration compared to thermoneutral controls than either type of cooling alone: M = 337%, VE = 326%, fR = 198%, VT = 178%. The oxygen extraction from the ventilatory gas remained relatively constant among the different groups. fR, VT and VE were all significantly linearly related to M over the wide range studied. These relationships were independent of whether cooling was central or external. Respiratory changes induced by the onset and end of spinal cord cooling were immediate and closely correlated with the magnitude of shivering. It is unlikely that changes in arterial and venous blood gases during shivering effected the major portion of the respiratory response. Thus, it is suggested that a control mechanism of the respiratory center via afferents from the shivering muscles is important in increasing respiration during central or external cooling.