Influences of lung mechanoreceptors and carotid chemoreceptors on the response of respiratory muscle activity to tracheal occlusion

We examined the responses of respiratory muscle electromyograms (EMGs) from internal (IIC) and external intercostal (EIC) muscles and diaphragm (DIAP) to three successive occluded breaths in anesthetized spontaneously breathing rabbits. Both inspiratory and expiratory muscle EMGs progressively increased in the course of tracheal occlusion. An increase in these muscle EMGs was still observed after release of tracheal occlusion, but those effects were short-lasting. In a separate series of experiments, for assessment of possible reflex effects involved, the responses of slowly adapting pulmonary stretch receptor (SAR), rapidly adapting pulmonary stretch receptor (RAR), and carotid chemoreceptor activities to tracheal occlusion lasting for three respiratory efforts were also examined. The inspiratory discharge of SARs decreased but the expiratory discharge of SARs increased during tracheal occlusion. Although carotid chemoreceptors increased their activity in the latency of 3-6s after the onset of tracheal occlusion, the activity of RARs was greatly reduced throughout the period of tracheal occlusion. A transient increase in both carotid chemoreceptors and RARs was still observed after release of tracheal occlusion. These results suggest that alterations of inspiratory and expiratory muscle EMGs produced by tracheal occlusion would appear to be mediated by the afferent inputs from lung mechanoreceptors and carotid chemoreceptors.     

Expiratory versus inspiratory efforts in suffocating pigeons

The respiration of anaesthetized pigeons, suffocated to death by tracheal occlusion, is followed by means of the intratracheal pressure tracing. A special procedure allows to distinguish expiratory from inspiratory efforts.The overall expiratory effort about equals the inspiratory one. During the agony, however, the release of expiratory energies increases whereas inspiratory activity is vanishing more and more.On the basis of the period of agony, a screening procedure is developed to search for substances which would selectively influence the release of expiratory or inspiratory energies respectively.     

Ventilatory and occlusion-pressure responses to exercise in trained and untrained children

Summary Pattern of breathing and mouth occlusion pressure were investigated during an incremental and exhaustive ergocycle test in untrained and trained 11 to 13 year old boys. At each level of exercise, the trained group had lower ventilation, a lower respiratory equivalent, and a lower respiratory rate. These results suggest that trained subjects have more efficient ventilation. Lower ventilation coincided with a smaller mean inspiratory flow (V_T/T_I), while the ratio of inspiratory to total breath (T_I/T_TOT) was unchanged. In contrast, mouth occlusion pressure and the index of neuromuscular inspiratory drive were the same up to 60 W for the two groups, and tended to be slightly lower in the trained boys above this level.     

Inspiratory versus expiratory efforts in pigeons: A search for selective drug influence

Respiratory activity of anaesthetized pigeons was stimulated by occluding the trachea. Inspiratory and expiratory efforts were measured in an early and in the agonal period of prolonged tracheal occlusions.In the early period the mean change in intratracheal pressure amounted to –0.79 cm H₂O and +0.73 cm H₂O per breath. These mean pressures are considered to represent an equivalent of the mean inspiratory and expiratory activity of that period. The corresponding figures in the agonal period were –1.18 and +2.48 cm H₂O, respectively.A palette of 10 drugs was tested to see whether they could alter respiratory efforts. None of the drugs, including the CNS-stimulants, was able to increase the efforts in either of the two periods. Some of the drugs (ethylurethane, pentobarbitone, codeine and 37059¹)) led to an impairment of the efforts performed in the early period, to about the same extent in both inspiration and expiration. One drug (37059) led to an impairment of the expiratory efforts in the agonal period and to an increase of the inspiratory efforts at the same time.     

Affective modulation of inspiratory motor drive

The present study aimed to explore inspiratory motor drive as measured by inspiratory occlusion pressure (P100) during affective picture viewing. P100 is the decrease in mouth pressure that develops 100 ms after an inspiratory effort against a closed breathing circuit. The P100 is a measure of the "central respiratory drive." Seventy-eight healthy women viewed four pictures series (160 s) varying in content: neutral, positive, threat, or pain. They also rated each picture series on pleasantness and arousal. An occlusion was applied at the onset of inspiration in 33% of the breaths. The threat and the pain picture series were associated with an increased P100 and were rated as most unpleasant and highest in arousal. We conclude that inspiratory motor drive is affectively modulated and is a measure of the respiratory response to threatful stimuli.     

Action potentials in parasympathetic and sympathetic efferent fibres to the trachea and lungs of dogs and cats

1. Action potentials were recorded from seventy-four single and twenty-nine small multifibre nerve strands efferent to the trachea and lungs of cats and dogs. From the pathway (vagal or sympathetic), spontaneous activity, conduction velocity and responses to various interventions the efferent fibres were classified in the following way.2. Group I, vagal. These had a mean conduction velocity of 9.7 m/sec, and had a respiratory but seldom a cardiac rhythm. Their discharge was inhibited during hypertension caused by injections of adrenaline and during inflation of the lungs, but was increased during tracheal occlusion, stimulation of peripheral chemoreceptors and irritation of the larynx. The fibres are thought to be constrictor to the airways.3. Group II, sympathetic. These had a mean conduction velocity of 0.85 m/sec and usually had inspiratory and cardiac rhythms. Their discharge usually responded qualitatively as that of group I fibres to the various interventions, but with clear quantitative differences. They are divided into three subgroups on the basis of their responses to injections of adrenaline and to asphyxial stimuli.4. Group III, vagal and sympathetic. These had a mean conduction velocity of 9.0 m/sec, very slow discharge rates and often an expiratory and cardiac modulation. They were activated during hypertension due to adrenaline and often by tracheal occlusion, chemoreceptor stimulation, laryngeal irritation and lung inflation. Their motor action is unknown.5. Group IV, vagal and sympathetic. These had conspicuous cardiac rhythms resembling those of vascular baroreceptors, but their discharge could not be correlated with arterial blood pressure. Their mean conduction velocity was 6.6 m/sec. Some were active after combined vagotomy and sympathectomy. Together with some unclassified fibres, those of group IV are thought to be aberrant afferent nerves or collateral afferent branches, and possibly to subserve local reflexes.6. The results are discussed in relation to nervous control of effector tissues in the airways and autonomic nervous control generally.     

Non-invasive semi-quantitative measurements of tidal pressure-volume and flow relations of lung in COPD patients

Movement of the suprasternal fossa as detected by surface inductive plethysmography (SIP) has been utilized as a non-invasive means for estimation of intrapleural pressure in the calculation of lung compliance. The purpose of the present study was to ascertain whether pulmonary resistance and work of breathing could also be obtained with SIP. A new calibration procedure based upon substituting values for inspiratory total respiratory resistance measured by forced oscillations into an uncalibrated SIP deflection-flow loop was utilized to convert the SIP waveform to a pressure recording. This permitted estimation of lung compliance, expiratory pulmonary resistance and work of breathing which were then compared to simultaneously measured intraesophageal pressure derived values. Nine seated patients with varying degrees of obstructive airways disease were studied. No differences were found between the SIP and intraesophageal derived group mean values for any parameters, viz inspiratory and expiratory pulmonary resistance, lung compliance and work of breathing. The least variable measurement between the two methods was the work of breathing in which eight of the nine patients had values deviating less than 25% from unity. Values for lung compliance were slightly more divergent and expiratory pulmonary resistance showed large variation. The present investigation indicates that surface inductive plethysmographic detection of suprasternal fossa movement reflects intrapleural pressure swings in a semiquantitative manner; it serves as a non-invasive research technique for estimation of lung compliance, pulmonary resistance and work of breathing.     

Differences in mouth occlusion pressure and breathing pattern between arm and leg incremental exercise

The aim of the study was to compare breathing pattern, mouth occlusion pressure, mean inspiratory flow and the ratio of mouth occlusion pressure to mean inspiratory flow at the same power output and carbon dioxide output during arm and leg incremental exercise. Mouth occlusion pressure was used as an index of inspiratory neuromuscular activity and its ratio to mean inspiratory flow as an index of the ‘effective’ impedance of the respiratory system. Eight normal subjects performed two incremental exercise tests, one with arms, the other with legs, on different weeks and in randomized order, and on two identical cycle ergometers. The power output was increased by steps of 25 W for arms and 50 W for legs every 4 min until exhaustion. At the same power output, oxygen consumption, carbon dioxide output, ventilation, mean inspiratory flow, mouth occlusion pressure, ‘effective’ impedance (P<0.001) and respiratory frequency (P<0.01) were higher during arm exercise than during leg exercise, whereas inspiratory time (P<0.05) and expiratory time (P<0.01) were lower. At the same carbon dioxide output, mouth occlusion pressure, ventilation, ‘effective’ impedance (P<0.001) and respiratory frequency (P<0.01) were higher and expiratory time (P<0.05) was lower during arm exercise. In conclusion, the higher inspiratory neuromuscular activity and impedance of the respiratory system during arm exercise and the differences observed in ventilation and breathing pattern at equal carbon dioxide output seem related to the differences in exercising muscle afferents and the presence of an increased load due to contraction of rib cage muscles to stabilize posture.     

Tracheal sounds and airflow dynamics in surgically treated unilateral vocal fold paralysis.

The aim of this study was to investigate the changes in tracheal sounds and airflow dynamics in patients who underwent surgical medialization of a unilaterally paralysed vocal fold. Ten adults with unilateral vocal fold paralysis but no history of pulmonary diseases were included. Vocal fold medialization was performed by an injection of autologous fascia into the paralysed vocal fold. Recording of tracheal sounds, flow-volume spirometry and body plethysmography were carried out before and 4-14 months after the operation. The mean number of inspiratory wheezes per respiratory cycle increased from 0.02 (range 0-0.10) to 0.42 (range 0-0.86) and the mean number of expiratory wheezes per respiratory cycle from 0.03 (range 0-0.20) to 0.36 (range 0-0.89). The increment was statistically significant (P=0.03 and P=0.04, respectively). The mean expiratory sound amplitude, in terms of root mean square (RMS), increased from 31.5 dB (range 24.0-38.0) to 34.9 dB (range 25-42) (P=0.03) and the average peak inspiratory flow (PIF) decreased from 4.63 l s-1 (range 2.84-7.51) to 4.03 l s-1 (range 2.27-6.68) (P=0.01). The results indicate that when the paralysed vocal fold is brought into midline by a surgical procedure, the prevalence of inspiratory and expiratory wheezes increases and sound intensity rises. According to this preliminary data tracheal sound analysis gives additional information for the assessment of the subtle changes in the larynx.     

Scalene muscle activity during progressive inspiratory loading under pressure support ventilation in normal humans

We hypothesized that (1) in healthy humans subjected to intermittent positive pressure non-invasive ventilation, changes in the ventilator trigger sensitivity would be associated with increased scalene activity, (2) if properly processed – through inspiratory phase-locked averaging – surface electromyograms (EMG) of the scalenes would reliably detect and quantify this, (3) there would be a correlation between dyspnea and scalene EMG. Surface and intramuscular EMG activity of scalene muscles were measured in 10 subjects. They breathed quietly through a face mask for 10 min and then were connected to a mechanical ventilator. Recordings were performed during three 15-min epochs where the subjects breathed against an increasingly negative pressure trigger (−5%, −10% and −15% of maximal inspiratory pressure). With increasing values of the inspiratory trigger, inspiratory efforts, dyspnea and the scalene activity increased significantly. The scalene EMG activity level was correlated with the esophageal pressure time product and with dyspnea intensity. Inspiration-adjusted surface EMG averaging could be useful to detect small increases of the scalene muscles activity during mechanical ventilation.     

不同工种石棉肺患者CT肺功能成像指标的差异性研究

目的 采用多层螺旋CT肺功能成像技术评价不同工种石棉肺患者的肺功能指标改变及特点.方法 将30例石棉肺患者按工种分为压型组、梳纺组和原棉组,每组10例.分别于受试者深吸气末和深呼气末屏气行全肺扫描,测定肺容积指标(最大吸气与呼气末肺容积、肺容积差、肺容积比)、平均肺密度指标(吸气与呼气末平均肺密度、肺密度差、肺密度比)和小气道指标(吸气与呼气末壁厚直径比率、吸气末支气管壁面积百分比).结果 压型组、梳纺组和原棉组在性别、年龄、接触史、分期(Ⅰ期)方面差异均无统计学意义(均P＞0.05).肺容积、平均肺密度和小气道指标中,3组间呼气末平均肺密度、呼气末左肺平均肺密度、呼气末右肺平均肺密度、呼气末与吸气末平均肺密度比、吸气末壁厚直径比率、吸气末支气管壁面积百分比和呼气末壁厚直径比率差异均具有统计学意义(均P＜0.05);进一步两两比较发现,梳纺组的上述指标分别与原棉组和压型组比较,差异亦均具有统计学意义(均P＜0.05),而原棉组和压型组间差异均无统计学意义(均P＞0.05);3组间其余指标差异均无统计学意义(均P＞0.05).结论 与压型组和原棉组比较,梳纺组石棉肺患者的肺气肿及小气道壁和肺泡隔纤维性增厚更为明显,应加强对这部分人的保护.     

Inspiratory muscle adaptations following pressure or flow training in humans

Skeletal muscle adapts differently to training with high forces or with high velocities. The effects of these disparate training protocols on the inspiratory muscles were investigated in ten healthy volunteers. Five subjects trained using high force (pressure) loads (pressure trainers) and five trained using high velocity (flow) loads (flow trainers). Pressure training entailed performing 30 maximal static inspiratory efforts against a closed airway. Flow training entailed performing 30 sets of three maximal dynamic inspiratory efforts against a minimal resistance. Training was supervised and carried out 5 days a week for 6 weeks. Inspiratory flow rates and oesophageal pressure-time curves were measured before and after training. Peak inspiratory pressures during maximal static and dynamic efforts and peak flows during the maximal dynamic efforts were calculated. The time-to-peak pressure and rate of rise in peak pressure during maximal static and dynamic manoeuvres were also calculated before and following training. Maximal static pressure increased in the pressure training group and maximal dynamic pressure increased in the flow training group. Both groups increased the rate of pressure production (dP/dt) during their respective maximal efforts. The post-training decrease in time-to-peak pressure was proportionately greater in the flow trainers than in the pressure trainers. The differences in time-to-peak pressure between the two groups were consistent with the different effects of force and velocity training on the time-to-peak tension of skeletal muscle.     

Respiratory muscle performance with stretch‐shortening cycle manoeuvres: maximal inspiratory pressure–flow curves

Aim: To test the hypothesis that the maximal inspiratory muscle (IM) performance, as assessed by the maximal IM pressure–flow relationship, is enhanced with the stretch‐shortening cycle (SSC). Methods: Maximal inspiratory flow–pressure curves were measured in 12 healthy volunteers (35 ± 6 years) during maximal single efforts through a range of graded resistors (4‐, 6‐, and 8‐mm diameter orifices), against an occluded airway, and with a minimal load (wide‐open resistor). Maximal inspiratory efforts were initiated at a volume near residual lung volume (RV). The subjects exhaled to RV using slow (S) or fast (F) manoeuvres. With the S manoeuvre, they exhaled slowly to RV and held the breath at RV for about 4 s prior to maximal inspiration. With the F manoeuvre, they exhaled rapidly to RV and immediately inhaled maximally without a post‐expiratory hold; a strategy designed to enhance inspiratory pressure via the SSC. Results: The maximal inspiratory pressure–flow relationship was linear with the S and F manoeuvres (r² = 0.88 for S and r² = 0.88 for F manoeuvre, P < 0.0005 in all subjects). With the F manoeuvre, the pressure–flow relationship shifted to the right in a parallel fashion and the calculated maximal power increased by approximately 10% (P < 0.05) over that calculated with the S manoeuvre. Conclusion: The maximal inspiratory pressure–flow capacity can be enhanced with SSC manoeuvres in a manner analogous to increases in the force–velocity relationship with SSC reported for skeletal muscles.     

Perception of multiple-breath inspiratory resistive loads in males and females

Resistive load magnitude estimation (ME) was measured over multiple breaths in male and female subjects. It was hypothesized that multiple breaths against a range of resistive loads would result in a change in the perceived load magnitude as a function of load magnitude and the number of inspiratory efforts. It was further hypothesized that males and females would differ in their perceptual response to sustained breathing against inspiratory resistive loads. The subjects were tested in a sound isolated room and respired through a non-rebreathing valve, the inspiratory port connected to the loading manifold. The subject inspired to a peak airflow target for each breath. Each R load was presented for 10 continuous breaths. The load was estimated at breath 1, 5, and 10 using a modified Borg scale. Each 10-breath load presentation was presented in a randomized block. There was no significant group difference between the ME for breath 1 and 10 for small R loads, but a significant group difference for large R loads. The ME for males did not change between breath 1 and 10 for the small load magnitudes, but decreased with large loads. The ME for the 10th breath of the large R load was greater than the 1st breath for females. Males estimated the large R load on the 1st breath the same as females but the ME on the 10th breath was significantly less for males compared to females. These results demonstrate that magnitude estimation of large resistive loads with a sustained 10-breath trial elicits significant increases in females, but significantly decreased in males. The increase in ME may represent increased respiratory discomfort for females and the decrease habituation in males.     

Characteristics of inspiratory inhibition by occlusion of both external carotid and basilar arteries in cats.

Effects of the occlusion of both the external carotid and basilar arteries on the inspiratory activity were studied in anesthetized, vagotomized, paralyzed, and artificially ventilated cats. Integrated phrenic nerve activity was used as an index of the inspiratory activity. Blood pressure in the lingual artery, located downstream from the occluded external carotid arteries, was measured as the arterial pressure of the upper brain stem during occlusion. The basilar artery was occluded at the boundary between the medulla and pons. Occlusions of the external carotid arteries and basilar artery suppressed the phrenic nerve activity to finally disappear within 1 min (phrenic nerve apnea, 45 out of 50 occlusions in 6 cats). The blood pressure in the upper brain stem was 16.6 +/- 5.7 mmHg (mean +/- S.D.) during occlusions. These effects of occlusion on the phrenic nerve activity were also observed during hypercapnia and hypoxia, although they were not so remarkable as those during normocapnia and normoxia. The results indicate that the upper part of the brain stem operates a profound facilitatory mechanism on the medullary inspiratory activity.     

Respiratory muscle performance with stretch-shortening cycle manoeuvres: maximal inspiratory pressure-flow curves

AIM: To test the hypothesis that the maximal inspiratory muscle (IM) performance, as assessed by the maximal IM pressure-flow relationship, is enhanced with the stretch-shortening cycle (SSC). METHODS: Maximal inspiratory flow-pressure curves were measured in 12 healthy volunteers (35 +/- 6 years) during maximal single efforts through a range of graded resistors (4-, 6-, and 8-mm diameter orifices), against an occluded airway, and with a minimal load (wide-open resistor). Maximal inspiratory efforts were initiated at a volume near residual lung volume (RV). The subjects exhaled to RV using slow (S) or fast (F) manoeuvres. With the S manoeuvre, they exhaled slowly to RV and held the breath at RV for about 4 s prior to maximal inspiration. With the F manoeuvre, they exhaled rapidly to RV and immediately inhaled maximally without a post-expiratory hold; a strategy designed to enhance inspiratory pressure via the SSC. RESULTS: The maximal inspiratory pressure-flow relationship was linear with the S and F manoeuvres (r2 = 0.88 for S and r2 = 0.88 for F manoeuvre, P < 0.0005 in all subjects). With the F manoeuvre, the pressure-flow relationship shifted to the right in a parallel fashion and the calculated maximal power increased by approximately 10% (P < 0.05) over that calculated with the S manoeuvre. CONCLUSION: The maximal inspiratory pressure-flow capacity can be enhanced with SSC manoeuvres in a manner analogous to increases in the force-velocity relationship with SSC reported for skeletal muscles.     

Inspiration inhibiting effect of etorphine-derivatives

The inspiration inhibiting vagal reflex as elicited in rabbits by tracheal occlusion in inspiratory position, is strongly increased by etorphine and its derivatives, the 19-isoamylderivative being of outstanding activity.     

Ventilatory responses to hypercapnia in divers and non-divers: effects of posture and immersion

The aim of this study was to determine the effects on respiratory drive of two factors, one mechanical (lung volume) and one chemical (sensitivity to hypercapnia), that are involved in determining the breath-hold duration (BHD). Functional residual capacity was measured by helium dilution with the subject seated in air, seated in water and in the prone position in water. Hyperoxic hypercapnia rebreathing (Read's method) was carried out under identical environmental conditions to assess the effects of CO₂ pressure on respiratory centre output by measuring ventilation, mean inspiratory flow and occlusion pressure. Sixteen healthy volunteers were tested, 8 trained divers and 8 non-divers. Functional residual capacity decreased for the postures seated in water (30.8%–34.8%) and for prone position in water (20.3%–20.9%) when compared to the posture seated in air (P<0.0001), all subjects pooled. No difference was found between groups. The slopes of the linear regression, which characterised the sensitivity to CO₂ and were determined with the rebreathing tests, revealed differences between the two populations (ventilation: P<0.0001; mean inspiratory flow: P<0.05). No difference was found for occlusion pressure or between the different postures. These results confirmed a lower sensitivity to CO₂ for trained divers. This adaptation was shown to decrease respiratory centre activity at the origin of the breath-hold breaking point. The immersion, did not influence respiratory drive, despite a decrease in lung volumes. The authors suggest that these findings may be explained by a specific apnoea training and a pronounced bradycardia in immersion. Electronic Publication     

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 role of arterial chemoreceptors in the breath-by-breath augmentation of inspiratory effort in rabbits during airway occlusion or elastic loading

1. The breath-by-breath augmentation of inspiratory effort in the five breaths following airway occlusion or elastic loading was assessed in anaesthetized rabbits from changes of airway pressure, diaphragm e.m.g. and lung volume.2. When the airway was occluded in animals breathing air, arterial O(2) tension fell by 20 mmHg and CO(2) tension rose by 7 mmHg within the time of the first five loaded breaths.3. Inhalation of 100% O(2) or carotid denervation markedly reduced the breath-by-breath progression but had little or no effect on the responses at the first loaded breath.4. These results indicate that the breath-by-breath augmentation of inspiratory effort following addition of a load is mainly due to asphyxial stimulation of the carotid bodies, rather than to the gradual emergence of a powerful load-compensating reflex originating in the chest-wall, as postulated by some workers.5. The small residual progression seen in animals breathing 100% O(2) or following carotid denervation was not eliminated (a) by combining these procedures or (b) by addition of gas to the lungs to prevent the progressive lung deflation which occurred during airway occlusion.6. Bilateral vagotomy, when combined with carotid denervation, abolished the residual breath-by-breath progression of inspiratory effort.