Inspiratory muscle forces and endurance in maximum resistive loading

1985 ◽  
Vol 58 (5) ◽  
pp. 1608-1615 ◽  
Author(s):  
G. L. Jones ◽  
K. J. Killian ◽  
E. Summers ◽  
N. L. Jones
Keyword(s):  
Peak Inspiratory Pressure ◽  
Respiratory Muscles ◽  
Normal Subjects ◽  
Inspiratory Pressure ◽  
Endurance Capacity ◽  
Breathing Patterns ◽  
O2 Uptake ◽  
Maximum Resistance ◽  
Inspiratory Muscles ◽  
Resistive Loads

The ability of the respiratory muscles to sustain ventilation against increasing inspiratory resistive loads was measured in 10 normal subjects. All subjects reached a maximum rating of perceived respiratory effort and at maximum resistance showed signs of respiratory failure (CO2 retention, O2 desaturation, and rib cage and abdominal paradox). The maximum resistance achieved varied widely (range 73–660 cmH2O X l-1 X s). The increase in O2 uptake (delta Vo2) associated with loading was linearly related to the integrated mouth pressure (IMP): delta Vo2 = 0.028 X IMP + 19 ml/min (r = 0.88, P less than 0.001). Maximum delta Vo2 was 142 ml/min +/- SD 68 ml/min. There were significant (P less than 0.05) relationships between the maximum voluntary inspiratory pressure against an occluded airway (MIP) and both maximum IMP (r = 0.80) and maximum delta Vo2 (r = 0.76). In five subjects, three imposed breathing patterns were used to examine the effect of different patterns of respiratory muscle force deployment. Increasing inspiratory duration (TI) from 1.5 to 3.0 and 6.0 s, at the same frequency of breathing (5.5 breaths/min) reduced peak inspiratory pressure and increased the maximum resistance tolerated (190, 269, and 366 cmH2O X l-1 X s, respectively) and maximum IMP (2043, 2473, and 2913 cmH2O X s X min-1, but the effect on maximum delta Vo2 was less consistent (166, 237, and 180 ml/min). The ventilatory endurance capacity and the maximum O2 uptake of the respiratory muscles are related to the strength of the inspiratory muscles, but are also modified through the pattern of force deployment.

Effect of ventilatory drive on the perceived magnitude of added loads to breathing

1982 ◽  
Vol 53 (4) ◽  
pp. 901-907 ◽  
Author(s):  
J. G. Burdon ◽  
K. J. Killian ◽  
E. J. Campbell
Keyword(s):  
Power Function ◽  
Muscle Force ◽  
Peak Inspiratory Pressure ◽  
Normal Subjects ◽  
Inspiratory Pressure ◽  
Resistive Load ◽  
Sensory Magnitude ◽  
Magnitude Scaling ◽  
Ventilatory Drive ◽  
Resistive Loads

Using open-magnitude scaling we studied the importance of ventilatory drive on the perceived magnitude of respiratory loads by applying a range of externally added resistances (2.1–77.1 cmH2O X l-1 X s) to normal subjects at rest and at three increasing levels of ventilatory drive induced by exercise, CO2-stimulated breathing, and hypoxia. Under all conditions studied the perceived magnitude of the added loads increased with the magnitude of the resistive load and as the underlying level of ventilatory drive increased. When the results were expressed in terms of peak inspiratory pressure, the perceived magnitude was related to the magnitude of the peak inspiratory pressure by a power function (mean r = 0.97). These results suggest that the perceived magnitude of added resistive loads increased with increasing ventilatory drive, in such a manner that the increase in sensory magnitude is proportional to the increase in the inspiratory muscle force developed and suggests that something dependent on this force mediates the sensation.

Respiratory mechanics and breathing pattern during and following maximal exercise

1984 ◽  
Vol 57 (6) ◽  
pp. 1773-1782 ◽  
Author(s):  
M. Younes ◽  
G. Kivinen
Keyword(s):  
Time Course ◽  
Maximal Exercise ◽  
Dynamic Pressure ◽  
Respiratory Muscles ◽  
Normal Subjects ◽  
Esophageal Pressure ◽  
Inspiratory Pressure ◽  
Elastic Recoil ◽  
Inspiratory Muscles ◽  
Inspiratory Muscle Fatigue

We looked for evidence of changes in lung elastic recoil and of inspiratory muscle fatigue at maximal exercise in seven normal subjects. Esophageal pressure, flow, and volume were measured during spontaneous breathing at increasing levels of cycle exercise to maximum. Total lung capacity (TLC) was determined at rest and immediately before exercise termination using a N2-washout technique. Maximal inspiratory pressure and inspiratory capacity were measured at 1-min intervals. The time course of instantaneous dynamic pressure of respiratory muscles (Pmus) was calculated for the spontaneous breaths immediately preceding exercise termination. TLC volume and lung elastic recoil at TLC were the same at the end of exercise as at rest. Maximum static inspiratory pressures at exercise termination were not reduced. However, mean Pmus of spontaneous breaths at end exercise exceeded 15% of maximum inspiratory pressure in five of the subjects. We conclude that lung elastic recoil is unchanged even at maximal exercise and that, while inspiratory muscles operate within a potentially fatiguing range, the high levels of ventilation observed during maximal exercise are not maintained for a sufficient time to result in mechanical fatigue.

Sustained isocapnic hypoxia suppresses the perception of the magnitude of inspiratory resistive loads

2000 ◽  
Vol 89 (1) ◽  
pp. 47-55 ◽  
Author(s):  
R. S. Orr ◽  
A. S. Jordan ◽  
P. Catcheside ◽  
N. A. Saunders ◽  
R. D. McEvoy
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Peak Inspiratory Pressure ◽  
Normal Subjects ◽  
Inspiratory Pressure ◽  
Respiratory Resistance ◽  
Stimulus Magnitude ◽  
Mean Values ◽  
Central Nervous System Depressant ◽  
Resistive Loads

The sensation of increased respiratory resistance or effort is likely to be important for the initiation of alerting or arousal responses, particularly in sleep. Hypoxia, through its central nervous system-depressant effects, may decrease the perceived magnitude of respiratory loads. To examine this, we measured the effect of isocapnic hypoxia on the ability of 10 normal, awake males (mean age = 24.0 ± 1.8 yr) to magnitude-scale five externally applied inspiratory resistive loads (mean values from 7.5 to 54.4 cmH2O · l−1 · s). Each subject scaled the loads during 37 min of isocapnic hypoxia (inspired O2 fraction = 0.09, arterial O2 saturation of ∼80%) and during 37 min of normoxia, using the method of open magnitude numerical scaling. Results were normalized by modulus equalization to allow between-subject comparisons. With the use of peak inspiratory pressure (PIP) as the measure of load stimulus magnitude, the perception of load magnitude (Ψ) increased linearly with load and, averaged for all loaded breaths, was significantly lower during hypoxia than during normoxia (20.1 ± 0.9 and 23.9 ± 1.3 arbitrary units, respectively; P = 0.048). Ψ declined with time during hypoxia ( P = 0.007) but not during normoxia ( P= 0.361). Our result is remarkable because PIP was higher at all times during hypoxia than during normoxia, and previous studies have shown that an elevation in PIP results in increased Ψ. We conclude that sustained isocapnic hypoxia causes a progressive suppression of the perception of the magnitude of inspiratory resistive loads in normal subjects and could, therefore, impair alerting or arousal responses to respiratory loading.

Detection Latency of Added Loads to Breathing

1982 ◽  
Vol 63 (1) ◽  
pp. 11-15 ◽  
Author(s):  
J. G. W. Burdon ◽  
K. J. Killian ◽  
E. J. M. Campbell
Keyword(s):  
Peak Inspiratory Pressure ◽  
Normal Subjects ◽  
Reciprocal Relationship ◽  
Respiratory Cycle ◽  
Curvilinear Relationship ◽  
Similar Relationship ◽  
Detection Latency ◽  
Mechanical Information ◽  
Resistive Loads ◽  
Comparable Magnitude

1. Detection latency of a range of added elastic (0·95–4·50 kPa/l) and resistive (0·73–3·29 kPa l−1 s) loads to breathing were measured in five normal subjects. Detection latency was defined as the time from the onset of the breath to detection of the load. 2. Detection latency followed a curvilinear relationship when plotted as a function of the magnitude of the added loads. A similar relationship was found with both elastic and resistive loads although detection latencies to added elastances were longer than for added resistances. 3. When the added load was expressed in terms of comparable magnitude (peak inspiratory pressure) detection latencies for added elastances were found to be consistently longer than for added resistive loads. 4. These studies show that the detection latency to added inspiratory loads follows a reciprocal relationship, that detection latencies for elastic and resistive loads are clearly different and suggest that these loads are detected during the respiratory cycle at a time when the mechanical information regarding muscular pressure is greatest.

Effect of thoracoabdominal breathing patterns on inspiratory effort sensation

1987 ◽  
Vol 62 (4) ◽  
pp. 1665-1670 ◽  
Author(s):  
J. W. Fitting ◽  
D. A. Chartrand ◽  
T. D. Bradley ◽  
K. J. Killian ◽  
A. Grassino
Keyword(s):  
Normal Subjects ◽  
Motor Command ◽  
Esophageal Pressure ◽  
Inspiratory Effort ◽  
Breathing Patterns ◽  
Borg Scale ◽  
Rib Cage ◽  
Inspiratory Muscles ◽  
Main Variable ◽  
Unique Relationship

The respiratory sensations evoked by added inspiratory loads are currently thought to be largely mediated by the activity of the inspiratory muscles. Because of the differences in proprioceptors and in afferent and efferent innervations among the inspiratory muscles, we hypothesized that the sensation evoked by a given load would be different when the motor command is directed mainly to rib cage muscles or mainly to the diaphragm. To test this hypothesis, we studied six normal subjects breathing against several inspiratory resistances while emphasizing the use of rib cage muscles, or the diaphragm, or a combination of both. At the end of 10 loaded breaths the subjects rated the perceived magnitude of inspiratory effort on a Borg scale. A linear and unique relationship (r = 0.96 +/- 0.02; P less than 0.001) was found between the sensation and esophageal pressure (Pes) in the three thoracoabdominal breathing patterns. We conclude that the level of Pes, whether generated mainly by the rib cage muscles or the diaphragm, is the main variable related to the sensation of inspiratory effort under external inspiratory loads.

The Rate of Isometric Inspiratory Pressure Development as a Measure of Responsiveness to Carbon Dioxide in Man

1975 ◽  
Vol 49 (1) ◽  
pp. 57-68 ◽  
Author(s):  
A. W. Matthews ◽  
J. B. L. Howell
Keyword(s):  
Initial Rate ◽  
Ventilatory Response ◽  
Pressure Change ◽  
Normal Subjects ◽  
Inspiratory Pressure ◽  
Pulmonary Mechanics ◽  
Inspiratory Muscles ◽  
Pressure Development ◽  
Respiratory Centre ◽  
Very High

1. A technique has been developed for assessing CO2 responsiveness by measuring the maximum rate of isometric inspiratory pressure change at the mouth [(dP/dt)max.]. 2. By use of a rebreathing technique, the (dP/dt)max. response to CO2 was shown to correlate well with the ventilatory response in thirty-two normal subjects. 3. The addition of an external flow resistance sufficient to reduce the ventilatory response by a mean of 33.4% produced no significant mean change in the (dP/dt)max. response in thirty subjects. 4. In six patients recovering from bronchial asthma, reduction of airways obstruction led to a mean increase in the ventilatory response of 109% without any significant mean change in the (dP/dt)max. response. 5. An increase in lung volume did not reduce the (dP/dt)max. response in five normal subjects. 6. At very high lung volumes, six normal subjects were able to develop a higher (dP/dt)max. during voluntary inspiratory efforts than has been recorded during spontaneous breathing response to CO2. 7. It is believed that (dP/dt)max. represents the initial rate of development of force by the inspiratory muscles before this can be modified by mechanical loading, proprioceptive feedback mechanisms or conscious response and can therefore be used to study changes in the motor output of the respiratory centre in response to ventilatory stimuli independently of pulmonary mechanics.

Relation between work output of respiratory muscles and end-tidal CO2 tension

1963 ◽  
Vol 18 (3) ◽  
pp. 497-504 ◽  
Author(s):  
J. Milic-Emili ◽  
J. M. Tyler
Keyword(s):  
Carbon Dioxide ◽  
Pulmonary Ventilation ◽  
Respiratory Muscles ◽  
Normal Subjects ◽  
Work Output ◽  
Inspiratory Muscles ◽  
Expiratory Muscles ◽  
End Tidal ◽  
End Tidal Co2

End-tidal CO2 tension, pulmonary ventilation, and work output of respiratory muscles were determined in six normal subjects breathing various mixtures of carbon dioxide in air, with three graded resistances added to both inspiration and expiration. In two individuals, the resistances were also added separately to inspiration or expiration. A linear relationship was found between work output of inspiratory muscles and end-tidal CO2 tension; this relationship was uninfluenced by added resistance. No consistent relationship was observed between either ventilation or work output of expiratory muscles and end-tidal CO2 tension. These results suggest that carbon dioxide controls directly the activity of inspiratory muscles alone and that the activity of expiratory muscles is only coincidentally involved. The possible role of intrinsic properties of respiratory muscles and of nervous mediation in the control of breathing is discussed. Submitted on October 22, 1962

Dissociation between diaphragmatic and rib cage muscle fatigue

1988 ◽  
Vol 64 (3) ◽  
pp. 959-965 ◽  
Author(s):  
J. W. Fitting ◽  
T. D. Bradley ◽  
P. A. Easton ◽  
M. J. Lincoln ◽  
M. D. Goldman ◽  
...  
Keyword(s):  
Muscle Fatigue ◽  
Normal Subjects ◽  
Breathing Patterns ◽  
Recruitment Pattern ◽  
Rib Cage ◽  
Inspiratory Muscles ◽  
Resistive Breathing ◽  
Emg Power Spectrum ◽  
The Mean ◽  
Substantial Degree

To assess rib cage muscle fatigue and its relationship to diaphragmatic fatigue, we recorded the electromyogram (EMG) of the parasternal intercostals (PS), sternocleidomastoid (SM), and platysma with fine wire electrodes and the EMG of the diaphragm (DI) with an esophageal electrode. Six normal subjects were studied during inspiratory resistive breathing. Two different breathing patterns were imposed: mainly diaphragmatic or mainly rib cage breathing. The development of fatigue was assessed by analysis of the high-to-low (H/L) ratio of the EMG. To determine the appropriate frequency bands for the PS and SM, we established their EMG power spectrum by Fourier analysis. The mean and SD for the centroid frequency was 312 ± 16 Hz for PS and 244 ± 48 Hz for SM. When breathing with the diaphragmatic patterns, all subjects showed a fall in H/L of the DI and none had a fall in H/L of the PS or SM. During rib cage emphasis, four out of five subjects showed a fall in H/L of the PS and five out of six showed a fall in H/L of the SM. Four subjects showed no fall in H/L of the DI; the other two subjects were unable to inhibit diaphragm activity to a substantial degree and did show a fall in H/L of the DI. Activity of the platysma was minimal or absent during diaphragmatic emphasis but was usually strong during rib cage breathing. We conclude that fatigue of either the diaphragm or the parasternal and sternocleidomastoid can occur independently according to the recruitment pattern of inspiratory muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Is low-level respiratory resistive loading during exercise perceived as breathlessness?

1987 ◽  
Vol 73 (6) ◽  
pp. 627-634 ◽  
Author(s):  
R. Lane ◽  
L. Adams ◽  
A. Guz
Keyword(s):  
Loading Condition ◽  
Work Of Breathing ◽  
Respiratory Muscles ◽  
Normal Subjects ◽  
Low Level ◽  
Resistive Loading ◽  
The Subject ◽  
Resistive Loads ◽  
Exercise Induced ◽  
Subjective Estimates

1. The effect of adding low-level (2.7 cmH2O 1−1 s) external respiratory resistive loads on exercise-induced breathlessness has been examined in naive normal subjects; the intensity of this loading was chosen to simulate that confronting an asthmatic subject during exercise. 2. Each of 18 subjects performed two separate tests in which workload was oscillated while the respiratory loading was changed every minute between no loading, inspiratory loading only, and inspiratory plus expiratory loading. Each loading condition was given three times, and both these changes and those in workload were unpredictable as far as the subject was concerned. 3. The purpose was to ‘confuse’ subjects and obtain subjective estimates of their intensity of breathlessness independent of any expectation associated solely with the readily perceptible changes in external resistances to breathing. The study design was balanced for the group as a whole, both in terms of workload and respiratory loading condition. 4. The addition of these respiratory resistive loads during exercise did not result in a significant increase in the intensity of breathlessness. 5. Estimates of the rate of work of breathing revealed that this increased more with respiratory loading than it did as ventilation rose throughout the test; on the other hand, the intensity of breathlessness increased by a greater extent with continued exercise compared with the changes accompanying the addition of respiratory loads. 6. It is concluded that the intensity of the sensation of breathlessness experienced by normal subjects during exercise is not simply a reflection of an increased rate of work of breathing being performed by the respiratory muscles. 7. It is further suggested that similar studies in which internal resistances are increased experimentally are indicated in order to analyse the factors underlying the breathlessness of asthma.

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