Pressure-flow effects on endurance of inspiratory muscles

1986 ◽  
Vol 60 (1) ◽  
pp. 299-303 ◽  
Author(s):  
F. D. McCool ◽  
D. R. McCann ◽  
D. E. Leith ◽  
F. G. Hoppin
Keyword(s):  
Normal Subjects ◽  
Esophageal Pressure ◽  
Inspiratory Flow ◽  
Inspiratory Muscle ◽  
Negative Slope ◽  
Muscle Endurance ◽  
Inspiratory Muscles ◽  
Wide Range ◽  
Flow Effects ◽  
Forced Breathing

We examined the effects of varying inspiratory pressures and flows on inspiratory muscle endurance. Four normal subjects performed voluntary forced breathing with various assigned inspiratory tasks. Duty cycle, tidal volume, and mean lung volume were the same in all tasks. Mean esophageal pressure, analogous to a pressure-time integral (PTes), was varied over a wide range. In each task the subject maintained an assigned PTes while breathing on one of a range of inspiratory resistors, and this gave a range of inspiratory flows at any given PTes. Inspiratory muscle endurance for each task was assessed by the length of time the task could be maintained (Tlim). For a given resistor, Tlim increased as PTes decreased. At a given PTes, Tlim increased as the external resistance increased and therefore as mean inspiratory flow rate (VI) decreased. Furthermore, for a given Tlim, PTes and VI were linearly related with a negative slope. We conclude that inspiratory flow, probably because of its relationship to the velocity of muscle shortening, is an independent variable importantly influencing endurance of the inspiratory muscles.

Oxygen cost of breathing during fatiguing inspiratory resistive loads

1989 ◽  
Vol 66 (5) ◽  
pp. 2045-2055 ◽  
Author(s):  
F. D. McCool ◽  
G. E. Tzelepis ◽  
D. E. Leith ◽  
F. G. Hoppin
Keyword(s):  
Lung Volume ◽  
Normal Subjects ◽  
Esophageal Pressure ◽  
Inspiratory Flow ◽  
Energy Utilization ◽  
Whole Body ◽  
Inspiratory Flow Rate ◽  
Inspiratory Muscles ◽  
Inspiratory Resistance ◽  
Resistive Loads

When a subject breathes against an inspiratory resistance, the inspiratory pressure, the inspiratory flow, and the lung volume at which the breathing task takes place all interact to determine the length of time the task can be sustained (Tlim). We hypothesized that the mechanism actually limiting tasks in which these parameters were varied involved the rate of energy utilization by the inspiratory muscles. To test this hypothesis, we studied four experienced normal subjects during fatiguing breathing tasks performed over a range of pressures and flows and at two different lung volumes. We assessed energy utilization by measuring the increment in the rate of whole body O2 consumption due to the breathing task (VO2 resp). Power and mean esophageal pressure correlated with Tlim but depended also on lung volume and inspiratory flow rate. In contrast, VO2 resp closely correlated with Tlim, and this relationship was not systematically altered by inspiratory flow or lung volume. The shape of the VO2 resp vs. Tlim curve was approximately hyperbolic, with high rates of VO2 resp associated with short endurance times and lower rates of VO2 resp approaching an asymptotic value at high Tlim. These findings are consistent with a mechanism whereby a critical rate of energy utilization determines the endurance of the inspiratory pump, and that rate varies with pressure, flow, and lung volume.

Inspiratory muscles during exercise: a problem of supply and demand

1988 ◽  
Vol 64 (6) ◽  
pp. 2482-2489 ◽  
Author(s):  
P. Leblanc ◽  
E. Summers ◽  
M. D. Inman ◽  
N. L. Jones ◽  
E. J. Campbell ◽  
...  
Keyword(s):  
Lung Volume ◽  
Static Pressure ◽  
Total Lung Capacity ◽  
Supply And Demand ◽  
Normal Subjects ◽  
Esophageal Pressure ◽  
Maximum Exercise ◽  
Lung Capacity ◽  
Inspiratory Muscles ◽  
Residual Capacity

The capacity of inspiratory muscles to generate esophageal pressure at several lung volumes from functional residual capacity (FRC) to total lung capacity (TLC) and several flow rates from zero to maximal flow was measured in five normal subjects. Static capacity was 126 +/- 14.6 cmH2O at FRC, remained unchanged between 30 and 55% TLC, and decreased to 40 +/- 6.8 cmH2O at TLC. Dynamic capacity declined by a further 5.0 +/- 0.35% from the static pressure at any given lung volume for every liter per second increase in inspiratory flow. The subjects underwent progressive incremental exercise to maximum power and achieved 1,800 +/- 45 kpm/min and maximum O2 uptake of 3,518 +/- 222 ml/min. During exercise peak esophageal pressure increased from 9.4 +/- 1.81 to 38.2 +/- 5.70 cmH2O and end-inspiratory esophageal pressure increased from 7.8 +/- 0.52 to 22.5 +/- 2.03 cmH2O from rest to maximum exercise. Because the estimated capacity available to meet these demands is critically dependent on end-inspiratory lung volume, the changes in lung volume during exercise were measured in three of the subjects using He dilution. End-expiratory volume was 52.3 +/- 2.42% TLC at rest and 38.5 +/- 0.79% TLC at maximum exercise.

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.

Ventilatory compensation for changes in functional residual capacity during sleep

1987 ◽  
Vol 62 (3) ◽  
pp. 1299-1306 ◽  
Author(s):  
R. L. Begle ◽  
J. B. Skatrud ◽  
J. A. Dempsey
Keyword(s):  
Tidal Volume ◽  
Functional Residual Capacity ◽  
Minute Ventilation ◽  
Muscle Length ◽  
Normal Subjects ◽  
Conscious State ◽  
Inspiratory Muscle ◽  
Compensatory Response ◽  
Inspiratory Muscles ◽  
Residual Capacity

The role of conscious factors in the ventilatory compensation for shortened inspiratory muscle length and the potency of this compensatory response were studied in five normal subjects during non-rapid-eye-movement sleep. To shorten inspiratory muscles, functional residual capacity (FRC) was increased and maintained for 2–3 min at a constant level (range of increase 160–1,880 ml) by creating negative pressure within a tank respirator in which the subjects slept. Minute ventilation was maintained in all subjects over the entire range of increased FRC (mean change +/- SE = -3 +/- 1%) through preservation of tidal volume (-2 +/- 2%) despite slightly decreased breathing frequency (-6 +/- 2%). The decrease in frequency (-13 +/- 2%) was due to a prolongation in expiratory time. Inspiratory time shortened (-10 +/- 1%). Mean inspiratory flow increased 15 +/- 3% coincident with an increase in the slope of the moving time average of the integrated surface diaphragmatic electromyogram (67 +/- 21%). End-tidal CO2 did not rise. In two subjects, control tidal volume was increased 35–50% with CO2 breathing. This augmented tidal volume was still preserved when FRC was increased. We concluded that the compensatory response to inspiratory muscle shortening did not require factors associated with the conscious state. In addition, the potency of this response was demonstrated by preservation of tidal volume despite extreme shortening of the inspiratory muscles and increase in control tidal volumes caused by CO2 breathing. Finally, the timing changes we observed may be due to reflexes following shortening of inspiratory muscle length, increase in abdominal muscle length, or cardiovascular changes.

scholarly journals Accuracy of noninvasive estimates of respiratory muscle effort during spontaneous breathing in restrictive diseases

2003 ◽  
Vol 95 (4) ◽  
pp. 1542-1549 ◽  
Author(s):  
Francisco García-Río ◽  
José M. Pino ◽  
Angeles Ruiz ◽  
Salvador Díaz ◽  
Concepción Prados ◽  
...  
Keyword(s):  
Spontaneous Breathing ◽  
Respiratory Muscle ◽  
Usual Interstitial Pneumonia ◽  
Neuromuscular Diseases ◽  
Normal Subjects ◽  
Esophageal Pressure ◽  
Chronic Obstructive ◽  
Obstructive Pulmonary Disease ◽  
Transdiaphragmatic Pressure ◽  
Inspiratory Muscles

Mean inspiratory pressure (Pi), estimated from the occlusion pressure at the mouth and the inspiratory time, is useful as a noninvasive estimate of respiratory muscle effort during spontaneous breathing in normal subjects and patients with chronic obstructive pulmonary disease. The aim of this study was to compare the Pi with respect to mean esophageal pressure (Pes) in patients with restrictive disorders. Eleven healthy volunteers, 12 patients with chest wall disease, 14 patients with usual interstitial pneumonia, and 17 patients with neuromuscular diseases were studied. Pi, Pes, and mean transdiaphragmatic pressure were simultaneously measured. Tension-time indexes of diaphragm (TTdi) and inspiratory muscles (TTmu) were also determined. In neuromuscular patients, significant correlations were found between Pi and Pes, Pi and transdiaphragmatic pressure, and TTmu and TTdi. A moderate agreement between Pi and Pes and between TTmu and TTdi was found. No significant correlation between these parameters was found in the other patient groups. These findings suggest that Pi is a good surrogate for the invasive measurement of respiratory muscle effort during spontaneous breathing in neuromuscular patients.

Influence of lung volume on oxygen cost of resistive breathing

1986 ◽  
Vol 61 (1) ◽  
pp. 16-24 ◽  
Author(s):  
P. W. Collett ◽  
L. A. Engel
Keyword(s):  
Lung Volume ◽  
Work Of Breathing ◽  
Respiratory Muscles ◽  
Normal Subjects ◽  
Constant Load ◽  
Inspiratory Muscle ◽  
Mechanical Coupling ◽  
Inspiratory Muscles ◽  
Inspiratory Resistance ◽  
Residual Capacity

We examined the relationship between the O2 cost of breathing (VO2 resp) and lung volume at constant load, ventilation, work rate, and pressure-time product in five trained normal subjects breathing through an inspiratory resistance at functional residual capacity (FRC) and when lung volume (VL) was increased to 37 +/- 2% (mean +/- SE) of inspiratory capacity (high VL). High VL was maintained using continuous positive airway pressure of 9 +/- 2 cmH2O and with the subjects coached to relax during expiration to minimize respiratory muscle activity. Six paired runs were performed in each subject at constant tidal volume (0.62 +/- 0.2 liters), frequency (23 +/- 1 breaths/min), inspiratory flow rate (0.45 +/- 0.1 l/s), and inspiratory muscle pressure (45 +/- 2% of maximum static pressure at FRC). VO2 resp increased from 109 +/- 15 ml/min at FRC by 41 +/- 11% at high VL (P less than 0.05). Thus the efficiency of breathing at high VL (3.9 +/- 0.2%) was less than that at FRC (5.2 +/- 0.3%, P less than 0.01). The decrease in inspiratory muscle efficiency at high VL may be due to changes in mechanical coupling, in the pattern of recruitment of the respiratory muscles, or in the intrinsic properties of the inspiratory muscles at shorter length. When the work of breathing at high VL was normalized for the decrease in maximum inspiratory muscle pressure with VL, efficiency at high VL (5.2 +/- 0.3%) did not differ from that at FRC (P less than 0.7), suggesting that the fall in efficiency may have been related to the fall in inspiratory muscle strength. During acute hyperinflation the decreased efficiency contributes to the increased O2 cost of breathing and may contribute to the diminished inspiratory muscle endurance.

scholarly journals Evolution of inspiratory and expiratory muscle pressures during endurance exercise

2000 ◽  
Vol 88 (1) ◽  
pp. 234-245 ◽  
Author(s):  
Bharath S. Krishnan ◽  
Trevor Zintel ◽  
Colm McParland ◽  
Charles G. Gallagher
Keyword(s):  
Respiratory Muscle ◽  
Minute Ventilation ◽  
Normal Subjects ◽  
Progressive Increase ◽  
Cycle Ergometer ◽  
Linear Increase ◽  
Inspiratory Muscles ◽  
Linear Relationships ◽  
Wide Range ◽  
The Relationship

We investigated the relationship between minute ventilation (V˙e) and net respiratory muscle pressure (Pmus) throughout the breathing cycle [Total Pmus = mean Pmus, i (inspiratory) + mean Pmus, e(expiratory)] in six normal subjects performing constant-work heavy exercise (CWHE, at ∼80% maximum) to exhaustion on a cycle ergometer. Pmus was calculated as the sum of chest wall pressure (elastic + resistive) and pleural pressure, and all mean Pmus variables were averaged over the total breath duration. Pmus, i was also expressed as a fraction of volume-matched, flow-corrected dynamic capacity of the inspiratory muscles ([Formula: see text]).V˙e increased significantly from 3 min to the end of CWHE and was the result of a significantly linear increase in Total Pmus (Δ = 43 ± 9% from 3 min to end exercise, P < 0.005) in all subjects ( r = 0.81–0.99). Although mean Pmus, i during inspiratory flow increased significantly (Δ = 35 ± 10%), postinspiratory Pmus, i fell (Δ = −54 ± 10%) and postexpiratory expiratory activity was negligible or absent throughout CWHE. There was a greater increase in mean Pmus, e (Δ = 168 ± 48%), which served to increaseV˙e throughout CWHE. In five of six subjects, there were significant linear relationships betweenV˙eand mean Pmus, i( r = 0.50–0.97) and mean Pmus, e( r = 0.82–0.93) during CWHE. The subjects generated a wide range of Pmus, i/[Formula: see text]values (25–80%), and mean Pmus, i/[Formula: see text]increased significantly (Δ = 42 ± 16%) and in a linear fashion ( r = 0.69–0.99) withV˙ethroughout CWHE. The progressive increase inV˙e during CWHE is due to 1) a linear increase in Total Pmus, 2) a linear increase in inspiratory muscle load, and 3) a progressive fall in postinspiratory inspiratory activity. We conclude that the relationship between respiratory muscle pressure andV˙e during exercise is linear and not curvilinear.

Inspiratory muscle relaxation rate after voluntary maximal isocapnic ventilation in humans

1991 ◽  
Vol 70 (5) ◽  
pp. 2173-2180 ◽  
Author(s):  
D. A. Mulvey ◽  
N. G. Koulouris ◽  
M. W. Elliott ◽  
C. M. Laroche ◽  
J. Moxham ◽  
...  
Keyword(s):  
Relaxation Rate ◽  
Flow Rate ◽  
Early Onset ◽  
Minute Ventilation ◽  
Muscle Relaxation ◽  
Normal Subjects ◽  
Inspiratory Muscle ◽  
Inspiratory Flow Rate ◽  
Inspiratory Muscles ◽  
Progressive Loss

We have investigated whether the capacity of the inspiratory muscles to generate pressure and flow during a ventilatory load is related to changes in inspiratory muscle relaxation rate. Five highly motivated normal subjects performed voluntary maximal isocapnic ventilation (MIV) for 2 min. Minute ventilation and esophageal, gastric, and transdiaphragmatic pressures were measured breath by breath. We observed that ventilation, peak inspiratory and expiratory pressures, and inspiratory flow rate declined from the start of the run to reach a plateau at 60 s that was sustained for the remainder of the exercise. In a subsequent series of studies, MIV was performed for variable durations between 15 and 120 s. The normalized maximum relaxation rate of unoccluded inspiratory sniffs (sniff MRR, %pressure loss/10 ms) was determined immediately on stopping MIV. Sniff MRR slowed as the duration of MIV increased and paralleled the decline in inspiratory pressure and ventilation observed during the 2-min exercise. No further slowing in MRR occurred when ventilation became sustainable. We conclude that, during MIV, the progressive loss of ventilation and capacity to generate pressure is associated with the early onset and progression of a peripheral fatiguing process within the inspiratory muscles.

Pressure-time product, flow, and oxygen cost of resistive breathing in humans

1985 ◽  
Vol 58 (4) ◽  
pp. 1263-1272 ◽  
Author(s):  
P. W. Collett ◽  
C. Perry ◽  
L. A. Engel
Keyword(s):  
Tidal Volume ◽  
Work Rate ◽  
Inspiratory Flow ◽  
Inspiratory Pressure ◽  
External Work ◽  
Inspiratory Muscles ◽  
Pressure Time ◽  
Wide Range ◽  
Pressure Independent ◽  
Pressure Time Product

We examined the relationship between the pressure-time product (Pdt) of the inspiratory muscles and the O2 cost of breathing (VO2 resp) in five normal subjects breathing through an external inspiratory resistance with a tidal volume of 800 ml at a constant end-expiratory lung volume [functional residual capacity, (FRC)]. Each subject performed 30–40 runs, each of approximately 30 breaths, with inspiratory flow rates ranging from 0.26 +/- 0.01 to 0.89 +/- 0.04 l/s (means +/- SE) and inspiratory mouth pressures ranging from 10 +/- 1 to 68 +/- 4% of the maximum inspiratory pressure at FRC. In all subjects VO2 resp was linearly related to Pdt when mean inspiratory flow (VI) was constant, but the slope of this relationship increased with increasing VI. Therefore, Pdt is an accurate index of VO2 resp only when VI is constant. There was a linear relationship between the VO2 resp and the work rate across the external resistance (W) for all runs in each subject over the range of W 10 +/- 1 to 137 +/- 21 J/min. Thus, at a constant tidal volume the VO2 resp was related to the mean inspiratory pressure, independent of flow or inspiratory duration. If the VO2 resp were determined mainly during inspiration, then for a given rate of external work or O2 consumption, VI would be inversely related to mean inspiratory pressure. Efficiency (E) was 2.1 +/- 0.2% and constant over a large range of VI, pressure, work rate, or resistance and was not altered by the presence of a potentially fatiguing load. The constant E over such a wide range of conditions implies a complex integration of the recruitment, mechanical function, and energy consumption of the muscles utilized in breathing.

Decay of inspiratory muscle activity in chronic airway obstruction

1981 ◽  
Vol 51 (6) ◽  
pp. 1388-1397 ◽  
Author(s):  
G. Citterio ◽  
E. Agostoni ◽  
A. Del Santo ◽  
L. Marazzini
Keyword(s):  
Airway Obstruction ◽  
Time Course ◽  
Normal Subjects ◽  
Inspiratory Muscle ◽  
Resistive Load ◽  
Tonic Activity ◽  
Persistence Time ◽  
Elastic Load ◽  
Inspiratory Muscles ◽  
Chronic Airway

Relative decay rate of inspiratory muscle electrical activity (RDRI) in patients with chronic airway obstruction increased with decreasing expiratory time (TE), being faster than in normal subjects for a given TE. Time course of decay was similar in shape to that of normal subjects, whereas persistence time of activity during expiration was about half. Hence, braking action of inspiratory muscles in patients was smaller than in normal subjects. No tonic activity of inspiratory muscles was found in patients, even when frequency was increased and hyperinflation enhanced. Hence tonic activity of inspiratory muscles found by others in asymptomatic asthmatic or normal subjects after histamine inhalation seems elicited by histamine. In normal subjects breathing under resistive load, RDRI became similar to that of patients for a given TE: tonic activity of extradiaphragmatic inspiratory muscles occurred only if frequency was voluntarily increased at least three times, an unphysiological condition with resistive load. Under discontinuous inspiratory elastic load, RDRI of patients decreased or did not change, whereas previously that of normal subjects was found to increase.

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