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.

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.

Influence of inspiratory flow rate and frequency on O2 cost of resistive breathing in humans

1988 ◽  
Vol 65 (2) ◽  
pp. 760-766 ◽  
Author(s):  
D. S. Dodd ◽  
P. W. Collett ◽  
L. A. Engel
Keyword(s):  
Flow Rate ◽  
Duty Cycle ◽  
Normal Subjects ◽  
Work Rate ◽  
Inspiratory Flow ◽  
Inspiratory Flow Rate ◽  
Contraction Frequency ◽  
Mouth Pressure ◽  
Resistive Breathing ◽  
Residual Capacity

We examined the combined effect of an increase in inspiratory flow rate and frequency on the O2 cost of inspiratory resistive breathing (VO2 resp). In each of three to six pairs of runs we measured VO2 resp in six normal subjects breathing through an inspiratory resistance with a constant tidal volume (VT). One of each pair of runs was performed at an inspiratory muscle contraction frequency of approximately 10/min and the other at approximately 30/min. Inspiratory mouth pressure was 45 +/- 2% (SE) of maximum at the lower contraction frequency and 43 +/- 2% at the higher frequency. Duty cycle (the ratio of contraction time to total cycle time) was constant at 0.51 +/- 0.01. However, during the higher frequency runs, two of every three contractions were against an occluded airway. Because VT and duty cycle were kept constant, mean inspiratory flow rate increased with frequency. Careful selection of appropriate parameters allowed the pairs of runs to be matched both for work rate and pressure-time product. The VO2 resp did not increase, despite approximately threefold increases in both inspiratory flow rate and contraction frequency. On the contrary, there was a trend toward lower values for VO2 resp during the higher frequency runs. Because these were performed at a slightly lower mean lung volume, a second study was designed to measure the VO2 resp of generating the same inspiratory pressure (45% maximum static inspiratory mouth pressure at functional residual capacity) at the same frequency but at two different lung volumes. This was achieved with a negligibly small work rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of an intellectual task on breathing after voluntary hyperventilation

1996 ◽  
Vol 81 (3) ◽  
pp. 1379-1387 ◽  
Author(s):  
K. Chin ◽  
M. Ohi ◽  
M. Fukui ◽  
H. Kita ◽  
T. Tsuboi ◽  
...  
Keyword(s):  
Video Game ◽  
Minute Ventilation ◽  
Normal Subjects ◽  
Inhibitory Effect ◽  
Inspiratory Flow Rate ◽  
Short Term ◽  
Voluntary Hyperventilation ◽  
Term Potentiation ◽  
The Central Nervous System ◽  
Increased Activity

We investigated the effects of an intellectual task on posthyperventilation (PHV) breathing by using a video game. Eight normal subjects were placed in a supine positions. The game task by itself led to increase ventilation compared with the control tasks via an increase in the average inspiratory flow rate (P < 0.01) and the respiratory frequency (P < 0.001). After hypocapnic voluntary hyperventilation (VHV), the task led to a decrease in the 1-min PHV breathing level compared with the control tasks after VHV [after VHV, first 60 s average minute ventilation while watching television and while playing a video game are 5.54 +/- 2.91 (SD) and 2.05 +/- 1.40 l/min, respectively; P < 0.01]. Only one subject showed PHV apnea for at least 10 s during the control protocol, whereas seven of the same eight subjects showed PHV apnea while performing the task. After isocapnic VHV, the task still led to a decrease in PHV breathing compared with the control tasks. However, this decrease was smaller than in the hypocapnic studies and was only significant during the first 15 s of recovery. These results suggest that increased activity in the higher centers of the central nervous system has an inhibitory effect on PHV breathing at a time when the effects of short-term potentiation after VHV, hypocapnia, and perhaps other mechanisms would be expected to be acting on breathing.

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.

Importance of inspiratory flow rate in the cough response to citric acid inhalation in normal subjects

1990 ◽  
Vol 78 (5) ◽  
pp. 521-525 ◽  
Author(s):  
Manuel J. Barros ◽  
Stefano J. Zammattio ◽  
P. John Rees
Keyword(s):  
Citric Acid ◽  
Flow Rate ◽  
Geometric Mean ◽  
Normal Subjects ◽  
Forced Expiratory Volume ◽  
Inspiratory Flow ◽  
Inspiratory Flow Rate ◽  
Flow Rates ◽  
Cough Response ◽  
The Mean

1. The cough response to inhalation of citric acid is produced mainly by irritation of the larynx and trachea. Variations in the inspiratory flow rate might lead to changes in deposition of the drug, and consequently in the cough threshold. 2. We have studied the effect of three different inspiratory flow rates in 11 normal, non-smoking subjects (nine males, aged 23–39 years), who inhaled nebulized citric acid (2.5–640 mg/l). The test finished when a cough. was produced at each inhalation (cough threshold) or the maximum concentration was reached. 3. The inspiratory flow rate was limited with a fixed resistance and displayed on a screen so that the subjects could reach a constant inspiratory flow rate of 50, 100 and 150 l/min with a submaximal inspiratory effort. 4. The mean (sd) inspiratory flow rates achieved were 51.4 (5.3), 86.2 (16.6) and 134.4 (22.9) l/min. Baseline forced expiratory volume in 1 s and functional vital capacity were not different on the 3 study days. 5. The cough threshold (geometric mean and 95% confidence intervals) was 21 (9–54) mg/l at an inspiratory flow rate of 50 l/min and 43 (13–141) mg/l at 150 l/min (P <0.05). The amount of drug tolerated by the subjects before the cough threshold was achieved was 5.2 (2.0–13.8) mg at an inspiratory flow rate of 50 l/min and 11.6 (3.4–39.8) mg at 150 l/min (P <0.05). The number of coughs per inhalation was 1.6 (1.1–2.0) at an inspiratory flow rate of 50 l/min and 1.1 (0.7–1.5) at 150 l/min (P <0.05). 6. We conclude that lower inspiratory flow rates were associated with a greater cough stimulus in the citric acid challenge procedure used in this study. This may be related to increased laryngeal deposition. The inspiratory flow rate is a variable which should be controlled in the performance of cough challenges with citric acid.

scholarly journals Inspiratory muscle relaxation rate assessed from sniff nasal pressure.

Thorax ◽  
1994 ◽  
Vol 49 (11) ◽  
pp. 1127-1133 ◽  
Author(s):  
D Kyroussis ◽  
G Mills ◽  
C H Hamnegard ◽  
S Wragg ◽  
J Road ◽  
...  
Keyword(s):  
Relaxation Rate ◽  
Muscle Relaxation ◽  
Inspiratory Muscle ◽  
Nasal Pressure

Influence of global inspiratory muscle fatigue on breathing during exercise

1996 ◽  
Vol 80 (4) ◽  
pp. 1270-1278 ◽  
Author(s):  
P. Sliwinski ◽  
S. Yan ◽  
A. P. Gauthier ◽  
P. T. Macklem
Keyword(s):  
Tidal Volume ◽  
Muscle Fatigue ◽  
Minute Ventilation ◽  
Inspiratory Muscle ◽  
Abdominal Muscles ◽  
Maximal Power Output ◽  
Lung Inflation ◽  
Rib Cage ◽  
Inspiratory Muscles ◽  
Inspiratory Muscle Fatigue

We evaluated the effect of global inspiratory muscle fatigue (GF) on respiratory muscle control during exercise at 30, 60, and 90% of maximal power output in normal subjects. Fatigue was induced by breathing against a high inspiratory resistance until exhaustion. Esophageal and gastric pressures, anteroposterior displacement of the rib cage and abdomen, breathing pattern, and perceived breathlessness were measured. Induction of GF had no effect on the ventilatory parameters during mild and moderate exercise. It altered, however, ventilatory response to heavy exercise by increasing breathing frequency and minute ventilation, with minor changes in tidal volume. This was accompanied by an increase in perceived breathlessness. GF significantly increased both the tonic and phasic activities of abdominal muscles that allowed 1) the diaphragm to maintain its function while developing less pressure, 2) the same tidal volume with lesser shortening of the rib cage inspiratory muscles, and 3) relaxation of the abdominal muscles to contribute to lung inflation. The increased work performed by the abdominal muscles may, however, lead to a reduction in their strength. GF may impair exercise performance in some healthy subjects that is probably not related to excessive breathlessness or other ventilatory factors. We conclude that the respiratory system is remarkably adaptable in maintaining ventilation during exercise even with impaired inspiratory muscle contractility.

Effectiveness of mask and helmet interfaces to deliver noninvasive ventilation in a human model of resistive breathing

2005 ◽  
Vol 99 (4) ◽  
pp. 1262-1271 ◽  
Author(s):  
Fabrizio Racca ◽  
Lorenzo Appendini ◽  
Cesare Gregoretti ◽  
Elisa Stra ◽  
Antonio Patessio ◽  
...  
Keyword(s):  
Noninvasive Ventilation ◽  
Pressure Support ◽  
Breathing Pattern ◽  
Minute Ventilation ◽  
Face Mask ◽  
Inspiratory Muscle ◽  
Human Model ◽  
Inspiratory Muscles ◽  
Potential Benefits ◽  
Internal Volume

The helmet, a transparent latex-free polyvinyl chloride cylinder linked by a metallic ring to a soft collar that seals the helmet around the neck, has been recently proposed as an effective alternative to conventional face mask to deliver pressure support ventilation (PSV) during noninvasive ventilation in patients with acute respiratory failure. We tested the hypothesis that mechanical characteristics of the helmet (large internal volume and high compliance) might impair patient-ventilator interactions compared with standard face mask. Breathing pattern, CO2 clearance, indexes of inspiratory muscle effort and patient-ventilator asynchrony, and dyspnea were measured at different levels of PSV delivered by face mask and helmet in six healthy volunteers before (load-off) and after (load-on) application of a linear resistor. During load-off, no differences in breathing pattern and inspiratory muscle effort were found. During load-on, the use of helmet to deliver pressure support increased inspiratory muscle effort and patient-ventilator asynchrony, worsened CO2 clearance, and increased dyspnea compared with standard face mask. Autocycled breaths accounted for 12 and 25% of the total minute ventilation and for 10 and 23% of the total inspiratory muscle effort during mask and helmet PSV, respectively. We conclude that PSV delivered by helmet interface is less effective in unloading inspiratory muscles compared with PSV delivered by standard face mask. Other ventilatory assist modes should be tested to exploit to the most the potential benefits offered by the helmet.

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