Sustainable inspiratory pressures over varying flows, volumes, and duty cycles

1990 ◽  
Vol 69 (5) ◽  
pp. 1875-1882 ◽  
Author(s):  
T. L. Clanton ◽  
B. T. Ameredes ◽  
D. B. Thomson ◽  
M. W. Julian
Keyword(s):  
Tidal Volume ◽  
Duty Cycle ◽  
Dynamic Pressure ◽  
Breathing Patterns ◽  
Transdiaphragmatic Pressure ◽  
Lung Inflation ◽  
Duty Cycles ◽  
Pressure Time ◽  
Endurance Tests ◽  
Normal Humans

This study identifies the influence of flow (0.5-2.0 l/s), duty cycle (0.29-0.57), and tidal volume (1.08-2.16 liters) on sustainable inspiratory muscle pressure (Pmus) and transdiaphragmatic pressure (Pdi) development. Six normal humans performed endurance tests using an isoflow method, which allowed for measurements of maximum dynamic Pmus and Pdi, with controlled lung inflation. The subjects repeated maximum dynamic voluntary inspirations for 10 min. Pressures dropped exponentially from initial measurements at rest (Pmusi or Pdi) to sustainable values (Pmus or Pdis). As flow and tidal volume increased, maximum initial and sustainable pressures decreased significantly. However, at a constant duty cycle, the sustainable dynamic pressures remained predictable fractions of initial dynamic pressures (i.e., Pmuss/Pmusi or Pdis/Pdii), regardless of changes in flow and tidal volume. In contrast, as duty cycle increased, the sustainable fractions significantly decreased for both Pdi and Pmus. For example, at a duty cycle of 0.29, Pmuss/Pmusi was approximately 0.71, and at a duty cycle of 0.57, Pmuss/Pmusi was approximately 0.62. Calculated sustainable pressure-time indexes varied significantly between 0.16 to 0.32 for Pmus and 0.11 to 0.22 for Pdi over the breathing patterns studied. We conclude that 1) the maximum dynamic pressure that can be sustained at a given duty cycle is a predictable fraction of the maximum dynamic pressure that can be generated at rest when measured under the same conditions of inspiration and 2) the sustainable fraction of initial dynamic pressure significantly decreases with increasing duty cycle.

Diaphragmatic blood flow in the dog

1986 ◽  
Vol 60 (2) ◽  
pp. 554-561 ◽  
Author(s):  
H. Bark ◽  
S. M. Scharf
Keyword(s):  
Blood Flow ◽  
Duty Cycle ◽  
Stimulus Frequency ◽  
Phase Flow ◽  
Transdiaphragmatic Pressure ◽  
Relaxation Phase ◽  
Duty Cycles ◽  
Tension Time ◽  
Phrenic Artery ◽  
Electromagnetic Flow Probe

In anesthetized mongrel dogs we measured the blood flow in the left phrenic artery (Qdi), using an electromagnetic flow probe, before and during supramaximal phrenic nerve stimulation (pacing). This was done at constant respiratory rate (24/min) but at three different stimulation frequencies at a duty cycle of 0.4 (20, 50, and 100 Hz) and at three different duty cycles at a stimulation frequency of 50 Hz (duty cycle = 0.2, 0.4, and 0.8). Qdi was unchanged during diaphragm contraction until transdiaphragmatic pressure (Pdi) was greater than approximately 11 cmH2O, whereafter it began to decrease, reaching zero at Pdi approximately 20 cmH2O. Thus, when Pdi was greater than 21 cmH2O, all flow occurred during relaxation. Qdi averaged over the entire respiratory cycle (Qt) was less at duty cycle = 0.8 than under the other conditions. This was because of decreasing length of relaxation phase rather than a difference of relaxation phase flow (Qr), which was maximal during all conditions of phrenic stimulation. During pacing-induced fatigue, Qt actually rose slightly as Pdi fell. This was due to an increase in contraction phase flow while Qr remained constant. The relationship between Qt and tension-time index was not unique but varied according to the different combinations of duty cycle and stimulus frequency.

Effect of respiratory apparatus on respiration

1984 ◽  
Vol 57 (2) ◽  
pp. 475-480 ◽  
Author(s):  
C. Weissman ◽  
J. Askanazi ◽  
J. Milic-Emili ◽  
J. M. Kinney
Keyword(s):  
Tidal Volume ◽  
Duty Cycle ◽  
Breathing Pattern ◽  
Minute Ventilation ◽  
Inspiratory Flow ◽  
Percentage Increase ◽  
Breathing Patterns ◽  
Normal Volunteers ◽  
Abdominal Operation ◽  
Respiratory Apparatus

A mouthpiece plus noseclip (MP & NC) is frequently used in performing measurements of breathing patterns. Although the effects the apparatus exerts on breathing patterns have been studied, the mechanism of the changes it causes remains unclear. The current study examines the effects on respiratory patterns of a standard (17-mm-diam) MP & NC during room air (RA) breathing and the administration of 2 and 4% CO2 in normal volunteers and in patients 2–4 days after abdominal operation. When compared with values obtained with a noninvasive canopy system, the MP & NC induced increases in minute ventilation (VE), tidal volume (VT), and mean inspiratory flow (VT/TI), but not frequency (f) or inspiratory duty cycle, during both RA and CO2 administration. The percentage increase in VE, VT, and VT/TI caused by the MP & NC decreased as the concentration of CO2 increased. During RA breathing, the application of noseclip alone resulted in a decrease in f and an increase in VT, but VE and VT/TI were unchanged. The changes were attenuated during the administration of 2 and 4% CO2. Reducing the diameter of the mouthpiece to 9 mm abolished the alterations in breathing pattern observed with the larger (17-mm) diameter MP.

Effects of tension, duty cycle, and arterial pressure on diaphragmatic blood flow in dogs

1989 ◽  
Vol 66 (2) ◽  
pp. 968-976 ◽  
Author(s):  
S. N. Hussain ◽  
C. Roussos ◽  
S. Magder
Keyword(s):  
Blood Flow ◽  
Arterial Pressure ◽  
Duty Cycle ◽  
Phrenic Nerve Stimulation ◽  
Gradual Decline ◽  
Transdiaphragmatic Pressure ◽  
Duty Cycles ◽  
Severe Hypotension ◽  
Internal Mammary ◽  
Pressure Part

We investigated the selective effects of changes in transdiaphragmatic pressure (Pdi) and duty cycle on diaphragmatic blood flow in supine dogs at normal arterial pressure (N), moderate hypotension (MH), and severe hypotension (SH) [mean arterial pressure (Part) of 116, 75, and 50 mmHg, respectively]. The diaphragm was paced at a rate of 12/min by bilateral phrenic nerve stimulation. Left phrenic (Qphr-T) and left internal mammary (Qim-T) arterial flows were measured by electromagnetic flow probes. Changes in Pdi and duty cycle were achieved by changing the stimulation frequencies and the duration of contraction, whereas Part changes were produced by bleeding. With N and at a duty cycle of 0.5, incremental increases in Pdi produced peaks in Qphr-T and Qim-T at 30% maximum diaphragmatic pressure (Pdimax) with a gradual decline at higher Pdi. With MH and SH, blood flow peaked at 10% Pdimax. At any given Pdi, blood flow was lower with MH and SH in comparison to N. The effect of duty cycle was tested at two levels of Pdi. With N and at low Pdi (25% Pdimax), blood flow rose progressively with increases in duty cycle, whereas at moderate Pdi level (50% Pdimax) blood flow peaked at a duty cycle of 0.3, with no increase thereafter. With MH, blood flow at low Pdi rose linearly with increasing duty cycle but to a lesser extent than with N, and at a moderate Pdi flow peaked at a duty cycle of 0.3. With SH, blood flow at low and moderate Pdi was limited at duty cycles greater than 0.3 and 0.1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Physiological mechanisms of dyspnea during exercise with external thoracic restriction: Role of increased neural respiratory drive

2014 ◽  
Vol 116 (5) ◽  
pp. 570-581 ◽  
Author(s):  
Cassandra T. Mendonca ◽  
Michele R. Schaeffer ◽  
Patrick Riley ◽  
Dennis Jensen
Keyword(s):  
Tidal Volume ◽  
Balloon Catheter ◽  
Respiratory Drive ◽  
Exercise Tests ◽  
Transdiaphragmatic Pressure ◽  
Pressure Time ◽  
Sensory Intensity ◽  
Dynamic Operating ◽  
Mechanistic Basis ◽  
The Relationship

We tested the hypothesis that neuromechanical uncoupling of the respiratory system forms the mechanistic basis of dyspnea during exercise in the setting of “abnormal” restrictive constraints on ventilation (VE). To this end, we examined the effect of chest wall strapping (CWS) sufficient to mimic a “mild” restrictive lung deficit on the interrelationships between VE, breathing pattern, dynamic operating lung volumes, esophageal electrode-balloon catheter-derived measures of the diaphragm electromyogram (EMGdi) and the transdiaphragmatic pressure time product (PTPdi), and sensory intensity and unpleasantness ratings of dyspnea during exercise. Twenty healthy men aged 25.7 ± 1.1 years (means ± SE) completed symptom-limited incremental cycle exercise tests under two randomized conditions: unrestricted control and CWS to reduce vital capacity (VC) by 21.6 ± 0.5%. Compared with control, exercise with CWS was associated with 1) an exaggerated EMGdi and PTPdi response; 2) no change in the relationship between EMGdi and each of tidal volume (expressed as a percentage of VC), inspiratory reserve volume, and PTPdi, thus indicating relative preservation of neuromechanical coupling; 3) increased sensory intensity and unpleasantness ratings of dyspnea; and 4) no change in the relationship between increasing EMGdi and each of the intensity and unpleasantness of dyspnea. In conclusion, the increased intensity and unpleasantness of dyspnea during exercise with CWS could not be readily explained by increased neuromechanical uncoupling but likely reflected the awareness of increased neural respiratory drive (EMGdi) needed to achieve any given VE during exercise in the setting of “abnormal” restrictive constraints on tidal volume expansion.

Acoustic-Reflex Dynamics for Pulsed Signals

1978 ◽  
Vol 21 (2) ◽  
pp. 295-308
Author(s):  
Terry L. Wiley ◽  
Raymond S. Karlovich
Keyword(s):  
Duty Cycle ◽  
Acoustic Impedance ◽  
Normal Hearing ◽  
Broadband Noise ◽  
Threshold Shift ◽  
Temporary Threshold Shift ◽  
Acoustic Reflex ◽  
Stapedius Muscle ◽  
Duty Cycles

Contralateral acoustic-reflex measurements were taken for 10 normal-hearing subjects using a pulsed broadband noise as the reflex-activating signal. Acoustic impedance was measured at selected times during the on (response maximum) and off (response minimum) portions of the pulsed activator over a 2-min interval as a function of activator period and duty cycle. Major findings were that response maxima increased as a function of time for longer duty cycles and that response minima increased as a function of time for all duty cycles. It is hypothesized that these findings are attributable to the recovery characteristics of the stapedius muscle. An explanation of portions of the results from previous temporary threshold shift experiments on the basis of acoustic-reflex dynamics is proposed.

Normoxic and hypoxic breathing pattern in newborn grey seals

1989 ◽  
Vol 67 (2) ◽  
pp. 483-487 ◽  
Author(s):  
Jacopo P. Mortola ◽  
Clement Lanthier
Keyword(s):  
Tidal Volume ◽  
Breathing Pattern ◽  
Halichoerus Grypus ◽  
Breathing Rate ◽  
Allometric Relationships ◽  
Breathing Patterns ◽  
Hypoxic Conditions ◽  
Regulation Of Breathing ◽  
Expiratory Flow

We studied the breathing patterns of three newborn grey seals (Halichoerus grypus) at 2 – 3 days of age under normoxic and hypoxic conditions with the barometric technique, which does not require the animal to be restrained. Normoxic tidal volume was deeper and breathing rate slower than expected for newborns of this size on the basis of previously published allometric relationships. In addition, two characteristics were readily apparent: (i) occasional sudden long apneas, often exceeding 30 s in duration, and (ii) consistent brief interruptions of expiratory flow. Neither aspect is common in terrestrial newborns of this age, but both have been previously observed in adult seals. During hypoxia (10 min of 15% O2 and 10 min of 10% O2), ventilation increased markedly and steadily, at variance with what occurs in newborns of other species, indicating a precocial development of the regulation of breathing. This latter result also suggests that the blunted response to hypoxia previously reported in adult seals may be acquired postnatally with diving experience.

scholarly journals Impact of cervical spinal cord contusion on the breathing pattern across the sleep-wake cycle in the rat

2019 ◽  
Vol 126 (1) ◽  
pp. 111-123 ◽  
Author(s):  
Kun-Ze Lee
Keyword(s):  
Spinal Cord ◽  
Tidal Volume ◽  
Spinal Injury ◽  
Cervical Spinal Cord ◽  
Minute Ventilation ◽  
Respiratory Frequency ◽  
Breathing Patterns ◽  
Cord Injury ◽  
Spinal Contusion ◽  
Cervical Spinal Injury

The present study was designed to investigate breathing patterns across the sleep-wake state following a high cervical spinal injury in rats. The breathing patterns (e.g., respiratory frequency, tidal volume, and minute ventilation), neck electromyogram, and electroencephalography of unanesthetized adult male rats were measured at the acute (i.e., 1 day), subchronic (i.e., 2 wk), and/or chronic (i.e., 6 wk) injured stages after unilateral contusion of the second cervical spinal cord. Cervical spinal cord injury caused a long-term reduction in the tidal volume but did not influence the sleep-wake cycle duration. The minute ventilation during sleep was usually lower than that during the wake period in uninjured animals due to a decrease in respiratory frequency. However, this sleep-induced reduction in respiratory frequency was not observed in contused animals at the acute injured stage. By contrast, the tidal volume was significantly lower during sleep in contused animals but not uninjured animals from the acute to the chronic injured stage. Moreover, the frequency of sigh and postsigh apnea was elevated in acutely contused animals. These results indicated that high cervical spinal contusion is associated with exacerbated sleep-induced attenuation of the tidal volume and higher occurrence of sleep apnea, which may be detrimental to respiratory functional recovery after cervical spinal cord injury. NEW & NOTEWORTHY Cervical spinal injury is usually associated with sleep-disordered breathing. The present study investigated breathing patterns across sleep-wake state following cervical spinal injury in the rat. Unilateral cervical spinal contusion significantly impacted sleep-induced alteration of breathing patterns, showing a blunted frequency response and exacerbated attenuated tidal volume and occurrence of sleep apnea. The result enables us to investigate effects of cervical spinal injury on the pathogenesis of sleep-disordered breathing and evaluate potential therapies to improve respiration.

Augmentation of phrenic neural activity by increased rates of lung inflation

1981 ◽  
Vol 50 (1) ◽  
pp. 149-161 ◽  
Author(s):  
A. I. Pack ◽  
R. G. DeLaney ◽  
A. P. Fishman
Keyword(s):  
Tidal Volume ◽  
Volume Change ◽  
Neural Activity ◽  
Negative Pressure ◽  
Spontaneous Breathing ◽  
Moving Average ◽  
Constant Flow ◽  
Lung Inflation ◽  
Negative Pressure Ventilation ◽  
Single Breath

Studies were conducted in anesthetized paralyzed dogs using a cycle-triggered constant-flow ventilator, which ventilated the animal in phase with the recorded phrenic neural activity. Intermittently tests were performed in which the animal was ventilated with a different airflow for a single breath. Increased airflows, within the range generated during spontaneous breathing, caused an increased rate of rise of the moving average phrenic neurogram and a shortening of the duration of the nerve burst. The magnitude of the increase in the rate of rise of the neurogram was related to the level of inspiratory airflow. Tests with brief pulses of airflow showed that an increase in the rate of rise of the phrenic neurogram could be produced without inflating the lung above the resting tidal volume of the animal. Similar results were obtained with negative-pressure ventilation and the effects were abolished by vagotomy. This vagally mediated augmentation of phrenic neural output may accelerate the inspiratory volume change in the lung during spontaneous breathing at hyperpneic levels.

Coordination between rib cage muscles and diaphragm during quiet breathing in humans

1984 ◽  
Vol 57 (3) ◽  
pp. 899-906 ◽  
Author(s):  
A. De Troyer ◽  
M. Estenne
Keyword(s):  
Tidal Volume ◽  
Marked Reduction ◽  
Emg Activity ◽  
Quiet Breathing ◽  
Rib Cage ◽  
Intercostal Muscles ◽  
Inspiratory Activity ◽  
Normal Humans ◽  
Volume Range

The pattern of activation of the scalenes and the parasternal intercostal muscles was studied in relation to the pattern of rib cage and abdominal motion during various respiratory maneuvers in the tidal volume range in five normal humans. Electromyograms (EMG) of the scalenes and parasternal intercostals were recorded with bipolar needle electrodes, and changes in abdominal and rib cage displacement were measured using linearized magnetometers. The scalenes and parasternal intercostals were always active during quiet breathing, and their pattern of activation was identical; in both muscles the EMG activity usually started together with the beginning of inspiration, increased in intensity as inspiration proceeded, and persisted into the early part of expiration. In addition, like the parasternal activity the scalene inspiratory activity persisted until the tidal volume was trivial, increased during tidal inspirations performed with the rib cage alone, and was nearly abolished during diaphragmatic isovolume maneuvers. However, attempts to perform tidal inspiration with the diaphragm alone, while causing an increase in parasternal EMG activity, were associated with a marked reduction or a suppression of scalene EMG activity and a reduced substantially distorted rib cage expansion. In particular, the upper rib cage was then moving paradoxically.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Evaluation of cushions using dynamic pressure measurement

1991 ◽  
Vol 15 (3) ◽  
pp. 232-240 ◽  
Author(s):  
C. A. Bar
Keyword(s):  
Dynamic Pressure ◽  
Pressure Sores ◽  
Patient Assessment ◽  
Pressure Monitoring ◽  
Time Profiles ◽  
Pressure Time ◽  
Subject Variability ◽  
Dynamic Pressure Measurement ◽  
Ischial Tuberosities ◽  
Spinal Cord Injured

Reduction of pressures generated in the tissues overlying the ischial tuberosities is an important measure for predicting a cushion's effectiveness. In particular, the pressure-time relationship is significant in the prevention of pressure sores. In this study a dynamic pressure monitoring system was used to obtain pressure-time profiles for 25 spinal cord injured subjects. Each subject tested three types of cushion (Foam, Gel (Aberdeen) and Roho) for periods of two hours each during which routine activities were performed. Results obtained were broadly comparable with previous studies. Average pressures were: Foam 87.6mmHg (11.6kPa); Gel 68.6mmHg (9kPa) and Roho 54.6mmHg (6.7kPa). Pressure-time histograms are presented for three subjects for each cushion. These show inter-subject variability on the same cushion as well as intra-subject variability on different cushions. Therefore individual patient assessment is important in providing the most appropriate cushion. Dynamic pressure monitoring allows the pattern of pressure variation to be determined and hence the potential effectiveness of the cushion.

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