Changes In Duty Cycle Research Articles

The Changes of Breathing Pattern Observed During Maximal Exercise Testing in the Patients with Chronic Airflow Obstruction: the Correlation Between the Change of Inspiratory Duty Cycle and the Degree of Airflow Obstruction

Background : Normal humans meet the increased ventilatory need during exercise initially by the increase of tidal volume (TV) and later by the increase of respiratory frequency (Rf). And the inspiratory duty cycle (Ti/Ttot) is also increased more than 50% for the compensation of the decrease of respiratory cycle provoked by the increase of respiratory frequency. The patients with chronic airflow obstruction show rapid and shallow breathing pattern during exercise because of the decreased ventilatory capacity and the increased dead space ventilation. However, the studies about the change of inspiratory duty cycle are only a few and there is no literature about the relationship between the change of inspiratory duty cycle and the degree of airflow obstruction. Methods : The subjects were the twelve patients with chronic airflow obstruction (CAO) and ten normal people. The incremental exercise test was done. The increase of work load was 10 W in CAO group and 25 W in normal control group. The analysis of the results was done by the comparison of the parameters such as minute ventilation (VE), TV, Rf, physiologic dead space (Vd/Vt), and inspiratory duty cycle between the two groups. Each parameters were compared after transformation into % control duration base that means dividing the total exercise time into five fractions and % control duration data were obtained at rest, 20%, 40%, 60%, 80%, and max. Statistical analysis was done by repeated measure ANOVA using SAS program. Results : The changes of VE and TV were significantly different between two groups while the change of Rf was not significant. The decrease of Vd/Vt was significantly low in CAO group. Ti/Ttot was markedly increased from 38.4 + 3.0% at rest to 48.6 + 4.5% at max in normal control group while Ti/Ttot showed little change from 40.5 + 2.2% at rest to 42.6 + 3.5% at max. And the change of inspiratory duty cycle showed highly good correlation with the degree of airflow obstruction (FEV1%). (r=0.8151, p

CLOSED-LOOP CHARACTERISTICS OF VOLTAGE-MODE-CONTROLLED PWM BOOST DC-DC CONVERTER WITH AN INTEGRAL-LEAD CONTROLLER

A complete analysis of a voltage-mode-controlled pulse-width-modulated (PWM) boost DC-DC power converter is presented using a previously derived small-signal model for continuous conduction mode (CCM). All parasitic components such as the equivalent series resistance (ESR) of the filter capacitor, the ESR of the inductor, the transistor on-resistance, and the diode forward resistance and offset voltage are included in the model. A design procedure for an integral-lead controller including the loading effect of the voltage divider in the feedback loop is given. The Bode plots of the closed-loop control-to-output transfer function, input-to-output transfer function, input impedance, and output impedance are determined and illustrated for three values of the duty cycle. Step response plots of the PWM boost converter in the open-loop and closed-loop cases are shown for changes in line voltage and duty cycle.

Implications of a biphasic two-compartment model of constant flow ventilation for the clinical setting

Purpose: To investigate the theoretical effects of changing frequency (ƒ), duty cycle (D), or end-inspiratory pause length on the distribution of ventilation and compartmental pressure in a heterogeneous, two compartment pulmonary model inflated by constant flow. Methods: Differential equations governing compartmental volume changes were derived and solved. Validation was conducted in a mechanical lung analogue with two mechanically independent compartments. Model predictions were then generated over wide ranges of ƒ, D, or end-inspiratory pause. Results: Disparity of compartmental end-expiratory pressure was identified as the primary mechanism by which changes in f, D, or pause alter the distribution of ventilation. Distribution of peak pressures was less sensitive to such changes. Compartmental ventilation was much less uniform than compartmental peak pressure. Ventilation could not be made entirely uniform by changes of f, D, or pause within the usual clinical range. Conclusions: In a linear, two compartment model of the respiratory system, disparity of compartmental end-expiratory pressures is the primary mechanism by which changes of ƒ, D, or pause alter the distribution of ventilation during inflation with constant flow. Ventilation is less evenly distributed than peak alveolar pressure, and there are limits to the beneficial effects on the distribution of ventilation to be gained from manipulations of machine settings.

Effect of stimulus duty cycle and cycle frequency on power output during fatigue in rat diaphragm muscle doing oscillatory work.

Isolated rat diaphragm muscle was stimulated repetitively to induce fatigue, and the work done during each contraction was measured. Work per cycle was calculated by measuring force as the activated muscle was subjected to sinusoidal length changes (from 97 to 103% of L0, where L0 is rest length). Work was calculated from the loop formed when force was plotted against length. Work done was positive when the muscle was shortening and was negative when it was lengthening; net work was the difference. Work output was varied by changing the stimulus duty cycle (4, 8, or 16% of the total cycle duration) and cycle frequency (1, 2, or 4 Hz). The rate and extent of the decrease in power was influenced much more by changes in cycle frequency than by changes in duty cycle. Duty cycle and cycle frequency combinations that resulted in greater power in the prefatigue trials were associated with a more rapid rate of fatigue. However, net positive power at the end of the 15-min fatigue period was greater under these same conditions (i.e., high duty cycle and high cycle frequency). Fatigue in working diaphragm muscle depends more on cycle frequency than on duty cycle.

Respiratory response to positive and negative inspiratory pressure in humans

To investigate the effect of positive or negative inspiratory pressure on respiration, eight subjects breathed, either without or with added external dead space (V D, 600 ml), through either added inspiratory laminar flow resistances (RES; peak inspiratory airway pressure, Pinsp, down to −9 cmH 2O) or with inspiratory pressure support (IPS; Pinsp up to +10 cmH 2O). IPS, triggered by the subject's inspiratory effort, provided positive airway pressure throughout inspiration, but allowed for attainment of the subject's own respiratory pattern. The following main results were obtained with IPS or RES relative to the control (no IPS, no RES): 1. (1) with V d, IPS led to small, but significant, increases in tidal volume (V t), respiratory frequency (f r) and ventilation (V e), with no changes in inspiratory time (T i) or duty cycle (T i/T t). Mean inspiratory flow (V t/T i) increased, and mouth occlusion pressure 0.1 sec after onset of inspiration (P 0.1) decreased significantly with IPS. The changes during RES were essentially in the opposite direction; 2. (2) without V d, similar, but smaller effects were observed, and only the changes in V t/T i and P 0.1 during IPS were significant; 3. (3) highly significant decreases were observed during IPS in end-tidal P CO 2 (P et CO 2 ); on the average from 39.6 to 29.2 Torr without V d, and from 45.7 to 39.3 Torr with V d breathing. A small, but significant decrease in P et CO 2 occured also during RES with V d. We conclude that while resistive loading is nearly completely compensated with but small changes in P et CO 2 , inspiratory pressure support leads to marked hyperventilation, which is not effectively counteracted by central timing commands.

Breathing during prolonged exercise in humans.

1. Six normal subjects cycled to endurance or for 60 min at four work rates (WR 1-4): mean of 34% working capacity (93 watts for 60 min); 43% (120 watts for 56 min); 63% (177 watts for 37 min); and 84% (233 watts for 12 min), to determine how breathing pattern and dyspnoea change during prolonged activity. Four to six minutes were allowed to establish steady state and subsequent changes were considered to be endurance related. 2. Dyspnoea (Borg scale, 0-10) increased with the duration of activity at all work rates. 3. Ventilation (VE) did not change at WR1; increased from 44 to 47 l min-1 at WR2; from 60 to 88 l min-1 at WR3; and from 111 to 132 l min-1 at WR4. Dyspnoea was significantly and independently related to ventilation and duration of activity: dyspnoea = 0.004 VE1.36 time 0.25 (r = 0.81; partial F 202 and 26 respectively). 4. Inspiratory resistance did not increase at any work rate. Dynamic elastance remained constant during WR1, WR2 and WR3 but increased from 7.4 to 9.1 cmH2O l-1 during WR4. 5. Peak inspiratory pressure did not increase, and the increase in VE was accomplished by an increased breathing frequency without change in duty cycle. 6. Duration of activity is an important contributor to dyspnoea independent of changes in respiratory muscle contractile activity.

Recovery from fatigue of human diaphragm and limb muscles

This study was designed to compare the recovery from fatigue of human inspiratory and limb muscles using repeated maximal static contractions. Series of 18 maximal contractions of 10 sec duration were performed with a duty cycle of 50% for maximal inspiratory efforts (against a shutter at FRC), and with duty cycles of 5%, 10%, 20% and 50% for the elbow flexors in repeated studies on 6 subjects. The peak inspiratory pressure at the end of the series declined to 86.7% ± 5.3% (mean ± S.D.) of its initial value; maximal force of the elbow flexors declined to 83.5% ± 7.0% (5% duty cycle), 80.0% ± 5.5% (10% duty cycle), 70.0% ± 9.3% (20% duty cycle),and required approximately a 10-fold reduction in duty cycle to maintain over a series of contractions a force generating capacity comparable to that of the diaphragm. A small degree of ‘central’ fatigue developed progressively during all series of contractions but did not correlate with duty cycle. Fatigue-induced changes in twitch contraction properties varied with changes in duty cycle. Our major conclusions are that the human diaphragm has a marked capacity to recover from fatigue and that this may have been underestimated in previous studies from this and other laboratories.

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

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)

Effect of lung volume on breath holding.

The mechanism by which large lung volume lessens the discomfort of breath holding and prolongs breath-hold time was studied by analyzing the pressure waves made by diaphragm contractions during breath holds at various lung volumes. Subjects rebreathed a mixture of 8% CO2-92% O2 and commenced breath holding after reaching an alveolar plateau. At all volumes, regular rhythmic contractions of inspiratory muscles, followed by means of gastric and pleural pressures, increased in amplitude and frequency until the breakpoint. Expiratory muscle activity was more prominent in some subjects than others, and increased through each breath hold. Increasing lung volume caused a delay in onset and a decrease in frequency of contractions with no consistent change in duty cycle and a decline in magnitude of esophageal pressure swings that could be accounted for by force-length and geometric properties. The effect of lung volume on the timing of contractions most resembled that of a chest wall reflex and is consistent with the hypothesis that the contractions are a major source of dyspnea in breath holding.

Effects of breathing pattern on inspiratory muscle endurance in humans

Endurance of the inspiratory muscles was measured in normal volunteers using a threshold resistance that produced a relatively constant mouth-pressure load, independent of inspiratory flow rate (VTI). Breathing pattern was controlled by visual feedback from an oscilloscope. Endurance was measured as the length of time (Tlim) a target VTI could be maintained with maximum effort. Effects of changes in breathing pattern on Tlim were compared with control measurements made the same day. Increases in VTI or in duty cycle (inspiratory time/total period) shortened Tlim, whereas decreases lengthened Tlim. However, effects of changes in VTI were less than equivalent changes in tidal volume produced by alterations in duty cycle. Furthermore, when two breathing pattern changes were altered simultaneously to keep the rate of external inspiratory work (Winsp) constant, significant effects due to changes in duty cycle were still observed. In conclusion, 1) both VTI and duty cycle have significant effects on measurements of inspiratory muscle endurance and 2) the effects of VTI are less than the effects of duty cycle for the same Winsp.

Modelling and analysis of d.c.-d.c. converter using y-parameters

This paper describes an impulse-response method to find the low-frequency y-parameters of d.c. to d.c. switching converters in both the continuous and discontinuous modes. Using an example of a forward converter, the applications of the y-parameters are illustrated by the determination of: the general equivalent circuit; the d.c. output voltage; the critical condition between continuous and discontinuous modes of operation; the equivalent circuit under steady state condition; the transfer function between small change in d.c. input voltage and the resultant change in d.c.output voltage; the transfer function between small change in duty cycle and the resultant change in d.c. output voltage. The y-parameter approach can easily be applied to other types of converter circuits. Its simplicity makes it particularly suitable for more complex types of converters

Brass keyer system for electronic organ

A keying arrangement for electronic organs in which a tone signal consisting of a square wave having, for example, a fifty percent duty cycle is connected to the input of the keyer circuit, and the output thereof, upon the depression of a playing key, consists of a pulse train with the amplitude rising at a controlled rate and the pulse width or duty cycle decreasing at a controlled rate but lagging the increase in amplitude so as to closely duplicate the playing of a muted brass instrument in the attack fashion. A muted brass tremulant affect is achieved by applying a cyclically time variant signal to modulate the pulse amplitude and pulse duty cycle, again with the change in duty cycle lagging the change in amplitude. The circuitry for accomplishing this comprises a diode keyer wherein a pair of resistor-capacitor circuits having different time constants control the keyer to effect variations in pulse amplitude and duty cycle over respective intervals of time.

An on-chip back-bias generator for MOS dynamic memory

An on-chip back-bias generator for 64K dynamic MOS RAM has been developed.The use of this generator achieves the goal of a single 5 V power supply part while preserving the advantages of substrate bias in n-channel MOS technology. These advantages include the elimination of substrate injection current from localized forward biasing of diodes, improved speed and power characteristics, and a larger differential data signal on the bit sense lines. The generator circuit avoids several pit-falls on on-chip V/SUB BB/ generation. The circuit pumps to a known regulated voltage. This avoids substrate drift with changes in substrate current resulting from changes in cycle time. This drift will change device characteristics and degrade storage levels. A unique two-level reference scheme avoids changes in substrate bias voltage that otherwise result from the shift in V/SUB BB/ between precharged and active memory states when memory duty cycle changes. The standby power used by the generator is only 0.74 mW.

Influence of exercise and CO2 on breathing pattern of normal man.

Ventilatory patterns during rest, CO2 inhalation (2, 3, and 4%) and three levels of exercise were analyzed in supine men using a canopy system for noninvasive measurements. Changes in tidal volume (VT) and breathing frequency (f) with equal increases in minute ventilation (VE) differed significantly during exercise and CO2 inhalation. Increases in VE during exercise was accompanied by increases in VT and f. During CO2 inhalation, the change in frequency was less than during exercise. However, when analyzed in terms of inspiratory flow (VT/TI) and inspiratory duty cycle (TI/Ttot), the response to both stimuli was similar. With increases to twice control VE both TI/Ttot and VT/VI increased. Thereafter only VTTI increased with increasing VE. At rest, inspiratory time on a breath by breath basis increased minimally with VT, while changes in inspiratory flow accounted for the variability in VT. These two respiratory stimulants appear to increase ventilation through different mechanisms when analyzed in terms of VT and f. However, changes in inspiratory flow and duty cycle are similar in both.

Engine Life, Usage, and Cycle Selection

IFE problems in engines are insidious. We find performance problems as soon as an engine is tested, but life problems often do not appear until years later when hundreds of engines are in the field. Over the years, almost every manufacturer has had life problems, resulting in strenuous activity by engine companies and sponsoring agencies first to solve the immediate problems and then to improve life prediction methods. A complicating factor in military engines is that the duty cycle actually flown can be quite different from the design duty cycle, because of the need to develop airplane tactics and engine usage after the engine is developed. Components which would have functioned satisfactorily under the design duty cycle develop severe life problems under different duty cycles. Major modifications are needed, costs rise, and vigorous efforts are made to solve a major problem that would have been routine if confronted early in the design cycle. Engine manufacturers devote a large effort to life analysis and prediction as part of the detail design phase. It has been suggested that more emphasis should be placed on life requirements and possible duty cycle changes during preliminary design in order to evaluate their effects on cycle selection and overall system performance. This paper reviews the General Electric Company's approach to this problem, some typical results, and some conclusions that can be drawn from this work.

Ultrasonic Study of Vocal-Fold Vibration in Normal and Nasalized Vowels

Nasal coupling reduces the over-all intensity of a vowel, requiring greater vocal effort to match intensity of a nonnasal vowel. The question is to what extent increased vocal effort for nasal vowels is reflected by a change in duty cycle of vocal-fold vibration. Duration of the vibratory open phase was taken as the time within each cycle during which ultrasonic transmission through the larynx was blocked by reflection from the glottal rim. This measurement is consistent over the small range of transducer positions permitting the ultrasonic beam to pass through the approximate vertical and horizontal midpoint of the vocal folds. At matched microphone signal smplitudes, duty cycles differ for normal and nasalized sustained vowels, spoken at the same vocal fundamental frequency. Results are reported for preadolescent boys. [This investigation was supported by a NIH Grant.]

Temporary Threshold Shift With Changing Duty Cycle

Temporary Threshold Shift With Changing Duty Cycle

Temporary Threshold Shift with Changing Duty Cycle

The empirical rule that interrupted noise having an on-fraction R produces R times the TTS that the same noise would produce if on continuously (the on-fraction rule) was tested for R≈0.5 and for various duty cycles from 1 min to 16 min. The TTS from the 1-min and 2-min duty cycles agreed with the value predicted by the rule, but the 4-min, 8-min, and 16-min duty cycles gave respectively 1.07, 1.21, and 1.29 times the R-based values. This result indicates that the on-fraction rule breaks down when on-off times exceed about 1 min, but that the rule may be extended for periodic or nearly periodic noises by incorporating correction factor based on the length of the period.

Automatic Frequency Control of Magnetrons

A practical AFC system for both X-band and Ku-band magnetron radar transmitters has been developed. This system meets the needs of three radar systems currently in production. Frequency stabilization is accomplished by electronically controlling the magnetron load impedance. Therefore, the magnetron ``pulling figure'' is put to use. The closed loop AFC system maintains frequency stability to better than ±2 Mc at Ku-band and ±1.5 Mc at X-band frequencies over wide environmental conditions. The system dynamically compensates for deviations in frequency due to temperature, vibration, shock, changes in duty cycle, drift with life, and poor voltage regulation. The response time of the AFC system is such that, starting at the limits of thle capture range, ``on frequency'' response is Obtained within the first five pulses of the magnetron. One of the radar systems requires a considerable delay between groups of pulses. For this radar, the AFC system provides a memory to hold the conditions for ``on frequency'' response during the delay periods. A qualitative analysis of the closed-loop system is made with reference to the Rieke Diagram. It is shown how a single magnetron has been used to meet two different sets of system performance requirements. System operation and hardware are discussed with reference to practical difficulties.

Multiplex Employing Pulse-Time and Pulsed-Frequency Modulation

A microwave communication system giving two-channel voice transmission over a single carrier is described. Diplexing is accomplished by the use of two types of modulation, rather than by time or frequency division. One channel is transmitted by a form of pulse-time modulation using 1-microsecond pulses at a mean repetition rate of 10 kc, and the other channel by frequency modulation of the pulsed microwave carrier (FM burst). The addition of the pulsed-FM channel requires no additional carrier power or change of duty cycle. Cross talk is negligible. The double system is applicable to most of the common forms of pulse-time modulation. Time-division techniques are as applicable as in systems employing pulse-time modulation alone. If a time-division index of n is employed, i.e., that necessary to give n channels in a straight pulse-time time-division multiplex system, the employment of the diplex system described gives 2n channels. Compared to a straight pulse-time time-division system giving 2n channels, the double-modulation system results in economies in synchronizing equipment, and provides a better signal-to-noise ratio on the pulse-time portion of the system, but requires some additional bandwidth.