JOURNAL
OF APPLIED
Vol. 38, No. 3, March
PHYS~OLOFY 1975.
A sinusoidal
Printed
in U.S.A.
load generator
for use in cycle ergometry
FREDERIC P. TORRES, BRIAN J- WHIPP, STEPHEN N. STEEN, AND Diuision uj Respiratory Physiology and Medkine, Harbor General Hospital, University of California, Los Angeles, School of Medicine, Torrance, California 90509
P., BRIAN J- WHIPP, STEPHEN IV. STEEN, A sinusoidal load generator for use in cycle ergometry . J . Appl. Physiol. 38(3) : 554-557. 1975.~we have modifled an electromagnetically braked cycle ergometer to provide a sinusoidally varying work load. This was accomplished by applying a low-frequency sinusoidal voltage at the inputs of the electromagnets using a sinusoidal potentiometer, whose shaft was driven by a variable-speed motor, and a voltage-programmable power supply to amplify the signal. The frequency range is currently 0.0017-0.03 Hz. This technique for sinusoidal work loads allows the period, amplitude, and mean position to be easily changed from a console, even during a test if required. AND
TORRES, 77
cycle
FREDERIC
KARLMAN
ergometer;
work
loads;
frequency
WASSERMAN
integrated circuitry are now available (8038, Intersil, Cupertino, Calif.), the frequency range of interest to us closely approaches the lower limit of their range. We therefore chose the electromechanical solution of connecting a voltage source across a sinusoidal potentiometer, whose shaft is driven by a variablespeed motor. Varying the motor speed changes the frequency
WASSERMAN.
sinusoidal
ISARLMAN
analysis
INFORMATION regarding the dynamic behavior of a physiological control system may be obtained by the application of a sinusoidal forcing function and observing the gain and phase characteristics of the system’s response (11, 14). Such analyses have been previously applied to the cardiovascular (1, 2, 15, 18, 19) and respiratory systems (6-8, 16) to excellent effect. Current interest in the kinetics of exercise metabolism (3, 12, 13, 17) and respiratory control (4, 9, 10, 18) and especially with regard to the relationships between these functions suggests that an accurate sinusoidal load generator (SLG), whose sine-wave characteristics may be readily altered would prove useful. To this effect we have modifled a standardly used electromagnetically braked cycle ergometer to allow the work rate to be altered sinusoidally with the amplitude, period and mean position of the sine wave to be under operator control. IMPORTANT
FIG, 1. Relationship between voltage applied of a Lanooy cycle ergometer and resulting work
to the electromagnet rate.
METHODS
Electromagnetically braked ergometers of the Lanooy (Godart, DeBilt, Holland) type have proved most useful in exercise physiology as they provide a constant work load over a wide range of pedaling frequencies. Change in work load is accomplished by changing DC voltage applied to its electromagnets. The DC voltage is obtained after rectification and filtering from an adjustable auto transformer (Variac). Except for marked nonlinearity1 below 25 W, the applied voltage versus work-load characteristics of this ergometer is linear (Fig. 1). Substituting a sinusoidal voltage of very low frequency at the inputs of the electromagnets produces a corresponding sinusoidal load variation. The frequency range of interest for our studies was from 0.0017 to 0.033 Hz corresponding to a period of approximately 10 min to 30 s, respectively. Few commercially available signal generators are capable of outputting usable signals in that low range. Although wave-form generators utilizing -. l Normal operation of this ergometer compensates for nonlinearity by providing the appropriate nonlinear graduation of the work-load meter,
L ______--___
-------------A
FIG. 2. Block diagram of system for sinusoidal work rates on a cycle ergometer. Region within dashed line represents the sinusoidal load generator. Period, load swing, and load bias are controls which allow variation of the sine wave. For further discussion, see text.
of the signal; increasing or decreasing the voltage across the potentiometer will produce a corresponding change in the amplitude of the signal. As shown by the system block diagram in Fig. 2, this signal is amplified further by a voltage programmable power supply prior to delivery to the electromagnets of the ergometer. This technique is therefore applicable to any electromagnetically braked ergometer. 554
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on December 27, 2018.
SIMJSOIDAL
LOAD
555
GENERATOR
The only modification necessary in the control panel of the ergometer is the addition of a two-pole, two-position switch, &, that allows one to select a “sine” or a %onstant” load (see Fig. 3). In the “sine” position, the electromagnets are energized by the sinusoidal output of t ze power supply. In “constant,” the circuit is restored to its original condition. Switch Sd is placed electrically “ahead” of the panel meter, and thus allows monitoring of the work load in either sine or constant load mode while preserving the original calibration of the instrument.
FIG.
11 to allow
3. Schematic diagram of the control panel on the Lanooy * 1 .* E . ,, 1 .I 11 1 aselectron ~1 constant ioaa or sinusoiaal loaa 0peraIlon.
FIG. 4. Schematic diagram of the sinusoidal load the power supply and the variable voltage source.
generator.
SINUSOIDAL
GENERATOR
CIRCUITRY
The schematic diagram of the SLG is shown in Fig. 4. The circuit consists of a dual zener regulated + 6-V supply and a motor speed control board (Minarik, Los Angeles). The speed control allows roughly a 20-to-l speed reduction, thereby controlling the period of the sine wave. A low-rpm and low-torque permanent magnet motor (e.g., Brevel, model 14R-A153B) was used in conjunction with a set of three spur gears to obtain the The 12-V input to the speed control proper frequency range.
ergolneter.
Essential
LOAD
Note
feature
the placement
is the placement
of switch
S4 which
of the sinusoidal
modifies
the ergometer
potentiometer
relative
to
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on December 27, 2018.
556
TORRES,
board was regulated by transistor Qr and zener diode lN5242 to minimize line voltage variations. The dual supply is simply realized with a bridge rectifier and two zener diodes. Their outputs are continuously variable (0 to +6 V) through R4 and KS. The sinusoidal potentiometer is connected across the positive 6-V supply. The output of the negative 6-V supply is connected directly to the programmable input of the power supply (Sorensen, DCR 300). With respect to the programmable input of the power supply, the 6-V negative source is in series with the sinusoidal signal from the potentiometer and thus provides a variable bias on which the sinusoidal wave is added. The amplitude of the sine wave depends on the setting of R 4. We have therefore termed 114 the “Load Amplitude” control and Rg the “Load Bias” control. These functions are demonstrated in Fig. 5. RB and.& (Fig. 3) are IO-turn 1 (h potentiometers with a counting dial that permits accurate setting of the work-load bias and amplitude. Component selection was
/75
r
08
FIG. 5. Three examples of sinusoidal Mean position on the cycle ergometer. period of the sine wave may be readily strip-chart recorder.
RESULTS
altered
AND
This study was supported by National Institutes of Health HL-11907, HL-14967, and HI1-05916. B. J. Whipp is an Established Investigator of the American Association. Address reprint reqlrests to B. J. Whipp. Received
for publication
5 July
84
uptake
r P ftft
1
I
11
Grants Heart
1974.
pired sured breath
.‘titfw
WASSERMAN
DISCUSSION
FIG.
P 02
AND
Figure 5 clemonstrates three examples of sinusoidal work patterns which were generated by the SLG and recorded on the strip-chart recorder. Figure 6 represents a representative response pattern of expired Aow (Vexp), Pco 2, and PO 2, sampled from the mouthpiece, and the on-line breath-by-breath computation (5, 17) of 02 uptake (voz). The phase lag between work rate and VOW is readily apparent from such a display. Frequency analysis of such responses to various sinusoidal forcing functions should provide important information with respect to the interaction of ventilatory, pulmonary gas exchange, and metabolic variables during exercise. Techniques for providing sinusoidal work loads have previously been successfully applied to the treadmill (1, 2) and cycle ergometer (18, 19). Ashkar (1) attached a multispeed gear module to the control panel of a treadmill and Wigertz (19) and his associates (7, 15) utilized a cam-and-follower device with a variable resistor to modify an electrically braked cycle ergometer. Our method differs from those previously used, in that it allows the mean load, the period, and the amplitude of the work function to be easily varied from a console, even during a test if required.
rate patterns developed bias), amplitude, and and is displayed on a
(load
STEEN,
based mainly on availability. Any voltage programmable power supply giving 200-V DC at 1 A would be adequate. The value of the sinusoidal potentiometer is also not critical, and it may range anywhere from I to 10 ka without modifying the existing circuit. The complete SLG unit, as described, is contained within a standard 19 x 6 in rack panel.
0
work
WHIPP,
6. On-line recording of exflow, CO2 and 02 tension (meaat the mouth) and the breath-bycomputation and display of 02
in response
to a sinusoidal
work
load on a cycle ergometer. Time scale is represented by the marker at top of figure. Interruptions on the time marker
tj
mmHg
u~~~c~c~cc~~L~~uyu~~-u~~
are at I-rnin
intervals.
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on December 27, 2018.
SINUSOIDAL
LOAD
557
GENERATOR
REFERENCES 1. ASHKAR, E. Circulatory response to Am. J. Physiol. 222 : 7U7--792, 1972. 2. ASHKAR, cuencia 3. BASON, kinetics Physiol. 4. BEAVER, start and
sinusoidal
exercise
in
dogs.
E. Efectos de la Modulation de1 Ejercicio sobre la frecardiaca en el perro. Rev. Sot. Arx. 13iol. 43: 152, 1967. R., C. E. BILLINGS, E. L. Fox, AND R. GERKE. Oxygen for constant work loads at various altitudes. J. Aj~flZ. 35: 497-500, 1973. W. I,., AND K. WASSERMAN. Transients in ventilation at end of exercise. J. A#/. Physiol. 25 : 390--WI, 1968.
5. BEAVER, W. I,., K. WASSERMAN, AND 13. J. W~XIPX). On-line computer analysis and breath-by-breath graphical display
OF APPLIED
Vol. 38, No. 3, March
PHYS~OLOFY 1975.
A sinusoidal
Printed
in U.S.A.
load generator
for use in cycle ergometry
FREDERIC P. TORRES, BRIAN J- WHIPP, STEPHEN N. STEEN, AND Diuision uj Respiratory Physiology and Medkine, Harbor General Hospital, University of California, Los Angeles, School of Medicine, Torrance, California 90509
P., BRIAN J- WHIPP, STEPHEN IV. STEEN, A sinusoidal load generator for use in cycle ergometry . J . Appl. Physiol. 38(3) : 554-557. 1975.~we have modifled an electromagnetically braked cycle ergometer to provide a sinusoidally varying work load. This was accomplished by applying a low-frequency sinusoidal voltage at the inputs of the electromagnets using a sinusoidal potentiometer, whose shaft was driven by a variable-speed motor, and a voltage-programmable power supply to amplify the signal. The frequency range is currently 0.0017-0.03 Hz. This technique for sinusoidal work loads allows the period, amplitude, and mean position to be easily changed from a console, even during a test if required. AND
TORRES, 77
cycle
FREDERIC
KARLMAN
ergometer;
work
loads;
frequency
WASSERMAN
integrated circuitry are now available (8038, Intersil, Cupertino, Calif.), the frequency range of interest to us closely approaches the lower limit of their range. We therefore chose the electromechanical solution of connecting a voltage source across a sinusoidal potentiometer, whose shaft is driven by a variablespeed motor. Varying the motor speed changes the frequency
WASSERMAN.
sinusoidal
ISARLMAN
analysis
INFORMATION regarding the dynamic behavior of a physiological control system may be obtained by the application of a sinusoidal forcing function and observing the gain and phase characteristics of the system’s response (11, 14). Such analyses have been previously applied to the cardiovascular (1, 2, 15, 18, 19) and respiratory systems (6-8, 16) to excellent effect. Current interest in the kinetics of exercise metabolism (3, 12, 13, 17) and respiratory control (4, 9, 10, 18) and especially with regard to the relationships between these functions suggests that an accurate sinusoidal load generator (SLG), whose sine-wave characteristics may be readily altered would prove useful. To this effect we have modifled a standardly used electromagnetically braked cycle ergometer to allow the work rate to be altered sinusoidally with the amplitude, period and mean position of the sine wave to be under operator control. IMPORTANT
FIG, 1. Relationship between voltage applied of a Lanooy cycle ergometer and resulting work
to the electromagnet rate.
METHODS
Electromagnetically braked ergometers of the Lanooy (Godart, DeBilt, Holland) type have proved most useful in exercise physiology as they provide a constant work load over a wide range of pedaling frequencies. Change in work load is accomplished by changing DC voltage applied to its electromagnets. The DC voltage is obtained after rectification and filtering from an adjustable auto transformer (Variac). Except for marked nonlinearity1 below 25 W, the applied voltage versus work-load characteristics of this ergometer is linear (Fig. 1). Substituting a sinusoidal voltage of very low frequency at the inputs of the electromagnets produces a corresponding sinusoidal load variation. The frequency range of interest for our studies was from 0.0017 to 0.033 Hz corresponding to a period of approximately 10 min to 30 s, respectively. Few commercially available signal generators are capable of outputting usable signals in that low range. Although wave-form generators utilizing -. l Normal operation of this ergometer compensates for nonlinearity by providing the appropriate nonlinear graduation of the work-load meter,
L ______--___
-------------A
FIG. 2. Block diagram of system for sinusoidal work rates on a cycle ergometer. Region within dashed line represents the sinusoidal load generator. Period, load swing, and load bias are controls which allow variation of the sine wave. For further discussion, see text.
of the signal; increasing or decreasing the voltage across the potentiometer will produce a corresponding change in the amplitude of the signal. As shown by the system block diagram in Fig. 2, this signal is amplified further by a voltage programmable power supply prior to delivery to the electromagnets of the ergometer. This technique is therefore applicable to any electromagnetically braked ergometer. 554
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on December 27, 2018.
SIMJSOIDAL
LOAD
555
GENERATOR
The only modification necessary in the control panel of the ergometer is the addition of a two-pole, two-position switch, &, that allows one to select a “sine” or a %onstant” load (see Fig. 3). In the “sine” position, the electromagnets are energized by the sinusoidal output of t ze power supply. In “constant,” the circuit is restored to its original condition. Switch Sd is placed electrically “ahead” of the panel meter, and thus allows monitoring of the work load in either sine or constant load mode while preserving the original calibration of the instrument.
FIG.
11 to allow
3. Schematic diagram of the control panel on the Lanooy * 1 .* E . ,, 1 .I 11 1 aselectron ~1 constant ioaa or sinusoiaal loaa 0peraIlon.
FIG. 4. Schematic diagram of the sinusoidal load the power supply and the variable voltage source.
generator.
SINUSOIDAL
GENERATOR
CIRCUITRY
The schematic diagram of the SLG is shown in Fig. 4. The circuit consists of a dual zener regulated + 6-V supply and a motor speed control board (Minarik, Los Angeles). The speed control allows roughly a 20-to-l speed reduction, thereby controlling the period of the sine wave. A low-rpm and low-torque permanent magnet motor (e.g., Brevel, model 14R-A153B) was used in conjunction with a set of three spur gears to obtain the The 12-V input to the speed control proper frequency range.
ergolneter.
Essential
LOAD
Note
feature
the placement
is the placement
of switch
S4 which
of the sinusoidal
modifies
the ergometer
potentiometer
relative
to
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on December 27, 2018.
556
TORRES,
board was regulated by transistor Qr and zener diode lN5242 to minimize line voltage variations. The dual supply is simply realized with a bridge rectifier and two zener diodes. Their outputs are continuously variable (0 to +6 V) through R4 and KS. The sinusoidal potentiometer is connected across the positive 6-V supply. The output of the negative 6-V supply is connected directly to the programmable input of the power supply (Sorensen, DCR 300). With respect to the programmable input of the power supply, the 6-V negative source is in series with the sinusoidal signal from the potentiometer and thus provides a variable bias on which the sinusoidal wave is added. The amplitude of the sine wave depends on the setting of R 4. We have therefore termed 114 the “Load Amplitude” control and Rg the “Load Bias” control. These functions are demonstrated in Fig. 5. RB and.& (Fig. 3) are IO-turn 1 (h potentiometers with a counting dial that permits accurate setting of the work-load bias and amplitude. Component selection was
/75
r
08
FIG. 5. Three examples of sinusoidal Mean position on the cycle ergometer. period of the sine wave may be readily strip-chart recorder.
RESULTS
altered
AND
This study was supported by National Institutes of Health HL-11907, HL-14967, and HI1-05916. B. J. Whipp is an Established Investigator of the American Association. Address reprint reqlrests to B. J. Whipp. Received
for publication
5 July
84
uptake
r P ftft
1
I
11
Grants Heart
1974.
pired sured breath
.‘titfw
WASSERMAN
DISCUSSION
FIG.
P 02
AND
Figure 5 clemonstrates three examples of sinusoidal work patterns which were generated by the SLG and recorded on the strip-chart recorder. Figure 6 represents a representative response pattern of expired Aow (Vexp), Pco 2, and PO 2, sampled from the mouthpiece, and the on-line breath-by-breath computation (5, 17) of 02 uptake (voz). The phase lag between work rate and VOW is readily apparent from such a display. Frequency analysis of such responses to various sinusoidal forcing functions should provide important information with respect to the interaction of ventilatory, pulmonary gas exchange, and metabolic variables during exercise. Techniques for providing sinusoidal work loads have previously been successfully applied to the treadmill (1, 2) and cycle ergometer (18, 19). Ashkar (1) attached a multispeed gear module to the control panel of a treadmill and Wigertz (19) and his associates (7, 15) utilized a cam-and-follower device with a variable resistor to modify an electrically braked cycle ergometer. Our method differs from those previously used, in that it allows the mean load, the period, and the amplitude of the work function to be easily varied from a console, even during a test if required.
rate patterns developed bias), amplitude, and and is displayed on a
(load
STEEN,
based mainly on availability. Any voltage programmable power supply giving 200-V DC at 1 A would be adequate. The value of the sinusoidal potentiometer is also not critical, and it may range anywhere from I to 10 ka without modifying the existing circuit. The complete SLG unit, as described, is contained within a standard 19 x 6 in rack panel.
0
work
WHIPP,
6. On-line recording of exflow, CO2 and 02 tension (meaat the mouth) and the breath-bycomputation and display of 02
in response
to a sinusoidal
work
load on a cycle ergometer. Time scale is represented by the marker at top of figure. Interruptions on the time marker
tj
mmHg
u~~~c~c~cc~~L~~uyu~~-u~~
are at I-rnin
intervals.
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on December 27, 2018.
SINUSOIDAL
LOAD
557
GENERATOR
REFERENCES 1. ASHKAR, E. Circulatory response to Am. J. Physiol. 222 : 7U7--792, 1972. 2. ASHKAR, cuencia 3. BASON, kinetics Physiol. 4. BEAVER, start and
sinusoidal
exercise
in
dogs.
E. Efectos de la Modulation de1 Ejercicio sobre la frecardiaca en el perro. Rev. Sot. Arx. 13iol. 43: 152, 1967. R., C. E. BILLINGS, E. L. Fox, AND R. GERKE. Oxygen for constant work loads at various altitudes. J. Aj~flZ. 35: 497-500, 1973. W. I,., AND K. WASSERMAN. Transients in ventilation at end of exercise. J. A#/. Physiol. 25 : 390--WI, 1968.
5. BEAVER, W. I,., K. WASSERMAN, AND 13. J. W~XIPX). On-line computer analysis and breath-by-breath graphical display
