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Background and purpose In order to identify sleep disorders by thoracic impedance plethysmography (TIP), we propose several new techniques: the application of an adaptive filter, a scaled Fourier linear combiner (SFLC) to eliminate cardiac-derived fluctuation in the impedance waveform, and the use of heart rate variability (HRV) to ascertain whether the airflow is obstructed. Patients and methods Laboratory simulation experiments on four healthy individuals and actual overnight measurements on five patients with sleep disorders were carried out. Amplified thoracic impedance change (Δ Z ), ECG, a phonocardiograph, a pneumotachograph and a standard polysomnograph were recorded. The SFLC was applied to Δ Z to selectively extract the cardiac-synchronous component (Δ Z CSC ), and the remainder of the waveform (Δ Z REM ) was low-pass filtered to estimate the waveform driven by respiration. The HRV was divided into respiratory synchronous (HRV R ) and low frequency (HRV L ) components. Results The SFLC could drastically extract Δ Z CSC from Δ Z and thereby demonstrate a Δ Z REM pattern quite similar to the flow–volume curve of the pneumotachograph. Central sleep apnea could be identified as the cessation of Δ Z REM and concomitant attenuation of HRV R . Obstructive sleep apnea could be identified as the maintenance of rhythmic but attenuated variations of Δ Z REM accompanied by asynchronous fluctuation of HRV R against Δ Z REM . Central hypopnea could be identified as a normal but attenuated waveform in both Δ Z REM and HRV R . A large fluctuation in HRV L was observed during repetitive appearances of apnea/hypopnea in the nocturnal experiments. Conclusion The modified TIP together with HRV provides a superior tool for accurate and convenient definition of sleep apnea syndromes.

In order to elucidate the beat-to-beat changes of the systolic time intervals (STI) during exercise, we proposed new techniques relating to an adaptive filter and detection algorithms for B- and X-points in the impedance cardiograph (ICG). Six male subjects underwent a ramp bicycle exercise up to maximum intensity during which an ECG, ICG and phonocardiogram (PCG) were continuously measured. Following the application of an adaptive filter, the scaled Fourier linear combiner (SFLC), to the first derivative (dZ/dt) of the base impedance (deltaZ) and PCG waveforms, the B- and X-points were automatically determined. For the B-point detection we used three criteria: the zero-crossing point (B(zero)), the 15% response point (B15%) of the negative peak of the dZ/dt (dZ/dt(min)) and a new algorithm (B(new)). The X-point was separately determined by using the ICG and PCG waveforms. It was found that the shape of the dZ/dt waveform directly affected the determination of the B- and X-points. The B-points determined using B(zero) and B15%, criteria were sometimes unstable caused by the location of a notch preceding the dZ/dt(min) compared to the B(new). The time difference between the X-points measured by the ICG and PCG was mostly within +/- 20 milliseconds but statistically significant. Although a wide variation was seen in R-R intervals, the STI were more stable. The relationships between HR and STI from rest to maximal exercise showed a gentle curvilinear relationship. It is suggested that the STI can be obtained precisely on a beat-to-beat basis by using the adaptive filter and detection algorithms for the inflection points of the ICG even during maximum exercise.

The effect of exercise intensity on the power spectral properties of the periodic oscillation of the skin blood flow was investigated with respect to the variability of heart rate in 7 healthy male subjects. The skin blood flow (SBF) and heart rate (HR) were measured by a laser-Doppler flowmeter on the forehead skin, and by an ECG, at rest and during bicycle exercise in three different intensities; unloaded, 50 and 100 W. An alcohol ingestion test was additionally performed on two subjects in the resting condition. Power spectral density (PSD) was calculated by means of fast Fourier transform (FFT). The peak frequency (PF) and integration of PSD (iPSD) of each component was estimated to compare conditions and parameters. In the SBF fluctuation, two major components were usually observed: one synchronous with cardiac contraction rhythm (HFF) which shifted to a higher frequency band with exercise; the other was located in a lower frequency band (LFF) ranging from about 0.1 to 0.2 Hz and did not shift with exercise. The PF of the LFF in the SBF was significantly different from that of the HR, called Mayer waves. The iPSD of the LFF in the SBF increased with increasing intensity of exercise but finally decreased at the highest intensity for which the HFF exhibited a marked increase. The LFF in the SBF disappeared after oral ingestion of alcohol that induced an increase of the SBF. From these spectral analyses, it is proposed that the LFF in the SBF is mainly related to the vasoconstrictor activity through the skin sympathetic pathway, and that the intensity of exercise does not modulate the periodicity of this fluctuation.

The purpose of this study was to estimate the differences in neuromuscular fatigue among prolonged pedalling exercises performed at different pedalling rates at a given exercise intensity. The integrated electromyogram (iEMG) slope defined by the changes in iEMG as a function of time during exercise was adopted as the measurement for estimating neuromuscular fatigue. The results of this experiment showed that the relationship between pedalling rate and the means of the iEMG slopes for eight subjects was a quadratic curve and the mean value at 70 rpm [1.56 (SD 0.65) microV.min-1] was significantly smaller (P0.01) than that at 50 and 60 rpm [2.25 (SD 0.54), and 2.22 (SD 0.68), respectively]. On the other hand, the mean value of oxygen consumption obtained simultaneously showed a tendency to increase linearly with the increase in pedalling rate, and the values at 70 and 80 rpm were significantly higher than those at 40 and 50 rpm. In conclusion, it was demonstrated that the degree of neuromuscular fatigue estimated by the iEMG changes for five periods of prolonged pedalling exercise at a given exercise intensity was different among the different pedalling rates, and that the pedalling rate at which minimal neuromuscular fatigue was obtained was not coincident with the rate at which the minimal oxygen consumption was obtained, but was coincident with the rate which most subjects preferred. These findings would suggest that the reason why most people prefer a relative higher pedalling rate, even though higher oxygen consumption is required, is closely related to the development of neuromuscular fatigue in the working muscles.

To examine the ventilatory response at the onset of passive leg movements during sleep in man and the concomitant changes in cardiac output (Qc), five healthy male subjects had their knee joints extended and flexed alternately at a frequency of about 60.min-1 for about 8 s. Minute ventilation (VI), respiratory frequency, tidal volume, end-tidal partial pressure of carbon dioxide and of oxygen, stroke volume (SV), heart rate (fc) and Qc were measured before, during and after passive leg movement during sleep stage III or IV (SLEEP). These values were compared with those of the awake condition (AWAKE). The VI increased significantly (P0.05) compared with the mean of five breaths preceding the movement (pre-movement) within one or two breaths at the onset of passive leg movements in both conditions. The difference between the mean of the first and second breaths after the onset of leg movement and pre-movement was 5.2 (SEM 1.9) l.min-1 for SLEEP and 2.7 (SEM 1.1) l.min-1 for AWAKE, respectively. Four of the five subjects showed a larger increase in ventilation during SLEEP compared with AWAKE. The fc increased significantly (P0.05) at the beginning of the passive movement in all cases, while SV showed an increase or decrease so that Qc showed no significant change in either condition. These results would suggest that afferent drive from moving limbs could produce an increase in ventilation without any change in Qc.

The effect of exercise on the increase of exhaled CO in smokers compared to non-smokers has not been clarified yet. In this study we compared the dynamics of exhaled CO before, during and after exercise between smokers and non-smokers. A group of 8 smokers and a group of 8 non-smokers underwent a bicycle exercise in a ramp fashion to near maximum intensity. Ventilation and gas exchange, and CO exhalation were continuously measured every 30-s before, during and after the exercise. The fraction of CO (F CO) in the exhaled air decreased gradually, but the total amount of exhaled CO $$ (\dot{V}_{{{\text{CO}}}} )$$ increased in a linear manner during the ramp exercise, and F CO and $$ \dot{V}_{\text{CO}} $$ returned to the pre-exercise level within several minutes after exercise in all subjects. A linear relationship was observed between $$ \dot{V}_{{{\text{O}}_{ 2} }} $$ and $$ \dot{V}_{\text{CO}} ,$$ and between $$ \dot{V}_{\text{E}} $$ and $$ \dot{V}_{\text{CO}} $$ in both the whole period of measurement and during the ramp exercise period in all subjects. However, the $$ \dot{V}_{\text{CO}} $$ at 0 W, the peak $$ \dot{V}_{\text{CO}} $$ and the slope coefficients in the regression equation between $$ \dot{V}_{\text{CO}} $$ and $$ \dot{V}_{{{\text{O}}_{ 2} }} , $$ and between $$ \dot{V}_{\text{CO}} $$ and $$ \dot{V}_{\text{E}} $$ in the ramp exercise as well as the entire periods of measurement were significantly higher in smokers compared with those in non-smokers, and these were correlated with the number of cigarettes smoked per day. It was concluded that CO exhalation increases linearly with the increase of $$ \dot{V}_{{{\text{O}}_{ 2} }} $$ and $$ \dot{V}_{\text{E}} $$ during exercise, and habitual smoking shifts these relationships upward depending on the number of cigarettes smoked daily.

In order to clarify whether leg-cooling after supramaximal treadmill exercise will change lactate disappearance rate from venous blood, blood lactate, calf blood flow, and skin temperature were determined in cold application and non-cold application recovery. In the cooling experiments, both legs were cooled with ice packs for 23 min during recovery. The skin temperature was significantly lower in the cold application as compared with the non-cold application. However, no significant difference was found in the blood lactate and/or calf blood flow between cold and non-cold conditions. In addition, there was no significant difference in the slope of regression line (blood lactate/blood flow) between cold and non-cold applications. These results suggest that no significant difference in the blood lactate between cold and non-cold applications could be explained by the lack of difference in the blood flow between cold and non-cold applications.

The surface electromyogram (EMG) from active muscle and oxygen uptake (\(\dot VO_2 \)) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W · min−1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The\(\dot VO_2 \) was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMGbp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake (\(\dot VO_{2 max} \)) and the iEMGbp between 10 and 30, and 10 and 40 W · min −1 ramp exercises (P < 0.05). However, no significant differences were obtained in\(\dot VO_{2 max} \) and\(\dot VO_2 \) corresponding to the iEMGbp during the four ramp exercises. With respect to the relationship between\(\dot VO_2 \) and exercise intensity during the ramp increments, the\(\dot VO_2 \)-exercise intensity slope showed significant differences only for the upper half (i.e. above iEMGbp). These results demonstrated that the\(\dot VO_{2 max} \) and\(\dot VO_2 \) at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to\(\dot VO_{2 max} \) and the iEMGbp was varied by the change of ramp slopes. In addition, the significant differences in the\(\dot VO_2 \) exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.

New filtering algorithms; a modified scaled Fourier linear combiner (mSFLC) and a modified ensemble averaging (mEA) are proposed to remove the phase distortion of the impedance waveform caused by SFLC. Performance of the filters is assessed from the shape of the filtered waveform and the estimation of systolic time intervals. It was found that the mSFLC and mEA could compensate for drawbacks of the SFLC and precisely reproduce the impedance waveforms; however, misinterpretation and attenuation in the cardiac variables may be caused when abrupt changes or irregularities occur in the source waveform.

The purpose of this study was to assess the validity of an adaptive filter, the scaled Fourier linear combiner (SFLC), in the impedance cardiography (ICG). Eight healthy males underwent constant-load bicycle exercise at different intensities from unloaded to near maximal intensity. The stroke volume (SV) and cardiac output (Q) measured by ICG at each condition were compared with those by the CO2 rebreathing method. We found that the noises were greatly reduced in the impedance waveform and that the inflection points, so-called the B- and X-points, were clearly detected even during strenuous exercise using the SFLC. Although a high correlation was observed between Qs measured by the two methods, the mean values of Qs in each method differed significantly and the regression line also differed significantly from the identity line. Likewise, a significant correlation was observed between SVs obtained by the two methods, but a significant difference in the group mean values and a trend of the regression line were observed. These findings suggest that the use of SFLC in ICG improves the performance in eliminating the noises and in detecting the inflection points in the waveform, thereby contributing to the accurate and beat-to-beat measurements of SV and Q especially during exercise.

In order to examine the origin and role of nitric oxide (NO) in exhaled air during exercise, exhaled NO outputs of 8 healthy human subjects were compared using different breathing methods, through the mouth or nose, at two intensities of bicycle exercise. The concentration of NO in the exhaled air and ventilatory gas exchange variables were measured by a chemiluminescence analyzer and a mixing chamber method, respectively. The concentration and total output of NO in the expired air was significantly higher under nasal breathing than under oral breathing for both exercise intensities, whereas no significant difference was observed in cardiorespiratory variables between them. NO output increased significantly when exercise intensity was increased from unloaded (0 W) to 60 W under nasal breathing, but not under oral breathing. A negative correlation among subjects was found between NO output and minute ventilation in both breathing methods only for unloaded exercise. Data indicate that nasal airways have a large contribution, at least 50% of total NO output in the exhaled air during nasal breathing, but this nasal NO may have no further modulation on respiratory function during submaximal exercise by healthy humans.

This study was designed to examine the optimal pedaling rate for pedaling exercise at a given work intensity for cyclists. Six college-aged cyclists each performed six sessions of heavy pedaling exercise at individually selected work rates based on their aerobic capacity. The optimal pedaling rate was evaluated on the basis of minimal neuromuscular fatigue as evidenced by the integrated electromyogram (iEMG) slope defined by the changes in iEMG as a function of time. The means of the iEMG slope demonstrated a quadratic curve versus pedaling rate. The mean values at 80 rpm (0.53 (SD 0.20) μV.min -1 ) and 90 rpm (0.67 (SD 0.23) μL.min -1 ) were significantly smaller than those values at any other pedaling rate. On the other hand, the mean value of oxygen uptake (VO 2 ) expressed as a percent of the subject's maximal VO 2 (% VO 2max ) at each pedaling rate also showed a quadratic curve with minimal values at about 60 or 70 rpm. VO 2 at 70 rpm (84.0 (SD 5.0) % VO 2max ) was significantly smaller than those values at 80 rpm (86.3 (SD 3.5) % VO 2max ), 90 rpm (87.4 (SD 3.8) % VO 2max ), and 100 rpm (90.1 (SD 3.8)% VO 2max ). These data strongly suggest that the optimal pedaling rate estimated from neuromuscular fatigue in working muscles is not coincident with the pedaling rate at which the smallest VO 2 was obtained, but with the preferred pedaling rate of the subjects. Our findings also suggest that the reason that cyclists prefer a higher pedaling rate is closely related to the development of neuromuscular fatigue in the working muscles.

Ventilatory responses at the onset of passive and active exercise with different amount of exercising muscle mass were studied in 10 healthy male subjects. Four exercise tests were performed for each subject with appropriate intervals on the same day, i.e., two voluntary exercises of one leg or both legs and two passive exercises of one leg or both legs. Inspiratory minute volume (VI), end-tidal CO2 and O2 partial pressures (PETCO2, PETO2) were measured breath-by-breath using a hot-wire flowmeter, infrared CO2 analyzer, and a rapid O2 analyzer. Average values of VI were obtained from 5 breaths at rest preceding exercise and the first and second breaths after the onset of exercise. The ventilatory response to exercise was calculated as the difference (delta) between the mean of exercise VI and mean of resting VI. In this study, the PETCO2 decreased by about 0.5 Torr in four exercise tests, though the decrement of PETCO2 was not statistically significant. The average values and standard deviation of delta VI were 4.22 +/- 1.63 l/min for the one leg and 6.46 +/- 1.80 l/min for the two legs in the active exercise, and were 2.46 +/- 1.12 l/min for the one leg and 3.44 +/- 1.55 l/min for the two legs in the passive exercise, respectively. These results suggest that in awake conditions, the ventilatory response at the onset of passive or active exercise does not increase additively with the increasing amount of muscle mass being exercised.

Changes in the time courses of VO2 during constant-load exercise were examined in connection with other cardiorespiratory and blood chemical parameters. Eleven healthy male subjects performed a ramp exercise and three to six constant-load exercises at varying degrees of load using an electro-braked bicycle ergometer. Heart rate, ventilation, and gas exchange were measured during both types of exercise, and chemical parameters of the subject's blood (blood gas, pH, lactate, and electrolytes) were determined during two intensities of constant-load exercise. The time courses of cardiorespiratory and blood chemical data 3 min after the onset of constant-load exercise were fitted by linear regressions to see whether these parameters had reached the steady state or not. Heart rate increased significantly at a lower intensity of constant-load exercise than VE, VO2, and VCO2. While the increase in VCO2 was slower than that of VO2, a definite difference in time courses was not found between VE and VO2. The time courses of changes in blood gas, pH, bicarbonate, and lactate were not correlated with those of VO2. However, changes in blood potassium concentration were closely correlated with those of VO2 in terms of time courses and magnitude. This suggests the possibility that blood potassium may play an important role in the control of VO2 time course during constant-load exercise.

Blood flow in the right and left forearms was determined by venous occlusion plethysmography in ten healthy male subjects before and after training with a hand ergometer. The subjects in group A and B were trained using work loads of 1/3 and 1/2, respectively, of maximum grip strength 6 days/week for 6 weeks. It was found that the blood flow in the left (untrained or contralateral) forearm during exhaustive training of the right hand increased gradually with increasing training periods, and that after 6 weeks of training, grip strength, endurance and peak blood flow of the forearm increased significantly not only in the trained forearm, but also in the untrained forearm. From these results, it is suggested that the increase of blood flow in the contralateral limb after training may, at least in part, be related to the cross transfer effect of muscular endurance.

Calf and thigh blood flows in both of right and left legs were measured simultaneously after isometric contraction of the right thigh muscle. Isometric contraction was performed at a force of about 50% of maximal voluntary contraction for 15 sec. The thigh blood flow of the right leg increased immediately after voluntary contraction in all subjects, while the calf blood flow of right leg decreased conversely in spite of exercised ipsilateral leg.