About

Stan M. Yamashiro is a Professor of Biomedical Engineering and Electrical and Computer Engineering at the University of Southern California. He holds a doctoral degree in Electrical Engineering from USC, obtained in 1970, and has been a faculty member at USC since 1974, progressing from Assistant Professor to his current professorship. His teaching areas include cardiovascular and pulmonary physiology, instrumentation, and signal processing. His research has encompassed a wide range of topics including bio-instrumentation, medical electronics, respiratory physiology, magnetocardiography, laser instrumentation, and gas exchange enhancement. Currently, his research focuses on developing mathematical models related to the training and use of Extracorporeal Membrane Oxygenators (ECMO). He has contributed to understanding respiratory control during exercise through optimal control models, exploring the prediction of breathing patterns, and developing numerical procedures based on the calculus of variations to facilitate the exploration of optimization hypotheses. Additionally, his work in magnetocardiography involves studying the cardiac conduction system and atrial repolarization, utilizing high spatial correlation data and geostatistical prediction methods to improve the interpretation of cardiac signals during rest and exercise.

Research topics

• Medicine
• Anesthesia
• Cardiology
• Physics
• Internal medicine
• Mechanics
• Biology
• Thermodynamics
• Chemistry
• Animal science

Selected publications

• Quantifying ventilatory control with 3% CO2 inhalation during exercise

  Frontiers in Physiology · 2025-04-25

  articleOpen access

  Introduction: CO2 mediated ventilation is mainly controlled by two homeostatic mechanisms. The central chemoreceptors are slower mechanisms that focus on blood pH sensing in the brain stem while the peripheral chemoreceptors are quicker to respond and reside in the carotid bodies. Quantification of these mechanisms in humans remain debated. Objective: To quantify the impact that the central and peripheral chemoreceptors have on ventilation in response to changes in PETCO2 during exercise with normoxic breathing and 3% CO2 inhalation. Method: Six healthy males participated in a 5-stage bike protocol with and without 3% CO2 inhalation. We analyzed the time series data of their breath-by-breath PETCO2 and ventilation and generated a one input-one output model via the Laguerre expansion technique (LET) to construct the gain function and quantify the low (0.002-0.029 Hz) and high (0.03-0.15 Hz) frequency components using the weighted gain averages (WGA) as estimators of central and peripheral chemoreflex mechanisms respectively. Results: 3% CO2 inhalation caused a significant increase the high frequency WGAs at rest and in all levels of exercise except heavy exercise. The low frequency WGAs, however, only maintain significance during rest and the baseline session of exercise. Conclusion: Changes in WGA can be used as quantitative estimates of central and peripheral chemoreflexes. 3% CO2 activates both reflexes and is more apparent in the higher frequency WGAs during exercise due to the oxygen dependent mechanisms effects of exercise.

  PublisherOA PDFDOI

• Influence of aging and perception tasks on EEG during step-up/down movement exercise

  Gazzetta Medica Italiana Archivio per le Scienze Mediche · 2024-02-01

  articleOpen accessSenior author

  BACKGROUND: This study aimed to examine whether the electroencephalogram (EEG) signals during step-up/down movement exercise could be amplified by aging and visual perception tasks (VPT).METHODS: Ten males in 20s, 10 males in 40s, and 10 males in 70s carried out step-up/down movement exercise for 5 min with and without VPT. EEG during step-up/down movement exercise was measured using a wireless electroencephalograph (EMOTIV EEG headset). We analyzed the averaged power spectral density (PSD) for all electrodes with time frequency analysis, and a phase locking index (PLI) with phase synchronization quantification. Statistical comparisons were made using two-way ANOVA.RESULTS: PSD magnitude in three waves (theta, alpha, beta) for 40s and 70s were higher than 20s (P<0.05). Moreover, PSD magnitude increased with VPT in alpha and beta waves (P<0.05). PLI of theta wave in the 20s and 70s increased with VPT (P<0.05). PLI of alpha wave for 70s was higher than 20s and 40s (P<0.05). In PLI of the beta wave, 70s without VPT was higher than 20s and 40s without VPT (P<0.05). 40s with VPT was lower than 20s and 70s with VPT (P<0.05).CONCLUSIONS: EEG signals during step-up/down movement exercise increased with aging and was enhanced by VPT. Additionally, the phase pattern may help explain the differences in cognitive functions for VPT between age groups.

  PublisherDOI

• Effect Of 3% Co2 Inhalation On Vo2 And Vco2 Kinetics During Heavy Intensity Exercise

  Medicine & Science in Sports & Exercise · 2024-09-16

  articleSenior author

  Hypercapnic gas (HC) inhalation increases ventilation (VE) and decreases the respiratory exchange ratio during constant work-rate exercise (CWE) at heavy intensity. Hypoxia (HP) increases the time constant (τ) of oxygen uptake (VO2) in phase II during CWE at heavy intensity. Thus, it was hypothesized that HC inhalation alters VO2 and carbon dioxide output (VCO2) kinetics during CWE at heavy intensity. PURPOSE: This study tested the hypothesis that HC inhalation altered τVO2 and τVCO2 during CWE at heavy intensity. METHODS: Seven healthy males (23 ± 2 yrs) carried out the incremental maximum exercise tests while breathing; 1) ambient air (Air); 2) HC (21% O2, 3% CO2, N2 = balance); or 3) HP (16% O2, N2 = balance). Each subject performed CWE at 80%VO2max intensity for 6 min on three occasions. Subjects breathed Air, HC, or HP from 10 min before the start of exercise until the end of the exercise. τVO2, τVCO2, and τVE in phase II were estimated with a nonlinear least-squares fitting procedure. Statistical analysis was performed by one-way ANOVA with a post hoc test. RESULTS: τVO2 for HP was significantly higher than for Air (28.5 ± 5.6 vs. 21.7 ± 4.1 sec, p < 0.05), while τVO2 for HC (26.2 ± 5.9 sec) was not significantly different from Air and HP. The amplitude of VCO2 for HC was significantly less than for Air and HP (2222 ± 284 vs. 2919 ± 334 vs. 2872 ± 410 ml/min, p < 0.05), but τVCO2 for HC was not significantly different from Air and HP (44.2 ± 5.6 vs. 45.8 ± 17.5 vs. 40.5 ± 8.5 sec). The baseline of VE for HC was significantly higher than for Air and HP (16.9 ± 2.4 vs. 11.6 ± 1.8 vs. 11.0 ± 2.0 L/min, p < 0.05), but τVE for HC was not significantly different from Air and HP (53.5 ± 13.5 vs. 50.5 ± 10.2 vs. 50.2 ± 10.4 sec). CONCLUSIONS: 3% CO2 gas inhalation led to increased VE at rest and decreased VCO2 during CWE at heavy intensity but had no impact on both VO2 and VCO2 rising dynamics in phase II. This work was supported in part by JSPS KAKENHI Grant Number 21K11463. This work was supported in part by JSPS KAKENHI Grant Number 21K11463

  PublisherDOI

• Infant periodic breathing and apneic threshold

  Physiological Reports · 2024-01-01 · 1 citations

  articleOpen access1st authorCorresponding

  A mathematical model was proposed to predict the role played by apneic threshold in periodic breathing in preterm infants. Prior models have mainly applied linear control theory which predicted instability but could not explain sustained periodic breathing. Apneic threshold to CO2 which has been postulated to play a major role in infant periodic breathing is a nonlinear effect and cannot be described by linear theory. Another previously unexplored nonlinear factor affecting instability is brain vascular volume change with CO2 which affects time delay to chemoreceptors. The current model explored the influences of apneic threshold, central and peripheral chemoreceptor gains, cardiac output, lung volume, and circulatory time delay on periodic breathing. Apneic threshold was found to play a major role in ventilatory responses to spontaneous sighs. Sighs led to apneic pauses followed by periods of periodic breathing with peripheral chemoreceptor CO2 gain, cardiac output, and lung volume were at reported normal levels. Apneic threshold when exceeded was observed to cause an asymmetry in the periodic breathing cycling and an increased periodic breathing frequency. Sighs in infants occur frequently enough to lead to repeated stimulation within the epoch duration of periodic breathing for a single sigh. Multiple sighs may then play a major role in promoting continuous periodic breathing in infants. Peripheral chemoreceptor gain estimated using endogenous CO2 led to validated predicted periodic breathing cycle duration as a function of age. Brain vascular volume increase with CO2 contributes to periodic breathing in very young (1-2 day old) preterm infants.

  PublisherOA PDFDOI

• Modeling Long-Term Facilitation of Respiration During Interval Exercise in Humans

  Annals of Biomedical Engineering · 2023-09-26 · 2 citations

  articleOpen access1st authorCorresponding

  Abstract Long-term facilitation (LTF) of respiration has been mainly initiated by intermittent hypoxia and resultant chemoreceptor stimulation in humans. Comparable levels of chemoreceptor stimulation can occur in combined exercise and carbon dioxide (CO 2 ) inhalation and lead to LTF. This possibility was supported by data collected during combined interval exercise and 3% inhaled CO 2 in seven normal subjects. These data were further analyzed based on the dynamics involved using mathematical models in this study. Previously estimated peripheral chemoreceptor sensitivity during light exercise (40 W) with air or 3% inhaled CO 2 approximately doubled resting sensitivity. Ventilation after a delay increased by 17.0 ± 2.48 L/min ( p &lt; 0.001) during recovery following 45% maximal oxygen uptake ( $$V_{{{\text{O}}_{2} \max }}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>V</mml:mi> <mml:mrow> <mml:msub> <mml:mtext>O</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> <mml:mo>max</mml:mo> </mml:mrow> </mml:msub> </mml:math> ) exercise consistent with LTF which exceeded what can be achieved with intermittent hypoxia. Model fitting of the dynamic responses was used to separate neural from chemoreceptor-mediated CO 2 responses. Exercise of 45% $$V_{{{\text{O}}_{2} \max }}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>V</mml:mi> <mml:mrow> <mml:msub> <mml:mtext>O</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> <mml:mo>max</mml:mo> </mml:mrow> </mml:msub> </mml:math> was followed by ventilation augmentation following initial recovery. Augmentation of LTF developed slowly according to second-order dynamics in accordance with plasticity involving a balance between self-excitatory and self-inhibitory neuronal pools.

  PublisherOA PDFDOI

• Effect of 3% CO2 inhalation on pulmonary gas exchange kinetics during constant work-rate exercise

  Gazzetta Medica Italiana Archivio per le Scienze Mediche · 2022-10-01

  article

  BACKGROUND: The present study examined whether 3% carbon dioxide (CO2) gas inhalation alters time constants for the primary component of oxygen uptake (τV̇O2) and CO2 output (τV̇CO2) during constant-work-rate exercise (CWE) at both light and heavy intensities.METHODS: Seven males performed 6 min light intensity (45% V̇O2 max) exercise and 6 min heavy intensity (80% V̇O2 max) exercise while inhaling normal air or an enriched CO2 gas (3% CO2, 21% O2, balance N2). τV̇O2 and τV̇CO2 were analyzed with nonlinear least-squares fitting procedure from breath by breath data.RESULTS: τV̇O2 and τV̇CO2 in phase-II were reduced by 3% CO2 during CWE at both light and heavy intensities (P<0.05). In heavy intensity exercise, τV̇O2 in phase-III did not differ between 3% CO2 and Air. On the other hand, the V̇CO2 slow component in phase-III did not appear in four of seven subjects for both 3% CO2 and air conditions.CONCLUSIONS: These findings suggest that 3% CO2 led to decreased τV̇O2 and τV̇CO2 in phase-II during CWE in both light and heavy intensities.

  PublisherDOI

• Adapting a Human Physiology Teaching Laboratory to the At-Home Education Setting

  Biomedical Engineering Education · 2021-07-21 · 1 citations

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Effect of 3% CO2 inhalation on respiratory exchange ratio and cardiac output during constant work-rate exercise

  The Journal of Sports Medicine and Physical Fitness · 2021 · 3 citations

  Senior authorCorresponding
  • Medicine
  • Cardiology
  • Anesthesia

  BACKGROUND: The aim of this study was to examine whether the decrease in respiratory exchange ratio (RER) during constant work-rate exercise (CWE) with 3% carbon dioxide (CO<inf>2</inf>) inhalation could be caused by the combination of the decrease in CO<inf>2</inf> output (V̇CO<inf>2</inf>) and the increase in oxygen uptake (V̇O<inf>2</inf>). In addition, we investigated the effect of 3% CO<inf>2</inf> inhalation on cardiac output (Q̇) during CWE. METHODS: Seven males (V̇O<inf>2max</inf>: 44.1±6.4 mL/min/kg) carried out transitions from low-load cycling (baseline; 40w) to light intensity exercise (45% V̇O<inf>2 max</inf>; 89.3±12.5 W) and heavy intensity exercise (80% V̇O<inf>2max</inf>; 186.5±20.2 W) while inhaling normal air (Air) or an enriched CO<inf>2</inf> gas (3% CO<inf>2</inf>, 21% O<inf>2</inf>, balance N<inf>2</inf>). Each exercise session was 6 min, and respiratory responses by Douglas bag technique and cardiac responses by thoracic bio-impedance method were measured during the experiment. RESULTS: Ventilation for 3% CO<inf>2</inf> was higher than for air through the experiment (P<0.05). Steady and non-steady state RER and V̇CO<inf>2</inf> for 3% CO<inf>2</inf> were less than for air in both light and heavy intensities (P<0.05), but V̇O<inf>2</inf> and Q̇ did not differ between the two conditions. CONCLUSIONS: 3% CO<inf>2</inf> inhalation induced the decrease in RER during CWE at light and heavy intensities, which was due to the decrease in V̇CO<inf>2</inf>. The promoted ventilation with 3% CO<inf>2</inf> did not lead to the increase in V̇O<inf>2</inf>. Moreover, 3% CO<inf>2</inf> inhalation did not affect Q̇ during CWE at light and heavy intensities.

  PublisherDOI

• Modeling cerebral blood flow and ventilation instability due to CO₂

  Journal of Applied Physiology · 2021 · 5 citations

  1st authorCorresponding
  • Anesthesia
  • Cardiology
  • Medicine

  .

  PublisherDOI

• Altered chemosensitivity to CO ₂ during exercise

  Physiological Reports · 2021 · 11 citations

  1st authorCorresponding
  • Medicine
  • Anesthesia
  • Internal medicine

  increased in exercise with the peripheral chemoreceptors playing a dominant role. This separation of central and peripheral contributions was not previously reported. This chemoreceptor stimulation can lead to augmented ventilation consistent with LTF.

  PublisherDOI

Recent grants

• NIH Grant R01HL016390

  NIH · $1.3M · 1994

Frequent coauthors

• Fred S. Grodins

  15 shared

• Takahide Kato

  12 shared

• J. R. Romaniuk

  Case Western Reserve University

  6 shared

• S.D. Ghazanshahi

  California State University, Fullerton

  5 shared

• Takaaki Matsumoto

  Kitasato University

  5 shared

• James B. Bassingthwaighte

  University of Washington

  4 shared

• Taichi Hayasaka

  National Institute of Technology, Toyota College

  3 shared

• Yuki Matsuda

  Jikei University School of Medicine

  3 shared

Education

• Ph.D., Biomedical Engineering

  University of Southern California

  1990

• M.S., Biomedical Engineering

  University of Southern California

  1986

• B.S., Mechanical Engineering

  University of California, Los Angeles

  1983