Dempsey, Jerome A.

Abstract The sections in this article are: Regulation of the Upper Airway During Exercise Anatomy and Physiology of the Upper Airway Contractile Properties and Endurance of Upper Airway Muscles Changes in Upper Airway Flow Resistance During Exercise Upper Airway Muscle Activities during Exercise Oronasal Distribution of Respiratory Airflow Effects of Exercise on Passive Respiratory Mechanics Elastic Properties Total Lung Capacity Expiratory Flow Rates, Vital Capacity, and Residual Volume Breathing Pattern During Exercise Mechanical Breathing Pattern Methods of Assessment of Respiratory Muscle Contraction Pattern of Respiratory Muscle Contraction Influence of Sensory Feedback on Breathing Pattern Influence of Respiratory Mechanics on Breathing Pattern Influence of Duration of Exercise on Breathing Pattern Influence of Mode of Exercise on Breathing Pattern Breathing Pattern during Recovery from Exercise Physiological Implications of Exercise Breathing Pattern Importance of Respiratory Load in Regulation of Exercise Hyperpnea Helium‐Oxygen Unloading Unloading with Pressure Assist Conclusion Locomotor‐Respiration Interdependence Entrainment—the Most Obvious Locomotor‐Respiratory Interaction How Does Entrainment Effect Ventilation? Is there Stronger Evidence to Support a Significant Biomechanical Effect of Locomotion on Respiration in Dogs? Are Biomechanical Effects Important in Entrainment in Humans? Locomotory: Respiratory Interactions, Independent of Entrainment Conclusion Respiratory Muscle Perfusion and Energetics Oxygen Cost of Hyperpnea Respiratory Muscle Blood Flow Exercise‐Induced Respiratory Muscle Fatigue Respiratory System Design Assessment of Diaphragm Fatigue in Animal Models Glycogen Depletion Fiber Type Recruitment Definition of Fatigue Task Failure vs. Objective Assessment of Fatigue Contractile Changes with Fatigue Predicting Respiratory Muscle Fatigue During Exercise Application of Resting Tests to Respiratory Muscle Function During Exercise Assessment of Respiratory Muscle Fatigue in Humans Volitional Tests Volitional Tests Applied to Exercise Nonvolitional Tests Bilateral Phrenic Nerve Stimulation ( BPNS ) Characteristics of Diaphragm Fatigue High‐ vs. Low‐Frequency Fatigue Sites and Mechanisms of Respiratory Muscle Fatigue Central Fatigue in Humans Neurotransmission Fatigue Bilateral Phrenic Nerve Stimulation Applied to Exercise Short‐Term Exercise Endurance Exercise Factors Contributing to the Decline in Twitch Pdi Following Exercise Role of Diaphragmatic Force Output in Fatigue Consequences of Exercise‐Induced Diaphragmatic Fatigue Fatigue vs. Task Failure Does Training of Respiratory Muscles Affect Exercise Performance? Altered Respiratory Muscle Recruitment with Fatigue Physical Training Effects on Respiratory Muscles Respiratory Muscle Morphology and Contractile Properties Whole‐Body Training: Effects on Rodent Respiratory Muscles Whole‐Body Exercise: Effects on Human Respiratory Muscle Performance Specific Respiratory Muscle Training Respiratory Sensation During Exertion Mechanisms of Respiratory Sensations during Exercise Methods of Assessing Respiratory Sensations Respiratory Movements An Urge to Breathe A Sense of Respiratory Effort Respiratory Sensation as a Respiratory Controller during Exercise Respiratory Sensation as a Limiting Factor during Exercise Conclusions Summary—Pulmonary System Limitations and Their Effects on Exercise Performance Absence of Pulmonary System Limitations in the Normally Fit Contrasting Adaptabilities: Demand vs. Capacity Alveolar Capillary Diffusion Surface of the Lung Ventilatory Limitations/Constraints Inadequate Alveolar Ventilation and Limitations Endurance Exercise Performance Special Circumstances Favoring Pulmonary Limitations to Exercise Performance in Health Hypoxia of High Altitudes Aging Effects on Pulmonary Limitations

We assessed the cardiovascular responses to systemic normocapnic hypoxia in five normal subjects, five double lung transplant patients with lung denervation and intact hearts, and five patients with denervated hearts. Progressive normocapnic hypoxia was induced over 10–15 min and maintained for 2–3 min each at 90, 87, 84, and 80% arterial O2 saturation (SaO2). Normal subjects showed the most pronounced mean increase in heart rate (dHR/dSaO2 = 0.86 +/- 0.13 beat/min per 1% SaO2). Three lung-denervated subjects had normal tachycardiac responses (1.6, 0.9, and 0.69 beats/min per 1%), whereas the other two had distinctly lower responses (0.34 and 0.39 beat/min per 1%). Most of the lung-denervated subjects also showed a significant tachycardia with even mild hypoxia; none showed a bradycardiac response to any level of hypoxia. In the heart-denervated group, hypoxic tachycardia was significantly lower than normal (0.29 +/- 0.13 beat/min per 1%). We conclude that vagal feedback from the lungs is not required for the normal chronotropic response to hypoxia in humans; however, this mechanism may contribute significantly to the marked variability in hypoxic-induced tachycardia found among human subjects. These data in humans contrast with the progressive bradycardiac response to hypoxia reported in vagally denervated (or nonhyperpneic) dogs and cats.