Basic principles of control of breathing

The metabolic demands of the body, including consumption of oxygen and removal of carbon dioxide, vary widely in health and disease. Ventilation must adjust to meet these demands and accommodate volitional and behavioral activities. Control of breathing depends on a complex and intricate feedback control system that integrates these automatic and volitional aspects of ventilation. Sensors, including chemoreceptors and lung volume receptors, relay information to a central controller located primarily in the medulla. The central controller integrates this information and determines the level of activation of the effectors (the respiratory motoneurons and muscles), which affects ventilation and gas exchange. Inputs from suprapontine structures, including the cerebral cortex, are also important in integrating volitional aspects of breathing into the control system.     

Effects of assisted mechanical ventilation on control of breathing

Summary During spontaneous breathing, the respiratory muscle pressure (Pmus) waveform is determined by a complex system consisting of a motor arm, a control center, and various feedback mechanisms that convey information to the control center. During assisted mechanical ventilation, the pressure delivered by the ventilator (Paw) is incorporated into the system and may alter the Pmus waveform, which in turn modifies the function of the ventilator. Thus, the response of Pmus to Paw and the response of Paw to Pmus constitute the two components of patient-ventilator interaction as well as of control of breathing during assisted mechanical ventilation. The response of Paw to Pmus depends on: 1) the mode of ventilatory support; 2) the mechanics of the respiratory system, and 3) the characteristics of the Pmus waveform. On the other hand the response of Pmus to Paw is mediated through four feedback systems: 1) mechanical; 2) chemical; 3) reflex, and 4) behavioral. It follows that the system that controls the act of breathing may be considerably modified by mechanical ventilation. The physician dealing with a mechanically ventilated patient should take into account the interaction between the respiratory effort and the function of the ventilator and be aware that the ventilatory output may or may not reflect the various aspects of control of breathing. Received: 13 July 1998 Accepted: 26 October 1998     

Effects of assisted mechanical ventilation on control of breathing

During spontaneous breathing, the respiratory muscle pressure (Pmus) waveform is determined by a complex system consisting of a motor arm, a control center, and various feedback mechanisms that convey information to the control center. During assisted mechanical ventilation, the pressure delivered by the ventilator (Paw) is incorporated into the system and may alter the Pmus waveform, which in turn modifies the function of the ventilator. Thus, the response of Pmus to Paw and the response of Paw to Pmus constitute the two components of patient-ventilator interaction as well as of control of breathing during assisted mechanical ventilation. The response of Paw to Pmus depends on: 1) the mode of ventilatory support; 2) the mechanics of the respiratory system, and 3) the characteristics of the Pmus waveform. On the other hand the response of Pmus to Paw is mediated through four feedback systems: 1) mechanical; 2) chemical; 3) reflex, and 4) behavioral. It follows that the system that controls the act of breathing may be considerably modified by mechanical ventilation. The physician dealing with a mechanically ventilated patient should take into account the interaction between the respiratory effort and the function of the ventilator and be aware that the ventilatory output may or may not reflect the various aspects of control of breathing.     

Nutritional control of aging

For more than 60 years the only dietary manipulation known to retard aging was caloric restriction, in which a variety of species respond to a reduction in energy intake by demonstrating extended median and maximum life span. More recently, two alternative dietary manipulations have been reported to also extend survival in rodents. Reducing the tryptophan content of the diet extends maximum life span, while lowering the content of sulfhydryl-containing amino acids in the diet by removing cysteine and restricting the concentration of methionine has been shown to extend all parameters of survival, and to maintain blood levels of the important anti-oxidant glutathione. To control for the possible reduction in energy intake in methionine-restricted rats, animals were offered the control diet in the quantity consumed by rats fed the low methionine diet. Such pair-fed animals experienced life span extension, indicating that methionine restriction-related life span extension is not a consequence of reduced energy intake. By feeding the methionine restricted diet to a variety of rat strains we determined that lowered methionine in the diet prolonged life in strains that have differing pathological profiles in aging, indicating that this intervention acts by altering the rate of aging, not by correcting some single defect in a single strain.     

Effect of inflammation on the aging microcirculation: impact on skeletal muscle blood flow control

To meet the metabolic demands of skeletal muscle, the vasculature supplying these vascular beds has to be connected to respond in a coordinated uniform manner, thus providing the necessary oxygen and nutrients during increased activity. The skeletal muscle microcirculation is the major resistance network controlling vascular blood supply and it is the integrity of the endothelium lining the blood vessels that is paramount in facilitating this action. Aging is a major risk factor for cardiovascular disease and is associated with significant increases in inflammatory agents that negatively impact the vasculature. Several inflammatory agents such as cytokines (tumor necrosis factor-a), advanced glycation products (AGEs), and matrix metalloproteinases (MMPs) along with storage cells for inflammatory mediators (mast cells) are associated with a chronic "low-grade inflammation" state that has been observed over the course of the aging process. Current research suggests that these age-related increases in inflammatory agents can disrupt the microvascular endothelium and thus impair blood flow. This impairment could exacerbate the common age-related disease states such as hypertension, diabetes, congestive heart failure, and sarcopenia, leading to increased mortality and morbidity.     

应重视对睡眠呼吸障碍的诊治

对睡眠呼吸障碍诊治的研究，国外迄今已有３０余年，我国亦逾１０年，随着诊治技术和临床研究的不断深入，对此类疾患的认识已有较大的提高，诊治工作也已取得较大的进展。但由于我国地广人多，这类疾患的发病率高，合并症多，病死率高，从全国来说，诊治工作起步较晚，仍...     

Effect of posture on ventilation and breathing pattern during room air breathing at rest

We measured minute ventilation (VE), tidal volume (VT), mean inspiratory flow (VT/TI), and occlusion pressure (P.1) in 10 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(l)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance [R(l)]. Highest values for VT, VE, VT/TI, P.1, and effective inspiratory impedance [P.1/(VT/Ti)] were observed in the supine posture. Values for P.1 and P.1/(VT/TI in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P.1 and P.1/(VT/TI) in recumbent postures were qualitatively similar to the decrease in Cdyn(l) and increase in R(l), there was no significant correlation between them, probably reflecting the complex relationship between P.1/(VT/TI) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration.     

Interaction of swallowing and control of breathing

Although it is well known that swallowing interacts with respiration, information about the relationship between respiration and swallowing is limited. In this paper we described the interaction between swallowing reflex and respiration. In experimental animals, reflex swallowing can be elicited readily by electrical stimulation of the superior laryngeal nerve, and the effects of depressants on this reflex can be assessed by changes in the latency of responses and the number of swallows elicited. The swallowing reflex is independent of the background respiratory activity and a decrease in PaO2 depresses the swallowing reflex, whereas changes in Paco2 have no effect. In human subjects, the swallowing reflex can be induced by injections of a small amount of water into the pharynx. Like the responses in animals, the responses in humans can be assessed by changes in the latency of responses and the number of swallows. Using this technique, we evaluated the effects of nasal CPAP on the swallowing reflex. Our results showed that nasal CPAP remarkably depresses the swallowing reflex.     

睡眠呼吸障碍对慢性心力衰竭的影响

睡眠呼吸障碍在慢性心力衰竭中的发病率远高于普通人群，睡眠呼吸障碍对慢性心力衰竭的转归有相当重要的影响。正确认识两者的关系，并给予恰当的处理有着十分重要的意义。     

Effect of intranasal obstruction on breathing during sleep

While nasal mucosal stimulation in animals has been reported to produce central apneas and while nasal packing in humans is known to produce sleep-disordered breathing, it is controversial whether intranasal obstruction in humans produces predominantly central or obstructive apnea. To answer this question, we studied eight normal men by having them sleep in random order with their nose open or occluded with petrolatum gauze. Esophageal pressure was measured to detect respiratory effort, and standard techniques were used to monitor and score the stages of sleep. Intranasal occlusion increased both the number of apneas plus hypopneas per hour of sleep and the minutes of obstructive events per hour of sleep (p less than 0.05). The minutes of central events per hour of sleep also increased significantly but not to the degree that occurred with obstructive events. Nasal obstruction produced no immediate changes in pulmonary function. The subject with the highest resistance measured through the mouth with the pulse flow method had the most apneas following nasal occlusion. We conclude that intranasal obstruction produces predominantly obstructive apneas and hypopneas during sleep.     

Effect of posture on ventilation and breathing pattern during room air breathing at rest

We measured minute ventilation (V_E), tidal volume (V_T), mean inspiratory flow (V_T/T_I), and occlusion pressure (P_.1) in 10 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(l)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance [R(l)]. Highest values for V_T, V_E, V_T/T_I, P_.1, and effective inspiratory impedance [P_.1/(V_T/T_i)] were observed in the supine posture. Values for P_.1 and P_.1/(V_T/T_I in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P_.1 and P_.1/(V_T/T_I) in recumbent postures were qualitatively similar to the decrease in Cdyn(l) and increase in R(l), there was no significant correlation between them, probably reflecting the complex relationship between P_.1/(V_T/T_I) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration. An erratum to this article is available at .     

The control of breathing in clinical practice

The control of breathing results from a complex interaction involving the respiratory centers, which feed signals to a central control mechanism that, in turn, provides output to the effector muscles. In this review, we describe the individual elements of this system, and what is known about their function in man. We outline clinically relevant aspects of the integration of human ventilatory control system, and describe altered function in response to special circumstances, disorders, and medications. We emphasize the clinical relevance of this topic by employing case presentations of active patients from our practice.