Learning to breathe? Feedforward regulation of the inspiratory motor drive

Respiratory psychophysiology and COVID-19: A research agenda

After multiple waves of the COVID-19 pandemic, it has become clear that the impact of SARS-CoV-2 will carry on for years to come. Acutely infected patients show a broad range of disease severity, depending on virus variant, vaccination status, age and the presence of underlying medical and physical conditions, including obesity. Additionally, a large number of patients who have been infected with the virus present with post-COVID syndrome. In September 2020, the International Society for the Advancement of Respiratory Psychophysiology organized a virtual interest meeting on 'Respiratory research in the age of COVID-19', which aimed to discuss how research in respiratory psychophysiology could contribute to a better understanding of psychophysiological interactions in COVID-19. In the resulting current paper, we propose an interdisciplinary research agenda discussing selected research questions on acute and long-term neurobiological, physiological and psychological outcomes and mechanisms related to respiration and the airways in COVID-19, as well as research questions on comorbidity and potential treatment options, such as physical rehabilitation.

Ventilatory neural drive in chronically hypercapnic patients with COPD: effects of sleep and nocturnal noninvasive ventilation

Sleep brings major challenges for the control of ventilation in humans, particularly the regulation of arterial carbon dioxide pressure (P _aCO2 ). In patients with COPD, chronic hypercapnia is associated with increased mortality. Therefore, nocturnal high-level noninvasive positive-pressure ventilation (NIV) is recommended with the intention to reduce P _aCO2 down to normocapnia. However, the long-term physiological consequences of P _aCO2 "correction" on the mechanics of breathing, gas exchange efficiency and resulting symptoms (i.e. dyspnoea) remain poorly understood. Investigating the influence of sleep on the neural drive to breathe and its translation to the mechanical act of breathing is of foremost relevance to create a solid rationale for the use of nocturnal NIV. In this review, we critically discuss the mechanisms by which sleep influences ventilatory neural drive and mechanical consequences in healthy subjects and hypercapnic patients with advanced COPD. We then discuss the available literature on the effects of nocturnal NIV on ventilatory neural drive and respiratory mechanics, highlighting open avenues for further investigation.

How does homeostasis happen? Integrative physiological, systems biological, and evolutionary perspectives

Homeostasis is a founding principle of integrative physiology. In current systems biology, however, homeostasis seems almost invisible. Is homeostasis a key goal driving body processes, or is it an emergent mechanistic fact? In this perspective piece, I propose that the integrative physiological and systems biological viewpoints about homeostasis reflect different epistemologies, different philosophies of knowledge. Integrative physiology is concept driven. It attempts to explain biological phenomena by continuous formation of theories that experimentation or observation can test. In integrative physiology, "function" refers to goals or purposes. Systems biology is data driven. It explains biological phenomena in terms of "omics"-i.e., genomics, gene expression, epigenomics, proteomics, and metabolomics-it depicts the data in computer models of complex cascades or networks, and it makes predictions from the models. In systems biology, "function" refers more to mechanisms than to goals. The integrative physiologist emphasizes homeostasis of internal variables such as Pco₂ and blood pressure. The systems biologist views these emphases as teleological and unparsimonious in that the "regulated variable" (e.g., arterial Pco₂ and blood pressure) and the "regulator" (e.g., the "carbistat" and "barostat") are unobservable constructs. The integrative physiologist views systems biological explanations as not really explanations but descriptions that cannot account for phenomena we humans believe exist, although they cannot be observed directly, such as feelings and, ultimately, the conscious mind. This essay reviews the history of the two epistemologies, emphasizing autonomic neuroscience. I predict rapprochement of integrative physiology with systems biology. The resolution will avoid teleological purposiveness, transcend pure mechanism, and incorporate adaptiveness in evolution, i.e., "Darwinian medicine."

Interoceptive cues predicting exteroceptive events

The growing body of research on interoceptive conditioning has predominantly focused on associative learning paradigms that investigated the formation of intero-interoceptive or extero-interoceptive associations. Yet, little research has explored whether interoceptive sensations can enter an intero-exteroceptive association. Therefore, in an interoceptive conditioning paradigm, healthy participants experienced a respiratory resistance for 8s, causing mild dyspnea (interoceptive conditioned stimulus, CS), that was either paired to an aversive electrocutaneous stimulus (unconditioned stimulus, US) (experimental condition, n=25), or presented in an unpaired fashion (control condition, n=25) during the acquisition phase. In a subsequent extinction phase, the US was not delivered anymore. US-expectancy, skin conductance responses (SCR), and eyeblink startle EMG were used as indices of associative learning. During acquisition, we observed stronger US expectancies during the CS as compared to the intertrial interval in the experimental group, but not in the control group, nor during extinction. In line, only in the experimental group did skin conductance responses to the CS increase across acquisition. The pattern of the eyeblink startle data did not reach statistical significance. In sum, interoceptive sensations can become associated with exteroceptive events.

Respiratory Changes in Response to Cognitive Load: A Systematic Review

When people focus attention or carry out a demanding task, their breathing changes. But which parameters of respiration vary exactly and can respiration reliably be used as an index of cognitive load? These questions are addressed in the present systematic review of empirical studies investigating respiratory behavior in response to cognitive load. Most reviewed studies were restricted to time and volume parameters while less established, yet meaningful parameters such as respiratory variability have rarely been investigated. The available results show that respiratory behavior generally reflects cognitive processing and that distinct parameters differ in sensitivity: While mentally demanding episodes are clearly marked by faster breathing and higher minute ventilation, respiratory amplitude appears to remain rather stable. The present findings further indicate that total variability in respiratory rate is not systematically affected by cognitive load whereas the correlated fraction decreases. In addition, we found that cognitive load may lead to overbreathing as indicated by decreased end-tidal CO₂ but is also accompanied by elevated oxygen consumption and CO₂ release. However, additional research is needed to validate the findings on respiratory variability and gas exchange measures. We conclude by outlining recommendations for future research to increase the current understanding of respiration under cognitive load.