The psychophysiology of the sigh: II: The sigh from the psychological perspective

Cervical spinal cord hemisection impacts sigh and the respiratory reset in male rats

Cervical spinal cord injury impacts ventilatory and non-ventilatory functions of the diaphragm muscle (DIAm) and contributes to clinical morbidity and mortality in the afflicted population. Periodically, integrated brainstem neural circuit activity drives the DIAm to generate a markedly augmented effort or sigh-which plays an important role in preventing atelectasis and thus maintaining lung function. Across species, the general pattern of DIAm efforts during a normal sigh is variable in amplitude and the extent of post-sigh "apnea" (i.e., the post-sigh inter-breath interval). This post-sigh inter-breath interval acts as a respiratory reset, following the interruption of regular respiratory rhythm by sigh. We examined the impact of upper cervical (C2 ) spinal cord hemisection (C2 SH) on the transdiaphragmatic pressure (Pdi ) generated during sighs and the post-sigh respiratory reset in rats. Sighs were identified in Pdi traces by their characteristic biphasic pattern. We found that C2 SH results in a reduction of Pdi during both eupnea and sighs, and a decrease in the immediate post-sigh breath interval. These results are consistent with partial removal of descending excitatory synaptic inputs to phrenic motor neurons that results from C2 SH. Following cervical spinal cord injury, a reduction in the amplitude of Pdi during sighs may compromise the maintenance of normal lung function.

Putting back respiration into respiratory sinus arrhythmia or high-frequency heart rate variability: Implications for interpretation, respiratory rhythmicity, and health

Research on respiratory sinus arrhythmia, or high-frequency heart rate variability (its frequency-domain equivalent), has been popular in psychology and the behavioral sciences for some time. It is typically interpreted as an indicator of cardiac vagal activity. However, as research has shown for decades, the respiratory pattern can influence the amplitude of these noninvasive measures substantially, without necessarily reflecting changes in tonic cardiac vagal activity. Although changes in respiration are systematically associated with experiential and behavioral states, this potential confound in the interpretation of RSA, or HF-HRV, is rarely considered. Interpretations of within-individual changes in these parameters are therefore only conclusive if undertaken relative to the breathing pattern. The interpretation of absolute levels of these parameters between individuals is additionally burdened with the problem of residual inspiratory cardiac vagal activity in humans. Furthermore, multiple demographic, anthropometric, life-style, health, and medication variables can act as relevant third variables that might explain associations of RSA or HF-HRV with experiential and behavioral variables. Because vagal activity measured by these parameters only represents the portion of cardiac vagal outflow that is modulated by the respiratory rhythm, alternative interpretations beyond cardiac vagal activity should be considered. Accumulating research shows that activity of multiple populations of neurons in the brain and the periphery, and with that organ activity and function, are modulated rhythmically by respiratory activity. Thus, observable health benefits ascribed to the cardiac vagal system through RSA or HF-HRV may actually reflect beneficial effects of respiratory modulation. Respiratory rhythmicity may ultimately provide the mechanism that integrates central, autonomic, and visceral activities.