The cerebral regulation of cardiovascular and respiratory functions

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

The role of air pollution and lung function in cognitive impairment

Air pollution has been associated with impaired lung and cognitive function, especially impairment in visuo-construction performance (VCP). In this article, we evaluate whether the effect of air pollution on VCP is mediated by lung function.

We used data from the SALIA cohort (baseline 1985–1994 and follow-up 2007–2010) including 587 women aged 55 years at baseline. Particulate matter (PM) and nitrogen dioxide (NO2) exposures at baseline were estimated via land-use regression models. Lung function was characterised by averages between baseline and follow-up. We used age- and height-controlled Global Lung Initiative (GLI) z-scores of forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and FEV1/FVC. VCP was assessed at follow-up with the CERAD-Plus neuropsychological test battery and causal mediation analysis was conducted.

An increase of one interquartile range in FEV1 and FVC was positively associated with VCP (β=0.18 (95% CI 0.02–0.34) and β=0.23 (95% CI 0.07–0.39), respectively). The proportion of the association between NO2 on VCP mediated by FEV1 was 6.2% and this was higher in never smokers (7.2%) and non-carriers of the APOE-ε4 allele (11.2%). However, none of the mediations were statistically significant.

In conclusion, air pollution associated VCP was partially mediated by lung function. Further studies on the mechanisms underlying this pathway are required to develop new strategies to prevent air pollution induced cognitive impairment.

Neuronal control of breathing: sex and stress hormones

There is a growing public awareness that hormones can have a significant impact on most biological systems, including the control of breathing. This review will focus on the actions of two broad classes of hormones on the neuronal control of breathing: sex hormones and stress hormones. The majority of these hormones are steroids; a striking feature is that both groups are derived from cholesterol. Stress hormones also include many peptides which are produced primarily within the paraventricular nucleus of the hypothalamus (PVN) and secreted into the brain or into the circulatory system. In this article we will first review and discuss the role of sex hormones in respiratory control throughout life, emphasizing how natural fluctuations in hormones are reflected in ventilatory metrics and how disruption of their endogenous cycle can predispose to respiratory disease. These effects may be mediated directly by sex hormone receptors or indirectly by neurotransmitter systems. Next, we will discuss the origins of hypothalamic stress hormones and their relationship with the respiratory control system. This relationship is 2-fold: (i) via direct anatomical connections to brainstem respiratory control centers, and (ii) via steroid hormones released from the adrenal gland in response to signals from the pituitary gland. Finally, the impact of stress on the development of neural circuits involved in breathing is evaluated in animal models, and the consequences of early stress on respiratory health and disease is discussed.

Heart Rate Variability, Homeostasis, and Brain Function

Measures of heart rate variability (HRV) are major indices of the sympathovagal balance in cardiovascular research. These measures are thought to reflect complex patterns of brain activation as well and HRV is now emerging as a descriptor thought to provide information on the nervous system organization of homeostatic responses in accordance with the situational requirements. Current models of integration equate HRV to the affective states as parallel outputs of the central autonomic network, with HRV reflecting its organization of affective, physiological, “cognitive,” and behavioral elements into a homeostatic response. Clinical application is in the study of patients with psychiatric disorders, traumatic brain injury, impaired emotion-specific processing, personality, and communication disorders. HRV responses to highly emotional sensory inputs have been identified in subjects in vegetative state and in healthy or brain injured subjects processing complex sensory stimuli. In this respect, HRV measurements can provide additional information on the brain functional setup in the severely brain damaged and would provide researchers with a suitable approach in the absence of conscious behavior or whenever complex experimental conditions and data collection are impracticable, as it is the case, for example, in intensive care units.

Sleeping like a baby--does gender influence infant arousability?

INTRODUCTION

Victims of the sudden infant death syndrome (SIDS) may have preexisting abnormalities in their arousal pathways, inhibiting the progression of subcortical activation (SCA) to full cortical arousal (CA). Approximately 60% of SIDS victims are male, and it has been suggested that male infants have delayed cortical maturation compared to females. We hypothesized that CA frequency would be lower and CA threshold would be higher in male infants during both active (AS) and quiet (QS) sleep.

METHODS

50 healthy term infants (21 male, 29 female) were studied with daytime polysomnography at 2-4 weeks and 2-3 months after birth. Arousal from sleep was induced using a pulsatile air-jet to the nostrils at increasing pressures.

RESULTS

At 2-4 weeks, arousability from AS was similar in males and females, however during QS, male infants required a lower stimulus to induce SCA and CA. This gender difference in arousal threshold was not observed at 2-3 months. CA frequencies were similar between genders during both sleep states at both ages, though overall, CA was more frequent in AS than in QS.

CONCLUSIONS

This study demonstrated that at 2-4 weeks, male infants were easier to arouse than female infants during QS. There were no significant effects of gender on total arousability or SCA and CA frequencies at 2-3 months, the age of peak SIDS incidence. Thus, although male infants are at greater risk of SIDS than female infants, this difference is unlikely to be associated with gender differences in CA threshold or frequency.

Lung function and cognitive ability in a longitudinal birth cohort study

OBJECTIVE

The objective of this study was to examine the association between forced expiratory volume in 1 second (FEV1) and cognitive ability in midlife in the normal population.

METHODS

Multiple regression was used to test associations between FEV1 and cognitive function in 1778 men and women in the MRC National Survey of Health and Development, also known as the British 1946 birth cohort. Analyses were adjusted for sex, body size (birth weight, adult height, weight, and chest circumference), socioeconomic status, lifetime smoking, and a range of health indicators, including early respiratory vulnerability (infant lower respiratory infection, childhood asthma, and exposure to atmospheric pollution).

RESULTS

FEV1 at 43 years was associated with slower psychomotor speed (peg placement) at the same age and with slower decline in psychomotor speed (letter search speed) from 43 to 53 years, independently of the previously mentioned potential confounders. These independent associations were not observed, however, for adult verbal ability, verbal memory, or rate of decline in memory, which were significantly explained by socioeconomic status and adolescent cognitive ability. In a subsequent analysis, adolescent cognition was positively associated with FEV1, although not with rate of decline in FEV1 from 43 to 53 years, again independently of the previously mentioned confounders.

CONCLUSIONS

Cognitive function and FEV1 are positively associated across the life course. One possible explanation lies in the parallel action of endocrine, autonomic, and motor control systems on respiration and higher mental function. Because respiration and mental function are both associated with functional capacity and survival, this is a matter of potential clinical significance.

Ventilatory behavior during sleep among A/J and C57BL/6J mouse strains

The pattern of breathing during sleep could be a heritable trait. Our intent was to test this genetic hypothesis in inbred mouse strains known to vary in breathing patterns during wakefulness (Han F, Subramanian S, Dick TE, Dreshaj IA, and Strohl KP. J Appl Physiol 91: 1962-1970, 2001; Han F, Subramanian S, Price ER, Nadeau J, and Strohl KP, J Appl Physiol 92: 1133-1140, 2002) to determine whether such differences persisted into non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Measures assessed in C57BL/6J (B6; Jackson Laboratory) and two A/J strains (A/J Jackson and A/J Harlan) included ventilatory behavior [respiratory frequency, tidal volume, minute ventilation, mean inspiratory flow, and duty cycle (inspiratory time/total breath time)], and metabolism, as performed by the plethsmography method with animals instrumented to record EEG, electromyogram, and heart rate. In all strains, there were reductions in minute ventilation and CO2 production in NREM compared with wakefulness (P < 0.001) and a further reduction in REM compared with NREM (P < 0.001), but no state-by-stain interactions. Frequency showed strain (P < 0.0001) and state-by-strain interactions (P < 0.0001). The A/J Jackson did not change frequency in REM vs. NREM [141 +/- 15 (SD) vs. 139 +/- 14 breaths/min; P = 0.92], whereas, in the A/J Harlan, it was lower in REM vs. NREM (168 +/- 14 vs. 179 +/- 12 breaths/min; P = 0.0005), and, in the B6, it was higher in REM vs. NREM (209 +/- 12 vs. 188 +/- 13 breaths/min; P < 0.0001). Heart rate exhibited strain (P = 0.003), state (P < 0.0001), and state-by-strain interaction (P = 0.017) and was lower in NREM sleep in the A/J Harlan (P = 0.035) and B6 (P < 0.0001). We conclude that genetic background affects features of breathing during NREM and REM sleep, despite broad changes in state, metabolism, and heart rate.

Behavioural correlates of conditioned ventilatory responses to hypoxia in rats

To examine the possible contribution of behavioural arousal to ventilatory conditioning, we performed a differential conditioning experiment using two odours as the paired conditioned stimulus (CS + ) and unpaired conditioned stimulus (CS-) and a hypoxic mixture (7.5% O2) as the unconditioned stimulus (US) in 24 adult male rats. Vanillin was the CS + and rose the CS - in half the rats, and vice versa in the other half. Each rat underwent 26 paired CS + /hypoxia trials and 26 CS - trials in alternation, followed by two CS + only and two CS - trials to test for conditioning. Analysis of breathing variables and behavioural scores during the test showed two qualitatively different conditioned responses. The initial conditioned response was characterised by short breath durations (TT), frequent sniffing episodes, and arousal responses. Following this, a specific, conditioned increase in tidal volume (VT) and levelling off of sniffing and motor activities occurred. The early TT-response and late VT-response to CS + both contributed to an increase in ventilation (VI). The present data show that the association of an odour and hypoxia elicits a biphasic ventilatory conditioned response, of which the first component is integrated into conditioned arousal.