Long-term hypercapnia is starting to be studied in respiratory conditions such obstructive sleep apnea, chronic obstructive pulmonary disease and obesity hypoventilation syndrome.
Animal studies of long term responses to hypercapnia have demonstrated an initial (within hours) increase in ventilatory drive followed by a decrease in this response over the long-term (days–weeks) in response to continued hypercapnia. ….The working hypothesis of the 2019 research on this topic, is that is that during long-term hypercapnia, galanin co-release from RTN [retrotrapezoid nucleus of the brainstem] neurons may counterbalance glutamatergic inputs to respiratory centers to downscale energetically wasteful hyperventilation, thereby having a role in neuroplasticity by contributing to a decrease in ventilation, through the inhibitory effects of galanin. Adaptation of Respiratory-Related Brain Regions to Long-Term Hypercapnia: Focus on Neuropeptides in the RTN Ayse Sumeyra Dereli1, Zarwa Yaseen1, Pascal Carrive2 and Natasha N. Kumar1* ORIGINAL RESEARCH ARTICLE
Front. Neurosci., 13 December 2019 | https://doi.org/10.3389/fnins.2019.01343
No one knows why this is so. Yet.
Maybe this explains the slow breathing rate Paula displays, not to mention the thousands of depressed patients displaying slow breathing described by Dr Emile Kraepelin in his research on Manic Depressive Insanity.
Maybe all were suffering from exacerbations of chronic hypercapnia. Gradual and chronic hypercapnia may have no symptoms [Merck Manual] till it worsens and causes [mild?] respiratory failure. [and mental confusion].
Chronic hypercapnia with or without symptoms also seems to change neurons expressing serotonin. These changes might be corrected by serotonin boosters.
Chronic hypercapnia in goats were found to cause a 50% decrease in neutrons necessary to synthesize serotonin in parts of the brainstem. The researchers concluded that “chronic hypercapnia has a major impact on the 5HT neuromodulatory system which is important in the control of breathing”. Decreased Number of Brainstem Serotonin (5-HT) Neurons During Chronic Hypercapnia in Goats. Kirstyn Buchholz, Nicholas Burgraff, John LeClaire, Suzanne Neumueller, Lawrence Pan, Matthew Hodges, and Hubert Forster Published Online:1 Apr 2019Abstract Number:731.8 The Faseb Journal; Physiology https://www.fasebj.org/doi/abs/10.1096/fasebj.2019.33.1_supplement.731.8
Many of the mechanisms seen in goats are conserved in humans too.