Too slow breathing accompanied by too slow/decreased locomotor activity. Kraepelin was convinced form his physical examinations of bipolar depressed patients that their breathing rate was problematic at rest and causing retention of acids [PCO2].
Locomotor activity seems to be an emergent property of the respiratory pump muscle system.
The respiratory pump system is made up of the spine, the ribs, the sternum, and the muscles and nerves that serve ventilation [the process of moving air in and out of the body.]
The lungs have no skeletal muscles of their own. The work of breathing is done by the diaphragm, the muscles between the ribs (intercostal muscles), the muscles in the neck, and the abdominal muscles.
Breathing is usually automatic, controlled subconsciously by the respiratory center at the base of the brain. Breathing continues during sleep and usually even when a person is unconscious. People can also control their breathing when they wish, for example during speech, singing, or voluntary breath holding. Sensory organs in the brain and in the aorta and carotid arteries monitor the blood and sense oxygen and carbon dioxide levels. Normally, an increased concentration of carbon dioxide is the strongest stimulus to breathe more deeply and more frequently. Conversely, when the carbon dioxide concentration in the blood is low, the brain decreases the frequency and depth of breaths. During breathing at rest, the average adult inhales and exhales about 15 times a minute. https://www.merckmanuals.com/home/lung-and-airway-disorders/biology-of-the-lungs-and-airways/control-of-breathing
Remember that Paula only breaths 3-5 breaths/minute using abdominal muscles in health and during depressive episodes. Does this mean that she does not experience rising carbon dioxide in the blood as a stimulus? Or does it mean that her PCO2 is low. Deep breathing will blow off too much carbon dioxide but abnormally slow breathing means she may not be exchanging enough air. Only an arterial blood gas test will tell us if her CO2 blood levels are too low or too high. And why is only 5 breaths per minute fine during health. Does anyone breath at so low a rate?
Remember the post when I discuss the normal range of breathing rate in healthy adults, from 3 breaths per minute to 30 breaths per minute at rest.
It seems we may not know as much as we think about breathing at rest.
It does seem clear that locomotor activity IS a stimulus for increased breathing frequency, as it should be.
Being physically ill with an infection or heart failure or blood loss should also raise breathing rate but in Paula, it doesn’t…..why?
We think that bipolar attacks are different stages of response of the body to asphyxiation due to attacks of respiratory failure due to lack of adequate response from the respiratory pump muscles in an emergency weakening the body [like infection].
The first response would be to conserve energy, stop moving, ….or maybe the voluntary muscles are weakened from lack of circulating air even if the necessary ratio of air is OK.
Maybe we have no clue wha happens during a very gradual unchecked respiratory failure due to an impaired respiratory pump system.
Of Sound Mind 