Effects of external elastic and threshold loading on breathing in man

¹ Departments of Environmental Medicine and Psychiatry, The Johns Hopkins University, Baltimore, Maryland

Conscious human subjects, seated in a soundproof chamber, were made at intervals to inspire through external elastic or threshold loads for from 4 to 15 breaths With threshold loading of –5 to –15 cm H₂O (13 subjects) initially, the first loaded breath was smaller than preceding breaths with tidal volume returning to normal within 6 breaths. With further presentations, tidal volume returned to control values sooner. After six presentations, 10 subjects had no diminution in tidal volume on the first loaded breath. With elastic loading, of 10 cm H₂O/liter (five subjects) and 19.5 cm H₂O/liter (four subjects) a different type of adaptation occurred. This was characterized by decreased tidal volume and increased frequency. With the larger load, after three presentations frequency was increased during loaded breathing, due to a conscious effort by the subjects. The results show that repeated presentation of an elastic or threshold load leads to a change in the response to the load in a manner analogous to the learning of voluntary motor acts.

Submitted on July 9, 1964

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