Ventilatory responses to threshold loaded respiration in man
Krieger, A.J.; Caruso, J.; Sapru, H.N.
American Surgeon 43(9): 554-561
1977
ISSN/ISBN: 0003-1348 PMID: 900646 Document Number: 114168
In postoperative patients one frequently observes respiratory difficulty in excess of what is indicated by physical alterations in respiratory mechanics. This would suggest that some patients lack normal compensatory mechanisms which respond to mechanical changes in the lung. It is entirely possible that inadequacy of compensatory mechanisms is present before surgery and predisposes patients to respiratory distress. In the clinical environment elaborate testing is precluded by the physical status of the patients. Thus, a noninvasive procedure has been designed to apply stress to the respiratory system in order to study the effect of stress at increasing levels of CO2. In this test a subject's respiration is measured as he rebreathes a mixture of 7% CO2 and 93% O2 from a closed system. On successive trials, fixed pressure inspiratory threshold loads are applied in sequence. With this type of load the increased work required to inspire a given volume depends only on the increased inspiratory pressure. In most normal subjects CO2 response was incrementally depressed when threshold loads were introduced. Patients with brain stem lesions showed a greater depression at higher loads. This may indicate a reduced ability to tolerate increased loads to breathing.