Interaction between chemical ventilatory drive and respiratory compensation for flow-resistive loading.

DIscuSsIoN The normal occlusion pressure response to elastic loads in COPD patients in whom the response to flow loads is impaired indicates that the diminished response to flow loads cannot be explained by decreased muscle performance or fatigue. Rather, this phenomenon appears to represent a specific defect perhaps in the recognition of the resistive load by mechanoreceptors or in the interpretation of the sensory input in patients with COPD. This notion is consistent with the magnitude estirna-tion studies of Gottfried et al' in which the ability of COPD patients to consciously detect and quantify changes in airflow resistance was found to be impaired. Zechman and Davenport' pointed out that detection of flow-resistive loads occurs at midinspiration and corresponds to peak flow, while elastic loads are perceived towards the end of inspiration corresponding to maximal change in lung volume.' He predicted that a resistive load should not interfere with the detection of elastic loads since at end inspiration air flow is zero. Our findings of a normal response to elastic loads in patients with chronic airways obstruction is consistent with their predictions. The relationship between the respiratory sensations elicited by external loads and the magnitude of the neuromuscular response is still unclear. It seems reasonable to believe that the intensity of the sensation elicited by a load might influence the motor respiratory response. REFERENCES 1Altose MD, McCauley WC, Kelsen SC, et al: Effects of hypercapnia and inspiratory flow resistive loading on respiratory activity in chronic airways obstruction. al: The perception of changes in airflow resistance in normal subjects and patients with chronic airways obstruction. Chest 73:286-288 (suppl), 1978 3 Zechman FW, Davenport PW: Temporal differences in the detection of resistive and elastic loads to breathing. What happens to the FRC during CO., rebreathing? A. (Nochomovitz): We measured the FRC in 3 patients and there was no significant change from baseline. Q. (Cherniack): What does an increased FRC do to the perception of external loading? A. (Nochomovitz): I don't know. C. (Altose): We have studied a group of patients who had recovered from acute respiratory failure. After recovery, one-half of them returned to normocapnia while approximately one-half remained hypercapnic. Although all patients had clear abnormalities of hypercapnic and hypoxic respiratory responses, abnormalities in respiratory sensation were noted only in those patients who remained in chronic respiratory failure. Q. (Zwillich): Does abnormal load response predict which COPD patient will develop high Pco.,? A. …