Oxygen cost of increasing tidal volume and diaphragm flattening in obstructive pulmonary disease.

Full Abstract

Hypercapnia is associated with a shallow breathing pattern in patients with severe chronic obstructive pulmonary disease (COPD). We sought to determine the oxygen cost of increasing tidal volume and to relate this to hypercapnia [arterial PCO2 (PaCO2) > or = 45 Torr] and diaphragm flattening. We studied 3 normal subjects and 12 patients with stable but comparably severe COPD (forced expired volume in 1 s 1.01 +/- 0.09 liters) who had baseline PaCO2 ranging from 36 to 56 Torr. Oxygen consumption was measured during the subject's native breathing pattern and then while tidal volume was increased by 20%; minute ventilation was held constant by proportionately slowing frequency. There was a significant oxygen cost of increasing tidal volume for hypercapnic patients (235 +/- 23 to 260 +/- 25 ml O2/min; P = 0.002); no significant oxygen cost was observed in normal or eucapnic patients. This oxygen cost was positively correlated to baseline PaCO2 (r2 = 0.88, P < 0.001) and degree of diaphragm flattening assessed from chest radiographs (r2 = 0.74, P < 0.05). Although others have shown that force generation is preserved during chronic hyperinflation (G. A. Farkas and C. Roussos. J. Appl. Physiol. 54: 1635-1640, 1983; T. Similowski et al. N. Engl. J. Med. 325: 917-923, 1991), we conclude that diaphragm flattening produces mechanical inefficiency that may contribute to limiting the effective operating range of the respiratory muscles during tidal breathing.

Author information

Author/s: Pitcher, W D (WD); Cunningham, H S (HS);

Affiliation: Pulmonary and Critical Care Medicine Division, University of Texas, Southwestern Medical Center, Dallas 75216.

Journal and publication information

Publication Type: Journal Article; Research Support, U.S. Gov't, Non-P.H.S.

Journal: Journal of applied physiology (Bethesda, Md. : 1985) (J Appl Physiol), published in UNITED STATES. (Language: eng)

Reference: 1993-Jun; vol 74 (issue 6) : pp 2750-6

Dates: Created 1993/10/01; Completed 1993/10/01; Revised 2006/11/15;

PMID: 8365977, status: MEDLINE (last retrieval date: 2/18/2009, IMS Date: )

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